苜蓿气体射流冲击联合常温通风干燥装备设计及试验
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摘要
针对苜蓿干燥存在的处理量小、耗能高、叶片损失率高的问题,该文将紫花苜蓿的干燥过程分为高温和常温两个干燥段,设计了气体射流冲击联合常温通风干燥装备,包括基于狭缝型气体射流冲击管的气体射流冲带式干燥机和基于环境条件自动控制的常温通风箱式干燥机。利用计算流体动力学软件Fluent对狭缝型气流冲击管内部的流场进行数值模拟。结果显示增设扰流板可以改善狭缝型气体射流冲击管喷嘴出口气流速度分布的均匀性,速度变异系数由不设扰流板情况下的51.1%降为7.7%;利用单片机控制系统进行信息采集并控制通风的进行,解决夜间物料吸湿回潮、发热的问题。以紫花苜蓿作为原料对干燥装备的性能进行试验验证,结果表明:气体射流冲击联合常温通风干燥的苜蓿具有批次处理量大(150 kg/h)、叶片损失率小(干草的叶片损失率为1.5%)、能耗低(单位去水能耗3 408 k J/kg)的优点。研究结果为低能耗、低叶片损失率的苜蓿干燥技术与装备提供参考。
In order to solve the problems of alfalfa drying, such as smaller drying capacity, high energy consumption, and high leaf loss rate, an alfalfa dryer based on air-impingement jet and normal temperature ventilation was designed in current work. The alfalfa drying process was divided into 2 parts: high-temperature drying in air-impingement jet belt dryer based on the slit type air-impingement tube to improve the drying speed, and then drying at room temperature in the normal temperature ventilation apparatus to save energy. The slit type air-impingement tube is the main structure of air-impingement jet belt dryer. Flow field in slit type air-impingement tube was simulated using Fluent 14.0 CFD(computational fluid dynamics) software. The spoiler was added in this tube to improve the airflow uniformity of slit type nozzle exit. The location and height of spoiler are important influence factors of airflow uniformity. The structure of slit type air-impingement tube was optimized with the method of numerical simulation for flow field in which the spoiler had different parameters. The optimal parameter of spoiler was obtained, which then offered an optimum model that the variance coefficient of flow velocity was 7.7% through the 0.1-1.0 m section of nozzle exit. In order to collect information and realize automatic control, a single chip microcomputer system was designed for the room temperature ventilation apparatus. The PT100 and SHT11 sensors were used in the automatic control system to monitor the temperature and relative humidity of environment and grass. PIC16F1947 was used as the main control chip to control and dispose the information and control fan operation so as to solve the problem of moisture reabsorbtion of alfalfa in low temperature and high relative humidity environment. Alfalfa was adopted to test the performance of the normal temperature ventilation equipment combined with air-impingement jet. One group of experiment was that air-impingement jet belt dryer was used to dry alfalfa in different temperature and material thickness to the moisture content of about 45%-50%, and after that the material was dried at room temperature in the ventilation apparatus to the final moisture content of about 15%. It was observed that the moisture content of alfalfa with the thickness of 6 cm was reduced from 78.3% to 45% after 5 min drying. It can be concluded that air-impingement jet belt dryer has the ability of rapid drying for alfalfa even in high thickness. Additionally, the temperature of alfalfa was below 65 ℃ in the process of drying, which was beneficial to save thermal sensitive nutritions of alfalfa. The room temperature ventilation apparatus based on automation control could extensively reduce energy consumption of alfalfa drying. It can be concluded that the normal temperature ventilation dyer combined with hot air-impingement jet has the advantages of low-energy consumption and low leaf loss rate, as the leaf loss rate is less than 1.5%, and the energy consumption per kilogram moisture removal is 3408 k J which is reduced by 53% compared with hot air drying. This paper exhibits a designed new equipment for alfalfa drying, the normal temperature ventilation dryer combined with air-impingement jet, which is very important to solve the problems of high energy consumption and high leaf loss rate of the current alfalfa drying equipment.
In order to solve the problems of alfalfa drying, such as smaller drying capacity, high energy consumption, and high leaf loss rate, an alfalfa dryer based on air-impingement jet and normal temperature ventilation was designed in current work. The alfalfa drying process was divided into 2 parts: high-temperature drying in air-impingement jet belt dryer based on the slit type air-impingement tube to improve the drying speed, and then drying at room temperature in the normal temperature ventilation apparatus to save energy. The slit type air-impingement tube is the main structure of air-impingement jet belt dryer. Flow field in slit type air-impingement tube was simulated using Fluent 14.0 CFD(computational fluid dynamics) software. The spoiler was added in this tube to improve the airflow uniformity of slit type nozzle exit. The location and height of spoiler are important influence factors of airflow uniformity. The structure of slit type air-impingement tube was optimized with the method of numerical simulation for flow field in which the spoiler had different parameters. The optimal parameter of spoiler was obtained, which then offered an optimum model that the variance coefficient of flow velocity was 7.7% through the 0.1-1.0 m section of nozzle exit. In order to collect information and realize automatic control, a single chip microcomputer system was designed for the room temperature ventilation apparatus. The PT100 and SHT11 sensors were used in the automatic control system to monitor the temperature and relative humidity of environment and grass. PIC16F1947 was used as the main control chip to control and dispose the information and control fan operation so as to solve the problem of moisture reabsorbtion of alfalfa in low temperature and high relative humidity environment. Alfalfa was adopted to test the performance of the normal temperature ventilation equipment combined with air-impingement jet. One group of experiment was that air-impingement jet belt dryer was used to dry alfalfa in different temperature and material thickness to the moisture content of about 45%-50%, and after that the material was dried at room temperature in the ventilation apparatus to the final moisture content of about 15%. It was observed that the moisture content of alfalfa with the thickness of 6 cm was reduced from 78.3% to 45% after 5 min drying. It can be concluded that air-impingement jet belt dryer has the ability of rapid drying for alfalfa even in high thickness. Additionally, the temperature of alfalfa was below 65 ℃ in the process of drying, which was beneficial to save thermal sensitive nutritions of alfalfa. The room temperature ventilation apparatus based on automation control could extensively reduce energy consumption of alfalfa drying. It can be concluded that the normal temperature ventilation dyer combined with hot air-impingement jet has the advantages of low-energy consumption and low leaf loss rate, as the leaf loss rate is less than 1.5%, and the energy consumption per kilogram moisture removal is 3408 k J which is reduced by 53% compared with hot air drying. This paper exhibits a designed new equipment for alfalfa drying, the normal temperature ventilation dryer combined with air-impingement jet, which is very important to solve the problems of high energy consumption and high leaf loss rate of the current alfalfa drying equipment.
引文
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[7]Xiao Hongwei,Zhang Qian,Wang Jun,et al.Chapter 6:Hot air impingement heating of food products[M].In Amit K.Jaiswal edited Food Processing Technologies:Impact on Product Attributes,2016,CRC Press,Boca Raton,Fl,USA(pp.93-111).
[8]Xiao Hongwei,Mujumdar Arun S.Chapter 12:Impingement drying:Applications and Future Trends[M]//Prabhat K,Nema,Barjiinder Pal Kaur,and Arun S.Mujumdar.Drying Technologies for Foods:Fundamentals&Applications.2014,New India Publishing Agency,New Delhi,India(pp.279-299).
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[12]Xiao Hongwei,BaiJ unwen,Xie Long,et al.Thin-layer air impingement drying enhances drying rate of American ginseng(Panaxquinquefolium L.)slices with quality attributes considered[J].Food and Bioproducts Processing,2015,94(2):581-591.
[13]Xiao Hongwei,Yao Xuedong,Lin Hai,et al.Effect of SSB(superheated steam blanching)time and drying temperature on hot air impingement drying kinetics and quality attributes of yam slices[J].Journal of Food Process Engineering,2012,35:370-390.
[14]Xiao Hongwei,Gao Zhenjiang,Lin Hai,et al.Air impingement drying characteristics and quality of carrot cubes[J].Journal of Food Process Engineering,2010,33:899-918.
[15]Pakhomov M A,Terekhov V I.Numerical study of fluid flow and heat transfer characteristics in an intermittent turbulent impinging round jet[J].International Journal of Thermal Sciences,2015,87(1):85-93.
[16]王丽红,高振江,林海,等.脉动式气体射流冲击干燥机[J].农业机械学报,2011,42(10):141-144.Wang Lihong,Gao Zhenjiang,Lin Hai,et al.Pulsed air-impingement dryer[J].Transactions of the Chinese Society for Agricultural Machinery,2011,42(10):141-144,(in Chinese with English abstract)
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[19]刘祖铃.狭缝喷嘴组冲击射流传热性能研究[D].重庆:重庆大学,2012.Liu Zuling.Study of Heat Transfer Characteristics of an Array of Impinging Slot Jets[D].Chongqing:Chongqing University,2012.(in Chinese with English abstract)
[20]伍钦,蔡梅琳,曾朝霞,等.等直径流量分配管的计算[J].华南理工大学学报:自然科学版,2000(7):94-98.Wu Qin,Cai Meilin,Zeng Zhaoxia,et al.The calculation of equal-diameter flow rate distribution pipe[J].Journal of South China University of Technology:Natural Science Edition,2000(7):94-98.(in Chinese with English abstract)
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[22]李麟,饶宇,万超一.狭缝宽度对分离式柱肋冷却通道内传热与流动影响的数值计算[J].上海交通大学学报,2014,48(6):756-760.Li Lin,Rao Yu,Wan Chaoyi.A numerical study of thermal performance and pressure loss in a cooling channel with detached pin fins[J].Journal of Shanghai Jiao Tong University,2014,48(6):756-760.(in Chinese with English abstract)
[23]代建武,肖红伟,白竣文,等.气体射流冲击干燥机气流分配室流场模拟与结构优化[J].农业工程学报,2013,29(3):69-76.Dai Jianwu,Xiao Hongwei,BaiJ unwen,et al.Numericalsimulation and optimum design on airflow distribution chamber of air-impingement jet dryer[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2013,29(3):69-76.(in Chinese with English abstract)
[24]Kurnia J C,Sasmito A P,Peng X,et al.Performance and potential energy saving of thermal dryer with intermittent impinging jet[J].Applied Thermal Engineering,2016,113:246-258.
[25]于勇,张俊明,姜连田,等.FLUENT入门与进阶教程[M].北京:北京理工大学出版社,2004.
[26]Svensson K,Rohdin P,Moshfegh B.A computational parametric study on the development of confluent round jet arrays[J].European Journal of Mechanics-B/Fluids,2015,53:129-147.
[27]车刚,汪春,李成华,等.紫花苜蓿热风干燥特性与工艺的试验研究[J].黑龙江八一农垦大学学报,2004,16(4):36-39.Che Gang,Wang Chun,Li Chenghua,et al.Study on airflow drying characteristic and technology of alfalfa[J].Journal of Heilongjiang Bayi Agricultural University,2004,16(4):36-39.(in Chinese with English abstract)
[28]赵艳忠,王忠江,郑先哲,等.热风温度对苜蓿薄层干燥速度的影响[J].农机化研究,2008,30(12):116-118.Zhao Yanzhong,Wang Zhongjiang,Zheng Xianzhe,et al.Effect of temperature on alfalfa drying rate[J].Journal of Agricultural Mechanization Research,2008,30(12):116-118.(in Chinese with English abstract)
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[2]李改英.淋雨对苜蓿霉变的影响与苜蓿优化青贮技术的研究[D].郑州:河南农业大学,2009.Li Gaiying.Effect of Raining to the Mildew of Alfalfa and Study on the Optimized Silage Techniques for Alfalfa[D].Zhengzhou:Henan Agricultural University,2009.(in Chinese with English abstract)
[3]郑先哲,蒋亦元.苜蓿干燥特性试验研究[J].农业工程学报,2005,21(1):159-162.Zheng Xianzhe,Jiang Yiyuan,Experimental study on the drying process characteristics of alfalfa[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2005,21(1):159-162.(in Chinese with English abstract)
[4]王建英,郑先哲,董航飞.干燥条件对苜蓿品质的影响[J].东北农业大学学报,2010,41(3):125-129.Wang Jianying,Zheng Xianzhe,Dong Hangfei.Effect of drying conditions on alfalfa forage quality[J].Journal of Northeast Agricultural University,2010,41(3):125-129.(in Chinese with English abstract)
[5]熊明红,周粉富,李键.苜蓿草烘干设备的研究[J].江苏农机化,2003,19(3):19-20.Xiong Minghong,Zhou Fenfu,Li Jian.Research of alfalfa drying equipment[J].Jiangsu Agricultural Mechanization,2003,19(3):19-20.(in Chinese with English abstract)
[6]王建英.四重滚筒牧草干燥机工艺研究及附属设备设计[D].哈尔滨:东北农业大学,2010.Wang Jianying.Study on Alfalfa Drying Base on the Four-Fold Rotary Dryer and a Design of its Auxiliary Equipment[D].Harbin:Northeast Agricultural University,2010.(in Chinese with English abstract)
[7]Xiao Hongwei,Zhang Qian,Wang Jun,et al.Chapter 6:Hot air impingement heating of food products[M].In Amit K.Jaiswal edited Food Processing Technologies:Impact on Product Attributes,2016,CRC Press,Boca Raton,Fl,USA(pp.93-111).
[8]Xiao Hongwei,Mujumdar Arun S.Chapter 12:Impingement drying:Applications and Future Trends[M]//Prabhat K,Nema,Barjiinder Pal Kaur,and Arun S.Mujumdar.Drying Technologies for Foods:Fundamentals&Applications.2014,New India Publishing Agency,New Delhi,India(pp.279-299).
[9]高振江.气体射流冲击颗粒物料干燥机理与参数试验研究[D].北京:中国农业大学,2000.Gao Zhenjiang.Experimental Research on Mechanism and Parameters of Air-impingement Jetdrying of Particulate Materials[D].Beijing:China Agricultural University,2000.(in Chinese with English abstract)
[10]Xiao Hongwei,Law Chung-Lim,Sun Dawen,et al.Color change kinetics of American ginseng(Panaxquinquefolium)slices during air impingement drying[J].Drying Technology,2014,32(4):418-427.
[11]Wang Dong,Dai Jianwu,Ju Haoyu,et al.Drying kinetics of American ginseng slices in thin-layer air impingement dryer[J].International Journal of Food Engineering,2015,11(5):701-711.
[12]Xiao Hongwei,BaiJ unwen,Xie Long,et al.Thin-layer air impingement drying enhances drying rate of American ginseng(Panaxquinquefolium L.)slices with quality attributes considered[J].Food and Bioproducts Processing,2015,94(2):581-591.
[13]Xiao Hongwei,Yao Xuedong,Lin Hai,et al.Effect of SSB(superheated steam blanching)time and drying temperature on hot air impingement drying kinetics and quality attributes of yam slices[J].Journal of Food Process Engineering,2012,35:370-390.
[14]Xiao Hongwei,Gao Zhenjiang,Lin Hai,et al.Air impingement drying characteristics and quality of carrot cubes[J].Journal of Food Process Engineering,2010,33:899-918.
[15]Pakhomov M A,Terekhov V I.Numerical study of fluid flow and heat transfer characteristics in an intermittent turbulent impinging round jet[J].International Journal of Thermal Sciences,2015,87(1):85-93.
[16]王丽红,高振江,林海,等.脉动式气体射流冲击干燥机[J].农业机械学报,2011,42(10):141-144.Wang Lihong,Gao Zhenjiang,Lin Hai,et al.Pulsed air-impingement dryer[J].Transactions of the Chinese Society for Agricultural Machinery,2011,42(10):141-144,(in Chinese with English abstract)
[17]周娟娟,王欣荣,吴建平,等.调制方式对苜蓿青干草干燥特性和营养品质的影响[J].草业科学,2013,30(8):1272-1277.Zhou Juanjuan,Wang Xinrong,Wu Jianping,et al.Effects of different making methods on the drying characteristics and nutrition quality of medicago sativa hay[J].Pratacultural Science,2013,30(8):1272-1277.(in Chinese with English abstract)
[18]李长友,麦智炜,方壮东,等.高湿稻谷节能干燥工艺系统设计与试验[J].农业工程学报,2014,30(10):1-9,294.Li Changyou,Mai Zhiwei,Fang Zhuangdong,et al.Design and test on energy-saving drying system for paddy with high moisture content[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2014,30(10):1-9,294.(in Chinese with English abstract)
[19]刘祖铃.狭缝喷嘴组冲击射流传热性能研究[D].重庆:重庆大学,2012.Liu Zuling.Study of Heat Transfer Characteristics of an Array of Impinging Slot Jets[D].Chongqing:Chongqing University,2012.(in Chinese with English abstract)
[20]伍钦,蔡梅琳,曾朝霞,等.等直径流量分配管的计算[J].华南理工大学学报:自然科学版,2000(7):94-98.Wu Qin,Cai Meilin,Zeng Zhaoxia,et al.The calculation of equal-diameter flow rate distribution pipe[J].Journal of South China University of Technology:Natural Science Edition,2000(7):94-98.(in Chinese with English abstract)
[21]刘占一,宋保维,黄桥高,等.基于CFD技术的泵喷推进器水动力性能仿真方法[J].西北工业大学学报,2010,28(5):724-729.Liu Zhanyi,Song Baowei,Huang Qiaogao,et al.Applying CFD technique to calculating successfully hydrodynamic performance of water jet pump[J].Journal of Northwestern Polytechnical University,2010,28(5):724-729.(in Chinese with English abstract)
[22]李麟,饶宇,万超一.狭缝宽度对分离式柱肋冷却通道内传热与流动影响的数值计算[J].上海交通大学学报,2014,48(6):756-760.Li Lin,Rao Yu,Wan Chaoyi.A numerical study of thermal performance and pressure loss in a cooling channel with detached pin fins[J].Journal of Shanghai Jiao Tong University,2014,48(6):756-760.(in Chinese with English abstract)
[23]代建武,肖红伟,白竣文,等.气体射流冲击干燥机气流分配室流场模拟与结构优化[J].农业工程学报,2013,29(3):69-76.Dai Jianwu,Xiao Hongwei,BaiJ unwen,et al.Numericalsimulation and optimum design on airflow distribution chamber of air-impingement jet dryer[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2013,29(3):69-76.(in Chinese with English abstract)
[24]Kurnia J C,Sasmito A P,Peng X,et al.Performance and potential energy saving of thermal dryer with intermittent impinging jet[J].Applied Thermal Engineering,2016,113:246-258.
[25]于勇,张俊明,姜连田,等.FLUENT入门与进阶教程[M].北京:北京理工大学出版社,2004.
[26]Svensson K,Rohdin P,Moshfegh B.A computational parametric study on the development of confluent round jet arrays[J].European Journal of Mechanics-B/Fluids,2015,53:129-147.
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