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HVAC School - For Techs, By Techs

Nov 17, 2020

In this short podcast episode, Bryan talks about the differences between single-phase and two-phase refrigeration. This particular episode is about the fundamentals of physics, chemistry, and science in general.

When we talk about phases, we're referring to the changes in the states of matter. We typically think of the states of matter as solid, liquid, and gas. In refrigeration systems, the refrigerant usually changes from a liquid to a vapor in the evaporator and then from a vapor to a liquid in the condenser; that is an example of two-phase refrigeration. We get two-phase refrigeration anytime we're changing the state of matter in order to accomplish refrigeration.

When you change the state of matter, you transfer a lot more heat than with a single-phase system. You get more heat in and out between phases due to latent. Between a solid and a liquid, the energy that goes towards the phase change is the latent heat of fusion. Between a liquid and a gas, the energy that goes into the phase change is the latent heat of vaporization. It takes a lot more heat to condense or boil water than it does to change its temperature by one degree, so we take advantage of that capacity to absorb heat into the boiling refrigerant.

There are also forms of single-phase refrigeration, including John Gorrie's open-refrigeration machine. Gorrie's machine was just compressing and decompressing air; it was not changing the state of the air. In single-phase refrigeration, we can't make use of the extra energy from changing states. In those cases, condensers would be gas coolers.

However, when you think about it, the process of refrigerating the space is a form of single-phase refrigeration; we don't change the phase of the air. So, we merely use two-phase refrigeration to drive single-phase refrigeration.


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