Heat exchanging question 1

[bjamesw]

Hello,

I'm wondering about the efficiency and application of a heat exchanger for a diesel driven pressure washer. I'm estimating for a 1.litre four cylinder water cooled diesel at 3000rpm driving a 5gpm@5000psi belt driven pump at 1800rpm.
I wonder if someone could help me to roughly estimate the effects of a compact high pressure heat exchanger fed from an engine coolant bypass, heating the high pressure flow from the pump.

At 5gpm would there be any exchange of heat worth troubling with?

Would, assuming 5gpm of cold water flowing through a very efficient exchanger, the diesel engine be unable to maintain proper operating temperature?

Thank you very much
Bjamesw

 

[Docengineheat]

Here's some rough guesses. . . . .

At five gallons per minute, you are looking at heating 40 pounds of water a minute.

I'm guessing that your four cylinder, one liter diesel will use two gallons of diesel an hour (might be a high estimate, but work with me here!)

A typical diesel engine will reject about 25% of the fuel energy through the cooling system. Diesel fuel has about 140,000 BTUs per gallon of fuel. If you're using two gallons a hour, that's 280,000 BTUs/hour or 4666 BTUs/min. If 25% of this winds up in the cooling system, that's 1166 BTU/min available for heating the water. Now you say that you're using 40 pounds of water a minute through your pressure washer. Assuming a 100% efficient heat exchanger, each pound of water will absorb 1166/40 = 29.1 BTUs. A BTU is defined (roughly) as the amount of heat necessary to raise the temperature of water one degree Fahrenheit.

Therefore, you would be able to raise the temperature of your pressure washer water about 30 degrees using an engine coolant heat exchanger.

You could double the amount of water heating if you also used an exhaust heat exchanger.