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3.6. Desorber - DES
3.6 Desorber - DES
In the desorber the weak water-LiBr solution enters (either sub cooled or
saturated liquid) and is mixed with the solution in the desorber, which
is heated up by the heating water circuit. Hereby the refrigerant (water)
is evaporated, and strong solution LiBr (which is saturated) is returned
towards the absorber. See figure 3.7.
Figure 3.7: Desorber component. Weak solution (ws,i) enters the desorber and is heated by the
heating water (h,i and h,o). Refrigerant in gas phase (r,o) is sent out through an outlet at the
top, while the strong solution (ss,o) leaves at the bottom of the desorber.
The desorber is made up by a reservoir of solution in which some
heat exchanger tubes with the warm heating water run. On top there is a
gas phase of refrigerant. In the model it is assumed that the temperature
is the same throughout the liquid phase and the gas phase. So when
the weak LiBr solution enters the reservoir, it instantly becomes perfectly
mixed with the rest of the liquid phase.
It is also assumed that the outlet temperature of the refrigerant
(superheated steam) is the same as the outlet temperature of the solution,
after all, the water has been evaporated from the solution (at which point
they must have the same temperature), and no heating or cooling is
assumed to happen to the gas after the evaporation (hence T ss,o = T r,o ),
see figure 3.8.
Since it is assumed that the temperature of the solution is the same
throughout the desorber, only the heating water changes temperature.
Hence the closest approach temperature difference appears between
the outlet temperature of the heating water (T h,o ) and the mutual
temperature of the refrigerant and solution (T ss,o = T r,o ):
∆T minr,o = T h,o − T ss,o (3.29)
Since only the heating water changes temperature during the heat
exchange process, the effectiveness will be based on the heating water
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