Closed cooling multi pass????

[MOP]

I have 2 exchangers a 3 pass and a 4 pass Merc. Both are the same 4" X 20" same tube count. I will be running the BB Merc bronze engine mounted pump, which has quite a bit more capacity than the drive pumps, I have two pulleys one that will run crank speed the other maybe 20-25% slower. I think the 4 pass cooler is for a stern drives and the 3 pass is for engine mounted pumps. I will be moving a lot of water and am thinking the 3 pass will let it move faster, I will be running a pressure relief valve to dump excess. Any thoughts greatly appreciated.

Phil

[RvR]

Aim the outlet nozzle aft. Sounds like you have the makings of jet drive assist :D

[gcarter]

Hi Phil;
It may be the opposite, with a higher velocity, it may need another pass to have enough contact time.
But what do I know?

[MOP]

George I remember when I was a kid helping a friend with his midget, it had a cross fire Ford 60. He had a lot of trouble with T stats, he ended up pulling the the T stats out only to find out it over heated in a few laps. One of the old timers gave him two washers to put on the head inlets to slow the flow and it cured the problem and ran at a decent temp. In thinking about it I will try the big pulley with the 3 pass, slow the flow and keep the pressure down a bit. I can always swap things around to get it where it works best, I am hoping to run it as a full system.

Phil

[RvR]

Mop I assume your plan is to layout the system similar to the attached pic. Without performance specifics on each of the components it’s difficult to make a definitive analysis but my gut feeling atm is that the 4 pass will perform better. The passage for the 4 pass will be slightly smaller than the 3 pass and thus a higher velocity but the higher velocity will also mean a higher heat transfer coefficient between the tubes and the water.

What pressure do you expect to set the pressure relief at? Will it be the predominant pressure drop in the system at high speeds or do you expect the losses in the HX to dominate?

I suspect the washers in the midget improved cooling because they slowed down the flow in the radiator. As I understand the system you propose the velocity in the radiator won’t be affected by either HX.

If you want to consider instrumenting temperature and logging it so you can have hours of fun looking at data on your computer you might consider a Hobo data logger http://www.onsetcomp.com/Products/Product_Pages/HOBO_H08/H08_family_data_loggers.html You can tape their thermocouple to what ever surface you want to monitor and take home hours of data :D