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Time for a heater...
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8122pbrainard View Drop Down
Grand Poobah
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Joined: September-14-2006
Location: Three Lakes Wi.
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Points: 41045 		Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: January-25-2021 at 6:44pm
Originally posted by TRBenj TRBenj wrote:



Having no real background with thermodynamics, my back of the napkin logic would have thought that moving hot water through the core more rapidly (before it has a chance to cool) would allow the most heat transfer. I would have guessed the reduction at the return would slow the flow though the core down and make it less effective at pulling heat out, but apparently that logic is flawed.

Tim,
I don't feel your logic is flawed and Gary's is. There has to be another reason for the restriction. 


54 Atom

77 Tique

64 X55 Dunphy

Keep it original, Pete
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8122pbrainard View Drop Down
Grand Poobah
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Points: 41045 		Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: January-25-2021 at 7:39pm
Originally posted by 8122pbrainard 8122pbrainard wrote:

You need heat tranfer in the core.

"Heat transfer occurs at the channel wall. Turbulent flow, due to the agitation factor, develops no insulating blanket and heat is transferred very rapidly. Turbulent flow occurs when the velocity in a given water channel is high. "

For better heat transfer, velocity helps to strip the thermal blanket off the tube walls and in some cases turbulators are even used inside tubes.


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Keep it original, Pete
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KENO View Drop Down
Grand Poobah
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Points: 11112 		Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: January-25-2021 at 8:46pm
Well the way I see it is....

If you tap off of the intake manifold right before the thermostat for the driving force and you tap back into the system with the return water going into the inlet of the circulating pump either through the connection on the pump or thru a tee on the inlet to the circulating pump like in the Heatercraft instructions the driving force to provide flow is only due to the differential pressure across the circulating pump.

That differential pressure is not much at all at idle speed so there's not much flow to the heater core .

Now if you hook into the suction of the raw water pump with a tee for the return water from the heater (like Gary has done) you have a higher differential pressure because the inlet to the raw water pump is under a vacuum whenever the RWP is operating.

As far as the restriction, at least logically you would think that ..........

Small hole = more restriction= less flow=lower temperature

Big hole=less restriction =more flow= more heat

But it seems like there's that age old argument about the fluid spending enough time in a heat exchanger to transfer it's heat the best (depending on a lot of design factors).

Heatercraft seems to say the hole size was derived from testing with no real explanation of the testing.

I kinda figure that if I had 2 of the y fittings, I'd drill one out to a bigger sized hole and try it for myself ( and use a valve before the wye so I could have a "variable sized hole" in that return line that could be adjusted for best heater and cooling system performance.

I guess it seems like I agree with Pete who agrees with Tim on the flow and maybe we're all a little curious about the hole size and how it was derived Wink
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KENO View Drop Down
Grand Poobah
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Points: 11112 		Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: January-26-2021 at 6:27am
For a real world example that we're all familiar with

Some auto heaters use a flow control valve to vary the flow through the heater core and when you move the control to hotter, the valve opens allowing more flow and the temperature goes up.

You don't go in the cooler direction and lower flow to raise temperature. Wink

Lots of vehicles these days use blend doors on the air side and constant flow on the coolant side, so this doesn't pertain to all vehicles, but you should get the idea.
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GottaSki View Drop Down
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Points: 3363 		Post Options Post Options   Thanks (0) Thanks(0)   Quote GottaSki Quote  Post ReplyReply Direct Link To This Post Posted: January-26-2021 at 8:22am
I can report I'll loose heat if idle speed in gear is around 650, around 750 the heat returns, and plenty of it.
When I place the core at feet level, no loss of heat occurs at low idle

I imagine with a t return to raw inlet, the still- warm return water is diluted with the main flow, and most these btus dumped out the exhaust, very little return heat makes it back into the engine replacing the exiting water, like having a stat bypass putting cold water into the engine continuously
The orifice could possibly inhibit higher flow the core would see under nonidle conditions.
"There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing."

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