View Full Version : Pressure in a R-407C cylinder

16-06-2016, 01:45 AM
Hi guys,

I have a bet with a friend. The question is:

We have a cylinder with R-407C in a store at 25C. Initially the cylinder is full of liquid, and we start to leak refrigerant from the cylinder so we have different states with a) 100% liquid, b) 75% liquid, c) 25% liquid and d) 0% liquid. Among the different states we let the cylinder reach the equilibrium temperature with the ambient, having always a temp. of 25C before the pressure measurement. We need to know the pressure in the bottle in the states a), b), c), and d). Important: The leak of refrigerant is always in liquid, never vapour, for the blend not to be corrupted.

Does somebody have the answer?

Thank you in advance!

16-06-2016, 06:13 AM
Until the last drop of liquid comes out the bottle the pressure should be the same. Referring to a pt chart, read the liquid value which I make 58psi.

Cheers, Andy.

16-06-2016, 01:23 PM
Hi Andy, then, we have no pressure glide? How match that measurement to the mollier chart i which we see different pressures at different % of liquid for a temp. given?

16-06-2016, 05:27 PM
Was taught years ago, to find what refrigerant in unmarked cylinder, check cyl temp and pressure at that temp and find corresponding refrigerant for that temp and pressure on your slide rule, bobs your uncle. But there were only 3 main refrigerants then, R12, R22 and R502. As already stated, quantity of refrigerant in cyl was irrelevant, be it full or partial, pressure always the same.Think that was part of the f gas years ago.

16-06-2016, 08:00 PM
Thank you for your answers. I know the relation P-T is constant in state changes. But i thought it is the truth for pur refrigerante or azeotropic blends. But, if we hace a zeptropic blend... is it also true? When i look at the moolier chart for R407C i ser i pressure glide between the bubble Point and the dew Point for a given temperature. So, how must i interpretate that?
Thank you for your help!

16-06-2016, 08:43 PM
The glide occurs only when changing state from liquid to gas or the other way round.

Your refrigerant in the bottle isn't subcooled, just at its saturation point so it will lie somewhere along the left hand line of the middle bit of the chart at the corresponding pressure.
Each time you take a bit out the refrigerant will remain at its saturation point. When all the liquid has gone you will start to creep across to the right hand side crossing the lines of constant quality but also start to lose pressure.

A bit abstract but you've got me thinking how the line across the chart would go as the bottle empties out. Somewhere to the bottom right but still on the saturated vapour line but when you are left with nothing not sure where that leaves you on the chart. Best I stick to my comparator!

As I think about it not sure how you move across to the left as your R407C is changing composition so the PT chart becomes redundant I guess. I would like to experiment but as you know, (initiate sarcasm mode) F Gas police are everywhere these days and their highly trained noses would have me in no time (sarcasm mode off).

16-06-2016, 08:51 PM
What difference does it make how much vapour is on top of the liquid? It's the mean temperature that determines the pressure, so long as there is some liquid left in the container.

16-06-2016, 09:07 PM
Read a little, read a lot