In this paper the variation of temperature field along the duct of a solar air heater is studied using specially developed a three dimensional model .The finite volume method [FVM] is used to solve the governing equations. The effect of different operating parameters is studied such as air mass flow rate, inlet air temperature and duct aspect ratio [duct height/duct width] or what is known as flow depth. It is found that as the flow depth or aspect ratio is reduced the air is more uniformly heated through the duct cross section especially at duct exit where the air temperature becomes uniform across the duct. This shown on isothermal contours map at different cross sections. It is also found that the bulk exit air temperature increases with increasing the absorber plate temperature, i.e increasing the absorber plate temperature by about 60% gives an increase in bulk air temperature by about 9.5 oC, and the bulk exit air temperature increases with reducing air mass flow rate and flow depth, i.e. the decrease of mass flow rate by (27%) increases the bulk exit air temperature by about 3.3804 oC, and reducing the flow depth by about 33.333% increases the bulk exit air temperature increases about 4.45 oC). Also the local air temperature growth [temperature along duct height at the centre line] increases with reducing the mass flow rate and flow depth. The results also show that as the inlet air temperature increases the bulk exit air temperature increases for same mass flow rate, i.e. the increase in inlet air temperature by about 10 oC gives an increase in the exit bulk air temperature by about 6.5 oC).
Key words: solar air heater, renewable energy, solar energy, flow depth.