Modeling And Performance Study On Desiccant Wheel For Marine Rotary Desiccant Air-Conditioning

Marine rotary dehumidification air conditioning system can directly use ship waste heat as the driving heat source of the system to achieve energy saving.The desiccant wheel is the key equipment of the whole desiccant air conditioning system,which absorbs and removes the moisture in the air.According to the law of conservation of mass and energy,the heat and mass transfer process of desiccant wheel is analyzed,and the adsorption state of desiccant wheel is calculated by D-A equation,thus the mathematical model of desiccant wheel is constructed.On the basis of solving and verifying the mathematical model,the performance of desiccant wheel under different working conditions was simulated by using the simulation mathematical model.Firstly,according to the basic working principle and structure of desiccant wheel,the control body for simulation modeling is established.The heat and mass transfer processes of desiccant wheel are described and analyzed respectively.The adsorption process of desiccant runner is analyzed and five different types of adsorption isotherms are introduced.The theoretical basis is provided for the measurement and analysis of water vapor adsorption by desiccant runner and the mathematical modeling of desiccant wheel in the next step.Secondly,fine porous silica gel was selected as desiccant for desiccant wheel.According to the principle of static volume method,micromeritics 3Flex solid surface analyzer was used to test and obtain the adsorption and desorption isotherms of 77K nitrogen on silica gel.The structure of silica gel was characterized by BET,H-K and BJH methods.Using silica gel as adsorbent,the adsorption isotherms of water vapor at 20?,30?and 40?were obtained in the range of 0-1kPa.According to the test results,the adsorption process of water vapor on silica gel with microporous structure belongs to the type III adsorption isotherm,which can be described mathematically by D-A equation.The D-A equation was used to model the adsorption data,and the adsorption isotherms at three groups of temperatures were fitted with the relative pressure as a variable.The fitting error is less than 5.5%.It is shown that the D-A equation can accurately describe the adsorption process of water vapor on silica gel.Finally,a mathematical model of desiccant wheel is established by using the adsorption model of desiccant fitted by D-A equation,and the simulation errors are 8%and 6.3%respectively under the conditions of variable inlet air temperature and humidity,which shows that the mathematical model is reasonable.The performance of a desiccant wheel(radius 450mm×thickness 200 mm)was simulated by using the established mathematical model.The simulation results show that the desiccant wheel has good dehumidification effect in low temperature and high humidity environment.With the increase of the inlet temperature of the treated air from 26?to 34?,the unit dehumidification capacity decreases by 1.6 g/kg.Regeneration temperature has little effect on dehumidification performance in the range of100?~120?.Considering only the heat transfer from regeneration zone to dehumidification zone,the unit dehumidification capacity of desiccant wheel decreases gradually with the increase of regeneration temperature.In the range of 4r/h~8r/h,the unit dehumidification capacity of the desiccant wheel increases with the increase of the wheel speed.And the dehumidification capacity per unit volume of mass air by desiccant wheel will decrease when the air handling capacity increases from 500 m~3/h to 900 m~3/h,therefore,it is necessary to select reasonable air handling capacity according to the geometric size of desiccant wheel.