小型太阳能热风油菜籽循环干燥设备试验研究及模拟优化

发布时间：2018-04-23 17:15

本文选题：油菜籽 + 太阳能　；参考：《华中农业大学》2017年硕士论文

【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。
[Abstract]:Rapeseed is widely cultivated in the Yangtze River Basin in China. It provides the main raw materials for the production of vegetable oil and feed protein. It is an oil crop with high economic value and development potential. The new rapeseed has the characteristics of high moisture content, strong hygroscopicity and not easy to heat dissipation. At present, the mechanization level of rapeseed drying in China is low, and most of the farmers still use the traditional way of spreading, not only time-consuming and working, but also the mixing of the impurities (dust, soil, sand, insects and so on) in the drying process, which directly affects the quality of rapeseed. In view of the above problems, more reasonable mechanical drying should be chosen. Mechanical drying has the advantages of strong handling capacity, high space utilization, high drying efficiency and high quality, and can effectively reduce the loss of landing. According to the actual needs of rural production in China, combined with the current global shortage of fossil energy, the use of solar energy as a heat source in the drying process is a better drying method. In order to meet the requirements of low energy efficiency and low energy efficiency in the process of rapeseed drying, a small solar hot air rapeseed drying equipment was designed to meet the requirements of low energy efficiency and high efficiency. The main research contents and conclusions are as follows: the main research contents and conclusions are as follows: with rapeseed as the drying object, the influence of the inlet hot wind speed (2m/s-5m/s), the speed of the sieve impeller (30r/min-60r/min), the material circulation rate (500kg/h-800kg/h) and other factors on the water content change It is concluded that the inlet wind speed and the material circulation rate of the drying chamber have a certain effect on the results, but there is no obvious change in the drying curve at different impeller speeds. When the wind speed reaches 4-5m/s and the material circulation rate is 700-800kg/h, the speed of the rapeseed water cut is faster when the speed of the screen impeller blade is kept at the left and right of 50r/min. More ideal results. According to the results of the single factor test, in order to explore the optimal combination of the equipment, three experimental factors are selected, which are the inlet wind speed, the material circulation rate and the heat collection mode, and the drying rate is used as the evaluation index. The order of the main and secondary effects on the index is as follows: the heat collection method, the import wind speed, the material. The optimal operation parameters of the equipment are as follows: selecting the corrugated solar collector, the inlet wind speed of the drying chamber is 5m/s, the speed of the screen impeller is 50r/min, the material circulation rate is 800kg/h. The drying curve is fitted to the mathematical model of the drying characteristic equation under the condition of the drying curve. The V fin of the key parts of the drying equipment is used by CFD technology. The internal temperature distribution and flow line distribution of the collector and corrugated plate solar collector are numerically simulated. The results show that there is an uneven air temperature distribution inside the two heat exchangers. The left half of the V fin heat collector and the high temperature around the ribs are in the dead zone. The upper left corner of the corrugated collector is out of the upper corner. In the present red high temperature region, the air flow velocity is low and the heat loss is larger. When the air inlet is entered into the collector, the instantaneous flow velocity is greatly reduced, which has a great influence on the convection heat transfer process. In order to solve the above problems, the relative structure of the solar air collector is improved. It is dry as soon as possible. The heat air temperature is needed to improve the uniformity of the air flow field inside the solar collector and to enhance the convection heat transfer. From the two angles of the size parameters of the ventilation diameter and the structure of the fin plate of the heat absorbing plate, the air flow rate is increased and the air flow through the heat absorbing plate has been increased by comparing the ventilation diameter to the original 1.5 times. The flow direction of the flow is more sufficient, but the direction of the air flow is restricted under the action of the ribs, and there is still some vortex flow in the low speed region. In order to further solve the problem of the uneven heat transfer inside the solar collector, the shape of the fin surface and the arrangement of the surface of the heat absorbing plate are optimized. A type of I fin heat collector is designed, and the internal gas of the collector is designed. The drainage area is divided into 5 serpentine circuitous channels, and then the heat transfer area and the path length are increased. The numerical simulation results show that the temperature distribution increases along the gas flow direction, presents a positive temperature gradient, and the outlet air temperature is obviously higher than that before the improvement. The internal air velocity is obviously higher than the other two types of heat collector, and the average flow velocity is over. The optimization of the structure after 2.5m/s. is of great significance for improving the collector efficiency, raising the hot air temperature and accelerating the drying process of rapeseed.

【学位授予单位】：华中农业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S226.6

【参考文献】