【作者】 张鹏；

【导师】 樊啟洲；

【作者基本信息】 华中农业大学 ， 农业机械化工程， 2017， 硕士

【摘要】 油菜广泛种植于我国长江流域,为植物油及饲用蛋白质等的生产提供主要原料,是具有较高经济价值及发展潜力的油料作物。新收油菜籽具有含水率高,吸湿性强且不易散热等特点,收获时节潮湿的环境气候极易导致油菜籽霉变、酸败等现象,造成了严重损失。目前我国油菜籽干燥作业机械化水平较低,大部分农户仍采用传统摊晒方式,不仅费时费工,而且干燥时杂质(灰尘、土壤、沙石、昆虫等)的混入,直接影响油菜籽的品质。针对以上问题,应选择更加合理的机械干燥方式。机械干燥具有处理能力强,空间利用率高,干燥效率及品质高等优点,并可有效降低落地损失。根据我国农村生产实际需要,结合目前全球化石能源匮乏现状,使用太阳能作为干燥过程中的热源,是一种比较好的干燥方式。设备所供给的太阳能热风具有清洁卫生,节能环保,成本低廉等优势。为进一步满足油菜籽干燥过程中低能耗高效率的要求,设计研制了一种小型太阳能热风油菜籽循环干燥设备。以此设备作为研究对象进行油菜籽干燥试验,结合试验结果对干燥设备关键部件太阳能集热器内部流场分布进行数值模拟,主要研究内容和结论如下:以油菜籽为干燥对象进行试验,研究干燥室进口热风风速(2m/s-5m/s)、筛网叶轮转速(30r/min-60r/min)、物料循环速率(500kg/h-800kg/h)等因素对含水率变化的影响,分析得出干燥室进口风速及物料循环速率对结果均存在一定影响,而不同筛网叶轮转速下干燥曲线无明显变化。当风速达到4-5m/s,物料循环速率为700-800kg/h,筛网叶轮叶片转速保持在50r/min左右时,油菜籽含水率下降速度较快,可获得较为理想的结果。根据单因素试验结果,为探究设备最优工艺参数组合,选取进口风速、物料循环速率、集热方式三个试验因素进行正交试验研究,以干燥速率作为评价指标,可得对该指标影响的主次顺序依次为:集热方式、进口风速、物料循环速率。设备运行最优参数组合为:选取波纹型太阳能集热器,干燥室进口风速为5m/s,筛网叶轮转速为50r/min,物料循环速率为800kg/h,对此条件下干燥曲线进行拟合获得干燥特性方程数学模型。。运用CFD技术对干燥设备关键部件V型肋片集热器及波纹板太阳能集热器内部温度分布及流线分布进行数值模拟分析,结果显示两种集热器内部均存在空气温度分布不均匀的现象。其中V型肋片集热器左半部分区域以及肋片周围温度较高,出现通风死区。波纹型集热器左上角出现红色高温区域,该处空气流速较低,产生的热损失较大。当外界空气自进风口进入集热器内部时,瞬间流速产生了大幅降低,这对对流换热过程产生了较大影响,为解决以上问题对太阳能空气集热器进行相关结构改进。为尽快达到干燥所需热风温度,改善太阳能集热器内部空气流场均匀性,增强对流换热,从通风口径尺寸参数及吸热板肋片结构两个角度出发对集热器进行优化,通过对比得出将通风口径增至原有的1.5倍后,空气流量有所增加,流过吸热板时发生的对流换热更充分。但在肋片作用下空气流动方向受到一定制约,低速区域仍存在部分漩涡流动。为进一步解决太阳能集热器内部换热不均的问题,对吸热板表面肋片形状及排布方式进行优化,设计了一种I型肋片集热器,将集热器内部气体流域分割成5条蛇形迂回流道,进而增加换热面积及路径长度。数值模拟分析结果显示,其温度分布沿气体流动方向递增,呈现正向温度梯度,出口空气温度相比改进前明显升高。且内部空气流速明显高于其他两种类型集热器,平均流速超过2.5m/s。该结构优化对改善集热效率,提高热风温度,进而加快油菜籽干燥进程具有十分重要的意义。更多还原

【Abstract】 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.更多还原