Solar collectors with tubes partially filled with porous substrates

In this work, the thermal performance of a conventional collector is improv ed by inserting porous substrates at the inner walls of the collector tubes . The porous substrates improve the convective heat transfer coefficient be tween the tube wall and the fluid. This improvement is investigated numeric ally and its effects on the efficiency and the useful gain of the collector are evaluated. It is found that inserting the porous substrate may raise t he collector efficiency considerably, especially at high values of the over all heat loss coefficient.