# Heat transfer between 2 liquids

1. Feb 22, 2007

### eaboujaoudeh

I don't know if classical physics is the best place to put this, cause normally i would have put it in the engineering section. There is no governing equation right now to describe heat flow between 2 liquids?
another question: flow between 2 liquids is governed by convection, if we place an imaginary plate between the 2 liquids and consider the equations between horizontal plate and fluid to find the thermal conductivity of both liquids and the plate. then we take the thickness of the plate to be zero, then we would be left with an equation containing 2 thermal conductivity values and no conduction value thus we would be able to calculate the heat transfer as if the plate never existed.
question 3. I need to find the heat loss from a heated pool to ambient cool air, if no formula exists isn't there an approximation or something that i can use?
Thnx to anyone who could reply to that!

2. Feb 22, 2007

### Integral

Staff Emeritus

As for the last part.

Assume Newtons law of cooling, then take some real temperature data. I would measure the air and pool temperature something like twice an hour for 24 hrs. Then do some data fitting to determine a bulk heat loss parameter.

You could also track the current draw of your heaters through a night to determine heat loss.

3. Feb 22, 2007

### eaboujaoudeh

my first question was i wanted to know if there is one emperical equation that can define heat transfer between 2 liquids in contact with each other but not mixing. btw nice idea ur answer, wierd i didn't think about it !! thnx

4. Feb 23, 2007

### FredGarvin

I donj't know how you would have interaction between two fluids without mixing. This is more of a thermo problem than a heat transfer problem. If the fluids are flowing, then perhaps it could be related via the difference in enthalpies from the first law.

As far as the pool problem, are you assuming a breeze over the pool (forced) or just natural convection?

5. Feb 23, 2007

### eaboujaoudeh

well i have to account for both cases, and actually air and water are two flowing fluids that don't really mix together. so the air is constantly cooling the pool and i have to know how much the cooling is so i could provide enough heat to keep the pool at a constant temperature

6. Feb 23, 2007

### siddharth

As Integral suggested, you should be able to solve this with Newton's law of cooling.

7. Feb 23, 2007

### eaboujaoudeh

just checked out newton's law of cooling, it doesn't give me the energy which is in terms of convection (h in W/m2 C). don't forget i want to know the energy loss in W so i can make it up by another source. i tried taking Free convection theories, but i'm not sure about my answer, anyone familiar with Gratshoff Prandtl principles??

8. Feb 23, 2007

### Integral

Staff Emeritus
$$\frac {dT} {dt} = k ( T_e - T)$$
You also need and initial condition, say T(0) = T 0

Newtons law of cooling employs a bulk parameter, k that is not assosiated with any specific heat transfer mechanism. It encompasses all mechanisms.

Indeed a wind blowing over your pool will yield a different k then a still day.