Insulated paraffin wax coolant heat exchanger

[benfrogg]

The difference is the "phase transfer heat storage potential." Wax can go through a phase change at a high temperature. The theory is that this stored energy has a higher available storage capacity than storing warm coolant alone. That being said, there are documented benefits of storing warm coolant and the impact on FE. So, if I can make even a minor improvement over storing coolant alone (say, keeping low heat longer than just coolant), I should be able to see a net gain in efficiency.
That's the theory anyway. I suppose that's why this is an experiment board!

Thanks for all the input.
I'll post some schematics when I get some drawn up.
B

[theclencher]

Originally Posted by theholycow

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.

Huh? You know that engine pre-heat is one of the very best methods available to us to reduce emissions and increase fuel economy. You're on an economy site recommending A REMOTE STARTER?!? I think those damn things should be outlawed.

You know that Prius has a thermal bottle just for that reason.

[theclencher]

Originally Posted by Jay2TheRescue

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.

Did you not see the mention of "phase change"?

Don't diddle with cut-off valves. If coolant is circulating through the heater core, but the blower is off, that means there isn't much heat exchanging going on, and any differences there may be from cutting off that circulation will be too small to notice.

[theholycow]

Originally Posted by theclencher

Huh? You know that engine pre-heat is one of the very best methods available to us to reduce emissions and increase fuel economy. You're on an economy site recommending A REMOTE STARTER?!? I think those damn things should be outlawed.

You know that Prius has a thermal bottle just for that reason.

I agree with you 100%. That's why I think a propane heater is counterproductive. It's not likely to be any more fuel-efficient than a remote starter, and it's surely less cost-efficient. Those little propane tanks are much more expensive than the equivalent amount of gasoline.

Neither a propane heater nor a remote starter is productive for being more efficient than a cold start.

[benfrogg]

Food for thought:
http://www.rubitherm.com/english/pag...lossary_04.htm

This article is about heating systems. It does say that the latent heat storage of 100% wax is much better than water. (nothing about coolant, which I'm sure is similar)

It also says it's not as good for dramatic temperature changes. I'm guessing this might mean that it's not as good as I thought for this purpose? Need some feedback on this data!
B

[theclencher]

If I'm not mistaken, they are talking about dumping water into a tank with wax and having them mix. And if I'm not mistaken, we were considering a vessel with a heat exchanger such that the coolant and wax never contact.

I know the aftermarket industry developed at least one auto thermal system. And Toyota has such as system in production. Might as well learn what they did.

[benfrogg]

I think you are referencing the Prius. It uses a coolant thermos and a 12v pump to move hot coolant out on shut down and back in on warm up.

The article is talking (I think anyway) about a heat exchanger. They are comparing a water only type system (like a boiler mate you might buy from the depot) to using a similar system with wax. The ratio of water to wax in the charts is making reference to the fact that there are additives available to add to the wax. Such additives diminish the effectiveness of the wax to hold heat.
The last paragraph says that a wax type heat exchanger is much better for reduced temperature change differentials. So, if the differential is less than 40df, it is considered much more efficient than a water only system. In my case, the wax will have to hold it's temperature for as long as possible. Incoming coolant (after an hour or two) will likely be cooler to the tune of 40df or maybe more. (assuming the wax maintains 122df) At that temperature, heat transfer would still be superior to just storing hot coolant.
If, after 6-7 hours the temp inside was still near 122df (and that's a big if), incoming coolant would likely be ambient air temp or so. That means it could be as low as 0df or possibly lower. At that rate, (inferring this data from the charts) the wax would perform no better than water. (or coolant, in our case)

I theorize that shorter duration stops would be dramatically more efficient in terms of warm up time than coolant storage alone. Longer trips would be about the same as storing hot coolant alone. Starting from dead cold (say overnight) would be worse than it is now as you'd have to get that wax back up to operating temp too. Hence, in my situation, the block heater.

Additionally, I think insulating the underhood area within reason could improve this as well. I anticipate being able to entirely block my grill when the temperature drops more. (I have an led that tells me when the fan is on)

At this point, I think the minimal cost of such an experiment would make this worthwhile to try out. A couple of cans of great stuff/a rigid foam box will be a very good insulator to keep that wax/coolant as warm as possible for several hours.

Any other thoughts?
B

[benfrogg]

Oh, I did notice what you are talking about. This article seems to be talking about non-contact systems and "hybrid" systems whereas water directly contacts paraffin. Either way, the principal is the same. One just has to factor in the loses of the heat exchanger itself.

On other note is that the last paragraph says that"The above diagrams very clearly show that latent heat storage units are not suitable for storing hot water for domestic use, since such systems exhibit high working temperature differences (heating water from 15 ?C to 65 ?C). In such an application area latent heat storage units offer neither a technical nor an economic advantage compared with hot water storage units."
That says to me that there is no advantage of using wax versus storing hot coolant when the car is very cold except that the wax is more likely to keep warmer longer as a result of latent heat storage brought on my the phase change. That being said, this system would only be as efficient as storing coolant in a thermos after a long shut down and no block heater.

I can easily monitor the temp inside the unit. If it is less than the temperature of the block on start up, I'd use a simple valve to control flow to it. The venturi setup allows me to block flow to it without stopping the bypass system from working.

B

[theclencher]

I'd say the data is unique to water/wax mixed in the same vessel, that's what all that proportioning and charting is, and it doesn't apply to anything else.

[GasSavers_Erik]

Originally Posted by benfrogg

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!


B

Actually, you can refill them. I just bought this adapter awhile ago, but I haven't tried it yet.

Without controlling flow with valves, it seems like any coolant based heat storage device would only increase thermal mass (it takes just as much heat to change the wax into liquid as it gives up going to a solid), which would increase your warm up to thermostat opening time because it would absorb some of the heat that would otherwise be quickly increasing engine temp- Which would only balance out its effect of keeping the engine warmer after it had been sitting a few hours.

If valves were used, I think your idea would work nicely.

If you want to decrease warm up time without valving, IMHO you would need to either conserve the heat in the engine block (with something like an engine blanket), use an outside energy source (like your block heater) or find another waste heat source- like drawing heat from the exhaust manifold. Maybe a hot air intake would help a little bit... or somehow heating coolant with the exhaust manifold while avoiding a steam explosion

Here is another idea to reduce warm up time on many Honda engines. If your engine is similar to my old 87 carbed D series engine, then the thermostat is in a hosing that is connected to the lower (cold) radiator hose (come to think of it, it is the same with my 94 Accord 2.3L). Since the upper radiator hose rises in elevation from the outlet on the cylinder head to the point where it connects to the upper radiator tank, even with the thermostat closed, convection currents would allow the hot coolant from the head to enter the upper rad tank and cold coolant from the upper rad tank to "fall" into the head. This would increase warm up time. A simple solution would be to buy a couple of curved rad hoses and make a U shaped loop out of upper rad hoses to prevent these convection currents of coolant before the thermostat opens.