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A 7-cm-external-diameter, 18-m-long hot-water pipe at 80°C is losing heat to the surrounding air at 5°C by natural convection with a heat transfer coefficient of 25 W/m2·°C. Determine the rate of heat loss from the pipe by natural convection, in kW. The rate of heat loss from the pipe by natural convection is:________.

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princessesther2011

Answer:

The rate of heat loss from the pipe by natural convection is 4×10^-4 kW.

Explanation:

Q = kA(T1 - T2)/L

k is heat transfer coefficient = 25 W/m^2.°C

A is area of the pipe = πd^2/4 = 3.142 × 0.07^2/4 = 3.84895×10^-3 m^2

T1 - T2 is change in temperature = 80 - 5 = 75°C

L is length of the pipe = 18 m

Q = 25 × 3.85895×10^-3 × 75/18 = 0.4 W = 0.4/1000 = 4×10^-4 kW