Energy analysis and modeling study of combined activated carbon-silica gel/methanol adsorption ice production system
In this article, the transient modelling for a new construction of the Adsorption cold production was investigated. This system, named in this work the combined Adsorption Ice Production system (com-AIP system), was filled by both silica gel (SG) and activated carbon (AC) together in one adsorption reactor as the adsorbent and methanol as the adsorbate and refrigerant. A fined-tube heat exchanger was designed (named combined adsorption reactor) in order to contain two different adsorbents in the adsorption reactor and increase the heat transfer ability between the particles of adsorbents and heat exchanger fins. As a result the input energy required from the external heat source is saved and the coefficient of performance COP of the com-AIP system is improved. The mass flow rate of refrigerant increases and consequently, the refrigeration energy Qe rises too. A cycle simulation computer program of this innovative bed was developed to analyze the refrigeration energy and COP variations by varying heat transfer fluid (hot, cooling and chilled water) inlet temperatures and adsorption/desorption cycle time. The transient behavior of heat and mass transfer fluids has been also studied. Under the standard test conditions of 100 °C hot water, 24 °C cooling water, and 15 °C chilled water inlet temperatures, the simulation results showed that the amount of the ice produced per cycle of 5.34 kg and 0.73 COP can be achieved from the com-AIP system. It was found that the system performance is very much sensitive to the mass flow rate of the refrigerant. The cycle time of the system is not dependent on the amount of the adsorbents but is strongly dependent on driven temperature of heat exchange fluid and the design of the heat exchanger. The com- adsorption reactor allows using the advantages of physical properties of both adsorbents SG and AC. Consequently, this innovative com-AIP system utilizes effectively low-temperature heat sources of temperature between 65 and 100 °C, because of the inferior thermodynamic properties of methanol and the low regeneration temperature from silica gel and activated carbon as adsorbents. This strategy (com-AIP system) is completely different from the conventional adsorption reactors, which are filled with one adsorbent in one bed or in two beds.