Study On The Comprehensive Performance Of Condensing And Dehumidifying System With Outdoor Fresh Air As Natural Cold Source In Bulk Curing Barn

Tobacco is an important economic crop in China,with large planting area and high yield.Tobacco baking process is necessary part for tobacco to exert its commercial value.The energy consumption of tobacco baking and the baking quality of tobacco are two aspects that people pay most attention to.In the current bulk curing barn,open dehumidification method is adopted,which leads to a large amount of waste heat loss of dehumidification air and high energy consumption.In addition,there are a lot of aroma components which are beneficial to improve the baking quality of tobacco in dehumidification airflow of open-type bulk curing barn.The closed hot air circulation is expected to improve the quality of tobacco drying.Under this background,it is of great significance to effectively use the residual heat of dehumidification air flow in bulk curing barn,and exp lore new high-efficiency,energy-saving,quality-enhancing and efficiency-enriching baking facilities and its dehumidification characteristicsIn view of the limitation of the open-type dehumidification of traditional bulk curing barn,based on the energy-saving approach of closed hot air circulation,a condensing and dehumidifying system with outdoor fresh air as natural cold source in bulk curing barn is proposed.Through numerical simulation and experimental methods,the heat transfer performance,dehumidification performance,energy saving performance and quality improvement performance of condensing and dehumidifying system of bulk curing barn are studied.The main research contents and conclusions are as follows:(1)Based on the analysis of the operating conditions of tobacco bulk curing and the distribution of dehumidification load,a condensing and dehumidifying system with outdoor fresh air as natural cold source in bulk curing barn is proposed.The system is composed of main components such as dehumidifier with outdoor fresh air as the natural cold source,dehumidifying airflow fan,fresh air fan,circulating fan,wind valve,water pan,drainpipe etc.The geometric model of the system was established,and the working principle and air treatment process of the system were analyzed.(2)For the dehumidifier with outdoor fresh air as the natural coo ling source,a computational fluid dynamics model of the flow and heat transfer of dehumidifying airflow in the dehumidifier is established.By using the computational fluid dynamics simulation software Fluent,the velocity,temperature and water vapor mas s fraction distribution in the dehumidifier are numerically simulated,and the heat exchange performance and dehumidification performance of the dehumidifier are calculated and analyzed.The results show that after condensing and dehumidifying,the outlet temperature and water vapor mass fraction of the dehumidifying airflow decrease,and the heat transfer performance and dehumidification performance is good.The average sensible heat efficiency,latent heat efficiency and total heat efficiency of the dehumidifier are 52.81%,26.82%and 36.35%,respectively.And the maximum dehumidification a mount is 34.89kg/h in the later stage of color-fixing(3)The influence of heat pipe spacing and inlet velocity of dehumidifying airflow on heat transfer performance and dehumidification performance of dehumidifier is analyzed by numerical simulation Combined with the operating conditions of bulk curing of tobacco leaves and the distribution of dehumidification load,optimized heat pipe spacing(45mm)and suitable inlet velocity of dehumidifying airflow(2m/s～3 m/s)were obtained.(4)According to the results of numerical simulation,a condensing and dehumidifying device with outdoor fresh air as the natural cold source in bulk curing barn was built.Using the three-stages curing technology of tobacco,tested and analyzed the heat transfer performance,dehumidification performance,energy saving performance and tobacco quality improvement performance of condensing and dehumidifying system with outdoor fresh air as natural cold source in bulk curing barn.The experimental test re sults show that the average sensible heat efficiency,latent heat efficiency,and total heat efficiency of the dehumidifier are 52.75%,21.23%,and 33.19%,respectively.The dehumidification load of color-fixing stage is the largest,and the dehumidification capacity of the system can reach 32.92kg/h in color-fixing stage.Compared with the control bulk curing barn,the experimental bulk curing barn equipped with a condensing and dehumidifying device with outdoor fresh air as natural cold source which can save fuel and baking costs.Average fuelde creased 0.57kg/kg,baking costs decreased 0.48 yuan/kg.The proportion of first-class tobacco increased 7.4%,the proportion of middle-class tobacco decreased 2.2%,the proportion of lower-class tobacco decreased 5.2%,and the average price of flue-cured tobacco increased 0.87 yuan/kg.