Civil Engineering Reference
In-Depth Information
15.6.8 Rotary Regenerator
This exchanger consists of a disk, made of materials with a significant heat
capacity, which rotates side by side between cold gas and hot gas ducts. The disk
acts as an intermediate medium: it stores heat from the hot gas and it transfers heat
when it moves in the area of the cold gas duct. The effectiveness of this system is
very high, more than 90 %.
Attention must be paid to cross-contamination between the gas streams; this can
be reduced by special devices such as labyrinth seals.
15.7
Practical Examples
Example 1
Cooling water-to-process water exchanger (log-mean method)
A process water flowing at 8 kg/s must be cooled from a temperature of 110
C
to a temperature of 40
C using cooling water at the same flow rate. The inlet
temperature of the cooling water is 15
C and the desired outlet temperature is
85
C. The pressure of the two fluids is around 0.3 MPa. A preliminary evaluation
of possible heat exchangers is required (see Sect.
15.5.1
for the log-mean tempera-
ture method).
Given temperatures:
110
C
T
lo
¼
40
C
T
1i
¼
15
C
T
2o
¼
85
C
T
2i
¼
Step 1
Calculate the heat flow rate
Q
of the two streams:
- Stream 1 (hot water):
Q
¼
8
4,186
(110
40)
¼
2,344,000 W
¼
2,344 kW
- Stream 2 (cold water):
Q
¼
8
4,186
(85
15)
¼
2,344,000 W
¼
2,344 kW
Step 2
Calculate the difference between the temperatures of the fluids at the two sides of a
counterflow exchanger:
T
1i
T
2o
¼
¼
25
C
110
85
T
1o
T
2i
¼
¼
25
C
40
5
25
C (in this case, it is constant along the counterflow exchanger).
T
¼
25 K
¼
Δ
R
¼
(110
40)/(85
15)
¼
1
P
¼
(85
15)/(110
15)
¼
0.73
Correction factor FT is preliminarily assumed to be equal to 1.
