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.

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.

]]>The experimental investigation of heat transfer enhancement and flow analysis in a diffuser using vortex generators (VGs) is carried out. Two diffuser angles are examined. One and two VG pairs are considered. The velocity profile at the diffuser inlet is uniform and the flow is a developing one. The VGs are placed on the side opposite to the heated surface. It is observed that the heat transfer enhancement is more with the two pair case. The Reynolds number based on inlet velocity and diffuser length is in the range 2.3 to 3.6E05. The maximum enhancement is 62% at constant Reynolds number and 40% at constant dissipation. The enhancement increases with the angle of attack of the VG and decreases with the diffuser angle and with Reynolds number.

]]>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.

]]>A numerical study on the effect of the effect of elliptical and flattened tube bundle geometry on the convective heat transfer and pressure drop is presented in this article. The analysis has been carried out to evaluate the performance of these bundle geometries in the design of a compact and effective single phase shell and tube heat exchanger. The temperature, velocity, and pressure drop profiles are obtained from solving the mass, momentum, and energy conservation equations. The comparison is made for inline and staggered bundle with different pitch to diameter ratio and inlet velocity for elliptical and flattened tubes. The pitch to diameter ratio is varied from 1.25 to 2.5 for Reynolds number ranging from 200 to 2000 which is in the laminar flow region. The heat transfer coefficient over the staggered and inline tube bundle decrease with an increase in pitch. The same kind of variation is also observed for the pressure drop in the case of both elliptical and flattened tube bundle. The study shows that the transverse pitch with respect to cross flow affects more than the longitudinal pitch.

]]>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 .

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 work presents a numerical investigation of turbulent forced convection of a nanofluid over a heated cavity in a horizontal duct. Heat transfers in separated flows are frequently encountered in engineering applications, such as: heat exchangers, axial and centrifugal compressor blades, gas turbines blades, and microelectronic circuit boards. Thus, it is very essential to understand the mechanisms of heat transfer in such regions in order to enhance heat transfer. Different volume fractions of nanoparticles are presented in the base fluid and different types of nanoparticles are used. The objective of this study is to check the effect of nanofluid on heat transfer in such a configuration. Numerical simulations are performed for pure water and four nanofluids (Cu, CuO, Ag, and Al_{2}O_{3}). The results are analyzed through the thermal and dynamical fields with a particular interest to the skin friction coefficient and Nusselt number evolutions. The average Nusselt number increases with the volume fraction of nanoparticles for the whole tested range of Reynolds number. A correlation of average Nusselt number versus Reynolds number and volume fraction of each type of nanoparticles over the cavity wall is proposed in this paper.

An experimental investigation was conducted to explore the maximum heat transfer in a serpentine shaped microchannel by varying the hydraulic diameter, flow rates and with influence of Al_{2}O_{3} nanofluid. Microconvection is an important area in heat transport phenomena. Surface area is one of the important factors in high heat transfer in a microchannel heat exchanger. In this study, serpentine shaped microchannels of hydraulic diameters 810, 830, 860, and 890 μm are analyzed for the optimizing the hydraulic diameter to get enhanced thermal performance of the microchannel. A copper material microchannel having length a of 70 mm is used. Flow rate also varied from 1 lpm (Litres per minute) to 3.5 lpm for optimization with nanofluid as a medium. From numerical study it is observed that as the hydraulic diameter decreases from 890 μm to 810 μm the pressure drop increases with a decrease in hydraulic diameter. Also as heat input to the microchannel increases from 5 watts to 70 watts. From analysis it is observed that the hydraulic diameter of the microchannel is a major factor in microchannel heat transfer which is dependent on flow rate of fluid in the microchannel. The results also show that suspended Al_{2}O_{3} nanoparticles in fluids have enhanced heat transfer when compared to the base fluid.

In this paper, a numerical simulation technique is developed to investigate the qualitative and quantitative behaviour of Cu-nanoparticles in a porous medium vis-a-vis the heat transfer enhancements—buoyancy driven flow in a two-dimensional square cavity, with moving walls is presented. The model utilizes the finite volume approach to solve the Brinkman–Darcy equations for Cu-nanoparticles in a porous media. Discretization is carried out for convective and diffusive fluxes using Quadratic Upwind Interpolation for Convective Kinematics (*QUICK*) and central difference schemes, respectively. Tri-Diagonal Matrix Algorithm is invoked to solve the set of algebraic equations. The Darcy number (Da), Prandtl number (Pr), and volume fraction (*χ*) are varied from 10^{−3} to 10^{−1}, 3 to 7, and 0% to 20%, respectively. Insight into the cause of variations in isotherms, streamlines, Nusselt number (Nu), and mid-plane velocities is explicated. The present numerical results are compared with the existing literature and found to be in good agreement. Even though nanoparticles slightly hinder the activity of the fluid, they can augment the average Nu by 90% for Pr = 7, Da = 0.1, and *χ* = 20% as compared to the absence of nanoparticles. Their efficacy is more prominent for flows with higher Da and Pr. Quantitative values for Nu were obtained for various combinations of Pr, Da, and *χ*.

An analysis is carried out to discover the influence of a rotating nanofluid over a stretching surface. The two phase nanofluid model is used for this study. Two types of nanoparticles, namely copper and titanium oxide are used in our analysis with water as the base fluid. The governing system of partial differential equations along with the corresponding boundary conditions are presented and then transformed into a set of nonlinear ordinary differential equations using suitable similarity transformations. These equations are solved numerically by means of an iterative procedure called the midpoint integration scheme along with Richardson extrapolation. The results for flow and heat transfer characteristics are presented through graphs against nanoparticle volume fraction and rotation parameter for both types of nanoparticles. Quantities of physical interest such as local skin friction coefficients and local heat flux rate at the stretching surface are computed and analyzed. Numerical values for skin frictions and local heat flux rate are computed in the absence of nanoparticle volume fraction and rotation and they are found to be in very good agreement with the existing published literature.

]]>Wetting kinetics, kinematics, and cooling performance of vegetable oils (sunflower, gingelly, palm, and coconut oils) during quenching of Inconel 600 probe were studied using goniometry, online video imaging, and cooling curve analysis. The results were compared with a conventional mineral oil quench medium. Improved wettability was obtained for vegetable oils with lower viscosity. Cooling curve analyses showed three stages of cooling for both mineral and vegetable oils. Video imaging of the quenching process and differential scanning calorimetry analysis confirmed that the first stage of cooling was caused by the formation of vapor film in mineral oil and due to the occurrence of a heated liquid layer around the quench probe surface in vegetable oils. Vegetable oils showed continuous boiling phenomenon during the convective cooling stage of quenching. The cooling performance of vegetable oils was found to depend on the concentration of mono-unsaturated fatty acid. The heat extracting capability of vegetable oils with lower mono-unsaturated fatty acid oils was found to be higher. However, no correlation was observed between fatty acid composition and uniformity of heat transfer. When compared to mineral oil quenching, vegetable oil quenching produced faster wetting kinematics and better cooling performance.

]]>Laminar forced convection heat transfer and nanofluids flow in an equilateral triangular channel using a delta-winglet pair of vortex generators is numerically studied. Three nanofluids, namely; Al_{2}O_{3}, CuO, and SiO_{2} nanoparticles suspended in an ethylene glycol base fluid are examined. A two-phase mixture model is considered to simulate the governing equations of mass, momentum and energy for both phases and solved using the finite volume method (FVM). Constant and temperature dependent properties methods are assumed. The single-phase model is considered here for comparison. The nanoparticle concentration is assumed to be 1% and 4% and Reynolds number is ranged from 100 to 800. The results show that the heat transfer enhancement by a using vortex generator and nanofluids is greater than the case of vortex generator and base fluid only, and the latest case provided higher enhancement of heat transfer compared to the case of a base fluid flowing in a plain duct. Considering the nanofluid as two separated phases is more reasonable than assuming the nanofluid as a homogeneous single phase. Temperature dependent properties model provided higher heat transfer and lower shear stress than the constant properties model.

The thermal and velocity profiles of various nanofluid systems on a rotating disk are simulated. Finite difference method, the orthogonal collocation method, and the differential quadrature method (DQM) of numerical approaches are used to solve the governing equations and are compared to determine the faster and more accurate solution procedure. Five nanoparticles Al, Al_{2}O_{3}, Cu, CuO, and TiO_{2} solved in three base fluids water, ethylene glycol, and engine oil are considered to be used on the disk at different volume fractions. A new general algorithm is presented for solving equations of a rotating-disk problem quickly and accurately and it is found that the DQM method is the best approach for this numerical simulation. Heat transfer performance of a rotating disk would be much better enhanced with water based Al nanofluid. A wide range of results for different base–fluid combinations with nanoparticles is presented with untransformed 3D results and effects of the variation of different parameters provides comprehensive insight and prevents inaccurate deductions.

Prediction of surface heating rates is of prime importance for the hypersonic flow regime. Experimental and conventional computational efforts overlook the heat transfer phenomenon in the solid due to the rigid assumptions involved in the solution methodologies. In order to address this fact, conjugate heat transfer (CHT) studies are carried out using various coupling techniques to examine their implementation abilities. Three types of solution methodologies are adopted, namely, decoupled, strongly coupled, and loosely coupled analysis. This study is also focused on looking into the effect of a hypersonic flow field on wall heat flux for a finite thickness insulating cylinder at moderately large time scales. Increase in wall temperature and decrease in surface heat flux have been noticed using strong and loose coupling techniques with an increase in simulation time. Decoupled fluid and solid domain analysis is found to be useful for typical shock tunnel test durations (∼1 ms) while investigations with loose coupling techniques are advisable for time scales corresponding to flight testing (∼1 s). Efforts are also made to reason the discrimination in prediction of stagnation point heat flux using conventional computational and experimental analysis.

]]>This study involves the numerical solution of the laminar heat transfer in a separating and reattaching flow by simulating the flow and heat transfer downstream of a backward-facing step. The in-house finite volume code has been implemented employing a hybrid differencing scheme and the SIMPLE algorithm for the pressure–velocity coupling. Three principal parameters governing heat transfer in this geometry, that is channel expansion ratio (ER), Reynolds number (Re), and Prandtl number (Pr), are systematically varied in the range ER = 1.111 to 2, Re = 1 to 200, and Pr = 0.71 to 100, and the simple correlations between these parameters have been elucidated. A series of important findings have been established by analyzing the results some of which are: (1) there is an associated shifting of the point of maximum heat transfer with respect to the flow-reattachment point with gradually decreasing the values of ER and (2) the heat transfer enhancement increases with the increase in Pr number as a result of the compression of the thermal boundary layer and the maximum Nusselt number varies as .

]]>Lattice Boltzmann simulations were conducted for the free convective flow of a low-Prandtl number (Pr = 0.0321) fluid with internal heat generation in a square enclosure having adiabatic top and bottom walls and isothermal side walls. The problem of free convection with volumetric heat source has represented itself in connection with advanced engineering applications, such as water-cooled lithium–lead breeder blankets for nuclear fusion reactors and liquid metal sources of spallation neutrons for subcritical fission systems. A single relaxation time (SRT) thermal lattice Boltzmann method (LBM) was employed. While applying SRT, a D2Q9 model was used to simulate the flow field and temperature field. Results have been obtained for various Rayleigh numbers characterizing internal and external heating from 10^{3} to 10^{6}. Flow and temperature fields in terms of stream function and isotherms in the enclosure were predicted for these cases. The temperature of the fluid in the enclosure was found higher than the heated wall temperature at high values of internal Rayleigh numbers. The internal heat generation affected the rate of heat transfer significantly as two convection loops are observed in the enclosure. The average Nusselt number at the heated and cold wall was determined for all the cases.

The heat recovery steam generator (HRSG) and duct burner are parts of a combined cycle which have considerable effect on the steam generation. The effect of the gas turbine, duct burner and HRSG on power generation is investigated to reduce exergy destruction and power loss in the gas turbine. The results show that with an increase in duct burner flow rate, pressure loss in the recovery boiler increases, steam generation increases on the HP side while it decreases on the LP side. With a reduction in the HP pinch point, thermal recovery increases while the LP pinch point does not have a significant effect. Then, power loss due to pressure drop in the gas turbine and the electricity cost are considered as two objective functions for optimization. Finally, the sensitivity analysis on ambient temperature, compressor pressure ratio, fuel lower heating value, duct burner fuel rate, condenser pressure and main pressure are performed and results are reported. It is concluded that with an increment in compressor pressure ratio, the duct burner flow rate and consequently steam generation increases while electricity cost decrease.

]]>A device was designed for measuring the permeability of cement clinker accumulation in three dimensions. In addition, the equivalent permeability and equivalent thermal resistance coefficient were introduced to evaluate the penetration ability in high temperature. First, the equivalent permeability of the accumulation in three dimensions was measured at a room temperature of 298 K and the order of magnitude was decided to be 10^{−6}. The difference degree of equivalent permeability was less than 15% in each direction; Then the rule of equivalent permeability in three-dimensional changed with temperature was obtained by the air-cooled experiments of the cement clinker accumulation at an initial temperature – 773 K; Finally, the law of equivalent thermal resistance coefficient was obtained through comparing the change of the permeability from high temperature to room temperature. The results showed that the equivalent thermal resistance coefficient change with temperature was nonlinear and the equivalent thermal resistance coefficient changed from 1.0 to 1.3 when the temperature was in the range of 298 K to 773 K.

The effect of the lubricant flow in the micro-grooves which resulted from the machining can be expressed in the flow fluid and heat transfer during the mechanical lubrication process. In this paper, a thermal lattice Boltzmann model (LBM), which consists of the heat viscous dissipation term, was proposed to investigate on the lubricants flow and heat transfer in the micro-grooves. The heat, generated in the lubricating flowing process, was equivalent to a heat source R (*x*, *t*) within the fluid and added to the internal energy distribution function. The effect of the heat generated by the fluid on the flow and temperature field can be derived by comparing these two models. The results showed that the fluid temperature rises slower than the mainstream area on account of the vortex motion in the grooves. When the heat source is added to the function, the vortex became larger and the solid boundary was heated by the fluid. Thus, the improved thermal lattice Boltzmann method can accurately simulate the flow of lubricants.

A computer program was developed for the performance analysis and design optimization of a cylindrical shell and helical tube type HFC134a condenser and its predicted results were verified against the experimentally determined data. The computer model is based on a numerical method of cell discretization. The local values of variables like heat transfer rate, pressure drop, and the properties of refrigerant are calculated on the basis of appropriate theoretical and empirical correlations available in the literature and the mass, momentum, and energy balance is applied to each cell. The whole sequential and iterative procedure to satisfy the boundary conditions of each cell and of the whole condenser has been transformed into a computer program written in C++. This computer model was used in a parametric study to analyze the effects of varying the input parameters of both fluids on the performance of the condenser. It gives the optimal values of refrigerant mass velocity and of the tube diameter against the available conditions of external cooling fluid, mass flow rate of refrigerant, and degree of subcooling of the refrigerant at the condenser outlet. Its utility was found in the performance optimization of an existing condenser as well as in the design optimization of a new condenser.

]]>Pulsed jets in different configuration are potentially considered for enhancing transport phenomenon generally. Flow and temperature field in a pulsed impinging jet are simulated numerically by solving the governing equations using the control volume method. Ensemble Averaging Method as well as Phase Averaging has been employed for reporting the results in this study. In order to simulate a pulsating jet, inlet velocity profile was exerted as a time dependent sinusoidal and step signals. The results of this simulation showed an oscillatory jet could lead to an increase in jet development and its cross section with the wall and also a more uniform Nusselt profile would be obtained compared to the steady jet. For parametric investigations and extracting flow and thermal characteristics of a pulsed impinging jet, the effects of various parameters including flow frequency and amplitude and heat flux frequency were considered. It has been seen that Nusselt number varies by the changes in frequency, amplitude and the type of the excitation. It has been shown that the oscillating impinging jet has a better performance rather than the steady case when the excitation amplitude and frequency increase. Finally, it is also observed how a thermal field is going to respond with two pulsating inputs.

]]>An experimental investigation of evaporative effectiveness and mass transfer coefficient on a bundle of tubes of an evaporative tubular heat dissipator is presented. Based on the experiments, correlations of evaporative effectiveness and mass transfer coefficient are derived using multiple regression analysis. A statistical model is developed to correlate the operating variables using design of experiment approach by selecting central composite design of a response surface methodology. Results shown in this article indicate that as the cooling film flow rate increases, evaporative effectiveness and mass transfer coefficient increases provided that the air flow rate is constant which is flowing from underneath the tubes of the evaporative tubular heat dissipator. Derived correlations are helpful in improvement of the design of heat transfer devices and many other engineering applications. Consideration of relative humidity of upstreaming air as one of the operating variables leads to the contribution to heat and mass transfer study of evaporative tubular heat dissipators in the present investigation.

]]>A numerical investigation of magnetoconvective boundary layer slip flow along a nonisothermal continuously moving permeable nonlinear radiating plate in Darcian porous media is reported. The concentration dependent mass diffusivity, viscous dissipation, Joule heating, and chemical reaction are taken into account. A Lie group of transformation is applied to the governing transport equations and boundary condition to find the corresponding similarity equations. Furthermore, the similarity equations with the relevant boundary conditions are solved numerically using the Runge-Kutta-Fehlberg fourth-fifth order numerical method. Numerical results for the dimensionless velocity, temperature, and concentration distributions as well as friction factor, local Nusselt, and local Sherwood numbers are discussed for various controlling parameters. It is found that that the dimensionless concentration increases whilst the rate of mass transfer decreases with the mass diffusivity parameter. An excellent correlation is found between the present results and published results. The study finds applications in the polymer industry and metallurgy.

]]>In this paper, the indirect method of finite element analysis was built for analyzing temperature and stress field of an H-beam heating process via Ansys software. The convection and radioactive heat flux were calculated, respectively for the solutions of temperature field, the offspring of the Ansys software. The solutions of temperature field were the initial conditions for stress field calculation. The temperature field and stress field were analyzed for an H-beam under different conditions; its result, which is the change of temperature and stress, will be a theoretical basis for an H-beam heating control.

]]>Optimal homotopy asymptotic method (OHAM) is used to obtain solutions for nonlinear ordinary differential equations (ODEs) arising in fluid flow and heat transfer at a nonlinear stretching sheet. The solutions for skin friction and temperature gradient for some special cases are tabulated and compared with the available numerical results in the literature. Moreover, OHAM is found to be very easy to use and the technique could be used for solving coupled nonlinear systems of ordinary differential equations arising in science and engineering.

]]>In this paper, Eulerian, mixture and single phase models are used to simulate laminar and turbulent forced convective flow of SiO_{2}-EG nanofluid in a microtube. The comparison between the three approaches and other formula shows that for laminar and turbulent flow the single phase model shows higher heat transfer enhancement and is more precise in comparison to the other Eulerian and mixture models.

A rotating platform was used to create dynamic load, and the mixture air–water two-phase flow and boiling steam–water two-phase flow were obtained in an inclined test pipe. By changing the parameters, such as inclination of the test pipe, rotational speed, inlet temperature, flow rate, and so on, the experiments for two-phase flow in the pipe at inclination of 0°, 45°, and 66° were conducted, respectively. The effects of acceleration and inclination on their flow and heat transfer characteristics were investigated. The two-phase flow patterns in inclined pipes under rotation conditions were caught with a video camera. The images show that the impact mixed flow and churn flow were found in this research. The results show that the acceleration and pipe inclination significantly influence the flow characteristic and heat transfer of the two-phase pipe flow. As the directions of the dynamic load and the gravity are opposite to the flow direction, the greater the dynamic load and inclination, the higher the pressure drop and the heat emission, and the lower the flow rate, the void fraction, and the fluid temperature. Therefore, the dynamic load and gravity will improve the flow resistance, enhance heat emission and reduce the heat gained by the fluid.

]]>Heat dissipation is an important issue in compactness and weight of equipment. Heat dissipaters are not only chosen for their thermal performance but also for other design parameters such as weight, cost and reliability depending on applications. The present paper reports an experimental study to investigate the heat transfer enhancement over vertical rectangular fin arrays equipped with lateral circular perforations. The cross-sectional area of the rectangular duct was 200 mm × 80 mm. The data used in performance analysis were obtained experimentally for aluminum at 200 Watts heat input, by varying the fin thickness, size of perforations and varying Reynolds number range 2.1 × 10^{4} to 8.7 × 10^{4}. Using the Taguchi experimental design method, optimum design parameters and their levels were investigated. Average Nusselt number was considered as a performance characteristics. An L_{9} (3^{3}) orthogonal array was selected as an experimental plan. Optimum results were found by experimenting with porosity, Reynolds number and thickness of the fin. It is observed that the Reynolds number and maximum porosity have a larger impact on Nusselt number.

Increasing the performance of a Heat Recovery Steam Generator **(**HRSG) through efficient utilization of energy associated with flue gases coming out of gas turbines in combined cycle power plants is finding a significant place in research. Amongst different approaches the second law analysis is well suited for finding out the loss of exergy at various locations, its type, and magnitude. Such information is of use in the design of new HRSG technologies and to reduce the inefficiencies in existing HRSGs. This paper presents the exergy analysis of the HRSG for calculating exergy losses, heat transfer and pressure losses for different physical components. Study indicates that various sub sections of heat recovery steam generator having different physical parameters like fin density, fin thickness, fin height, tube diameter and fin spacing show a noticeable effect on exergy loss minimization.

Entropy generation of an Al_{2}O_{3}–water nanofluid due to heat transfer and fluid friction irreversibility has been investigated in a square cavity subject to different side-wall temperatures using a nanofluid for natural convection flow. This study has been carried out for the pertinent parameters in the following ranges: Rayleigh number between 10^{4} and 10^{7} and volume fraction between 0 and 0.05. Based on the obtained dimensionless velocity and temperature values, the distributions of local entropy generation, average entropy generation, and average Bejan number are determined. The results are compared for a pure fluid and a nanofluid. It is totally found that the heat transfer, and entropy generation of the nanofluid is more than the pure fluid and minimum entropy generation and Nusselt number occur in the pure fluid at any Rayleigh number. Results depict that the addition of nanoparticles to the pure fluid has more effect on the entropy generation as the Rayleigh number goes up.

This study investigates the effects of the wall waviness on forced convection and its fluid flow in a channel bound by two wavy walls. The lattice Boltzmann method based on the boundary fitting method is used to simulate flow and thermal fields in the corrugated channel. The problem is investigated for different Reynolds numbers (50 to 150), wall amplitudes (0 to 0.35), number of wall wavelength (2 to 8), and phase difference of the walls (0 to 270) when the Prandtl number is equal to 0.71 for air flow. The study represents the significant effects of wavy walls on flow and thermal fields in a two-dimensional channel. It is found when the phase difference between the channel walls has a value equal to 90°; the best heat transfer rate can be achieved in comparison with other geometrical conditions and the flow is likely to be periodically unsteady at lower Reynolds numbers.

]]>In this paper, the performance of organic Rankine cycle with a two-stage turbine and internal heat exchanger, considering different dry hydrocarbons as working fluid, has been analyzed. This thermodynamic analysis is done using Engineering Equation Solver version 8.379 software. The influence of working fluid reheating has been studied and the critical temperatures for the thermal and exergy efficiencies are determined. Results show that thermal and exergy efficiencies increase with working fluid reheating and also through a two-stage turbine. RC-318 is a good replacement for R-236fa, R-113 has a better efficiency than R-236fa, R-245fa, and iso-butane and finally cyclohexane can achieve the highest efficiency. Although the maximum value of efficiencies for each one of working fluids are different, but all of these maximum values almost happen at a unique value of relative pressure of the cycle. The same result has been presented for variation of turbine inlet temperature.

]]>This paper investigates the radiation and chemical reaction effects on Casson non-Newtonian fluid *towards a porous stretching surface* in the presence of thermal and hydrodynamic slip conditions. The governing boundary layer conservation equations are normalized into nonsimilar form using similarity transformations. A numerical approach is applied to the resultant equations. The behavior of the velocity, temperature, concentration, as well as the skin friction coefficient, Nusselt number, and Sherwood number for various governing physical are discussed. Increasing the radiation parameter decreases the temperature. An increase in the rheological parameter (Casson parameter) induces an elevation in the skin friction coefficient, the heat and mass transfer rates. The larger the β values the closer the fluid is in behavior to a Newtonian fluid and further departs from plastic flow. Temperature of the fluid was found to decrease with increasing values of the Casson rheological parameter. The most important non-Newtonian fluid possessing a yield value is the rheological Casson fluid, which finds significant applications in polymer processing industries, biomechanics, and chocolate food processing.

This paper presents linear and nonlinear stability analyses of thermal convection in a dielectric fluid saturated sparsely packed porous layer subject to the combined effect of time-periodic gravity modulation (GM) and an AC electric field. In the domain of linear theory, the critical stability parameters are computed by the regular perturbation method in the form of a perturbation series in powers of frequency of modulation. The local nonlinear theory based on the truncated Fourier series method gives information on convection amplitudes and heat transfer. The principle of the exchange of stabilities is found to be valid and subcritical instability is ruled out. Based on the governing linear autonomous system, several qualitative results on stability are discussed. The sensitive dependence of the solution of a Lorenz system of electrothermal convection subject to the choice of initial conditions points to the possibility of chaos. Low-frequency g-jitter is found to have a significant stabilizing influence, which is in turn diminished by an imposed AC electric field. The role of sparseness of the porous layer, viscosity ratio, and normalized porosity on the stability criterion and on heat transport is determined.

]]>Laminar boundary layer slip flow from a stretching surface in a nanofluid-saturated homogenous, isotropic porous medium is studied numerically. A Newtonian heating boundary condition in the presence of thermal radiation is incorporated and a Darcy model utilized for the porous medium. The model used for the nanofluids include the effects of Brownian motion and thermophoresis. A group theoretical analysis is conducted to generate similarity transformations. The governing transport equations are nondimensionalized and rendered into a set of coupled similarity ordinary differential equations using similarity transformations. The transformed equations are then solved using the Runge–Kutta–Fehlberg fourth-fifth order numerical method with shooting technique. It is shown that the physical quantities of interest depend on a number of parameters. The results are presented in tabular and graphical forms. Comparison of the present numerical solutions with published work shows very good agreement. The study finds applications in high-temperature nanotechnological materials processing.

]]>In this paper, the effects of chemical reaction on free convective flow of electrically conducting and viscous incompressible immiscible fluids are analyzed. The coupled nonlinear equations governing the heat and mass transfer are solved analytically and numerically with appropriate boundary conditions for each fluid and the solutions have been matched at the interface. The analytical solutions are solved by using regular perturbation method valid for small values of perturbation parameter and numerically by using finite difference method. The numerical results for various values of thermal Grashof number, mass Grashof number, Hartman number, viscosity ratio, width ratio, conductivity ratio, and chemical reaction parameter have been presented graphically in the presence and in the absence of electric field load parameter. In addition, the closed form expression for volumetric flow rate, Nusselt number, species concentration, and total heat rate added to the flow is also analyzed. The solutions obtained by finite difference method and perturbation method agree very well to the order of 10^{−4} for small values of perturbation parameter.

Natural convection is extensively used in cooling of large scale electrical and electronic equipments. This work involves study of flow and heat transfer characteristics in enclosures with partial openings having an internal heat source at higher Rayleigh number (*Ra _{h}* > 10

This work is devoted to the numerical study of the interaction of an inclined plane turbulent jet with a moving horizontal isothermal hot wall. The inclination of the jet allows the control of the stagnation point location. The numerical predictions based on statistical modeling are achieved using second order Reynolds stress turbulence model coupled to the enhanced wall treatment. The jet Reynolds number (Re), surface-to-jet velocity ratio (*R*_{sj}); and optimal inclination angle of the jet (α) are varied. The calculations are in good agreement with the available data. The numerical results show that the heat transfer is greatly influenced by the jet Re and the velocity of the moving wall. The local Nusselt number (Nu) decreases with increasing *R*_{sj} (until *R*_{sj} = 1). However, the optimal inclination of the jet enhances heat transfer and modifies significantly the stagnation point location. Average Nu is correlated according with the problem parameters as .

In this paper, we investigate the peristaltic transport of a non-Newtonian viscous fluid in an elastic tube. The governing equations are solved using the assumptions of long wavelength and low Reynolds number approximations. The constitution of blood has a non-Newtonian fluid model and it demands the yield stress fluid model: The blood transport in small blood vessels is done under peristalsis. Among the available yield stress fluid models for blood flow, the non-Newtonian Herschel–Bulkley fluid is preferred (because Bingham, power-law and Newtonian models can be obtained as its special cases). The Herschel–Bulkley model has two parameters namely the yield stress and the power-law index. The expressions for velocity, plug flow velocity, wall shear stress, and the flow rate are derived. The flux is determined as a function of inlet, outlet, external pressures, yield stress, amplitude ratio, and the elastic property of the tube. Further when the power-law index *n* = 1 and the yield stress and in the absence of peristalsis, our results agree with Rubinow and Keller [*J. Theor. Biol*. **35**, 299 (1972)]. Furthermore, it is observed that, the yield stress, peristaltic wave, and the elastic parameters have strong effects on the flux of the non-Newtonian fluid flow. Effects of various wave forms (namely, sinusoidal, trapezoidal and square) on the flow are discussed. The results obtained for the flow characteristics reveal many interesting behaviors that warrant further study on the non-Newtonian fluid phenomena, especially the shear-thinning phenomena. Shear thinning reduces the wall shear stress.

Forced convective laminar flow of different types of nanofluids such as Al_{2}O_{3}, CuO, SiO_{2}, and ZnO, with different nanoparticle size 25, 45, 65, and 80 nm, and different volume fractions which ranged from 1% to 4% using ethylene glycol as base fluids were used. A three-dimensional microtube (MT) with 0.05 cm diameter and 10 cm in length with different values of heat fluxes at the wall is numerically investigated. This investigation covers Reynolds number (Re) in the range of 80 to 160. The results have shown that SiO_{2}-EG nanofluid has the highest Nusselt number (Nu), followed by ZnO-EG, CuO-EG, Al_{2}O_{3}-EG, and finally pure EG. The Nu for all cases increases with the volume fraction but it decreases with the rise in the diameter of nanoparticles. In all configurations, the Nu increases with Re. In addition, no effect of heat flux values on the Nu was found.

This research paper mainly deals with exergy, economic, and environmental investigation of a 250 MW steam power plant located in Iran. In order to model this power plant, energy balance equations are used and each part of the power plant is modeled accordingly. Further by introducing the boiler as the main source of irreversibility, two approaches are presented to improve the boiler performance, reduction of excess air, and temperature reduction of gasses leaving the stacks. To study the effect of these two approaches, an objective function including the cost rate of exergy destruction of boiler, fuel cost, and cost rate of environmental impact is presented. The optimization process is done using a genetic algorithm. It is concluded that by optimizing, 20% reduction in the overall cost rate and 88% reduction in the cost rate of environmental impact can be achieved.

]]>In this paper, an analysis is performed to study the effects of mass transfer and chemical reaction on laminar flow in a porous pipe with an expanding or contracting wall. The pipe wall expands or contracts uniformly at a time dependent rate. The governing equations are reduced to ordinary differential equations by using a similarity transformation. An analytical approach, namely, the homotopy analysis method is applied in order to obtain the solutions of the ordinary differential equations. The convergence of the obtained series solutions is analyzed. The effects of various parameters on flow variables have been discussed. It is noticed that the wall expansion ratio significantly increases the axial velocity and the concentration for the case of wall expansion and it decreases the axial velocity for the case of wall contraction irrespective of injection or suction. Further, it is observed that the concentration (ϕ) decreases for a destructive chemical reaction () and increases for a generative chemical reaction (). The concentration reduces as Schmidt number () increases. The corresponding problem related to the porous pipe flow with a stationary wall can be recovered from the present analysis in the limiting case where the wall expansion ratio approaches to zero (i.e., ).

]]>A mathematical study is presented for the collective influence of the buoyancy parameter, convective boundary parameter and temperature dependent viscosity on the steady mixed convective laminar boundary flow of a radiative magneto-micropolar fluid adjacent to a vertical porous stretching sheet embedded in a Darcian porous medium. The fluid viscosity is assumed to vary as an inverse linear function of temperature. Using appropriate transformations, the governing equations of the problem under consideration are transformed into a system of dimensionless nonlinear ordinary differential equations, which are then solved with the well-tested, efficient finite element method. The results obtained are depicted graphically to illustrate the effect of the various important controlling parameters on velocity, microrotation, and temperature functions. The skin friction coefficient, wall couple stress, and the rate of heat transfer have also been computed and presented in tabular form. Comparison of the present numerical results with earlier published data has been performed and the results are found to be in good agreement, thus validating the accuracy of the present numerical code. The study finds applications in conducting polymer flows in filtration systems, trickle bed magnetohydrodynamics in chemical engineering, electro-conductive materials processing, and so on.

]]>This study proposes the preliminary simulation of a single cylinder spark ignition engine with waste heat recovery system. To harvest waste heat energy from the engine exhaust a thermoelectric generator coupled to a vapor absorption refrigeration (VAR) system was proposed in this simulation work. Parametric simulation of engine, thermoelectric generator and VAR using thermodynamic relations was carried out in MATLAB – Simulink software. An attempt has been made mathematically to integrate engine, thermoelectric generator and VAR system to study the effect of engine load, speed, equivalence ratio on thermoelectric output and coefficient of performance (COP) of a VAR system. In this study, the VAR system runs by taking heat energy from the exhaust gas and the electric power produced by a thermoelectric generator was utilized to run the pump of the refrigeration system. It was found that COP of the absorption refrigeration system depends on engine load, speed and air fuel equivalence ratio. The study also reveals that about 10% to 15% of the total exhaust energy can be harvested using this system.

]]>We study the effect of thermal convective boundary condition and yield stress on free convection heat transfer for a pseudo-plastic and Newtonian fluid past a permeable vertical flat plate which is embedded in a Darcian porous medium in the presence of heat generation/absorption numerically. Instead of using similarity transformations available in the literature, we have developed them by one point transformation and hence transform the governing boundary layer equations into corresponding similarity equations. The resulting similarity equations were solved using Runge–Kutta–Fehlberg fourth fifth (RKF45) order numerical method. The effect of the governing parameters, namely the power index of pseudo-plastic fluids *n*, the rheological parameter Ω, heat generation/absorption parameter *Q*, suction/injection parameter , and the convective heat parameter *B* on the dimensionless velocity, the temperature and the heat transfer rates were investigated. A close agreement is found between our results and published results. Our present study finds application in printing and polymer industries and fluid phenomena associated with concentrated suspensions.

This paper aims to analyze the heat transfer by the first and second laws of thermodynamics for the flow of two immiscible couple stress fluids inside a horizontal channel under the action of an imposed transverse magnetic field. The plates of the channel are maintained at constant and different temperatures higher than that of the fluid. The flow region consists of two zones, the flow of the heavier fluid taking place in the lower zone. No slip condition is taken on the plates and continuity of velocity, vorticity, shear stress, couple stress, temperature, and heat flux are imposed at the interface. The velocity and temperature distributions are derived analytically and these are used to compute the dimensionless expressions for the entropy generation number and Bejan number. The results are presented graphically. It is observed that the imposed magnetic field reduces the entropy production rate near the plates.

]]>In this study, the lattice Boltzmann method is used in order to investigate the natural convection in a cavity with linearly heated wall(s). The bottom wall is heated uniformly and the vertical wall(s) are heated linearly, whereas the top wall is insulated. Investigation has been conducted for Rayleigh numbers of 10^{3} to 10^{5}, while Prandtl number is varied from 0.7 to 10. The effects of an increase in Rayleigh number and Prandtl number on streamlines, isotherm counters, local Nusselt number and average Nusselt number are depicted. It has been observed that the average Nusselt number at the bottom wall augments with an increase in Prandtl number.

The heat transfer characteristics of a single round air jet impingement on a high temperature steel plate were examined experimentally using a single-point temperature measurement method, incorporated with solving the inverse heat conduction problem. During the experiments, the temperature of the steel plate varied from 1073 K to 373 K, the Reynolds number was set to 27,000, the nozzle to plate spacing was set to 4. The results indicated that the radial distribution of the local Nusselt number is bell-shaped at the initial stage of the transient cooling process. As the cooling process continues, the local Nusselt numbers decrease and a second peak occurs at *r*/*D* = 2. The area averaged Nusselt number are in accordance with the correlation proposed by Hofmann and Martin at first and then decrease significantly, but this trend is not obvious at *r*/*D* > 10.

Effects of wall confinements on the laminar flow and heat transfer around a heated tapered trapezoidal bluff body are investigated numerically in the confined domain (Reynolds number, Re = 1 to 40; blockage ratio = 0.125 to 0.5; and Prandtl number, Pr = 0.71). The onset of flow separation is found between Re = 4 and 5 for the blockage ratio of 0.125 and between Re = 5 and 6 for the blockage ratios of 0.25 and 0.5. If compared with a long circular obstacle on the basis of equal projected area, the total drag coefficient of the trapezoidal cylinder is found to be larger than the circular one, but an opposite trend is observed for the heat transfer. The augmentation in heat transfer for trapezoidal and circular cylinders is found to be approximately 46, 72, 74, and 65 percent for Re = 1, 5, 10, and 40, respectively for the blockage ratio of 0.25. The maximum enhancement in heat transfer for a tapered trapezoidal bluff body with respect to a square bluff body is found to be approximately 104 percent and 101 percent for blockage ratios of 0.25 and 0.5, respectively. Finally, simple correlations of wake length, drag, and average cylinder Nusselt number are established.

]]>This paper presents the numerical study of mixed convection in a two-sided lid driven porous cavity due to temperature and concentration gradients. The top and bottom walls are stationary and insulated. The left and right walls are moving at an equal velocity (*V*_{o}) in the same direction. The temperature and concentration are kept high at the right wall and low at the left wall. The governing equations are discretized using finite volume method. The pressure–velocity coupling is performed by the SIMPLE algorithm. A third order differed QUICK scheme is applied at the inner nodes and a second order central difference scheme is used at the boundary nodes. The flow behavior and heat transfer are analyzed for different nondimensional numbers, such as, 1 × 10^{−4} ≤ Ri ≤ 10, 1 × 10^{−4} ≤ Da ≤ 0.1 and 0.7 < Pr < 10. The present numerical results are compared with the literature and are in good agreement. For the above selected nondimensional numbers, the heat and fluid flow behavior is investigated using local and average Nusselt (Nu) and Sherwood (Sh) numbers. Results show that the convection flow is significant up to Da = 0.1, beyond that the effect of porosity is negligible. The effect of Prandtl number (Pr) on average Nu is found to increase significantly.

In this paper, an exact analytical solution for fully developed convective heat transfer in equilateral triangular ducts under constant heat flux at the walls is presented. The previous studies have been performed using numerical methods and to the knowledge of authors, this study is the first EXACT analytical solution about the heat convection in triangular ducts. Here, the finite series expansion method is used to derive the closed form of dimensionless temperature distribution. The Nusselt number and dimensionless temperature at the center of the cross section were calculated equal to 28/9 and 5/9, respectively. The present analytical solution could be useful in analysis of the heat convection in microfluidics and designing compact heat exchangers.

]]>This work concerns the thermal studies and applications of suspensions of nanoparticles in fluids, that is, nanofluids. They have been traditionally used for heat transfer applications due to their low thermal conductivity, taking into account the rising demands of modern technology. They show substantial augmentation of their thermal properties and their distinctive features offer more potential for many applications. Most of the publications on nanofluids are about understanding their behavior so that they can be utilized. The straight enhancement of nanofluids is paramount in many industrial applications, nuclear reactors, transportation, and electronics as well as in biomedicine and food. Our theoretical research focuses on presenting the wide range of applications that involve nanofluids, prominence on their improved properties that are controllable. It is the specific characteristics that these nanofluids possess that make them suitable for such applications. We are certain that this paper will be used by researchers in the nanofield.

]]>This study is concerned with the stagnation point flow and heat transfer over an exponential stretching sheet via an approximate analytical method known as optimal homotopy asymptotic method (OHAM). The governing partial differential equations are converted into ordinary nonlinear differential equations using similarity transformations available in the literature. The heat transfer problem is modeled using two-point convective boundary condition. These equations are then solved using the OHAM approach. The effects of controlling parameters on the dimensionless velocity, temperature, friction factor, and heat transfer rate are analyzed and discussed through graphs and tables. It is found that the OHAM results match well with numerical results obtained by *Runge–Kutta Fehlberg fourth-fifth order* method for different assigned values of parameters. The rate of heat transfer increases with the stretching parameter. It is also found that the stretching parameter reduces the hydrodynamic boundary layer thickness whereas the Prandtl number reduces the thermal boundary layer thickness.

In this paper, modeling and optimization of Al_{2}O_{3}–water nanofluid flow in horizontal flat tubes is performed using a combination of computational fluid dynamics (CFD) and response surface methodology (RSM). At first, nanofluid flow is solved numerically in various flat tubes using CFD techniques and the heat transfer coefficient () and pressure drop () in tubes are calculated. The numerical simulations are performed using two phase mixture model by FORTRAN programming language. The flow regime and the wall boundary conditions are assumed to be laminar and constant heat flux respectively. In the second step, numerical data of the previous step will be used for a parametric study, modeling and optimization of nanofluid flow in flat tubes using the RSM technique.It is shown that the results include important design information on nanofluid parameters in flat tubes. The important design information about the relationship between design variables and responses will not be achieved without the simultaneous use of CFD and optimization approaches.

This paper presents an investigation on finite time thermodynamic (FTT) evaluation of a solar-dish Stirling heat engine. FTTs has been applied to determine the output power and the corresponding thermal efficiency, exergetic efficiency, and the rate of entropy generation of a solar Stirling system with a finite rate of heat transfer, regenerative heat loss, conductive thermal bridging loss, and finite regeneration process time. Further imperfect performance of the dish collector and convective/radiative heat transfer mechanisms in the hot end as well as the convective heat transfer in the heat sink of the engine are considered in the developed model. The output power of the engine is maximized while the highest temperature of the engine is considered as a design parameter. In addition, thermal efficiency, exergetic efficiency, and the rate of entropy generation corresponding to the optimum value of the output power is evaluated. Results imply that the optimized absorber temperature is some where between 850 K and 1000 K. Sensitivity of results against variations of the system parameters are studied in detail. The present analysis provides a good theoretical guidance for the designing of dish collectors and operating the Stirling heat engine system.

]]>The laminar boundary layer flow and heat transfer of Casson non-Newtonian fluid from a semi-infinite vertical plate in the presence of thermal and hydrodynamic slip conditions is analyzed. The plate surface is maintained at a constant temperature. Increasing velocity slip induces acceleration in the flow near the plate surface and the reverse effect further from the surface. Increasing velocity slip consistently enhances temperatures throughout the boundary layer regime. An increase in thermal slip parameter strongly decelerates the flow and also reduces temperatures in the boundary layer regime. An increase in the Casson rheological parameter acts to elevate considerably the skin friction (non-dimensional wall shear stress) and this effect is pronounced at higher values of tangential coordinate. Temperatures, however, are very slightly decreased with increasing values of Casson rheological parameter. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21115

]]>In this article, we investigate the nonlinear steady-state boundary-layer flow, heat and mass transfer of an incompressible Jeffrey non-Newtonian fluid past a vertical porous plate. The transformed conservation equations are solved numerically subject to physically appropriate boundary conditions using a versatile, implicit finite-difference technique. The numerical code is validated with previous studies. The influence of a number of emerging non-dimensional parameters, namely, Deborah number (*De*), Prandtl number (*Pr*), ratio of relaxation to retardation times (*λ*), Schmidt number (*Sc*), and dimensionless tangential coordinate (*ξ*) on velocity, temperature, and concentration evolution in the boundary layer regime are examined in detail. Furthermore, the effects of these parameters on surface heat transfer rate, mass transfer rate, and local skin friction are also investigated. It is found that the velocity is reduced with increasing Deborah number whereas temperature and concentration are enhanced. Increasing *λ* enhances the velocity but reduces the temperature and concentration. The heat transfer rate and mass transfer rates are found to be depressed with increasing Deborah number, *De*, and enhanced with increasing *λ*. Local skin friction is found to be decreased with a rise in Deborah number whereas it is elevated with increasing *λ*. And an increasing Schmidt number decreases the velocity and concentration but increases temperature. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21111

This laminar fluid study investigates the effects of a magnetic field on the entropy generation during fluid flow and heat transfer due to an exponentially stretching sheet. Using the suitable transformations we have obtained the analytical solutions for momentum and energy equation in terms of Kummer's function. The velocity and temperature profiles are obtained for various physical parameters which are utilized to find the entropy generation number *N*_{s} and the Bejan number *Be*. The effects of various parameters on entropy production number and the Bejan number are studied through graphs using velocity and temperature profiles. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21112

The problem of steady two-dimensional free convective flow of a Walters fluid (model *B* ′) in a porous medium between a long vertical wavy wall and parallel flat wall in the presence of a heat source is discussed. The channel is divided into two passages by means of a thin, perfectly conductive plane baffle and each stream will have its own pressure gradient and hence the velocity will be individual in each stream. The governing equations of the fluid and the heat transfer have been solved subject to the relevant boundary conditions by assuming that the solution consists of two parts: a mean part and disturbance or perturbed part. Exact solutions are obtained for the mean part and the perturbed part is solved using long wave approximation. Results are presented graphically for the distribution of velocity and temperature fields for varying physical parameters such as Grashof number, wall temperature ratio, porous parameter, heat source/sink parameter, product of non-dimensional wave number, and space-coordinate and viscoelastic parameter at different positions of the baffle. The relevant flow and heat transfer characteristics, namely, skin friction and the rate of heat transfer at both walls, has been discussed in detail. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21118

Analytical analysis of unbalanced heat exchangers is carried out to study the second law thermodynamic performance parameter through second law efficiency by varying length-to-diameter ratio for counter flow and parallel flow configurations. In a single closed form expression, three important irreversibilities occurring in the heat exchangers—namely, due to heat transfer, pressure drop, and imbalance between the mass flow streams—are considered, which is not possible in first law thermodynamic analysis. The study is carried out by giving special influence to geometric characteristics like tube length-to-diameter dimensions; working conditions like changing heat capacity ratio, changing the value of maximum heat capacity rate on the hot stream and cold stream separately and fluid flow type, i.e., laminar and turbulent flows for a fully developed condition. Further, second law efficiency analysis is carried out for condenser and evaporator heat exchangers by varying the effectiveness and number of heat transfer units for different values of inlet temperature to reference the temperature ratio by considering heat transfer irreversibility. Optimum heat exchanger geometrical dimensions, namely length-to-diameter ratio can be obtained from the second law analysis corresponding to lower total entropy generation and higher second law efficiency. Second law analysis incorporates all the heat exchanger irreversibilities. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21109

]]>The stability of a thin layer of viscoelastic fluid flowing through a porous medium down a non-uniformly heated inclined plane with a constant temperature gradient along the plane is considered. The film flow system is influenced by gravity, mean surface tension, thermocapillary forces, viscoelastic forces, porosity, and permeability of porous medium. We seek a solution of the stability problem in a series in small wave numbers, and the obtained results, when the plane is heated in the downstream direction, show that the Marangoni, Galileo, and Biot numbers, porosity, and permeability of the porous medium have dual roles in the stability of the flow system, while the viscoelastic parameter and angle of inclination have stabilizing effects, and the Prandtl number has a destabilizing effect. The effects of these physical parameters are also discussed in the case when the plane is cooled in the downstream direction, and we found that their effects are opposite to those of the previous case. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21105

]]>A one-dimensional mathematical model has been used for a three-sector desiccant wheel (two sectors with purge) with different flow arrangements. The model considers both gas and solid side resistance and shows a good agreement with experimental results. This model has been used to conduct a comparative performance analysis in both the effective adsorption and effective regeneration sector of a desiccant wheel. It was found that an effective regeneration sector gives better results for the performance parameters (rotation of wheel, regeneration temperature, velocity, and ambient moisture) as compared to an effective adsorption sector. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21103

]]>A thermal lattice Boltzmann method-based analysis was performed to numerically investigate the heat transfer by natural convection from an enclosure with a large vertical side opening. The height of the opening was less than the enclosure height and the vertical wall opposite to the opening was maintained at constant temperature. A parametric study was carried out for different values of Rayleigh number (*Ra*) ranging from 10^{3} to 10^{5} with air as the working fluid for three opening sizes and three opening locations. The Prandtl number was fixed at 0.71 and the enclosure aspect ratio was also fixed at 2 in all calculations. With Boussinesq approximation, the temperature distribution and stream functions in the enclosure were predicted. The profile of the normal velocity component at the opening location was determined. The opening size affects the stratification and recirculation pattern within the enclosure. The average Nusselt number at the heated wall was determined for all cases. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21110

An analysis is presented to investigate the effects of a chemical reaction on an unsteady flow of a micropolar fluid over a stretching sheet embedded in a non-Darcian porous medium. The governing partial differential equations are transformed into a system of ordinary differential equations by using similarity transformation. The resulting nonlinear coupled differential equations are solved numerically by using a fourth-order Runge–Kutta scheme together with shooting method. The influence of pertinent parameters on velocity, angular velocity (microrotation), temperature, concentration, skin friction coefficient, Nusselt number, and Sherwood number has been studied and numerical results are presented graphically and in tabular form. Comparisons with previously published work are performed and the results are found to be in excellent agreement. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21090

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