Thermal Contact Resistance Research Articles

Prismatic Spreading–Constriction Expression for the Improvement of Impedance Spectroscopy Models and a More Accurate Determination of the Internal Thermal Contact Resistances of Thermoelectric Modules

Thermoelectric (TE) devices can convert heat to electrical power or use electrical power to generate a temperature difference. Their characterization is essential to develop devices with higher efficiency. Impedance spectroscopy models have been developed in the last few years, and it has become a highly advantageous method for TE system characterization. Recently, it has been shown that this technique can also be used to determine internal thermal contacts (between the TE legs and the metallic strips that connect them and between the metallic strips and the outer layers). Here, we developed for the first time a spreading–constriction expression which does not assume cylindrical geometry. The enhanced model is also used to characterize four TE devices from different manufacturers, highlighting overestimations up to 13% when the previous cylindrical approximation is used. A code is provided in the Supporting Information ready to fit the experimental data. This study positions impedance spectroscopy as a powerful tool to detect and monitor issues during manufacturing or operation of TE devices, which typically occur at the contacts.

Evaluation of Efficiency for Miniscale Thermoelectric Converter under the Influence of Electrical and Thermal Resistance of Contacts

Mass-produced thermoelectric modules are mainly fabricated with Bi2Te3-based materials. Due to the limited world reserves and the high price of tellurium, it must be saved. The miniaturization of thermoelectric converters is one of the modern trends to diminish the use of tellurium, reduce the cost of modules and expand the range of their applications. The main disadvantage of miniature thermoelectric converters operating in cooling or generating modes is their low energy efficiency, caused by the effect of electrical and thermal resistances of contacts, interconnectors and insulating plates. We propose an improved method for evaluating the maximum efficiency that takes into consideration the impact of these unwanted resistances. This method can also be used to design the modules with the optimal structure for cooling and energy generation, and not only to study their performance. The effect of undesirable electrical and thermal resistances on the maximum efficiency of cooling and generating converters made of Bi2Te3-based materials is analyzed. It is shown that the efficiency of miniature modules can be significantly improved if these resistances are reduced to their rational values. The decrease in electrical contact resistance is the predominant factor. The rational values to which it is advisable to decrease the electrical contact resistance have been determined. In the development of miniscale module technology, it is necessary to focus on such rational contact resistance values.

ВЛИЯНИЕ КОНТАКТНОГО ТЕРМИЧЕСКОГО СОПРОТИВЛЕНИЯ БИМЕТАЛЛИЧЕСКИХ МАТЕРИАЛОВ НА ИНТЕНСИВНОСТЬ ТЕПЛООБМЕНА

The influence of the structural material of heat exchange pipes and the contact thermal resistance of the heat transfer surface on the intensity of heat exchange is considered. An approach to the determination of contact thermal resistance is proposed. The necessity of taking into account the contact thermal resistance in the design of heat exchangers is shown

Interface heat transfer for hydronic heating: heating tests of concrete blocks and numerical simulations

ABSTRACT A comprehensive understanding of the heat transfer mechanism of hydronically-heated structures is crucial to predicting their heating performance. However, few studies considered the heat transfer at the interface of heating pipe and host material. In this paper, heat transfer at two critical interfaces for hydronically-heated concrete structures, e.g. pipe-concrete interface and concrete-air interface, has been tested and analyzed. Two concrete blocks, one with an embedded cross-linked polyethylene (PEX) pipe and one with an attached PEX pipe, were fabricated to represent heated bridge decks for the heat transfer study. The two blocks were tested inside a freezer box in a series of heating response tests at varied room and fluid temperatures. Measured temperatures at different depths were used to find the convection heat transfer coefficient and the thermal contact conductance between the concrete and PEX pipe through equations developed via finite difference method (FDM). Finite element models (FEM) of the two blocks were developed to verify the thermal contact values derived from a 1-D thermal resistance model. A comprehensive analysis of the temperature response of the models was performed, especially at the two interfaces, and the FEM models were able to predict the lab measurements accurately. The obtained contact heat transfer coefficient and the FEM models can be used for all hydronically-heated structures.

Thermal Performance of Liquid Metal Pastes Containing low Content of Metal Particles for Thermal Interface Materials in IC Module Electronics

In recent years, considerable attention has been paid to gallium-based liquid metal alloys in their use as thermal interface materials for GPU, APU, and HPC in PC and super computers due to its considerably high thermal conductivity and low contact thermal resistance. Gallium-based Liquid metal paste containing low content of metal particles (LMP-MPs) to enhance thermal performance and controllable BLT of the prepared liquid metal composites for thermal interface materials (TIMs) prepared by in-situ introducing gallium oxide into the liquid metal alloys will be reported in our recent research. In this paper, we will report effect of the composition, particle size/types, and bond line thickness on thermal properties of the LMP-MPs. Thermal properties of the LMP-MPs were measured at 50o C using a thermal tester, TIMA5, based on ASTM-D5470 test methodology. It was found in the present study that the composition and types of metal particles, and BLT have significant influence on thermal conductivity, and the conductivity values increase with an increase of the content of metal particles and BLT. However, thermal resistance varies with the change of composition and BLT of LMP-MPs. Scanning electron microscope (SEM) was used to characterize microstructure of LMP-MPs with different metal particles and sizes. Micrographic morphology of the LMPs-MPs shows continuous frame structure observed with SEM, which could keep liquid metals from spreading out and stabilize the phase. We eventually found the LMP-MPs have the better wetting and adhesion properties on bare Cu, glass and bare Si surface than liquid metal alloys that endows good printability to the LMP-MPs. Continuous monitoring of thermal resistance of LMP-MPs at 45o C and 89o C using a house-made thermal tester shows stable thermal resistance after a few months, which indicates LMP-MPs have excellent thermal reliability in ambient atmosphere.

Structural upgrading and thermal-machanical stress analysis of plasma facing components for HL-2M tokamak

Upgrade of plasma facing components (PFCs) is necessary since the first plasma was successful in December 2020 for HL-2M tokamak. During the first plasma, the 2 mm thickness stainless steel 316L was employed for first wall to protect vacuum vessel and other in-vessel components (e.g. diagnostic components). As the running parameters of the plasma increase gradually, the carbon-based materials would be used for first wall and divertor as the plasma facing materials (PFMs) due to it could withstand high thermal loads. The maximum expected operational thermal load to the PFM is ∼7 MW/m2 over a 2 cm wide band for 5 s for lower divertor. And the carbon-fiber-composite (CFC) is adopted to the lower divertor due to it has better thermal conductivity and strength compared with ordinary carbon-based materials. CFC is attached to the heat sink plate by brazing to reduce their interface contact thermal resistance. The lower divertor with high thermal shock needs to be designed with cooling structure to bring the thermal energy out of the vacuum vessel rapidly. The thermal-hydraulic analysis of lower divertor have been carried out, and the results show that the cooling performance satisfy the thermal design requirements. While the high-purity graphite was adopted for first wall with the smaller thermal load (∼0.3 MW/m2, pulse time 5 s). Their thermal energy would be transferred to the vessel wall by the means of thermal radiation and thermal conduction, then convection to the cooling water in the interlayer of vacuum vessel at a cooling time of 15 min. These graphite tiles are mechanically attached to the back-plate. The structural assessment results show that current structural design satisfies the requirements under the above thermal loads based on thermal analysis and elastic-plastic analysis.

Cu/oriented-carbon nanotubes composite with ultralow thermal contact resistance

In this paper, a simple material preparation method is proposed to meet the requirements of efficient heat exchange interface materials for spacecraft on-orbit modular assembly. First, carbon nanotubes (CNTs) were uniformly dispersed on the surface of spherical copper (Cu) powder, and then the bulk was obtained by hot-pressing sintering. Finally, the Cu on the surface was removed by electrolysis, so that the CNTs can protrude from the surface to a certain height. After contacting with the matching materials, the exposed CNTs can fill the inevitable pores at the interface, increase the heat transfer channel, and effectively reduce the interface thermal contact resistance (TCR). By adjusting the type of CNT, contact pressure, the height of CNT protruding from the surface of Cu powder, the minimum TCR of the interface between the obtained Cu/oriented carbon nanotube (Cu/OCNT) composite and pure Cu was 25.4 mm2 K W−1 under 2.26 MPa, which is superior to most existing commercial thermal interface materials. Moreover, the heat exchange interface designed based on the prepared materials can be repeatedly contacted and separated, which is expected to provide a solution for the heat exchange of on-orbit modular assembly spacecraft.

A numerical study of PCM battery thermal management performance enhancement with fin structures

Phase change material (PCM) cooling is regarded as a promising thermal management technique to realize a proper battery working temperature. However, the low thermal conductivity of PCM restricts its practical applications. In this study, the impact of aluminum fin insertion on the thermal performance of PCM thermal management is explored. Couples of fin structure shapes were adopted and their performances were compared. It is demonstrated from the simulation results that, among the fin structures investigated in this study, the bifurcated fin structures achieved the lowest battery maximum temperatures, specifically, the battery temperature was reduced by 6.16 K compared to the pure PCM case under 5C discharge (5C means that battery is discharged from full of charge to 0% state of charge in 1/5 h). The 2-branch bifurcated fin structure could realize a further 0.50 K temperature drop than the single-branch counterpart. Besides, the impacts of various parameters were investigated. The maximum temperature at the end of 5C discharge process was reduced from 314.30 K to 311.36 K when the fin quantity increased from 3 to 8. The maximum battery temperature reaches up to 313.80 K if the thermal contact resistance between the battery and fin structure grows to 0.0025 W/(m2⋅ K) with 8 fins while it could be decreased by 1.21 K if the contact resistance reduced half to 0.00125 ((m2⋅ K)/W. The maximum battery temperature was found to decrease by 0.27 K with PCM width enlarged from 28 mm to 29 mm.

Synthesizing copper-doped silicon/carbon composite anode as cost-effective active materials for Li-ion batteries

Potentially useful anodic material with prospects for use within rechargeable lithium-ion batteries are fabricated from silicon (Si)-based compounds. The active Si/electrolyte contact and weak conductivity, however, constantly produce side reactions, which dramatically reduce cycling stability. The only metallic current collector that demonstrates to facilitate lithium-ion transfer and electron conduction without alloying reactions is copper (Cu). In this study, we created Si-based multicomponent anode materials made of Si/Cu/Cu3Si alloy nanoparticles (Si/Cu/Cu3Si@C) coated in amorphous carbon. This is accomplished utilizing a straightforward, low-cost approach that combines hydrothermal technology and high-intensity ball milling. To further increase conductivity, Si/Cu/Cu3Si alloy is used as the active component. Through the use of a micro-sized amorphous carbon-coated structure, the volume problem of the active material can be successfully resolved. Additionally, the micro-sized amorphous carbon may inhibit nanoparticle agglomeration and alloy interfacial side reactions. As a result, it is anticipated that the Si/Cu/Cu3Si@C composite will display favorable electrochemical performances and possess a remarkable reversible specific capacity of 984 mAh g−1 at 0.5 C. The GITT test is used to determine the DLi+ of the Si/Cu/Cu3Si@C electrode, which ranges from 10−11 to 10−8 cm−2 s−1. Additionally, the full-cell is constructed by coupling a Li(Ni1/3Co1/3 Mn1/3)O2(NCM111) cathode with a solution-based chemically Si/Cu/Cu3Si@C anode that exhibits an enhanced initial coulombic efficiency (84.9%) and outstanding cycle performance.

Effect of load application method on thermal contact resistance and uniformity of temperature distribution

Traditionally, the research on thermal contact resistance based on real rough surfaces is often limited to the uniform load. This study investigated the effects of the material, surface roughness, pressure load, and temperature on the thermal contact resistance and contact interface temperature distribution non-uniformity under a concentrated load. First, rough surfaces with different surface roughness degrees were generated by using a random generation method, and microscopic contact numerical models of three different materials were established. Then, the real contact area of different pressure loads under uniform and concentrated loads were calculated. Finally, heat transfer analysis was performed at different temperatures based on the microcontact state, the thermal contact resistance and the contact interface temperature distribution non-uniformity were calculated. Compared with the uniform load, the thermal contact resistance and the non-uniformity of the temperature distribution were improved under the concentrated load, and the effect was more obvious under the conditions of a large pressure load and small surface roughness degree. In addition, it was found that the uniformity of the temperature distribution on the contact surface was proportional to the real contact area and temperature instead of the thermal contact resistance except when the real contact area was very small.

Effect of thermal contact resistance on the CHF and HTC for pool boiling heat transfer

In recent years, there has been increasing interest in the demand for heat dissipation of electronic devices. Constructing micro/nanostructures and using nanofluid for the pool boiling heat transfer have proved to be a notoriously effective method to increase the critical heat flux (CHF) as well as the heat transfer coefficient (HTC). When the tested samples with micro/nanostructures are soldered to the upper of the heated copper block, the CHF boiling curves of the tested samples always shift right, which may be caused by the thermal contact resistance (TCR) from the soldering interface. However, it is rarely for the research to be reported the effect of the thermal contact resistance on the pool boiling heat transfer performance. This paper highlights the effect of the TCR on the CHF and HTC for pool boiling heat transfer by comparing the boiling curve of the non-soldering, the soldering, and the Rohsenow curve. The relationship between the difference in temperature with increased heat flux is established by measuring the TCR of the soldering interface, and the relationship at the different soldering interface morphology has been explored. The results show that the CHF boiling curve with soldering shift right 106–144 % than that of the non-soldering, and the HTC decreases by 45.6–63.5 %. The shifted boiling curve could be corrected by the relationship between the TCR with increased heat flux. However, the boiling curve cannot be corrected by the relationship when the soldering interface has voids. This work demonstrates that the deviation between the boiling curve of soldering with the boiling curve of non-soldering is universal for engineering applications by comparing similar studies. Regardless of whether soldering is used in pool boiling heat transfer experiments, the Rohsenow curve is still an important reference, but the effect of TCR must be considered in the pool boiling curve of soldering.

Experiments and finite element analysis on a hybrid polymer gear rack

This article presents the results of experiments and finite element analysis on a hybrid polymer gear concept. The study aimed to investigate the effectiveness of the hybrid gear concept by using a rack tooth geometry.The results of the experiments have shown that the hybrid gear concept improves the heat evacuation from the flank and root regions, potentially increasing the load-carrying capacity. Additionally, the results of the experiments were compared with those obtained from the finite element analysis to validate the numerical model. The results showed that the hybrid polymer gear rack exhibited good thermal performance, and the finite element analysis accurately predicted the behaviour of the gear rack specimens. The study also analyses the influence of the interference fit on the contact pressure and thermal contact conductance in a hybrid polymer gear concept, taking into account surface roughness and temperature. It provides insights for optimizing the press fit to ensure efficient heat dissipation in practical applications.Overall, the study provides valuable insights into the potential use of hybrid polymer–metal materials in gear applications and supports the validity of the hybrid gear concept.

Inverse Estimation of Effective Thermal Conductivity of Multilayer Materials Considering Thermal Contact Resistance

Abstract Multilayer materials have been widely used in engineering applications, attributed to excellent thermo-mechanical performances. However, the thermal or mechanical properties of multilayer materials remain elusive, owing to contact behaviors etc. factors. In order to address this issue, an innovative method is employed to estimate the effective thermal conductivity (ETC) of multilayer materials considering thermal contact resistance (TCR) between layers, and the equivalence performance is investigated by solving three-dimensional inverse heat conduction problems. First, the equivalence method is validated by available experimental data of a multilayered insulation composite material. Then, the precision of different equivalence methods is compared, and the results indicate that the anisotropic equivalence method has higher accuracy than the isotropic and orthotropic equivalences for the five-layer material in the present work. Finally, the robustness and stability of the anisotropic equivalence method are evaluated in detail. The present work provides a new alternative method for predicting the effective thermal conductivity of multilayer materials.

Fractal model of thermal contact conductance of rough surfaces based on elliptical asperity

PurposeThe purpose of this study is to present a fractal model of thermal contact conductance of rough surfaces based on elliptical asperity.Design/methodology/approachThe effects of contact load, fractal dimensional, fractal roughness and eccentricity on thermal contact conductance of rough surfaces were investigated by using numerical simulation.FindingsThe results indicate that the thermal contact conductance of rough surfaces increases with the increase of the contact load, increases with the increase of the fractal dimension and decreases with the increase of the fractal roughness. The thermal contact conductance of rough surfaces increases with the increase of eccentricity. The shape of the asperity of rough surfaces has an important influence on the thermal contact conductance of rough surfaces.Originality/valueA fractal model of thermal contact conductance of rough surfaces based on elliptical asperity was established in this study. The achievements of this study provide some theoretical basis for the investigation of thermal contact conductance of bolted joint surfaces.

The effects of interfacial thermal contact resistance between yarns and matrixes on the thermophysical property of the plain woven C/SiC composite

The plain woven C/SiC composites with high thermal shock resistance are widely used in aerospace applications. For this composite, thermal contact resistance (TCR) has an unneglectable contribution to the thermophysical property. In this work, the influence of the TCR on the thermophysical property of a real 2D plain woven C/SiC composite is studied. X-ray CT scanning is used to obtain the microstructures of the C/SiC composite, and the complex structures are restructured and transformed into standard cube grids based on the theory of the intersection of rays and triangles. Combining with finite difference method (FDM) and multiple GPUs acceleration, an efficient approach for numerically predicting the thermophysical property of the real C/SiC composite is established. Based on the Laser Flash Method (LFM) and Differential Scanning Calorimeter (DSC) method, the effective thermal conductivities (ETCs) of the C/SiC composite at different temperatures are obtained experimentally. The results show that ETCs predicted by our numerical method are closer to the measured ones when TCR is considered. Through the numerical simulation and theoretical analysis, the correlation between the ETC and TCR is obtained, which is proved to be a typical Logistic function, and the physical meanings of various constants in the correlation are determined and discussed. Besides, the thermal response time increases with the TCR increasing, simultaneously, the distributions of isotherms and heat-flux trajectories more approach the distributions of fiber yarns in the material.

Development and potential use of MWCNT suspended in vegetable oil as a cutting fluid in machining of Monel 400

The heat dissipation problem that arises when machining difficult to cut materials can be mitigated by using nano-cutting fluids, which have a much higher thermal conductivity value than the basic lubricants. Since the heat carrying capacity of the Minimum Quantity Lubrication (MQL) system is significantly lower than that of other coolants, a number of nano-additives are used to increase its cooling effectiveness. Therefore, this study firstly focuses on the assessment of nano-cutting fluids and theirsignificant efficacy in the machining operation of nickel-based alloys. Multi-walled carbon nanotube (MWCNT) suspended in vegetable oil is compared with distinct cooling environmental conditions namely, dry, MQL and cryogenic carbon dioxide (CO2). The novelty of this work is that the different volume fractions of 0.2 – 1 wt% of MWCNT were dispersed to study the contact angle, viscosity and thermal conductivity of the prepared molecular liquid and then, the potential of MWCNT suspended in vegetable oil is used to evaluate the outcomes of surface roughness (Ra), cutting temperature (CT) and tool wear (Vb) while machining Monel 400 alloy. The outcomes affirmed that employing nano MQL in machining operations resulted in a mean reduction of about 65% in the temperature evolved concerning no coolant condition. Additionally, the use of nanoparticles leads to an improved surface finish and abridged tool wear.

PVDF-HFP/PAN/PDA@LLZTO Composite Solid Electrolyte Enabling Reinforced Safety and Outstanding Low-Temperature Performance for Quasi-Solid-State Lithium Metal Batteries.

Lithium-ion batteries (LIBs) have achieved a triumph in the market of portable electronic devices since their commercialization in the 1990s due to their high energy density. However, safety issue originating from the flammable, volatile, and toxic organic liquid electrolytes remains a long-standing problem to be solved. Alternatively, composite solid electrolytes (CSEs) have gradually become one of the most promising candidates due to their higher safety and stable electrochemical performance. However, the uniform dispersity of ceramic filler within the polymer matrix remains to be addressed. Generally, all-solid-state lithium metal batteries without any liquid components suffer from poor interfacial contact and low ionic conductivity, which seriously affect the electrochemical performance. Here we report a CSE consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), polydopamine (PDA) coated Li6.4La3Zr1.4Ta0.6O12 (LLZTO) (denoted as PDA@LLZTO) microfiller, polyacrylonitrile (PAN), and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP). Introducing only 4 μL of liquid electrolyte at the electrode|electrolyte interface, the CSE-based cells exhibit high ionic conductivity (0.4 × 10-3 S cm-1 at 25 °C), superior cycle stability, and excellent thermal stability. Even under low temperatures, the impressive electrochemical performance (78.8% of capacity retention after 400 cycles at 1 C, 0 °C, and decent capacities delivered even at low temperature of -20 °C) highlights the potential of such quasi-solid-state lithium metal batteries as a viable solution for the next-generation high-performance lithium metal batteries.

Realizing the Accurate Measurements of Thermal Conductivity over a Wide Range by Scanning Thermal Microscopy Combined with Quantitative Prediction of Thermal Contact Resistance.

Quantitative thermal performance measurements and thermal management at the micro-/nano scale are becoming increasingly important as the size of electronic components shrinks. Scanning thermal microscopy (SThM) is an emerging method with high spatial resolution that accurately reflects changes in local thermal signals based on a thermally sensitive probe. However, because of the unclear thermal resistance at the probe-sample interface, quantitative characterization of thermal conductivity for different kinds of materials still remains limited. In this paper, the heat transfer process considering the thermal contact resistance between the probe and sample surface is analyzed using finite element simulation and thermal resistance network model. On this basis, a mathematical empirical function is developed applicable to a variety of material systems, which depicts the relationship between the thermal conductivity of the sample and the probe temperature. The proposed model is verified by measuring ten materials with a wide thermal conductivity range, and then further validated by two materials with unknown thermal conductivity. In conclusion, this work provides the prospect of achieving quantitative characterization of thermal conductivity over a wide range and further enables the mapping of local thermal conductivity to microstructures or phases of materials.

Thermal resistance study and numerical optimization of plate fin-and-tube with mechanical expanded joint

This paper analyzed the mechanical expanded joint process of a plate fin-and-tube heat exchanger and the geometry of the fin's tube-hole in an effort to reduce the thermal contact resistance between the fin and the base tube and improve the tube-fin's heat transfer capability. A plate fin-and-tube heat exchanger was used in the heat transfer performance experiment, and a novel experimental technique was used to estimate the thermal contact resistance between the fins and the tube. By using the finite element simulation, the post-expansion contact stress between the fin and the base tube was calculated, and a correlation between the contact stress and the thermal contact resistance was established. The simulation approach optimizes the expansion parameters and design of the fin's tube-hole. Based on the fin type of the specimen, simulation calculations were performed by adjusting the expansion interference and the interval between the fin's tube-hole and the base tube before the expansion. The results of the calculations indicate that, within a certain range, increasing the expansion interference and lowering the interval between the tube-hole and the base tube can increase contact stress and decrease thermal contact resistance. Changing the shape of the specimen's tube-hole can more efficiently to reduce thermal contact resistance. In order to alter the shape, a power function curve was applied to the original straight part of the fin profile.

Study on heat transfer characteristics of annular pulsating heat pipe with temperature oscillation characteristic

A new annular structure of pulsating heat pipe (APHP) was designed for evacuated solar collector. To reduce the contact thermal resistance and alleviate the overheating problem, each tube of the pulsating heat pipe can be installed to fit snugly against the inner wall of evacuated tube. Experiments on filling ratio, heat transfer distance, inclination angle, and working fluid were carried out. The flow circumstances and heat transfer performance were analyzed based on the difference in frequency and amplitude of temperature oscillation curve and thermal resistance data. The results showed that high-frequency and low-amplitude temperature curve appeared when the APHPs were in the situation of low flow resistance, normally accompanied with better heat transfer effect. The optimum filling ratio and inclination angle are 60% and 60 °, respectively. The heat transfer performance of APHP decreased with the increase of heat transfer distance. The APHPs charged with self-rewetting fluid demonstrated a significant effect on heat transfer enhancement. Over different heat transfer distance, the application of self-rewetting fluid reduced the thermal resistance on average by 32.46%, 34.15% and 37.40%, respectively.