Electric water pump effect on warm up times

[serialk11r]

Ah I see, you're running the pump full speed most of the time.

Slowing the pump should increase warmup time. In the computer watercooling scene, it was well known that higher flow always increased heat transfer rate, but going with a higher powered pump would cause the water to heat up more and would start to increase your average temperatures. Since an engine block has rather long coolant passages, perhaps it would be more useful to note that in particular, radiators benefit from greater coolant flow rates.

If your block is at some effective average temperature, higher flow makes the temperature of the water more consistent. The heat transfer rate (local) is proportional to the temperature difference. If you have hotter water on one side, colder at another area, same average temperature, the water is absorbing more heat at the cold area, but it's also absorbing less heat at the hot area.

If anything, having the pump dump some extra energy into the water would decrease warmup time, and greater flow would increase the cooling of the block, and extract a greater amount of heat per unit time, which is what matters.

[Frank Lee]

I don't think you can draw such parallels between computer cooling and ICEs. For one thing, ICEs have thermostats. And then some of that simply made no sense to me.

[serialk11r]

This is with the thermostat closed, sir :P
He's saying less coolant flow would make warmup faster. Thermostat is closed, I know that. More coolant flow cools the engine off better = more heat transferred from engine to water = faster warmup. Anything wrong?

The parallels to computer cooling are completely valid, because they refer to tests done with nothing else in the loop. I guess I should've said, heat transfer is always better with faster flow.

[Frank Lee]

Originally Posted by serialk11r

Ah I see, you're running the pump full speed most of the time.

Slowing the pump should increase warmup time. In the computer watercooling scene, it was well known that higher flow always increased heat transfer rate, but going with a higher powered pump would cause the water to heat up more and would start to increase your average temperatures. Since an engine block has rather long coolant passages, perhaps it would be more useful to note that in particular, radiators benefit from greater coolant flow rates.

If your block is at some effective average temperature, higher flow makes the temperature of the water more consistent. The heat transfer rate (local) is proportional to the temperature difference. If you have hotter water on one side, colder at another area, same average temperature, the water is absorbing more heat at the cold area, but it's also absorbing less heat at the hot area.

I have serious reservations about the notion an ICE water pump could be going so fast as to add energy to the coolant and increase it's temperature.

Slowing the pump should have little to no effect on warm-up times, but if there is any effect, I would expect it to be a reduced warm-up time.

Smokey Yunick says it is possible to spin the water pump too fast and what happens is it reduces the amount of heat the coolant picks up as it isn't in there long enough to gain as much heat as it would if it wasn't hurried through.

If anything, having the pump dump some extra energy into the water would decrease warmup time, and greater flow would increase the cooling of the block, and extract a greater amount of heat per unit time, which is what matters.

Contradicts itself...

[serialk11r]

No, if the water is moving faster, the water picks up less heat with each pass it makes through the engine but it runs through the engine more often. The water isn't going anywhere, it's being recirculated. Now if the thermostat wasn't there, it wouldn't be so clear of a picture.

And you are correct, the water pump would add only a trivial amount of heat. I don't know why I mentioned it, I just thought it might be good to.

There's nothing contradictory, you're extracting heat from the engine block which I think we can all accept as being hotter than the coolant.

More flow=better cooling, this is always true. If you're recirculating said cooling water, it equates to faster heating of the water. This is all I can say, I'm out for the night :P

[Frank Lee]

There's a pdf re: BMW elec pump IIRC it has some good explanations...

[Tesla]

I've heard the slow flow argument before, the laws of thermodynamics say that heat transfer increases as the temp differential increases, so if you put cold coolant into the engine more heat will be trasnsfered than if you put hot coolant in. All pumps have an ideal speed at a set load where maximum flow is achieved if the pump is slower it doesn't work to max efficiency, if the pump is much faster cavitation occurs where the fluid being pumped is just held within the fins and the pump spins without doing much actual pumping.
If you know what this speed is then this is the maximum speed to run the water pump irrespective of engine speed or coolant temp. Having said that the issues of compromise arise, what are the actual gains to be made, there seems to be a lot of suggestions, but no hard facts, I'd go with Frank on the engine pump with reduced speed, providing the driver is a hypermiler otherwise leave as standard.