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Old 02-12-2018, 05:52 PM   #1
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Default Coolant volume vs. displacement or HP

Im working on an engine design for a liquid cooled inline twin. Im wondering if anyone has information about how much internal volume and/or internal surface area is needed for the internal water passages. The coolant would be raw pond water and the pump rate could be infinitely adjustable. The displacement would be 62ccs total. The fuel would be propane and the anticipated load rpm would be 1500-1800. Any thoughts?


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Old 02-12-2018, 08:55 PM   #2
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Hi John,

You have posed a difficult question there ! Water, or any coolant for that matter, will adsorb heat as long as the heat source is hotter than the coolant. The speed at which the coolant adsorbs the heat is dependant upon its volume, temperature and the rate of flow. So a slow flow will adsorb more heat in a given time frame. Also the area that is providing the heat source has to be taken into account along with the amount of energy generating the heat. It has been a very long time since I did the maths for this type of system. Basically energy in equals energy out. You will also have to calculate backwards for the heat loss when cooling your coolant down.

Maybe a read of these web sites will help:

https://elementsofheating.wordpress....rticular-time/

http://nessengr.com/techdata/watercool/watercool.html

At least this will give you a starting point.
Good luck with your engine design.


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Old 02-13-2018, 12:56 AM   #3
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Thanks Baron. Both are good reading. I don't have the required education level to apply it however. Good old seat-of -the-pants reasoning may be in order.
The interesting part is in the article that mentions heat transfer in oil as being better than that of water. Maybe an oil-cooled engine with a radiator would be a viable alternative.
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Old 02-13-2018, 05:15 AM   #4
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Default oli cooling

The HKS 700 E light sport aircraft engine uses air cooled cylinders and oil cooled cylinder heads. It has been a production engine available in the U.S. for the last 17 yrs or so.
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Old 02-13-2018, 08:03 AM   #5
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I think water (the typical water/glycol mix for radiator purposes) is the better cooling liquid. There is heat capacity &then there is specific heat. (I hope Ihave this right, been out of school a long time

An objects heat capacity describes the amount of heat required to change the temperature of that object by a certain amount. Specific heat is the amount of heat required to change the temperature of a substance by one degree (generally C).

Discusses interplay of cooling medium & thermal conductivity of materials
http://koolance.com/cooling101-heat-transfer

oil vs water vs all kinds of things
https://www.engineeringtoolbox.com/s...ids-d_151.html

a lot of what are called oil cooled are combo air+oil in specific applications
https://mechanics.stackexchange.com/...s-water-cooled
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Old 02-13-2018, 10:40 AM   #6
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Quote:
Originally Posted by BaronJ View Post
Water, or any coolant for that matter, will adsorb heat as long as the heat source is hotter than the coolant.
Just a small point here Baron, but it's aBsorb. The process of aDsorption is very different.

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Originally Posted by petertha View Post
There is heat capacity &then there is specific heat. (I hope Ihave this right, been out of school a long time
You confused yourself a little - these are the same quantities and relate to the amount of energy required to raise the temperature of the material by a given amount, and is expressed as units of energy per unit of mass per degree.

I believe the second quantity you were trying to describe is thermal conductivity, which is the energy flow per unit area per degree, so the higher the temperature difference and larger the contact area, the more heat transfer. We need to compare different substances with the same conditions to evaluate effectiveness.

So, in short, the specific heat capacity of water is around 4.2 joules per gram per degree Kelvin (or Celsius) and mineral oil around 1.7 joules per gram per degree. This means if we have the same mass of each substance and add the same amount of heat to them, the oil will increase in temperature by over double the amount the water will.

Looking at thermal conductivity, water has better conductivity by a factor of over treble that of most oils, so even with the increased temperature of the oil due to it's lower specific heat capacity, the water will still get rid of its heat faster (not to mention the higher temp oil will severely reduce its ability to actually remove heat from the engine).

So in really short terms, don't replace the water in your radiator with oil!
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Old 02-13-2018, 11:23 AM   #7
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Quote:
Originally Posted by BaronJ View Post
The speed at which the coolant adsorbs the heat is dependant upon its volume, temperature and the rate of flow. So a slow flow will adsorb more heat in a given time frame.
This is only true for the increase in coolant temperature. For removal of heat from the source, the faster the flow the more heat is removed. If you slow down the coolant flow the coolant gets hotter and heat flux reduces due to the smaller temperature differential.

If you've got access to unlimited cold pond water, you can pump it through nice and quick and it will strip away massive amounts of heat, so internal volume won't be overly critical. Most model engines have issues dumping the heat from the fixed volume of coolant rather than getting heat into the coolant itself. You've basically got access to unlimited coolant volume so that won't be an issue for you.
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Old 02-13-2018, 01:02 PM   #8
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If you don't mind letting the cat out of the bag, what will this engine be running? If you are using pond water as a coolant have you considered adding a thermostat?
Have you considered air cooling? A proper fan and duct system my be simpler to build than a full "wet" cooling system. Air cooled working engines always bring deutz diesel engines to my mind.

GJ
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Old 02-13-2018, 05:54 PM   #9
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Hello Al,

I was never great at spelling Its way over 50 years since I did anything like this, so that gives you an idea of how little I remembered from what was then Chemistry / Physics... I'm glad I went for Electrickery
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Old 02-13-2018, 09:00 PM   #10
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The aircooled engine will last longer life due short time to heat up the engine to working temperature. The engine with small water jacket will rise fast up to working temperature than the engine with big water jacket. I will select the engine with small water jacket + thermostat to control working temperature.

The normal working temperature is 85-120 degree celsius/185-248 degree Fahrenheit.


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