Thats it in a nutshell. 'Not really interested' Don't try to learn anything. Keep a closed mind. If it doesn't agree with your misconceptions deny it. Treat all others opinions as rubbish. You are the Delphic oracle. Only what you say is true.
Delusional.
Have you read the current thread on greenhouse heaters? It's relevant to this :-)
If you've ever tried melting snow/ice, you know it takes a lot of energy to convert it from solid to liquid. Ditto boiling water - getting from
98-100 degrees takes a lot less than 100-102 (at atmospheric pressure...), because you've got to convert it to a gas.The converse is also true - you can extract a lot of energy when you convert something from a liquid to a solid - a lot more than just changing the temperature of a solid would give you. That energy is described as latent heat, hence the name of the store.
The box contains a solution which melts at say 60 deg. I imagine the paper referred to in the wiki talk gives the actual temperature.
Melt it by running hot water through it in pipes. Stop car, stop water flow. Ensure box is adequately insulated - it'll cool from 100 to 60 degrees in my example, but then stay at 60 for a lot longer as the contents freeze.
Come back to car, run cold water through box which is still at 60 degrees, extract the rest of the heat. Box will stay at 60 until the contents are all frozen, then the temperature will drop.
And yes, the container could be aluminium. Not necessarily the most obvious choice for the outside - it conducts heat too well, which would make it a good material for the heat exchanger. But they might insulate outside that.
I certainly wouldn't. They're not known as the Haynes Book of Lies (HBoL) for nothing.
If it's like those crystallising hand warmers, as long as fully "charged/melted", the latent heat will be stored more or less indefinitely.
Tim
I'm always happy to learn. However, I like to learn facts. Not just some vaguely remembered ramblings.
It does seem to be the case that BMW offered some form of latent heat store on some models in some markets. What certainly isn't clear is which ones. And the fact that they no longer do so - but now rely on an auxiliary fuel burning heater - probably says it's a fact not worth learning about. Except to avoid the concept.
Right. How do they transfer heat to the hands - but not to the air when not needed? It's not something I've used.
Um, you hold them in your hand. How else? Heat is only released when they're "provoked" to crystallise. Until then, they're inert.
Tim
In message , "Dave Plowman (News)" writes
They only produce heat when 'activated'. IIRC They contain a super saturated solution of Sodium Acetate or whatever. They usually have a metal disc in which you push/flex. This starts off the crystallization, which is exothermic, so producing the heat.
You recharge them by putting in hot water, reverses the crystallization,
I think you may be confusing temperature for heat. The fact that they stay constant in temperature during phase changes does not mean they're not losing (or gaining) heat energy.
Even when extremely well insulated such heat stores will eventually become exhausted. What's worse is that the constant temperature will maintain the rate of heat loss unlike a hot water bottle where the rate of heat loss drops with declining temperature.
In a practical heat store system that can be fitted into a car, it may be designed to retain 50% over a 24 hour period where 50% is sufficient to meet a minimum requirement. Doubling up the volume of both heat storage medium and the insulation would allow you to extend the storage time to 48 hours or longer for the same amount of residual heat energy.
For this type of heat store, there are two parameters to juggle with. One is the quantity of the heat storage medium for a given thickness of insulation such as a doubling to extend the storage time by a factor of two. The other is to double up the insulation for the same quantity of heat storage medium to half the rate of heat loss to achieve the same result. And, of course, various combinations of those two parameters depending on the relative costs of insulation versus heat storage medium.
Given a free hand you could design such a heat store to stay viable for weeks, let alone days but, however you design it, the heat energy will eventually all leak away regardless. You certainly can't store heat energy indefinitely, there's a well defined heat loss mechanism involved.
You're referring to chemically activated hand warmers where two different chemicals remain seperated until you rupture the seperating membrane by squeezing and kneading the bag. This is totally different to the heat storage system being discussed in this thread.
What you're describing is a one shot deal (like a zinc carbon cell) whereas what's being discussed here is a rechargable heat store (like a lead acid cell) where the crystals can be melted by heat from the engine cooling system in a reversal of the heat loss process that makes it act as a heat source whenever it's charged up.
Sad. Haynes are a very respectable publishers of manuals and have been for many years. Hundreds of thousands of people have used them. But, hey, you're the expert not them.
Not.
don't bother trotting out petty examples of where Haynes may have been wrong in some minor detail.
Here we go again. (If you saw it why did you make your claim that it didn't refer.) Why would he have to know the difference between an E38 and an E39 ? (In fact he did know the difference them, hence his disclaimer. Fact is y ou didn't bother reading it properly.And what's with all this esoteric refe rence to E38s E39s . Just call them BMW 5 series or BMW 7 series that way t he majority of people will know what you are talking about. But perhaps tha ts the idea. Its a secret club. Only us members will have the arcane knowle dge to discuss things. Grow up.
Not all all. I'm referring to the "liquid" hand warmers that are charged by heating in hot water until the bag contents are fully liquified. Once all the crystals are dissolved, the bag can be allowed to cool. To trigger heat release, a small metal disk inside the bag is flexed producing an audible click. This forms a nucleus for the supersaturated liquid to crystallise around. During this crystallisation process heat is released.
Go to any outdoor shop and you'll see these as well as the "one-shot" iron filing filled ones.
Tim
I think you're missing the point that heat is only released when crystallisation is provoked. Whether the BMW one operated like this or not I don't know but I DO know that the crystallising hand warmers that you can buy can be left in a drawer for months once "charged" but will produce heat when required.
It's the latent heat of crystallisation that is released when activated, not simple stored heat.
Tim
unlike a cheaper rival's books who seem to have vanished. "If the windscreen wiper fails to operate connect a volt meter across the terminals and check that a current of 5 amps is being drawn". (you couldn't actually reach the terminals since the motor was buried somewhere under the dashboard)
Ebay generally have a load of them for sale, ex GPO vans ISTR. They're used in boats also.
Why ? Oh come one give us some examples of the heinous mistakes Haynes have made. Which of course are irrelevant to the discussion at hand
Yup, we have some here in fact, last used last winter, they will still get hot when used :-)
this kind of thing:
Well glad to see you finally bit the bullet and admitted you were wrong. Even if with ill grace.
Just remembered an occasion when somebody used a load of those as an Auxiliary car heater following an unplanned stopover in a Scottish Hotel car park following a reasonable Hogmanay night. Bloke hadn't really planned to stay but fortunately had a box of them. Found in the morning in the car covered with a coat and a load of warmers shivering his bollocks off. They may have worked better if in his inebriated state he hadn't totaly ripped most of them in half spilling the crystals all over the car interior.
G.Harman
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.