A rectangular fin 1.0 ft long, 1.0 ft wide, and 2in. thick loses heat to the atmosphere at70 F. The base of the fin is at 270 F.If h = 2Btu/h*ft2* F and the thermal conductivity of the fin is 24Btu/h*ft* F, find:(a) The fin efficiency.(b) The total rate of heat loss from the fin.Ans. (a) 70.5%. (b) 712 Btu/h.

A rubber insulated copper wire 2 mm diameter is carrying electric current and exposed to a uniform temperature of air at 40°C. What will be the maximum steady current in amperes that can be allowed if the rubber insulation is not to get heated above 45°C? Insulation thickness=1 mm Thermal conductivity of rubber= 0.15 W/m-K Air film coefficient= 10 W/m2-K Electrical resistivity of copper=10-7 ohm-m A 10.45 A В 2.1 A C) 14.5 A D 4.25 A E 9.65 A F None of these

A glass window of width W = 1 m and height H = 2 m is 5 mm thick and has a thermal conductivity of k 1.4 W/m K. If the inner and outer surface temperatures of the glass are 15°C and -20°C, respectively, on a cold winter day, what is the rate of heat loss through the glass? To reduce heat loss through windows, it is cus- tomary to use a double pane construction in which adjoining panes are separated by an air space. If the spacing is 10 mm and the glass surfaces in contact with the air have temperatures of 10°C and -15°C, what is the rate of heat loss from a 1 m x 2 m window? The thermal conductivity of air is k, = 0.024 W/m.K.

Estimate the natural convection heat transfer coefficient of the horizontal pipe. The temperature of the outer surface of the pipe is 120 ° C. The ambient air temperature is 25 ° C. The outer diameter of the pipe is 10 cm. Convection coefficient = Answer W / m² ° C.