Modeling Evapotranspiration Effects on Air Flowing in a Small Glass Roofed Tunnel

Abstract

A preliminary investigation into the feasibility of erecting a solar chimney power plant requires a model incorporating all possible aspects of such a power plant and giving results on an hourly basis. Possible agricultural activities underneath the outer section of the solar collector would require a model predicting the changing state of the air due to evapotranspiration effects as it flows from the perimeter of the collector to the chimney in the center. The vegetation temperature and irrigation requirements need to be determined in order to ascertain how far inward crops may be planted without being subjected to heat stress. A small experimental glass roofed tunnel was constructed, planted with grass, and the changing state of the air, drawn over the grass by a fan, was determined using wet- and dry-bulb temperature measurements and the mass flow rate of the air. Starting off with a known air state inlet condition, conservation and the Penman-Monteith equations were applied to subsequent 1-m lengths of the tunnel and the state of the air at the outlet was predicted and compared with the measured state of the air. The predicted and measured values were found to be in agreement within experimental limits giving confidence in incorporating this model into the larger model of the solar chimney.