Simulation and application of temperature field of carbon fabric wet clutch during engagement based on finite element analysis

The temperature plays a significant role in the tribology properties and failure of friction materials during engagement of wet clutch. In order to obtain the temperature field of carbon fabric wet clutch, the thermal model was developed and the finite element analysis was conducted with the heat flux, convective and conductive heat-transfer taken into account. The predicted temperatures of thermometer hole were compared with experimental values. The effects of the thermal parameters on the temperatures of engagement and the damage of carbon fabric composites were investigated. Results show the thermal is evaluated as effective and can well predict the temperature field. The lower skeletal density, lower specific heat capacity and higher thermal conductivity are indispensable for the purpose of lowering the temperature of engagement. The highest temperature appears at R = 0.0509 m, where the damage of friction lining easily occurs.     

MULTIPLE ENGAGEMENT WET CLUTCH HEAT TRANSFER MODEL

To optimize the thermal performance of transmission wet clutches during multiple engagements, a general thermal numerical model has been developed. At every cycle, temperatures are computed throughout the clutch materials until a periodic steady state is achieved. One cycle is characterized by (a) an engagement period where the separator plate is contacting the friction lining with heat being generated while some cooling is provided by the oil passing through friction material grooves; (b) a locked stage of separator plate and friction lining contact during which the heat generation is zero while oil cooling through the grooves continues; and (c) a cooling period with the separator plate completely disengaged from the friction lining while the oil cools both surfaces. Temperatures are calculated from the transient numerical solution of the heat conduction equation in two dimensions. The finite difference technique based on an implicit numerical scheme is employed. This approach is verified by comparison with a known solution as well as experimental data, and a sample run is presented for conditions representative of an actual clutch assembly.     

Thermal Stresses and Distortion Developed in Mild Steel DH36 Friction Stir-Welded Plates: An Experimental and Numerical Assessment

Welding processes involve localized heating which in turn give rise to thermal stresses and distortion. Friction stir welding (FSW) is a solid state joining process where temperatures below melting are experienced. Nonetheless, some degree of thermal heating and consequently thermal stresses develop at the joint. This study aims to quantify the stresses developed in friction stir welding of mild steel DH36 plates, through an experimental and numerical investigation. The temperatures and transient strains developed during FSW, are experimentally measured and used to validate thermo-elastoplastic numerical models. These models are used to investigate the evolution of thermal stresses and distortion for different welding parameters.     

Going below the wet-bulb temperature by indirect evaporative cooling: Analysis using a modified ε-NTU method

The objective of this paper is to study a method to achieve sub-wet bulb temperature by indirect evaporative cooling of air (without using a vapor compression machine). For this purpose, an analytical model is developed based on the effectiveness-NTU method (ε-NTU). The main idea for achieving a sub-wet bulb temperature by indirect evaporative cooling of air is by indirectly pre-cooling the working air before it enters the wet passage. It is shown that a modified analytical model for indirect evaporative coolers could be based on the ε-NTU method for sensible heat exchangers when proper adjustments are made by redefining the potential gradients, transfer coefficient, heat capacity rate parameters and assuming a linear saturation temperature-enthalpy relation of air. This modified model is used to find the performance of a regenerative indirect evaporative cooler. The model results show very good agreement with results from experimental measurements and a numerical model.     

Temperature in the railway disc brake at a repetitive short-term mode of braking

The finite element (FE) model to determine the transient temperature field in the ventilated disc brake of the traction diesel multiple unit (DMU) has been proposed. The advantage of the developed numerical model is the representation of mutual motion of the stationary pad and the rotating disc, by a heat source of arbitrary shape moving over the stationary disc. Computations were carried out for the pad and the disc separately introducing the heat partition ratio. Both the single and the multiple modes of braking were examined. The calculated distributions in contact temperature were compared with the corresponding results obtained from analytical solutions of the boundary-value thermal problem of friction, and with experimental data determined by the method of thermocouples. It was demonstrated that the calculated mean temperature on the friction surfaces of the brake components and the bulk temperature of the disc during multiple brake application agree well with the corresponding results, obtained by methods mentioned above.     

Temperature distribution during multipass welding of plates

Welding is one of the most important material-joining processes widely used in industry. Low carbon steel plates and AISI type 304 stainless steel plates with 6, 8 and 12 mm thicknesses are widely used in the fabrication of pressure vessels and other components. These plates are mostly joined together by multipass welding methods. The temperature distribution that occurs during multipass welding affects the material microstructure, hardness, mechanical properties and the residual stresses that will be present in the welded material. Very limited experimental data regarding temperature distribution during multipass welding of plates is available in the literature. Experimental work was carried out to find out the temperature distribution during multipass welding of the above plates. The temperature distribution curves obtained during the experiments are presented. Average maximum temperature rise during each pass of welding is calculated and plotted against the distance from the weld pad centre line. From these plots, the maximum temperature rise expected in the base plate region during any pass of welding operation can be estimated.     

THE DYNAMIC BEHAVIOR OF A BAYONET-TYPE THERMAL DIODE

The time-dependent heat transfer and temperature variation of a bayonet-type thermal diode are theoretically investigated. A one-dimensional analytical model is developed to predict the dynamic behavior of the diode during heating, and a lumped-system approximation is employed for the cooling phase. Results of the analytical model and FLUENT are compared with experimental data of a bayonet thermal diode tested in Utah. Measured solar flux, ambient and room temperatures for a 24-hour period are used as the input data for the analytical model and the numerical calculation. The diode temperature variations predicted by the analytical model and FLUENT are in good agreement with experimental data. The simple analytical model is therefore capable of predicting the diode performance under real weather conditions.     

Thermal transport analysis in parallel-plate channel filled with open-celled metallic foams

Forced convective heat transfer in highly porous, open-celled metallic foams sandwiched between two infinite parallel plates is analytically modeled using the Brinkman-Darcy and two-equation models. With uniform heat flux, closed-form solutions for fully developed flow and heat transfer are obtained. Nusselt number with explicit expression is derived and the analytical results are verified by existing experimental data. To examine the effect of axial heat conduction neglected in the analytical modeling, numerical simulations, which are verified by the analytical solution, are performed. A modified fin analysis method with improved predicting accuracy compared with the conventional fin analysis method by introducing equivalent foam temperature is also put forward. The predictions obtained with the analytical model, the numerical simulation and the modified fin analysis method are compared with each other, and their pros and cons are discussed. Finally, a systematic parametric study is conducted on heat transfer in parallel-plate channels filled with metallic foams, with useful suggestions for practical designs obtained.     

Modelling of heat transfer between two rollers in dry friction

An analysis of heat transfer between two rollers in dry friction is presented in this paper. The contact is peripheral and is assumed to be imperfect. The heat transfer at the interface is modelled by a thermal contact resistance. The heat flux is generated by dry friction at the interface. The two rollers are cooled by convection. A numerical model has been developed to determine the steady state temperature in rollers. Taking into account the transport phenomenon due to motion, the mesh is correlated with the velocity. The accuracy of the mesh is validated by comparison with an available analytical solution developed for a single roller in rotation. The thermal behaviour is analysed with respect to: (i) the velocity, (ii) the heat convection coefficient, and (iii) the thermal contact resistance. The evolutions of the temperature and the partition coefficient of frictional heat are presented and discussed.     

Numerical modeling and experimental investigation of a prismatic battery subjected to water cooling

In this paper, a numerical model using ANSYS Fluent for a minichannel cold plate is developed for water-cooled LiFePO₄ battery. The temperature and velocity distributions are investigated using experimental and computational approach at different C-rates and boundary conditions (BCs). In this regard, a battery thermal management system (BTMS) with water cooling is designed and developed for a pouch-type LiFePO₄ battery using dual cold plates placed one on top and the other at the bottom of a battery. For these tasks, the battery is discharged at high discharge rates of 3C (60?A) and 4C (80?A) and with various BCs of 5°C, 15°C, and 25°C with water cooling in order to provide quantitative data regarding the thermal behavior of lithium-ion batteries. Computationally, a high-fidelity computational fluid dynamics (CFD) model was also developed for a minichannel cold plate, and the simulated data are then validated with the experimental data for temperature profiles. The present results show that increased discharge rates (between 3C and 4C) and increased operating temperature or bath temperature (between 5°C, 15°C, and 25°C) result in increased temperature at cold plates as experimentally measured. Furthermore, the sensors nearest the electrodes (anode and cathode) measured the higher temperatures than the sensors located at the center of the battery surface.     

Stress and plastic deformation of MEA in fuel cells: Stresses generated during cell assembly

A linear elastic–plastic 2D model of fuel cell with hardening is developed for analysis of mechanical stresses in MEA arising in cell assembly procedure. The model includes the main components of real fuel cell (membrane, gas diffusion layers, graphite plates, and seal joints) and clamping elements (steel plates, bolts, nuts). The stress and plastic deformation in MEA are simulated with ABAQUS code taking into account the realistic clamping conditions. The stress distributions are obtained on the local and the global scales. The first one corresponds to the single tooth/channel structure. The global scale deals with features of the entire cell (the seal joint and the bolts). Experimental measurements of the residual membrane deformations have been provided at different bolts torques. The experimental data are in a good agreement with numerical predictions concerning the beginning of the plastic deformation.     

Estimation of the equivalent perfusion rate of Pennes model in an experimental bionic tissue without blood flow

This study designs an experiment to investigate the equivalent perfusion rate of Pennes model when the bionic tissue has no blood feeding. This experimental model is constructed by stainless steel plates to be a hollow cube, and inside filled in with agar gel as the bionic tissue. A heating plate on the top of agar gel cube gives a certain heat generation into the bionic tissue, and three thermocouples at different positions measure the transient temperature during the experiment. On the other hand, this study uses a software package to simulate the tissue temperature using the Pennes model based on the experimental parameters. Moreover, an algorithm applying the conjugated gradient method can find the equivalent perfusion rate in Pennes model by the iterating comparison between the numerical and experimental temperatures. The results show that the equivalent parameters found by this algorithm conform to the expected values, and the predicting temperatures calculated by the Pennes model with the theoretical perfusion rate also agree with the experimental data. This result indicates that not only the experiment is accurate, but also the numerical method for finding the equivalent parameters is reliable. This accurate and reliable experimental and numerical method will be applied to future research for finding the equivalent perfusion rate in Pennes model and equivalent heat transfer coefficient in porous model when the tissue has blood flow.     

Numerical model for the performance prediction of a PEM fuel cell. Model results and experimental validation

This work presents a Computational Fluid Dynamics (CFD) model developed for a 50 cm² fuel cell with parallel and serpentine flow field bipolar plates, and its validation against experimental measurements. The numerical CFD model was developed using the commercial ANSYS FLUENT software, and the results obtained were compared with the experimental results in order to perform a model validation. A single parameter, namely the reference exchange current density, was fitted to calibrate the model results. All other model parameters were determined from technical data sheets, literature survey, or experimental measurements. A discussion on different validation issues and model parameters is provided. The results of the numerical model show a good agreement with the experimental measurements for the different bipolar plates and range of operating conditions analysed. However, inaccuracies in the results in the mass-transport polarization region were observed, presumably when liquid water in the channels produces a blockage effect that cannot be modelled with the multiphase flow model currently implemented.     

Analysis of the temperature distribution in a guarded hot plate apparatus for measuring thermal conductivity

A guarded hot plate apparatus (GHPA) is used to measure the thermal conductivity of insulating materials. This apparatus uses a circular heat source. It was studied the applications of such kind of heat sources. The particular problem for which the solution is developed here concerns with the use of a heater embedded in a central plate and guard ring to generate a heat flux. An elegant closed form analytical solution was obtained for this problem. The Green’s function formulation was used to compute the distribution of temperatures in the central plate and the guard. The analytic results were compared with measurements made on aluminum plates and it was found that they are in good agreement with experimental data with a standard deviation of 3%. These results can be used for obtaining the average temperature in the plates, which are used as the representative temperature. Likewise, the position of the main temperature zone was determined; this position is the one where the thermocouples should be placed on the plates of GHPA.     

Analysis of the thermal buckling of annular disks in clutches under the condition of radial temperature gradient

The buckling deformation model of annular disks subjected to thermal stresses caused by a radial temperature gradient is established, and the leading thermal stresses for buckling are studied. Multidisk clutch sliding experiments were designed to investigate the influence of the radial temperature gradient on the buckling of separator disks in a multidisk clutch. A separator disk with three temperature measurement holes was used to study the process of buckling by recording the output torque and the change in radial temperature. The theoretical results are verified by multidisk clutch sliding experiments. These analyses show that as the temperature gradient increases, the thermal stresses generated by the radial temperature gradient begin to influence the buckling deformation of the friction components. If the friction components are thinner than the critical thickness h_cr, the circumferential thermal stresses play a leading role in the buckling deformation. Conversely, the buckling deformation caused by the radial thermal stress will play a leading role.     

Vaporization of a liquid by direct contact in another immiscible liquid Part I: vaporization of a single droplet Part II: vaporization of rising multidroplets

The present work is an experimental and theoretical study of the vaporization by direct contact of refrigerant R113 and n-pentane dispersed into a column of water flowing countercurrently. The vaporization of a single droplet in a stagnant liquid medium, and the evaporation of a multidroplet flowing system are studied. A formalism has been developed to determine the effective exchange surface for the bubble-droplet during its rise in an immiscible liquid. The numerical results are in good agreement with the experiments. The mechanical equilibrium of a bubble-droplet was studied when considering only the surface tension forces. The results obtained in the precedent analysis about the liquid-liquid area estimation were explained. Experiments were performed to investigate the influence of the different parameters on the behaviour of the direct contact vapour generator. A dimensional analysis based on characteristic transfer times was done. From this point of view correlations were established for determining the volumetric heat transfer coefficient and the exchange efficiency. For a multidroplet flowing system an analytical model was proposed giving the evolution of the void fraction and the temperature of each fluid along the exchange column. Experimental and numerical results were compared.     

Experimental Study and Thermal Analysis on the Buckling of Friction Components in Multi-Disc Clutch

A full-scale multi-disc clutch test bench was set up and some sliding experiments were conducted to investigate the temperature evolution processes in low and high lubrication regimes. Friction discs with single friction lining were used and arranged back-to-back in order to preserve possible evidences of buckling. Temperatures were measured with thermocouples from four different radii on the mid-plane of the separator disc. Two different kinds of temperature variation processes with obvious critical points of cone shape buckling were obtained. These temperatures can be divided into three effective stages that represent different deformation status of the discs in these experiments. The temperature fields in the contacting separator disc and friction disc were studied through a transient heat conduction model, and the results show that the temperatures measured by the thermocouples from the separator disc can represent the average temperatures in both of the separator disc and friction disc for a long sliding time. By comparing the computational critical moments of the friction components with the experimental results, the capability of the curved beam model for predicting the critical moments of cone buckling was validated.     

Comparison of a small-scale 3D PCM thermal control model with a validated 2D PCM thermal control model

A three-dimensional (3D) numerical model was developed to simulate the use of a phase change material linked to a photovoltaic (PV) system to control the temperature rise of the PV cells. The model can be used to predict temperatures, velocity fields and vortex formation within the system. The 3D predictions have been compared with those from a previously developed experimental validated two-dimensional (2D) finite-volume heat transfer model conjugated hydro-dynamically to solve the Navier–Stokes and energy equations. It was found that for the systems simulated with appropriate boundary conditions, the 2D model predictions compare well with those of the 3D model. The 3D model was used to predict the temperature distributions when the heat transfer to the phase change material was enhanced by high thermal conductivity pin fins.     

连续螺旋折流板管壳式换热器动态特性研究及预测

建立了可进行壳管式换热器动态特性试验研究系统,通过试验研究的方法对水-油为换热工质的连续螺旋折流板管壳式换热器动态特性进行了试验研究,进口流量扰动为等百分比流量特性,研究了4种流量扰动方式下水和油出口温度的动态响应。同时研究了在一定Re数下,不同的流体扰动量对换热器进出口温升的影响,得到了换热器进出口温升与流体扰动量之间的关联式。实验表明,液液换热系统温度的动态响应时间比较长,研究发现在正负的流量扰动下,换热器进出口温度变化呈现线性变化,进出口温升在正负流量扰动下其变化曲线具有对称特征。分别建立了有限差分数值预测模型及人工神经网络模型对换热器油侧的出口温度进行了动态预测,预测结果与试验值符合良好,人工神经网络的预测结果要好于数值模拟预测,其偏差绝对值在1.3%以内,表明人工神经网络在进行复杂的系统辨识时具有一定的参考及应用价值。     

Finite Element Analysis of Thermoelastic Instability in Intermittent Sliding Contact

A finite element model is developed for the frictionally excited thermoelastic instability problem in intermittent sliding contact with finite geometries and realistic friction materials. The existing analytical solutions are used to validate the method in several limiting cases. It is concluded that some caution must be taken for the commonly used strategy of assuming time-averaged frictional heat generation for intermittent contact. The predictions made by the half-plane analytical solution that assumes thermally nonconductive and rigid frictional surface considerably overestimate the dimensionless critical speeds of realistic brake or clutch systems. Longer wavelength perturbations become unstable at a dimensionless sliding speed approaching zero, as opposed to the converged value of unity in the half-plane solution. Averaging the heat input over the entire circumference is appropriate only when the period of frictional contact is longer than that of separation. These results merit the use of the finite element method in more general applications involving intermittent contact.