Radiators, thermodynamics & fluid-mechanics questions

[fitterski]

Why would the radiator input hose from the engine pump be larger than the radiator output hose to the engine thermostat? For the Cummins 5.9 diesel the first is 2-1/4" and the second 1-3/4".

If I connect two ATV radiators in parallel the flow will of course 'favor' the path of least resistance. Will this be a more or less pro-rata differential or more than that? If one of the hose lengths is say 90% of the other will that draw more than a proportionally higher flow into that one?

Much more complex, how to calculate the radiator requirement for an engine like a Cummins 5.9 12-valve diesel that will operate at ambient temperatures of 0c and less at 40% power on average? The heat generated will be less than the fuel BTU value because work also gets done and because the engine block also bleeds heat. I plan to use two 9.5"x15" core single row radiators with fans but If I can get away with it I'd rather use only one.

TIA

 

[LD1]

I really dont think a single small ATV radiator, will keep a cummins running at 40% cool, even if it is below freezing.

I wouldnt even trust the job to just 2 ATV radiators.

The real question though.....why do you want such a large engine but only a 9.5x15 radiator??

 

[fitterski]

I really dont think a single small ATV radiator, will keep a cummins running at 40% cool, even if it is below freezing.

I wouldnt even trust the job to just 2 ATV radiators.

The real question though.....why do you want such a large engine but only a 9.5x15 radiator??

I heard of diesel rams pulling a hood in front of the radiator in winter and that the thermostat on some hardly ever opened. I understand that in cruise most diesels don't work that hard, the only diesel I ever 'drove' before was a rabbit and I really had to load it to get any heat into the cabin but I don't have any other practical experience to lean on. The ambient BTW will be more like -10c to -20c.

The reason I want it to be no bigger than absolutely necessary is that it's going on a snow-blower, an extremely violent environment with space constraints and rads are extremely vulnerable.

 

[Agvg]

How big is the blower and how much snow?
Why a big engine if you don't need the power?

 

[fitterski]

How big is the blower and how much snow?
Why a big engine if you don't need the power?

See my sig, or
Deutz powered JD Snow Blower from Hell 29 - YouTube
It isn't horsepower I need but torque, this engine will give me over 400 ft-lbs at 1600, at about half of the available power. Snow blower impellers work between 600 and 1000 rpm becoming less efficient above 700 and my 2.5:1 gearing geometry is about max due to space & weight constraints. The last engine gave me about 200 ft-lbs, this will double that.

 

[ChristopherJ]

Why would the radiator input hose from the engine pump be larger than the radiator output hose to the engine thermostat?

Heat exchangers are generally throttled on the outlet rather than the inlet.

This keeps the fluid in the heat exchanger at a higher pressure, therefore gases are less likely to come out of solution, therefore you get better heat transfer, less chance of gas-binding of the heat exchanger.

Source: I was a nuclear-trained submarine mechanic for twenty years.

 

[fitterski]

Heat exchangers are generally throttled on the outlet rather than the inlet.

This keeps the fluid in the heat exchanger at a higher pressure, therefore gases are less likely to come out of solution, therefore you get better heat transfer, less chance of gas-binding of the heat exchanger.

Source: I was a nuclear-trained submarine mechanic for twenty years.

I learn something every day!!! I always thought that the 7 or 15 psi came from gas pressure. The two ATV radiators offer about 1/3 the area of the diesel truck that the engine came from, that truck was probably engineered to haul a trailer uphill in 35c ambient so I 'think' I might be ok.

 

[texasranger556]

You could mount heat exchangers somewhere on the blower like a snowmobile. The exchanger on my 900 Arctic Cat was surprisingly small for 150 HP.

 

[pmsmechanic]

I assume that you are going to use metal tubing for the framework. If the two rads are somewhat short on cooling you could always run some coolant through part of the frame. Especially snow blowing as there is usually lots of cold air and snow blowing around. Good luck!

Edited to add that some irrigation pumping units in this area are cooled by heat ex changers. About 24 feet of 1.5 inch metal pipe inside an 8 inch pipe is plenty to cool an 80 hp natural gas pumping unit in the heat of summer

 

[Stimw]

Diesels run better at their rated temperature.
Fuel consumption and parts expansion are an issue if run too cold.
I would use the original radiator with proper thermostat and shutters on it.
Semi's can even have covers on the front that can be buttoned or unbuttoned for control.
Air flow is the key. I once drove a 1993 KW 20 miles back to the shop with a broken fan clutch in 84* weather.
The engine only ran about 10* warmer and I watched it very closely!

 

[fitterski]

You could mount heat exchangers somewhere on the blower like a snowmobile. The exchanger on my 900 Arctic Cat was surprisingly small for 150 HP.

Good news man! I like to hear things like this :dance1:

The higher the temp diff. the more efficient the rad. Thermostat is 192F & OAT will be about 5F. The engine is actually the smoothest and safest place (once blew the chute deflector right off, it landed 70 feet away in the snow). With a small 3d footprint of around 17x12x8 I expect to bolt the 'cooling pack' to the engine with reasonable integrity. If it's not enough I can always upgrade.

BTW if anyone is interested 1" copper plumbing fittings slip right into the 7/8" rad hose like it was a glove ...at 1/100 of the price of some *rad-fittings* that I've seen.

 

[ArlyA]

$10 says there is a reason that manufacturers are not doing this on current blowers. Like snow sticking everywhere, you don't want it.

You could mount heat exchangers somewhere on the blower like a snowmobile. The exchanger on my 900 Arctic Cat was surprisingly small for 150 HP.

 

[Dave M7040]

Why bother with a rad at all. Solve your cooling with software.

Modern engine and their computers manage to avoid damage from excessive heat by rotating which cylinder is allowed to work. The non working cylinders are cooled by air passing through them.

Cadillac, on their Northstar V8 of around 2002, was the first consumer gas engine to provide this limp home capability for their owners.

Formula one engines, clearly the most sophisticated in the world, keep their cool in the same manner when sitting on the starting grid.

Diesels work this self cooling even better as their is no air throttle so easier air movement through the engine.

My third year thermodynamics course taught me that NPSH is a critical factor in pumping fluids, especially for cooling. That is why the suction hose is larger than the discharge hose.

When plumbing multiple heat exchangers into a system (i.e. radiators) best engineering practice would be to use the "reverse return" piping method to keep flows naturally balanced.

Many diesel engines are designed as an air cooled prime mover so get one of those and it will work in the hottest weather.

Dave M7040

 

[Agvg]

Or get a Deutz air cooled diesel and have no worries about cooling.

 

[texasranger556]

Why bother with a rad at all. Solve your cooling with software.

Modern engine and their computers manage to avoid damage from excessive heat by rotating which cylinder is allowed to work. The non working cylinders are cooled by air passing through them.

Cadillac, on their Northstar V8 of around 2002, was the first consumer gas engine to provide this limp home capability for their owners.

Formula one engines, clearly the most sophisticated in the world, keep their cool in the same manner when sitting on the starting grid.

Diesels work this self cooling even better as their is no air throttle so easier air movement through the engine.

My third year thermodynamics course taught me that NPSH is a critical factor in pumping fluids, especially for cooling. That is why the suction hose is larger than the discharge hose.

When plumbing multiple heat exchangers into a system (i.e. radiators) best engineering practice would be to use the "reverse return" piping method to keep flows naturally balanced.

Many diesel engines are designed as an air cooled prime mover so get one of those and it will work in the hottest weather.

Dave M7040

Good luck modifying the software in a 12 valve!

 

[farm boy00]

How much space are you really going to gain by doing 2 smaller radiators versus the factory radiator?? And the factory one is already designed and if it gets too cold put a cover on it

 

[Mace Canute]

Heat exchangers are generally throttled on the outlet rather than the inlet.

This keeps the fluid in the heat exchanger at a higher pressure, therefore gases are less likely to come out of solution, therefore you get better heat transfer, less chance of gas-binding of the heat exchanger.

Source: I was a nuclear-trained submarine mechanic for twenty years.

I don't think anyone who doesn't under stand this should be fooling around redesigning the cooling system.

 

[Egon]

It's also desirable to keep full liquid contact in an exchanger so no hot spots can develop.

 

[fitterski]

Or get a Deutz air cooled diesel and have no worries about cooling.

That's what this engine is replacing

BTW just because it's air cooled doesn't mean there's no need for temp. control. It's just that on a Deutz you modulate the air flow instead of the liquid coolant.

 

[fitterski]

Diesels run better at their rated temperature.

That's why Cumins raised the thermostat to 192F. That BTW is what sums everything up, the coolant in the block should never be much above thermostat temperature. Once the engine has warmed up, being below it could happen with a thermostat stuck open. I will have precise coolant temp as well as EGT indication to monitor.