Question

Heat is convected away from an object at the rate given by the following formula h is a coefficient that depends on the shape and the orientation of the object. Calculate the rate of convective heat loss in watts for an unclothed person standing in air at 23 deg C. Assume that the skin temperature is 34 deg C and that body surface area is 1.5 m sq.. Calculate for all three air speeds given below. h = 6 air speed = still h = 12 air speed = 1m/sec h = 28 air speed = 5m/sec 5m/sec A solar still is used to make fresh water from salt water by evaporation. Assume that during a summer day that 1000 BTU/ft sq of solar energy falls on the surface of the salt. water. Determine how many inches of water are evaporated in 30 days. Assume that 1040 BTU's is needed to distill one pound of water.

Can someone answer number one? Thanks.

Answer 1

Data Given

$\Delta T = 23^{0}C- 34^{0} C = -11^{0} C$

Area A == 1.5 m²

Part A) h = 6 W/m².⁰C, v = 0

$\frac{\Delta Q}{\Delta t}= hA\Delta T = 6 W/m^{2}.^{0}C\times 1.5 m^{2}\times (-11^{0}) C= -99 W$

Part B)

$\frac{\Delta Q}{\Delta t}= hA\Delta T = 12 W/m^{2}.^{0}C\times 1.5 m^{2}\times (-11^{0}) C= -198 W$

Part C)

$\frac{\Delta Q}{\Delta t}= hA\Delta T = 28 W/m^{2}.^{0}C\times 1.5 m^{2}\times (-11^{0}) C= -462 W$