Question

please show me how I can finds the answers of these two examples

Example 1: Design of a Solar Heater (Black bodies: no convection) A square flat plate collector is exposed to solar radiation from both the sides. The exposed surface of the plate has an absorptivity of 1.0 for solar radiation. On a clear summer day on the earth's surface the solar radiation flux is approximately 1140 W/m2 and the surrounding air temperature is 25oC. Determine the surface temperature? Solution: At each side of the front plate: Qsolar absorbed-ơ A TS4 gs = 1140 W/m2 As x 1 140 = 2 x As x 5.67A 10-8 W/(m2 K4) Example 2: The surface considered in Example 1 is the upper surface of an enclosure and the lower surface is receiving radiation from the upper surface while losing heat from the other side only by convection (heat transfer coefficient is 0.003 W/em2.K) to a heat exchange fluid. Assume no convection within the enclosure. The enclosure is very narrow in the vertical direction. Calculate the temperatures at the upper surface and the lower surface Solution: gs 1140 Wm2 At the upper surface Q-solar absorbed Q.rad to the sky & to the lower surface & gained from the lower surface at T2 a = 1.0 a Osolar= eSAs(T14-724) 1.0 x As x 1140 1.0x 5.67x10-8 x As [T14-T24] π-2500 -30 W/m2.oC Example 2: Design of a Solar heater. Calculate the temperatures at the upper surface and the lower surface of the solar energy collector. Solution: At the lower surface Q. Absorbed by radiation-Q.rad to the sky +Q.conv the fluid by convection e s As(T14-T24) h As (T2 - Tf) 1.0 x 5.67x 10-8 x As [T14-724] = 0.003x 104 xAs (T2-298) A pair of nonlinear algebraic equations and can be solved by trial and error: The results are: T1-44.4 oC, T2 36 oC

Answer 1

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