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Assume I have a refrigerator at 0C and I put a can of soda at the center of the refrigerator. The temperature inside the refrigerator will be increased to 5C after I put the soda in, but will go back to 0C after a while

If I consider the speed of cooling, should I keep the pressure inside the refrigerator be atmosphere pressure? OR I should create vacuum inside the refrigerator

If I consider the energy efficiency, should I keep the pressure inside the refrigerator be atmosphere pressure? OR I should create vacuum inside the refrigerator

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  • $\begingroup$ Refrigerators work mainly by convective heat transfer, and that is why many of them have a fan inside of them to circulate air. What does that imply regarding an answer to your question? $\endgroup$ May 29, 2023 at 22:11

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You should keep it at atmospheric pressure because of the thermal conductivity. A vacuum is an under pressure or a space that is devoid of matter, therefore it is a very good isolator. The second best isolator is stationary air, so if you want to cool the can as fast as possible you should have a decent airflow in the fridge to abstract the heat from the can.

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  • $\begingroup$ If I use ideal gas equation, PV/T = constant. Since V is the same, T decreases when P decrease. Does it mean that the refrigerator will be easier go to a lower temperature? $\endgroup$
    – Marco
    Mar 26, 2015 at 2:46
  • $\begingroup$ @Marco From the ideal gas equation you can only deduce that if you were to suddenly lower the pressure the temperature would drop (keeping $V$ constant). The soda can isn't part of the ideal gas and the temperature of the can doesn't drop (at least not immediately). If you want to know if it's easier to go to a lower temperature you can have a look at the heat capacity at constant $V$. en.wikipedia.org/wiki/…. The heat capacity only depends on $N$ so for constant density it will stay the same $\endgroup$ Dec 7, 2021 at 12:28
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In a vacuum the can would be unable to give any kind of convection current to the fridge so only radiation and conduction would be allowed. since the can is at a similar temperature to the fridge the radiation exchange would be very small. the source is not powerful enough to initiate substantial heat transfer. And if it was on the rack, then only that rack that was in contact with the can would be working on transferring particle intensity.

At atmospheric pressure, you would have an abundance of particles in contact with the can. So convection currents would allow for a 3Dimensional heat transfer.

I would also add that if the fridge was under vacuum the can itself would expand a bit due to a weakened normal force acting on it. Which would reduce internal energy intensity of fluid inside due to increased volume area. so heat transfer would be even slower.

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