air to water heat exchanger

[waterworks178]

can anyone tell me what the restriction in airflow is through any types of air to water heat exchanger ?

My application is recovering 80 degree C hot air flow from an air cooled engine to heat water.


Maybe this type of heat exchanger ?

 

[IRstuff]

With so much information to go on, I'd predict that it will suck.

If you want to heat water, then you should have a liquid to liquid exchanger.

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[1gibson]

You shouldn't have to look very hard to find a source of waste heat from an IC engine, air passing by the engine would not be my first choice. Run plain tubing near the exaust.

Or kill two birds with one stone and attach the water heater tubing directly to the engine block...

 

[waterworks178]

Tis an air cooled engine, there is no water involved, all the heat is blown away up a ducting.

 

[1gibson]

Right, no water involved.

Unless you attach/affix/weld/bond tubing/piping filled with water directly to the engine, to both heat the water and help cool the engine, as I am suggesting.

 

[btrueblood]

"Unless you attach/affix/weld/bond tubing/piping filled with water directly to the engine, to both heat the water and help cool the engine, as I am suggesting."

Thus voiding the warranty, if not causing problems with thermal stresses that the engine was never designed for. Air-cooled industrial IC engines typically have finned aluminum heads, with very little metal thickness to which to attach water channels. Recovery of the cooling heat is pretty much going to have to be done by the HX method that the OP is looking at. If a water-cooled engine is available to do the same job, then yes, he should look at those (they typically last longer too, though are more expensive and heavier per unit hp).

As far as the OP's question, you will need to run tests for the specific engine and hx combination you are looking at. You need to avoid blockage of the airflow (limiting the cooling of the engine), so tests with and without the hx in place should be done, measuring cylinder head and oil sump temperatures, and any other points the engine mfgr. might ask for. The local engine rep should be able to hook you up with the manufacturer's engineering department, and they may be able to give you advice, up to and including reccommended test procedures for verifying the cooling performance of the engine installation. If you are just doing a one-off, as opposed to being an OEM, they may or may not pick up the phone for you. Good luck.

 

[Compositepro]

The vast majority of energy consumed by any IC engine ends-up as heat going out the exhaust. If you want to recover heat, that is where to get it from. It is also a lot easier. You could possibly even modify a gas water heater, if you understand the safety hazards.

 

[btrueblood]

Sure, but the OP didn't ask about that.

"It is also a lot easier."

Um, thermodynamically yes, but as a practical matter it isn't. It's more complicated, both in metallurgy and the control aspects - screw it up and you can make a lovely little steam bomb, as most IC's exhaust at temperatures up over 1000 deg. F. When I was in that job, we would use both methods on a single machine to maximize heat recovery. Adding a water block on the oil filter, and recovery on the shaft side of the device, also contributed.

 

[Compositepro]

It make some difference if this is a stationary or mobile application. Air cooled engine seems would be mobile, but wanting to heat water seems more like a stationary application. As a practical matter, however, extracting heat from exhaust gas is still far easier than from the air around an engine.

 

[rmw]

Water works,

You have now given enough information to hazard an answer to your question. Unless you intend to put a flow inducing device somewhere in the system I can state that the device you show the photo of will add too much pressure loss to your air cooled engine's cooling air stream. Don't attempt it if it will do no more than restrict engine cooling air flow.

rmw

 

[waterworks178]

As i said the HX would need to be a bigger area than the standard ducting coming off the engine to make up for the restriction.