Heat Transfer in Double-Pass Solar Air Heater: Mathematical Models and Solution Strategy

Multipass air collectors are commonly used because they produce higher air temperature than that of a single-pass one due to reduced top heat loss. In this chapter, two mathematical models of convection and radiant heat transfer in a double-pass solar air heater were presented. They included an average temperature model and a model of temperature variation along the airflow direction. The method for solving these two mathematical models was reported. The average temperature model was solved by dealing with a system of linear algebraic equations, whereas the other model was derived as ordinary differential equations and solved by a numerical integration. The calculation programs were developed in EES software. The computation time of temperature variation model was about 0.9 s, but that of the average temperature model was negligible. Outcomes from two solutions were almost identical. The largest error of the outlet air temperature was 2.1%. The models are applicable to multipass collectors with or without recycling airflow