对流换热过程的分析

本文用热力学第一及第二定律分析对流换热过程中传热及流动两方面的性能,建立定量分析换热性能的(火用)损失率关系式,并利用它确定各种基本换热过程在给定条件下的最佳使用范围,以及比较各种换热方式的性能差异,为工程上采用换热过程提供综合性能评价的指标.

An Analysis of Exergy Loss in Convective Heat Transfer

The convective heat transfer process is analyzed using the first and second law of thermodynamics and the exergy loss rate equations are derived, which show quantitatively the irreversibility of heat transfer and fluid flow in the process. The equations can be used for evaluating the performance of heat transfer and fluid flow and for determining the optimal Reynolds number of a specific convective process as well as for behavior comparison between various heat transfer modes. As examples of convective haat transfer, the flow along a flat plate, the flow inside a pipe, that across a cylinder and free convection are discussed. The general conclusion is that the convective process of a smaller scale going on in a range of lower Reynolds number will have a relatively smaller exergy loss rate and that the performance of flow along a flat plate or inside a pipe is better than that of a flow across a cylinder.