Handbook of air conditioning and refrigeration / Shan K

14.12 CHAPTER FOURTEEN
Also,
Thermal Analysis
C cir �
When the absorption chiller operates at steady-state condition, the heat balance analyses for the
main system components, in Btu/h�ton, are shown below:
In the evaporator, for 1 ton of refrigeration load (kW) Q rl, in Btu/h�ton ref (kW/kW ref),
In the absorber, the heat of entering water vapor is equal to the heat of leaving water vapor in the
evaporator:
where h 1, h 5 � enthalpy of solution leaving and entering absorber, Btu/lb (kJ/kg)
Q ab � heat to be removed from absorber, Btu/h�ton ref (kW/kW ref)
(14.5)
where X1, X5 � mass fraction of LiBr in diluted and concentrated solution leaving and entering
absorber
m˙ s1 � mass flow rate of diluted solution per ton of refrigeration, lb/h�tonref (kg/s�kWref) m˙ s5 � mass flow rate of concentrated solution entering absorber per ton of refrigeration,
lb/h�tonref (kg/s�kWref) m˙ s7, m˙ s9 � mass flow rate of partly concentrated solution per ton of refrigeration at points 7
and 9, respectively, lb/h�tonref (kg/s�kWref) m˙ rl, m˙ rh � mass flow rate of refrigerant boiled off from low-temperature generator and hightemperature
generator per ton of refrigeration, lb/h�tonref (kg/s�kWref) Ccir � circulating factor
To help determine the status of the solution in the absorption cycle of a double-effect, direct-fired,
reverse parallel flow absorption chiller as shown in Figs. 14.3 and 14.5, the state points of the cycle
are defined as follows:
1 � Mean condition of the diluted solution
leaving the absorber
2 � Dilute solution leaving the low-temperature
heat exchanger
3 � Partly concentrated solution leaving
the low-temperature generator
4 � The condition of the mixture of partly
concentrated and concentrated
solutions entering the low-temperature
heat exchanger
m˙ s5 � X 1m˙ r
X 5 � X 1
X 1
X 5 � X 1
Heat of leaving heat of entering refrigeration
water vapor � liquid
�
load
m˙ rh ve � m˙ rh lc
5 � Concentrated solution entering the
absorber
6 � Partly concentrated solution leaving
high-temperature heat exchanger
7 � Concentrated solution leaving hightemperature
generator
8 � Concentrated solution leaving hightemperature
heat exchanger
9 � Partly concentrated solution leaving
low-temperature generator
� m˙ r(h ve � h lc) � Q rl
Heat of entering heat of entering heat of heat to be removed
�
water vapor
�
solution leaving solution
�
from absorber
m˙ r h ve � m˙ s5 h 5
� m˙ s1h 1
� Q ab
(14.6)
(14.7)