Transient Heat Transfer Analysis Research Articles

Numerical investigation of the mechanical response of semi-rigid base asphalt pavement under traffic load and nonlinear temperature gradient effect

The effectiveness of any pavement design based on the mechanistic procedure depends on the accuracy of the mechanical parameters used such as stresses and strains. Hence, an effective and realistic prediction of these parameters when traffic and environmental data are provided is a step towards the future design of more sustainable pavement structures. This study investigated the distribution of the mechanical parameters in three new semi-rigid pavement structures with typical functional and structural requirements, specially designed to withstand various distresses of semi-rigid pavements. The response of these pavements to the combined effect of the nonlinear thermal gradient and moving axle load was examined by means of an advanced 3D pavement FE modeling. The model integrated mechanical and thermophysical properties of each pavement material, studied the transient dynamic effect of wheels load, and employed transient heat transfer and implicit dynamic analysis. Field measurements of these experimental pavement structures at the RIOH-Track test site in Beijing, China, as well as relative climatic data were used to verify and validate the accuracy of the developed model. Comparison of the numerical and experimental results indicated that the developed model predicted accurately the characteristic non-linear distribution of temperature along with the pavement depth and the pavement response to the combined effect of the nonlinear temperature gradient and traffic load. The influence of three main factors affecting the distribution of the mechanical parameters, namely; the bonding conditions between the pavement’s layers, the vehicle speed and the axle load amplitude were evaluated. In addition, fatigue analysis of the asphalt layers and the semi-rigid layers was performed to evaluate the theoretical service life of each pavement structure. The findings of this study underscored that the non-linear temperature gradient, despite being often neglected in mechanistic modeling, is a key parameter for accurate prediction of the distribution of stresses and strains in pavement system. Moreover, the results indicate that the lowest traffic speed and the extra weight extension of the truck axle have an adverse effect on mechanical parameters. Furthermore, the improvement of contact conditions at the interface results in good performance. Overall, the conclusions obtained in this study provides a reference for the design of semi-rigid pavement structures.

Performance improvement of integrated thermal protection system using shaped-stabilized composite phase change material

In this study, an innovative integrated thermal protection system (ITPS) concept that incorporates shaped-stabilized composite phase change material into corrugated core ITPS structure is proposed to strengthen the thermal protection performance. First, the heat transfer characteristics were investigated through both the heat insulation experiment and numerical transient heat transfer analysis. Then, the load bearing capacity is researched through the sequential thermal-mechanical coupling method. Finally, based on the established numerical analysis models, a global optimization procedure was established to verify the advantages of the proposed structure under the actual reentry conditions. Experimental and simulation results show agreement with each other on the thermal insulation ability. And a reduction of 18.46% in maximum bottom face sheet temperature was observed in the experiments when compared with the traditional ITPS. Moreover, the optimization results showed that the proposed ITPS achieved a reduction of 14.32% in weight and a decrease of 46.09% in thickness with respect to the traditional ITPS, which thereby contributes to the lightweight and high structural efficiency of the vehicle design.

Transient heat transfer analysis in packed beds: Entropy generation model and multi-objective optimization

Due to the important role of the unsteady heat transfer process of packed beds in industrial production, the construction of the transient heat transfer model is of great significance for the operation and optimization. The present study performs a transient thermal analysis of packed bed, in which the convective heat transfer and conductive thermal resistance within the particles are considered simultaneously. A mathematical model is established of the total entropy generations (0−t) contributed by viscous dissipation and heat transfer; the influence of particle diameter, air flow rate, and pressure drop, is then investigated. Because of the time cost, these results present some different trends from the steady-state process. Furthermore, for a laboratory heat transfer system, with the aid of the genetic algorithm we adopt a multi-objective genetic algorithm model and modified expressions of the entropy generations are set as objective functions. Finally, optimal operational and structural parameters are obtained for different fan power settings. When the fan power is 300 W, the optimal particle diameter and inlet wind speed are 14 mm and 2.4 m/s, respectively. The results also suggest that the time cost is reduced with increasing fan power consumption.

Effect of loss in concrete cover during fire on the predicted temperature distribution

The paper presents a numerical study conducted using in-house code for 2D transient heat-transfer analysis. The code solves the governing differential equations for transient heat-transfer using finite difference scheme and iterative solver. The code takes the information related to loss of concrete cover as an input and update the thermal boundary conditions (moving BCs). The validation of the code against experimental results available in literature has been presented. The paper also presents a parametric study to investigate the effect of corner spalling on predicted reinforcement temperatures for a beam. The parameters investigated includes: depth of lost concrete cover, time at which the cover is lost and fire exposure (ISO-834 and design fire). As expected, higher reinforcement temperatures were observed for higher loss of corner concrete corner cover but the effect of smaller cover loss (28% diagonal cover) was negligible. It was also observed that for longer fire exposures, depth of lost cover is more important than the time at which it is lost. In case of design fire exposure, it was observed that; large cover lost during heating-phase results in a higher temperature, which still occur during the cooling-phase but earlier as compared to the reference case.

Unsteady CHT analysis of a solid state, sensible heat storage for PHES system

Purpose The aim of this study is to identify key factors limiting efficiency of pumped heat energy storage systems and determine some general features of transient behavior of solid state, sensible heat storages. Moreover, it aimed at establishing a feasible approach to transient conjugate heat transfer (CHT) analyses for such applications. Design/methodology/approach A zero-dimensional analytical model is used to determine the system efficiency sensitivity to efficiency of its components. Analysis of argon gas flow in an exemplary configuration of layered bed thermal energy storage is presented. The analysis incorporates a unsteady reynolds averaged navier stokes model with conjugate heat transfer between gas and solid storage core. Findings It is established that exergetic efficiency of the heat storage is one of the key factors for the system’s overall performance. Three full cycles of storage charging and discharging having 17 h physical time in total are simulated, with calculation of exergetic efficiency for each of the cycles. From standpoint of the system efficiency, it is concluded that the presented heat storage kind has limited exergetic efficiency because of severe temperature drop at the solid–fluid interface in comparison to granular kind of heat storage devices. From the methodological standpoint, it is concluded that calculating the exergetic efficiency of the heat storage by direct computational fluid dynamics (CFD) analysis requires significant amount of walltime and computational resources. Originality/value The paper presents unconventional approach to using standard CFD tools by exploiting numerical diffusion to numerically suppress high-frequency solution oscillations. This strategy grants that the analysis, otherwise requiring impractically long computation walltime, is completed within a practical time.

Fluid-structure interaction analysis of transient convection heat transfer in a cavity containing inner solid cylinder and flexible right wall

PurposeThis paper aims to investigate the fluid structure interaction analysis of conjugate natural convection in a square containing internal solid cylinder and flexible right wall.Design/methodology/approachThe right wall of the cavity is flexible, which can be deformed due to the interaction with the natural convection flow in the cavity. The top and bottom walls of the cavity are insulated while the right wall is cold and the left wall is partially heated. The governing equations for heat, flow and elastic wall, as well as the grid deformation are written in Arbitrary Lagrangian–Eulerian formulation. The governing equations along with their boundary conditions are solved using the finite element method.FindingsThe results of the present study show that the presence of the solid cylinder strongly affects the transient solution at the initial times. The natural convection flow changes the shape of the flexible right wall of the cavity into S shape wall due to the interaction of the flow and the structure. It is found that the increase of the flexibility of the right wall increases the average Nusselt number of the hot wall up to 2 per cent.Originality/valueTo the best of the authors' knowledge, the unsteady natural convection in an enclosure having a flexible wall and inner solid cylinder has never been reported before.

Experimental and numerical analysis of transient heat transfer from inclined tube bundles

This paper investigates the effects of tube arrangement and pitch on the performance of a single row bundle of bare tubes. A transient simulation is conducted to analyze flow and heat transfer characteristics of this problem. Velocity fields obtained from numerical simulation are validated against those obtained using particle image velocimetry in this work. Heat transfer and pressure drop for the flat bundle are found to be in good agreement with available data in the literature. In addition to flat bundles, two cases of inclined bundles, i.e., A and V frames, are investigated. Compared to a flat bundle, while these two cases lead to lower heat transfer rate by about 30% (maximum), the pressure drop of a flat bundle can be higher by about 60%. Finally, a correlation for predicting the drag coefficient as a function of maximum (bundle) velocity is presented.

Effect of heat transfer optimization on brake noise characteristics of automotive disc brake

Heat effect is one of the most important factors affecting the brake noise level. The finite element model for transient heat transfer analysis of disc brake is established based on heat transfer control equation and heat dissipation boundary conditions of dynamic convection. According to the NVH test and modal calculation, the brake noise characteristics are tested and analyzed. Meanwhile, the heat transfer simulation is verified and shows high accuracy. The discrete data for the response surface function are obtained by the Central Composite Design method with the peak temperature and mass as the target variables. The error of regression function is judged by fitting decision coefficient, correcting decision coefficient and root mean square error. By the optimizing mathematical model, the brake disc temperature peak can be greatly reduced and the heat transfer ability is obviously optimized without mass increasing, the time with temperature above 120 °C can be reduced by 46 %. Through the comparison of brake noise level before and after optimization, it can be known that the noise level can be significantly decreased after structural optimization, except the first order resonance frequency. The optimization result has good social and economic value.

Thermal Analysis of Paper Board Packaging with Phase Change Material: A Numerical Study

Phase change materials (PCM) absorb, store, and release thermal energy by changing phase, usually between solid and liquid, to maintain a regulated temperature. Compared with conventional sensible heat storage materials, PCMs can absorb or release large amount of heat without a significant change in temperature until the phase change process is complete. There are many potential applications of PCMs, including energy storage system, electronic/battery cooling, thermal management in buildings, and temperature controlled packaging. This study fundamentally explores the effect of the presence of PCMs on the heat transfer characteristics of packaging wall. The presence of PCM is studied in two different configurations: a layer of PCM embedded in the center of a paper board, and uniformly distributed PCM particles within a paper board. The numerical results presented here are based on a transient conjugate heat transfer analysis with natural convection present on the both sides of the packaging wall. A parametric study is performed on the PCM layer thickness to determine the impact of PCM on isolating the package interior temperature from ambient conditions over an extended time. The numerical results show significant reduction in the transfer of heat from the exterior to the interior of the packaging wall in the presence of PCM. This extends the time for the interior temperature to equalize with the exterior temperature under the operating conditions considered in this study.

Development of efficient distortion prediction numerical method for laser additive manufactured parts

Part distortion is a technical bottleneck in the field of laser solid forming additive manufacturing (AM). Finite element modeling has shown great power in analyzing and predicting thermal distortion during laser AM process. However, as the global size of the manufactured component increases, the conventional numerical method appears limited due to the long computation time. In this paper, the temperature distribution and the evolution of a Ti-6Al-4V thin wall during the AM process were investigated first via the transient heat transfer analysis. “Quasi-steady state” characteristic of the temperature distribution was observed after depositing several layers. Based on this, an efficient equivalent temperature field (ETF) method was developed to predict thermal distortion by extracting the quasi-steady temperature field and applying it as a thermal boundary during mechanical analysis. The developed ETF method was validated by the good agreement in the predicted distortion distribution pattern and magnitude compared with that predicted by the conventional move heat source numerical method. The developed ETF method in this paper significantly saved computation time by above 90% during mechanical analysis. Furthermore, the distortion of laser additive manufactured thin wall with 266 layers was successfully predicted by the ETF method within several hours. The maximum deviation is 29.3% compared with the experimental results. The proposed method provides the possibility to predict distortion for large-scale AM parts, which may have the potential application in engineering.

Efficient numerical analysis of transient heat transfer by Consecutive-Interpolation and Proper Orthogonal Decomposition

The consecutive-interpolation technique has been introduced as a tool enhanced into traditional finite element procedure to provide higher accurate solution. Furthermore, the gradient fields obtained by the proposed approach, namely consecutive-interpolation finite element method (CFEM), are smooth, instead of being discontinuous across nodes as in FEM. In this paper, the technique is applied to analyze transient heat transfer problems. In order increase time efficiency, a model- reduction technique, namely the proper orthogonal decomposition (POD), is employed. The idea is that a given large-size problem is projected into a small-size one which can be solved faster but still maintain the required accuracy. The optimal POD basis for projection is determined by mathematical operations. With the combination of the two novel techniques, i.e. consecutive-interpolation and proper orthogonal decomposition, the advantages of numerical solution obtained by CFEM are expected to be maintained, while computational time can be significantly saved.

A Study on Activation Algorithm of Finite Elements for Three-Dimensional Transient Heat Transfer Analysis of Directed Energy Deposition Process

Heat transfer finite element analysis (FEA) for directed energy deposition (DED) process is crucial to properly estimate the residual stress in the additive manufactured part. The material deposition of the DED process is generally simulated by activation of finite elements. However, the activation algorithm of inactive finite elements is complicated. Besides, existing element activation algorithm is not suitable for highly focused energy source. In order to overcome these discrepancies, an inactive element activation algorithm with two-element cross section has been proposed for simulating a DED process using a high intensity laser heat flux. The nodal temperature during the element activation has been evaluated. The proposed algorithm has been implemented into the heat transfer FEAs for multilayer and planar depositions to investigate the applicability of the proposed algorithm. Finally, the results of FEAs using the proposed algorithm have been compared to those of commercial software SYSWELD.

Transient natural convection heat transfer analyses from a horizontal cylinder

Experiments are conducted to analyze the power-on transient natural convection heat transfer around a horizontal cylinder heated in air. The heat flux ranges from 177 W/m2 to 2426 W/m2 and Rayleigh number from 4.13 × 104 to 4.35 × 104. The effects of transient heat transfer data on different angular position of the thermocouple (0°, 90°, 180°) are reported. The results indicate that the transient heat transfer around the cylinder is strongly affected by the position of thermocouples. The test rig working condition is verified by comparing the steady-state natural convection heat transfer data with those obtained from the literature. It is observed that the transient heat transfer data obtained at 90° and 180° are higher than that of stagnation point (0°). Finally, based on the transient data, correlations are presented to predict the heat transfer behavior around the heated cylinder.

Intense pulsed light sintering of Cu nano particles/micro particles-ink assisted with heating and vacuum holding of substrate for warpage free printed electronic circuit

In this work, intense pulsed light (IPL) sintering process was investigated with vacuum stretching and heating of the polymer substrate for warpage free printed electronics circuit. The IPL irradiation energy and substrate heating temperature were optimized to obtain high electrical conductivity, high adhesion strength, and little warpage of printed Cu electrodes pattern on the polyimide (PI) substrate. Scanning electron microscopy and x-ray diffraction were conducted to characterize microstructure and transformation crystal phase of the IPL sintered Cu nanoparticle (NP)/microparticle (MP)-ink film. The resistivity of IPL sintered Cu NP/MP-ink films was measured using the four-point probe method and profilometer. In order to monitor IPL sintering process, in-situ resistance and temperature monitoring of Cu NP/MP-ink were conducted. Also, a transient heat transfer analysis was performed using finite-element analysis software to predict temperature gradients of Cu NP/MP-ink and polymer substrate during IPL light sintering process. As a result, the optimal IPL light sintered Cu NP/MP-ink film (vacuum applied, 150 °C heating, and irradiation energy: 3.5 J/cm2) had a low resistivity 6.94 μΩ·cm and 5 B level of adhesion strength with almost no warpage of PI substrate.

Effect of solar temperature field on a sea-crossing cable-stayed bridge tower

Based on the transient temperature field theory of heat conduction, the solar temperature field calculation model of a sea-cross cable-stayed bridge tower was established and calculated through transient heat transfer analysis, with the largest sea-cross construction project of Kong–Zhuhai–Macao Bridge as an example. The main parameters, including the solar elevation angle, azimuth angle, radiation absorption coefficient, and length of overhang, were incorporated. The proposed model was verified by comparing the measured data with the predicted values of both the temperature field and temperature deformation. The analysis results and monitoring data achieved a good agreement, which reveals that integrating numerical analysis with field monitoring data can be utilized to thoroughly understand the effects of a solar temperature field on a sea-crossing cable-stayed bridge tower. The research results guide the construction of the bridge.

Theoretical analysis of transient heat and mass transfer during regeneration in multilayer fixed-bed binder-free desiccant dehumidifier: Model validation and parametric study

A numerical model is presented for the prediction of transient heat and mass transfer characteristics during the regeneration process in a multilayer fixed-bed, binder-free desiccant dehumidifier. Experiments were carried out in a previous study that provided the benchmark data for validation of the current model under different temperatures and velocities of the regeneration air. A spherical microsphere silica gel having a pore diameter of 2.7 nm was used as the adsorbent during the experiments. In the first part of this study, model validation was performed for different temperatures (314.4–325.0 K) and velocities (0.6–0.9 m s−1) of regeneration air. The results showed that at a fixed regeneration temperature (325.0 K), the model predicted mass of the desorbed water as well as the desiccant bed and air temperatures were in a good agreement with the previously reported experimental results. With a decrease in the temperature and velocity of the regeneration air, the model slightly underpredicted the experimentally obtained mass of the desorbed water; however, the deviation remained within a reasonable limit. Upon validation, a parametric study was carried out to show how the heat and mass transfer characteristics of the microsphere silica gel during desorption depended on the intrinsic material properties (e.g., desorption rate constant, diffusivity, and desorption isotherm) and mechanical design parameters of the device (e.g., convective heat transfer coefficient, porosity, and thickness of the desiccant bed).

Time-step constraints for finite element analysis of two-dimensional transient heat diffusion

In a FE analysis of transient heat transfer, a lower limit of the time-step size exists below which numerical oscillations of temperatures may occur. Although time-step constraints for simulating 1D heat diffusion have been well established in the literature, the conclusions cannot be directly applied to 2D cases. In this paper, both analytical and computational studies are carried out to obtain the time-step constraints for 2D linear and quadratic elements. It is noted that in the simulation of 2D heat diffusion employing quadratic elements is not always beneficial. Recommendations are provided on selecting the numerical scheme to minimise numerical oscillations.

Investigation of thermal responses during metallic additive manufacturing using a “Tri-Prism” finite element method

Temperature distribution and thermal history have been demonstrated to greatly affect the microstructure of additive manufacturing (AM)-fabricated part, and further dedicate its mechanical properties. This paper, thus, develops an accurate and high-efficiency linear six-node “Tri-Prism” element for transient nonlinear heat transfer analyses of the selective electron beam melting (SEBM) of Ti-6Al-4V alloy. A stepwise activated approach is used to model the material layer-by-layer deposition process for the SEBM simulation. The physics of interaction between the electron beam and the material is modeled by a Goldak double-ellipsoid volumetric heat source. A backward difference technique featured with the unconditional stability is employed to address the transient heat conduction equations. In order to handle the material nonlinear and radiation issues, an accelerated Newton-Raphson method (ANRM) is utilized herein. Two examples of transient heat transfer are first given to demonstrate the accuracy and efficiency of “Tri-Prism” element. Finally, the thermal responses of an aircraft engine blade fabricated by SEBM are comprehensively investigated.

Experimental and numerical study of low frequency pulsed Nd:YAG laser heating of slip cast fused silica ceramics for laser assisted turning process considering laser beam overlapping

Machining of ceramics often involves many challenges due to their high hardness, brittleness, and low thermal conductivity. Laser assisted machining (LAM) is a promising technology for improving the machinability of hard-to-cut materials. In this work, the effect of laser heating in the LAM process on slip cast fused silica (SCFS) ceramics is investigated by presenting a numerical thermal analysis of laser effects on material behavior. A transient three-dimensional heat transfer analysis for laser assisted turning (LAT) of SCFS is performed using finite element method. Temperature distributions in SCFS cylindrical specimens are obtained. Moreover, the influence of laser parameters such as power, translational speed, and feed rate on the temperature field are studied. To increase the absorptivity of the ceramic surface, a coating is applied, and the absorptivity of the coated surface is determined by carrying out a series of experiments. Experiments are performed to validate the numerical transient heat transfer finite element model. In addition, the effects of spot overlapping of pulsed laser on temperature distribution and absorptivity of SCFS workpiece are studied. It is for the first time that effect of laser beam overlapping on low frequency pulsed laser heating in LAT is formulated and completely investigated.

Numerical prediction of effective thermal conductivity of ceramic fiber board using lattice Boltzmann method

Application of the lattice Boltzmann method has been extended for the analysis of combined transient conduction and radiation heat transfer through highly porous fibrous insulation media. Firstly, LBM has been employed for the analysis of combined mode of transient conduction radiation heat transfer in a 2 D rectangular enclosure containing an absorbing, emitting and scattering medium and results are compared with already published ones. The results have been found in good accord for different values of radiation-conduction parameter, scattering albedo and south (hot) wall emissivity. Furthermore, the proposed LBM for the calculation of effective thermal conductivity of ceramic fiber board has been employed. A random-generation growth method for generating micro morphology of natural ceramic fiber board has been selected. The conductive, radiative and effective thermal conductivity has been numerically estimated using the present LBM. It is found that the predicted effective thermal conductivity for different values of fibrous bulk density is in good agreement with the experimental data.