Active Thermal Cooling Technologies - Low Energy Cooling for Sustainable Buildings - page 171

of the available liquid ammonia into the helium gas atmosphere, not even with high
external evaporator inlet temperatures of around 25 ◦ C. Therefore, the falling film
evaporator needed to be rebuilt with either more or longer evaporation tubes so that a
larger heat transfer surface would exist, which would lead to a smaller film thickness
and, therefore, a longer delay time. Also, the issue of liquid distribution into the evap-
orator tubes plays an important role in the evaporator performance. At the given very
low condensate flow rates it is extremely difficult to obtain an even distribution of
liquid into all the tubes of the evaporator. Experiments with metal wicks and annular
capillary systems are currently being carried out to improve the liquid distribution.
First Experimental Results from the Third Prototype The experimental inves-
tigations of the third prototype with marketable dimensions were focused on the
combined evaporator-GHX-absorber unit and the newly designed generator (see
Figure 5.60).
The heating temperature range of the generator was reduced from 150 to 175 ◦ C
for the first prototype to 110 to 155 ◦ C for the second prototype and then to 100 to
150 ◦ C for the third prototype. Very stable operation was achieved during the first
experiments; however, cooling water temperatures and the cooling power obtained
were rather low (see Figure 5.61).
The first experimental results gave evaporator cooling capacities from 0.7 up to
3.0 kW and COPs between 0.12 and 0.38. The evaporator temperatures chosen were
12/6 ◦ C and 18/15 ◦ C (see Figure 5.62). The cooling water temperatures at a constant
Figure 5.60 Components of the third prototype