antifreeze - mcn
Wed, 21/12/2011 - 14:35
Specific heat or latent heat? If I remember my physics from 40 years ago, latent heat is when the medium changes phase. Specific heat is the heat energy required to change the temperature of the medium.
Thu, 22/12/2011 - 15:17
#2
Re: antifreeze - mcn
Jiffy67. Having just received my copy of this weeks MCN through the letterbox I can now see what you are getting at.
In this weeks tech watch Kevin referred to water as having a high latent heat.
It does (apparently). That's it's "trump card", which is played when all else fails. "a whopping 540 calories per gram to convert water at 100 degrees centigrade, into steam at the same temperature." (quoted from Kevin Cameron's book sportbike performance handbook).
It also has a very high specific heat. "1 calorie per gram, per degree centigrade, which is 3 times higher than that of aluminium" (KC)
In the context of Kevin's article I wouldn't know whether he meant to say specific heat or latent heat, you'll have to politely ask him.
Perhaps he should have said both.
I'm glad you raised the point as it is well worth raising.
Thu, 22/12/2011 - 15:52
#3
Re: antifreeze - mcn
Ha, can't remember what I wrote in MCN but you're right, latent heat is associated with phase changes, specific heat is to do with the energy it takes to cause a fixed temperature rise.
The problem in the context of cooling systems is that antifreeze has a much lower specific heat than water, so if you have too high a proportion of that, the system's capacity for removing heat from the engine is reduced, and the coolant temperature can rise too much.
Sat, 24/12/2011 - 18:54
#4
Re: antifreeze - mcn
"The problem in the context of cooling systems is that antifreeze has a much lower specific heat than water, so if you have too high a proportion of that, the system's capacity for removing heat from the engine is reduced, and the coolant temperature can rise too much."
That supports my expeciences with regular antifreeze.
If I remember correctly with regular antifreeze the maximum freezing protection was at about a 60% antifreese to 40% water mixture.
In my area of the woods typically the antifreeze to water mix is about 50% for all temperaure operation.
I also seem to recall that 100% antifreeze in a cooling system actually raises the freezing point.
So 100% pure water would cool a bike better than an antifreeze to water mixture. The problem with just water is corrosion and mineral deposits when tap water is used. Just water alone also lowers high temperature protection and increases the chance of possible coolant boiling.
JAG
.
Sun, 01/01/2012 - 00:14
#5
Re: antifreeze - mcn
OK, thanks everyone. Imagine a kettle. Heating the water up from whatever temperature it comes into the house to boiling point (to make tea) takes about 2 minutes with the average device. That's specific heat. Once it is boiling, it takes ages to boil it dry (and you have to keep resetting it). That's latent heat. I suppose what I was trying to say is that Kevin confused me by writing latent heat instead of specific heat. Ah well, life's not perfect.
Happy New Year to everyone.
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Latent heat is the amount of heat energy released or absorbed during a phase change.
Specific latent heat is the amount of heat energy needed to complete a phase change, expressed per unit of mass of the substance concerned.
Specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius.
Had to look that one up!
All 3 terms mean something similar so it would be very easy to confuse the issue. I'm intrigued as to why you need to know. (not that just needing to know in itself is not enough!)