Here is a quick walk-through of a typical ammonia-water chiller you may find useful.
An aqueous ammonia concentrated solution is evaporated using a heat source to generate a nearly dehydrated ammonia vapor. The vapor is at a decently high pressure.
The dehydrated ammonia vapor continues to the condenser where it is cooled and condensed. The pressure is slightly lowered.
The condensate then passes through an expansion valve lowering the temp and pressure of the fluid.
The ammonia liquid now enters the evaporator where it takes on heat from the substance being cooled (where the refrigeration takes place). After taking on this heat the ammonia liquid flashes and exits the evaporator as a vapor.
After exiting the evaporator as a vapor ammonia is pulled into the liquid phase by absorption. In the absorber unit an ammonia water mist is usually introduced. The ammonia vapor has a high affinity to this solution. The concentrated ammonia liquid is collected usually at the bottom of the unit and pumped to the generator. Where step 1 begins.
You will notice unlike the traditional refrigeration cycle we are using a pump to take the fluid from low to high pressure. There isn’t a compressor.
Now to answer your specific concern about how water is boiling and condensing at different temperatures:
In the absorption chiller, the condenser is at a relatively high
pressure. This is because its feed is coming from the generator whose
purpose is to heat up the aqueous ammonia solution to achieve
separation from the two compounds. The effluent hot dehydrated
ammonia's saturated pressure will therefore be relatively high.
In the evaporator section of the chiller (downstream and where we are
chilling the external fluid) the entering ammonia liquid concentrate
is at a lower temp (Te) and pressure. Why? Because it was just
throttled through an expansion valve. Hence the saturated vapor temp
of evap unit is lower than that of condenser unit.
To Answer your specific concern about the applicability of ammonia water chilling to LiBr.
- How does ammonia-water chiller apply to a different technology like
water-LiBr chiller? Simply put the coolant role played by ammonia
in the example is played by water in the LiBr chiller. The
absorption role played by water in the example above is played by
In the absorption chilling cycle pressures and temperatures will vary
greatly depending on what unit you are talking about, but there isn’t
any whacky thermo going on here. You described the generator being
coldest and at low pressure in the problem statement, usually the
generator is at the highest pressure and the hottest. I don’t know
your set-up but you may have confused the generator with the