- #1

MysticDream

- 83

- 4

This is great. Now I can calculate the heat transfer rate, my log mean temperature difference, and overall heat transfer coefficient using standard formulas. I can also calculate the effectiveness of my heat exchanger and the number of transfer units using the NTU method.

Now I realize I need different results. I may need to change the parameters of my heat exchanger, but I don't want to waste time and money building and testing different setups to get the desired results.

I realize I will need to change the input temp of one of my fluids and/or the surface area of my exchanger (linearly). I know I can use the NTU method to calculate the heat transfer rate and outlet temps

**IF**

**I know my**

**overall heat transfer coefficient**. I can calculate my overall heat transfer coefficient from my first test using:

My question is , if I change the values of one (or both) of my inlet temps OR I change the surface area value OR I change the mass flow rate, can I use the

**SAME overall heat transfer coefficient**from the above formula throughout all temps and areas and still obtain an accurate result using the NTU method?

I was surprised to find out how difficult it is to get a clear answer to this question through internet searches. There are many descriptions and examples of what an overall heat transfer coefficient is and how to use it in one specific case, however, I was not able to find any information about it's practical use in calculating results by changing parameters. Of what use would an overall heat transfer coefficient be if it is not a constant for a particular heat exchanger that could allow you to change parameters to predict the results?