ABSTRACT

The parameters that largely influence the design and performance of a parabolic trough collector system for delivering process heat are optical efficiency, incidence angle modifier, solar irradiation data, and receiver heat loss. The heat loss and optical properties of a receiver greatly influence the overall efficiency of the solar thermal system. This paper focuses the attention on the experimental investigation of heat loss associated with a non-evacuated receiver subjected to i). Uniform wall heat flux (UWHF) and ii). Non – uniform wall heat flux (NUWHF) boundary condition. A series of heat-loss measurements are carried out in the novel test stand capable of emulating both the boundary conditions, on the indigenous non – evacuated receiver developed for moderate temperature process heat applications. A comparative analysis of natural and forced convection heat loss associated with the bare and glass-covered receiver is performed. The results show that the non – uniform wall heat flux boundary condition has a decisive influence over the forced convection heat loss, especially at higher wind velocities. The work concludes that i) the surface temperature of the receiver associated with natural convection heat loss and subjected to NUWHF boundary condition is1.5– 5% higher than the receiver subjected to UWHF boundary condition. ii) In forced convection mode of heat loss the surface temperature of the receiver is 4–13% higher than the receiver subjected to UWHF. Thus, a more realistic characterization of the thermal behaviour of a non-evacuated receiver for moderate temperature process heat application is possible only by investigating the receiver subjected to non – uniform heat flux distribution. Such a characterization of the receiver will considerably influence the aperture area and thus the cost of the collector to deliver process heat.

摘要

主要影响用于输送过程热量的抛物线槽收集器系统的设计和性能的参数是光学效率、入射角调节器、太阳辐射数据和接收器热损失。接收器的热损失和光学特性极大地影响了太阳能热系统的整体效率。本文重点关注与受 i) 影响的非抽真空接收器相关的热损失的实验研究。均匀壁面热通量 (UWHF) 和 ii)。非均匀壁面热通量 (NUWHF) 边界条件。在能够模拟两种边界条件的新型测试台上，在为中等温度过程热应用开发的本地非抽真空接收器上进行了一系列热损失测量。对与裸露和玻璃覆盖的接收器相关的自然对流和强制对流热损失进行了比较分析。结果表明，非均匀壁面热通量边界条件对强制对流热损失具有决定性影响，尤其是在较高风速下。工作得出的结论是：i) 与自然对流热损失相关并受 NUWHF 边界条件影响的接收器的表面温度比受 UWHF 边界条件影响的接收器高 1.5-5%。ii) 在热损失的强制对流模式下，接收器的表面温度比承受 UWHF 的接收器高 4-13%。因此，只有通过研究受非均匀热通量分布影响的接收器，才能更真实地表征非真空接收器在中等温度过程热应用中的热行为。接收器的这种特性将显着影响孔径面积，从而影响收集器传递过程热量的成本。