# What is a safe and efficient temperature range for absorption chiller generators?

I've read that the role generators play in the absorption chiller cycle is to concentrate the salt solution so that the evaporator/absorber can maintain a vacuum by constant absorption of vapour entering from the evaporator. Now considering the vacuum conditions, water could boil at 3°C, which can easily serve our purpose of concentrating the salt solution.

Why then, do we have to use temperatures of around 80°C? How does a higher generator temperature affect the cycle, provided all other factors remain constant? And why does too high a generator temperature become dangerous/inefficient?

Also, if possible, explain the relationship between the gas and liquid phases of water at the generator and condenser, because I believe that the more you evaporate water off, the higher the head pressure becomes, and thus raises the boiling point as the salt solution becomes concentrated.

I love diagrams. So if one of you could provide one to visually explain the concept, I'd be grateful.

• Would the temperatures be defined by where it has to work? Jun 12 at 9:13
• @SolarMike I don't understand what you mean. Elaborate please. Jun 13 at 0:58
• How absorption chillers work is a complex process. There are plenty of resources on this cycle, but all will assume you are proficient with steam cycles and phase diagrams, plus the chemistry of solutions. This is not the right forum for teaching you all that. Suffice it to say that the generator is boiling the solution, so it needs to be hot, and it needs to be at a higher temp and pressure than the evaporator/absorber because heat only move from hot to cold; it's the delta in the boiling point temps that makes the device work. Jun 13 at 6:50
• @TigerGuy I just have a simple misunderstanding maybe. When you vacuum out air from this setup initially, do the evaporator/absorber AND generator/condenser compartments become vacuum OR ONLY the evaporator/absorber one does? Jun 14 at 4:44
• only the evap/absorber Jun 14 at 5:03