RE: Dew point / bubble point?


Hi, I was a little confused when watching your videos, you say to use dew point for superheat, and bubble point for sub cooling. 

But, as far as I see it, dew point would occur in a condenser, and bubble point would occur in an evaporator? Would it not? 

Any info greatly appreciated

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6 Answers

@macmaw, I can’t comment yet but here’s my response to your last questions:


The adiabatic expansion makes it a little screwy but wherever that subcooled liquid crosses that threshold, that is the bubble point – i.e. where the liquid begins to evaporate, boil, etc. This happens almost instantaneously leaving the orifice of the metering device and this is what’s referred to as “flash gas”.  So in short, yes the liquid is only 100% coming out of the orifice but as soon as it enters the suction piping a good percentage of it “flashes off” so you never really “see it”. I made some changes to that first diagram to illustrate this in a more real-world scenario where there is subcooled liquid entering the metering device (the first image was 0F subcooling at the metering device). Hopefully you can see a visual depiction of about how much of that gas flashes off coming out the metering device.


Rookie Answered on August 22, 2018.
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