Environmental Engineering Reference
In-Depth Information
Duhring's rule for the solution field, where the internal temperatures of the generator
T G , condenser T C , absorber T A and evaporator T E are combined:
( T G
T A )
( T C T E )
B
=
(6.2)
For single effect water/lithiumbromide absorption chillers theDuhring factor ranges
between 1.1 and 1.2 for normal operating conditions. For a single effect ACM or
DACM with the ammonia/water, working pair the Duhring factor is between 1.6 and
2.4.
The cooling power Q E delivered by the evaporator of the machine is then a simple
function of the double temperature difference t
Q E = s ( t t min )
(6.3)
The slope s in Equation 6.4 contains the transferred power UA between external
and internal circuits and the enthalpy differences in each component related to the
specific evaporation enthalpy. For example, for the condenser C E is obtained from the
enthalpy difference between the incoming refrigerant vapour and the exiting liquid
refrigerant: C E =
h exit,cond ) /q evaporation . Likewise in the generator, G E
is calculated using the enthalpy difference between the expelled refrigerant and the
solution outlet and A E with the enthalpy difference between the incoming refrigerant
vapour and the incoming weak solution for the absorber. The intersection t min is
given by the performance of the solution heat exchanger:
( h entry,cond
G E
UA G +
B C E
1
A E
UA A +
1
UA E
s
=
UA C +
(6.4)
Q gx
UA G +
Q ax
UA A
t min =
(6.5)
The solution heat loss Q gx describes the enthalpy difference between generator
outlet and solution inlet, that is after the heat exchanger:
m sr h solution,outlet
h solution,inlet
Q gx =
(6.6)
Likewise Q ax contains the enthalpy difference between the solution entering the ab-
sorber, that is returning from the heat exchanger, and the solution exiting the absorber,
multiplied by the rich solution mass flow. The generator power is also a function of
s and the double temperature difference t . In addition the solution heat loss Q gx  Search WWH ::

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