vapour compression cycle

[Brian_UK]

Think of the refrigerant in a storage cylinder, it is at one pressure and one temperature yet, it contains liquid with a gas on top.

The example your tutor has given is also correct but not with at one temperature as asked in your first question.

Your second description is of a working system.

As one Brian to another, what is your overall knowledge of refrigeration systems? We tend to assume that you are doing the F-Gas as a fore-runner to something else.

edit:
Have a look at this Sporlan pipework diagram, ignore most of the equipment but concentrate on the main components, namely, compressor, condenser, expansion device and evaporator. The different states of the refrigerant are shown in different colours and now try a relate those states to the temperatures and pressures given by your tutor.
http://www.sporlanonline.com/5-158_092008.pdf

[brian connolly]

[QUOTE=Brian_UK;244854]

The example your tutor has given is also correct but not with at one temperature as asked in your first question.

thanks brian, not sure how to do these quotes and things so bare with me. not sure what you meant by above quote. and you said my second description was of a working system which is correct but im still not sue how a refrigerant can be a vapour at a low temp and high temp and a liquid in between. obviously im picking something up wrong but can you see what im trying to say? i havent looked at your link yet as am tired and probably wouldnt be able to take it in.

to answer your question im a plumber and have installed a lot of heat pumps which got me interested in refrigeration, i have done a basic course on the vapou compression cycle but the tutor only explained at what stages the refrigerant was a vapour and when it was a liquid. now im doing the f gas course and there is temperatures involved and they are confusing me.

[brian connolly]

looking at your post again brian, your point about the cylinder may be the thing that clears it up for me. so it is possible to have a refrigerant at a certain temp/pressure and be either a vapour or a liquid??????

[Brian_UK]

so it is possible to have a refrigerant at a certain temp/pressure and be either a vapour or a liquid??????

Yes, simply.

Refrigeration cycle, in simple terms...Pressures and temperatures for indication only.

Compressor sucks in low pressure vapour, 1bar 5°C, compresses vapour and discharges it (act of compression generates heats, think bicycle pump) now 10bar at 60°C.
High pressure/temperature vapour enters condenser at 10bar 60°C, air blown over condenser to cool hot vapour. Vapour now cools and condenses back to a liquid, temperatures has dropped to 30°C but pressure still at 10bar.

10bar liquid now passes through expansion device which lowers it pressure from 10bar to 1bar to enter the evaporator. Act of dropping pressure reduces temperature and you have a mix of liquid/vapour at the start of the evaporator. Pressure of 1 bar remains and temperature now down to 5°C as the vapour leaves the evaporator and gets sucked in again by the compressor.

A very rough description, yes it is late, but hope it helps a bit.

[brian connolly]

thanks brian

im not sure if you have cleared it up for me or confused me even more. you mention the refrigerant being at 10 bar and 30 degrees and 10 bar and sixty degrees. if this is the case i have got this completely wrong. our lecturer gave us a slide rule and told us the pressure /temp relationship was constant so looking at the slide rule r404a at 10 bar is 20 degrees c. because of this slide rule i assumed that when r404a was at 10 bar it always had to be 20 degrees c. i dont expect a reply as its but will be up for another while anyway trying to get my head around this

thanks again brian

[MikeHolm]

Yes, simply.

Refrigeration cycle, in simple terms...Pressures and temperatures for indication only.

Compressor sucks in low pressure vapour, 1bar 5°C, compresses vapour and discharges it (act of compression generates heats, think bicycle pump) now 10bar at 60°C.
High pressure/temperature vapour enters condenser at 10bar 60°C, air blown over condenser to cool hot vapour. Vapour now cools and condenses back to a liquid, temperatures has dropped to 30°C but pressure still at 10bar.

10bar liquid now passes through expansion device which lowers it pressure from 10bar to 1bar to enter the evaporator. Act of dropping pressure reduces temperature and you have a mix of liquid/vapour at the start of the evaporator. Pressure of 1 bar remains and temperature now down to 5°C as the vapour leaves the evaporator and gets sucked in again by the compressor.

A very rough description, yes it is late, but hope it helps a bit.

Brian, the one point in your description that stands out for me is the fact that upon entering the condenser, you can go from 60C/10bar to 30C/10bar (the pressure does not reduce). It would seem to me that in order to NOT have a pressure reduction, the volume in the system, condenser and subsequent pipework would have to be much smaller than that which moves the vapour and this is why the pressure does not change much.

The act of condensing the vapour to liquid should, at first glance, reduce the pressure as well as the temp (regardless of area volume). The non changing pressure side of this can be confusing to people.

[brian connolly]

exactly whats confusing me, if you look at the gauges a certain pressure has a certain temp,is this not always the same regardless of state

[Brian_UK]

Brian, the one point in your description that stands out for me is the fact that upon entering the condenser, you can go from 60C/10bar to 30C/10bar (the pressure does not reduce). It would seem to me that in order to NOT have a pressure reduction, the volume in the system, condenser and subsequent pipework would have to be much smaller than that which moves the vapour and this is why the pressure does not change much.

The act of condensing the vapour to liquid should, at first glance, reduce the pressure as well as the temp (regardless of area volume). The non changing pressure side of this can be confusing to people.

Good point Mike, I was trying to keep it as simple as possible just before bedtime. I did say however that the act of cooling the vapour has reduced it's temperature, pressure losses are more than needed here I think.

Mind you, I'm always open to criticism.

[chillerman2006]

The act of condensing the vapour to liquid should, at first glance, reduce the pressure as well as the temp (regardless of area volume). .

Hi Mike

download these moving pics mate

boyles law https://rapidshare.com/files/3621119...yles_s_law.gif

charles law https://rapidshare.com/files/1749579...arle_s_Law.gif

picture paints a thousand words as they say !

R's chillerman