Explain what is meant by an 'overall heat transfer coefficient

[Tiberious]

Homework Statement

(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. 


Homework Equations

None provided.

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.

 

[CWatters]

(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)

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

1/U_T = 1/U₁ + 1/U₂ + 1/U₃ …… 1/U_N

where U_T is the overall heat transfer coefficient and U_N is the heat transfer coefficient of layer N.

(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.

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.