Maybe I may respond to post by inserting blue text within your quote.

Quote Originally Posted by desA View Post
I think that you are confused on the technical definitions of x (vapour fraction).

Thankyou for your kind interpretation of my understanding of X - the vapour fraction.

If you do want to refer to 'x' then it may be wiser to keep this to the LP portion of the graph - this is the traditional place in which it is used in relation to the vapour compression cycle.

Well, X occurs in the condenser and the evaporator and always has I beleive, in fact in seems to occur everywhere within the bell (inside the saturation line). I take note of your desire to more precisely position the quoted X and propose XC and XE for condenser and evap respectively, XCT will be the value somewhere along the cap tube.

The reason for this is that the cycle is defined on full saturated liquid at point 3.

Not sure that is an absolute! There are instances when point 3 (h3) is inside the saturation curve, for instance in a classic freezer. You might like to give some references for the cycle being strictly 'saturation'. Otherwise to me its a diagram that descibes what is happening and can have h3 wherever it may be.


There should be NO vapour fraction going into a cap tube, or TXV - none...

I hope you are absolutely sure about that! There seems to be some (many in fact) references that show vapour entering the cap tube is part of the whole process especially when operating in freezer temperature ranges (all else being normal (average) world conditions). In fact Supco report on a design that actually introduced vapour into the cap tube entrance.

"In the early 1960s, a manufacturer of window air conditioners took advantage of bubbles entering a cap
tube by placing a small heater around the strainer before the cap tube inlet. The thermostat was in
reality a rheostat that controlled the intensity of heat to the strainer—which in turn regulated the
amount of bubbles entering the cap tube. The first stage of heat to the strainer was to reduce the
subcooled liquid temperature (increasing the bubble length). The second stage was to create a boiling
action, in various heat intensities, to decrease the overall efficiency of the evaporator."
From
THEORY OF THE CAP TUBE AS A
REFRIGERANT CONTROL
By Henry Ehrens, Sr Engineer - Sealed Unit Parts Co., Inc
There are many other referances that you may wish to discover.


If there is, then the design needs to be altered - the cap tube is not meant as a total system imbalance corrector.

You might like to clarify that comment and provide some eveidence that it is not the total system imbalance corrector, preferably something published rather than conjecture.

If you do want to refer to the vapour fraction in some other place, then it may be wiser to state clearly 'x=0 @ HP' or something similar, to avoid confusion.
Chef