A NUMERICAL STUDY OF INSTANTANEOUS HEAT TRANSFER DURING COMPRESSION AND EXPANSION IN PISTON-CYLINDER GEOMETRY

A numerical analysis of the flow and heat transfer in a gas confined by a moving piston inside a valveless cylinder is presented. Repeated compression and expansion of the gas in the cylinder causes it to heat up. The in-cylinder heat transfer is out of phase with the bulk gas-wall temperature difference and the conventional Newton law is not applicable. Instead of being proportional to bulk gas-wall temperature difference the heat transfer should also depend on the time derivative of the bulk gas temperature. An understanding of the in-cylinder heat transfer is essential in modeling compressors, internal combustion engines, and other reciprocating machines. In the present paper the unsteady compressible axisymmetric flow inside the cylinder is modeled using a moving coordinate system and a finite volume methodology. The existing phase difference between the heat transfer and the gas-wall temperature difference is explored.     

NUMERICAL STUDY ON TURBULENT FLOW AND HEAT TRANSFER IN CIRCULAR COUETTE FLOWS

Abstract

A numerical study is performed to investigate heat transfer and fluid flow in the entrance and fully developed regions of an annulus, consisting of a rotating, insulated inner cylinder and a stationary, heated outer cylinder. Several different k-ε turbulence models are employed to determine the turbulent kinetic energy, its dissipation rate, and the heat transfer performance. The governing boundary layer equations are discretized by means of a control volume finite difference technique and numerically solved using the marching procedure. In the entrance region the axial rotation of the inner cylinder induces a thermal development and causes an increase in both the Nusselt number and the turbulent kinetic energy in the inner cylinder wall region. In the fully developed region, an increase in the Taylor number causes an amplification of the turbulent kinetic energy over the whole cross section, resulting in a substantial enhancement in the Nusselt number. These transport phenomena are also affected by the radius ratio and Reynolds number.     

大孔径复合透明蜂窝结构中对流-辐射耦合传热的计算

在假定透明蜂窝壁面具有漫发射和漫反射性质的基础上对大孔径复合透明蜂窝中的对流、导热和辐射的耦合传热进行了分析,研究了吸热板的发射比、蜂窝孔的高宽比、宽度等参数对热系数的影响,并讨论了蜂窝孔内的自然对流情况。     

A FINITE DIFFERENCE METHOD FOR SOLVING 3-D HEAT TRANSPORT EQUATIONS IN A DOUBLE-LAYERED THIN FILM WITH MICROSCALE THICKNESS AND NONLINEAR INTERFACIAL CONDITIONS

We develop a finite difference method for solving 3-D heat transport equations in a double-layered thin film with microscale thickness and nonlinear interfacial conditions. The scheme is solved by using a preconditioned Richardson iteration, so that only two tridiagonal linear systems with nonlinear interfacial conditions are solved at each iteration. Applying a parallel Gaussian elimination coupled with Newton's iteration to solve these two linear systems with nonlinear interfacial conditions, we develop a domain decomposition algorithm for thermal analysis of the double-layered thin film. Numerical results for thermal analysis of a gold layer on a chromium padding layer are obtained.     

光漏斗导光聚能高温相变储热直接供热式太阳能炉的性能研究

设计制作了一台利用光漏斗导光聚能并具有高温相变储热功能的直接供热式太阳能炉,介绍了其结构和运行原理.在稳态提供光能的条件下,对其性能进行了实验测试,给出了装置的升温曲线和降温曲线.利用ANSYS软件,对其储热过程进行了仿真模拟,给出了模拟结果.对影响装置性能的因素进行了分析和讨论.结果表明,在提供光能300W的条件下,装置6h储能达到饱和,温度达到约200℃,给用户的供热功率约700W,系统散热功率小于50W.     

A DOMAIN DECOMPOSITION METHOD FOR SOLVING 3-D HEAT TRANSPORT EQUATIONS IN A DOUBLE-LAYERED CYLINDRICAL THIN FILM WITH SUBMICROSCALE THICKNESS AND NONLINEAR INTERFACIAL CONDITIONS

A domain decomposition method is developed for solving 3-D heat transport equations in a double-layered cylindrical thin film with submicroscale thickness and nonlinear interfacial conditions. The heat transport equations are discretized based on the hybrid finite elementfinite difference (FE-FD) method. The schemes are solved by using an iteration, so that only two-block tridiagonal linear systems with nonlinear interfacial conditions are solved. Finally, a parallel Gaussian elimination coupled with the Newton iteration is applied to solve these two systems with nonlinear interfacial conditions. Numerical results for thermal analysis of a gold layer on a chromium padding layer are obtained.     

A NUMERICAL STUDY OF THE EFFECT OF WINDOW CONFIGURATION ON THE EXTERNAL HEAT AND SMOKE SPREAD IN BUILDING FIRE

This article presents a numerical study of external heat and smoke spread caused by compartment fires in multistory buildings. Usually, a building fire causes not only hazard to the occupants in that compartment, but also poses a possible threat to the occupants in other compartments, in particular to those located at upper stories. In this study, three scenarios with different window configurations are performed on the basis of the Navier–Stokes equations and the standard k– k model. Analysis of the computational results found that the window configurations and area as well as its location affect the heat and smoke pattern and in turn the safety of the occupants at upper stories. This implies that window design for multistory buildings, in terms of fire safety, should be carefully considered.     

自然环境下湿分分层土壤中热湿迁移规律的研究

建立描述存在干饱和层时的土壤热湿传递的数学模型并进行数值模拟，获得自然环境下土壤中温度、湿分分布以及水分蒸发的动态特性，分析干饱和土壤层对土壤热湿迁移及水分蒸发的影响。数值模拟获得实验支持。     

太阳能-地热道路融雪系统路面传热特性的数值研究

初步建立了道路融雪系统的路面传热模型,并基于典型年逐时气象数据与复合边界条件,进行了稳态传热数值模拟,分析了不同埋管深度和加热温度对道路融雪性能的影响,得到了最大和待融热负荷与降雪量、环境温度、相对湿度以及风速等因素之间的关系,可为工程设计应用提供必要的参考依据。