Theoretical And Experimental Investigations Of The Equilibrium Study For Fluidized Bed Adsorption Refrigeration

The development of more effective systems for utilizing energy resources is becoming increasingly important. Rapid development in the developing countries is leading to significant increases in global energy consumption. About 15% of the energy consumption in the world is going on the refrigeration and heat pump systems for food and medicines preservation, human comfort and other purposes. This trend has both economic and environmental implications. In recent years, the production of greenhouse gases and other environmental concerns associated with the combustions of fossil fuels and the depletion of the ozone layer by the refrigerant used in the refrigeration and heat pump have received increased attention.The development of low thermally driven refrigeration system can help to reduce the impact of growing energy needs by improving the effectiveness with which fossil fuel resources are used. These systems use the low thermal energy such as waste heat, solar energy, geothermal energy etc, to provide cooling and heating directly. By doing so, they can eliminate the inefficiencies associated with the conversion of thermal energy to electricity as required by traditional vapour compression refrigeration. The ability to use thermal energy directly for cooling and heating purpose also provides for rural people of developing countries, without access to modern electricity and industries with better opportunities for the use of renewable energy sources for the former one and the recovery of waste heat for the latter. The solid sorption refrigeration and heat pump system is one of the promising thermally driven refrigeration systems. Adsorption refrigeration cycles can provide high performance, simple operation, no moving parts and wide operating temperature ranges.On the other hand, in modern design of adsorption refrigeration and heat pump, the choice of the appropriate adsorbent-adsorbate pair is one of the key factors determining the performances and also the behavior of the system. In this thesis, equilibrium of some low pressure substance working pairs and the performances of adsorption refrigeration using a fluidized bed adsorber are investigated. These performances are generally dependent on the adsorption and desorption capacities, and also to the latent heat of the vaporization of the refrigerant. So the equilibrium study of a working pair is considered as the first step of each adsorption refrigeration and heat pump system design.In the first part of this work, a deep equilibrium study using a thermobalance of the zeolite and two natural environmentally working fluids named ethanol and water is presented and the equilibrium data are obtained. The modified Dubinin-Astakhov (DA) equation is used to calculate some equilibrium coefficients, the results show that the maximum adsorption capacity of water is higher than that of the ethanol and especially at low temperature. Thermal desorption is also carried out in order to evaluate the desorption capacity at different desorption temperatures and then deduced the cooling capacity, the results show that the desorption capacity of water is higher than that of ethanol at all temperatures and also ethanol need a high temperature to be regenerate from zeolite 13X, which means ethanol is very hard to regenerate from the zeolite 13X. In the second part, the activated carbon coconut shell as adsorbent with two alcohols named methanol and ethanol, and an HCFC refrigerant named R123 with low ODP, short lifetime and also very low GWP are investigated using the same thermobalance. The equilibrium study is carried out and equilibrium data are obtained, the same form of a modified DA equation is used to investigate the data in order to find some parameters of the equation, the results show that the maximum adsorption capacity of R123 is higher than that of the ethanol and methanol at all adsorption temperatures. Thermal desorption is also carried out and the results demonstrate that the desorption capacity of R123 is higher than that of alcohols at all desorption temperature and especially at low temperature. At last, the cooling capacity is calculated. After the deeply equilibrium adsorption and thermal desorption studies and also for the reasons of security, and thermophysical properties such pressure, density, the R123-activated carbon is chosen as working pair for the new refrigeration system using a fluidized bed adsorber.Finally the new working pair is used on the fluidized bed for a test set-up. An experimental study is carried out. Temperature profiles at various operating conditions were measured. Adsorption and desorption at different levels are investigated and the desorbed mass is obtained at given temperatures of the bed, condenser and evaporator. The data of intermittent mode are used to calculate the performances of the new adsorption refrigeration system. A new correlation between the heat of adsorption and the adsorption capacity is found. The obtained SCP shows that the new system performances are much better than the traditional ones for an intermittent adsorption refrigeration system.The performances of the new system obtained varied between 0.13 to 0.23 for the COP whiles the SCP between 128.2 to 176.70 W/kg for condenser, bed and heat source temperatures respectively 28℃, 92℃and 180℃. The average performances from the experiment results are the about 0.16 for the COP and 140 W/kg for the SCP.