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richardb14
20-06-2011, 07:00 PM
Just looking through 2079 revision questions, does anyone know where to find a two phase mix on a mollier chart? :(

richardb14
20-06-2011, 07:02 PM
without trying to look stupid, is a two phase mix just a vapour?

install monkey
20-06-2011, 07:34 PM
just skip that question and make sure u get the others right-u only need 29 out of 40, hope u dont get the same questions as me, all about kyoto,motreal odp's,gwp's and other crap!-any consilation plumbers can pass it!!!

frank
20-06-2011, 08:19 PM
The quality lines on the Mollier chart refer to the 2 phase mix. Saturated liquid on the left and saturated vapour on the right of the inverted curve. (Dew Point/Bubble Point)

RatsPom
21-06-2011, 08:37 PM
6753

A 2 phase mixture occurs as the liquid refrigerant goes through the TEV and becomes a 2 phase mix of vapour and refrigerant, the "evaporation" process on the mollier chart.

Hope that helps

Quality
21-06-2011, 09:02 PM
Ok describe the state of refrigerant in the liquid receiver on a correctly charged system at 50% load.
I would say sub-cooled liquid at the bottom saturated vapour at the top ultimatley a saturated two phase mixture.
What a load of carp the 2079 exam is

richardb14
21-06-2011, 10:04 PM
even better, just saw this one:

a cylinder 50% full of R22 is at a pressure of 7 bar (gauge) when the temperature is 15'c. If the temperature was 25'c and the pressure was 7 bar(g), the refrigerant would be a

a) superheated vapour
b) sub-cooled liquid
c) saturated vapour
d) two phase mixture


now my understanding has always been that if you have a gauge pressure from a bottle and an outside temperature you can tell which refrigerant is in the cylinder using a PT chart, now this question is basically saying you can have R22 in a bottle at 7 bar and an outside temperature of 25'c and its still R22 at 7bar?

I have found out the answer to the question is a) superheated vapour.

now again am I just being stupid or does this actually make sense and I'm missing the point lol

install monkey
21-06-2011, 10:07 PM
2079 answer is still a 2 phase mix

richardb14
21-06-2011, 10:11 PM
See if push came to shove i would have opted for that anser as well, but the answer is supposedly a) superheated vapour

install monkey
21-06-2011, 10:13 PM
i argued about that-if you have a bottle of r22r-lets be correct here and u use 4-5 kg of gas out of it youve still got 5-8kg of r22r then u use the same bottle on a hot day and tip it upside down and youve still got liquid in the bottle the ratio may have changed but still it is a 2 phase mix. that said i might of got it wrong-

mikeref
21-06-2011, 10:58 PM
See if push came to shove i would have opted for that anser as well, but the answer is supposedly a) superheated vapour
The bottle could not have had liquid in it. If you had 7 bar at 15c and 7 bar at 25c, then you have no liquid there to change the bottle pressure. Two phase would mean liquid + vapour. Trick question..mike.

Tony
22-06-2011, 11:37 AM
a cylinder 50% full of R22

What does this mean?

What is the other 50% then?

mikeref
22-06-2011, 11:17 PM
What does this mean?

What is the other 50% then?
I would argue that this question would be invalid in the exam as R22, if bottle was really half full, could not be at that pressure at 15c or 25c. Question would be valid if it read... If an R22 bottle had 7 bar pressure @ 15c and then was raised to 25c and pressure remained the same, the refrigerant would be? Superheated vapour.

richardb14
27-06-2011, 11:32 AM
Right ok, having discussed this in great detail I have the answer, basically the only way r22 can be at 7 bar AND at 25'c is if the 'cylinder' wasn't in fact a 'cylinder' as we know it (bottle), it would have to be some kind of balloon and allow for the expansion, this being the case then the answer would have to be superheated vapour. It's a bit of a trick question as you literally cannot apply physics to the question.

I found an even better one than that as well! Apparently r290 has more direct GWP than R22 because it is flammable and would create c02, thus giving a GWP of 1, Although listed as a GWP of 0. Just the IOR being ridiculous once more. Look out for that one