a refrigerator uses refrigerant-134a as the working fluid and operates on the vapor-compression refrigeration cycle. the evapora
2 answers:
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Answer:
Net heat transfers: during summer = 52.253 W/m^2 during winter = 119.375 w/m^2
Explanation:
Given data :
Room temperature throughout the year = 20⁰c = 293 k
Room temperature during summer = 27⁰c = 300 k
Room temperature during winter = 14⁰c = 287 k
surface temperature of a person throughout the year = 32⁰c = 305 k
coefficient of heat transfer by natural convection (h)= 2 w /m^2 k
emissivity = 0.9
An explanation to the condition of feeling chilled during the winter and comfortable during summer can be explained with the calculation below
The heat transfer from the surface body of a person the the room is carried out by convection and this can be calculated as
q = hΔt = 2 * ( 305 - 293) = 2 * 12 = 24 w /m^2
also calculate heat transfer through radiation using this formula
εσ [ (Temperature of body)^4- (temperature of room at each season)^4 ]
ε = 0.90,(emissivity) σ = 5.67 *10^-8 w/^2 . k ( Boltzmann's constant)
during summer :
= (0.90)*(5.67*10^-8)* ( 305^4 - 300^4 ) = 28.253 W/m^2
therefore the net heat transfer during the summer = 24 w/m^3 + 28.253 W/m^3 = 52.253 W/m^2
During winter :
= (0.90)*(5.67*10^-8) * ( 305^4 - 287^4 ) = 95.375 W/m^3
therefore the net heat transfer during the winter
= 24 w/m^3 + 95.375w/m^3 = 119.375 w/m^2