Effect Of Contact Resistance Research Articles

Study of Thermal Conductivity and Geometry Wall Contact Resistance Effect of Granular Active Carbon for Refrigeration and Heat Pumping Systems

The commercial success of sorption refrigeration and heat pump systems depends on a good heat and mass transfer in the adsorbent bed, which allows higher coefficients of performance and greater specific heating or cooling power that reduce capital costs. In this study the thermal conductivity and thermal contact resistance of vibrated and compressed granular active carbon and binary mixtures of active carbon are investigated using two types of conductivity measurements: a steady-state measurement between flat plates and a transient hot tube measurement. With these results is possible to draw conclusions on how the wall geometry, particle size distribution, and bulk density affect the overall thermal performance. Results show that using binary mixtures of grains and powder gives results superior to those of either grains or powder alone. The conductivity of the binary mixtures increases roughly linearly with bulk density and the 2/3 grain mixture achieves the highest densities. The method used to achieve compaction (vibration or compression) did not seem to affect the result. Thermal contact resistances reduce with increasing density but do vary with the mixture ratio, also appearing to be best with a 2/3 grain–1/3 powder mixture.

Contact fault characterisation of complex silicon solar cells: a guideline based on current voltage characteristics and luminescence imaging

AbstractHighest efficiency solar cells in industrial and R&D environments are increasingly sensitive to local performance limiting processing faults, which are best characterised by spatially resolved characterisation techniques. This work contains a discussion on the processing faults related to contact resistance and finger interruptions in interdigitated back contact silicon solar cells, which are prime example for a complex cell structure. Using experimental and simulated current–voltage measurements and luminescence images, we explore the strongly non‐linear effect of poor local contact resistances on the global series resistance, fill factor, short circuit current density and efficiency. A good agreement between global and spatially resolved characterisation of faults is found, and potential artefacts are discussed. In conclusion, we present seven cases of contacting faults in interdigitated back contact cells with distinct characteristics that can be identified using a flow chart of experiments. The resulting guideline should assist silicon solar cell manufacturers in localising and quantifying local contacting faults that reduce the cells efficiency in manufacturing of complex solar cells. Copyright © 2015 John Wiley & Sons, Ltd.

Thermal conductivity of granular porous media: A pore scale modeling approach

Pore scale modeling method has been widely used in the petrophysical studies to estimate macroscopic properties (e.g. porosity, permeability, and electrical resistivity) of porous media with respect to their micro structures. Although there is a sumptuous literature about the application of the method to study flow in porous media, there are fewer studies regarding its application to thermal conduction characterization, and the estimation of effective thermal conductivity, which is a salient parameter in many engineering surveys (e.g. geothermal resources and heavy oil recovery). By considering thermal contact resistance, we demonstrate the robustness of the method for predicting the effective thermal conductivity. According to our results obtained from Utah oil sand samples simulations, the simulation of thermal contact resistance is pivotal to grant reliable estimates of effective thermal conductivity. Our estimated effective thermal conductivities exhibit a better compatibility with the experimental data in companion with some famous experimental and analytical equations for the calculation of the effective thermal conductivity. In addition, we reconstruct a porous medium for an Alberta oil sand sample. By increasing roughness, we observe the effect of thermal contact resistance in the decrease of the effective thermal conductivity. However, the roughness effect becomes more noticeable when there is a higher thermal conductivity of solid to fluid ratio. Moreover, by considering the thermal resistance in porous media with different grains sizes, we find that the effective thermal conductivity augments with increased grain size. Our observation is in a reasonable accordance with experimental results. This demonstrates the usefulness of our modeling approach for further computational studies of heat transfer in porous media.

Silicon Nanowire Arrays Based On-Chip Thermoelectric Generators

Thermoelectric generators (TEGs) can improve the net power consumption of electronic packages by generating power from the chip waste heat. In this paper, a 3-D computational model of electronic package with silicon nanowire (Si-NW)-based embedded TEGs has been developed and the effect of crucial geometric parameters, contact resistances, and thermal properties, such as pitch length and length of Si-NWs, the electrical contact resistivity at Si-NW interface, thermal contact resistivity at TEG-package interface, and filling material thermal conductivity on power generation, has been evaluated. The analysis has shown how modifying some crucial parameters from their current values in different experimental studies affect power generation, e.g., decreasing the pitch length from 400 to 200 nm doubled the power generation, increasing the Si-NW length from 1 to 8 $\mu \text{m}$ increased power generation by a factor of three and decreasing contact resistivity by one order of magnitude from $1.0\times 10^{-11}\Omega \,\cdot \,\text{m}^{2}$ enhanced the power generation by a factor of two. This paper has estimated the energy conversion efficiency of 0.15% for 8- $\mu \text{m}$ long Si-NWs using the best thermoelectric properties available from different experimental studies. Finally, performance of Si-NW-based TEG has been compared against the Bi2Te3 superlattice-based TEGs and the crucial parameters of Si-NW TEGs have been identified which should be the focus of the future studies.

Transient responses of bi-layered structure based on generalized thermoelasticity: Interfacial conditions

Multi-layered structures are always designed to apply in the harsh environment, e.g. high temperatures and impact loads, etc. In this work, thermoelastic analysis of a bi-layered structure is implemented in the context of generalized thermoelasticity, e.g. GL model. To distinguish from existed works, the thermal contact resistance and the elastic wave impendence at the interface are considered. Accordingly, they may degenerate into the continuous conditions by selecting ideal parameters. In the numerical part, a semi-analytical solution is obtained by using the Laplace transform method, upon which the effects of the thermal contact resistance, elastic wave impendence ratio, thermal conductivity ratio and heat capacity ratio on the responses are studied. And finally, some concluding remarks are summarized, based upon which the structure may be optimized by adopting suitable material ratio in both thermal and elastic sense.

Bulk transport and contact limitation of MoS2 multilayer flake transistors untangled via temperature-dependent transport measurements

Rational use of novel high-performance semiconductors in field-effect transistors (FETs) requires exact knowledge of the dominating charge transport mechanisms. In particular, the distinction between contact- and semiconductor-limited transport is important in FETs with small channel lengths. Here, we analyze the relative contributions of contact limitation and intrinsic conductivity of FETs based on mechanically exfoliated multilayers of the high performance n-type semiconductor molybdenum disulfide (MoS2). Based on a lithography-free fabrication process, we realize FETs with room temperature mobility (μ) of up to 46.8 cm2/Vs and ION/IOFF ratio of up to 105. Using temperature- and bias-dependent charge transport measurements, we are able to show that the intrinsic bulk transport in the flake can be best described by a phonon-limited band transport model with a conductive bulk at room temperature that freezes out upon cooling of the sample. In addition, we notice an increase of μ by a factor of 2–5 when using a self-assembled monolayer (SAM)-modified SiO2/MoS2 interface. More importantly, we show that the choice of drain–source bias (VDS) is crucial when interpreting MoS2 transport measurements, while for large VDS the intrinsic semiconductor transport properties can be observed, a strong contact limitation appears at low VDS. Our combined measurements allow us to distinguish between the effect of bulk and semiconductor/dielectric interface transport and the effect of contact resistance on the electrical transport properties.

Modeling the temperature distribution and performance of a PEM fuel cell with thermal contact resistance

In this paper, a 3-D, nonisothermal numerical model with anisotropic property of gas diffusion layer (GDL) is applied to investigate the effect of thermal contact resistance (TCR) between rib and GDL, channel and rib width, and different heat transfer coefficients on the temperature distribution and performance of a single PEM fuel cell. A proper thermal contact resistance in this model is determined by comparing the predicted temperature variation between plate and cathode electrode to the available experimental results. The numerical results proved that to improve the prediction accuracy of temperature distribution and cell performance, the effect of TCR cannot be neglected. An underestimate of 1.5K is found when cell output voltage to be 0.6V of the case without TCR. And it is found that the rib and channel width and the ratio between them have an obvious effect on heat and mass transfer processes occurred in the electrode. The relatively optimum rib to channel width ratio is found to be 1.0mm/0.8mm, and the narrower the channel and rib widths the better the performance when their widths equal to each other. By comparing the temperature distribution between different heat transfer coefficients, it is found that when natural air convection is applied to cooling down the PEM fuel cell, the generated heat cannot be removed completely, however, when liquid water is used as the cooling fluid, the heat removed ability greatly exceeds the real demands of single PEM fuel cell, and the temperature of water must be heated to a proper value (larger than 333K for the cases studied) to prevent over cooling of fuel cell.

Energy and exergy analysis of thermoelectric heat pump system

Exergy analysis has gained significance in analysing thermal energy systems as it locates and quantifies the irreversibilities in the system. This paper investigates the thermoelectric heat pump systems through exergy analysis. Four thermodynamic models of the thermoelectric heat pump considering the internal and external irreversibilities are developed and analysed in MATLAB Simulink environment with temperature dependent material properties for various operating temperatures. Moreover, analytical expressions for exergy efficiency and irreversibilities for the thermoelectric heat pump are derived. The results show that the exergy efficiency of the thermoelectric heat pump increases with increase in ΔTh. For a typical operating condition in an irreversible thermoelectric heat pump with 31 thermocouples and when TH and TC of 313K and 303K respectively, the maximum energy and exergy efficiency obtained are 4.01 and 12.81% at same optimum current of 5.55A. The results also show that the effect of internal irreversibilities is more pronounced than the external irreversibilities in the performance of the thermoelectric heat pump. The effects of irreversible heat transfer and contact resistance in the exergy efficiency are also studied. This study will be helpful in designing the actual thermoelectric heat pump systems.

Analytical solution of temperature distribution in resistance spot welding

In this study, an analytical model based on integral transformations was developed to predict nugget diameters in resistance spot welding of 1.5 mm thick 5083-O aluminum alloy sheets. Welding time was fixed at six cycles. However, welding current and electrode pressure were changed; experiments were carried out for both situations. First, the effect of contact resistance on nugget diameters was studied. During the welding process, three electrode forces were selected at 2500, 3000, and 3500 N, and the welding current was fixed at 20 kA. Second, the effect of welding current on the nugget diameter was investigated. In the investigation, the electrode force was fixed at 3000 N, and the welding current was varied at 20, 25, and 30 kA. To improve accuracy, a correction factor to thermal expansion was considered. Finally, the effect of welding time on thermal history was investigated theoretically.

Effects of bolt torque and contact resistance on the performance of the polymer electrolyte membrane electrolyzers

The effect of bolt torque and contact resistance on the performance of Proton Exchange Membrane (PEM) Electrolyzers are investigated by a 50 cm2 cell. The cell is designed and manufactured in house. The performance and contact resistance of the cell with three different gasket materials for demanding bolt torques are measured. The pressure distribution inside the cell is obtained by using pressure sensitive films. The pressure acting on the membrane electrode assembly (MEA) is calculated by analyzing and quantifying intensities of pressure film images. 3D plots of pressure distribution for predefined bolt torque values are obtained to understand the pressure distribution over the active area. The performance of the cell is enhanced when bolt torque is increased. However, beyond a value, relatively weak cell components such as diffusion layers are damaged and performance loss is observed due to the mass transfer limitations. The best efficiency is reached at 15Nm bolt torque for Polytetrafluoroethylene (PTFE) and Ethylene Propylene Diene Monomer (EPDM) gaskets. For silicon gasket best efficiency is reached at 15Nm at lower current densities and at 10Nm at higher current densities. Increasing clamping pressure is found to be developing more contact points between the interfaces and results in decrease in contact resistance inside the cell.

抵抗スポット溶接における弾塑性接触・電流・熱伝導3連成解析モデルの検討

Interactions between elasto-plastic contact deformation, electric current and heat conduction produces complicated triply coupled effect in the resistant spot welding. Since the coupled effect affects weld strength, the coupled finite element analysis is required to determine welding parameters such as welding current, electrode force, welding time and electrode shape.This paper discusses in detail the elasto-plastic contact, electric current and thermal conduction triply coupled analysis method. The coupled analysis method uses modified electrical contact resistance model, modified thermal contact resistance model and iterative partitioned coupled algorithm suitable for strong coupled problem. The validity of the method are discussed under the different condition such as welding current, electrode force, welding time, material and number of the steel sheets. The analysis result of nugget growth curve agrees very well with experimental result for two sheet welding. The validity is confirmed by not only nugget growth curve but also surface temperature of steel sheet and electrode for three sheet welding with high tension steel. The solution convergence is discussed for the iterative partitioned coupled algorithm and the conventional coupled algorithm. Since the coupled effect is strong for between electric current and thermal conduction, the choice of the coupled algorithm is important for the resistance spot welding analysis. Effect of elasto-plastic contact deformation, change of electric current distribution and thermal conduction on resistance spot welding are discussed from the viewpoint of coupled effect. The coupled model with ability to simulate the chain of coupled effect is required to improve the analysis reliability. The importance of temperature dependency of material property, electrical contact resistance, thermal contact resistance and latent heat effect are also discussed.

Study on Section Temperature Field of Concrete-Filled Double Steel Tubular Columns under Fire

Finite element model was built in order to study the section temperature field of concrete-filled double steel tubular columns through the software of ANSYS. Moisture of concrete and thermal contact resistance were considered in the model. Based on the Eurocode 2, specific heat of concrete was modified in order to consider the effect of moisture. Contact elements were created in the interface between steel tube and concrete in order to consider the effect of thermal contact resistance. The effects of diameter of steel tube and type of aggregate to section temperature field were studied. Distribution of section temperature field is given on the concrete-filled double steel tubular columns, which provides the basis for the analysis of fire resistance capability.

Comparison of experimental and simulated effective thermal conductivity of polymer matrix filled with metallic spheres: Thermal contact resistance and particle size effect

In this paper, we present a numerical and experimental study of a composite material with conducting spheres embedded in a polymer matrix. Our main objective is to study how the particle size and thermal contact affect the overall thermal properties of composites. In the numerical study, finite elements method is used to model heat transfer and to calculate the effective thermal conductivity. A periodical method was used to measure simultaneously thermal conductivity and diffusivity of the composite consisting of an epoxy resin matrix filled with brass spheres of different sizes. A comparison between the numerically calculated, measured and analytical thermal conductivity values for various samples is performed and the significance of the findings is discussed in the paper.

A New Guarded Hot Plate Designed for Thermal-Conductivity Measurements at High Temperature

The Laboratoire National de Metrologie et d’Essais has developed a new guarded hot-plate apparatus operating from $$23\,^{\circ }\hbox {C}$$ to $$800\,^{\circ }\hbox {C}$$ in the thermal-conductivity range from $$0.2\,\hbox {W}{\cdot }\hbox {m}^{-1}{\cdot }\hbox {K}^{-1}$$ to $$5\,\hbox {W}{\cdot }\hbox {m}^{-1}{\cdot }\hbox {K}^{-1}$$ . This facility has been specifically designed for measuring medium thermal-conductivity materials at high temperature on square specimens (100 mm side), which are easier to machine than circular ones. The hot plate and cold plates are similar with a metering section independent from the guard ring. The specimens are laterally isolated by an air gap of 4 mm width and can be instrumented by temperature sensors in order to reduce effects of thermal contact resistances between the specimens and the heating plates. Measurements have been performed on certified reference materials and on “calibrated” materials. Relative deviations between thermal conductivities measured and reference values are less than 5 % in the operating range.

Thermal Analysis of High-Current DC Disconnector Used in ITER Poloidal Field Converter

This paper presents the thermal analysis of a high-current dc disconnector which will be used in ITER poloidal field converter. The analysis is based on the finite element method, and thermal-electric module in ANSYS Workbench is adopted. An analysis model involving the effect of contact resistance is first built and then a thermal simulation is performed under the nominal working condition. In addition, the temperature rise test of the dc disconnector prototype has been done to verify the analysis result. The results from the simulation and the prototype test are consistent with each other very well. Proved by the test result, the analysis method presented in this paper is of valuable reference for the structure design of high-current dc disconnectors.

Experimental investigation of high temperature thermal contact resistance between high thermal conductivity C/C material and Inconel 600

Abstract Thermal contact resistance at the assembly interface plays an important role in high temperature structure design and safety assessment. Thermal contact resistance between high thermal conductivity C/C material and superalloy Inconel 600 was experimentally investigated in the present paper. They are widely used in thermal protection structures of heat-pipe-cooled leading edges to enhance interface heat transfer. Results showed that thermal contact resistance between the two materials is about 5 × 10−5 m2 K/W, and it is necessary to take into account the effect of the thermal contact resistance in high thermal conductivity C/C material related thermal structure design.

Thermo-Electric Modeling of Nanotube-Based Environmental Sensors

Free-standing electrically conductive nanotube and nanobridge structures offer a simple, small-scale, low-power option for pressure and temperature sensing. To sense pressure, a constant voltage is applied across the bridge. At small scales, the heat transfer coefficient is pressure-dependent. The change in the heat transfer coefficients results in the circuit operating at higher temperatures, with different resistances, at low pressures. This in turn will lead to a change in the electrical resistivity of the system. If the system is held at constant voltage, this can be measured as a change in the current in such systems, representing a simple alternative to existing Pirani gauges. The current work simulates the Joule heating, conduction and convection heat transfer of a 5 μm long suspended single-wall carbon-nanotube, incorporating temperature-sensitive material properties. The simulation allows prediction of the thermo-electrical response of the systems. The results agree with the trends observed in existing devices. Additional results look at the effects of system length, temperature, and contact resistances between the substrate and the device.

Thermal characteristic analysis of high-speed motorized spindle system based on thermal contact resistance and thermal-conduction resistance

In view of thermal resistance problem of the motorized spindle system, this paper proposes a thermal resistance network model of spindle-bearing-bearing pedestal based on the fractal and Hertz contact theory. According to this model and Kirchhoff’s law, the heat balance equations for thermal nodes are established and solved with Gauss-Seidel iterative method to gain temperature values of the main thermal nodes. In order to accurately understand thermal characteristics of the motorized spindle system, the effect of thermal contact resistance and thermal-conduction resistance is taken into consideration. Thermal simulation analysis is carried out on the motorized spindle system. On a precision horizontal machining center, the temperature rise of motorized spindle parts is implemented under different rotational speeds with LMS data acquisition system. It is shown that temperature values based on thermal resistance network model agree well with those of simulation analysis and experimental results. What is more, the whole thermal deformations of the main components of the motorized spindle system are analyzed.

Effect of atomic layer deposition temperature on the performance of top-down ZnO nanowire transistors.

This paper studies the effect of atomic layer deposition (ALD) temperature on the performance of top-down ZnO nanowire transistors. Electrical characteristics are presented for 10-μm ZnO nanowire field-effect transistors (FETs) and for deposition temperatures in the range 120°C to 210°C. Well-behaved transistor output characteristics are obtained for all deposition temperatures. It is shown that the maximum field-effect mobility occurs for an ALD temperature of 190°C. This maximum field-effect mobility corresponds with a maximum Hall effect bulk mobility and with a ZnO film that is stoichiometric. The optimized transistors have a field-effect mobility of 10 cm2/V.s, which is approximately ten times higher than can typically be achieved in thin-film amorphous silicon transistors. Furthermore, simulations indicate that the drain current and field-effect mobility extraction are limited by the contact resistance. When the effects of contact resistance are de-embedded, a field-effect mobility of 129 cm2/V.s is obtained. This excellent result demonstrates the promise of top-down ZnO nanowire technology for a wide variety of applications such as high-performance thin-film electronics, flexible electronics, and biosensing.

An explicit analytical model for rapid computation of temperature field in a three-dimensional integrated circuit (3D IC)

3D integrated circuits (3-D ICs) technology is a promising approach for next-generation semiconductor microelectronics. A 3D IC is formed by vertical interconnection of multiple substrates containing active devices which offer reduced die footprint and interconnect length. Thermal management of a multi die stack is a significant research challenge, for which rapid temperature computation in a 3D IC is desirable. This manuscript presents a non-iterative heat transfer model for predicting the three-dimensional temperature field in a multi-die 3D IC. The non-iterative model is much faster and accurate in comparison to finite element simulation and recently presented iterative models for temperature computation. The analytical model is used to compute the temperature field of a 3D IC with a large number of die. The model is also used to examine the effect of various parameters on the computed temperature field. In particular, the effect of thermal contact resistance is presented. The model and results presented in this manuscript are expected be useful in rapid computation and effective thermal design of 3D ICs.