Refrigeration advice.

[piman]

Hello all,

I wish to build a water cooler (ice bank) using an IBC (1000litre capacity) and need to size the evaporator tubes to put into this vessel. The condensing unit I'm looking at is about a 1 1\2 H.P. unit.

Are there any refrigeration engineers out there who could advise?

Alec

 

[Omniata]

What are you actually trying to cool?!

An IBC ice bath is a bit big for a standard cooler freezer to maintain at low temp, especially freezing...

How do you plan on cooling it? With a freezer compressor/cooling unit modified?

Any diagrams might be useful...

 

[piman]

Hello Omniata,

the cooled water is to be pumped into a water jacketed 2,500 litre beer fermenting vessel and the beer needs to be chilled to about 5 degrees C (from 22 degrees C) over a period of 24 to 36 hours.

Pubs use a similar system but with a much smaller unit. A water tank with small bore pipe (approx 6mm) is coiled around the perimeter of the water tank and is the evaporator of a refrigeration unit. The evaporator pipes develop a build up of ice around them.

I just want to make a larger version but need some guidance in the diameter and length of pipework to make up the evaporator? Obviously the IBC will be well lagged also.

Alec

 

[Omniata]

They will probably have a freon based coolant in them as well......

Leave it with me, I'll put my thinking cap on and get back to you with a water based solution.
You can use a 50:50 mixture of salt and ice in the IBC to get the cooler down to -18°C! Then leave the tap open to let the water drain out...

When I finish work I'll get on it straight away...

 

[drivewasher]

Hello Omniata,

the cooled water is to be pumped into a water jacketed 2,500 litre beer fermenting vessel and the beer needs to be chilled to about 5 degrees C (from 22 degrees C) over a period of 24 to 36 hours.

Pubs use a similar system but with a much smaller unit. A water tank with small bore pipe (approx 6mm) is coiled around the perimeter of the water tank and is the evaporator of a refrigeration unit. The evaporator pipes develop a build up of ice around them.

I just want to make a larger version but need some guidance in the diameter and length of pipework to make up the evaporator? Obviously the IBC will be well lagged also.

Alec

IIRC the pub coolers you describe use a solution of glycol and water between the evaporator and the 6mm pipes that contain the beer.
This is because you can get glycol (antifreeze) solution down less than 0 degrees

 

[Omniata]

One suggestion is to take the output from the cylinder to be cooled and feed it into a reservoir tank. Then pump from here through similar sized tube/pipe up to the IBC then take the pipe into narrow copper pipe through an adaptor.
The narrower the better as the increase in pressure will cause the liquid to heat, thus cooling it and creating a pressure drop at the other end will cool it further, as it passes through the ice bath...

You'll need an ideal mixture of 80:20, glycol:water for continuous cold cooling or more glycol if you want to go colder in the cooling element...

Edit: It's better to have the hot feed enter at the top so the heat rises in the IBC and less heats the bottom. It could approach -10°C in a 50:50 ice:salt mixed coolant

 

[eil]

I see that your in Shropshire, do you know of ant bulk milk tank engineers, as I understand a fullwood 5000 ltr has around a 4hp condensing unit on them working on R404a, or do you know any farmers with the older ice bank type of tanks you could then copy!. most of them are DX systems now I would think. Milk is cooled from 25 to 4*c in about 10 hrs in the ice bank type if I recollect. if you want to do your own calcs there is this free program.
http://www.et.web.mek.dtu.dk/Coolpack/UK/reg-download.html

 

[rtbcomp]

........ Then pump from here through similar sized tube/pipe up to the IBC then take the pipe into narrow copper pipe through an adaptor.
The narrower the better as the increase in pressure will cause the liquid to heat, thus cooling it and creating a pressure drop at the other end will cool it further, as it passes through the ice bath...

...

Does that work for a liquid? I know it works for a gas. Couldn't you use compressed air?

 

[Omniata]

Does that work for a liquid? I know it works for a gas. Couldn't you use compressed air?

Water and glycol has a higher specific heat capacity and density compared to compressed air, it acts like a sponge absorbing heat into it.
You could use compressed air, however to get the same effective cooling effect you'd need a tremendous flow from a compressor...

Edit: You can't see the effects on a liquid unless there are two extremes of pressure and temperature within a system.
As I described the piping, look at the back of a fridge Although freon it's a liquid in the environment it operates with a hot and cold side...

 

[rtbcomp]

What I was meaning does moving a liquid from high to low pressure cause a drop in temperature like it does for a gas, we all know the PV/T = pv/t formula for gasses.

The freon is a gas when it enters the pump where compression causes it to give up it's latent heat of vapouristion. It is pumped as a liquid into the cooling coil where it boils, causing the latent heat to be absorbed from its surrounding. The "warm" freon gas is the re-compressedand the cycle repeats.

 

[Omniata]

What I was meaning does moving a liquid from high to low pressure cause a drop in temperature like it does for a gas, we all know the PV/T = pv/t formula for gasses.

Moving a liquid through a pressure difference only really works well when the liquid has a high specific heat capacity such as water and glycol. It's not as well noticed but increasing the pressure as you start to enter the cooler will force the liquid to release energy as it's density marginally increases...
Causing a pressure drop to a large bore tube/pipe towards the end of the cooler will allow the liquid to absorb energy as its pressure decreases, being it the cooler it can't and so if enough glycol isn't present it could freeze.

A lot of it relates more to fluid dynamics and can be more easily appreciated by trying to explain it in terms of effective surface area and time spent cooling, the physical chemistry is still the same though

The freon is a gas when it enters the pump where compression causes it to give up it's latent heat of vapouristion. It is pumped as a liquid into the cooling coil where it boils, causing the latent heat to be absorbed from its surrounding. The "warm" freon gas is the re-compressedand the cycle repeats.

True but not for all freons, R134a boils at -20°C and so may only exist in the gas phase in the compressor itself. It's used as a domestic refrigerent but due to it's higher boiling point isn't economial for freezers at low temperature. It typically has the expansion sections fitted to force condensation and pressurisation before leaving the radiator/cooler and entering the radiator/cooler...


Edit: You need a pressure drop related to the pressure increase and time at that pressure....

 

[Omniata]

rtbcomp, would this be better in the "brew room" ?

Edit: Piman, do you have any pictures of the vessel and pump, plus dimensions of the tube/pipe you intend to use??

 

[rtbcomp]

I think as it's a technical discussion and it relates to the original post I think it's best here. It's just that I've never heard of the cooling effect of a liquid during a drop in pressure!

 

[Omniata]

Think of it in terms of friction and apply it like electricity flowing through a wire
Go from thick wire to thin at high current and there's appreciable heating...

Liquid pressures don't really vary much but through a large temperature and pressure change the effects are measurable to quite an extent...

The temperature change comes about as the flow dynamics of the fluid increase so as more can move more quickly it rapidly absorbs energy through a drop, or loses it through an increase in pressure...


Piman if you go from scaffold sized pipe to 1/4" gas pipe though your going to need one hell of a pump to shift the fluid.
Ideally you'll need a header tank at the top of the silo, the top of which is above the highest fluid level in the silo, this should provide a head pressure to assist the pump.
It might be wise to set two in parallel, one at the start of the cooling coil and one at the end, in a "push pull" configuration...

Edit: It also takes longer for liquids to respond to pressure drops, they cool faster at high pressure but only if in the high pressure system for longer, so a really long coil is needed. Also the pressure drop needs to be sudden and massive to have any appreciable effect.
Unfortunately to get a high flow rate the smallest point in the system is the restriction and so needs to in this instance be of thick walled but narrow copper pipe to get the best heat conduction properties.

 

[Omniata]

Rtbcomp, to be honest this is the first time I've used physical chemistry in the past eight years and applied it to a real life scenario.
Even my dad was impressed at being able to apply it and he'd been in the industry at a research level for 40 years!!

 

[eil]

What is an IBC bath chaps

 

[Omniata]

"Industrial Bulk Container", they hold about 1000 litres, typically white and cube shaped.

A bath just means the top cut out and filled with ice, or coolant, to cool something you drop or put in it...

 

[eil]

Right like a bulk milk tank

 

[Omniata]

Pretty much got it in one Eil!!


Piman keep us posted on how you get on with this I would like to visit to see this in operation if/when you go live but I think your a bit far away

Propylene glycol might be a better choice instead of ethylene glycol as it's melting point is a lot lower that the -18°C the salt:ice bath will reach, you'd need to run trials in a lab setup with different proportions of propylene glycol to water until the "freezing" effect in a salt:ice bath isn't too noticeable.

You will need a small amount of water there as it has the highest specific heat capacity and so will absorb more energy per degree temperature rise than the glycol and so will have a more thorough cooling effect.
Combined with propylene glycol you might be able to freeze the beer in the silo

I'll see what other coolants I can find in my books and if you've got a disposable supply of CO2 being in the brewing industry you may be able to make a dry ice:acetone bath so the pressure differentials don't need to be quite so great...

 

[eil]

Has to be propylene glycol as its to be used with foodstufs. Like you omnia I would like to know more of what he`s got in mind, but having a 1 1/2 hp condensing unit is not strictly where he should start.