Methods for determining the temperature of a plastic net under solar and thermal radiation conditions

Abstract

To determine the energy transfer through a plastic net-covered structure, the temperature of the net (Tn) is an essential parameter. The perforated nature of nets and the effects of solar and thermal radiation, during the daytimes, make it is impossible to measure Tn correctly by using most types of thermometer. Therefore, Tn has never been theoretically estimated or experimentally measured in the presence of solar and thermal radiation. In this study, Tn was simulated by determining the emissive power of the net (En) and the net emittance (εn). To determine En and εn, the net was tacked onto a wooden frame; thermal radiation balance was applied below and above the net surfaces and above the substrate underneath the frame. The downward and upward thermal radiation fluxes were measured below and above the net to be used in the simulation. A simple measuring method was proposed to predict Tn using a thermocouple junction of 0.3 mm in diameter (copper constantan, type-T) inserted into the net texture. The measured values of Tn were in agreement with those predicted by the simulation. The mean absolute difference between the measured and the simulated values of T n ranged from 0.75°C to 1.9°C for all the nets tested. For nets with low porosity, the inserted junction should keep exposing to the surrounding environment. However, for nets with high porosity, the inserted junction should be shielded from radiation to improve measurements in the correct direction. © 2014 Elsevier B.V. All rights reserved.