Contact Heat Transfer Research Articles

The contact heat transfer between the plane-parallel strip and the semi-infinite foundation

The analytical solution of a boundary-value problem of heat conduction for tribosystem, consisting of a plane-parallel strip sliding with a constant velocity on a surface of semi-infinite foundation, is obtained. It is assumed that the thermal contact between strip and foundation is imperfect. The asymptotic formulae of temperature for small and large time values were found, too. The influence of the contact heat transfer on temperature distribution in materials of frictional pair such as FMK-11 metal–ceramic strip–ChNMKh cast iron foundation, was investigated.

Performance and effective kinetic models of methane steam reforming over Ni/YSZ anode of planar SOFC

Under mass/heat transfer and species diffusion limitations, the detailed thermodynamic investigations and experimental measurements were carried out to study and evaluate the performance of methane steam reforming and to develop its effective kinetic models over Ni/YSZ anode of the planar solid oxide fuel cell developed by Central Research Institute of Electric Power Industry (CRIEPI) of Japan. Based on the kinetic models of methane steam reforming developed by Xu and Froment, the effective kinetic models were developed. Combining the experiment data with the iteration calculation, the effective factor (Ce) is found to be 5.0 × 10−4. Using these effective kinetic models, the detailed distributions of temperature, species, methane conversion, and carbon formation and gasification activity are presented under wide range of operating conditions. The results show that the local temperature in the reactor and the methane conversion are sensitive to the operating parameters. The region of the lowest local temperature and the most possible region of carbon formation are at the front of the porous anode sample. Due to the limitation of contact time, heat transfer and species diffusion, the methane conversion appreciably decreases with an increase of S/C ratio.

Two-dimensional Temperature Distribution of Strip in Preheating Furnace of Continuous Annealing Line

Two-dimensional temperature distributions of the steel strip are studied by the energy balance method with the aid of finite-element analysis. The space of the preheating furnace is divided into several enclosures in which the mechanisms of heat convection, heat radiation, and contact heat transfer are taken into account. The longitudinal and transverse temperature distributions of the strip are finally iteratively calculated by using the method of energy balance. The strip exhibits a significant temperature rise after contact with the rolls and shows a nonuniform temperature distribution along the width direction with smaller magnitude at two sides.

B134 直接接触蓄熱装置の熱出力向上(固液相変化を伴う伝熱現象II)

There is growing interest in the newly developed technology to store heat energy at the temperature of 200 degrees Celsius or lower from industrial plants, which has until now been dissipated. And also, it is important to utilize such waste effectively in order to save energy. A new thermal energy storage/retrieval system, which employs erithritol as heat storage medium and direct contact heat transfer technology as the method for the heat exchange between the heat medium and heat storage material, has been developed. In this system, it is important to evaluate and prove a heat output from the heat storage device. For instance, the performance to maintain heat output high will lead to good economical efficiency. In this study, in order to increase the heat output, tow types of the heat storage device, conventional and improvement type, were manufactured and compared the performance with each other. As a result, improvement type of device which include metal separate plate in the thermal storage media layer have a advantage of increasing heat output.

Analyses of ice slurry formation using direct contact heat transfer

In the present study, ice slurry is produced by direct contact heat transfer between water and a coolant, Fluroinert FC 84. An analytical model has been developed to predict the growth of ice around the injected supercooled coolant droplets, which involves phase change and heat transfer between layers. During the journey of the coolant droplets through the ice generator, detachment of ice layer formed on the droplets occurs. Equations have been development to describe the process of detachment. Experiments were performed to validate the model developed to predict the ice generation. Parametric studies were then carried out on ice growth rate for different variables, such as droplet diameters and initial liquid temperatures. Both droplet diameters and initial liquid temperatures play an important role in the ice formation around the supercooled liquid surface. Ice growth rate increases with the increase of the droplet diameter, while the growth rate decreases with the increase of the initial temperature of the liquid droplet. For an ice slurry system, it is found that the predicted values of ice slurry generation are in good agreement with the experimental findings.

Heat and Mass Transfer in an Indirect Contact Cooling Tower: CFD Simulation and Experiment

The present work is focused on the computational analysis of heat and mass transfer in an indirect contact cooling tower. The main objectives of the study are to contribute to the understanding of heat and mass transfer mechanisms involved in the problem and to check the possibility of making use of a commercial computational fluid dynamics (CFD) code for simulating mass and heat transfer phenomena occurring in indirect cooling towers. The CFD model uses as boundary conditions the temperatures of the tubes obtained by a correlation model developed by Mizushina. The available mass transfer correlations for indirect cooling towers are presented and compared with a correlation obtained from CFD simulations. The assumption of analogy between heat and mass transfer is also discussed.

“Vacuum” friction and heat exchange of a nano- and a microparticle with a solid surface

The most general relativistic formulas for the tangential force of the fluctuation-electromagnetic interaction and the rate of thermal heating of a spherical neutral particle moving in vacuum near the surface of a condensed medium are obtained for the first time in dipole approximation. It is shown that the existence of a fluctuation-induced magnetic moment for a conducting particle is responsible for a considerable increase in the vacuum heat-exchange rate as compared to contact and radiative heat transfer (in accordance with the Stefan law). It is noted that the coincidence of the absorption peaks for the particle and the surface in the microwave range can explain the damping forces observed for nanoprobes in the dynamic mode of the atomic force microscope.

Measurement of Heat Transfer for Thermoforming Simulations

Thermoforming is a polymer processing technique in which an extruded sheet is heated to its softening temperature and then deformed through the application of mechanical stretching and/or pressure into a final shape. The stretching operation is often performed by the movement of a mechanical plug, which contacts some areas of the sheet. During contact it is known that conductive heat transfer between the plug and sheet materials is an important factor in determining the process output. Attempts are currently being made to build realistic simulations of the thermoforming process and it is therefore extremely important that these heat transfer effects are included. However, the measurement of thermal contact conductance (TCC) between polymer pairs is extremely difficult in practice and there are no published values in literature. In this study, an axial conductive heat flow test rig has been developed and used to measure the TCC between contacting polymer pairs. Preliminary results between PVC and PTFE have shown that the value of thermal conductance is very small compared to published values for polymer/metal interfaces. Tests have also been carried out on Hytac®-B1X and PP. The TCC values were found to lie between 28.2-34.4 W/m 2 -K for average interface temperature between 45-75 °C. There was a slight increase in TCC with increasing interface temperature up to a temperature of about 70 °C. However, more experiments will be required to ascertain this. Further tests are being carried out to measure the TCC between different polymer pairs, and to assess the effects of variables such as surface roughness and contact pressure. These results will then be used to develop realistic models for contact heat transfer in thermoforming simulations.

Thermal analysis of slurry ice production system using direct contact heat transfer of carbon dioxide and water mixture

This research studies the heat transfer characteristic during ice formation of a direct contact heat transfer between carbon dioxide and water mixture. This research is divided into two parts. For the first part, the low temperature carbon dioxide, between − 15 and − 60 °C, is injected into water initially at 28 °C and exchanges heat directly. The flow rate of carbon dioxide is varied between 0.003 and 0.017 kg/s while the volume of water is between 1 and 3 L. From the experiment, it is found that the effectiveness of the direct contact heat transfer between the carbon dioxide and the water is closed to 100%. Moreover, the lumped model is found to be used for predicting the temperature of water and the mass of ice formation quite well. However, for this technique, the blockage of ice around the injector always occurs. To avoid this problem, slurry ice is considered instead of pure ice. In the second part of this work, the thermal behavior of the slurry ice by direct contact heat transfer technique between carbon dioxide and water mixture is investigated. Compressor oil and Tween 60 are mixed with water for making slurry ice and it is found that the suitable composition is water/oil/Tween 60 at 100/6/1 by volume. Again, the lumped model can be used for predicting the temperature of water mixture and the mass of slurry ice quite well.

High heat load tests on W/Cu mock-ups and evaluation of their application to EAST device

Tungsten has been considered as the primary candidate plasma-facing materials (PFM) for the EAST device. Three actively cooled W/Cu mock-ups with an interlayer made of tungsten–copper alloy (1.5 mm) were designed and manufactured. The tungsten armors, pure sintered tungsten plate (1 mm) and plasma-sprayed tungsten coatings (0.3 and 0.9 mm), were bonded to the interlayer by brazing and depositing respectively. All mock-ups can withstand high heat flux up to 5 MW/m 2 and no obvious failure was found after tests. The thermal performance experiments and microstructure analyses indicated the structure of mock-ups possess good thermal contact and high heat transfer capability. WCu alloy as an interlayer can largely reduce the stress due to the mismatch and improve the reliability. The mock-up with 0.9 mm coating had the highest surface temperature than the other two mock-ups, delaminations of this mock-up were found in the near surface by SEM. The primary results show that pure sintered tungsten brazed to WCu alloy is a possible way, and thick plasma-sprayed coating technique still need to be improved.

Simultaneous removal of CO2, SO2, and NOx from flue gas by liquid phase dehumidification at cryogenic temperatures and low pressure

The current paper presents a new process for postcombustion carbon capture. An historical survey of the cryogenic techniques used in the chemical industry for the removal of acid vapours is given, with particular emphasis on two Ryan—Holmes-based processes. The paper suggests that these two processes have the potential to achieve CO2 separation from flue gas with high second law efficiency. A further variation on these processes is then proposed enabling the simultaneous capture of CO2, SO2, and NO x from flue gas produced in conventional or combined cycle power stations, burning pulverized coal or heavy bunker fuels. The proposed process absorbs these vapours by dehumidification using a cooled liquid absorbent, at low pressure (close to atmospheric) and cryogenic temperatures. A feature of the process is the use of direct contact heat transfer to perform the major cooling and heating operations thus reducing the plant size and cost while improving efficiency. The paper starts with a discussion of the most suitable absorbent for the process; liquid SO2 is suggested and a simplified analysis of an absorption column is conducted using the technique developed by Souders and Brown. This analysis shows that with only four theoretical stages and an acceptable liquid/gas ratio of two, SO2 is able to absorb CO2 and leave a residual concentration of CO2 in the flue gas equivalent to 90 per cent carbon capture. The final section of the paper describes the use of dilute H2SO4 as a precooling stream to reduce the temperature of the flue gas prior to it entering the CO2 scrubbing section. It is proposed to produce the necessary H2SO4 from the constituents of the flue gas using similar reactions to those of the ‘lead-chamber process’. The H2SO4 stream is also used to reheat the flue gas before it is passed to the chimney. It is shown that an important attribute of the H2SO4 stream is its role as a ‘lean-oil’, reducing SO2 emissions from the power station to well below the levels required by future legislation.

Effects of Surface Roughness on Contact Heat Transfer between Contacting Particles

The objective of this work is to establish a constitution equation of the contact heat transfer between colliding particles for the Discrete Element Method (DEM) simulations. Since the thermal resistance model is available to estimate the contact heat transfer, the heat transfer between two particles (spheres) was measured by changing surface roughness. The result of this is that the contact heat transfer increased as surface roughness increased. This tendency is opposite to a general one in the thermal resistance model. This would be caused by the geometric condition of the spherical contact plane. Larger surface roughness yields larger contact area. This effect would be larger than that of increasing thermal resistance. Moreover, we tried to directly observe the surface under contact condition by using a laser microscope in order to examine the surface conditions in detail. The cross-sectional profile of contacting particles was successfully detected. The macroscopic contact area calculated by considering the surface roughness well agreed with the observed one.

Ice Slurry Formation in a Cocurrent Liquid-Liquid Flow

A new technique for ice slurry production was explored. Multiple small water-drops were formed in another immiscible chilled liquid by a single-nozzled atomizer and frozen in the fluidized bed by direct contact heat transfer. Experiments were conducted to investigate the dynamic behaviors of the ice crystal making system. The results demonstrate that the ice crystals could be produced continuously and stably in the vertical bed with the circulating coolant of initial temperature below −5°C. The size distribution of the ice crystals appears non-uniform, but is more similar and more uniform at lower oil flow rate. The mean ice crystal size rests seriously with the jet velocity and the oil flow rate. It decreases with decreasing the oil flow rate, and reaches the maximum at an intermediate jet velocity at about 16.5 m·s −1. The ice crystal size is also closely related to the phenomenon of drop-coalescing, which can be alleviated considerably by reducing the flow rate or lowering the temperature of the carrier oil. However, optimization of liquid-liquid atomization is a more effective approach to produce fine ice crystals of desired size.

Determination of thermal contact resistance from transient temperature measurements

The temperature distribution in combustion engine components is highly influenced by thermal contact resistance. For the prediction and optimisation of the thermal behaviour of modern combustion engines knowledge about the contact heat transfer is crucial. Available correlations to predict the contact resistance are simplifications of the real geometric conditions and only tested for moderate pressures up to 7 MPa. Typical combustion engine applications include contact pressures up to 250 MPa. The experimental approach presented here to derive the thermal contact resistance in terms of contact heat transfer coefficients for high temperature and high pressure conditions is based on transient infrared temperature measurements. Two bodies initially at two different temperatures are brought in contact and the surface temperature histories are recorded with a high-speed infrared camera. The contact heat flux is calculated by solving the related inverse problem. From the contact heat flux and from the measured temperature jump at the interface the contact heat transfer coefficient is calculated. The inverse method used for the calculation of the heat flux is based on the analytical solution for a semi-infinite body and a step response to a Neumann boundary condition. This method provides an algorithm that is used in a sequential manner. The use of “future” temperature data greatly improve the stability of the governing equations and reduce the sensitivity to measurement errors.

Predicting of Temperature Distribution in Direct Contact Heat Transfer

An experimental and theoretical investigation of three phase direct contact heat transfer by evaporation of refrigerant drops in an immiscible liquid has been carried out. Refrigerant Rl2 and R134a were used for the dispersed phase, while water and brine were the immiscible continuous phase. A numerical analysis is presented to predict the temperature distribution throughout the circular test column radially and axially is achieved. Experimental measurements of the temperature distribution have been compared with the numerical results and are discussed .A comparison between the experimental and theoretical results showed acceptable agreement and applicability of the derived equations. Comparison with other related work showed similar behavior.

CFD modeling of large-scale LH2 spills in open environment

In earlier work the three-dimensional time dependent fully compressible CFD code ADREA-HF was applied against large-scale LH2 release experiments in the vicinity of buildings. In the present contribution the ADREA-HF code is applied to simulate large-scale LH2 spill tests in open, unobstructed environment. A series of simulations were performed to investigate on the effects of the source model (jet or pool), the modeling of the earthen sides of the pond around the source and the inclusion of a contact ground heat transfer. The predicted hydrogen concentrations (by vol.) are compared against the experimental at the available sensor locations. In addition the predicted structure of the concentration field is compared against the experimental, which was originally derived from temperature measurements. Modeling the source as a two-phase jet pointing downwards, including the modeling of the earthen sides of the pond as a fence and the contact heat transfer to the ground gave the best agreement with respect to experimental behavior.

Modeling of Transient Thermal Contact Resistance out of Conjugate Gradient Method

AbstractTemperature profile at contacting pairs of any material combination is crucial in many engineering applications. A new experimental approach is suggested to estimate the contact heat transfer coefficient as well as the thermal contact resistance. This method is based on temperature infrared measurements of contact bodies and then solve the inverse problem with conjugate gradient method. Different affecting parameters are studied namely; surface roughness, presence of interlayer, applied pressure and bodies temperature difference. The time dependant heat transfer coefficients resulting from the proposed method need to be validated by a computer model. Close results are shown with slight deviation by the increase of the applied pressure and the temperature difference.

Finite element analysis and experimental confirmation of warm hydroforming process for aluminum alloy

Abstract The hydroformability of an extruded aluminum alloy at elevated temperatures was investigated in this study. To properly analyze the process, it is necessary to account for the variation in the mechanical properties of the aluminum that depend on the forming temperature and the heat conduction during warm hydroforming. Simulations coupling the plastic deformation and temperature distribution in the warm hydroforming process were performed and compared with experimental data. The multi-purpose finite element code DEFORM-2D can handle the calculations, but requires significant computation time if contact heat transfer between the die, the tube, and the pressure medium occurs. Experiments were conducted with a high temperature tribometer (pin-on-disk) allowing the measurement of the friction coefficient for the aluminum alloys at several temperatures. These friction results are applied to the coupled simulation. From the simulations, the optimal process parameters, such as internal pressure and preset temperature on hydroformability, can be found. The comparison of the finite element analysis with the experimental results shows that the hydroformability trends (given by bulge height) and the temperature distribution of the tube specimen agree well with one another. The finite element results also showed that the temperature distribution did not strongly affect the hydroformability of the aluminum tubes.

Effect of thermal contact heat transfer on solidification of Pb–Sn and Pb-free solders

The effect of thermal contact heat transfer on the solidification of spherical droplets of four solder alloys, namely, Sn–37Pb, Sn–9Zn, Sn–0.7Cu and Sn–3.5Ag, was studied using SOLIDCAST simulation package. A significant drop in the arrest time was observed for increase in heat transfer coefficient from 1000 to 2000 W/m 2 K. Effect of contact conductance and thermal diffusivity of solder alloys on arrest time is quantified by the power relation, β = m( ϕ) n where β and ϕ are defined as arrest time and heat transfer parameters, respectively. Experiments were also carried out to investigate the effect of cooling rate on solidification behaviour of the solder alloys used in simulation. The results indicated the significant effect of mould material on interfacial heat flux and metallurgical microstructure.

Direct-Contact Heat Transfer Coefficient for Condensing Vapour Bubble in Stagnant Liquid Pool

Direct-contact heat transfer involves the exchange of heat between two fluids by bringing them into intimate contact with each other. While one of the fluids involved is the continuous phase or the ‘quiescent phase’, the other, which is intimately mixed with the former, is called as the ‘dispersed phase’. The advantage of direct-contact heat transfer is that it generates a very high value of overall heat transfer coefficient resulting in higher heat transfer efficiency. This overall heat transfer coefficient is at its maximum at the instant when the two fluids (phases) make their contact. The value of the heat transfer coefficient decreases rapidly due to the additional heat transfer resistances built up such as the condensate layer and so on. This rapid process has made experimental measurement of the initial heat transfer coefficient illusive. So far there has been only one such analytical expression that has been derived to describe this initial process. The same authors also devised an experimental technique for measuring the direct contact heat transfer coefficient during this initial phase. However, while the experimental technique of the abovementioned authors was adequate, their analytical expression to evaluate the direct-contact heat transfer coefficient was incorrect. In this paper, five mathematical expressions have been presented for estimation of the direct-contact heat transfer coefficient for a condensing vapour bubble. Of these, three have been exclusively derived here and the other two are modifications from the already existing expressions. Comparisons have been made with the available experimental results and the physics revealed by the comparisons are described.