Design Of Double Evaporator Normally Closed Heat Pump Drying System And Study On Drying Characteristics Of Kelp Knot

Heat pump drying technology has the advantages of energy saving and environmental protection,high product quality,etc.In recent years,it has received great attention from many researchers.The design of new heat pump drying system and the study of material drying characteristics have become hot research topics.In this paper,a new type of double-evaporator normally-closed heat pump drying system is proposed,and the structural flow and main control logic of the system are determined.The main refrigeration components in the system are designed and selected.The double evaporator is often built.The closed heat pump drying system test bench,with the kelp junction as the material,carried out systematic experimental and theoretical research on the performance of the heat pump drying system,the drying characteristics of the kelp junction heat pump and its influencing factors,and the mathematical model of the kelp junction heat pump drying.Some meaningful research results:(1)The selection of major refrigeration components such as compressor,condenser,dehumidification evaporator,pump thermal evaporator,thermal expansion valve,circulating fan,pump thermal evaporator fan and exhaust heat humidifier was completed by design calculation.A double-evaporator normally closed new heat pump drying system was designed,which solved the problems of long startup time of single evaporator system and thermal and humidity imbalance of closed system.(2)During the heat pump drying process,the air temperature in the middle and lower parts of the material chamber is basically the same,the upper air temperature is always higher than the middle part and the lower part,and the temperature difference is close to 2.5°C;the surface temperature of the kelp knot is lower than 2°C in the middle and lower part of the material room in the early stage of drying.As the drying process continues,the temperature difference is continuously reduced,and the temperature is basically the same in the late drying stage.(3)Setting the drying temperature has a great influence on the drying rate.Within a certain range,the higher the temperature,the larger the drying rate,but the higher the temperature,the longer the heat mode of the unit pump may be,the drying rate will decrease,and the product quality will be improved.Unfavorable;increasing wind speed has a relatively small effect on the drying rate,and it shows the characteristics of weak early stage and strong late stage;although reducing the loading density can increase the drying rate,the unit dehumidification energy consumption ratio will also decrease;Properly expanding the pallet spacing helps to reduce drying time,but is limited by the volume of the material chamber.Under the test conditions,the drying temperature is set at 45°C,the wind speed is 1.5m/s,the loading density is 32.29kg/m~3,and the tray spacing is 180mm.The optimum drying process parameters for the drying of the kelp junction heat pump are SMER is1.625kg water/kWh.Pump heat mode running time 35min,drying time 260min.(4)Combining the test results,two empirical models of Henderson and Pabis model and Page model for kelp junction heat pump drying were established.By comparison,the Page model is more suitable for describing the drying process of kelp junction heat pump.Within the scope of the test conditions,Page is available.The model predicts the change of the water ratio of the kelp junction heat pump drying process with time,and the predicted value and the experimental value fit well.