Experiment of adsorption refrigeration system with working pairs of difluoromethane and activated carbon modified by sulfuric and nitric acids

Abstract

Adsorption refrigeration system is one of the thermal powered refrigeration that is needed to be developed due to its low performance, even though it has the advantage of utilizing low heat source in the form of either waste heat or solar energy. Its low heat and mass transfers and low specific power should be improved to increase its performance. Adsorption bed playing important role in adsorption refrigeration cycle should be improved by conducting a research on modification of activated carbon (AC) to increase their performance. Difluoromethane, famously known as R32, is chosen as adsorbate (refrigerant) since this low global warming-potential refrigerant proved high performance in vapor compression refrigeration system even though it is flammable. Local AC is chosen as adsorbent due to this material is easily found in market. The tests were conducted to obtain cooling effect, performance and the effect of final desorption temperature. An adsorption cooling system with two adsorption beds was tested by using difluoromethane with AC modified by sulfuric acid (H2SO4) and nitric acid (HNO3). Both these acids can improve the performance of AC characteristics compared to that of pure AC, in which average cooling capacity increases by 6.6% for both acids, and the average coefficient of performance (COP) increases by 9.8% for HNO3 and 5.1% for H2SO4. By using the final desorption temperatures of 55°C, 65°C and 75°C, the H2SO4 modified AC showed the cooling effect in the cooling cycle of between 17 to 36 kJ, and the obtained COP were 0.15, 0.18 and 0.20, while the specific cooling power (SCP) were between 4.4 to 6.1 W/kg AC for cycle time of 36, 40 and 50 min. The test results for HNO3 modified AC showed the value of cooling effect ranged between 17 kJ to 37 kJ for cycle time 36, 40, and 50 min at final desorption temperature of 55°C, 65°C and 75°C, respectively. The COP ranges were from 0.14 to 0.22, while the SCP ranges were from 4.0 to 6.3 W/kg AC.