Rotary Wind‐driven Triboelectric Nanogenerator for Self‐Powered Airflow Temperature Monitoring of Industrial Equipment

Abstract Heat dissipation performance is crucial for the operational reliability of industrial equipment, which can be monitored by detecting the wind or airflow temperature of the radiator. The emergence of triboelectric nanogenerators (TENGs) provides new routes for wind energy harvesting and self‐powered sensing. Herein, a rotary wind‐driven triboelectric nanogenerator (RW‐TENG) with soft‐contact working mode is newly designed to achieve tunable contact areas by utilizing the reliable thermal response of NiTi shape memory alloy (SMA) to air/wind temperature. The RW‐TENG can generate different triboelectric outputs under air stimulation with different speeds or temperatures, which is demonstrated as a power source for online monitoring sensors, self‐powered wind speed sensing, and airflow temperature monitoring. Specifically, a self‐powered sensor of wind speed is demonstrated with a sensitivity of 0.526 µA m−1 s between 2.2 and 19.6 m s−1, and a self‐powered monitoring device of high airflow temperature, which show relatively short response time (109 s), strong anti‐interference ability and outstanding long‐term durability. This study introduces an innovative route for real‐time detection of airflow temperature in wind‐cooled industrial equipment, showing broad application prospects for information perception and intelligent sensing of the industrial IoTs.


Supporting Note S1: The charge transfer process and potential distribution of RW-TENG during operation.
A physical model based on Maxwell equations has been created to validate the charge transfer process of RW-TENG theoretically in one typical cycle, which is similar to conventional wind-driven TENGs with freestanding working mode.Figure N1 displays the sectional view of the device, and the two electrodes (A/B) are connected in the open-circuit state.It is assumed that any overlap between the rotator and the electrode can be modeled as a parallel plate capacitor without considering its edge effect, as the thickness of FEP is considerably less than its width [1] .According to the model assumption, under state (i), the electric field generated by the tribocharges in the dielectric is a uniform electric field.The upper surface of electrodes A and B induce negative and positive charges, respectively.Using the Gauss theorem, the open-circuit voltage can be calculated from Equation (S1), by setting the infinite point as zero potential.
where ε0 is the vacuum dielectric constant (ε0=8.85×10 -1 F/m), and εr is the relative dielectric constant of FEP.Similarly, under state (iii), the open-circuit voltage can be calculated from Equation (S2).
In addition to the two unique states (i) and (iii), the general circumstances during the operation are considered as follows.Using state (ii) as an example, the potential difference distribution is analyzed during the sliding of RW-TENG from state I to state (iii) (i.e., 0＜θ＜θl).At this time, Therefore, the open-circuit voltage between A and B is shown in Equation (S7).
When area I equals area II, the open-circuit voltage can be calculated from Equation (S8).
Based on the same method, during the transition from state (iii) to state (i) (i.e., θl＜θ＜2θl), the open-circuit voltage between A and B is shown in Equation (S9).
As shown in Figure N3, the cooling system of the oil-immersed transformer consists of fans, oil pumps, oil-flow relay, and heat sink.The heat from winding and iron core is cooled by transformer oil that flows to the cooler body through the top oil pipe.Heat in transformer oil is dissipated to the outside through the cooling fans.The cooled low-temperature transformer oil returns to the oil tank through the oil pump and the oil-flow relay to cool the windings and iron core again.Among them, the oilflow relay can display changes in oil flow in the cooling system to monitor the operation of the oil pump.

Figure S3 .
Figure S3.Photograph of the as-fabricated wind cups with various (a) diameters, (b) arm lengths, and (c) numbers.

Figure S4 .
Figure S4.The transferred charge of the RW-TENG in (a) direct-contact mode and (b) soft-contact mode.

Figure S5 .
Figure S5.Charging curves of the capacitor (0.1 μF) by the RW-TENG under different wind speed conditions.

Figure S6 .
Figure S6.Measured relationship between the short-circuit current (peak value and frequency) and the wind speed under an air gap of 14 mm.

Figure S7 .
Figure S7.The short-circuit current of RW-TENG with curved SMA under various wind speeds.

Figure S8 .
Figure S8.Measured relationship between the short-circuit current, frequency and wind speed of RW-TENG with curved SMA.

Figure S11 .
Figure S11.The temperature distribution images of RW-TENG during long-term operation (35 min) under the "curved" state.

Figure S12 .
Figure S12.Current response waveform of RW-TENG toward various wind temperature stimulations under low rotating speed (initial rotation frequency f = 10 Hz).

Figure S13 .
Figure S13.Current response waveform of RW-TENG toward various wind temperature stimulations under high rotating speed (initial rotation frequency f = 20 Hz).

Figure S15 .
Figure S15.Force analysis of stator FEP during the operation of RW-TENG.As the rotator area increases, the stator FEP will be subjected to greater electrostatic attraction, therefore hindering the device rotation.

Figure S16 .
Figure S16.Triboelectric output voltage and current of RW-TENG under different humidity conditions (SMA of "flattened" state).

Figure S18 .
Figure S18.Current response waveform of RW-TENG toward various wind temperature stimulations when the environmental relative humidity is 50%.

Figure S19 .Figure S20 .
Figure S19.Current response waveform of RW-TENG toward various wind temperature stimulations when the environmental relative humidity is 70%.

Figure S21 .
Figure S21.Current response of RW-TENG with periodic 60℃ hot wind stimulation.The output short-circuit current increased from 1.69 μA to 2.34 μA with a heating time of 11.5 s, and then slightly decreased to 2.2 μA with an interval of 28.1 s, and then increased to 3.01 μA with another heating time of 23.4 s.

Figure S22 .
Figure S22.The output durability of RW-TENG with the SMA of "curved" state without hot wind simulation under continuous measurement of 1200 s.

Figure S23 .
Figure S23.The output durability of RW-TENG with the SMA of "flattened" state with 50℃ wind simulation under continuous measurement of 1200 s.

Figure S24 .
Figure S24.Response repeatability of the RW-TENG for five cycles.

Figure S25 .
Figure S25.(a) EDS spectrum of the shape memory NiTi alloy (Tg ~ 50℃).(b) Surface morphology of the shape memory NiTi alloy.(c-e) Element distribution of Ti and Ni.(f) DSC curves of the shape memory NiTi alloy (Tg ~ 50℃).EDS analysis reveals that Ni accounts for 41.5% and Ti accounts for 58.5%, and the element distribution is uniform.DSC curve reveals that the martensitic-austenite transformation happens above the austenite start temperature (As, 45℃), and all deformation completes below the austenite finish temperature (Af, 52℃).

Figure S27 .
Figure S27.Comparison of the current response and response time of RW-TENG (Tg of SMA: ~ 50℃).

Figure N1 .
Figure N1.The charge transfer process of RW-TENG during operation.Suppose that the surface charge density of FEP (ρFEP) is -σ, and the tribo-charge density on the rotator's surface (ρRotator) changes with the electrostatic balance process when the rotator slides.In addition, suppose that the thickness of FEP is d, the sliding angle of the rotator is θ, and the center angle of electrode A (or B) is θl.The influence of the stator's air gap (other than the insulation performance) is ignored.
electrodes A and B are divided into two areas: I and II.The rotator covers area II of electrode A and area I of electrode B. The rest area (not covered) is only affected by the negative tribo-charges on the FEP surface.As a result, area I of electrode A induces positive charges, and the charge density can be calculated from Equation (S3).total charge in electrode A is 0, the remaining negative charges are all distributed in area II, and the charge density is shown in Equation (S4).I and II in electrode B have the following surface charge density (Equation (S5)).this time, the surface positive charges on the rotator are redistributed, depending on how electrode A and B surface charges have changed.According to the assumption of parallel plate capacitor, the rotator's surface is approximately equipotential, so the potential difference between the rotator's surface and the electrodes can be calculated from Equation (S6).

Figure N3 .
Figure N3.Schematic diagram of the cooling system operation principle.The photograph was taken at the 500 kV main transformer.