The surface of a radiation shield facing a black hot wall at 400 K has a reflectivity of 0.95. Attached to the back side of the shield is a 25-mm-thick sheet of insulating material having a thermal conductivity of 0.016 W/m ⋅ K . The overall heat transfer coefficient (convection and radiation) at the surface exposed to the ambient air and surroundings al 300 K is 10 W/m 2 ⋅ K . (a) Assuming negligible convection in the region between the wall and the shield, estimate the heat loss per unit area from the hot wall. (b) Perform a parameter sensitivity analysis on the insulation system, considering the effects of shield reflectivity, ρ s , and insulation thermal conductivity, k . What influence do these parameters have on the heat loss from the hot wall? What is the effect of an increased overall coefficient on the heal loss? Show the results of your analysis in a graphical format.
The surface of a radiation shield facing a black hot wall at 400 K has a reflectivity of 0.95. Attached to the back side of the shield is a 25-mm-thick sheet of insulating material having a thermal conductivity of 0.016 W/m ⋅ K . The overall heat transfer coefficient (convection and radiation) at the surface exposed to the ambient air and surroundings al 300 K is 10 W/m 2 ⋅ K . (a) Assuming negligible convection in the region between the wall and the shield, estimate the heat loss per unit area from the hot wall. (b) Perform a parameter sensitivity analysis on the insulation system, considering the effects of shield reflectivity, ρ s , and insulation thermal conductivity, k . What influence do these parameters have on the heat loss from the hot wall? What is the effect of an increased overall coefficient on the heal loss? Show the results of your analysis in a graphical format.
Solution Summary: The author explains how to perform the energy balance on shield and the wall.
The surface of a radiation shield facing a black hot wall at 400 K has a reflectivity of 0.95. Attached to the back side of the shield is a 25-mm-thick sheet of insulating material having a thermal conductivity of
0.016
W/m
⋅
K
. The overall heat transfer coefficient (convection and radiation) at the surface exposed to the ambient air and surroundings al 300 K is
10
W/m
2
⋅
K
.
(a) Assuming negligible convection in the region between the wall and the shield, estimate the heat loss per unit area from the hot wall. (b) Perform a parameter sensitivity analysis on the insulation system, considering the effects of shield reflectivity,
ρ
s
, and insulation thermal conductivity, k. What influence do these parameters have on the heat loss from the hot wall? What is the effect of an increased overall coefficient on the heal loss? Show the results of your analysis in a graphical format.
2.A person stands in front of a fire at 650°C in a room where air is at 5°C. Assuming the body temperature to be 37°C and a connection coefficient of 6 W/m²K, the area exposed to convection as 0.6m2, determine the net heat flow from the body. The fraction of radiation from the fire of 1m² are reaching the person is 0.01
Consider a black spherical ball, with a diameter of 25 cm, is being suspended in air. Determine the surface temperature of the ball that should be maintained in order to heat 11.7 kg of air from 20°C to 30°C in the duration of 5 minutes.Given: cv = 718 J/kg∙K
Stefan-Boltzmann constant (σ) = 5.67 × 10–8 W/m2∙K
The surface temperature of the ball is Ts = _____ °C.
A radiation shield that has the same emissivity 3 on both sides is placed between two large parallel plates, which are maintained at uniform temperatures of T1 = 650 K and T2 = 400 K and have emissivities of E1 = 0.6 and E2 = 0.9, respectively. Determine the emissivity of the radiation shield if the radiation heat transfer between the plates is to be reduced to 15 percent of that without the radiation shield
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