# Having trouble with heat loss to environment problem

1. Jul 15, 2011

### sixateseven

Hi guys, I kept trying different searches in Google and it kept bringing me to threads on this forum, so I thought it was time to join.

I'm trying to calcuate the heat transferred into the environment from an air system and am having a bit of trouble... I really don't have very much experience with this at all and I feel like its a pretty common issue, but I don't know where to start.

The situation:

I have a system of non-insulated pipes, it starts at one location with warm air flowing through it, at one point the pipe splits and runs to two different air to air coolers. I know the size of the pipes, the materials, the k values, the lenghts of pipe, and the temps at all three end points... but I feel like just using the standard form of Fourier's law that I've found doesn't really work, the temperature inside the pipe isn't constant (it cools from points A-B and A-C) and I feel like there would be a curve made by the heat transfer.. Starting off with a greater value at the beginning, and decreasing as a curve as the air in the tube cooled.

Does anyone have any input on what I should be looking for as an equation? I'm seeing a situation where if you had a steam system, for example, and knew the lenght, pipe size, starting temp and environmental temp you could calculate the final temp... but like I said, I knew to this type of situation.

Any help would be awesome. Thank you in advance!

2. Jul 17, 2011

### shushu97

Conservation of energy.

3. Jul 20, 2011

### Winzer

shushu97 is correct.

$$\frac{dE_{sys}}{dt} = \dot{E_{In}}-\dot{E_{Out}}$$

You will have to look at convection and conduction.
Also, you will have to know flow characteristics of the air through
the pipes(velocites, density). This will allow you to calculate your
convection coefficient. You will have to make assumptions about
flow development.