Activated carbon, silica-gel and calcium chloride composite adsorbents for energy efficient adsorption cooling systems

In recent years, global warming and energy shortage have become more and more serious as economies develop rapidly all over the world. Adsorption cooling systems powered by solar energy or waste heat have drawn increasing attention, as such systems need neither CFCs nor HCFCs as the working fluid and neither fossil fuel nor electricity to drive them. Composite adsorbents were synthesized from activated carbon, silica-gel and CaCl2. The optimized condition for adsorption cooling systems was obtained when raw activated carbon was impregnated by soaking in 10 wt.% sodium silicate solution for 48 hours and then in 30 wt.% CaCl2 solution for 48 hours. A 0.805kg kg-1 of difference in equilibrium water uptake between 25°C and 115°C was recorded at atmospheric pressure. Besides, an adsorption rate test unit was built to study the adsorption isotherms and adsorption rates in which 0.23kg kg-1 of adsorption capacity was recorded at 27°C with a water vapor pressure of 900 Pa. The performance of a waste heat driven adsorption chiller by applying the novel composite adsorbent (silica activated carbon/CaCl2) was also studied. Modeling was performed to analyze the influence of the hot water inlet temperature, cooling water inlet temperature, chilled water inlet temperatures, and adsorption/desorption cycle time on the SCP and COP of the chiller system with the composite adsorbent. The simulation calculation indicates a COP value of 0.65 with a driving source temperature of 85°C in combination with coolant inlet and chilled water inlet temperature of 30°C and 14°C, respectively. The most optimum adsorption-desorption cycle time is approximately 360s based on the performance from COP and SCP. The delivered chilled water temperature is about 9°C under these operating conditions, achieving an SCP of 380W kg-1