# Heat transfer problem

1. Feb 22, 2008

### Lowis

Hi,

I have to determined the rate of heat transfer in a delivery dock when the big garage doors are open. I have tried a natural convection approach, but I lack the mass air flow from the inside of the garage (22°C) to the outside (-10°C). Or is there another way to calculate this?

2. Feb 28, 2008

### qbit

Yes. If I recall my thermodynamics correctly, there are three ways to calculate heat transfer: convection, conduction and radiation.
However, depending on the size of the garage and the size of the doors, my guess is that you are correct in assuming that convection would be the predominate factor.
Did your convection calculations assume lamina flow?

3. Feb 29, 2008

### Staff: Mentor

In practice, this is an unsolvable problem due to the variability of wind.

4. Mar 1, 2008

### jaap de vries

Russ is correct however almost everything in engineering is unsolvable because of variability in whatever.

I assume you are going for a ballpark estimate. You need to know the total size of your bay in M^3 then the size of the opening. Also important is if there are any heating vents that are blowing into the garage causing a slight overpressure. Do the garage doors open rolling up or do they tilt?

5. Mar 24, 2008

### Lowis

It is true that I only want an estimate. The total size of the bay is 1624 m^3 and there are 2 garage doors rolling up of 20 m^2 each. Yes there are 4 gaz unit heater in the bay and the whole thing is about those heater that are working too much to keep some water pipes from frozing. So, what would be your approach to determine the rate of heat transfer between the inside and the outside when one or 2 doors are open.

6. Mar 29, 2008

### jaap de vries

If that is your problem you might be able to simply use some heating tape/better pipe insulation to prevent this. Probably saves a lot of energy too.

7. Apr 1, 2008

### MJCfromCT

Proper ANSYS element?

8. Apr 1, 2008

### TVP45

An air curtain is a fairly common solution to this sort of problem.

9. Apr 1, 2008

### h2oski1326

You can solve something like this using Fluent and find some temperature distributions around your space, but that is likely more elaborate than you need to be.

Another solution would be to assume one mode of H.T. dominates in all situations (i.e. convection) and do some simple HT calculations to find out what is going on.

Either way you need to assume some sort of constant airflow into your space. Average wind speed and direction you can find from the NOAA website for your given city or one close to yours.

There are also some simple energy balance type programs out there (e.g. EnergyPlus) that could prove useful in this type of problem, you would again need to assume some environmental conditions.

It all depends on how elaborate you want to take this.

10. Apr 10, 2008

### Lowis

Thanks to all of you for helping me on that matter, I have solve my problem and there is no need for this forum anymore.

11. Apr 10, 2008

### Staff: Mentor

We'll keep the forum open just in case.