5 replies to this topic

[raajesh]

what is the actual procedure for estimation of the heat transfer coefficients while designing a shell and tube heat exchanger?

[Zauberberg]

First you pick up some of the literature values ("estimates"), and then choose the exchanger/geometry, and then calculate the heat transfer coefficients to verify if your assumption was correct. There is no procedure for estimation of U-values, those are experience-based rules.

http://www.cheresour...xchangers.shtml

[Root]

what is the actual procedure for estimation of the heat transfer coefficients while designing a shell and tube heat exchanger?

Raajesh,

You need to study in detail for HE design, and you can start from this equation;
U=hADelt T
where;
U= overall Heat duty
h=Heat transfer coefficient and this depend on R and hot and cold fluids
A= area of heat transfer
Delta T= delta T in between the stream you want to heat up.
Hope this will give you good starting point.
Cheers
Toor

[srfish]

what is the actual procedure for estimation of the heat transfer coefficients while designing a shell and tube heat exchanger?

There is an equation for the overall hear transfer coefficient for hydrocarbons at www.gulleyassociates.com. After you logon, click on Engineering Tips, then scroll down to the calculation section. The equation is a function of the average viscosities of the shell side and tube side. Again this is only for hydrocarbons.

[rizaldi]

First, you have to estimate the properties of the fluid at a specified temp. Since the temperature varies across the tube then you will need to do iterative solution of heat transfer coefficient. Temperatures will vary at different length positions of the tube.

Overall heat transfer coefficient is a combiantion of the internal heat transfer coefficient (hi) (transfer between inside tube fluid with tube wall), conduction at tube wall, and the outside heat transfer coefficient (transfer between tube wall to shell fluid).

You can find empirical equations for internal and external heat transfer coefficients (hi & ho) in many texbooks. Each equation usually only governs for specific condition (ex: laminer of turbulent flow, forced convection or natural convection, etc..)

You can use one of my example algorithms:

Step by Step calculation of Tx are:

1. Give Initial Guess of Tx =

2. Evaluate properties (Cp,ρ,μ) at

3. Calculate Segment Surface Area:
A =
4. Calculate fluid velocity (v)
v =
5. Calculate internal heat transfer Coefficient:
6. Evaluate shell Reynold Number
Re,shell =
7. Calculate Outside Heat Transfer Coefficient (function of Reynolds Number and Prandtal number of shell fluid ):
8. Calculate U = 1/[(1/hi) + (dx/k) + (1/ho)]
9. Calculate new value of Tx (Equation involve U )
10. Repeat Step 1- 9 until you get new value of Tx is same with previous Tx value.
11. Then, that is your U value...for specific point of tube location.

When the heat transfer coefficient is establshed, then you will need to evaluate temperature then evaluate the properties again..

[raajesh]

Thank you very much. I got the idea.