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I would like to cool 400 gallons of process water using a standared air conditioning condensing unit. I am going to store the 400 gallons at 34 degrees F and pump it as a coolant until it reaches a temperature of 52 degrees F. My total cooling load is aboout 60,000 B.T.U. and I have a recovery time of about four hours as this is a batch process. There is no latent heat load so I am planning to use a 30,000 B.T.U. chilling unit. I could use a Direct Expansion refrigerant to water heat exchanger with an expansion valve to meter the refrigerant and I can find the design calculations for this easily enough. I would like to know if I could instead immerse a length of copper tubing in the tank, for example 50 ft. of 3/8 copper, and get the desired refrigeration. I can find tables for various refrigerant to water or refrigerant to air heat exchangers but I cannot find anything that would give me an equivalent refrigerant to water direct immersion coil. I realize I will have to treat the water to prevent corrosion and loss of heat transfer capacity. Can anyone help with this. Thank you and let me add That I have read many of the topics on this forum looking for this information and found myself wandering about as I found other unrelated but fascinating topics.Bravo!
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Immersed Heat Exchanger
Started by Guest_bob1_*, Mar 17 2007 09:13 AM
3 replies to this topic
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#2
Art Montemayor
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Posted 17 March 2007 - 10:19 AM
Bob:
What you are proposing is easy. It's not hard to do.
However, it depends a lot on what you are really, specifically trying to do. What is your scope of work? We are professional engineers on this Forum, so we know our stuff. However, if you are laboring in a backyard project with a limited budget and a few nails, please be honest and tell us all the facts. We can sit here and write a lot of words and go around in circles for days until the real issues come out. That would waste a lot of time and disenchant a lot of the guys/gals.
We also need to know if you are a degreed engineer. This is important only because we don't want to start out talking over your head. That is not productive. We can whip this simple heat transfer problem; but we need to know all the constraints. We may have to resort to calculations and engineering sketches. These may have to be communicated in spreadsheet fashion. Is this OK? If we can't communicate that way, we'll have a problem.
Tell us the specifics. What refrigerant(s) are you proposing? Freons? Ammonia? Ethylene? It will make a big difference. If you don't furnish all the specific data required, we can't generate a specific response.
Await your response.
#3
Art Montemayor
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Posted 19 March 2007 - 08:12 AM
Bob:
Look at the attached Workbook. Is this what you are planning to do?
Water_Chiller__Coil_in_Box.xls 68KB
166 downloads
Look at the attached Workbook. Is this what you are planning to do?
Water_Chiller__Coil_in_Box.xls 68KB
166 downloads
#4
Guest_bob1_*
Guest_bob1_*
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Posted 19 March 2007 - 04:07 PM
Art, Thanks for your replies. I was away over the weekend or I would have been more prompt. Your workbook drawing is exactly what I am doing. I have considered the freezing and will use a freezestat in the water line. I am also using thermistor controls for greater accuracy. The return line back to the compressor has an accumulator to prevent liquid refrigerant from boiling in the compressor. I am using CHClF2, R-22 as the refrigerant.Boiling point -41.4 F, Vapor pressure 61.5 PSIG at 34F. I think I have to design for a temperature difference approaching zero at the end of the cooling cycle as the refrigerant temperature and the water temperature will approach unity. I am designing this system to prevent loss of critical cooling due to power interruption or mechanical failure, as a sort of fail-safe. My coolant circulating pump is 12 VDC with a deep cycle battery backup, so this system will run independent of the electrical grid, once the tank is "charged". I want to use an immersion coil rather than a DX heat exchanger just to keep the design simpler, one less pump and one less heat exchanger to clean and maintain. I still am having trouble figuring the sizing for the copper coils I need for my heat exchanger. I also may have to think about placement of the coils in the tank to provide some circulation by convection. I can use multiple coils coming off a main header or manifold, but I think the total length needed would be constant. I can't thank you enough for taking the time to look at this and I am hoping to hear more from you, or anyone else who may have some insight. Thanks, Bob.
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