Effect of generator temperature on the performance of the ammonia-water absorption refrigeration machine working with solar energy

Abstract

Absorption refrigeration machines are receiving a great attention from researchers and manufacturers worldwide since they utilize thermal energy that can be obtained from the sun in addition to that their working fluids do not harm the environment. One of the most common working fluids is the pair solution (ammonia-water) which allows us to obtain temperature as low as -60 [ºC]. The machine contains the generator, which has the function of releasing the refrigerant vapor, ammonia, from the liquid solution inside it by supplying it with heat from an external source like the sun. The boiling of the liquid solution is accomplished at constant pressure but with varying temperature from the boiling start temperature to the condensation start temperature, therefore, there is a big range of possible generator temperature values. Determining generator temperature that leads to the highest value of the coefficient of performance, COP, of the cycle is an important point because it indicates the least energy consumption for providing certain cooling load. In this research the effect of the generator temperature on the performance of the absorption refrigeration machine is studied for several evaporation temperatures and two different condensation temperatures. The results show that the highest value of the COP is achieved within the range of 1.011 ~ 1.055 of the ratio t_G/t_b (the ratio of the generator temperature to the start boiling temperature), i.e., at a temperature that is very close to the start boiling temperature of the liquid solution in the generator. The results also show that the range of the ratio t_G/t_b that provide the highest value of COP decreases with condensation temperature decrease.