Question about that wet stuff .... Water
Turbo Mini Forums

Does water absorb heat at the same rate that it disperses it?

Team Racing

i thnik it abosorbs it quicker, may be wrong but it rings a bell.

Heat transfer is a question of temperature difference. The larger the temperature difference, the faster the heat will transfer.

Jean

http://www.jbperf.com/

surely the material also has a bearing, alloy heat sinks and all that

maybe I'm wrong - its been a long week!

Look at "specific heat capacity" on wikipedia.

Will probably explain it better than me.

Why don't you use oil in your radiator?

There lies the answer.

Bugger off, I'm getting there.

Yes i moved to the darkside

Instagram @jdm_brett

yes all to do with specific heat capacity.

eg 1 joule of energy to increase or decrease the temp buy 1 deg C

the high the specific heat capcity the more energy required.

thats also why ally blocked and headed engines heat up and cool down quicker than cast iron engines as ally has a lower specific heat capacity than cast iron.

always looking for them bigger bunches of bannanas

Correctamundo.

Bugger off, I'm getting there.

It also depends on the state of the water, fog, spray mist or slug. The greater the surface area available for heat transfer the faster heat will be transfered/dissapated.

Own the day

2 interesting equations relating to heat exchange.

Q=mCp dT

Q= duty
Cp=specific heat capacity
dT=temperature rise.

So, for a given amount of energy, you can calculate a temp rise for a mass of a certain substance. Or shuffle it around and find unknowns.

Q=UA LMTD

U=term related to individual heat transfer coefficients
A= Surface area for heat exchange to take place.
LMTD=Log mean of the temperature difference (hot stuff to be cooled or cold stuff to be heated).

So, from the second one, you can calculate an area required for heat exchange for a given sized/materialed heat exchanger.

As Mr Joshua says, it all gets bloody complicated with U, the sum of the heat transfer coefficients. How well stuff conducts heat. If you have a copper exchanger of a certain thickness, that's fine, if you have a fluid (air or water) it gets bloody complicated and the fluid flow calculations (are doable) are very hard to understand. It takes into account mainly the type of flow, laminar/turbulent and the shape of your exchangers pipes/area can dicate hugely the outcome.

By having a peruse of the above, you can be pretty certain of the relationships in a heat exchanger.

Calculating U is bloody hard work. I have designed the odd heat exchanger in my time and the finer points of U were very confusing.

It's just as well the best attitude is "whack the biggest one you can find on"

Saves a lot of mucking about....

Bugger off, I'm getting there.

Not to mention that volume to surface area ratio also affects heat transfer rates

Own the day

Heat transfer rates are irrelevant, unless you divide the whole lot by time.

The relationships are the same without it.

You're right about the surface area/volume. The more laminar the flow, and the more circular the tube, the more crap the heat exchange.

So, if you get turbulent flow you introduce an obstacle to get it, hence resistance. You get really thin tubes which the flow forces the gradient of flow to be sudden in the tube, so you maximise the temperature gradient therefore heat transfer.

In short, if you want a really efficient heat exchanger, be prepared for some back pressure!!!

Bugger off, I'm getting there.

Apart from the issues of heat transfer, cooler efficiency etc, the answer is yes provided the conditions that affect heat transfer are the same on the heating and cooling.

The process of heating then cooling water is a reversible adiabatic process under the second law of thermodynamics.

Take a charge cooler circuit for example. Assume that the cooler and radiator have the same heat transfer properties.

If the compressor outlet temperature is 100 deg C and the ambient is 20 deg C, then the system would reach an equilibrium state with the water at 60 deg C. Both the heating and cooling would take place with a 40 deg C differential or delta T.

What you actually want in a charge cooler is lower water temperature and to achieve that you would put in a larger radiator that would avhieve a larger amount of heat transfer with a lower delta T.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

And you can make it even more complicated if you operate the "heat exchanger" at close to boiling point, or more specifically if the material of the heat exchanger (the heat source) is above the boiling point for the water's operating pressure.

Schrödinger's cat - so which one am I ???

Ah but there is a very exoyic and simple method of extracting heat from a fluid. If you send the fluid through a coupled turbine/impellor then a heat exchager then out through the identical turbine the energy put into said fluid by the first turbine will be extracted by the second less that removed by the heat exchanger. This principle is used on the airconditioning units on planes, I wonder if it can be used on a liquid?

Own the day

ok, thanks for your thougths, I've been able to follow some of them. My Reason for the question is I'm tyring to work out if in theory you have an engine with electric water pump, how do work out the optimal speed for the water to flow the the rad. There must be a speed which is too fast, and two slow?

If I added temp sensors so I could see what the temp drop was accros my rad would this help me at all??

Team Racing

This thread may help:



I drew this up for some reason:

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

Edited by evolotion on 10th Oct, 2008.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

i water cool my graphics cards in my pc and ive been told to add something called water-wetter which basically lowers the surface tension of water so that more of it is in contact with the metals that conduct heat to and from the water (water block and rad)
i think cars get around this by pressurising the cooling system to literally pack the water tighter around the components than if unpressurised. as well as raising the boiling point of course. its also pink lol.

did you know one calorie is a something equation where the energy it takes to heat one litre of pure water in one hour = 1 calorie or something . ha