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zebediah49 t1_j18x0wm wrote

Reply to comment by exbm in Why do we use phase change refrigerants? by samskiter

Note that this only works because of vapor pressure differences.

It is necessary that the compressor lower the pressure on the cold side such that its boiling point is below the cold reservoir temperature, and raise the pressure on the hot side such that that boiling point is above the hot reservoir temperature.

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St1cks t1_j190ivz wrote

The compressor doesn't cause the lower pressure side on its own. We use a type of metering device to achieve a flash off within the suction line. Ideally a 25/75 mix of liquid and gas should be present at the start of the evaporator coil. Metering devices can be fixed or adjusting, which generally use a sensing bulb attached at the inlet of the evaporator.

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zebediah49 t1_j191who wrote

This is true; you need some type of pressure drop device.

I give disproportionate credit to the compressor, due to it being the part that does the Work.

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exbm t1_j19rjrr wrote

You need to use a compressor some types of systems use external heat but all systems need a flow restricting device

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zebediah49 t1_j1a0qqf wrote

Strictly speaking many external-heat systems don't. They use an absorption refrigeration cycle, and while the partial pressure of the refrigerant components changes around, the total pressure of the system is approximately constant.

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