Experimental Research And Numerical Simulation On A Small Rapeseed Circulating Dryer Machine By Solar Hot Air

Rapeseed,planted widely in the Yangtze River in China,provides the main raw material for the production of vegetable oils and feed proteins with high economic value and development potential.The new rapeseed has characteristics of high water content,hygroscopic and difficult heat dissipation,which,by the harvest season humid climate,gets mildew and rancidity easily.Therefore,it is very important to adopt timely and efficient drying method.At present,the level of mechanization of rapeseed drying is scarce and most farmers are still using the traditional drying methods-spread out to dry rapeseed,not only time-consuming and labor-ground but dusty and insects-flooding,which have a greater impact on rapeseed.According to above problems,we should choose a more reasonable way of mechanical drying.Mechanical drying has the advantages of strong processing power,high space utilization,high drying efficiency and high quality,and it can reduce floor loss effectively.According to the actual needs of China's rural production,combined with the current status of global fossil energy scarcity,if solar energy worked as a heat source during drying,it would make the hot air provide with cleaner resource lower cost and energy saving.In order to further meet the requirements of low energy consumption and high efficiency during drying rapeseed,the device,a small rapeseed circulating dryer machine by solar hot air,was developed out of.The equipment was used as a research object for rapeseed drying test and the numerical simulation of the internal flow field distribution of the key components of the drying equipment was carried out with the experimental results.The main contents and conclusions are as follows:Rapeseed was tested as a dry object to study the changes in moisture content which should be influenced by several factors like hot air wind speed from the drying room inlet(2m/s-5m/s),rotation speed of the screen impeller(30r/min-60r/min),rate of material circulation(500kg/h-800kg/h),etc.,combining with those results to obtain the optimal operating conditions of equipment.The results show that the inlet wind speed and thematerial circulation rate of the drying chamber have some influence on the results,and the drying curve of the different screen impeller has no obvious change.When the wind speed,the screen blade rotation speed and the material circulation rate are 4-5m/s,45-55r/min and 700-800kg/h respectively,the ideal result can be obtained,both from the drying time and the drying efficiency.According to single factor test results,three experimental factors for inlet wind speed,material circulation rate and heat collection were selected for orthogonal test in order to explore the optimal combination of process parameters.The rapeseed drying rate was used as the evaluation index.Analysis of the order of the primary and secondary effects on the drying rate: collector mode,the inlet velocity,material recycling rate.Equipment operation optimal parameter combination: when using corrugated solar collectors and the inlet wind speed,material circulation rate and rotation speed of the screen impeller were5m/s,800kg/h and 50r/min,the mathematical model of which was obtained by fitting the drying curve under this condition.Using CFD technology V-drying equipment key distribution member numerical simulation analysis and corrugated fins collector plate solar collectors and the temperature distribution inside the flow line and the results show that two kinds of collectors are uneven temperature distribution phenomenon.This higher temperature in the V-ribbed sheet collector region and the left half of the surrounding fins and ventilation appears dead zone.Red high temperature area appears on the upper left corner of the corrugated collector,where the air flow rate is low and the heat loss is greater.When the outside air from the inlet enters the interior of the collector,the flow rate of the moment produced greatly reduced;this convection heat transfer process had a greater impact.To solve the above problems,solar air heaters need to be related to structural optimization.In order to achieve the desired temperature of hot air drying as soon as possible,to improve the air flow distribution uniformity inside the solar collector,to enhance convective heat transfer,we optimize the collector from two perspectives: the ventilator size parameter and the heat sink fin structure.By comparing the ventilation diameter to1.5 times the original,the air flow becomes larger,the air flow through the heat sink convection heat more fully.However,under the action of the air flow direction of the fins will be restricted and the low-speed swirling flow area portion remains.In order to further solve the problem of uneven heat transfer inside the solar collectors,the fin structure of the surface of the heat absorbing plate is improved.A type I fin collector was designed,we divide the internal gas field of the collector into five serpentine runways,which increase the heat transfer area and the ventilation path length.Numerical simulation analysis results show that its temperature distribution along the direction of gas flow increases,showing a positive temperature gradient and the outlet air temperature is significantly higher than before the improvement.Furthermore,the internal air flow rate is significantly higher than the other two types of collectors,whose average flow rate of up to 2.5m/s or more.The structural optimization is of great significance to improve the collection efficiency of solar collectors,increase the air temperature,and thus speed up the drying process rapeseed.