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1. Dec 2, 2014

PRIDES

I am a little confused, because I know how refrigerators work with a refrigerant and a compressor and heat exchanges, and I am looking to build one myself, just wondering because I was looking for refrigerator compressors online to buy. Do they have an inlet for refrigerant or is the refrigerant INSIDE of them already? It may seem dumb but all the how to's on refrigerators haven't the slightest mention of refrigerants.

2. Dec 2, 2014

Danger

It certainly shouldn't be included. If it is, don't buy it. I don't know whether or not the pump is where the intake port is located, but the whole system must be assembled and sealed before the fluid is introduced.

3. Dec 2, 2014

PRIDES

Does any compressor work with any refrigerant? Planning on using R134a BTW.

4. Dec 2, 2014

Danger

I don't think so. As with hydraulics, I suspect that different sealing and piping materials will have different chemical tolerances. Make sure that you obtain all components from the same supplier or at least check the spec sheets for each to see with what they're compatible. Also, I don't know about this at all, but there's an outside possibility that different fluids might require different pressures to work properly. All of the parts would have to be rated for whatever that is for the chosen fluid.
Definitely check with a professional, or at least someone here on PF who knows more than I do before buying anything. This stuff can be very dangerous if not treated with all due respect.

5. Dec 2, 2014

Staff: Mentor

Also there's the thermodynamic properties, which are specific to the compression ratio of the compressor. You need to make sure your compressor and refrigerant can work together.

6. Dec 2, 2014

PRIDES

Well, my aim is to design and build a small chest fridge. Would you happen to know much of refrigerators? Can I calculate the temperature difference using the equation q = m*c*t if the energy in the system remains the same? If the temperature of the heat exchange equalize with the surrounding temperature, then I could use for the radiator inside the fridge (amount of r134a (g)) * (c of r134a) * t = (mass of air in refrigerator) * (c of air)*t. Not sure if that could be applied to the exterior radiator though.

7. Dec 2, 2014

Danger

If it were me, I'd just take a bar fridge that's capable of working horizontally, laying it on its back, and building a cabinet around it.
Don't forget that you need adequate ventilation for air intake and heat exhaust.

8. Dec 2, 2014

PRIDES

I it were me, I would as well lol. But this is actually a project I might be funded for, so I'll take the chance to learn something new and to test the limits of my engineering ability.

9. Dec 2, 2014

Danger

Oh... that's different then.

10. Dec 2, 2014

Staff: Mentor

I'm an HVAC engineer, so not specifically refrigerators, but the thermodynamics of air conditioners is exactly the same.
No....but energy of what remains the same? Do you mean the energy absorbed inside and rejected outside? It isn't the same: the heat rejection includes the energy added by the compressor.
Refrigerators absorb and reject heat at constant temperature by vaporizing and condensing the refrigerant. So it is latent heat, not sensible heat that is being absorbed/rejected. The latent heat content is read from a table of refrigerant properties at different temepratures/pressures. But we're getting ahead of ourselves here -- this isn't a simple thing that can be learned in 5 minutes and uses just one equation.

You should start-off by reading-up on the thermodynamics of refrigeration: http://en.wikipedia.org/wiki/Vapor-compression_refrigeration

And if you'r really serious about doing this, you might want to pick up an intro thermodynamics textbook or even take a thermo class.

And what made you pick R-134a?
How far exactly do you need to go in making this from scratch? Can you cannibalize an old refrigerator for its parts, just re-using the whole refrigerant circuit as-is?

One problem here is depending on how serious of a project this is and where you live, you might not be legally permitted to do it yourself. Refrigerants are oftened controlled/regulated substances that require licensing to buy and work with yourself, depending on where you live and the specifics of the refrigerant, quantity and application. R-134a is being phased-out globally due to its high global warming potential.

There are also safety concerns: like if you are doing this in your basement there is a not small chance of killing yourself due to asphyxiation.

Last edited: Dec 2, 2014
11. Dec 2, 2014

PRIDES

Of course, I definitely do NOT expect to learn this in 5 minutes (I feel like I always give that impression :( ), thanks though. I probably will find a textbook or something I can use to learn a lot more. I do know a little of thermodynamics (definitely not enough at the moment), but when you say latent heat content, that is enthalpy, correct? So I should use latent heat of vaporization, of the refrigerant, AT whatever pressure and temperature it is at from wherever it is in the refrigeration cycle. (Sorry, I might ask questions too much)

12. Dec 2, 2014

Staff: Mentor

Latent heat just refers to heat from a phase change. Both latent and sensible heat are components of enthalpy.

13. Dec 2, 2014

PRIDES

I definitely could cannibalize an old refrigerator, only problem is I have none on hand (buying one might be easier than buying parts now that you mention it though). And no way I'd do this in my basement. In my garage or outside definitely.
I really haven't chosen any specific refrigerant, r134a seemed the most available when I was searching for refrigerant items during my experiments with r600a (see my earlier posts), but I do NOT want to harm the environment, so i'll find a safe refrigerant (r600a is flammable so).

14. Dec 3, 2014

Danger

That's what we're here for. Don't apologize for it.

15. Dec 3, 2014

Staff: Mentor

Yeah, we're just trying to ensure you know what you are getting yourself into.