【摘要】：在顆粒飼料制粒加工流程中,冷卻是最后一道工序,直接影響飼料成品的質(zhì)量。逆流冷卻器以其占地面積小、能耗低、操作簡便等優(yōu)點成為目前廣泛采用的顆粒飼料冷卻設(shè)備。本文以飼料逆流冷卻器為研究對象,針對其排料機構(gòu)漏料多、風(fēng)阻大,冷卻器內(nèi)風(fēng)速場均勻性差,冷卻機理的理論研究匱乏等問題,設(shè)計了改進型排料機構(gòu),有效改善了其工作性能。分析了不同排料方案下風(fēng)速場的均勻性指標(biāo),為排料機構(gòu)的結(jié)構(gòu)優(yōu)化提供參考。研究了進料過程造成的低料位對風(fēng)速均勻性的影響并提出了應(yīng)對措施。建立了冷卻過程的數(shù)學(xué)模型并研究了各工藝參數(shù)對冷卻過程的影響,為實際生產(chǎn)中工藝優(yōu)化策略提供了有效的理論指導(dǎo)。本文主要研究內(nèi)容如下:(1)利用SolidWorks設(shè)計了新型翻板排料機構(gòu),完成了冷卻器總體結(jié)構(gòu)設(shè)計,并對設(shè)備所有驅(qū)動系統(tǒng)進行了設(shè)計計算。(2)利用ANSYS分析了危險部件在工作狀況下的應(yīng)力、應(yīng)變以及最大變形量,包括箱體、翻板、設(shè)備支架、撒料器四部分。結(jié)果表明,所有應(yīng)力值均在材料許用應(yīng)力范圍內(nèi),最大變形量在設(shè)備工作許可范圍內(nèi)。(3)建立了6種排料方案下冷卻器的CFD模型,利用Fluent分別模擬了這6種方案下冷卻器內(nèi)的風(fēng)速場,在Matlab中進行數(shù)據(jù)處理,得出風(fēng)速場在X、Y、Z三個方向上的均勻性系數(shù)。結(jié)果表明:在水平面平行于進風(fēng)方向(X方向),隨氣流的上升,6種類型冷卻器內(nèi)風(fēng)速均勻性都有改善;在水平面垂直于進風(fēng)方向(Y方向),隨氣流的上升,5種方案下風(fēng)速均勻性系數(shù)基本保持恒定,而本文所設(shè)計的排料機構(gòu)下,風(fēng)速均勻性系數(shù)初始值較低,但隨著氣流的上升逐漸提高,對飼料的最終含水率影響不大;在豎直方向上(Z方向),4種方案下風(fēng)速均勻性隨氣流上升而增大,2種方案下風(fēng)速均勻性出現(xiàn)較大波動,這是由于多層排料結(jié)構(gòu)限制了風(fēng)速均勻性在豎直方向上的提升。通過研究低料位工況下的風(fēng)速場,發(fā)現(xiàn)將低料位計安裝高度控制在0.3m以上可降低進料過程中低料位對風(fēng)速均勻性的影響。(4)將飼料深床冷卻簡化為若干薄層,根據(jù)熱質(zhì)傳遞的基本理論推導(dǎo)了飼料冷卻干燥的偏微分方程;建立了飼料的干燥性能參數(shù)比熱、平衡含水率的模型及干燥介質(zhì)空氣的參數(shù)模型并確立了薄層干燥方程的形式;用向前差分方法對偏微分方程進行離散化處理后在Matlab軟件中編制程序進行數(shù)值計算,得出給定工況下任意干燥時間、任意料層高度處飼料的含水率、溫度及空氣的濕度、溫度;分析了空氣的初始溫度、濕含量、風(fēng)量(風(fēng)速),飼料的初始含水率、初始溫度,料層高度以及停留時間對飼料冷卻過程的影響。
[Abstract]:In the granulation process of pellet feed, cooling is the last process, which directly affects the quality of feed product. Countercurrent cooler has become a widely used pellet feed cooling equipment because of its advantages of small area, low energy consumption and easy operation. In this paper, the feed countercurrent cooler is taken as the research object. The improved discharging mechanism is designed in order to solve the problems such as much leakage, large air resistance, poor uniformity of wind velocity field in the cooler and lack of theoretical research on cooling mechanism. Its working performance is improved effectively. The uniformity index of wind velocity field under different discharge schemes is analyzed, which provides a reference for the structure optimization of discharging mechanism. The effect of low level of feed on the uniformity of wind speed was studied and the countermeasures were put forward. The mathematical model of the cooling process is established and the influence of various process parameters on the cooling process is studied, which provides an effective theoretical guidance for the process optimization strategy in practical production. The main contents of this paper are as follows: (1) A new type of tipping mechanism is designed by using SolidWorks, the overall structure of the cooler is designed, and all the driving systems of the equipment are designed and calculated. (2) the stress of the dangerous parts under the working condition is analyzed by using ANSYS. Strain and maximum deformation, including box, flip plate, equipment support, sprinkler four parts. The results show that all stress values are within the allowable stress range of materials, and the maximum deformation is within the working permission range of the equipment. (3) the CFD model of coolers under six discharge schemes is established. The wind velocity field in the cooler was simulated by Fluent, and the data were processed in Matlab. The uniformity coefficient of the wind velocity field in three directions was obtained. The results show that when the horizontal plane is parallel to the inlet direction (X direction), the uniformity of wind velocity in 6 types of coolers is improved with the increase of air flow. When the horizontal plane is perpendicular to the inlet direction (Y direction), the wind velocity uniformity coefficient remains basically constant under five schemes with the increase of the air flow, but the initial value of the wind speed uniformity coefficient is lower under the discharge mechanism designed in this paper. However, with the increase of air flow, the final moisture content of feed has little effect, and the uniformity of wind speed fluctuates with the increase of air flow under the vertical direction (Z direction). This is due to the multilayer layout structure which limits the vertical elevation of wind speed uniformity. By studying the wind velocity field under low material level condition, it is found that the influence of low material level on the uniformity of wind speed can be reduced by controlling the installation height of low material level meter above 0.3 m. (4) the feed deep bed cooling is simplified to several thin layers. According to the basic theory of heat and mass transfer, the partial differential equation of feed cooling and drying was deduced, and the specific heat, equilibrium moisture content model and air parameter model of drying medium were established, and the form of thin-layer drying equation was established. The forward difference method is used to discretize the partial differential equation and the program is compiled in Matlab software to calculate the moisture content, temperature, humidity and temperature of the feed at any drying time and any layer height under given working conditions. The effects of initial air temperature, moisture content, air volume (wind speed), initial moisture content, initial temperature, height of feed layer and residence time on the cooling process of feed were analyzed.
【學(xué)位授予單位】：陜西科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：S817.12

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