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5. SIMULATION AND RESULTS
Figure 5.3: A: Comparison of COP ABS for 1: a system without solution heat exchanger, 2:
at standard parameter configuration (∆T min,SHE X = 5 ◦ C) and 3: with ideal heat exchanging
(∆T min,SHE X = 0). B: The curves with dotted markers show the heat capacity flow of the weak
and strong solution. The curves with triangular markers show ∆T min at each end of the SHEX.
No SHEX
If the SHEX is not present, COP ABS will increase as long as T DES increases,
only limited by the maximum concentration of w ss (which is about 75%,
see appendix B.4 page 231). The explanation is that before evaporation
can take place, each kg of solution entering the desorber from the
absorber has to be heated up from 31 ◦ C (T ABSO ) to T DES which requires
energy without creating refrigerant. So it is an advantage to evaporate
as much water per kg of LiBr solution as possible. And this is done by
having a large difference in concentration between ws and ss (i.e. a high
desorber temperature).
Ideal SHEX
For the ideal SHEX (∆T min,SHE X = 0) COP ABS will have an optimum at
T DES = 72 ◦ C. At this point the difference in concentration of the strong
and weak solution is very small, which leads to a very large pumping
factor (PF), see figure 5.2B.
108
The reason why the SHEX makes a lower temperature more advanta-