# Heat Transfer Problem: Calculate Rate of Heat Transfer

• Lowis
In summary, Russ is trying to figure out the rate of heat transfer when the big garage doors are open. He has tried a natural convection approach, but lacks the mass air flow from the inside of the garage to the outside. There are three ways to calculate heat transfer, but depending on the size of the garage and the size of the doors, he guesses that convection would be the predominate factor. He also assumes that the convection calculations assume lamina flow, but in practice this is an unsolvable problem. There are several solutions to this problem, including an air curtain, using Fluent, or assuming one mode of heat transfer dominates in all situations.
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?

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?

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

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

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?

jaap de vries said:
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?

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.

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.

Proper ANSYS element?

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

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.

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.

Lowis said:
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.
We'll keep the forum open just in case.

## 1. What is heat transfer and why is it important to calculate the rate of heat transfer?

Heat transfer is the process of transferring thermal energy from one object to another. It is important to calculate the rate of heat transfer because it helps us understand how heat moves and is exchanged between different systems, and allows us to design and optimize processes and systems for efficient energy use.

## 2. What factors affect the rate of heat transfer?

The rate of heat transfer is affected by several factors, including the temperature difference between the two objects, the surface area of contact between the objects, the type of material the objects are made of, and the presence of any insulating materials.

## 3. How is the rate of heat transfer calculated?

The rate of heat transfer is calculated using the formula: Q/t = kA(T1-T2)/d, where Q/t is the rate of heat transfer, k is the thermal conductivity of the material, A is the surface area of contact, T1 and T2 are the temperatures of the two objects, and d is the distance between them.

## 4. How can heat transfer be controlled or manipulated?

Heat transfer can be controlled or manipulated through various methods, such as changing the temperature difference between the objects, increasing or decreasing the surface area of contact, using materials with different thermal conductivities, and adding insulating materials to reduce the rate of heat transfer.

## 5. What are some real-world applications of calculating the rate of heat transfer?

The calculation of the rate of heat transfer is used in various industries and fields, such as designing efficient heating and cooling systems in buildings, optimizing thermal management in electronic devices, and understanding heat transfer in chemical reactions and industrial processes.

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