- #1
Soren4
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Homework Statement
The following data refer to an electrically operated refrigerator:
- Efficiency : ## \xi = 2.4##
- Temperature inside: ##T_i = -9 ° C ##
- Temperature of the radiator ## T_r = 40 °C ##
- Room temperature: ## T_s = 35 °C##
- Total surface of walls: ## A = 3.2 m ^ 2 ##
- Average thickness of the walls: ## d = 4.0 cm##
- Thermal conductivity of the walls:## k = 2.0 · 10^-5 kcal / (m K s) ##
determine:
a) Required power to make this refrigerator work;
b) The change in entropy of the universe in one second, assuming that the room and the radiator are separated (no heat exchange between them);
c) The change in entropy of the universe in one second, assuming that the radiator exchanges heat with the room, remaining a constant temperature (the room is a thermal reservoir).
Answers##[(a) P = 122.8 W; (b) ΔS_u = 0.377 J / K; (c) ΔS_u = 0.399 J / K] ## [/ quote]
Homework Equations
##\xi=\frac{Q_{absorbed}}{|W_{absorbed}|}##
The Attempt at a Solution
What confuses me the most is the presence of the radiator: how can I deal with it?
Should I treat it as a further source of heat besides the room or somehow else?
Furthermore I don't understand what is the correct way to get a solution to the first question: I know that the machine absorb a power ##P'=\frac{P}{\xi}##, should I impose that ##P'## equals the flux of heat between room-fridge and radiator-fridge or something else?
A suggestion on how to set up a solution would be highly appreciated!