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[Wickfut]

I'm not a HVAC technician or engineer. I want to build a desktop refrigeration system to help me understand the refrigeration cycle. I have a compressor, a couple of old condenser coils, and a capillary tube. I'm unsure of which way the refrigerant travels through the system, ie liquid from bottom to top in the evaporator and top to bottom in the condenser?

[Brian_UK]

Things to remember with refrigeration systems are:

1: Compressor pump vapour (gas), liquid breaks them.

2: Expansion devices (capillary tube, expansion valves) require liquid not vapour at their inlet.

So, the compressor pumps out hot high pressure vapour to the TOP of the condenser coil (assuming air cooled). The airflow over the condenser coil condenses the vapour into liquid which drains out of the coil.

The liquid then flows to the expansion device where it is expanded into a liquid/vapour mix to feed the evaporator.

I don't think it matters quite so much which way it flows through the evaporator but personally I would feed at the bottom. Liquid at bottom, vapour boiling off at the top.

If using a filter drier between the condenser and the expansion device make sure that the filter outlet is at the bottom to ensure a liquid seal.

[Wickfut]

Hi Brian, thank you for confirming what I had thought. Thank you also for the tip on the filter/drier, I have never heard this but makes complete sense.

I was also shocked by the lack of response by other members of this forum to my request for help. I seriously think that technicians don't know this stuff! I live in the far east where everyone has air conditioning and there are 1000's of so-called ac technicians. When reaching out to these guys for help, I was amazed at their lack of understanding of the refrigeration cycle. Not one of the many I spoke with fully understood superheating or subcooling.

Stay safe!

Chris

[ErHon]

interesting, where do u live ?
i live in Kaohsiung, and have the exact same experience thats why i taught myself , reading lots of scientific papers and refrigeration forum like this, i learned a lot, its not rocket science and a lot of things are just logical, at least for me.

Designing a specific refrigeration circuit however, is another story, this is where the true professional shines. I am speaking from experience :D , i have a 'thing' sitting here that is still unfinished, although i know what the problem is, i am now lacking time to continue tinkering on it.

I do refrigeration as a side-thing for friends and family only, and 90% the time i get to unf*ck other 'engineers' f*ckups.
You got to remember, you live in a country where most people just memorizing knowledge to get through the exam, most of them here have not the slightest clue how to apply that knowledge, 9 times out of 10 its just plain SOP, poking here and there, see if something changes and it gets worse every year. Good and HONEST engineers are hard to find, and they are most likely very busy. I personally only know one, and he stopped doing service and repairs, because he has to compete with the low pricing of all those "betelnut chewing blokes" that are out there. He works at the parts store now, much easier life, even when he has to deal with 'technicians' who clearly have not the slightest clue what part they actually need. They just put back in what they took out, even if its the wrong part another 'technician' previously put in.

- superheat
- subcooling
- recovery machine
- nitrogen purging during brazing
- nitrogen pressure-testing
- changing oil in the vac pump
- proper vacuuming with a proper digital vac-gauge (yes they sell them here now too)
ect...

Its all foreign stuff to them, refrigerant gets released into the air if brazing needs to be done on the unit, afterwards new refrigerant will be put in, customer pays anyway, and refrigerant is still cheap, R22 and R12 is still possible to obtain, so why bother buying a recovery machine.
And some of them, even sniff R22, https://www.youtube.com/watch?v=XHxjGuLbkIg
but hey, other people sniff glue.

now on to a solution to YOUR actual problem
i suggest you bring back all those parts you got from the scrapyard/recycling place ;) and get an dehumidifier from there, its much easier to modify into what you have in mind, its also way more compact and easier on the eye.

disassemble it half way so u can still turn it on and watch/learn how the refrigeration cycle works, needless to say, there is mains voltage, be careful, 110V can kill you too, and/or burn ur house down if you accidentally short something, get one of those extension cords that have a resettable fuse and hook it up on to that, just in case.

I build my little recovery machine out of an really old (made out of sheet metal) Westing house R22 dehumidifier. Its so much easier to bolt/weld/screw on the additional stuff (filters/oil separators/piping,gauges) if the shell is metal. Also no need to worry about the thing melting into a hump of plastic if i need to braze on it. But metal ones are hard to find nowadays.

I work sometimes on one of those scrapyard and can pick up lots of goodies, dehumidifiers usually either leaked their 'juice' or just have a float switch that doesn't get pushed in all the way (for what ever reason) if u get the water bucket out and push it in by hand it usually turns on. Broken running caps (if they have one) or broken PTC's are not uncommon too but easy to fix and in the 100-150nt$ range each.
Make sure u don't pay more than 500nt$ for it, they are worth almost nothing to the scrapyard, 60-100nt$ for the little compressor AND fan motor, thats it, the rest is plastic 2nt$/kg.

Another way would be one of those water dispensers that have a cooler inside (easy distinguishable on the 3 instead of 2 taps for hot/warm/cold water, if your chinese isn't that great). Few years ago i build a fish tank-water-cooler for a friend out of one of these, he just added a thermostat, and now the thing is chugging away for a few years already, didn't even need to open the refrigeration circuit. Its as compact as it can get. Basically just a insulated stainless mini water tank, with copper pipe wrapped around it. Cold refrigerant flows thru the copper pipes cooling the tank with the water inside or flowing thru it.
Added forced fan cooling to the condenser since it has now a higher heat load to cope with, normally those are convection cooled, no additional fan needed.

have fun tinkering

[Wickfut]

Hi, I'm in Taipei. I'm actually on the mrt at the moment. I will answer you in full when I get home.

My Line is: Taipei_chris. We sound like kindred spirits. Please add me.

[Wickfut]

When I first read your reply I was a little distracted.

What exactly does this mean: "skip the rant / bragging part if you just want to know a way how to tackle your project"?

Are you referring to me?

[ErHon]

I have no idea why i wrote that line, just deleted it.
Far to long ago, can't remember what was in my mind that day.

How's ur project going ?

[DeniseDArt]

A system that keeps a space temperature below atmospheric temperature by extracting a specific amount of heat per unit time with an external source of work provided to it and rejects the heat added to it into atmosphere. The system includes evaporator, compressor, condenser and a throttling valve.

[Brian_UK]

A system that keeps a space temperature below atmospheric temperature by extracting a specific amount of heat per unit time with an external source of work provided to it and rejects the heat added to it into atmosphere. The system includes evaporator, compressor, condenser and a throttling valve.
Please explain how this helps the subject of this thread.