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Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
With my wife being away in Europe for 6 weeks with the kids, one night while looking into an almost empty fridge, i began pondering a thermal question.
Assuming the items in the refrigerator are already had the steady state temperature (neglecting energy required to initially cool them), and that thermal leakage is constant (inside to outside) . . .
Does it take more energy to maintain the contents of the refrigerator at the cooling temperature if its completely full vs. almost empty???
Registered Member #1497
Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801
I would think if the fridge has a large mass of water-containing food at low temperature, the overall environment inside would be harder to warm up since opening the fridge full means less warm air enters, and therefore less heat.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The simple answer: The same amount of energy, since the thermal path between fridge and ambient is the only way for heat to flow, and isn't affected by the objects inside it.
(The First Law says that if the objects are at their steady-state temperature, no heat will flow into or out of them, although it might flow through them as it leaks through the fridge walls.)
The complicated answer: The objects inside will block convection currents and insulate the walls, making the thermal leakage less than if the fridge were empty. But this isn't relevant since you specified the leakage to be constant.
Registered Member #187
Joined: Thu Feb 16 2006, 02:54PM
Location: Central Ohio
Posts: 140
I've been studying refrigeration systems for a little over a year now because it's just so cool (okay, you can take or leave the pun).
What everyone has told you so far is correct. Having many thermal masses in the refrigerator provides a large buffer for temperature changes. Also, as Dr. Conner pointed out, they also serve as baffles which stabilize the cold air currents when the door is opened, so the result is less heat flow into the contents.
Curious, are you really asking about the overall power consumption of the compressor in a real system, or just the heat flow in general as defined by thermodynamics?
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Thermodynamics question . . .
