3 ms·

I think it is simply that cooling a gas will reduce its pressure if you maintain constant volume (Ideal gas law). So when you open the door you warmup the air i

I think it is simply that cooling a gas will reduce its pressure if you maintain constant volume (Ideal gas law). So when you open the door you warmup the air inside, and when it cools down once to door is locked, the pressure is lower, locking the door. Then small leaks will equalize the pressure.

genewitch 5y ago
My side by side actually runs some pump that is not the compressor when you close the door. It runs for about 5 seconds, after which the doors are quite difficult to open. Air does not change temperature that fast without being forced to, so the idea that within 10 seconds it's harder to open because of a natural vacuum seems suspect. Maybe 5 minutes after?
- deleted 5y ago
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- antoinealb 5y ago
  I tried doing some math on this, since you got me thinking! Let's assume the "lock force" is 100N, and the surface of the fridge's door is 1 square meter. This means the pressure differential between inside and outside would be 100 Pa. One atmosphere is roughly 10^5 Pa, so you would need a pressure differential of 10^5 / 100 = 0.1% between inside and outside. Since PV=NRT, we deduce that DeltaP/P = DeltaT/T. Or, in other words, 0.1% pressure means 0.1% temperature. We live at around 300K, so that's 0.3K difference. A fridge is what, 0.5 m^3 ? And air is about 1.3 kg/m^3, specific heat of air is about 1kJ/kg, so we would be looking at removing 1.3 kg/m^3 * 0.5m^3 * 1 kJ/kg = 650 J in 10 seconds, or 65W. A fridge can apparently consume about 200W peak (from a quick Google search), so it seems feasible with an OK-tier efficiency. In addition, if you add a pump, you could also just add a mechanical lock, couldn't you ?
  - genewitch 5y ago
    Thanks for doing that math, truly. I always assumed it pulled air out from the top of the freezer compartment, just to remove some of the hottest air. Inefficiencies in the seal will let air leak back in eventually, but probably slow enough that it doesn't affect the internal temperature that much. Now I want to know the reasoning behind having a pump at all. >A fridge can apparently consume about 200W peak yes this seems right, i am able to run my fridge off an inverter connected to my vehicle battery if the power is out, even with a 150' run of extension cord - no issues at all, and 200W or thereabouts sounds like the numbers i saw.

genewitch 5y ago

My side by side actually runs some pump that is not the compressor when you close the door. It runs for about 5 seconds, after which the doors are quite difficult to open. Air does not change temperature that fast without being forced to, so the idea that within 10 seconds it's harder to open because of a natural vacuum seems suspect. Maybe 5 minutes after?

deleted 5y ago
[deleted]
antoinealb 5y ago
I tried doing some math on this, since you got me thinking! Let's assume the "lock force" is 100N, and the surface of the fridge's door is 1 square meter. This means the pressure differential between inside and outside would be 100 Pa. One atmosphere is roughly 10^5 Pa, so you would need a pressure differential of 10^5 / 100 = 0.1% between inside and outside. Since PV=NRT, we deduce that DeltaP/P = DeltaT/T. Or, in other words, 0.1% pressure means 0.1% temperature. We live at around 300K, so that's 0.3K difference. A fridge is what, 0.5 m^3 ? And air is about 1.3 kg/m^3, specific heat of air is about 1kJ/kg, so we would be looking at removing 1.3 kg/m^3 * 0.5m^3 * 1 kJ/kg = 650 J in 10 seconds, or 65W. A fridge can apparently consume about 200W peak (from a quick Google search), so it seems feasible with an OK-tier efficiency. In addition, if you add a pump, you could also just add a mechanical lock, couldn't you ?
- genewitch 5y ago
  Thanks for doing that math, truly. I always assumed it pulled air out from the top of the freezer compartment, just to remove some of the hottest air. Inefficiencies in the seal will let air leak back in eventually, but probably slow enough that it doesn't affect the internal temperature that much. Now I want to know the reasoning behind having a pump at all. >A fridge can apparently consume about 200W peak yes this seems right, i am able to run my fridge off an inverter connected to my vehicle battery if the power is out, even with a 150' run of extension cord - no issues at all, and 200W or thereabouts sounds like the numbers i saw.