| The solar adsorption refrigeration system with silica gel-water as working medium has developed rapidly with the characteristics of low temperature driving heat source required,simple structure and no moving parts.But its refrigeration performance is low,and the initial investment cost is high.Adsorption desalination technology is mainly through adsorbent such as silica gel to refrigerant water vapor adsorption and desorption to achieve the brine separation.The system can be powered by low-grade energy sources such as solar and geothermal energy of from 60 to 90℃.But the initial investment cost is high.In this paper,the adsorption refrigeration system and the adsorption desalination technology are combined(an integrated device and method of solar adsorption heating,cooling,water purification,invention patent CN 107576093 A).The adsorption and desorption characteristics of the adsorbent were measured by mechanism experiments.The concentration of ions in water were detected by ion chromatograph(ICS)and inductively coupled plasma chromatography(ICP).The influence of adsorption temperature and desorption temperature on the cooling coefficient(COP)and the cooling powerof unit adsorbent mass(SCP)was calculated by thermodynamic theory.Then the solar energy small refrigeration and water purification integration adsorption device was designed.The performance of adsorbent pairs was very important to the operation of the whole system,and the adsorption and desorption characteristics determined the size and refrigeration performance of the whole adsorption device.In this paper,macerating method was used to combine coarse pore(type C)silica gel with CaCl2 to form a composite adsorbent,then the the fine(type A),medium(type B),coarse(type C)and C/CaCl2 composite silica gel were characterized respectively by the specific surface area and aperture distribution analyzer(BET),scanning electron microscope(SEM)and energy spectrometer(EDS)and other instruments.The adsorption and desorption curves of different silica gels were measured by gravimetric method and the temperature programmed desorption,and the desorption activation energy and desorption heat of water were calculated.They were proved by calculation that the adsorption of pure silica gel to water molecule was physical adsorption,while the adsorption of CaCl2 molecule to water molecule was chemical adsorption.The desorption activation energy and desorption heat of C type silica gel were the lowest,and the adsorption capacity of C/CaCl2 silica gel was the largest.For the solar adsorption refrigeration system,the type C/CaCl2 silica gel with maximum adsorption was selected as adsorbent in areas with sufficient solar energy,and the type C silica gel with the lowest desorption activation energy and desorption heat was selected as adsorbent in areas with insufficient solar energy.According to the experimental data,the adsorption/desorption characteristics of different adsorbents were analyzed.In the actual system,the adsorption and desorption conditions were selected as the relative humidity of 50%,the adsorption temperature of 20℃,the desorption temperature of 90℃,and the surface density of 15.2866kg/m3.A large number of repeated adsorption/desorption experiments were conducted to study the attenuation characteristics of C type and C type/CaCl2 composite silica gel.With the increase of adsorption/desorption cycle times of the adsorbents,the adsorption percentage of the two kinds of adsorbents showed a decreasing trend.Heating the adsorbent that after a certain number of uses at high temperature(no more than 120 C)can effectively improve the adsorption performance of the adsorbent,and the number of times of use was increasing.It was not necessary to change the adsorbent too frequently The concentration of ions in water were detected by ion chromatograph(ICS)and inductively coupled plasma chromatography(ICP).The concentration of ions in the purified water obtained by silica gel adsorption and desorption was within the range specified in the national standard for drinking water hygiene(GB 5749-2010).It indicated that the purified water meeted the standard of drinking water.Based on the theoretical basis of engineering thermodynamics,the influence of adsorption temperature and heat source temperature on the COP and SCP of system was calculated and analyzed with the measured data in the experiment.The theoretical calculation provides certain analysis and guidance to select appropriate adsorption/desorption conditions for the practical operation of adsorption refrigeration system.Then the solar refrigeration heating water purification integration small adsorption device was designed.The adsorption bed,evaporator and condenser were designed and selected by calculation.The hot water tank size,cooling water tank size and other parameters were calculated and designed according to the cooling power and adsorption/desorption time.Then the design for the device was drawn. |
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