Author Topic: Closed Loop Cooling (With Plate Exchanger)  (Read 216 times)

veggie

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Closed Loop Cooling (With Plate Exchanger)
« on: November 09, 2018, 05:11:13 AM »
Hi All,

I have a question...

My 2 cylinder Kubota generator project is almost complete.
I am now working on the cooling system.
My preference is to use a 30 plate heat exchanger that I have kicking around and run a loop from the engine to the plate-exchanger and back.
Then connect whatever I want to the other side of the exchanger to cool the engine water ( Fan/Radiator, floor loop, wall radiator, etc..)
Is it best to have an open (to atmosphere) system on the engine loop? or is it ok to run a closed sealed loop on the engine side?
I prefer to have it sealed so that  I don't need a reservoir/buffer tank, and I assume some type of expansion tank would be required like those used in hydronic heating systems.
Any thoughts, ideas, suggestions on this ?

The engine has it's own water pump and thermostat just like a car engine.

Veggie
- 6/1 GM90 Listeroid - Delco 33si Alternator
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38ac

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Re: Closed Loop Cooling (With Plate Exchanger)
« Reply #1 on: November 09, 2018, 11:54:58 AM »
My Blackstone model MP  engine was originally sold as a set with a very large prime power generator. Its duties were to provide air for starting the big engine and to provide emergency power when the large engine was not operating. It was originally set up by Mirrless  Blackstone in a somewhat similar manner as you suggest. The engine water jacket was connected to a 80 gallon tank via thermosyphon and above that tank was a radiator connected via thermosyphon and equipped with a thermostat. The system was pressurized via 4lb cap on the radiator.  In operation that tank cooled the engine and when the tank got to a given  temperature the loop to the radiator opened up to cool the tank water. Odd was the fact that the radiator fan ran all the time being driven via belt from the crankshaft thus consuming power 100% of the time,needed or not.  I understand the added complication IF there was seperation of the fluids  and if heat was being used for some additional purpose. But since it used common fluid and the heat was simply being wasted the entire setup made no sense to me.

 In you case with planned use for the heat it makes sense. Yes you will need an expansion tank on the engine side of the system and I would run that side non pressurized.
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LowGear

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Re: Closed Loop Cooling (With Plate Exchanger)
« Reply #2 on: November 12, 2018, 07:38:44 AM »
I thought engines ran better when above 212 degrees.
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ajaffa1

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Re: Closed Loop Cooling (With Plate Exchanger)
« Reply #3 on: November 12, 2018, 08:34:08 AM »
Hi Veggie, I think that what you have shown in your diagram will work fine. The thermostat and internal water pump should circulate coolant well enough and allow the engine to run at a suitable temperature for efficiency, correct oil temperature and longevity.

There are a couple of weak points in the system:
Thermostat failure will cause the engine to overheat. I have had plenty of motor vehicles and have only ever had to change one thermostat!

Mechanical failure of the Kubota water pump or belt driving it will cause overheating. Again I have only had to replace a couple of water pumps in 40 years of driving, belts get changed during regular servicing.

Secondary water circulation pump to under floor heating etc. When I lived in the UK we had gas/oil fired central heating with Grundfos circulation pumps These are very simple electric pumps and I never had a problem.

Open or sealed system? I prefer a sealed system because you can run anti-freeze in it, depending on where you live. A pressurized cap will blow off steam in the event of a failure. The alternative might be an open expansion tank with a ball float valve, connected to your water supply, to ensure the header tank is always full.

Bob


veggie

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Re: Closed Loop Cooling (With Plate Exchanger)
« Reply #4 on: November 13, 2018, 02:38:01 PM »

Thanks guys,

ajaff1, your points about overheating are valid. I will be sure to add a high temp shutdown on the engine.
The engine has a fuel rack solenoid to allow shutdown from various sensors (Eg: Hi temp & low oil pressure)

cheers
- 6/1 GM90 Listeroid - Delco 33si Alternator
- Changfa R175 - Lease/Neville Alternator
- Kubota Z482 - 4kw
- JiangDong R165 Air cooled - 2 kw

BruceM

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Re: Closed Loop Cooling (With Plate Exchanger)
« Reply #5 on: November 13, 2018, 04:35:35 PM »
Pressure on the space heating side is a big help; the combo of a small pressure tank and air bleed valve at the highest point works very well and makes low power circ pumps happy no matter the convoluted plumbing route. A little bit of air causes a dramatic loss of pumping volume.

Heating water drives out the dissolved air gasses, so a pressurized sealed system with air bleed eliminates that air problem in a short time, and then your low oxygen levels will extend plumbing life.

Open systems provide a source of air to the water which causes corrosion and must be constantly driven off, so regular air bleed valve replacement will be necessary; about every 2 years. 

I use an open unpressurized system for my home heating, drawing direct from my 800 gallon solar hot water storage tank.  It's a pain as I have to draw a vacuum on the air bleed valve to keep air out.  It works but I wish I'd put a copper pipe exchanger in the tank so I could have a pressurized system.  I have to recharge the vacuum monthly through the winter, and the bleed valve must be replaced every other year, with subsequent air purge hassle.




cobbadog

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Re: Closed Loop Cooling (With Plate Exchanger)
« Reply #6 on: November 14, 2018, 11:32:20 PM »
I know next to nothing abut this under floor heating system as it is usually too hot here to want to heat a floor. But would a recovery set up similar to that used in cars be a help to keep your system topped up and free of air bubbles. I also think that you are referring to the gases in the coolant and minimising the gas there.
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