管板式太阳能集热器的热力学分析

Thermodynamic Analysis for Tube and Plate Solar Collector

依据热力学第一和第二定律,在考虑了太阳能集热器变热流密度和变管壁温度的实际工况的情况下,建立了管板式太阳能集热器的传热模型,并对其进行了热力学性能分析.提出了一种基于管内流动和传热过程中熵增原理的分析方法,并讨论了摩擦产生的比熵产和传热产生的比熵产以及使比熵产最小的最优雷诺数的影响因素和变化规律.其主要结论如下,当集热器单位面积上吸收的太阳辐射一定时,传热产生的比熵产随着雷诺数增大单调递减,摩擦产生的比熵产随着雷诺数增大单调递增加,当摩擦产生的比熵产逐渐达到与传热产生的比熵产同一量级时,出现一个最优的雷诺数使比熵产最小,这个最优雷诺数会随着流体与管壁的温差增大而增大.

Based on the first and second thermodynamic laws,with consideration of actual working conditions of solar collectors such as the variable heat flux and variable wall temperature,a heat transfer model of tube and plate solar collectors is established and then analyzed thermodynamically. An analytical method based on the entropy generation theorem for pipeline flow and heat transfer process is developed. The factors and the law affecting entropy production ratio generated by friction,entropy production ratio generated by heat transfer and entropy production ratio minimization of the Reynolds number are also discussed. The major conclusions are as follows.Under the condition of constant heat absorbed by unit area,the entropy production ratio generated by heat transfer increases and the entropy production ratio generated by friction decreases with increasing Reynolds number.When they are of the same order of magnitude,entropy production ratio minimization of the Reynolds number exists,and the Reynolds number grows with increasing temperature difference between tube and fluid.