Exspansion Valves,

[cool runings]

.

Wet bulb and Dry bulb refer to humidity measurement for air,

but there is Bubble point and Dew point or Liquid tempreature and Vapour temp.

It has everything to do with Zeotropic refrigerants with a large temp glide.

Take R407c for example... R407c has a 6 deg glide.

That means it starts boiling and finishes boiling over a 6 degree range.

The technical term is the saturation temperature.

If water boils at 100 degC in an open pan then it has a saturation temp of 100 degC

R407c saturates over a six degree range at any one given pressure.

So if you measure the superheat at the liquid temp or Bubble point then that
is the start of the glide process and it will take six degrees to fully turn to vapour at
the Dew point.

If you are setting the superheat setting to six degrees and measure the temp from the
Bubble or liquid temp, then when the liquid boils off it will still be at the Dew point temp
and therefore the risk of some liquid leaving the evaporator is possible.

All the best

coolrunnings

.