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Estimation of the “true temperature difference” from the logarithmic mean
temperature difference by applying a correction factor to allow for the
departure from true counter-current flow:
ΔT
m = Ft ΔT tm
(eq – 1.10)
Where ΔT m = true
temperature difference, the mean temperature difference for use in the design eq.
1.3.
Ft
= the temperature correction factor.
The correction factor is a
function of the shell and tube fluid temperatures, the number of tube and shell
passes. It is normally correlated as a function of two dimensionless temperature
ratios:
R = (T1 – T2) (eq – 1.11)
(t2 –
t1)
and
S = (t2 – t1) (eq – 1.12)
(T1 – t1)
R is equal to the shell-side fluid flow-rate times the fluid
mean specific heat; divided by the tube-side fluid flow-rate times the tube-side
fluid specific heat.
S is a measure of the
temperature efficiency of the exchanger.
For a 1 shell: 2 tube pass
exchanges, the correction factor is given by:
Ft
= . √(R2 + 1) ln [(1 – S)/(1 –
RS)] . (eq - 1.13)
(R – 1) ln [(2 – S (R + 1 - √(R2 + 1))/ (2 – S (R + 1 -
√(R2 + 1))]
The
derivation of equation 1.9 is for a 1 shell : 2 tube pass exchanger can be used
for any exchanger with an even number of tube passes. Plots of the same can be
seen in the books. Page:
1 |
2 |
3 |
4 |
5 | 6
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8 |
9 |
10 | 11 |
12 |
13 | 14 |
15 |
16 | 17 |
18 |
19 | 20
Introduction |
Combined heat transfer process |
Heat transfer in cooling tower |
Variables affecting performance of CT heat transfer |
Heat transfer within
cooling system (heat exchanger) |
Types of heat exchanger |
Basic design
procedure and theory |
Designing a test heat exchanger |
Log Mean Temperature
difference | L.M.T.D. Correction factors |
Overall heat transfer coefficient |
Elaborated method for calculating U values |
Effect of scale formation |
Condensation of steam |
Condenser, where the hot fluid temperature varies |
Significance of pressure |
Significance of flow rate |
Methods of checking steam
condenser performance |
Common conversion factors
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