Thermoelectric Legs Research Articles

Liquid metal-enhanced thermoelectric generator for high-temperature thermal harvesting

It is a challenge to achieve high output power of the thermoelectric generator (TEG) for high-temperature waste heat recovery due to the working fluids with low thermal conductivity (such as air) or low tolerance of temperature (water or oil). In this paper, the gallium-based liquid metal (LM) with a high boiling point (>1000 ℃) and thermal conductivity (>20 W/mK) are introduced to significantly enhance heat charging and discharging at the hot/cold sides of TEG. We also developed an electromagnetic induction pumping method for the effective LM-driven flow at high temperatures. A three-dimensional coupling multi-parameter optimization simulation model of LM-based TEG was developed to reveal the internal heat transfer and power generation mechanism for clarifying the impact factors of the performance. The results have shown that the power generation capacity can be effectively improved by increasing the inlet temperature (Thot-in). It is worth noting that the temperature difference (ΔT) of the TEG module is severely limited by the thermal resistance (Rcapacity) of the LM heat capacity, such as, when the flow rate of 2 L/min, the Rcapacity accounts for 90.6 % (0.020 ℃/W). It is easier to achieve a larger open circuit voltage by increasing the height of the thermoelectric leg, but the Pmax is constantly weakened. Compared with Xceltherm 600 and Solar salt, LM heat transfer fluid has more obvious advantages in enhancing the power generation performance of the system. The LM-based TEG experiment platform was established to study heat transfer and power generation characteristics. The results have demonstrated that good consistency was proved by comparing experimental and numerical data. And the Pmax of the LM-based TEG system is 0.16 W/cm2 at ΔT of 136 ℃. LM-based TEG can open new perspectives for broad applications in high-temperature waste heat recovery.

Investigating thin-film thermoelectric generators: Leg shape, TEG configuration, and contact resistance analysis

Thermoelectric generators (TEGs) are made of parallel p-type and n-type semiconducting legs which can directly convert temperature gradients into electricity. Theoretical studies have extensively explored the impact of the thermoelectric (TE) leg size and shape on the conversion efficiency of such bulk TEGs. However, in recent years, geometrically thin and film-shaped TEGs have gained attention for integration into wearable and flexible electronic devices, tapping into body heat as a power source. There is currently a lack of research on film-shaped TEGs, particularly regarding the performance of asymmetric TE leg shapes. This study investigates seven different TE leg shapes in thin-film TEGs, analyzing their electrical performance using COMSOL Multiphysics software. Results show that certain asymmetric TE leg shapes can yield over a 30% improvement in the produced open circuit voltage, as compared to conventional rectangular-shape TE legs. Furthermore, various configurations of thin-film TEGs were designed and analyzed, aiming to maximize device output power. Additionally, the study delves into the influence of electrical contact resistance on the performance of the optimal asymmetric TEGs. The proposed thin TE leg shapes and TEG configurations ae easily manufacturable and scalable using printing technology.

3D Printed Gelatin Methacrylate Hydrogel‐Based Wearable Thermoelectric Generators

AbstractThe present study focuses on the utilization of a hydrogel consisting of gelatin methacrylate (GelMA) and polyvinyl alcohol (PVA) as a matrix for hosting the redox couple Fe(CN)63−/4−. The hydrogel exhibits a discernable thermopower (Src) of 3 mV K−1. The beneficial effect of the hydrogel microstructure on the mechanical robustness is demonstrated by small‐angle X‐ray scattering (SAXS). Moreover, the hydrogel is used to construct a 3D printed thermoelectric generator (TEG) consisting of eight p‐type thermoelectric legs, which exhibits commendable thermoelectric properties, including an open‐circuit voltage of 64 mV and a power density of 4.0 mW m−2 under a temperature gradient (ΔT) of 2.5 K. These findings demonstrate that 3D printing both enhances the quality of the interface between the hydrogel and electrode and provides a promising method for a more facile TEG fabrication process with the potential for further applications in low‐grade waste heat harvesting.

Vertically designed high-performance and flexible thermoelectric generator based on optimized PEDOT:PSS/SWCNTs composite films

To solve the long-lasting challenge of low thermoelectric performance of flexible thermoelectric device (F-TEG), in this work, we report a three-dimensional vertically structured F-TEG composed of flexible, stable, and high-performing p- and n-type single-walled carbon nanotube (SWCNT)-based composite films. The p-type SWCNT-based composite film exhibits a high room-temperature power factor of >500 μW m−1 K−2, benefiting from the effective de-doping of the hybridized poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS) using a binary co-doping agent composed of NaHCO3 and the polar solvent ethylene glycol (EG). Simultaneously, the n-type SWCNT-based film doped with the amine-rich electron donor polyethyleneimine (PEI) is prepared, exhibiting a high room-temperature power factor of 185.4 μW m−1 K−2 and excellent air stability. By employing flexible supporting foam, vertical p-n thermoelectric legs are realized, and the F-TEG based on these legs exhibits a maximum open-circuit voltage of 23.2 mV and a maximum output power of 2.6 μW at a temperature difference of 48 K, demonstrating a competitive normalized power density of >2.5 μW cm−2 K−2, which advances the low-power flexible wearable field.

Upscaling Thermoelectrics: Micron-Thick, Half-a-Meter-Long Carbon Nanotube Films with Monolithic Integration of p- and n-Legs.

In order for organic thermoelectrics to successfully establish their own niche as energy-harvesting materials, they must reach several crucial milestones, including high performance, long-term stability, and scalability. Performance and stability are currently being actively studied, whereas demonstrations of large-scale compatibility are far more limited and for carbon nanotubes (CNTs) are still missing. The scalability challenge includes material-related economic considerations as well as the availability of fast deposition methods that produce large-scale films that simultaneously satisfy the thickness constraints required for thermoelectric modules. Here we report on true solutions of CNTs that form gels upon air exposure, which can then be dried into micron-thick films. The CNT ink can be extruded using a slot-shaped nozzle into a continuous film (more than half a meter in the present paper) and patterned into alternating n- and p-type components, which are then folded to obtain the finished thermoelectric module. Starting from a given n-type film, differentiation between the n and p components is achieved by a simple postprocessing step that involves a partial oxidation reaction and neutralization of the dopant. The presented method allows the thermoelectric legs to seamlessly interconnect along the continuous film, thus avoiding the need for metal electrodes, and, most importantly, it is compatible with large-scale printing processes. The resulting thermoelectric legs retain 80% of their power factor after 100 days in air and about 30% after 300 days. Using the proposed methodology, we fabricate two thermoelectric modules of 4 and 10 legs that can produce maximum power outputs of 1 and 2.4 μW, respectively, at a temperature difference ΔT of 46 K.

Numerical study of transient supercooling performance and thermal stress analysis of segmented annular thermoelectric cooler

A multiphysics-coupled numerical simulation of a segmental annular thermoelectric cooler (SATEC) was performed using a three-dimensional finite element method. A coupling model of the temperature, stress, and electric fields was established based on the three-dimensional transient states. Moreover, the effects of different pulse width (τ), pulse current amplitude (Pa), pulse current shape parameter (m), heat transfer coefficient (h), angle (θ), and length (H) of the thermoelectric leg on the SATEC transient properties and von Mises stress were studied. The results show that τ and Pa are the key influencing factors of SATEC. The larger the h, the more optimized the heat transfer effect of the SATEC hot end. However, when h increased to a certain value, the changes in the transient performance were insignificant. The optimal pulse can be achieved when the input pulse current Iop = 6.47 A and pulse width τ = 20 s. When the length of the thermoelectric leg H4 was 3 mm and the thermoelectric leg angle θ2 was 7°, the performance of SATEC was optimal, with Tc,min being 249.57 K, Tc,max being 279.50 K, thold being 5.5 s, and the maximum von Mises stress being 37.48 MPa. The results show that different supercooling indices and von Mises stresses could be obtained for different pulse current shapes. Geometric optimization of SATEC can improve the cooling performance and reduce the von Mises stress, thereby providing a theoretical reference for practical engineering applications and thermoelectric cooling research.

On-Chip Micro Temperature Controllers Based on Freestanding Thermoelectric Nano Films for Low-Power Electronics

HighlightsDense and flat freestanding Bi2Te3-based thermoelectric nano films were successfully fabricated by sputtering technology using a newly developed nano graphene oxide membrane as a substrate.On-chip micro temperature controllers were integrated using conventional micro-electromechanical system technology, to achieve energy-efficient temperature control for low-power electronics.The tunable equivalent thermal resistance enables an ultrahigh temperature control capability of 100 K mW−1 and an ultra-fast cooling rate exceeding 2000 K s−1, as well as excellent reliability of up to 1 million cycles.

Structural Study of the Thermoelectric Work Units Encapsulated with Cement Paste for Building Energy Harvesting.

Cement-based material encapsulation is a method of encapsulating electronic devices in highly thermally conductive cement-based materials to improve the heat dissipation performance of electronic components. In the field of construction, a thermoelectric generator (TEG) encapsulated with cement-based materials used in the building envelope has significant potential for waste heat energy recovery. The purpose of this study was to investigate the effect of cement-based materials integrated with aluminum heatsinks on the heat dissipation of the TEG composite structure. In this work, three types of thermoelectric work units encapsulated with cement paste were proposed. Moreover, we explored the effect of encapsulated structure, heat dissipation area, the height of thermoelectric single leg, and heat input temperature on maintaining the temperature difference between the two sides of the thermoelectric single leg with COMSOL Multiphysics. The numerical simulation results showed that under the conditions of a heat source temperature of 313.15 K and ambient temperature of 298.15 K, the temperature difference between the two sides of the internal thermoelectric single leg of Type-III can maintain a stable temperature difference of 7.77 K, which is 32.14% higher than that of Type-I and Type-II (5.88 K), and increased by 26.82% in the actual experiment. This work provides a reference for the selection and application of TEG composite structures of cement-based materials combined with aluminum heatsinks.

Fabrication of low-cost flexible thermoelectric generator using conductive HB graphite paint operated by solar radiation

Paper-based flexible thin film thermoelectric generators have emerged as a promising and feasible alternative to organic and inorganic conductors due to their ability to operate at room temperature within a limited temperature range. Here, a flexible solar thermoelectric generator (STEG) designed from a single material has been introduced, prepared by a simple painting method. We prepared HB graphite-based conductive paint and demonstrated a very unique method to design flexible STEG devices. The graphite paint shows p-type semiconductive behaviour, while, in conjunction with the polyethyleneimine (PEI) polymer, it acts as an n-type material. Based on the transport properties, the paint appears to be a good candidate for designing STEG devices. At room temperature, the power factor of 378 nW m−1 K−2 for p-type paint and 1.51 nW m−1 K−2 for n-type paint is obtained. In order to examine flexibility over the long term, the performance of the material was inspected through 300 repeated cycles, and transport properties (conductivity) were found to increase from 21 700 S m−1 to 73 500 S m−1 due to the excellent emulsifying properties of gum Arabic, which were confirmed by field emission scanning electron microscope analysis. To evaluate the performance of the thermoelectric (TE) generator, eight pairs of p–n legs are fabricated on normal copier (80 GSM) paper, and an output voltage of ∼0.1 mV K−1 (∼5.5 mV) for a temperature gradient T of up to ∼60 K was achieved. Further, the performance of flexible TE devices can be improved by increasing the number of thermoelectric legs and by sandwiching the device between Kapton tapes. Our work suggests a promising and simple approach to achieving cost-effective conversion of solar energy into electricity and highlights the potential of flexible STEGs for low-power applications.

N-Type PVP/SWCNT Composite Films with Improved Stability for Thermoelectric Power Generation.

Single-walled carbon nanotubes (SWCNTs) are one of the promising thermoelectric materials in applications of powering wearable electronics. However, the electrical performance of n-type SWCNTs quickly decreases in air, showing a low stability, and low-cost and effective solutions to improving its stability are also lacking, all of which limit practical applications. In this study, we studied the stability of PVP/SWCNT composite films, where oxygen and moisture from air should be responsible for the decreased stability due to oxidation and hydration. In this case, we found that coating with a 0.20 g mL-1 PVP/0.002 g mL-1 PVDF layer on the surface of PVP/SWCNTs can prevent the penetration of oxygen and moisture from air, improving film stability, where there is almost no reduction in thermoelectric performance after they are exposed to air for 60 days. Based on the stable n-type PVP/SWCNT films, a thermoelectric generator was fabricated, where poly(dimethylsiloxane) (PDMS) was used to coat the surface of the thermoelectric leg to further improve its stability. This generator showed high output performance, which achieved an open-circuit voltage of 10.6 mV and a power density of 312.2 μW cm-2 at a temperature difference of 50 K. Particularly, it exhibited high stability, where the output performance kept almost unchanged after exposure to high-humidity air for 30 days. This coating technology is also applicable to other air-sensitive materials and promotes the development and application of thermoelectric materials and devices.

Effect of Thermoelectric Legs on Electrical Performance of Single Leg Teg using Multiphyiscs Simulation

This paper was produced to examine the impact of the number of legs on TEGs while also demonstrating how to model and simulate a single-leg thermoelectric generator (TEG) using the COMSOL Multiphysics software platform. Using thermoelectric materials like SrTiO3 and Ca2FeMoO6, a simulation study of the performance of TEG was created. Therefore, by altering the hot side temperature from TH = 300K, 400K, and 500K and varying the load resistance from 0Ω to 20Ω, the influence of various performance metrics, such as output voltage and output power, has been demonstrated and investigated. It has been shown that the thermoelectric legs' material characteristics have a significant impact on how hot or cold the TE module is. Finally, it was discovered that single-leg TEG performs worse than TEG using a single thermocouple. By performing additional studies on the modeling of different numbers of TE legs, the performance of the TEG may therefore be further improved to help society deal with the energy issue.

Optimizing the performance of Bi2Te3 TECs through numerical simulations using COMSOL multiphysics

Manufacturers need to determine the best geometries for thermoelectric coolers (TECs) to achieve optimal performance. In this study, we employed the COMSOL Multiphysics software to simulate the performance enhancement of Bi2Te3 TEC. The TEC is constructed with alumina (Al2O3), copper (Cu), and bismuth telluride (Bi2Te3) materials. In particular, Al2O3 acts as an electric insulator for the top and bottom layers, Cu functions as a conductor, and Bi2Te3 serves as the p- and n-type thermoelectric (TE) legs between the Cu layers. The study examined how different TE leg heights (1.5 mm, 2 mm, and 2.5 mm) and shapes (square and rectangular) affected the TEC's performance. It looked at various factors, such as temperature gradient, electric potential, normalized current density, and total net energy rate. Additionally, the thickness effects of the insulator, conductor, and the TE leg pitch of the TEC have also been investigated. According to the obtained results, it has been determined that the square type of leg geometry has provided the best performance among the tested geometries, and it has been recommended that its leg geometry be 1.00 mm × 1.00 mm × 1.5 mm, the thickness be 0.375 mm for Al2O3 and 0.125 mm for Cu, and the pitch be 0.50 mm, as they are expected to yield satisfactory performance. The research study involved obtaining performance parameters for 18 TE elements utilized in the fabrication of TEC. The TEC-simulated results revealed the following performance metrics: ΔTmax = 73.94 K, Umax = 2.52 V, Imax = 3.00 A, Qmax = 4.42 W, R = 0.84 Ω, and Z = 0.002377 1/K.

Effect of nonuniform solar radiation on the performance of solar thermoelectric generators

Solar radiation must be concentrated before irradiating hot sides in solar thermoelectric generators (STEGs) to increase the temperature difference between hot and cold sides and thus enhance output performance. However, concentrated solar radiation is often nonuniform. This condition affects the output performance of STEGs. Herein, a thermal–electric coupled model of STEGs was constructed to investigate the thermoelectric performance of STEGs under nonuniform solar radiation. Results demonstrate that when the concentration ratio is low, increasing nonuniformity facilitates the increase in the output power of STEGs. When the concentration ratio is 60, output power increases by a maximum of 3.05 %, whereas the average temperature difference decreases by 4.44 K. When the concentration ratio is high, STEG output power peaks under a specific nonuniformity, and some thermoelectric legs at the edges of STEGs turn into load, affecting the overall STEG output performance. When the cold-side cooling performance is poor, the solar radiation input to STEGs should be made as uniform as possible to ensure the output performance and safe operation of STEGs. The results of this study provide guidance for the design of efficient STEGs.

Thermoelectric Sensor with CuI Supported on Rough Glass.

Thermoelectric generators convert heat into a potential difference with arrays of p- and n-type materials, a process that allows thermal energy harvesting and temperature detection. Thermoelectric sensors have attracted interest in relation to the creation of temperature and combustible gas sensors due to their simple operation principle and self-powering ability. CuI is an efficient p-type thermoelectric material that can be readily produced from a Cu layer by an iodination method. However, the vapor iodination of Cu has the disadvantage of weak adhesion on a bare glass substrate due to stress caused by crystal growth, limiting microfabrication applications of this process. This work presents a rough soda-lime glass substrate with nanoscale cavities to support the growth of a CuI layer, showing good adhesion and enhanced thermoelectric sensitivity. A rough glass sample with nanocavities is developed by reactive ion etching of a photoresist-coated glass sample in which aggregates of carbon residuals and the accumulation of NaF catalyze variable etching rates to produce local isotropic etching and roughening. A thermoelectric sensor consists of 41 CuI/In-CoSb3 thermoelectric leg pairs with gold electrodes for electrical interconnection. A thermoelectric leg has a width of 25 μm, a length of 3 mm, and a thickness of 1 μm. The thermoelectric response results in an open-circuit voltage of 13.7 mV/K on rough glass and 0.9 mV/K on bare glass under ambient conditions. Rough glass provides good mechanical interlocking and introduces important variations of the crystallinity and composition in the supported thermoelectric layers, leading to enhanced thermopower.

Achieving high thermoelectric conversion efficiency in Bi2Te3-based stepwise legs through bandgap tuning and chemical potential engineering.

In this study, we show that the energy conversion efficiency in thermoelectric (TE) devices can be effectively improved through simultaneous optimization of carrier concentration, bandgap tuning, and fabrication of stepwise legs. n- and p-type Bi2Te3-based materials were selected as examples for testing the proposed approach. At first, the Boltzmann transport theory was employed to predict the optimal temperature-dependent carrier concentration for high thermoelectric performance over a broad temperature range. Then, the synthesized n-Bi2Te3-xSex and p-Bi2-xSbxTe3 solid solutions were tested to evaluate their suitability for fabricating the stepwise thermoelectric legs. The output energy characteristics of the designed TE devices were estimated using numerical modeling employing the finite element method. The theoretical simulation revealed an improvement in the conversion efficiency between the best homogeneous and stepwise TE legs from 8.8% to 10.1% and from 9.9% to 10.8% in p-type and n-type legs, respectively, which is much higher than the efficiency of the industrial thermoelectric modules (3-6%). The measured conversion efficiency of the fabricated n- and p-type stepwise legs reached very high values of 9.3% and 9.0%, respectively, at the relatively small temperature gradient of 375 K. This work suggests carrier concentration and bandgap engineering accompanied by the stepwise leg approach as powerful methods for achieving high energy conversion efficiency in thermoelectric converters.

Solution-based 3D printed thermoelectric composite for custom-shaped thermoelectric generator applications

To fulfill the ever-increasing power demands of deep space exploration, the output performance of radioisotope thermoelectric generators, the only accessible power source, must be enhanced in several aspects, including thermoelectric properties of materials, geometry, welding, etc. In this study, we present our results on the development of a novel thermoelectric slurry suitable for the 3D printing of thermoelectric generators with optimized leg geometry. The rheological properties of the slurry are optimized by combining proper amounts of organic solvent, binder, and bismuth telluride-based thermoelectric powder. The addition of Cu to the slurry as a conductive additive are also investigated. The homogeneous dispersion of Cu within the material not only increases the electrical conductivity of the final thermoelectric leg significantly but also promotes the crystallization of the thermoelectric particles during the sintering process. These effects result in 3D-printed thermoelectric composites exhibiting ZT values up to 0.91 and extended optimum operating temperature range. Thermoelectric modules composed of 3D-printed thermoelectric legs show excellent output performance and structural strength. This work could also produce other special shaped thermoelectric devices to match irregularly shaped heat sources to reduce contact heat loss and improve output performance.

A comparative performance analysis of thermoelectric generators with a novel leg geometries

Thermoelectric (TE) devices utilize the Seebeck effect to produce electricity from waste heat. The optimization of TE leg geometry and its structure has lately drawn more attention to improving TE power generators. This study uses the finite element method to examine thermoelectric generators' thermal reliability and performance (TEGs) for novel TE leg designs. New leg shapes, such as a cross-vertical and butterfly, are introduced and contrasted with the squared (conventional) leg and other leg shapes, such as trapezoidal, cross-horizontal, I-shaped, X-shaped, and Y-shaped. The design of the main geometric parameters, including structure, height, volume, and surface area of the thermoelectric leg, is discussed in detail. As the TE leg has a larger heated surface area, the results demonstrate that the cross-vertical and butterfly legs perform 39.2% and 30.4%, respectively, higher than the squared (conventional) shape. However, the square-shaped leg shows the least thermal stress compared to other designs, especially at high thermal gradients. For low-temperature gradients (Th < 100 °C), the new TE leg designs of the cross-vertical and butterfly structures exhibit thermal stresses below the yield stress of bismuth telluride, indicating that their use is suitable for upcoming low-temperature gradient thermoelectric system applications.

Temperature Distribution in a Non-Prismatic Thermoelectric Leg and the Energy Conversion Efficiency

Abstract It has been proposed that asymmetric thermoelectric (TE) legs may enhance the TE energy conversion efficiency. This work presents an analytical model for the temperature field in non-prismatic TE legs and the energy conversion efficiency. Different from the models available in the literature, the present one-dimensional (1D) heat equation for thermal conduction in non-prismatic legs is derived from the general three-dimensional energy and charge balance laws and the thermoelectric constitutive relations considering Joule heating and the Seebeck effect on the heat flow. The temperature field in a TE leg with an arbitrary gradient of the cross sectional area is obtained using the 1D heat equation. The temperature field and energy conversion efficiency are calculated for exponential and quadratic Bi2Te3 legs as well as an exponential PbTe leg. The numerical results indicate that leg tapering has minimal effects on the temperature distribution in and energy efficiency of the non-prismatic leg under the prescribed cold and hot side temperatures boundary conditions provided that the volume of the leg remains the same. The energy efficiency of the tapered leg, however, can be significantly increased under the prescribed hot side heat flux condition. Finally, a simple estimate on the limitation of the 1D models for non-prismatic legs is discussed.

Kirigami-inspired organic and inorganic film-based flexible thermoelectric devices with built-in heat sink

Thermoelectric (TE) devices can convert heat to electricity directly, which offers a unique opportunity to realize waste heat recovery. However, conventional TE devices inevitably use heat sinks, which are bulky, rigid and heavy, limiting practical applications. Herein, we propose a fully integrated film-based TE device with intrinsically built-in fins as heat sink in a hexagonal honeycomb device structure, that simultaneously achieves high TE performance and conformability, as confirmed by experiments and modelling. A flexible Kapton substrate with copper electrodes, integrating either carbon nanotube (CNT) veils or bismuth telluride (Bi2Te3) TE ‘legs’, both of n- and p-type, achieved a remarkable specific power of 185.4 nW K−2 for a Bi2Te3-based device and 53.1 nW K−2 for a CNT-based device, thanks to the heat dissipation effect granted by the built-in fins. Besides, the addition of oriented polymer films interconnects, contracting when above their glass transition temperature, allowed a single substrate two-dimensional (2D) TE device to self-fold into a three-dimensional (3D) hexagonal honeycomb structure, with built-in fins, contactlessly and autonomously. The demonstrated shape-programmed kirigami-inspired scalable TE device paves the way for realising self-powered applications comprising hundreds of TE legs with both inorganic (e.g., Bi2Te3) and organic (e.g. CNT veils) TE materials and integrated heat sinks.

The Transient Cooling Performance of a Compact Thin-Film Thermoelectric Cooler with Horizontal Structure

Thermoelectric cooling is an ideal solution for chip heat dissipation due to its characteristics of no refrigerant, no vibration, no moving parts, and easy integration. Compared with a traditional thermoelectric device, a thin-film thermoelectric device significantly improves the cooling density and has tremendous advantages in the temperature control of electronic devices with high-power pulses. In this paper, the transient cooling performance of a compact thin-film thermoelectric cooler with a horizontal structure was studied. A 3D multi-physics field numerical model with the Thomson effect considered was established. And the effects of impulse current, thermoelectric leg length, pulse current imposition time, and the size of the contact thermal resistance on the cooling performance of the device were comprehensively investigated. The results showed that the model achieved an active cooling temperature difference of 25.85 K when an impulse current of 0.26 A was imposed. The longer the length of the thermoelectric leg was, the more unfavorable it was to the chip heat dissipation. Due to the small contact area between different sections of the device, the effect of contact thermal resistance on the cooling performance of the device was moderate.