Cu tube installed in a metal box. The surface of metal box is black and top surface is 1 m2 and exposed to direct sun light. The fresh air enters to Cu tube absorb heat and enters to food drying chamber. I used solar intensity a 0.85 W/m2 then inside metal box temperature became to 152 ‘C. I want to find out what was the wrong and how I solve it. Any comments and suggestions welcome you all.