Square plates freshly sprayed with an epoxy paint must be cured at 140°C for an
ID: 1718874 • Letter: S
Question
Square plates freshly sprayed with an epoxy paint must be cured at 140°C for an extended period of time. The plates are located in a large enclosure and heated by a bank of infrared lamps. The top surface of each plate has an emissivity of = 0.8 and experiences convection with a ventilation air stream that is at T = 27°C and provides a convection coefficient of h = 30 W/m2 · K. The irradiation from the enclosure walls is estimated to be Gwall = 450 W/m2 , for which the plate absorptivity is wall = 0.7. Determine the irradiation that must be provided by the lamps, Glamp. The absorptivity of the plate surface for this irradiation is lamp = 0.6. Assume steady-state.
Explanation / Answer
you need to make a balance between the heat that enters and the heat that is out the sistem, so
Q radiation + Q convection this 2 heats are out
Q lamp + Q wall this 2 are in
Qradiation= 0.8(5.67x10^-8)(140+273.15)^4 = 1321.61 W/m^2
Qconvection=(104-27)(30) = 2310 W/m^2
Qlamp= 0.6G
Qwall= 450x0.7 = 315 W/m^2
1321.61 W/m^2 + 2310 W/m^2 =0.6G + 315 W/m^2
G= 5527.68 W/m^2 is the irradiation of the lamps
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