In the refrigeration cycle, the refrigerant must undergo a change in state in order for the heat to be absorbed from the environment.
The refrigerant has the property of changing its state from liquid to vapor at normal room temperatures.
Have you ever felt your skin becoming cool whenever you put alcohol on it? Or even when a bit of petrol spilled onto your hands? It's because, the alcohol or petrol has evaporated when it comes in contact with your skin.
The result - heat is removed from your skin, and it feels cool!
In a closed-loop refrigeration circuit, the change of state from liquid to vapor is achieved mechanically by pressurizing the liquid at one end and forcing it through a small opening at another end.
Once the liquid comes out from the small opening, it expands into vapor. The effect is similar to the spray you get when you restrict the outlet of your garden hose. But water is not a refrigerant. It does not feel cold because it does not change to a vapor.
Bad example. But you get the idea? Pressurized restriction causes spray at the other end.
In many refrigeration circuits, the small opening is made in the form of a thermostatic expansion valve. Many other designs make use of small capillary tubes. In big chillers, orifice plates are common.
All of them achieve the same purpose - to expand the liquid to become vapor and to cause the evaporator tubes to become cold.
Until next time…
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