Handbook of air conditioning and refrigeration / Shan K

Point Temperature,°F Concentration, % Enthalpy, Btu/lb
1 95 58.5 42
2 150 58.5 67.5
3 180 60.2 85
4 192 63.0 97
5 120 63.0 55.5
6 260 60.2 122.8
7 305 66.0 150
8 203 66.0 107.5
The mass flow rates of partly concentrated solution to the high-temperature heat exchanger and to
combine with the concentrated solution from the high-temperature heat exchanger are equal.
Finally, the amounts of water vapor boiled off from the high- and low-temperature generators
are equal.
Calculate the effectiveness of the heat exchangers and the coefficient of performance of this absorption
chiller.
Solution. From a psychrometric table, at a condensing temperature of 98°F, the enthalpy of
saturated liquid water leaving the condenser h lc � 66.03 Btu/lb, and the enthalpy of saturated water
vapor leaving the evaporator h ve at an evaporating temperature of 42°F is 1079.5 Btu/lb. From
Eq. (14.3), the mass flow rate of refrigerant per ton of refrigeration is therefore
As described in the previous section, the concentration of dilute solution from absorber is
58.5%, and the mean concentration of solution entering the absorber is 63%. From Eq. (14.5), the
mass flow rate of concentrated solution for each ton of refrigeration produced is therefore
m˙ s5 �
m˙ r � 12,000
h ve � h lc
� 11.84 lb / h � ton ref
X 1
X 5 � X 1
From Eq. (14.4), the mass flow rate of diluted solution per ton of refrigeration is
From Eq. (14.13), the effectiveness of the low-temperature heat exchanger can be calculated as
� l � h 4 � h 5
h 4 � h 1
From Eq. (14.12), the effectiveness of the high-temperature heat exchanger can be calculated as
� h � h 7 � h 8
h 7 � h 3
m˙ r �
� 153.92 lb / h � ton ref
m˙ s1 � m˙ s5 � m˙ r � 153.92 � 11.84 � 165.76 lb / h � ton ref
The mass flow rate of water vapor boiled off from the high-temperature generator is
�
�
0.585
0.63 � 0585 (11.84)
97 � 55.5
97 � 42
150 � 107.5
150 � 85
� 0.75
� 0.65
m˙ rh � 0.5m˙ r � 0.5(11.84) � 5.92 lb / h � ton ref
�
REFRIGERATION SYSTEMS: ABSORPTION 14.15
12,000
1079.5 � 66.03