Mix and match physical components - can I do this?

Hi everyone,
( Because my knowledge is limited and your site is so extensive I'm unclear as to the best place to post this question. - please move it if it is necessary.)

I'd like to build something that will freeze a marble slab or a stainless steel plate to make ice cream.

First, I understand the theory or basic concepts of refrigeration; I even put ***** into my old 68 Cadillac way back in 1975.

That being said, I have always liked the GM A6 compressors from those older cars. They had an oil reservoir which I think is better than oil in the ***** - but I could be wrong, they were very efficient as I remember. I did a little research on this...

Here's the rundown on the compressor.
The model A-6 compressor was used by General Motors for more than 25 years. The A-6 was Frigidaire's first axial designed compressor. This compressor used a cast-iron cylinder and heads with a steel case and "swash" plate. The A-6 designation related to its axial design and the fact that it was a 6-cylinder compressor unit. The interior of the compressor also had an oil pickup and sump system to lubricate the internal parts. The A-6 compressor will push out 27,000 BTUs at 2,000 rpm (2.25 refrigeration tons) and as high as 42,000 BTUs at 4,000 rpm with a discharge rate of 240 p.s.i. That's enough cold air to cool a small house (most home window-mounted air conditioners are only rated from 5,000 to 12,000 BTUs). The compressor functions much in the same way an engine does but without the ignition and combustion strokes. An A-6 is rated at 1.5-inch bore with a 1.2-inch stroke and 207cc displacement. That's about 12 1/2 cubic inches. The A-6 is also highly adaptable. It can run in 6, 12 or 24-volt systems if you install the proper clutch coil.

They are a pretty resilient unit too; they can turn consistently at 6,500 rpm all day without overheating, and you can turn them in either direction and they will function in the same way.

I'm thinking that if I scavenge an old Car AC system with the A6 compressor, I can use the condenser, the dryer, the sight glass gadget and the expansion valve.

The evaporator is what needs to be different and it needs to be rectangular and flat so it can be put under a marble stone.

My question is this. Can I use the evaporator from an old freezer?
Here are some picture examples of what I'm thinking.

If the curve of this could be flattened
http://image.made-in-china.com/4f0j0...d-Ice-box-.jpg

If the tubes of these could be bent or cut and refastened to make it flat
http://image.made-in-china.com/4f0j0...vaporator-.jpg
http://image.made-in-china.com/2f0j0...Wire-Tube-.jpg

Can these things be connected in series?
http://i00.i.aliimg.com/photo/v2/537...evaporator.jpg

http://www.bizrice.com/upload/201201...evaporator.jpg

http://i01.i.aliimg.com/img/pb/479/7...744479_179.jpg

or can I make one out of copper tubing that sits on a plate?

How I got this idea is that I had a friend way back in the 80's that used an A6 to cool his house. He built an A-Frame out of two condensers and had a fan blowing upwards through that and he use a different evaporator. A washing machine electric motor powered the condenser. It worked GREAT!

I don't have an hands on experience or working knowledge about this regarding the size of the evaporator vs the size of the condenser.

I'm guessing that A6 would have plenty of power to do the job.

Any help or suggestions would be appreciated.

Thanks!

beast thing I would say is make the evap out of lots and loats of 3/8th pipe, use a roller or some thing to press them down to an olval shape then morter them onto your marble slab, then insulate the sides and bottom with polyurethane foam, use card board painted with wax to mold the foam as it is sprayed in.

that will be the start if the slab is larger then 4*8 feet use 1/2 inch pipe

you'd have to use a vfd with the drive motor to tune the compressor to your evap, thats where I'll stop for now and come back later once I think the system out more.

Quote:

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Originally Posted by The MG Pony

beast thing I would say is make the evap out of lots and loats of 3/8th pipe, use a roller or some thing to press them down to an olval shape then morter them onto your marble slab, then insulate the sides and bottom with polyurethane foam, use card board painted with wax to mold the foam as it is sprayed in.

that will be the start if the slab is larger then 4*8 feet use 1/2 inch pipe

you'd have to use a vfd with the drive motor to tune the compressor to your evap, thats where I'll stop for now and come back later once I think the system out more.

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Thanks for the reply.

Great suggestions. What are you suggesting for the mortar? I'm assuming that it would need to me non corrosive. Just as a passing thought, could Silicone or Epoxy be used as the adhesive?


The surface area of either the Stainless plate or the slab would be small. If circular it would probably not be more than 2' in diameter and rectangular about 3' or 4' foot long and about a 1 1/2 foot wide..

I don't know what vfd means (guessing - variable force drive???) and I have no clue as to what you mean by tuning a compressor to an evaporator. That's an interesting concept. Does tuning also apply to condensers as well? I'm sure that there are formulas - I'm good at math I just don't know any of the parameters.

Is an evaporator rated by size or capacity - length / diameter of the tubing? Number of coils?

Quote:

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Originally Posted by wizarddrummer

Thanks for the reply.

Great suggestions. What are you suggesting for the mortar? I'm assuming that it would need to me non corrosive. Just as a passing thought, could Silicone or Epoxy be used as the adhesive?


The surface area of either the Stainless plate or the slab would be small. If circular it would probably not be more than 2' in diameter and rectangular about 3' or 4' foot long and about a 1 1/2 foot wide..

I don't know what vfd means (guessing - variable force drive???) and I have no clue as to what you mean by tuning a compressor to an evaporator. That's an interesting concept. Does tuning also apply to condensers as well? I'm sure that there are formulas - I'm good at math I just don't know any of the parameters.

Is an evaporator rated by size or capacity - length / diameter of the tubing? Number of coils?

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The trouble with your project is you are starting from the wrong point.

In refrigeration the evaporator is sized first and then the compressor is
chosen accordingly so when MG says "tune your compressor to the evaporator"
he means that at some time in the future you will have to size the compressor
appropriately for the evap.

The VFD is Variable Frequency Drive (inverter) and it could be used to run the compressor
at a variable speed which in turn would help "tune" your comp to the evap.

If you using a stainless steel plate then braze the evap to it to get good surface contact.

As MG says this will require a lot of work and can't be done over one post, so
start with the evap and take it from there.

Regards

Rob

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Ok thank you rob, you covered the questions exactly as I meant to elaborate on! so I can skip to the next point!

As rob said the evap is normally sized for the load, and the load is usually calculated based on how fast we want to freeze our substance, as the marble will act as a cold bank sizing becomes not as critical as it normally would be for an air system, more pipe the better to a point, the game is surface area and as much contact as possible!

If you use epoxy it must be a type with hi thermal conductivity, we all know most mortars conduct heat better then most silicons hence why I said for mortar over all ells. with that size I'd use half inch, I'd wing it here and figure you'd need between 6.5k btuh for holding and about 12k btuh to pull down for speed, but a 6.5Kbtuh compressor will do the job just as well all the way through just slower for geting down to final temp. for making ice cream we'd be wanting about -6C ? seems like a good workable number for hand mixing aut to be soft enough?

Now here is the very important part as we need to select a refrigerant, so how will this system be tested and started up, do you have a professional who will be doing the final testing and charging for you? and what sort of running environment will it be in?

As a point of reference, an economy model soft-serve ice cream machine with one station has a capacity of 9.5 Btu/hr. A cold plate, being exposed to the atmosphere, will require extra capacity just to overcome heat absorption from the air.

I did some work with a food chiller many years ago that used glycol as the exchange medium and I believe some soft-serve units use this as well.

Thermal bonding epoxies are usually filled with aluminum powder plus a little fumed silica as a thickener. This formulation should not react with a copper coil.

Silicone has poor thermal conductivity and is often catalyzed with chemicals that react with copper. Brazing copper to stainless plate might also give you trouble. Stainless has a tendency to deform under the heat of brazing.

I couldn't find any literature on stone cold plates. I suspect they are bonded to solid aluminum evaporators or glycol cold plates made of 18-8 (SAE 304) stainless.

You may need something colder than a -6C at the evaporator. I'm guessing -10C may even be inadequate. Slow phase change of the custard leads to ice crystal growth which makes a gritty texture.

Quote:

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Originally Posted by The MG Pony

Ok thank you rob, you covered the questions exactly as I meant to elaborate on! so I can skip to the next point!

As rob said the evap is normally sized for the load, and the load is usually calculated based on how fast we want to freeze our substance, as the marble will act as a cold bank sizing becomes not as critical as it normally would be for an air system, more pipe the better to a point, the game is surface area and as much contact as possible!

If you use epoxy it must be a type with hi thermal conductivity, we all know most mortars conduct heat better then most silicons hence why I said for mortar over all ells. with that size I'd use half inch, I'd wing it here and figure you'd need between 6.5k btuh for holding and about 12k btuh to pull down for speed, but a 6.5Kbtuh compressor will do the job just as well all the way through just slower for geting down to final temp. for making ice cream we'd be wanting about -6C ? seems like a good workable number for hand mixing aut to be soft enough?

Now here is the very important part as we need to select a refrigerant, so how will this system be tested and started up, do you have a professional who will be doing the final testing and charging for you? and what sort of running environment will it be in?

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Thanks for the replies; sorry for not responding sooner. I've been ill the last few days.

Before I continue; the reason for my title: "Mix and match physical components - can I do this?" is that I am trying to find the absolute cheapest solution to do a proof of concept for this venture. By mixing and matching parts I am hoping to find a solution that uses off the shelf / pre manufactured items that are already fabricated for me (condenser, evaporator etc., and other components in salvage yards, metal reclaim yards, junk yards - wherever I might find an old fridge or complete AC system in a car that might work, to see if I can piece it together very, very inexpensively.

If the concept pays off; and there is a reasonable cash flow, I can invest in something more lavish.

Okay.

I get what you're saying about conductivity. In the back of my mind I had a slight concern when I mentioned Silicone.

I'm still confused about the mortar? Are we talking about Plaster? Cement? Something else?

How is this applied?

I learn something new every day, and this forum has opened my eyes to some new things - thank you.

Your replies lead to more questions for me. You talked about selecting refrigerants.

The unit I have in mind could be used indoors or outdoors and the climate where I am thinking about doing this would be very hot and somewhat humid. So the capacity would have to be pretty strong; The capacity of the system would have to render the surface to freezing very quickly and keep it there efficiently. Hence my affinity for the A6 compressor as it has some brute force.

When it comes to testing I can get a pro to work with me.

So, we begin. I will let you, the experts make recommendations regarding which Refrigerant out of the more than 350 or so I saw listed the Wikipedia.

How do I, as you say, size an evap for the load? How can I determine what my load is and knowing that, how do I determine the equivalent evaporator. I'm guessing it has to do with the type of refrigerant / pressure / expansion valve and volume of refrigerant in the evaporator?

Thanks.

Well for cheapnes and the environmental aspects R-290 wether tech grade or BBQ grade will do very nicely, since you can have a pro with you safety is in a good form, perticuler ensuring system is leak free, properly pressure tested and vacuumed. And will certainly yeild the temps you'd be aiming for with good efficiency. and another bonus is R-22 txv's will work with it un modified other then slight super heat adjusting.


evap will need to be about 3/8 or better copper pipe fassioned in a way you can achieve the max in surface area contact with your slab. The mortar can be any good mortar that will not react with the copper!

Now assuming the slab can be insulated in all areas othe rthen the tope and with the 9.5K btuH the other fellow referenced I'd say go with a 1Ton eq txv (Perhaps even a 1.5Tr balanced port) should offer very rapid pul down with good throttling at load & Temp.

Hope fully others will re-enforce this or have better ideas. But thats some ideas off the top of my head.

Side thought here is for such an aplication you need veriable capacity as opposed to cyclice control, so that the unit is all ways running never turning off, but to control temp we control compressor speed. this can be don manualy via engin throttle or a motor speed controller.

but it can be automated with the right control combos, others should be able to specify such a controll.

Quote:

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Originally Posted by The MG Pony

Well for cheapnes and the environmental aspects R-290 wether tech grade or BBQ grade will do very nicely, since you can have a pro with you safety is in a good form, perticuler ensuring system is leak free, properly pressure tested and vacuumed. And will certainly yeild the temps you'd be aiming for with good efficiency. and another bonus is R-22 txv's will work with it un modified other then slight super heat adjusting.


evap will need to be about 3/8 or better copper pipe fassioned in a way you can achieve the max in surface area contact with your slab. The mortar can be any good mortar that will not react with the copper!

Now assuming the slab can be insulated in all areas othe rthen the tope and with the 9.5K btuH the other fellow referenced I'd say go with a 1Ton eq txv (Perhaps even a 1.5Tr balanced port) should offer very rapid pul down with good throttling at load & Temp.

Hope fully others will re-enforce this or have better ideas. But thats some ideas off the top of my head.

Side thought here is for such an aplication you need veriable capacity as opposed to cyclice control, so that the unit is all ways running never turning off, but to control temp we control compressor speed. this can be don manualy via engin throttle or a motor speed controller.

but it can be automated with the right control combos, others should be able to specify such a controll.

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Thank you so much for the reply.
Please explain what a txv is.
I'm guessing, the way you continued it has something to do with physical components and that anything that works with R-22 will work with the r-290.

Sorry but I don't know what 1.5Tr balanced port is. You used a lot of vocabulary (and abbreviations) that I am not familiar with.

Why would it be better to have the compressor always on using variable speed to control the temperature?

Does this mean that using the Frigidaire A6 is still a good option for the compressor? It would be easy to connect a variable speed motor to it. What's the lowest rpm that a compressor such as the A6 (if you think that that is still a viable option) can operate?

Thanks for the clarification about the mortar.

You mentioned 3/8 copper pipe. Is there anyone that can tell me if the total amount of tubing makes a difference. In other words if I were to calculate the interior volume of the tubing; given a certain length, are there any calculations that tell me if I am above or below some threshold?

If I bend the copper tubing similar to a sine wave how close should the adjacent tubes be to each other? One inch? two inches?

Truth is, I don't even know enough about this subject to ask intelligent questions; which is why I came to this forum.

Thanks again.

The A6 is still a great canidate for the project.

the TXV is the device to expand the refrigerent to make it do work, the balanced port type act in a very stable way even if the rest of the system is floating a bit on the head pressure. The 1.5tr is the size, so it would be at 17,000btuH to start and at the end temp would be 9,000btu at the low end of its range

you would use 2 length of 1/2 to 3/4 copper, then run your 3/8 squiggles side to side tightly packed on it so it looked like a dense radiator

the reason we want it to all ways run is to keep your plate at it's ideal temp in a hot ambientI take it this is sort of a novelty soft serve idea? where you make it on location and sell off the plate? so by keeping the unit running we maintain percice temp of the product.