| Using solar energy to drive air conditioning system in summer to reduce the electricity power consumption is always a technological goal for researchers. Solar energy using in solid adsorption refrigeration system promote reducing traditional energy consumption. The use of environmentally friendly refrigerants can also avoid the destruction of enviroment. As a kind of green refrigeration technology of using low grade thermal energy, solar solid adsorption refrigeration technology has been paid wide attention in recent years.In the adsorption refrigeration system, the adsorption bed is the core component. Its performance depends both on the adsorption/desorption properties of adsorption working pairs and the structure of the adsorbent bed. Currently, the study of adsorption and desorption properties for adsorption working pairs is mostly conducted from the microscopic point. However, it is quite different of the test condition from the real system, because the adsorption properties would be affected by the thermal effect. In the present study, upon analyzing the variation of the material adsorption capacity exposed in moist air atmosphere of controlled temperature and humidity, the adsorption characteristic of the ZSM-5、13X、5A zeolite and allochroic silica gel to water-vapor have been verified experimentally. On the other hand, the desorption capability have been explored using a temperature-controlled vacuum desorption system. Due to the vacuum tube collector has high heating rate but low cooling rate, in this paper, a glass-vacuum tube adsorption bed using alloy tube as cooling channel was developed, and its temperature variation under the sun was studied. In addition, the photoperiod was analyzed theoretically, too.The results showed that the adsorption rate of material increases with the temperature and humidity. The dynamic adsorption capacity of 5A-II, 13X-II, 13X-I, 5A-I zeolite is faster. The equilibrium adsorption capacity of allochroic silica gel and 5A-Ⅱ, 13X-Ⅱzeolite is larger. The adsorption isotherm of allochroic silica gel follows an exponential function. It has a wide pore size distribution and a larger percentage of micropores. However, the adsorption isotherm of ZSM-5 and 5A-I zeolites show a ―S‖ curve, which is more suitable for the solar adsorption cooling system in summer. A larger percentage of micropores are existed in these types of adsorption materials. The simplified D-A equation could be used to predict the experimental adsorption isotherms of allochroic silica gel. The micro porous characteristics attained from the simplified D-A equation is fitted well with that from the microscopic test results. The desorption velocity and equilibrium desorption percentage are increased with the increase of temperature and vacuum, but the effect of temperature is more obvious.The temperature of the glass-vaccum adsorption bed using copper tube as the cooling channels is rised when exposed to the sun, and a time delay was found between the temperature and the solar irradiation intensity. The time delay dependents on the weather condition. The maximum temperature of the adsorption bed is increased with the increase of radiation heat, while the effect of its deployment is not obvious. In the radial direction, the inner temperature of adsorption bed is reduced with the decrease of the distance between test position and cooling alloy pipe. In the axial, the temperature is influenced by the end-cooling effect of the extending part of the alloy tube. The calculation method of photoperiod proposed in this paper could be used to accurately predict the photoperied of different areas in different seasons. The polar days and nights in north and south poles could also be elucidated in a reasonable way. |
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