Sciencemadness Discussion Board

Refrigeration Technology

Hermes_Trismegistus - 16-2-2004 at 22:41

Does anyone know of a site or easy to find book that explains the ins and out's of refrigeration technology?


In basic language?

Basically, I'd like to know how low temperature's and liquified gases and dry ice have been made in the past.

Saerynide - 17-2-2004 at 01:42

http://home.howstuffworks.com/refrigerator8.htm

Thats were I learned how a fridge worked :D

Iv4 - 5-4-2004 at 02:53

Belive it or not I actually do know a thing or two about cooling shit down.

The old(still used to this day I think)metho of making dry ice was to simply subject Co2 to immense presure(usualy with a piston)so it would go solid.

Most domestic frig's circulate CFC or a similer gas around pipes(like a radiater) to absorb heat.Liquid nitrogen and the sort is sometimes used for the large scale.

Some things(cant remeber off hand) have a heat in/electricvety out effect.This was used in that 'peltier' fad for cooling procesors.

Paramgentic materaials can store heat in thier field when a magnetic field is synched with them and then droped.This is one of the strongest coolers there is.I dont have the time ATM to go on further but I'll elaborate when I can.

If you have any Q's please feel free to ask :)

Liquid air manufacture

Esplosivo - 5-4-2004 at 03:15

This is a method of liquid air manufacture. Hope it will be of some help.

Carbon dioxide and water vapour have to be removed as otherwise they would solidify on cooling and block the piping og the liquification plant.

The air is then highly compressed (to about 200 atmp) and then passed through a coiled copper pipe. As it passes through a needle valve at the bottom of the tube it expands and cools down. The cooled air passes upwards through another tube surrounding the copper coil and cools the incoming compressed air, so that it in turn becomes cooler still. Eventually the air becomes so cool that it liquifies. The apparatus must be well lagged to prevent entry of heat from the environment.

The liquid obtained is pale blue in colour and is a mixture of colourless liquid nitrogen, liquid argon and pale blue liquid oxygen mainly. The gasses are then seperated by fractional distillation.

Attached is a simlified diagram of the apparatus used.

liquid_air_manufacture.jpg - 65kB

Iv4 - 6-4-2004 at 02:38

This has an excelent explanation of the magnetic cooling I was talking about.

Hey thats an excelent idea Explosivo, I thought about something similer once.It's basically YBCO or some other superconductive ceramic) wires twisted along with FAA(or some othe partamagnetic) wire.

Now when the magnetic cycles are started teh temp should keep droping untill the YBCO can go superconductive.

Bad link TV

Hermes_Trismegistus - 11-4-2004 at 10:17

Marvin - 11-4-2004 at 12:27

The link works here.

Paramagnetic cooling can get you absurdly low temperatures (<1mK IIRC), but only if you allready have very low temps to start with (like 4K).

If you compress CO2 it liquifies releasing a lot of heat, if you squirt this out of the nozzel it solidifies into snow. The CO2 'snow' is generally compressed into blocks with pistons and this is how dry ice is made.

avtr01 - 11-4-2004 at 13:01

"I think", if I remember correctly that the most common technique used to refrigerate gases (ie for oxygen, nitrogen, hydrogen) is a "Joule-Thompson" refrigerator. The idea is that when you compress a gas, it heats up, you then cool the heated gas to room temperature and let it expand in a "joule-thompson valve" and then you do that cycle a couple of times.

Joule-Thompson coefficient trivia

Magpie - 11-4-2004 at 20:48

I think Joule-Thompson expansive cooling is used to great practical advantage as avtr01 has indicated. It is also interesting to note that real gases can have negative JT coefficients as well as positive coefficients, depending on the pressure/temperature range involved. If the coefficient is negative the gas will heat when expanded. Ideal gases have JT = 0, neither heating nor cooling upon expansion.

Iv4 here

IvX - 20-4-2004 at 02:28

The low temps are for the supercundictive magnets?

Most ceramic superconducters work at liquid nitrogen temps.And it would gradually drop to that point(although it would take forever).

Marvin - 24-4-2004 at 09:14

The picture Esplosivo has posted gives the general idea.

The throttle valve cools the compressed air by JT expansion, and as it leaves to go back to the compressor that cools the incoming compressed air before expansion resulting in a furthur temperature drop. The result, is that the air gets cooler and cooler until eventually a small proportion of it liquifies and you start to get a yeild of liquid air. This is termed regenerative cooling, and was invented in 1895 by Linde (France) and Hampson (England).

Lindes actual aperatus was so badly insulated it took 2 days (with multi horsepower motors!) to get down to liquid air temperatures, but it did have one advantage over Hampsons, and at first glance it sounds like a disadvantage, its low pressure was much higher. JT cooling, the effect that cools the air passing through the throttle valve is a very weak effect in air, and the degree of cooling is proportional to the total drop in pressure, unlike adiabatic cooling in which the resulting temperature is proportional to the drop in pressure.

Hampsons cooler went from 50 atmospheres to 1 through the expander, thus getting 49 atm of cooling (since it varies with temperature, but is proportional to pressure difference, I'll give the pressure difference). Lindes went from 200atm to 50 atm, getting 150atm of cooling, but the recompressor only had to compress 4:1. That is to say for a given maximum pressure, Linde was getting 75% of the cooling, but only needing a 4:1 compressor doing the work. Hampson was getting 98% of the cooling, but his compressor had to go 50:1 volume wise. A second advantage of working with a 50atm low pressure, is that the boiling point of the gasses is higher, so you do less work to make the air liquid and the decreased thermal difference reduces loss through the insulation.

The problem is JT cooling is very very wasteful, at room temp its around a quarter of a degree per atmosphere for air. The gas when expanding, does no actual work (unlike adiabatic expansion, which will half its absolute temperature for a doubling in volume), and thus you are depending on molecular interaction effects for the cooling. Very few machines will work at liquid nitrogen temps, so making the gas do work is the hardest problem for improving things. State of the art, last I looked was to use the regenerative cooling setup, and to replace the expansion valve with a cryogenic turboexpander. This is basically a tiny fan which forces the gas to do work into a dummy load cooled by water and insulated from the gas. Efficiancies from 60 to 80% have been quoted and this gives you much more liquid air for a given amount of power into the compressor, and the best you could do industrially/semiindustrially last I heard.

A technology that still find uses are stirling engines, which are used to make smaller amounts of liquid air, from 1 litre a day to several litres an hour in typical lab machines. They are theoretically the most efficiant of any method, but the high complexity of the machine makes them useless for industrial production.

A method now abandoned for liquid gasses was the method of cascades, devised by Pictet for liquid oxygen. The basic idea is that if you cool a gas below its critical temperature, you can liquify it releasing a lot of heat. When you expand the liquid into a sufficiantly low pressure, you can force it to reduce the temperature to its triple point.

A fridge based on methyl chloride can go down to -103C and is used to cool ethylene below its critical temperature (9.5C), which can then be liquified and on expansion can produce a temperature down to -169C (its triple point) which is below the critical temperature of oxygen (-119C), which then can be compressed to a liquid. While going right down to the triple point values provides problems, there is sufficiant gap between the triple point and the critical point of the next lower gas to alow for non ideal operation under load.

Above its critical temperature, a gas cannot be liquified no matter how much pressure is applied. Cooling below its critical point alows latent heat of vapourisation to be used which is very effective for a given volume of coolent.

[Edited on 24-4-2004 by Marvin]

BromicAcid - 26-4-2004 at 19:36

Just a question, how much compression can be brought about by a compressor in the average window air conditioning unit in PSI or ATM or whatever, they're all interchangeable. I see them in the garbage all the time and there might be some experimentation to be had with these,

Mongo Blongo - 27-4-2004 at 12:12

How cold can thoes ammonia/hydrogen coolers get? I'm not sure how easy it would be to build one and get it to work well but they are interesting since they are powered by a flame.
More heat = lower temps???
These are the things I am talking about :

http://www.rvmobile.com/TECH/TROUBLE/COOLDOC.HTM

If you like that one, you'll love this one.

Hermes_Trismegistus - 27-4-2004 at 14:13

But ammonia/hydrogen systems don't take kindly to more heat input than they were designed for.

Don't play around, you will die.

Attachment: (ebook - free energy) - how to build a solar icemaker (1).pdf (347kB)
This file has been downloaded 1330 times

avtr01 - 27-4-2004 at 14:31

thats a pretty clever idea
I wonder if you could use the same principle with a different kind of chemical mixture to achieve colder temperatures

BromicAcid - 29-5-2004 at 11:40

The idea of cascade cooling the Marvin brings up and I've researched seems to be the best cooling technology that a mad scientist could go for to liquefy air. Currently I only have one air conditioner that I found in the garbage but and I therefor need more. Modification is simple on a mechanical level. Take out the blower motor and move the thermometer out of the way so it doesn't shut off the compressor. The cooling coils from the first air conditioner are wrapped around the compression coils on the second air conditioner and so on. The only difficulty is in changing out the coolant. My one unmodified air conditioner with the exception of the blower being removed and the thermostat being moved out the way will go down to -8C in a few minutes.

Marvin gave the gasses needed in his post a little up:
Quote:

A fridge based on methyl chloride can go down to -103C and is used to cool ethylene below its critical temperature (9.5C), which can then be liquefied and on expansion can produce a temperature down to -169C (its triple point) which is below the critical temperature of oxygen (-119C), which then can be compressed to a liquid.

Even if it does not work, what is lost in attempting it, around this time of year in my area air conditioners are in the garbage every week. The only investment would be in the replacement gasses, insulation, electricity, and some solder to shorten some of the piping or connecting your own.

jimwig - 29-5-2004 at 12:41

A cool subject - fur shure......

Ammonia absorption surely looks like something worth looking at closer. The technology is not that complex (ie fix it yourself) ---- just one little item. Who can get anhydrous liquid ammonia? not SWIJW.

Got a wiff once of NH4 - that was not a pleasant experience. KWIMB?

One could make HN4 but the corrosive factor is way out there. Stainless steel everthing.

Use the air liquefyer pictured earlier.

Seems like it all boils down to thermodynamics eh guys (and gals)? Hahhahhahahahha

Refrigerant 717 I do believe is the coolant in question. But a solar powered ammonia absoprtive unit would be completely off the grid!!!!

Modern Refrigeration and Air Conditioning is a pretty damn complete beginning book. Coffee table size with the repairman in mind.

BromicAcid - 29-5-2004 at 13:00

Jimwig, just for future reference, ammonia is NH3, NH4 is the ammonium cation and should be written NH4+ and is part of an ammonium salt such as ammonium nitrate NH4NO3. And the second time you write it you write HN4 which is an obvious mistake hopefully.
Quote:

One could make HN4 but the corrosive factor is way out there. Stainless steel everthing.

When making NH3 from OTC products corrosion is not really a massive problem, doesn't basically anything go for anhydrous ammonia with the exception of copper unless under stringent control?

As for the two gasses that would be necessary to continue the cascade cooling I have been wondering of the best methods to produce them. For methyl chloride I know of the reaction between methanol and HCl but does anyone have any practical information on the procedure? However I found an OTC source ;) I found a website that sells 'love meters' you know, a glass bulb at the top and one at the bottom connected my a series of tubes, well the site says the liquid contained within is methyl chloride! A couple of those could suffice hopefully without the distillation of HCl/CH3OH with a dry ice/acetone mixture for the condenser. But then about the ethylene, I've made it from H2SO4/EtOH fairly simply and H2O contamination in the product shouldn't be a problem as it is coming from conc H2SO4 but how to liquify the ethylene for insertion into the air conditioning system considering it has a Bp of -103.9 C maybe I should just find a place where I can buy a tank of it.....

[Edited on 5/30/2004 by BromicAcid]

IvX - 1-6-2004 at 04:05

I know we talked about this but paramag cooling might eb nice option here since from a construction standpoint i's somewhat simpler.

Those cristmas light controlers could even be used on a small scale to power a magnet wraped around ferro aomunium sulphate.

Perhaps even a section of paramag cooler could be attached to an AC?

basicelectromechanic - 7-12-2004 at 19:23

Quote:
Originally posted by BromicAcid
Just a question, how much compression can be brought about by a compressor in the average window air conditioning unit in PSI or ATM or whatever, they're all interchangeable. I see them in the garbage all the time and there might be some experimentation to be had with these,


A typical AC from the junkyard will use a R22 high temperature range compressor, suction runs around 60 psig and discharge around 275 psig when current approximates nameplate, these pressures are ballpark only, with an obstructed condensor discharge will approach roughly 400 psig before load overcomes torque arresting rotation or opening the motor protector ( inherent overload ). Capacity can be extrapolated outside of design range somewhat but it is not wise to project too far ( cylinder reexpansion volume, also R22 is known for high discharge valve temperature which is why it is seldom used in low temp application).
The newer equipment employing R410 exhibits higher pressures, condensors in new equipment typically operate around 600 psig ( I doubt any of it is in the junkyard yet, it is still new )
The cascade freezers I've worked with use either R500 or R22 in the high temp stage and either R13 or R503 in the low temp stage, negative 80C achievable. These are used in biolabs and in the manufacture of high end tantalum capacitors.
These high pressure refrigerants are very pricey and tricky, if you really do want to build a cascade I would suggest C02 for the low temp stage, it is affordable and it works.
Cascade lo temp stages are VAPOR charged and use a large vapor space in the evaporator. The absence of liquid in the lo temp stage in a condition of rest means the hermetic compressor will not explode from the pressure corresponding to ambient. During operation this large volume of vapor condenses into just enough liquid to let the machine operate.
Use of a 150 psi relief valve in the lo temp evap is typical.
To insure oil return ( lubricant is plenty viscous at 80 below ) suction flow should be downhill and an oil seperator in the discharge line would be prudent. Some machines use pentane in mixture with lubricant to improve return.

len1 - 6-1-2008 at 18:45

I was surprised to find out today that sale of refrigerants in Australia is restricted to refrigeration mechanics. The take about 3-4 weeks to come this time of year and charge the cost of the air conditioner for their services.

One workaround if you want airconditioning now is to synthesise your own. Is there a refrigerant that is relatively hassle free to make and is inert and non-toxic?

skippy - 6-1-2008 at 19:08

To me it seems an easier way would be to take the refrigerant out of a junked system. Also, I just read on wikipedia that propane can be used in systems designed for r22.

leu - 6-1-2008 at 20:20

Solar powered absorption refrigeration is probably one's most facile approach:

http://www.solarserver.de/solarmagazin/artikeljuni2002-e.htm...

http://en.wikipedia.org/PRIVOXY-FORCE/wiki/Adsorption_refrig...

http://www.solarhaven.org/SolarAirConditioning.htm

http://geoheat.oit.edu/bulletin/bull19-1/art62.htm

http://rexresearch.com/interefr/patents.htm

:cool:

undead_alchemist - 7-1-2008 at 08:51

Quote:
Originally posted by skippy
To me it seems an easier way would be to take the refrigerant out of a junked system. Also, I just read on wikipedia that propane can be used in systems designed for r22.


Yes you can use propane in an R22 system, it works very well.
Or you can use a mix of Isobutane and propane for use in an R12 system.

It only costs a few $ to fill a large system, when using propane.

You just have to make sure that its dry.

len1 - 17-11-2009 at 00:11

Well Ive finally got it done. Turns out you dont need any refrigerant to get one of those split-system air conditioners going. Its already included, the instructions (which nowadays contain mainly crap whose main aim is that the company dont get sued if youre a fool) just dont tell you that. I traced round the refrigeration circuit and found a large canister with R22.

The 2 copper pipe connectors to the indoor unit both have hidden valves, turned by hex keys, which flush the R22 into your pipes and indoor unit once youre sure the connection is air-tight. More than that, the return (gas) connector has a service port which can be used in 2 ways.

1) Once the R22 is in the copper pipes you attached, where it is now mixed with air (which at a working pressure of 6bar will occupy about 1/6 of your working volume since it doesnt liquify, and reduce efficiency), you can press on the pin in the service port, this will flush the gas out - 5/6 R22, 1/6 air. If your tubes are about 1 liter, you need flush out about 2 liters (measured by displacement in water) to reduce the content of air to about 1/6*1/4^2=10ml, which is acceptable. Theres about 500gms R22 in the system and its 86gms/mol, so thats about 6 moles. 2 liters is about 1/2 mole, so the loss is OK. It is certainly not true to say that you seriously compromise the system by doing so.

2) A better way, and one I chose, is to apply a rotary vacuum pump to the service port and reduce the pressure to a few microns, then open the R22 valve. The advantage of this (apart from no refrigerant loss) is that you can see if your flares are good and theres no leaks BEFORE letting out the R22. So theres no need to poke around with soapy water.

[Edited on 17-11-2009 by len1]