Latent heat recovery system, no radiator & advantages

[cptsideways]

I have had this idea for ages but never gotten round to doing something about it, so I thought I'd pass it by you lot. I have plenty of experience in the industrial sector recovering waste heat & putting it to good use elsewhere, its easily done & some basic engineering could see the idea to fruition.

Basic Idea
Recover the excess heat that our highly inefficient IC engines produce as waste. eg about 70% of the fuel used is wasted as heat.

The recovery system uses a large mass of high latent heat transfer material - eg parrafin wax that can be stored relatively safely in an LPG gas type container safely fixed in the boot of the car. Some simple pipework transfers the heat from the engine coolant to the wax & even exhaust heat could be recovered with a heat exchanger.

Once the heat is transferred on your commute you potentially have a large store of free heat, plug your car into your house heating system etc.

Pros
Free heating with some additional quick release plumbing from car to home
No need for radiator ducting all the time so aero advantages etc

Cons
Extra weight to lug around
Safety issues
What to do when the wax mass becomes saturated with heat

Need to know
How much wax mass required for vehicle type & size v typical commute etc
Fuel savings with aero mods available
How to engineer a fail safe etc


So over to you guys to do some maths & calculations if you thinks its viable I'll happily re engineer my Lupo 3L 1.2 Tdi or someother car I have about to experiment with.

[gone-ot]

Paraffin wax? Wouldn't a liquid "heat-sink" be better, especially since 'viscosity' changes could prove problematic at low ambient air temperatures?

[Tesla]

I like the idea in principle and have been pondering the same questions of how to use the waste heat from ICE, but have not found an effective solution yet.

Engine cooling systems can be problematic and effective operation is essential to prevent engine damage, so firstly I would suggest that engine system be kept as std as possible without a vast amount of additional piping & valves, so to this end I think you will need multiple heat transfer stages. Replace or add in hot side to existing radiator a water to water heat exchanger, this minimises any restriction or contamination issues of engine system, if there is a cross leak, it's not a major issue as it's only water.
Use the new water system to transfer the heat to the storage unit, this will require a pump and all associated filling, overflow and air bleeding hardware & design etc, transfer to heat storage could simply be multiple coiled tubes in the PCM and the vessel will obviously need to be well insulated and also have pressure safety and containment controls.
As a primary goal I would simply look at a system that could absorb heat of 1 hours driving and store this heat for a minimum of 24 hours to enable it to be used for quick engine warm up by reversing flow, this way you may be able to keep weight penalty down to 20-50kg, I think the house heating idea may be a bit too big as a starter.

[Daox]

Originally Posted by Old Tele man

Paraffin wax? Wouldn't a liquid "heat-sink" be better, especially since 'viscosity' changes could prove problematic at low ambient air temperatures?

Wax is used because of the latent heat storage benefit. The phase change from solid to liquid stores up a lot of BTUs for 'free' weight and size wise.

[cptsideways]

What I'd like to workout is the amount of heat a car puts out through its radiator, I presume this could be calculated as a function of its mpg's as a rough guess?

[roosterk0031]

http://ecomodder.com/forum/showthrea...age-26724.html

His plan was water based, but the idea is the same, the problem is you can store so little heat that it isn't worth all the work.

How many lbs of wax do you want to carry? From 80 dF to 200 dF including the latent heat it will hold about 126 btu's/lb. 200 lbs wax = 25,200 btus.

Wax is less dense than water, so 200 lbs of water would take less space, be easier to tie into the radiator, and give 120 btu's per lb. for a total of 24,000 btus for 200lbs of weight.

[Occasionally6]

To store the quantity of heat required without rejecting any of it is a big ask. As a quick feasibility check, @ ~6 liters/100km I use ~ 1 liter of fuel each daily trip. If we make the task simpler by only capturing heat from the cooling system and assume 43MJ/kg, 0.76kg/l and 30% of that heat into the cooling system, 16.97MJ will have to be absorbed by the storage system. It is reasonable to assume that @ 3l/100km, that goes to 0.5l and 8.49MJ:

Barium hydroxide has been used for latent heat storage in vehicles so starting with that:

From here:

Salt Hydrates - Melting points and Latent Energy

we need 8.49 (MJ)/6.55 (MJ/m^3) = 1.30 m^3 = 1300l of Ba(OH)2.8(H2O). It has to be insulated (vacuum?), paid for, will weigh 4.85 metric tons (just the Ba(OH)~ )and some provision for transferring heat to and from it made. Perhaps not.

A lesser quantity of stored heat might work, depending on what is the heat energy required to heat the house.

You might use something else to store the heat. Water to steam (2257kJ/kg) comes to mind, but then you need a pressure vessel, and maintaining the required temperature becomes an issue. (Paraffin wax has a latent heat of 147kJ/kg while Ba(OH).8H2O has 174kJ/kg, - and the heat is stored at a more useful temperature; 78C vs 47C.)

What will work is using stored heat to allow faster engine warm up. Cold start enrichment has a strong effect on fuel consumption, the shorter the trip, the greater the effect.

There used to be commercially available units to store cooling system heat but the units used in the various Prius models will be easier to find. As used items, less expensive too. (Maybe someone has already plumbed such a unit in and posted on here with the results?)