Experimental Study of a Diffusion Absorption Refrigeration Unit at Different Charge-Pressures

Diffusion absorption refrigeration (DAR) is a cooling technology without moving parts or the need for electrical input and can be driven purely by thermal energy, such as renewable- or waste-heat. In this work, the performance of an ammonia-water-hydrogen DAR unit was investigated experimentally at three different charge-pressures (15 bar, 18 bar, and 21 bar), two cooling temperatures (5 °C and 23 °C), and an ammonia concentration of 30%. The thermal power was supplied by an electrical heat-source to the generator and varied between 150 W and 700 W. The highest coefficient of performance (COP) was observed at a charge pressure of 15 bar, and was found to be 0.25 for a cooling temperature of 5 °C and 0.31 for a cooling temperature of 23 °C. In part-load operation, when the generator power was below 250 W, an increase in the charge pressure reduced both the cooling power and the COP. For a generator power between 250 W and 500 W, an increase in the charge pressure reduced the cooling power for a cooling temperature of 23 °C, but had no effect on the system’s cooling power for a cooling temperature of 5 °C, while no effect was observed on the COP. For a generator power above 500 W, an increase in charge pressure increased both the cooling power and the COP. Finally, a solar-powered DAR prototype, developed based on the above findings, was also tested. The diurnal performance of this unit is presented, showing the potential for activating DAR systems using low-cost solar heat-pipes.

Keywords:

cooling power , COP , DAR , solar cooling , pressure.