Active Thermal Cooling Technologies - Low Energy Cooling for Sustainable Buildings - page 163

60

expelled ammonia vapour
lifted weak solution

50

40

30

20

10

0

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0

Generator heat input / kW

Figure 5.50 Mass flow of ammonia vapour and lifted solution as a function of generator power

the weak solution or the rectified liquid concentration, and has been calculated using
empirical equations from Jain and Gable (1971).
For prototype 1, the calculated solution mass flows for external generator inlet tem-
peratures of 147 to 172 ◦ C resulted in values of 20 to 40 kg h − 1 for the weak solution
and 25 kg h − 1 up to 46 kg h − 1 for the rich solution. The values were obtained for an
external generator volume flow of 21 l min − 1 and an average total pressure of 20 ×

10 5 Pa. For the operation of prototype 2, lower external generator inlet temperatures
of 115 to 150 ◦ C were sufficient. The calculated average mass flow rates were between
14 and 45 kg h − 1 (see Figure 5.50) for the weak solution and between 17 and 53 kg h − 1
for the rich solution. The expelled ammonia vapour which was produced by the gen-
erator of prototype 1 was determined from all of the measurements between 4 and
8kgh − 1 . This should have given sufficient cooling capacity, but in the first pilot plant
the auxiliary gas circulation was insufficient and a fast ammonia saturation occurred
in the evaporator. Consequently, only limited evaporator cooling capacity could be
generated. The ammonia vapour mass flow of the generator of prototype 2 ranged
between 1 and 4 kg h − 1 during the first measurements. After modification of the plate
heat solution heat exchanger (SHX) to a coaxial heat exchanger, the ammonia liquid
mass flow reached higher values between 2.5 and 10 kg h − 1 depending on the external
generator inlet temperature and the volume flow. Therefore, the design values were
also obtained with the last set-up of the second pilot plant.
The developed bubble pumps worked over a wide range of temperatures as well
as external heating volume flow rates. Figure 5.51 shows a comparison of COPs and
evaporator cooling capacities at a high and a low generator external heating volume
flow of prototype 2 with coaxial SHX. The cooling capacities were approximately
30% higher when a high volume flow rate was used, enhancing the heat transfer.