In this article, we present a fully higher-order compact (FHOC) finite difference method to investigate the effects of heat flux on natural convection of nanofluids in a right-angle triangle cavity, where the left vertical side is heated with constant heat flux both partially and throughout the entire wall, the inclined wall is cooled, and the rest of walls are kept adiabatic. The Darcy flow and the Tiwari and Das’ nanofluid models are considered. Investigations with four types of nanofluids were made for different values of Rayleigh numbers with the range of 100 ≤ *Ra* ≤ 50,000, size of heat flux as 0.1 ≤ *ε* ≤ 1.0, enclosure aspect ratio as 0.5 ≤ *AR* ≤ 2.0, and solid volume fraction parameter of nanofluids with the range of 0% ≤ *ϕ* ≤ 20%. Results show that the average heat transfer rate increases significantly as particle volume fraction and Rayleigh numbers increase, and the maximum value of average Nusselt number is obtained by decreasing the enclosure aspect ratio. The results also show that the average heat transfer decreases with an increase in the length of the heater. Furthermore, multiple correlations in terms of the Rayleigh numbers and the solid volume fraction of four types of nanoparticles have been established in a general form.

The moisture content and heat transfer in a wet porous sand layer was influenced by the weather conditions while the layer was exposed outdoors. The changes in water content and temperature in the wet porous bed with water supplied due to the weather conditions differed from the case without water supplied via the bottom in the tests. A one-dimensional mathematical model describing the heat and mass transfer in the unsaturated porous layer was used to analyze the change of the water content, temperature and rate of water evaporation or vapor condensation in the wet porous layer. As the ambient temperature, relative humidity and solar irradiation changed periodically and the gravity and capillary affected the water transport greatly in the wet porous media, variations of water content and temperature occurred cyclically in the wet porous layer that was exposed to outdoor conditions. In the wet porous bed, the rate of the water evaporation or vapor condensation was closely related to the temperature, gradient of the temperature along the depth and the rate of temperature variation over time. The particle size and porosity associated with the permeability had great impact on the water content and its variation range in the wet porous media with water sucking ability while the weather conditions changed periodically. The simulations of the water content and temperature variation in the sand bed agreed with the test data. All these results can be used to analyze the behavior of heat and moisture in the unsaturated porous layer under weather conditions.

]]>This paper presents an experimental investigation of forced convection heat transfer in two heat sinks for electronic system cooling and investigated the comparisons of the thermal behavior of the mini- and microchannel heat exchangers. The hydraulic dimension of one of the heat sinks is 2 mm while that of the other is . Deionized water was used as the working fluid for studies conducted in both the heat exchangers. The effect of heat flux and volumetric flow rate (in laminar flow regime) on temperature and heat transfer coefficient is studied. Irrespective of the average heat transfer coefficient and the total thermal resistance, advantages and limitations of each device are analyzed and discussed in the light of experimental results. Furthermore, the results obtained from the experiments were in good agreement with those obtained from the design theory analyses.

]]>Low temperature stress is an important factor for turf growth in the northern high-latitude environment. A thermosyphon temperature controlling unit with a shallow geothermal source was proposed by analyzing present techniques to prolong the turf growing season in winter. Thermosyphon unit prototypes were developed and tested in a water park. The relations between ambient temperature, depth, material, structure, underground temperature, and root temperature were studied experimentally. The thermosyphon unit performance was analyzed. Results indicate that underground and root temperatures remain almost constant with an hourly ambient temperature. The root temperature remains steady due to the thermosyphon unit application. The underground temperature increases with the depth increase, and the increment is at most 1 °C. The root temperature of a copper thermosyphon unit is higher than that of a steel thermosyphon unit, and the temperature difference can reach 2 °C. The root temperature of a type I thermosyphon unit is higher than that of a type II, and the temperature increase is less than 1 °C. The root temperature variation due to the thermosyphon material is smaller with the increase in depth.

]]>This is an experimental and numerical study on the effect of air swirl vane angle on combustion characteristics of liquid fuel burners. The swirl vane angle varied in a range from 0° to 75° and the values of the dependent variables were determined. The flame temperature was measured by an S-type thermocouple and a Testo 350 XL gas analyzer was used to determine the NO and CO pollutant concentrations. Also, sprint CFD code along with suitable models was used in analytical modeling. The results indicate that there is an optimum angle for the swirl vane (approximately 45° for the case study). At the optimum angle, the average temperature of the flame increases as much as 12.5% and 28.5% in comparison with small and large angles, respectively. Therefore, combustion efficiency reaches its maximum level and CO emission is at an extremely low level. The results also demonstrate that large swirl angles decreases NO emission.

]]>The thermal characteristic of a spindle system is simulated by the finite element method. Temperature field and thermal deformation of the spindle system were simulated considering the establishment method of an entity model as well as boundary conditions of a finite element model, such as heat source, heat transfer coefficient, and thermal contact resistance between joints. Effects of the spindle system on thermal characteristics of the whole machine were discussed. Accuracy of the simulation was verified and compared with test results. The study shows that the key areas of temperature rise are located at the spindle bearing and spindle motor; thermal deformations of Y and Z directions are large; thermal characteristics of the spindle system have little influence on other parts. Thermal characteristics of the spindle system were optimized by changing the structures and sizes of the cooling passage located at the spindle box, and effectiveness of the optimization was verified by finite element simulation. The research results provide guidance for thermal characteristic simulation and optimization of machining centers.

]]>A one-dimensional mathematical model has been developed to investigate the effect of desiccant isotherm (adsorptive material) on the performance of the desiccant wheel. The model consists of four governing heat and mass transfer equations with some auxiliary conditions which are then solved using FlexPDE Software. The model shows good agreement with the experimental results obtained from the literature as well as with the experiment conducted by the author. In this paper the different adsorption isotherms have been characterized by a single parameter called the separation factor. The separation factors, *R* = 0.05, 0.1, 0.5, and 1 are analyzed under a different range of operating conditions. Investigation of these parameters is based on the wheel performance, index, that is moisture removal (MR) and dehumidification coefficient of performance (DCOP), as DCOP is more appropriate to reflect the utilization of heat energy in the regeneration process. The result of this study shows that there is a significant effect on the operating parameter on the isotherm shape. Across the entire range of operating condition single isotherm (*R* = 0.5 or *R* = 0.1) there is not a better adsorptive material choice but it varies with change in the operating conditions. The results of this study shows that the isotherm shape of *R* = 0.1 or 0.5 yields better results depending upon whether the given range of operating conditions are higher or lower.

In this work combined effects of the wall confinement and the power-law fluid viscosity on the heat transfer phenomena of contaminated bubbles are reported through numerical investigations. In order to delineate the effect of insoluble surfactants the spherical stagnant cap model is adopted. The solver is thoroughly validated by comparing the present results with their literature counterparts. Further, extensive new results are reported on the isotherm contours and average Nusselt numbers of confined contaminated bubbles in the range of conditions: Reynolds number, *Re*: 0.1 to 200; Prandtl number, *Pr*: 1 to 1000; power-law index, *n*: 0.2 to 1.6 and stagnant cap angle, α: 0 to 180°. Briefly, results are indicative of the following observations. The temperature contours are increasingly sucked towards the rear end of the bubble with the increase in Reynolds number and/or with the increase in Prandtl number and/or with the decrease in power-law index and/or with the decrease in stagnant cap angle. At *Re* ≤ 1 and *Pr* ≤ 10, the average Nusselt number is almost independent of power-law indices and the stagnant cap angle. For *Pe* > 10, regardless of values of the confinement ratio and Reynolds number, for α ≥ 60 the average Nusselt number decreases with an increasing stagnant cap angle whereas for α < 60 the effect of contamination is found to be insignificant. The increase in the average Nusselt number with an increasing confinement ratio would occur only at moderate to large values of Reynolds and Prandtl numbers regardless of the values of the power-law index provided that α ≥ 60°.

This paper focuses on fluid flow and heat transfer analysis over two heated cylinders arranged in tandem. The flow of water over heated cylinders faces a phenomenon of phase change from liquid (water) to vapor phase (steam). The mechanism of this phase change is studied through a numerical simulation supplemented with verification and validation of the code. The problem is simulated when flows from two cylinders in a tandem arrangement become interacting and noninteracting. The Eulerian model is used during simulation to comprehend the multiphase phenomena. The effect of spacing between these two cylinders and the Reynolds number effect are studied in this paper. The volume fractions of both the water and vapor phases and the heat transfer coefficients of both the cylinders have been computed and presented as findings of the problem.

]]>The combined effects of conjugation and magnetic field on the heat transfer enhancement in a laminar liquid metal flow past a thermally conducting and sinusoidally oscillating infinite flat plate are investigated. The wall materials used are compatible with the liquid metals and are assumed to be of finite thickness. Analytical solutions are obtained for the velocity and the temperature distributions. The combined effects of thermal conductivity, the thickness of the plate, and the transverse magnetic field on the net heat flux transported are analyzed in detail and it is found that such effects are same as those on the transverse temperature gradient at any frequency. Due to oscillation, the heat flux is enhanced by *O*(10^{3}). The optimum value of wall thickness and the corresponding boundary layer thickness for which the maximum heat flux is obtained are reported. The heat flux transported can be increased by choosing a wall of low thermal conductivity. A maximum increase of 52.03% in heat flux can be achieved by optimizing the wall thickness. These information may be useful while designing magnetohydrodynamic liquid metal heat transfer systems. All the results obtained are in good agreement with the results reported earlier.

This study aims to investigate convective heat transfer inside an annular tube under a constant wall temperature as the outer boundary condition. The outer wall temperature is set to 91 °C, while the other boundaries remained unchanged. For different volume concentrations of Cu as the nanoparticle (0.011, 0.044, and 0.171), the study has been pursued. The acquired data is used to develop a correlation for Nusselt number. The correlation is valid for a Cu/Base Ethylene Glycol nanofluid flow with the volume concentrations between 0.011 and 0.171 in the hydrodynamically fully developed laminar flow regime with Re <160 which is applicable in milli and micro channel heat exchangers.

]]>Radiation plays a dominant role in combustion space heat transfer. It is composed of three components, namely gaseous species radiation, soot radiation and crown surface radiation. The basis for model validation and the subsequent study of furnace operation is the spatial variation of radiant heat flux. Hayes and colleagues carried out measurements of crown incident radiant heat flux along the furnace axial centerline and developed a numerical model. However, the effect of soot was not quantified. In the present work, a numerical model is developed which considers the effect of soot radiation and is simulated using Fluent. The proposed model fits the experimental data of Hayes and colleagues within an error band of –6% to +14%.

]]>In this study, optimum propylene glycol (PG) brine-based nanofluids are being proposed as coolants for a wavy finned automotive radiator. Performance analysis is conducted and compared with conventional Ethylene Glycol (EG) brine and related nanofluids. A 25% PG brine has similar heat transfer characteristics to water at higher operating temperature ranges. The effects on radiator size, weight and cost, engine efficiency and fuel consumtion, and embodied energy saving and environmental impact are discussed as well. Compared to conventional coolant(EG water brine), for the same cooling capacity and radiator size, the coolant requirement and pumping power are reduced significantly by about 25% and 64%, respectively, whereas, for the same cooling capacity and mass flow rate, the radiator size and pumping power is reduced by 4.2% and 25.5%, respectively, with PG brine-based Ag nanofluids.Furthermore, by using optimum PG brine-based nanofluids, 3.5% of the embodied energy may be saved, which may yield reductions in radiator cost, engine fuel consumption and environmental costs.

]]>The current study presents an experimental investigation on evaluation of thermal performance of a single-pass double-glazed solar air heater with the use of packed bed paraffin wax as a phase change material (PCM). Moreover, the absorber plate is equipped with baffles attached over its top. Galvanized sheets with a thickness of 0.4 mm and total surface areas of 30 cm^{2} are chosen as baffles that are placed in a sequential manner over the absorber plate. The solar energy was stored in the packed bed PCM during the diurnal period (charging process) and was released at night for nocturnal use (discharging process). The tests were performed at three different mass flow rates of 0.009 0.014 and 0.017 resulting in the creation of different Reynolds numbers along the channel. The measured parameters were inlet, outlet, and the PCM temperatures under the meteorological condition of Mashhad, Iran. Energy and exergy efficiencies of the system have been calculated according to the first and second laws of thermodynamics. The experimental results illustrate that the daily energy efficiency varied between 20.7% and 26.8%, whereas the daily exergy efficiency varied between 10.7% and 19.5%.

In this paper, an experimental study of the condensation of water vapor from a binary mixture of air and low-grade steam has been depicted. The study is based upon diffusion heat transfer in the presence of high concentration of noncondensable gas. To simplify the study, experimental analysis is supported by empirical solutions. The experimental setup is custom designed for testing a new shell and tube type heat exchanger supplied by the manufacturer. Air–vapor mixture at 80 °C (max) and 20.2% relative humidity enters the heat exchanger at a mass flow rate of 480 kg/h and condenses 27 kg/h vapor using cooling water at an inlet temperature of 7 °C to 10 °C and mass flow rate of 3500 kg/h. By using the experimental data of constant inlet air mass fraction, mixture gas velocity, and different volumetric flow rate of the cold fluid, the local heat transfer coefficients are obtained. The main objective of this work is to establish an approximate value for surface area and overall heat transfer coefficient of a horizontal shell and tube condenser used in process space. Under designed working conditions, the condenser is found to work efficiently with 90% vapor condensation by mass.

]]>Radiative heat transfer with and without conduction in a differentially heated 2-D square enclosure is analyzed. The enclosure with diffuse gray boundaries contains radiating and/or conducting gray homogeneous medium. Radiatively, the medium is absorbing, emitting and scattering. On the south boundary, four types of discrete heated regions, viz., the full boundary, the left one-third, left two third and middle one third, are considered. In the absence of conduction, distributions of heat flux along the south boundary are studied for the effect of extinction coefficient. In the presence of conduction, distributions of radiation, conduction and total heat fluxes along the south boundary are analyzed for the effects of extinction coefficient, scattering albedo, conduction–radiation parameter, and south boundary emissivity. Effects of these parameters on centerline temperature distribution are also studied. To assess the performance of three commonly used radiative transfer methods, in all cases, the radiative transfer equation is solved using the discrete ordinate method (DOM), the conventional discrete ordinate method (CDOM) and the finite volume method (FVM). In the combined mode problem, with volumetric radiative information known from one of the three methods, viz., DOM, CDOM, and FVM, the energy equation is solved using the finite difference method (FDM). In all cases, the results from FDM-DOM, FDM-CDOM, and FDM-FVM are in good agreement. Computationally, all three sets of methods are equally efficient.

]]>Designing new and efficient heat engines and increasing the efficiency of previous ones is one of the researchers’ interests in the field of thermodynamics. In this regard, what is mainly concerned is to design a cycle with the positive features of previous cycles, such as less pollution, and higher power-to-weight ratio and efficiency. One of these cycles is the supercritical carbon dioxide cycle (SCDC). The main goal of this research is designing a highly efficient SCDC with pessimistic and relatively optimistic efficiencies of 45% and 47%. This paper includes the complete first law analysis of the designed cycle, designing and discussion of efficiency improvement methods and comparison of SCDC with other power cycles. The sensitivity of the cycle efficiency to some important parameters has also been studied.

]]>This paper presents a numerical investigation of the entropy generation and heat transfer in a ferrofluid (water and 4% Fe_{3}O_{4} nanoparticles) filled cavity with natural convection using a two phase mixture model and control volume technique. The effect of applying a nonuniform magnetic field on the entropy generation and heat transfer in the cavity and also the interaction of magnetic force and the buoyancy force are investigated.

Based on the obtained results, applying a magnetic field will enhance the heat transfer mechanism. Furthermore, by applying the nonuniform magnetic field on the ferrofluid filled cavity with natural convection, the total entropy generation is decreased considerably at higher Rayleigh numbers. Therefore, applying a magnetic field can be considered as a suitable method for entropy generation minimization in order to have high efficiency in the system.

The present study indicates the impact of different arrangements of dielectric barrier discharge (DBD) plasma actuators on temperature field in a channel flow. The modified lumped circuit element electro-static model was used to calculate induced Lorentz body force and plasma dissipation of the actuators. Different distributions of temperature in the modeled channel flow for each arrangement of actuators (one, two, and three attached actuators) are discussed. According to the numerical simulation, DBD plasma actuators are beneficial devices for increasing temperature in the channel flow, especially near the location of the actuators that can be considered for related applications. The actuators are modeled under an incompressible flow regime with low Reynolds number of 335, and the configurations of the actuators are set to be 3 KV for the peak voltage amplitude, 10,000 Hz for the voltage frequency, and Kapton as the dielectric.

]]>The primary objective of the present paper is to investigate the novel aspect of nanofluid flow near the stagnation-point past a permeable cylinder with chemical reaction. The prescribed surface heat and nanoparticle fluxes are also taken into account. The improved homotopy analysis method is introduced to obtain the recursively analytic solutions with high precision. The convergence of the obtained series solution is discussed explicitly. Besides, the effects of physically significant parameters on skin friction coefficient, local Nusselt number, local Sherwood number, as well as profiles of velocity, temperature, and nanoparticle volume fraction are examined and discussed in detail. It is found that the local Sherwood number increases when a chemical reaction occurs in the nanofluid. It is also indicated that the increase of the reaction rate parameter leads to a higher temperature and a lower nanoparticle volume fraction.

]]>In some regions with a specific climate, summer comfort in the rooms located below the roof becomes critical if the roof system is not well designed. In order to analyze the efficiency of this system a numerical model was developed. This model is based on the study of the natural convection coupled with radiative heat transfer in an inclined air channel. The configuration studied is an inclined channel formed by two parallel plates. The upper and lower plates were maintained at fixed temperatures. The air flow in the channel which is due to the buoyancy forces is fully turbulent and the turbulence was modeled by using the *k-ε* model. Some numerical results obtained were validated using the experimental works of Khedari and colleagues and those of Nouanégué and colleagues. The effect of physical and geometrical parameters and the radiative heat transfer on the channel behavior is shown. Correlations for Nusselt numbers and air flow rate were obtained as functions of the geometric parameters and the Rayleigh number. These correlations can be used in other models that represent this system.

In the coal chemical industry, an internal heating retort furnace is applied to the processing of low-temperature coal pyrolysis so as to produce semi-coke. Because the cooling water is used to reduce the temperature of semi-coke from 500 °C to 60 °C, the waste heat carried by the semi-coke is released. Meanwhile, the waste water of higher temperature involved with the hazardous substances is discharged into rivers or lakes, causing serious environmental pollution. In the present work, a constant temperature heat pipe is used to recover the waste heat. An iterative method is adopted to numerically solve the thermal resistances and the overall heat transfer coefficients. Results show that the conductivity thermal resistance decreases as the tube diameter increases. In the heating section, the main factors affecting the heat transfer are the thermal resistances of both the radiation heat transfer and the convective heat transfer. As the pressure climbs, the thermal resistance of radiation heat transfer increases, while the thermal resistance of convective heat transfer decreases. In addition, the overall heat transfer coefficients increase with the pressure. The heat transfer efficiency of the heat pipe is about 30%, and a higher economic benefit can be obtained.

]]>Magnetohydrodynamic (MHD) natural convection flow and associated heat convection in an oriented elliptic enclosure has been investigated with numerical simulations. A magnetic field was applied to the cylindrical wall of the configuration, the top and bottom walls of the enclosure were circumferentially cooled and heated, respectively, while the extreme ends along the cross-section of the elliptic duct were considered adiabatic. The full governing equations in terms of continuity, momentum, and energy transport were transformed into nondimensional form and solved numerically using finite difference method adopting Gauss–Seidel iteration technique. The selected geometrical parameters and flow properties considered for the study were eccentricity (0, 0.2, 0.4, 0.6, and 0.8), angle of inclination (0°, 30°, 60°, and 90°), Hartmann number (0, 25, and 50), Grashof number (10^{4}, 10^{5}, and 10^{6}), and Darcy number (10^{−3}, 10^{−4}, and 10^{−5}). The Prandtl number was held constant at 0.7. Numerical results were presented by velocity distributions as well as heat transfer characteristics in terms of local and average Nusselt numbers (i.e., rate of heat transfer). The optimum heat transfer rate was attained at e value of 0.8. Also, the heat transfer rate increased significantly between the angles of inclination 58° and 90°. In addition, Hartmann number increased with decreased heat transfer rate and flow circulation. A strong flow circulation (in terms of velocity distribution) was observed with increased Grashof and Darcy numbers. The combination of the geometric and fluid properties therefore can be used to regulate the circulation and heat transfer characteristics of the flow in the enclosure.

The effect of surface shape on laminar natural convective heat transfer from vertical isothermal hexagonal and octagonal flat plates embedded in a plane adiabatic surface, the adiabatic surface being in the same plane as the surface of the heated plate, has been numerically investigated. Results for the hexagonal and octagonal surface shapes with different aspect ratios have been obtained. It has been assumed that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces, this having been treated using the Boussinesq approach. The solution has been obtained by numerically solving the full three-dimensional form of governing equations, these equations being written in dimensionless form. The solution was obtained using the commercial finite volume method based cfd code, FLUENT^{©}14.5. The solution has the surface shape, the Rayleigh number, the dimensionless plate width and the Prandtl number as parameters. Results have only been obtained for a Prandtl number of 0.7 for Rayleigh numbers between 10^{3} and 10^{8} for various surface shapes with width-to-height ratios between 0 and 0.6. The effect of these parameters on the mean Nusselt number has been studied and empirical correlation equations for the mean heat transfer rate have been derived.

Radiation is the most important regime of heat transfer of a flame which is directly affected by temperature and emissivity coefficient of the flame. Natural gas has a nonluminous flame, although, the flame temperature is high, but, the emissivity coefficient of the flame is small. In this paper the impacts of synchronous combustion of small amounts of anthracite coal particles with natural gas on the detailed emissivity coefficient of the flame, radiative species and pollutant emissions were investigated experimentally and numerically. A sprint CFD code was used in numerical solution and the pollutants were measured by a Testo 350XL gas analyzer. The results showed that a small amount of coal particles injected into the hot flame of natural gas increases the volume distribution and radiation view factor of high-emissive intermediate solid soot particles in the flame which enhances the total flame emissivity coefficient. Also, coal particle injection leads to a decrease in the upstream flame temperature and an increase in the downstream region creating a more uniform temperature distribution and decreases the concentration of thermal NO pollutant of the natural gas flame. Furthermore, the role of solid soot particles on the total emissivity coefficient is remarkable, while an increase in CO_{2} and H_{2}O concentrations has an insignificant effect on the flame emissivity coefficient.

Nanofluids are emerging as alternative fluids for heat transfer applications due to enhanced thermal properties. Several correlations are available in open literature for heat transfer coefficient (HTC) and thermophysical properties of nanofluids. Reliability of correlations that use effective properties for estimation of HTC needs to be checked. Comparison of experimental HTC and that estimated from existing correlations is the main objective of the present study. An empirical correlation is developed with experimental data of the HTC for zinc–water and zinc oxide–water nanofluids. Experimental HTC is compared with that estimated from developed correlation and existing correlations. The range of Re considered for the study is 4000 to 18,000. Comparison indicated large deviation in experimental values and the values estimated from existing correlations. Based on comparison results, it can be concluded that the single-phase models of forced convective heat transfer cannot be extended to nanofluids.

]]>An attempt has been made to study the entropy generation analysis of couple stress fluid flow in an annulus between two concentric rotating vertical cylinders. There is a porous lining attached to the inside of an outer cylinder. The flow is under the influence of a radial magnetic field. The flow in the annular gap is caused by rotation of the cylinders. The Stokes couple stress flow model is employed. The flow in the porous sleeve is governed by Darcy's law. The velocity, temperature, entropy generation number, Bejan number, wall shear stress and heat transfer rate at the inner and outer cylinders are obtained numerically by employing a finite difference scheme with vanishing of couple stresses on the boundary. The effect of relevant parameters on the flow and entropy generation rate are discussed and depicted through graphs.

]]>In this paper, a direct numerical simulation of a two-phase incompressible gas–liquid flow for simulation of bubble motion and convective heat transfer in a microtube is presented. The microtube radius is 10 μm. The interface between the two phases is tracked by the volume of fluid method with the continuous surface force model. Newtonian flows are solved using a finite volume scheme based on the PISO algorithm. Numerical simulation is done on an axisymmetric domain with a periodic boundary condition for different values of pressure gradient, void fraction, and bubble period. Mean pressure gradient is fixed for each simulation. The superficial Reynolds numbers of gas and liquid phases studied are 0.3 to 7 and 5 to 210, respectively. Numerical results are coincident with the Serizawa regime map, and there is a linear relation between the void fraction and gas flow ratio. Simulation shows local Nusselt number increases in the presence of a gas bubble.

]]>In this research, a heat transfer oil based nanofluid including Ag nanoparticles was made by a novel one-step physical method known as Electrical Explosion Wire (E.E.W). The physical properties of the Ag nanoparticles were studied by high resolution transmission electron microscopy. Heat transfer oil was preferred because there are few works on oil based nanofluids in literature. The thermal conductivity of the heat transfer oil based Ag nanofluid at various mass fractions of 0.12%, 0.36% and 0.72% exhibited temperature-dependency and the pure thermal conductivity increases with temperature for different temperatures ranging from 40 to 100 °C, while the enhanced ratios are not constant. From an analysis of the rheological behavior point of view, it was found that the nanofluids showed Newtonian and Non Newtonian behavior for mass fraction less and more than 0.36% respectively. Also, the viscosity increment showed temperature-dependency, and its value increased with the Ag mass fraction at a fixed temperature. In addition, the specific heat capacity and density of nanofluids were studied experimentally and it was found that the range of specific heat capacity decreased with increasing of mass concentration.

]]>This study deals with an empirical investigation on the convective heat transfer of Cu/oil nanofluid flow inside a concentric annular tube with constant heat flux boundary condition and suggests a correlation to predict the Nusselt number. The average size of particles was 20 nm and the applied nanofluid was prepared by *Electrical Explosion of Wire* technique with no nanoparticle agglomeration during nanofluid preparation process and experiments. The nanofluid flowing between the tubes is heated by an electrical heating coil wrapped around it. The effects of different parameters such as the flow Reynolds number, tube diameter ratio, and nanofluid particle concentration on heat transfer coefficient are studied. Using the acquired experimental data, a correlation is developed for the estimation of the Nusselt number of nanofluid flow inside the annular tube. This correlation has been presented by using the exponential regression analysis and least-squares method. The correlation is valid for Cu/base oil nanofluid flow with weight concentrations of 0.12, 0.36, and 0.72 in the hydrodynamically full-developed laminar flow regime with Re <140, which is applicable in mini- and microchannel heat exchangers, and it is in good agreement with the experimental data.

This article is a comparative study of how the injection of micro kerosene droplets and pulverized anthracite coal particles affects soot particle nucleation inside natural gas flame and, subsequently, radiation. To this end, the yellow chemiluminescence of soot particles and IR photography were used to locate radiative soot particles and discover their qualitative distribution. The IR filter was tested with a Thermo Nicolet Avatar 370 FTIR Spectrometer for its spectral transmittance to be specified. Also, the spectral absorbance of soot particles, which are formed in flame, was measured by BOMEM FTIR. Furthermore, the variations of flame temperature, transient heat transfer, and thermal efficiency were investigated. The results indicate that, for equal heating values, kerosene droplets are more effective than coal particles in improving the radiation and thermal characteristics of natural gas flame. Also, kerosene droplets cause a higher rise in the temperature in flame downstream and make the axial flame temperature more uniform than coal particles do. In quantitative terms, when kerosene droplets were injected, the radiative heat transfer and thermal efficiency of flame were 93% and 35% higher than the corresponding values for the coal particles injection mode.

]]>The aim of this work is to study laminar mixed convection heat transfer characteristics within an obstructed enclosure by using the Lattice Boltzmann method. Flow is driven by a top cold lid while other walls are stationary and adiabatic. Hot cylinders are located at different places inside the cavity to explore the best arrangement. Comparison of streamlines, isotherms, average Nusselt number are presented to evaluate the influence of Richardson number and location of cylinders on flow field and heat transfer. Results indicate that heat transfer decreases with a rise of Richardson number for all considered arrays of cylinders. Among them, horizontally-located cylinders at the top of the cavity have the greatest heat transfer at all Richardson numbers. Horizontally located cylinders at the bottom of the cavity have the lowest heat transfer at Richardson numbers of 0.1 and 1 while the lowest heat transfer rate belongs to cross diagonal located cylinders at a Richardson number of 10.

]]>In this paper, the steady fully developed non-Darcy mixed convection flow of a nanofluid in a vertical channel filled with a porous medium with different viscous dissipation models is analyzed. The Brinkman-Forchheimer extended Darcy model is used to describe the fluid flow pattern in the channel. The transport equations for a nanofluid are solved analytically using the seminumerical-analytical method known as differential transformation method, and numerically with the Runge-Kutta shooting method. Finally, the influence of pertinent parameters, such as solid volume fraction, different nanoparticles, mixed convection parameter, Brinkman number, Darcy number, and inertial parameter on the velocity and temperature fields are shown graphically. The results show that velocity and temperature are enhanced when the mixed convection parameter, Brinkman number, and Darcy number increases whereas solid volume fraction and inertial parameter decreases the velocity and temperature fields. The obtained results show that the nanofluid enhances the heat transfer process significantly.

]]>Combined effects of slip velocity and volume fraction of slip spheres on the heat transfer characteristics of multiple slip spheres are numerically investigated within the framework of a free surface cell model combined with a linear slip velocity along the surface of the slip spheres. The governing conservation equations of the mass, momentum, and energy are solved by a segregated approach using a simplified marker and cell algorithm implemented on a staggered grid arrangement in spherical coordinates. The convection and diffusion terms of conservation equations are discretized using quadratic upstream interpolation for convective kinematics and second-order central differencing schemes, respectively. Prior to obtaining new results, this numerical solver is validated by comparison of present results with the existing literature values. Further new results are obtained for a range of conditions as; Reynolds number, Re: 0.1–200; Prandtl number, Pr: 1–100; volume fraction of slip spheres, *Φ*: 0.1–0.5 and slip parameter, *λ*: 0.01–100. The effects of these dimensionless parameters on isotherm contours and local and average Nusselt numbers are thoroughly delineated. Finally, a new empirical correlation for the average Nusselt number of multiple smooth slip spheres is proposed on the basis of present numerical results.

An experimental and numerical investigation of the thermal performance of three different nanofluids ethylene glycol-based CuO, water-based CuO, and Al_{2}O_{3} is done in a serpentine-shaped micorchannel heat sink. The microchannels considered ranged from 810 μm to 890 μm in hydraulic diameter and were made of copper material. The experiments were conducted with the Reynolds number ranging from approximately 100 to 1300. The forced convective heat transfer coefficient of nanofluids shows that there is an improved heat transfer rate compared to base fluids water and ethylene glycol. The experimental results also confirm that there is an earlier transition from laminar to turbulent flow in microchannels. The results prove that as the hydraulic diameter decreases there is increased pressure drop and the heat transfer coefficient increases for both the base fluids and nanofluids. The flow characteristics are discussed based on the pressure drop. While investigating the heat transfer coefficient of the three different nanofluids the nanofluid CuO/EG has the highest heat transfer coefficient as a result of the material's property. This research also will encourage young researchers to work on nanofluids of varying nanoparticle size and concentration to discover new results.

Flow over two isothermal offset square cylinders in a confined channel is simulated for different Reynolds numbers to disclose the forced convection heat transfer from the heated square cylinders to the ambient fluid. The spacing between the cylinder in the normal direction and the blockage ratio are fixed. The channel walls are covered by solid walls of thickness equal to the size of the cylinder and conjugate heat transfer is considered by including these walls. Heat transfer from the cylinders to the ambient fluid as well as that conducted within the solid wall through the conjugate interface boundary are investigated in connection with Reynolds number and are reported for both steady and periodic flows. Simulation is carried out for Reynolds number varying from 10 to 100 with air as the fluid. The onset of the vortex begins when the Reynolds number equals 48. The conjugate interface temperature declines when the Reynolds number grows. The isotherms in the solid wall show two dimensionality near the cylinder region.

]]>The strength in a high carbon wire is attributed to the pearlitic microstructure, which is required for ease of wire drawing. During cold drawing of high carbon steel wires, residual stress develops which has to be relieved in order to obtain the desired mechanical properties. To achieve this, the wire is passed through a closed loop online an induction furnace at a particular speed in order to heat it to a uniform temperature range. This research work presents the electromagnetic-thermal modeling of the induction heating of a moving wire based on the finite element method using the software package, COMSOL MultiphysicsTM. The furnace had a complicated geometry for the coils and this is, perhaps, for the first time an exhaustive study which is being reported. A unique grid generation technique was developed considering the skin effect. This work is aimed at enabling modeling of the process and will in turn be useful when defining individual parameters affecting the temperature distribution in a component, subjected to induction heating. The temperature distribution in the work piece depends primarily on parameters like coil position, line speed, frequency of the current, thermal and magnetic properties of the work piece, and so on. The impact of power supply frequency and line speed were studied during the heating of the moving wire (workpiece). An in-situ customized furnace of lower capacity was developed to carry out the validation experiments. The present modeling results are validated with online plant trial data and found to be in good agreement. Finally, the desired mechanical property achieved during trials was confirmed through tensile testing.

]]>The effects of different waste gas recovery sintering (WGRS) cases on iron ore sintering were determined through a sintering pot test and compared with conventional sintering (CS). Two key operational parameters were identified selectively, namely, the temperature and lean-oxygen content of recycled gas. The chosen values of these parameters for the sintering pot test were close to those in industrial production conditions. The proportion of the sintering mixture was standardized by ensuring the generation of mass-averaged particles with similar sizes. The changes in the sinter quality indices and in the process parameters under different WGRS cases were systematically analyzed to demonstrate the feasibility of replacing CS production with WGRS technology. The optimal temperature ranged from 200 °C to 250 °C, and the optimal oxygen content was 20%. Therefore, this work can guide the industrial application of WGRS in China considerably.

]]>Slab heating plays an important role in the production of iron and steel materials. However, it is a very complex process involving physical and chemical change. In this study, we built a numerical heat transfer model to predict the three-dimensional transient temperature field of a slab based on the implicit finite difference method. The model takes the growth of the oxide layer into account, as well as the impact on heat transfer. Slab temperature and oxide layer thickness were calculated in each step. The model considers three kinds of boundary conditions. It displays the temperature variation of each part of the slab in the furnace at all time, the heating curve, and the growth in the thickness curve of the oxide layer. This model can be used to control heating time, optimize the heating curve, and improve production efficiency, thereby reducing cost. The model is also useful for calculation of rolling force, as well as the control of carbon isolation and product microstructure.

]]>In this research, an oil-based nanofluid including Ag nanoparticles was made by a novel one-step physical method known as electrical explosion wire (*E.E.W*.). Highly concentrated applied nanofluids in this study remained stable for 38 days. The thermal conductivity of the nanofluids at various weight fractions 0.12%, 0.36%, and 0.72% (0.011%, 0.044%, and 0.171% Vol.) exhibited temperature dependency for different temperatures ranging from 40 °C to 100 °C, while the enhanced ratios are not constant. It is experimentally proved that the applied nanofluids with 0.12% wt. and 0.36% wt. showed Newtonian behavior and 0.72% wt. (0.171%Vol.) indicated non-Newtonian properties. In this study, due to the fact that the experimental results of thermal conductivity and viscosity were not predicted by the correlations presented in the literature, two general correlations to predict thermal conductivity, and viscosity of oil-based nanofluids, using any type of nanoparticle was presented. Obtained results from these correlations show a suitable accuracy between predicted values and experimental results of thermophysical properties of applied nanofluids and for published data of any oil-based nanofluids. The results showed that the proposed correlations are able to predict thermal conductivity and dynamic viscosity of any oil-based nanofluids with an acceptable accuracy.

A new mixed nanofluid (Cu/diamond–gallium [Cu/diamond–Ga] nanofluid) is proposed, and the mass ratio of Cu nanoparticles and diamond nanoparticles in the new mixed nanofluid is 10:1. The natural convection heat transfer of Cu/diamond–Ga nanofluid, Cu–gallium (Cu–Ga) nanofluid, and liquid metal gallium with different volume fractions in a rectangular enclosure is investigated by a single-phase model in this paper. The effects of temperature difference, nanoparticle volume fraction and the kinds of nanofluid on the natural convection heat transfer are discussed. The natural convection heat transfer of the three kinds of fluids is compared. It is found that Nusselt numbers of the Cu/diamond–Ga nanofluid along with *X* direction increases with the nanoparticle volume fraction and temperature difference. Cu/diamond–Ga nanofluid can enhance the heat transfer by 73.0% and 9.7% at low-temperature difference (Δ*T* = 1 K) compared with liquid metal gallium and Cu–Ga nanofluid, respectively. It also can enhance the heat transfer by 85.9% and 5.2% at high-temperature difference (Δ*T* = 11 K) compared with liquid metal gallium and Cu–Ga nanofluid, respectively.

This research work discusses the heat transfer improvement in a tractor radiator with nanosized particles of CuO with water as base fluid. The nano materials and its suspension in fluids as particles have been the subject of intensive study worldwide recently since pioneering researchers recently discovered the anomalous thermal behavior of these fluids. The engine cooling in heavy vehicles is an important factor for their performance in the intended application. Here, the tractor engine radiator cooling is enhanced by the nanofluid mechanism of heat transfer for its improved performance in agricultural work. Through the improvement of tractor engine cooling through the radiator a greater area can be ploughed and cultivated within a short time span. Heat transfer in automobiles is achieved through radiators. In this research work an experimental and numerical investigation for the improved heat transfer characteristics of a radiator using CuO/water nanofluid for 0.025 and 0.05% volume fraction is done with an inlet temp of 50 °C to 60 °C under the turbulent flow regime (8000 ≤ Re ≤ 25000). The overall heat transfer coefficient decreases with an increase in nanofluid inlet temperature of 50 °C to 60°C. The experimental results of the heat transfer using the CuO nanofluid is compared with the numerical values. The results in this work suggest that the best heat transfer enhancement can be obtained compared with the base fluid by using a system with CuO/ water nanofluid-cooled radiators.

]]>The present study is concerned with cooling a metal hydride tank during the charging process by using a water jacket and fins. Results indicate that the effect of the water jacket becomes more significant over time. Variation of the Reynolds number has no influence on the charging time in the turbulent regime while changing the flow regime from laminar to turbulent improves the results slightly. Furthermore, adding fins on the cooling jacket enhances the heat transfer significantly through better removal of the heat from the central region of the metal bed. Hence, the charging time was significantly reduced.

]]>An experimental investigation of the effect of mechanical vibrations of a copper flat circular surface on the pool boiling heat transfer coefficient of water at atmospheric pressure are presented in this paper. A vibration exciter was used to vibrate this copper test surface vertically. Effect of frequency and amplitude of vibration on the boiling heat transfer coefficient was studied. An increase in the heat transfer coefficient was observed at low frequency and amplitudes, at higher amplitude and frequency heat transfer deteriorates. Heat transfer coefficient increases up to 26% with vibration intensity, represented by vibrational Reynolds number.

]]>Thermal wave and dual phase lag bioheat transfer equations are solved analytically in the skin tissue exposed to oscillatory and constant surface heat flux. Comparison between the application of Fourier and non-Fourier boundary conditions on the skin tissue temperature distributions is studied. The amplitude of temperature responses increases and also the phase shift between the temperature responses and heat flux decreases under the non-Fourier boundary conditions for the case of an oscillatory surface heat flux. It is supposed the stable temperature cycles in order to estimate the blood perfusion rate via the existing phase shift between the surface heat fluxes and the temperature responses. It is shown that the higher rates of the blood perfusion correspond to lower phase shift between the surface temperature responses and the imposed heat flux.

]]>Flow patterns and local heat transfer coefficients were measured for air–water flow in a horizontal pipe. A technique based upon a cascade neural network was developed for simultaneously recognition of the flow pattern (FP) and the corresponding heat transfer coefficient (h_{TP}) for each FP. The results show good agreement between the estimated and the experimental values with 98.35% accuracy for FP and 95.6% accuracy for h_{TP}. The results were compared with the Kim and Ghajar heat transfer correlation. The findings revealed that the proposed model is efficient and predicts flow more accurately than the Kim and Ghajar correlation.

Effects of different waste gas recovery sintering (WGRS) methods on the quality index and process performance of the iron ore sinter were studied by a plant test, compared to the conventional sintering (CS). Two key operational parameters, namely, the temperature and oxygen content of the recycling gas, were selectively discussed. The values of these two parameters were measured in the gas-mixing chamber. The sintering mixture with a constant proportion was obtained ensuring the similar mass averaged particle sizes. The changes in the sintering process performance, such as the exhaust emission regulation, productivity, energy consumption, and sintering efficiency of the system, were analyzed. The quality indexes including the yield, chemical composition and size distribution of the sinter cake, the tumbler index (TI), and the reducibility (RI) in different methods of WGRS were also analyzed. Systematic analyses demonstrate the feasibility of replacing the CS production with the WGRS technology. The optimal temperature range of the recycling gas was 200 °C∼250 °C, and the suggested values of oxygen content was closed to 21%.

]]>In this study, the lattice Boltzmann method was used to solve the turbulent and laminar natural convection in a square cavity. In this paper a fluid with Pr = 6.2 and different Rayleigh numbers (Ra = 10^{3}, 10^{4},10^{5} for laminar flow and Ra = 10^{7}, 10^{8},10^{9} for turbulent flow) in the presence of a magnetic field (Ha = 0, 25, 50, and 100) was investigated. (Results show that the magnetic field drops the heat transfer in the laminar flow as the heat transfer behaves erratically toward the presence of a magnetic field in a turbulent flow. Moreover, the effect of the magnetic field is marginal for a turbulent flow in contrast with a laminar flow.The greatest influence of the magnetic field is observed at Ra = 10^{5} from Ha = 0 to 100 as the heat transfer decreases significantly.

The heat transfer of pool boiling in bead packed porous layers was experimentally investigated to analyze the effects of the bead material, bead diameter and the layer number of the porous bed on the transport of flux and the heat transfer coefficients. The glass and copper bead, the bead sizes of 4 mm and 6 mm as well as the bead packed porous structures ranging from one to three layers were chosen in the experiments. The pool boiling heat transfer in the bead packed porous structures and that on the plain surface were compared to analyze the enhancement of pool boiling heat transfer while the bead packed porous layers were employed. The maximum relative error between the collected experimental data of the pure water on a plain surface and the theoretical prediction of pool boiling using the Rohsenow correlation was less than 12%. Besides, the boiling bubble generation, integration and departure have a great effect on the pool boiling and were recorded with a camera in the bead stacked porous structures of the different layers and materials at different heat flux. All these results should be taken into account for the promotion and application of bead packed porous structures in pool boiling to enhance the heat transfer.

]]>There are many works on improving the performance of a cogeneration plant such as the implementation of a recuperator. In previous works, the authors modelled a gas turbine cycle considering the recuperator as a black box. In this paper, a cogeneration plant is modeled and optimized with details of recuperator parameters. For this purpose, 13 design variables for a plant as well as a recuperator are selected. Then, a genetic algorithm is applied to optimize exergy efficiency and total cost rate, simultaneously. This work included Energy, Economy, and Environmental factors which with Exergy provided *4E* analysis. A 36% decrease in total cost and a 33% increase in exergy efficiency in comparison with a simple gas turbine system were found. The above results for a gas turbine with a preheater and inlet cooling system reveal a 36% decrease in total cost and 35% increases in exergy efficiency. In addition, the optimum recuperator design parameters reveal that, higher effectiveness is more important than the investment cost. Moreover, a plant with higher exergy efficiency needs a recuperator with a lower pressure drop. Finally sensitivity analysis for variation of objectives functions with a change in fuel cost and interest rate are performed.

A polymer-based flat heat pipe (PFHP) was fabricated. The heat transfer performance was measured and analyzed when deionized (DI) water and acetone were used as the working fluid, separately. Input power ranging from 2.8 W to 14.2 W was provided to the evaporator section while the device was at different filling ratios. Experimental results revealed that, when the polymer-based flat heat pipe was laid in a horizontal position, the thermal resistance (1.02 K/W) was much smaller than that (4.6 K/W) of a copper plate with the same thickness at the thermal power of 10.3 W and the value decreased as the tilt angle changed from 0° to 90°.

]]>The problem of an unsteady magnetohydrodynamic stagnation point flow of an incompressible viscous fluid over a shrinking sheet is discussed in the presence of thermal radiation and boundary slip, which has not been documented to date in the literature. The governing boundary-layer equations are transformed to high order nonlinear and ordinary differential equations by similarity transformations and then solved numerically. The effects of magnetic parameter, unsteadiness parameter, radiation parameter, velocity, and thermal slip parameters on velocity and temperature are analyzed and discussed. It is found that dual solutions of both velocity and temperature fields exist for negative values of the velocity ratio parameter. The results indicate that dual solution domains of velocity and temperature expand as the unsteadiness parameter increases.

]]>The present numerical analyses are related to the cooling of a hybrid electric vehicle (HEV) battery module by water–ethanol mixture. The fluid is passed through a cold plate consisting of two rectangular channels of 0.01 m depth, 0.015 m width, and 0.15 m length. The battery module is represented by a heater placed below the cold plate. The single-phase pressure drop and single-phase heat transfer coefficient for water, water–ethanol mixture of mass fraction of 25%, 50%, and 75%, and ethanol are determined numerically for different heat fluxes of 10, 15, 20, and 25 kW/m^{2} and different Reynolds numbers 500, 1000, 1500, 2000, and 2500. To solve the Navier–Stokes equation, the pressure correction method was used and to solve the energy equation, the Lax–Wendroff explicit method is used. Numerical results obtained for water are compared with the literature correlations. The friction factor for water deviated by an average of 8.02% from the Lewis and Robertson equation. The Nusselt number for water deviated by 7.35% from the Churchill and Ozoe equation at lower Reynolds number 500 and at higher Reynolds number 2500, Nusselt number deviated by 13.68% from the Stephan equation. The results showed that the heat transfer coefficient increased with an increase in Reynolds number and heat flux. The effect of the increase in Reynolds number is more significant than the increase in heat flux. At higher ethanol mass fraction and higher Reynolds number the heat transfer coefficient increased with heat flux when compared to water. There is no significant decrease in heat transfer coefficient with an increase in ethanol mass fraction. The pressure drop increased and the heat transfer coefficient decreased with an increase in ethanol mass fraction.

Simultaneous estimation of thermophysical and optical properties such as the thermal conductivity, the scattering albedo, and the emissivity of a 1-D planar porous matrix involving combined mode conduction and radiation heat transfer with heat generation is reported. Coupled energy equations for the gas and solid phase account for the nonlocal thermal equilibrium between the two phases. Performances of the genetic algorithm (GA) and the global search algorithm (GSA) in simultaneous estimation of three properties are analyzed. Both the GA and the GSA utilize a priori knowledge of the axial gas temperature distribution, and the magnitudes of the convective and the radiative heat fluxes at the outer surface of the porous matrix. With volumetric radiative information needed in the solid-phase energy equation computed using the discrete transfer method, the two energy equations are simultaneously solved using the finite volume method. GSA provides better estimation, and computationally, it is much faster than the GA.

]]>This study examines two important parameters: the convective heat-transfer coefficient and radiative heat-transfer coefficient, which have a significant impact on coil temperature in a furnace. A new three-dimensional model is proposed for convective heat transfer, and the factors affecting the Nusselt number (*Nu*) are studied using the orthogonal test method. Finally, the relationship between the *Nu* number and flow rate is determined. Considering the complex geometric structure of a furnace, this study uses the Monte Carlo method to calculate the angle factor and obtains the radiant heat flux using a radiation network diagram. The calculated values are applied to steel coil temperatures for accurate boundary conditions. The results show that the temperature simulated by using the mathematical model is in good agreement with the experimental data obtained with the thermocouple insert experiment.

Experimental investigations of heat transfer characteristics and performance enhancement of shell and helical coil water coolers using external radial fins and different shells diameters were conducted. The study aims to enhance the water coolers performance in a trial to improve coil compactness. Two helical coils; one with a plain tube and the other with external radial fins, were tested in four shells of different tube diameters. Refrigerant passing inside the helical coils was used to cool water that enclose/passes in the space between the helical coil and the shell. Tests were conducted under mixed convection heat transfer regimes. Results showed performance and compactness enhancement with the insertion of external radial fins and increasing the shell diameter to helical coil diameter ratio. For nonfinned and finned coils, Nusselt number increased with increasing Reynolds number, Grashof number, and shell diameter. Correlations were predicted to give the Nusselt number in terms of Reynolds number, Grashof number, and shell diameters for finned and nonfinned helical coils. Correlations predictions were compared with present and previous experimental results and good agreements were obtained.

]]>An analysis is performed to study natural convective heat transfer in a vertical rectangular duct filled with a nanofluid. One of the vertical walls of the duct is cooled by a constant temperature, while the other wall is heated by a constant temperature. The other two sides of the duct are thermally insulated. The transport equations for a Newtonian fluid are solved numerically with a finite volume method of second-order accuracy. The influence of pertinent parameters such as Grashof number, Brinkman number, aspect ratio and solid volume fraction on the heat transfer characteristics of natural convection is studied. Results for the volumetric flow rate and skin friction for Copper and Diamond nanoparticles are also drawn. The Nusselt number for various types of nanoparticle such as silver, copper, diamond and titanium oxide are also tabulated. The results indicate that inclusion of nanoparticles into pure water improves its heat transfer performance; however, there is an optimum solid volume fraction which maximizes the heat transfer rate.

]]>Optimal design of an energy storage tank system is presented in this study. Total annual cost is considered as the objective. To minimize the total annual cost, 24 design parameters including the operational strategy of the chiller in each hour during a sample day are selected. A Particle Swarm Optimization (PSO) algorithm is used for three different strategies including partial storage (PS), full storage (FS), and variable storage (VS), separately. In addition, this procedure is performed for both electrical and absorption chillers. There was a 25.21% and 13.80% improvement in total annual cost observed in the VS strategy compared with the PS and FS strategies, respectively, in the case of an electrical chiller. Furthermore, 23.47% and 8.01% improvement in total annual cost is observed in the VS strategy compared with the PS and FS strategies, respectively, in the case of an absorption chiller. Moreover, the electrical chiller was found to be more suitable in this study but no sensible difference is observed in the FS strategy. Finally the optimum results of the PSO algorithm is compared with the Genetic Algorithm (GA) and differences are reported.

]]>This paper focuses on the effects of wall confinements (or blockage ratios) on the flow and heat transfer characteristics around a long equilateral triangular bluff body placed in a horizontal channel for Reynolds number (Re) range 1 to 80 and blockage ratio range 0.1 to 0.5 for air as the working fluid. The governing continuity, Navier–Stokes and energy equations along with appropriate boundary conditions are solved by using a finite volume method-based commercial solver Ansys Fluent. The total drag coefficient decreases with an increasing value of Re for a fixed value of the blockage ratio; however, it increases with an increasing value of the blockage ratio for a fixed value of Re due to the fact that the channel walls exert an extra retardation force on the obstacle. The onset of flow separation is delayed as the value of the blockage ratio increases. The critical Re (i.e., the transition to a time-periodic regime) exists between 45 and 46, 46 and 47, 58 and 59, and 79 and 80 for the blockage ratios of 0.1, 0.125, 0.25, and 0.5, respectively. The simple correlations for wake length, total drag coefficient, and average obstacle Nusselt number are obtained for the range of conditions covered.

]]>In this work, a transient heat conduction model is developed for rewetting a hot wall surface by a falling liquid film. In the model, the heat conduction in the rewetted wall is assumed to be two-dimensional. Convection heat transfer from the hot surface to rewetting fluid is considered negligible in the dry surface region ahead of the wet front. The numerical solution indicates that the rewetting process is mainly controlled by two-dimensional heat conduction in the rewetted wall, even for the walls of low Biot number, especially at low initial temperatures. The effects of Biot number and initial wall temperature on the rewetting velocity are investigated. Comparison of the results with previous studies is presented.

]]>This work is devoted to study the natural convection boundary-layer flow of nanofluids along a vertical flat plate with the effect of sinusoidal surface temperature variations. The model utilized for the nanofluid incorporates the effects of Brownian motion and thermophoresis. An appropriate set of dimensionless variables is used to transform the governing equations of the problem into a nonsimilar form. The obtained nonsimilar equations have the property that they reduce to various special cases previously considered in the open literature. An adequate and efficient implicit, tri-diagonal finite difference method is employed for the numerical solution of the obtained equations. Comparison with previously published work is performed and the results are found to be in excellent agreement. A representative set of numerical results for the dimensionless velocity, temperature and nanoparticle volume fraction, as well as the surface shear stress, rates of heat and nanoparticle volume fraction have been presented graphically and discussed to show interesting features of the solutions.

]]>This paper is about a separated reattaching flow over a hot rectangular obstacle. Two types of incoming flow are examined in order to show the influence of the external zone of the flow on the reattachment process. It comes about due to a wall jet and a boundary layer. The inner region of these two flows is similar, but their external regions are extremely different. The separating and reattaching flow phenomena are of particular interest in engineering fields such as for an aeronautical application. Wall jet flow over an obstacle occurs in many engineering applications such as environmental discharges, heat exchangers, fluid injection systems, cooling of combustion chamber wall in a gas turbine, automobile design, and others. In electronics cooling, the prediction of the Nusselt number distribution along the obstacles is necessary before the design of the apparatus. For a heated obstacle at a constant temperature, *T* = 350 K and an aspect ratio of 10 (*L* = 10 *H*), the problem parameters are: (a) jet exit Reynolds number (Re) ranged from 1000 to 50000, (b) incoming flow configuration (boundary layer and wall jet). The ratio between the thickness of the nozzle (b) to the obstacle height (*H*) are examined simultaneously. The formulation is based on the SST *k*–*ω* turbulence model. The results show that the increasing of nozzle thickness; enhances the heat transfer and considerably modifies the stagnation point location. The highest incoming flow momentum provides the greatest values of average Nusselt number. Such as the boundary layer case in comparison with the wall jet cases. The average Nusselt number is correlated according to problem parameters .

Extended surfaces are used in a variety of heat transfer applications owing to their ability in reducing the convection resistance by exposing a large surface area to the surrounding fluid. Surface modification in the form of perforations is a passive method of increasing the heat transfer rates with the additional benefit of weight reduction. This work deals with numerical investigation of heat transfer and friction from a perforated fin (with and without slot) subjected to forced convection. The perforated fin with slot has been found to have a maximum enhancement in heat transfer with the simultaneous increase in frictional losses versus that of a solid fin. Further, the perforated fin without slot has been able to transfer heat at a relatively higher rate with a considerable reduction in energy loss due to friction in comparison to a solid fin.

]]>Thermal modeling and optimal design of a combined cooling, heating, and power (CCHP) generation system are presented in this paper. A new procedure for simultaneous selection of the type (gas engine, diesel, gas turbine) and number of available prime movers (PMs) in a market, selecting PMs partial load, selecting the heating capacity of backup boiler as well as selecting the cooling capacity of electrical and absorption chillers available in the market are presented. A genetic algorithm (GA) with discrete and continuous decision variables is applied to select the equipment for the CCHP system by maximizing the actual annual benefit (AAB) as the objective function. The optimization problem is carried out for 1000 alternative states for electricity, cooling, and heating (E-Q-H) loads in the range of 500 kW to 5000 kW to investigate the effect of E-Q-H loads. Moreover, the optimization is performed at two SELL and NO-SELL modes. In the former case is the sale of the excess electricity to the network is allowed and in the latter one, it was not allowed to sell the excess electricity to the grid. A correlation in terms of E-Q-H loads is obtained to specify the effect of E-Q-H loads on optimum AAB values in SELL and NO-SELL modes. Using these correlations, designers can predict the maximum accessible AAB for any electricity, cooling, and heating loads in the above specified range.

]]>A mathematical model for predicting evaporation in the thin film region was developed and its analytical solutions were obtained for thin-film thickness, the heat transport per unit length and the total heat flux transport in the thin-film region. These analytical solutions show that the higher heat flux through the thin film region occurs due to the higher superheat. The maximum evaporative rate occurs when the effects of the increase in the temperature difference and in the thin film thickness on the heat flux *q* stay equal. A nanofluid, which is a colloidal mixture of nanoparticles (1 nm to 100 nm) and a base liquid (nanoparticle fluid suspensions), is employed as the working fluid. In a certain range, increasing the volume fraction of nanoparticles in the base fluid leads to decreasing the kinematic viscosity of the nanofluid and increasing the thermal conductivity, which influences the evaporation in the thin film region. The heat transfer rate per unit length and the total heat flux in the thin film region display various characteristics among the different type of nanofluids due to the differences of the kinematic viscosity and the thermal conductivity.