Study On Drying Process Characteristics Of Swirl Heat Pump

With the increasing discharge of urban sewage and industrial sewage,the amount of sludge also increases gradually,and the energy consumption and cost of sludge drying treatment are high.As a new drying method,traditional heat pump drying has the advantages of high efficiency,energy saving,low cost and controllable temperature.However,it takes too much time to dry materials and its drying capacity is low.Therefore,this paper proposes a swirl heat pump drying system that can strengthen heat transfer,which can reduce drying time and save drying cost to a certain extent.In this paper,the drying kinetics of rotating airflow was studied with sludge as drying material.The main contents are as follows:The density,initial moisture content,porosity and other physical parameters of sludge were measured.Based on the experimental data of drying characteristics,the thermal conductivity,inertial resistance coefficient and viscous resistance coefficient of sludge were fitted.Further comparison with the commonly used drying kinetics model showed that the two term model was highly consistent with the experimental results,so the model could be used to predict the drying process of sludge.In addition,the sludge drying characteristics under different conditions,the performance efficiency and economic benefits of heat pump drying system were analyzed.The airflow distribution in sludge drying process was simulated based on ANSYS software,and the simulation results were verified by experiments.Finally,the kinetic characteristics of sludge moisture migration were analyzed.The results show that when the drying temperature is 40°C and the air velocity is 3m/s,the drying time and drying cost under the rotating hot air condition are 21.43%and 22.22%less than those under the advection hot air condition,respectively.The simulation results of airflow distribution in sludge drying process show that the average velocity of sludge surface under rotating hot air condition is larger than that under flat hot air condition,and the larger the wind speed,the more obvious the difference between the two.The effective moisture diffusion coefficient of rotating hot air is 2.02×10^-9～5.05×10^-9m²/s,which is 12.69%～45.32%higher than that of horizontal hot air.Increasing the drying temperature and air supply velocity can shorten the drying time of sludge,and also can improve the effective moisture diffusion coefficient of sludge.The conclusion of this study can provide reference for the design and transformation of the swirl heat pump dryer.