Papers by Keyword: Transient Heat Transfer

Abstract: According to previous studies, the most effective, stable, and explicit numerical methods to deal with problems of heat transfer in building walls are the two recently published approaches, which are the modified Dufort-Frankel and leapfrog-hopscotch techniques, which are used in this study to make transient and long-term simulations (three months of the winter season) of 2-D space systems that enable us to execute these simulations with relatively short computational times to evaluate the two most effective versions of these methods. Our solution to a real-world engineering challenge involves investigating thermal bridges of different forms inside multilayer walls of buildings exposed to environmental factors specific to Hungary's climate, such as the outside temperature and sun radiation, to improve energy efficiency. The distributions of temperatures and the total heat loss (across the walls) are calculated for all cases (three layers without a thermal bridge three layers with thermal bridges in straight, bent, and L-shaped shapes).

Abstract: Vulcanization or curing process is a very important process in producing useful rubber products. The quality, performance as well as manufacturing cost of a rubber product are largely affected by the curing process. The curing process takes place when heat is transferred to the rubber compounds inside a heated mould. Curing of a thick article, such as a solid tire, often occurs under transient non-isothermal conditions. The temperature distribution in the rubber significantly affects the cure level distribution throughout the part, especially in a large rubber component. Therefore the ability to predict the distribution of cure level in a rubber part during curing is of great importance for improving the process efficiency and the quality of the final product. In this work, simulations of the curing process of a solid tire, consisting of three layers of different rubber compounds, were performed and the cure level distribution results were evaluated. The simulations are carried out using the commercial finite element software ABAQUS with the cure kinetics model for rubber implemented through the user subroutine UMATHT. The effects of the mold temperature and initial temperature of the solid tire on the cure level distribution and cure time were investigated.

Abstract: This paper deals with heat of hydration in a concrete structure at the early age. The influence of temperature on development of hydration heat in the concrete structure is implemented through a fuzzy-logic model of the degree of hydration. The transient heat transfer problem was solved as a three-dimensional finite element simulation. The whole process of calculation is implemented in MATLAB Environment. The result of this work provides temperature distribution in the structure for each time step, the maximum temperature in the structure, and the time when it occurs.

Abstract: The principle which the tool is embedded into the HSK shrink toolholder is expanding with heat and contracting with cold. The thermal cycle that the tool is embedded into or taken out the toolholder is heating toolholder and cooling it quickly. After a few thermal cycles, the HSK shrink toolholder is damaged with the way of thermal fatigue. The analysis of thermal fatigue is transient heat transfer and stress coupling and the temperature distributionstress and strain of every time are gained in thermal cycle. The fatigue of shrink tool holder is strain fatigue by analyzing the stress. The fatigue life is gained with Coffin-Manson formula.

Abstract: The research object is a micro heat exchanger (MHT) applied in chip cooling, a three dimensional simulation model is developed to analyze the transient heat transfer of the exchanger according to both exponential and periodic heat fluxes. Based on the computational results of the profiles of temperature and thermal stress, a comparison of performance of heat exchangers made of copper and silicon nitride compound is carried out. The results indicate that the capability of a copper heat exchanger is better than that of a silicon nitride exchanger under low load working condition due to the excellent thermal conductivity of copper. However, with large load fluctuations, the advantage of structure strength of compound makes the exchanger attractive since it has lower thermal stress and could guarantee a long-term stability. The efforts of this paper are referable for further research and development of micro heat exchangers.

Abstract: Nowadays, reusable launch vehicle (RLV) has become a research focus of the transportation system between ground and space and the space weapon system. RLV plays an important role in controlling the cost of space transportation and performing the orbital mission. Since RLV would suffer from the aerodynamic heating inevitably during reentry, the thermal protection system (TPS) is designed to prevent too much heat transmitting to the vehicle structure and maintain the vehicle structure below a specified temperature limit. Several studies were performed to develop an understanding of not only the thermal and structural analysis of ceramic tile thermal protection system on the space shuttle but also the controlling factors of TPS. The TPS is subjected to the reentry heating and pressure profile of the Access to Space vehicle, and the transient temperature distribution and the resultant thermal stresses in the system are computed. Comparisons between various studies based on different assumptions were examined. By comparing these results with more realistic ones, the differences are evaluated. Results suggest that the TPS analysis must be based on reasonable and realistic parameters. Thus, engineers have to keep in mind that all parameters should be chosen very carefully to achieve results that close to practical ones.

Abstract: Injection molded part with micro structures is extensively used as a heatsink, which will provide bright prospects for application. In this present study, analytical models with micro pins, micro holes and micro grooves were specially designed and built. Molding quality and transient heat transfer performance of these parts were investigated via the finite element methods. As research objective, warpage and residual thermal stress of each target under identical molding conditions was compared to evaluate the product quality, and heat dissipation performance of micro structures was applied to assess the applicability of plastic products used as heatsinks. Study results revealed that the part with micro grooves had better molding quality and heat dissipation effectiveness than others.

Abstract: There were many issues in numerical methods of heat transfer problems such as instability at a big time step length or grid size and no-existence of inverse matrix by time-precise integration method. For sake of avoiding instability and calculating an inverse matrix, a coupling method was put forward based on EFGM and IDPIM. Formulae were deduced according to EFGM and IDPIM. Results show that the coupling method has a higher accuracy and its stability is small subjected to the time step length or grid size, and is to deserve to be popularized.

Abstract: The convolution-type Gurtin variational principle is known as the only variational principle that is, from mathematics point of view, totally equivalent to the initial value problem system. In this paper, the governing equation of bars is first transformed to a new equation containing initial conditions by using convolution method. Then, a convolution-type semi-analytical DQ approach, which involves differential quadrature (DQ) approximation in space domain and an analytical series expansion in time domain, is proposed to obtain the transient response solution. The transient heat transfer examples show the proposed method is a very useful and efficient tool in transient heat transfer problems.

Abstract: Heat sinks enable the storage of energy that would otherwise be lost, thus ensuring significant energy-savings and fewer greenhouse gas emissions. Heat sinks also play the major role in the efficient temperature control of devices such as batteries. In principle, any material can act as a heat sink – traditionally, copper is used for many applications. However, copper is relatively expensive, has a high density and only a limited energy storage capacity. In contrast, a phase-change material (PCM) allows in effect an additional storage of energy through its phase change thus greatly increasing the achievable energy density. The aim of this work is the numerical analysis of the transient heat transfer in composite heat sinks containing phase-change materials. For the first time, a recently formulated Lattice Monte Carlo Method is applied to determine temperature distributions and the amount of energy transferred versus time in phase change materials.