The cool choice

IN VIEW of the rising electric rates and regulations banning CFC-based refrigerants, absorption cooling which can help reduce electrical loads during peak demand and which uses water, the cleanest refrigerant around, seems the viable choice. Acknowledging this advantage, researchers at the us-based Gas Research Institute (GRI) have set out to counter the main disadvantage facing an absorption chiller-its cumbersome size. (Grid, Vol. 18, No.2).

The absorption equipment uses an absorber and a gas-fired boiler instead of the traditional compressor. The absorber contains an absorbent solution, generally lithium bromide, which soaks up the vaporised water-based refrigerant. Then the water and lithium bromide solution are separated through the use of a gas-fired boiler, the absorbent solution remains a liquid and is cycled back to the absorber, while the high-pressure refrigerant vapour passes on to th 'e condenser, thus bringing about refrigeration.

However, this approach requires a large absorber surface area and one of the methods to reduce the absorber dimensions is to introduce organic additives into absorbent solutions that enhance heat and mass transfer. This, however, is problematic in advanced absorption equipment that operate at increased temperature range, since additives tend to break down at high temperatures. GRI is therefore sponsoring research to learn about the detailed mechanism involved in the working of these additives in order to tackle this handicap.

On the other hand, GRI, in another research project, is offeriug the eventual possibility of eliminating additives altogether. By using specially designed heat-exchanger tubes, the performance ofabsorbent solutions has been equalled or exceeded. "We found that we could double the absorption rate on the surface of the tube by altering its geometry," says GRI's Bill Ryan.

While researchers are bent on cutting absorption chillers down to size to make it user-friendly for both small and large scale refrigeration, manufacturers in USA have already started studying these options put forth for possible future commercialisation.