# Explain what is meant by an 'overall heat transfer coefficient

1. May 12, 2018

### Tiberious

1. The problem statement, all variables and given/known data
(I) Explain what is meant by an 'overall heat transfer coefficient'.
(II) Explain what is meant by fouling and what its effect will be on the value of the overall heat transfer coefficient.
2. Relevant equations
None provided.

3. The attempt at a solution
(I) The overall heat transfer coefficient (U) refers to the ‘overall’ heat transfer either by conduction or convection through a series of materials/layers. This is expressed by the equation:

Q = UA(T_2-T_1)
(II)Fouling references the formation of impurities; solidified process liquids and corrosion on surfaces over time. This extra layer of resistance has an adverse effect to the overall heat transfer coefficient. In some instances this newly formed fouling layer can become the largest resistance to heat transfer.

The above seem to be very short answers, but, they seem to answer the questions directly. Any advise ? I don't want to write volumes if not necessary.

2. May 17, 2018

### PF_Help_Bot

Thanks for the thread! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post? The more details the better.

3. May 28, 2018

### CWatters

That's the equation for the heat flow. I think for a fuller answer it might be worth adding an equation like...

1/UT = 1/U1 + 1/U2 + 1/U3 …… 1/UN

where UT is the overall heat transfer coefficient and UN is the heat transfer coefficient of layer N.

That's ok, but if I was picky I would say...

Fouling is the formation of a unwanted layer of impurities, solidified process liquids, or corrosion products on the surface of a heat exchanger. The thermal resistance of this layer increases the overall heat transfer coefficient and has an adverse effect on heat flow through the surface of the heat exchanger. In some instances this fouling layer can become the largest resistance to heat transfer.

Edit: Just noticed the OP was two weeks ago.