On Sun, 02 Dec 2007 18:38:37 GMT, "Sir Thomas of Cannondale"
wrote:

Heat exchangers.. if I were to use a small diesel for my sailboat that did
not have a
heat exchanger already attached to the engine ??

How do I size the heat exchanger? Does it go by horse power, size of engine
.. cylinders ..


Diesels are efficient thermal converters. Let's use a 40% thermal
efficiency at generating the rated horse power of the engine,
so it needs to dispose of the other 60% as heat.
Heat out of the exhaust, and heat into cooling water.

The exhaust can take care of itself, so your question amounts to this:
what factor of rated horse power should I allow for an engine cooling
heat exchanger?
Fuel thermal content = 100/40 of rated HP
That's 2.5 times rated HP
Exhaust thermal content = (say half the waste heat) =
(2.5 - 1 ) X 1/2 of rated HP = 0.75 of rated HP
leaving
Cooling heat also 0.75 of rated HP

This estimator gives the cooling requirement of a 10 HP diesel as
10 X 0.75 HP = 7.5HP or
7.5 X746 watts = 5.6 kW

It's a little bit conservative.

Brian W

Clear as mud?

Wow.. just as I thought.
===



"Brian Whatcott" wrote in message
...
On Sun, 02 Dec 2007 18:38:37 GMT, "Sir Thomas of Cannondale"
wrote:

Heat exchangers.. if I were to use a small diesel for my sailboat that
did
not have a
heat exchanger already attached to the engine ??

How do I size the heat exchanger? Does it go by horse power, size of
engine
.. cylinders ..


Diesels are efficient thermal converters. Let's use a 40% thermal
efficiency at generating the rated horse power of the engine,
so it needs to dispose of the other 60% as heat.
Heat out of the exhaust, and heat into cooling water.

The exhaust can take care of itself, so your question amounts to this:
what factor of rated horse power should I allow for an engine cooling
heat exchanger?
Fuel thermal content = 100/40 of rated HP
That's 2.5 times rated HP
Exhaust thermal content = (say half the waste heat) =
(2.5 - 1 ) X 1/2 of rated HP = 0.75 of rated HP
leaving
Cooling heat also 0.75 of rated HP

This estimator gives the cooling requirement of a 10 HP diesel as
10 X 0.75 HP = 7.5HP or
7.5 X746 watts = 5.6 kW

It's a little bit conservative.

Brian W

Clear as mud?