A horizontal, opaque surface at a steady-state temperature of 80°C is exposed to an airflow having a free stream temperature of
25°C with a convection heat transfer coefficient of 20 W/m2 ·K. The emissive power of the surface is 628 W/m2 , the irradiation is 1380 W/m2 , and the reflectivity is 0.30.
Determine the absorptivity of the surface.
Determine the net radiation heat transfer rate for this surface. Is this heat transfer to the surface or from the surface?
Determine the com-bined heat transfer rate for the surface. Is this heat transfer to the surface or from the surface?
Determine the absorptivity of the surface.
Determine the net radiation heat transfer rate for this surface. Is this heat transfer to the surface or from the surface?
Determine the com-bined heat transfer rate for the surface. Is this heat transfer to the surface or from the surface?
1 answer:
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Answer:
A) EXIT TEMPERATURE = 14⁰C
b) rate of heat transfer of air = - 13475.78 = - 13.5 kw
Explanation:
Given data :
diameter of duct = 20-cm = 0.2 m
length of duct = 12-m
temperature of air at inlet= 50⁰c
pressure = 1 atm
mean velocity = 7 m/s
average heat transfer coefficient = 85 w/m^2⁰c
water temperature = 5⁰c
surface temperature ( Ts) = 5⁰c
properties of air at 50⁰c and at 1 atm
= 1.092 kg/m^3
Cp = 1007 j/kg⁰c
k = 0.02735 W/m⁰c
Pr = 0.7228
v = 1.798 * 10^-5 m^2/s
determine the exit temperature of air and the rate of heat transfer
attached below is the detailed solution
Calculate the mass flow rate
= p*Ac*Vmean
= 1.092 * 0.0314 * 7 = 0.24 kg/s
