Values Of Thermal Contact Resistance Research Articles

Method for measuring thermal contact resistance of graphite thin film materials

Abstract Thermal contact resistance (TCR) is an important parameter in thermal analysis of materials. Because of many influential factors, it is difficult to find a general model or computational formula to calculate the TCR of a solid interface. In many engineering applications, TCR values are usually obtained through experiments. Unlike extensive research focusing on ordinary columnar materials, this paper aims at measuring the TCR values of graphite thin film materials. The technical challenge is that it is not convenient to embed thermocouples into such materials. To overcome this challenge, a steady-state method using a copper heat flux meter is developed, which provides a useful tool for indirect TCR measurement. In our experiments, the TCR values of the graphite thin film materials are successfully measured under different temperature and pressure levels. The results provide a valuable guideline for the use of this type of material in high-temperature, high-pressure applications.

Generalized Procedure for Improved Accuracy of Thermal Contact Resistance Measurements for Materials With Arbitrary Temperature-Dependent Thermal Conductivity

Thermal contact resistance (TCR) is most commonly measured using one-dimensional steady-state calorimetric techniques. In these experimental methods, a temperature gradient is applied across two contacting beams and the temperature drop at the interface is inferred from the temperature profiles of the rods that are measured at discrete points. During data analysis, thermal conductivity of the beams is typically taken to be an average value over the temperature range imposed during the experiment. Here, a generalized theory is presented that accounts for temperature-dependent changes in thermal conductivity. The procedure presented enables accurate measurement of TCR for contacting materials whose thermal conductivity is any arbitrary function of temperature. For example, it is shown that the standard technique yields TCR values that are about 15% below the actual value for two specific examples of copper and silicon contacts. On the other hand, the generalized technique predicts TCR values that are within 1% of the actual value. The method is exact when thermal conductivity is known exactly and no other errors are introduced to the system.

Effect of Load and Interface Materials on Thermal Contact Resistance between Similar and Dissimilar Materials

The thermal contact resistance (TCR) between similar and dissimilar materials (copper, aluminium, brass and type 304 stainless steel) was assessed. Copper foil, aluminium foil, lead and Sn-9Zn lead free solder were selected as thermal interface materials (TIMs). The interfacial contact pressure was varied by application of load on materials in contact. The interfacial heat flux was estimated by solving the inverse heat conduction problem (IHCP). At higher load, the temporal variation of thermal contact resistance showed early occurrence of peak and lower values of TCR. The use of thermal interface materials reduced the contact resistance between the hot source and cold sink materials. Among the interface materials used, Sn-9Zn lead free solder showed the lowest contact resistance. This was attributed to the solid to liquid phase transformation at higher temperatures and the conformance of the interface material to surfaces in contact. Factorial experiments were carried out to determine the significance of experimental variables on TCR. The analysis showed that the effect of applied load on TCR was significant compared to other parameters.

Thermal contact resistance in plate fin-and-tube heat exchangers, determined by experimental data and CFD simulations

Plate fin-and-tube heat exchangers operate in a cross-flow arrangement. The numerical studies of performance of these heat exchangers encounter difficulties in the proper prediction of the total gas side temperature difference, because thermal contact resistance between the fin and the tube is unknown. The local measurements of its value are difficult to carry out. This paper presents a modified method for estimating the mean value of thermal contact resistance in a plate fin-and-tube heat exchanger. The proposed computational method is based on the CFD simulations and experimental measurements and it allows an accurate prediction of the total gas-side temperature difference in a heat exchanger. Furthermore, this paper presents the modified method of determining the average heat transfer coefficient for the air flow, which is similar to the technique used for experimental data reduction.

A high-precision instrumentation of measuring thermal contact resistance using reversible heat flux

During measuring the thermal contact resistance (TCR) of solids by using traditional steady-state test methods, it is observed that the measured results are unavoidable to be impacted by the direction of exerting heat flux between dissimilar and similar metals. Such a directional effect has also been found for the cases between two solids of identical material with the same surface properties. Uncertainty analysis shows that the directional effect between two solids may result from the additive errors. In order to improve the measurement precision, we propose a method by using harmonic mean value of TCR in two directions of exerting heat flux to diminish the effect. Meanwhile, a modified experimental apparatus has been designed and established to high-precisely measure TCR between two solids of the identical material. To verify the accuracy of the method, the TCRs of samples of 99.999% standard pure copper and Elkonite copper–tungsten alloy 30W3 are measured and discussed in detail. The results show that the present method has high precision and can be used in a relatively wide range of TCR measurement for identical solids and the characterization of thermal interface materials.

Development of an Experimental Procedure for Thermal Contact Resistance Estimation at the Glass/Metal Contact Interface

In this paper, an experimental device is designed and developed in order to estimate thermal conditions at the glass/metal contact interface. This device is made of two parts: The upper part contains the tool (piston) made of bronze and a heating device to raise the temperature of the piston to 700 °C. The lower part is composed of a lead crucible and a glass sample. The assembly is provided with a heating system, an induction furnace of 6 kW for heating the glass up to 950 °C. The developed experimental procedure has permitted the estimation of the thermal contact resistance (TCR) using a developed measurement principle based on the inverse technique developed by Beck et al. (1985, Inverse Heat Conduction: III Posed Problems, Wiley Inter-science, New York). The semitransparent character of the glass has been taken into account by an additional radiative heat flux and an equivalent thermal conductivity. After the set-up tests, reproducibility experiments for a specific contact pressure have been carried out. Results show a good repeatability of the registered and estimated parameters such as the piston surface temperature, heat flux density, and TCR. The estimated value of TCR reaches 2 × 10−3 K m2/W with a maximum dispersion that does not exceed 6%.

Experimental validation of numerical study on thermoelectric-based heating in an integrated centrifugal microfluidic platform for polymerase chain reaction amplification.

A comprehensive study involving numerical analysis and experimental validation of temperature transients within a microchamber was performed for thermocycling operation in an integrated centrifugal microfluidic platform for polymerase chain reaction (PCR) amplification. Controlled heating and cooling of biological samples are essential processes in many sample preparation and detection steps for micro-total analysis systems. Specifically, the PCR process relies on highly controllable and uniform heating of nucleic acid samples for successful and efficient amplification. In these miniaturized systems, the heating process is often performed more rapidly, making the temperature control more difficult, and adding complexity to the integrated hardware system. To gain further insight into the complex temperature profiles within the PCR microchamber, numerical simulations using computational fluid dynamics and computational heat transfer were performed. The designed integrated centrifugal microfluidics platform utilizes thermoelectrics for ice-valving and thermocycling for PCR amplification. Embedded micro-thermocouples were used to record the static and dynamic thermal responses in the experiments. The data collected was subsequently used for computational validation of the numerical predictions for the system response during thermocycling, and these simulations were found to be in agreement with the experimental data to within ∼97%. When thermal contact resistance values were incorporated in the simulations, the numerical predictions were found to be in agreement with the experimental data to within ∼99.9%. This in-depth numerical modeling and experimental validation of a complex single-sided heating platform provide insights into hardware and system design for multi-layered polymer microfluidic systems. In addition, the biological capability along with the practical feasibility of the integrated system is demonstrated by successfully performing PCR amplification of a Group B Streptococcus gene.

Optimization of the Thermosetting Pultrusion Process by Using Hybrid and Mixed Integer Genetic Algorithms

In this paper thermo-chemical simulation of the pultrusion process of a composite rod is first used as a validation case to ensure that the utilized numerical scheme is stable and converges to results given in literature. Following this validation case, a cylindrical die block with heaters is added to the pultrusion domain of a composite part and thermal contact resistance (TCR) regions at the die-part interface are defined. Two optimization case studies are performed on this new configuration. In the first one, optimal die radius and TCR values are found by using a hybrid genetic algorithm based on a sequential combination of a genetic algorithm (GA) and a local search technique to fit the centerline temperature of the composite with the one calculated in the validation case. In the second optimization study, the productivity of the process is improved by using a mixed integer genetic algorithm (MIGA) such that the total number of heaters is minimized while satisfying the constraints for the maximum composite temperature, the mean of the cure degree at the die exit and the pulling speed.

Effect of Thermal Contact Resistance on Alumina Molten Particle Impacting onto a Metal Substrate

In this paper, a Finite Element Analysis is carried out in order to simulate the process of spreading and solidification of a micrometric molten droplet impinging onto a cold substrate. This process is a crucial key to have a good understanding of coatings obtained by means of thermal spraying. The effect of thermal contact resistance (TCR) on the droplet spreading and solidification was investigated using different values of TCR and different droplet sizes. The solidification time was found to be a linear function of the droplet diameter square. Viscous dissipation, wettability and surface tension effects are taken into account. The Level Set method was employed to explicitly track the free surface of molten droplets.

Experimental Investigation of Contact Resistance for Water Cooled Jacket for Electric Motors and Generators

The key to the successful implementation of water jacket frame cooling in high-power electric machines, such as permanent magnet, doubly fed induction, and synchronous generators, is the contact between the laminated stator core and the frame. For improved thermal design, it is important to quantify the contact thermal resistance between lamination and frame. This paper quantitatively presents the values of conventional stator lamination and frame interface resistance through experimental results. So far, no experimental investigation has been carried out to determine this resistance. The effects of several parameters, such as surface finish, shrink fit pressures, use of thermal grease, and phase change thermal interface material on thermal contact resistance, have been experimentally investigated. The obtained values of thermal contact resistance between laminations and frame can be applied for future thermal designs of electric machines to predict accurate thermal performance.

Optimal Design of Electrostatic Probe via Finite Element Method and Experimental Investigation

Thermal contact resistance (TCR) at the interface of different materials has been systematically investigated with a effective analytical method and appropriate values of TCR are obtained by theoretical calculation with measured parameters. In this paper, a novel optimal design used to decrease TCR in model via increasing the conical degree of AL2O3 ceramic barrel is developed, results indicated the heat transfer capability of Langmuir Probe (LP) can be improved by using this configuration. Numerical simulation of transient-state thermal analysis by ANSYS and experimental investigation have been used to evaluate the thermal state of LP under different analytical conditions, comparison of simulated results with the top-middle part of LP prepared by Pyrolytic Graphite and Carbon Fiber Composite are presented and an explanation of temperature variation based on the changes of the simulated results with the top part of LP designed by different sizes are demonstrated. Many constructive suggestions have been brought forward to define the best suited material, structures and other characteristics in order to produce the type of LP with high performance and practicability.

Formation of Solid Splats During Thermal Spray Deposition

This paper reviews the findings of recent research on the formation of solid splats by the impact of thermal spray particles on solid substrates. It discusses methods of describing the substrate, by characterizing both chemical (oxide layers) and physical (surface topography, adsorbed and condensed contaminants) aspects. Recent experiments done to observe impact of thermal spray particle are surveyed and techniques used to photograph particle impact and measure cooling rates described. The use of numerical modeling to simulate impact and deformation of impacting particles is appraised. Two different break-up mechanisms are identified: solidification around the edges of splats; and perforations in the interior of thin liquid films created by droplet spreading without solidification. These two modes can be reproduced in numerical models by varying the value of thermal contact resistance between the splat and substrate. A simple criterion to predict the final splat shape is presented.

A Microscopic Approach to Determine Electrothermal Contact Conditions During Resistance Spot Welding Process

This study deals with resistance spot welding process modeling. Particular attention must be paid to the interfacial conditions, which strongly influence the nugget growth. Imperfect contact conditions are usually used in the macroscopic model to account for the electrical and thermal volume phenomena, which occur near a metallic interface crossed by an electric current. One approach consists in representing microconstriction phenomena by surface contact parameters: The share coefficient and the thermal and electrical contact resistances, which depend on the contact temperature. The aim of this work is to determine the share coefficient and the contact temperature through a numerical model on a microscopic scale. This surface approach does not make it possible to correctly represent the temperature profiles, with the peak temperature, observed in the immediate vicinity of the interface and thus to define, in practice, the contact temperature correctly. That is why another approach is proposed with the introduction of a low thickness layer (third body) at the level of the interface the electric and thermal resistances of which are equivalent to the electrical and thermal contact resistance values. In this case, the parameters of the model are reduced to the thickness of the arbitrarily fixed layer and equivalent electric and thermal conductivities in the thin layer, the partition coefficient and the contact temperature becoming implicit. The two types of thermoelectric contact models are tested within the framework of the numerical simulation of a spot welding test. The nugget growth development is found to be much different with each model.

Predicting Thermal Contact Resistance Between Molten Metal Droplets and a Solid Surface

Thermal contact resistance between molten metal droplets (aluminum alloy 380 and bismuth) and solid plates (steel and brass) was measured experimentally. The diameter of the droplets was 4mm, and droplet impact velocity ranged between 1 and 3m∕s. Substrate temperature was varied from 25to300°C and roughness from 0.06to5.0μm. Substrate temperature variation under impacting droplets was measured using fast temperature sensors that had a response time of 40ns and recorded substrate temperatures at five different radial locations under each droplet. Thermal contact resistance during the first few milliseconds of impact was obtained by matching measured surface temperature variation with an analytical solution of the one-dimensional transient heat conduction equation. An analytical model of the deformation of a free liquid surface in contact with a rough solid was used to calculate the true area of contact between them and, thereby, the thermal contact resistance. Test results agreed well with predictions from the analytical model. Thermal contact resistance values ranged from 10−7to3×10−6m2K∕W, increasing with surface roughness and decreasing with rising impact velocity.

On the Enhancement of the Thermal Contact Conductance: Effect of Loading History

Abstract A resistance to heat flow exists at the junction of two surfaces. It has long been recognized that there exists a hysteresis effect, that is, the value of thermal contact resistance in the unloading process is less than that in the loading process at the same load. However, little work has been done in utilizing this phenomenon to enhance the thermal contact conductance. The present experimental work investigated the effect of loading history; in particular the number of load cycles and overloading pressure, on the thermal contact conductance. It was found that the value of the thermal contact conductance might be enhanced by up to 51 percent. A cost-effective way of enhancing the contact conductance is suggested. [S0022-1481(00)01601-7]

An Investigation of Key Factors Affecting Solder Microdroplet Deposition

This paper combines a theoretical model with experimental measurements to elucidate the role of key operating parameters affecting solder microdroplet deposition in the electronics manufacturing industry. The experimental investigation is used to evaluate the final deposit (bump) shapes and trends predicted by the model. The effects of substrate temperature, material composition, layer thickness, and thermal contact resistance (including surface oxidation) are delineated. Solder-deposit shape comparisons between experiments and modeling suggest that the value of thermal contact resistance may change with process parameters, and is probably dependent on the solder phase. It is established that inferences regarding the overall shape or solidification times of solder bumps using limited modeling trends should be made only after careful consideration of the substrate composition, accurate representation of the thermal contact resistance, and adequate resolution of the fluid dynamical oscillatory motion and its effects on solidification rates. It is shown that modeling tools can be used in conjunction with experiments to promote our fundamental understanding of the transport processes in the complex solder jetting technology.

Thermal Deformation of Machinetool-workpiece System Caused by Accumulating Chips : 1st Reaort; Thermal Conductivity of Accumulating Chips

One of the causes of the thermal deformation of a machinetool-workpiece system is the heat of chips piled on it. The amount of the thermal deformation due to this cause, however, is hardly yet known. Because, the values of thermal conductivity of accumulating chips and thermal contact resistance between accumulating chips and the surface of the system are hardly clarified. In this paper, the thermal properties mentioned above have been experimentally investigated by using accumulating chips made of different kinds of material and under different cutting conditions and moreover a theoretical investigation has also been carried out considering a model of accumulating ideal chips. From above results, it has been made clear that the value of the thermal conductivity of accumulating chips can be estimated by using the values of the thermal conductivity of the material, the void ratio and the number of chips per unit volume and that the value of thermal contact resistance can be approximately estimated by using the same factors mentioned above.

不規則微小突起をもつ機械加工面の接触伝熱機構 (第3報)

This paper deals with the comparison between the calculated values of thermal contact resistance and experimental results when interstitial material such as air or oil exists in the clearance of interface. The overall behaviour of thermal contact resistance is discussed by the calculated results which give a good fit to the experimental data. The conclusions obtained are as follows : (1) The calculation of thermal contact resistance involves the property that the effective thermal conductivity of air or oil at the interface decreases as the mean. distance of the clearance becomes small. (2) Thermal contact resistance decreases with an increase in thermal conductivity of interstitial material and undertakes smaller variation to the applied load than in vacuum environment. (3) Thermal contact resistance shows a linear increase to surface roughness on a double logarithmic chart. Although the harder contacting members enlarge the thermal contact resistance, its variation in the range of light applied load becomes considerably small with increasing thermal conductivity of interstitial ma-terial.

Method of calculating the thermal resistance of a contact between metal surfaces

The physical nature of the thermal resistance at a contact between rough metal surfaces is considered. By analogy with the thermal resistance of a plate having a variable cross section and also by analogy with the identical form of Ohm's and Fourier's laws, an expression is derived for the thermal resistance of such a contact. Experiments are carried out to determine the thermal resistance of a contact in vacuo and in air. These investigations show that the calculated values of thermal contact resistance are in satisfactory agreement with experiment.