Surface Area and Thermal Transfer ```Name: Paul I. Status: Student Age: 15 Location: N/A Country: N/A Date: November 2003 ``` Question: How does surface area affect solar heat absorption and cooling rates? Replies: In general heat exchange is proportional to surface area for smooth surfaces. For convoluted, porous, or rough surfaces the effective surface area may be quite different (larger) than the 'geometric' surface area however. Vince Calder The solar heat absorbed by a flat surface depends on the area of the surface, the cosine of the angle between the direction of the solar rays, and the absorptivity of the surface. Doubling the area doubles the rate of heat absorption. Rays normal to the surface produce the most heat (cos (0 degrees) = 1. Rays parallel to the surface produce no heat absorption (cos (90 degrees) = 0. Black surfaces absorb the most and white surfaces the least. A perfect mirror reflects all the light and none is absorbed. Cooling follows the same laws except for the angular dependence. Heat is radiated in all directions. Notice that a painted wall illuminated by a diffuse light source looks equally bright no matter what angle you observe it at. Black areas emit the most and white the least. Again, the amount of heat radiated depends linearly on the area (doubling the area doubles the rate of heat radiation). Best, Dick Plano... Click here to return to the Engineering Archives

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