Pompetravaini TRSK 2002/1, Operating Manual, Page: 26 / 32

Operating manual liquid ring vacuum pumps TRVK - TRSK
26
17 - ENGINEERING DATA
17.1 - INFLUENCE OF SERVICE LIQUID TEMPERATURE, SPECIFIC GRAVITY AND VISCOSITY ON PUMP
PERFORMANCE
The performance of liquid ring vacuum pumps is based on the use of water at 15°C as service liquid. With water at
different temperatures the pump capacity and the maximum attainable vacuum level will vary in function of the type of
pump, as illustrated by the curve sets of fig.26.
EXAMPLE: Pressure = 60 mbar - Water temperature = 24°C - Pump series TRVK - Capacity (15°C) = 12000 m
3 /h From
curves of fig. 26 we find the correcting factor of 0,85, therefore the actual capacity for the pump at the given
conditions will be: 12000 x 0,85 = 10200 m
3
/h.
The maximum suction pressure before incurring cavitation will be approximately 52 mbar.
Regarding the performance variation due to changes of specific gravity and viscosity, it can be assumed a proportional
variation in power consumption however, the changes in capacity at different pressures must be analysed case by case.
Please refer the conditions to POMPETRAVAINI when these corrections are needed.
Fig. 26
CAPACITY FACTOR
17.2 - SERVICE LIQUID TEMPERATURE CHANGE ACROSS THE PUMP
The service liquid of a liquid ring pump absorbs total heat Q
T
as follows:
Q
T
(kJ/h) = Q
c
+ Q
K
+ Q
R
where:
Q
C
= 0,9 x P x 3600 = Isothermal compression heat
Q
K
= m
V
x r = Condensation heat
Q
R
= m
g
x c
p
x
ΔT
a
= Cooling heat (generally negligible, ignored in calculation of Q
T
)
m
v
= mass condensed incoming vapour in kg/h
m
g
= mass incoming gas in kg/h
P = absorbed power at operating point in kW
c
P
= gas specific heat in kJ/Kg x K
r = heat of vaporisation in kJ/Kg
ΔT
a
= differential temperature in K, between incoming gas T
G
and service liquid discharge temperature (T
2
+
ΔT)
K = Kelvin temperature
Once the Q
T
is known it is possible to calculate the differential temperature
ΔT of the pump service liquid:

T
Q
Q c
T
A p
=
  
where:
Q
T
= total heat load before calculated in kJ/h
Q
A
= pump service liquid flow in m
3
/h
ρ
= service liquid density in kg/m
3
(water = 1000)
c
P
= service liquid specific heat in kJ/kg x K
(Some values for c
P
: Water = 4,2 - Air = 1,0 - Water Vapour = 1,84)
NOTE: It can be assumed that the discharge gas and service liquid have same temperature.
LIMITE CAPACITA' DI ASPIRAZIONE - Lowest allowable suction pressure
Service water temperature
TEMPERATURA DELL'ACQUA DI ESERCIZIO
50°C
45°C
40°C
35°C
32°C
30°C
28°C
26°C
24°C
22°C
20°C
18°C
16°C
15°C
14°C
12°C 10°C
PRESSIONE ASSOLUTA - Absolute pressure
PRESSIONE ASSOLUTA - Absolute pressure
R
AP
POR
T
O D
I P
OR
T
AT
A -
Te
mp
e
ra
tu
re
f
a
ct
o
r
1,4
1,3
1,2
1,1
1,0
0,9
0,8
0,7
0,6
0,5
0,4
0,2
25
150
150
Torr 20 50 30 100 200 300 500 700
mbar 1000 700 500 300 70 200 100 50 40 30
0,3
0,2
0,4
0,5
0,6
0,7
0,8
0,9
1,0
0,3
1,1
MAXIMUM OPERATING PRESSURE
SERVICE LIQUID TEMPERATURE
ABSOLUTE PRESSURE
ABSOLUTE PRESSURE