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Old 11-20-2010, 12:06 PM   #1
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Insulated paraffin wax coolant heat exchanger

So, hardly a new topic, but looking for advice on how to best implement it.

Back story-
I drive a lot. 500-700 miles per week, varying conditions, all year round. I play music for a living. I teach in 3 different locations and perform with 3 different groups in locations all over the state. I can run a block heater during the winter in the driveway, but the way back from teaching/gigs I have to let the car warm up on it's own.
However, I usually only spend 2-7 hours at these events. (sometimes twice a day) The car is always very cold when I want to leave.

Goals-
I want to have a SIMPLE paraffin wax heat exchanger that is run in line just after the heater core. (so it's bypassed the thermostat, and will be effective when the engine is cold)
I want this project to be cheap or free. I may have a free wax supply; there's a candle making place near my house. I'm sure they have a scrap wax pile of all kinds of colors/scents. I'm going to investigate that. I need probably 2 gallons or so.
I want to use a long piece of radiator hose run to the highest probable point under the hood (most likely where the old a/c condenser was located, in front of the exhaust mani). I would not use T's, I'd use elbows so the coolant has to flow through this hose whenever the engine is on.
I want to use the largest black iron pipe diameter sold locally. I think that is 2" or 3". I would fill it nearly to the top with hot wax and cap both ends with caps/pipe dope. The reason for this is it can take enormous pressure that expanding/reducing wax may create.
I want to use three lengths of pipe, wrapped with radiator hose around all three. I'd suspend these three pipes in an aluminum box. I'd wrap the pipe/hose assembly with tin foil. I'd then fill the box with Great stuff expanding foam insulation.
Finally a hose would run back to the top of the block.

Expected Complications-
Convection. Thermal convection to be precise. One thought on overcoming it is two simple one-way valves. I think the spring tension in them would be enough to keep convection from moving the coolant and or heat around once the engine starts to cool. Thoughts on this? (may interfere with my block heater's convection..... hmm...)
Being at the high point of the system will probably help a lot too.
I do not want to do the prius thing. Complicated 12v pumps, valves, hose routing, relays, etc. Expensive too.

More coolant in the system- longer cold warm ups? (negligible?)

Air Bleeding problems?

Clearance issues with exhaust manifold?

Added weight?

Total Cost?/Benefit ratio?


Location I want to put it on the car-
[IMG]<a href="http://s1213.photobucket.com/albums/cc473/benfroggg/?action=view&amp;current=HondaVXwebpicsandcl102.jp g" target="_blank"><img src="http://www.fuelly.com/attachments/forum/photobucket/img_158417_1_7302f90713c80173a44812a8e9ca9919.jpg" border="0" alt="Photobucket"></a>[/IMG]

Okay, that's all for now. Feedback is greatly appreciated.
Thanks!
B
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Old 11-20-2010, 05:06 PM   #2
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Re: Insulated paraffin wax coolant heat exchanger

Scrap wax? "Scrap" wax is just tossed into the next batch.
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Old 11-20-2010, 05:48 PM   #3
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Re: Insulated paraffin wax coolant heat exchanger

Does this coolant circuit have a valve that stops flow when heat is not needed in the cabin? ie does your temp selector knob works a valve on this hose?

If so- it almost seems like a wash to me- if it does manage to keep the coolant warm (say 120 degrees) after a few hours, then you would need to move the temp selector to hot so the engine can take in this hot water, but then overall it would slow down the coolant warming up once cooler water from the block began circulating through it (unless you move the temp lever to cold 20 seconds after you start the car to prevent this). You could them move the temp lever to hot only after the temp gauge showed that the engine was up near operating temp.

In summary, I think you will need to actively control the flow of coolant through this device because under some circumstances it could extend your warm up time.

Now, if it used heat from the exhaust manifold to melt the wax, then it would be a good thing overall.

Here's another approach:

Do you want to just jump in and drive away? Or would you mind waiting 10 minutes?

You have a lot of room under the hood- how about setting a Mister Heater Little buddy propane heater in there for 10 minutes- point it right at the block just beneath the exhaust manifold (unless you have a greasy engine block= fire hazard). I have one and it is quite impressive for its size. 5 hours burn time on a small propane cylinder.

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Old 11-20-2010, 10:29 PM   #4
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Re: Insulated paraffin wax coolant heat exchanger

The wax is an interesting concept but I'd start with a cardboard grille block and an engine blanket.
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Old 11-21-2010, 12:18 AM   #5
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Re: Insulated paraffin wax coolant heat exchanger

Grill block is done and has been for a while.
The heater does not have a valve that stops flow through the heater core. It is plumbed into the bypass circuit that moves coolant through the block before the thermostat opens. My volvo, on the other hand, is setup like you suggested so I am familiar with it.
The setup, in theory, should only increase the coolant capacity by a gallon or less. A 1" hose (or thereabouts) that was say 25' long doesn't hold all that much volume. Thus, warm ups that were from dead cold (say I spend the night at a friend's house or something) would be slightly longer.

When I leave from home, the 120v coolant heater will be bringing me near temperature before I get in. When I leave the gig, 2-7 hours after parking the car, the hope is that the wax is still in the process of changing from liquid to solid.

The only time this would be counterproductive would be if I parked for 24 hours or more and didn't use the block heater and the outside temp was less than 50df or so. I don't stay in hotels while on the road. I drive home and just get in very late. I still think this added amount of coolant would be mostly negligible in this instance. But who can be sure without trying it out!

Wax holds a constant temperature during this change. Lots of wax means it can theoretically hold a steady temperature in an insulated vessel for several hours.

The wax doesn't have to become liquid for the car to be warm. The coolant will move around inside the insulated compartment while it's getting warm. Before all of the wax is transformed back to liquid, the engine should make it to operating temperature.

Okay, that all being said, here's the other piece of the puzzle. If you only stored hot coolant, there would only be that much hot coolant available for the next start up. This system would store heat energy in an exchanger. So, the coolant in the compartment on start up would be warm or hot. Cold coolant coming in would absorb some of this energy before it left to head back to the block. Thereby rapidly warming the engine. It's not as though you only have 2 gallons of warm coolant and nothing else (like how the prius works).

Here's a quote from another user, trebuchet03 a while ago:

"Well.... here's something I just thought of - sorta. So I'm in a heat-mass transfer class (I'm a mech engineering student, yay classes!), and I'm studying for finals and one tidbit is heat capacity.

That got me thinking. We want to store a great deal of heat - not necessarily at a high temperature, just a lot of it. The thermal mass of the coolant, head, oil etc. is huge.

One great way to store heat is to take advantage of latent heat | heat of fusion -- which is heat/energy in solid-liquid phase changes. I need to do some research/calculations - but I suspect 3L of wax will hold more heat than 3L of coolant. I think paraffin wax (yes, I know - fire hazard if exposed) does the solid-liquid phase change around 50C. And I'm sure there's other suitable (albeit less accessible/more expensive) materials out there.

What's great about latent heat storage is that there's A LOT of it. And once you begin the phase change, the average temperature stays constant until the change completes. Now I just need to think of a way to implement - probably VIA some sort of "bucket" heat sink/ heat exchanger.

If anyone here subscribes to Autospeed (a great Aussie motor mag online), they actually talked about a theoretical inter cooler that used wax ("Performal") to basically make your IC a bigger heat sink (because after all, that's what it is for the most part). This idea is backwards to theirs :P"

Direct link to this discussion:
http://www.gassavers.org/showthread....heat+exchanger

50dc is 122df. That's not that far from operating temp of 195df. Block heaters don't get all the coolant much hotter than 122 either.

Paraffin's flash point is 390df. No worry of fire, especially since it's in a sealed vessel.

Scrap wax may be hard to come by. I assumed that dyed wax was not re-used as it is hard to get the color/scents out of it. (when making candles)
Shows what I know!

Still, paraffin is relatively cheap.


Anyway, what are everyone's thoughts?
Thanks for the input so far!
B
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Old 11-21-2010, 12:26 AM   #6
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Re: Insulated paraffin wax coolant heat exchanger

Oh, missed a couple things-
Engine blanket? Please expand on this one. I haven't heard of such things!

As for the mister heater, I'm trying to avoid using other forms of fuel if possible. Those un-refillable mini propane tanks are among my least favorite kind of energy storage. I know, it's probably splitting hairs when you consider the alternatives, but I just can't bring myself to buy those things and throw them out!
Also, there seems like a lot more wasted heat in that scenario. Some of the heat would be absorbed by the block, but much of it could escape out the cracks in the hood and the like.

The exhaust melting the wax idea is interesting. However, you may as well make an exhaust to coolant heat exchanger in that scenario.

I'd also like to add a thermometer (digital wired type) to the inside of the container. I could then monitor what the temp was after several hours.

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Old 11-21-2010, 03:39 AM   #7
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Re: Insulated paraffin wax coolant heat exchanger

I cover the entire engine compartment, underhood, with corrugated cardboard when there is almost no clearance (car) and 1" foil faced foamboard, foil down, when there is room (pickup). They provide noticeably better heat retention and are easy/cheap/free.
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Old 11-21-2010, 04:39 AM   #8
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Re: Insulated paraffin wax coolant heat exchanger

Quote:
Originally Posted by benfrogg View Post
I still think this added amount of coolant would be mostly negligible in this instance. But who can be sure without trying it out!

Wax holds a constant temperature during this change. Lots of wax means it can theoretically hold a steady temperature in an insulated vessel for several hours.

The wax doesn't have to become liquid for the car to be warm. The coolant will move around inside the insulated compartment while it's getting warm. Before all of the wax is transformed back to liquid, the engine should make it to operating temperature.
Wouldn't the thermal ballast (wax) be the issue, not the extra coolant? All that capacity...unless your heat exchanger works very slowly, warmup time when everything got cold would be long.

Quote:
Originally Posted by benfrogg View Post
As for the mister heater
Honestly I can't understand the point of that idea. It's fine if you're looking to get heat immediately when you turn on the car, but if you're trying to save fuel it seems counterproductive. Either way you could accomplish the same thing with a remote starter.
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Old 11-21-2010, 05:43 AM   #9
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Re: Insulated paraffin wax coolant heat exchanger

I suppose there's no free lunch when it comes to lots of energy storage capacity. I guess my only inclination is that it would be a rare occasion that I'd have to be starting from really cold. Assuming I'm able to run the block heater at home and am parked less than 6 hours, it seems like I should be able to use the system to my advantage.

One other thought for consideration is using this system with a venturi type t-valve (like those used in baseboard heating configurations) plumbed to the heater core lines. Then, if my dashboard digital temp gauge showed cold, I could just have a simple under hood shut off valve that could be activated. Thus, bypassing the system and starting normally until operating temperature. The same could be true during the summer months when I'm not using the block heater.

I wonder how much insulation I can fit under that hood?

Thanks all.
B
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Old 11-21-2010, 06:52 AM   #10
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Re: Insulated paraffin wax coolant heat exchanger

Personally, my feeling is that the heat exchanger is probably not going to make a noticeable difference. Water already has a high specific heat, I don't see where wax is going to make a significant difference overall. That being said, in reference to the extended warm up scenario. Have a cutoff solenoid or valve that could be shut off, and only opened once the engine has reached operating temperature.
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