顺流式谷物烘干机系统设计（全套含CAD图纸）
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下载后文件包含有 CAD 图纸和说明书,咨询 Q 197216396 或 11970985毕业设计（论文）题 目 顺流式谷物烘干机系统设计 学 院专业班级学生姓名指导教师下载后文件包含有 CAD 图纸和说明书,咨询 Q 197216396 或 11970985II摘要中国是粮食生产大国，而刚收获的粮食需要经脱水、干燥处理后才方便存储和运输，每年我 国都会因为未及时干燥而造成粮食的霉变和虫化，从而造成严重的损失。降低或除去物料中的水分称为干燥。在谷物收获中，干燥具有十分重要的意义。本设计针对这一问题设计了一台粮食烘干设备，在设计的过程中充分考虑了不同地区气候环境、干燥成本、干燥工艺、燃料等问题，并采用 CAD 软件制图，使之能明确的表达干燥机的整体结构。同时，使用系统结构简单，运行稳定可靠的 PLC 控制，实现谷物烘干全过程即进粮、循环烘干、出粮的自动控制。关键词：粮食储藏；谷物干燥机；CAD；PLC 控制；下载后文件包含有 CAD 图纸和说明书,咨询 Q 197216396 或 11970985IIIAbstractBecause China is a main grain producing countries, and freshly harvested grain needed by dehydration, drying treatment is convenient to store and transport, every year I will not timely dry and causing food mildew and insect, resulting in serious losses. To reduce or remove material moisture to dry. The grain harvest, drying has a very important significance. The design for the design of a grain drying equipment, the design fully consider the different regional climate environment, the cost of drying, drying process, fuel and other issues, and the use of CAD drawing software, which can clear the expression of drier overall structure. At the same time, the use of the system The system has simple structure, stable and reliable operation of the PLC control, and realizes the whole process of grain drying, namely, feeding, circulating and drying, and automatic control of the grain.Keywords: grain storage, grain dryer ,CAD，PLC control.下载后文件包含有 CAD 图纸和说明书,咨询 Q 197216396 或 11970985IV目录摘要 .IAbstract .II第一章 绪论 .11.1 谷物干燥的现状及发展趋势 .1 1.1.1 谷物干燥的意义 .11.1.2 谷物的特性及谷物干燥的机理 .21.2.3 影响粮食干燥过程的因素 .2 1.2 谷物干燥机简介 .31.2.1 对流换热式谷物干燥机 .31.2.2 辐射式干燥机 .81.2.3 导热式干燥机 .91.2.4 批量作业式干燥机 .9 1.2.5 连续作业方式干燥机 .10下载后文件包含有 CAD 图纸和说明书,咨询 Q 197216396 或 11970985V1.2.6 循环作业式干燥机 .101.3 谷物干燥用的燃料 .111.3.1 燃料的种类和成分 .121.4 谷物干燥用供热设备的种类 .13第二章 谷物干燥机设计 .172.1 谷物干燥系统的工艺流程设计 .172.2 干燥机的设计 .18 2.2.1 干燥机的外壳及工作室材料选择 .182.2.2 小时去水量计算 .18hw2.2.3 小时干燥能力 计算 .18tg2.2.4 加热室容积的确定 .19 2.2.5 缓苏室容积的确定 .192.2.6 冷却室容积的确定 .192.2.7 估计干燥机的总高度 .20总H2.3 风机参数的计算 .202.3.1 热风机流量 Q 计算 .202.3.2 风压计算 .212.3.3 选择热风机 .222.3.4 热风机供热计算 .22下载后文件包含有 CAD 图纸和说明书,咨询 Q 197216396 或 11970985VI2.3.5 选择冷风机 .232.3.6 角状管设计计算 .232.3.7 角状管样式及链接方式 .24第三章 升运机构及排粮机构的计算 .253.1 斗式提升机的选型与计算 .253.1.1 输送量的计算 .253.1.2 功率计算 .253.2 螺旋输送机的选型与计算 .263.2.1 螺旋输送机选型。 .263.2.2 螺旋输送机输送量的计算 .273.3 换热器计算 .273.3.1 换热器的换热量 .273.3.2 计算两种流体的“对数平均温度差” .273.3.3 计算换热器的总换热面积 .283.4 热风炉参数的计算 .283.4.1 小时耗煤量（ ）的计算 .28mG3.4.2 干燥机要求炉灶的供热量 .28 3.4.3 炉栅面积的计算 .293.4.4 炉膛容积 .293.4.5 炉高的确定 .29下载后文件包含有 CAD 图纸和说明书,咨询 Q 197216396 或 11970985VII3.4.6 热风炉的选择 .30第四章 PLC 控制系统的设计 .314.1 谷物烘干机的控制要求 .314.1.1、干燥温度的控制 .314.1.2、干燥速度的控制 .314.1.3、干燥间隙的设定 .314.1.4、谷物水分的控制 .324.2 自动控制系统设计 .324.2.1 谷物烘干工艺流程 .324.2.2 谷物烘干工艺要求： .324.2.3 PLC 与 CPU 型号的选择 .334.2.4 电路图及接线图 .344.2.5 流程图 .37结论 .39参考文献： .40 致谢 . 41下载后文件包含有 CAD 图纸和说明书,咨询 Q 197216396 或 11970985VIII下载后文件包含有 CAD 图纸和说明书,咨询 Q 197216396 或 11970985IX下载后文件包含有 CAD 图纸和说明书,咨询 Q 197216396 或 11970985X1任务书及开题报告题 目 顺流式谷物烘干机系统设计学 院专业班级学生姓名指导教师填 表 说 明21任务书中内容由指导教师本人填写，并经专业审定后，下发给学生。2开题报告中内容由学生根据任务书要求，经查阅资料、调研后填写。3开题报告一般在开始毕业设计（论文）工作的第 1-2 周内完成，由各专业或教研室组织安排开题。4开题报告应包括以下几个方面的内容：（1）课题的来源及选题的依据、意义，课题在理论或实际应用方面的价值以及可能达到的水平。（2）课题在国内外研究现状和水平。（3）课题研究的内容及拟采用的技术路线或研究方法（包括设计、实验、加工测试条件等）。（4）研究中的主要难点以及解决问题的方法。（5）设计（论文）的工作进度计划（以周为单位）。（6）主要参考文献。5填写不下可另加附页。6本材料装订顺序为：任务书、开题报告。1毕业设计（论文）任务书题 目 顺流式谷物烘干机系统设计题目类型 设计 论文 其他学生姓名 学 号学 院 专业班级指导教师 职 称系 主 任 主管院长任务下达日期 任务完成日期任务要求（课题目标、主要内容、技术参数、基本要求等）1、课题目标本课题是利用 PLC 作为控制核心，对收成的谷物进行干燥处理，利用plc 的控制使得干燥处理的过程更加自动化，使得干燥后的谷物更利于储藏和运输，并且设计时更考虑机器的多环境可操作性以及干燥成本，干燥工艺，燃料等方面的问题。本次设计的谷物干燥机是根据小时烘干玉米 15t 设计要求来确定的。在考虑到设备所要达到的处理量和干燥成本的情况下，对本干燥机要更注重风机、热风炉的设计和提升机输送机的型号的选择。本干燥机特点：1.干燥工艺先进，烘后品质好；2.降水幅度大，能使任意高水分的玉米一次降至安全水分；3.干燥成本较低；22、主要内容1） 设计准备（1）查阅 16 篇以上的与设计相关的参考文献，至少有 4 篇外文文献；（2）翻译一篇不少于 5000 字的相关的外文文献； （3）撰写开题报告，经指导老师审阅合格后方可进行设计工作。2） 技术参数（1）小时去水量计算公式： hOkgHWh /87215049（2）小时干燥能力: ：)%()/(21 tOHtMgt（3）加热室容积:29 （4）加热室高度：1.45m （5）估计干燥机总高度：14m （6）风压计算：617（pa） （8）热风机供热计算 )(01tCrQHh（9）输送量计算： Q=3.6 ai3、基本要求（1）掌握设计的基本要求及应遵循的基本原则；（2）初步掌握撰写设计说明书和可行性报告的基本内容和要求；（3）设计制作故障报警器，使得收集器在出现故障时第一时间发出警报，及时维修；（4）完成 plc 控制系统的梯形图设计，通过调试可以完成谷物干燥所需的控制； （5）绘制电路图和机械装配图。注：任务书必须由指导教师本人填写3毕业设计（论文）开题报告1、选题的依据、意义和理论或实际应用方面的价值谷物干燥是谷物收获后的一个重要环节，因为收获时为了减少田间落粒损失都注意适时收获，而适时收获的谷物其水分较大，如不及时干燥则必造成谷物霉烂变质。据统计，我国每年收获的粮食中由于干燥不及时而造成的霉烂损失达 5001000 万屯，估计占全年谷物总产量的 1.5%3%;在南方梅雨季节较长的省份（江苏、浙江、安徽、湖北以及上海等），每年粮食霉烂损失高达 10%左右，可见谷物干燥是一个不容忽视的问题。由此可以看出本次设计的主旨在于使用机器对收成的谷物进行适当的干燥，降低或除去谷物中打的水分，缩小农产品的体积，减轻重量，以便于储藏和运输。并且水分的降低不易引起霉变、酶化和虫化的状态减少不必要的损失，在一定程度上提高粮食的利用率。在干燥过程中主要是去掉机械结合水和部分物理、化学结合水。谷物是多孔型胶质体，这个水分则以不同的形式存在于谷粒表面、毛孔管中以及细胞内。当介质条件参数使它具有发散条件，即介质水蒸气分压力小于谷粒表面水蒸气压力时，则谷粒中的水分以液态或气态由谷粒里层向外扩散，并由表面蒸发。理想的干燥过程，应是谷粒内部的水分扩散速度与表面蒸发速度想等，但一般情况下由于选择干燥参数的不当及谷物本身特性所限，常出现两种速度不等的现象，即外控状态和内控状态。二、本课题在国内外的研究现状我国的谷物干燥（主要指机械干燥）始于 50 年代，50 年代初引进了苏联的高温干燥机应用于生产，后参照该机型结构和原理自行设计了大型高温干燥塔，逐步应用在北方的粮食系统中。6070 年代各地自行设计了多种中、小型谷物干燥机，有定点干燥机厂生产，逐步推广到全国。7080年代又自行设计了几种大、中型谷物干燥机，在粮食系统及国营农场中推广使用。全国各地拥有各种谷物干燥机近两万台，其中主要是中、小、大型干燥机约两千台左右。目前我国的谷物干燥机主要以烟煤为热源，使用燃煤热风炉供热，以热风为介质进行干燥，对粮食无污染。少数谷物干燥机（主要在农场）采用柴油炉供热直接干燥，热效率较高，但对粮食有一定程度的污染。国外较发达国家（美、俄、英、法、日等）的谷物干燥已有 50 多年的历史，大体经历了三个阶段，即 5060 年代的谷物干燥机械化阶段;60 70年代的谷物干燥自动化阶段；7080 年代的谷物干燥提高干燥质量和降低干燥成本阶段。90 年代主要是继续提高干燥质量、实现微机控制和微机管4理阶段。但各国的现时情况亦有所不同。三、课题研究的内容及拟采取的方法课题研究的主要内容：（1）在谷物烘干机的各种因素下，合理选择干燥机类型，设计干燥机的壳体、以及工作室的大小；（2）根据干燥机的类型合理选择所需的设备，例如热风机、冷风机、角状管、提升机、输送机、换热器等；（3）综合运行时的功能需要与特点，设计各层子控制系统辅助信息反馈原件控制拟采取方法：本课题主要研究在 plc 系统的控制下自动实现谷物烘干机的进料，干燥，出料的流程，并以安全性能和逻辑判断为依据设计 plc 控制梯形图。（1）收集视屏或文字资料，通过对比，整理参数优化设计的方法确定最后的设计参数。（2）和知道老师交流探讨确定系统的设计线路，确定方案。（3）通过对实际情况的分析得出最终的控制系统梯形图四、课题研究中的主要难点以及解决的方法主要难点： (1)烘干机各部位机构的设计以及风机，升粮机构，排粮机构的选择；（2）干燥室材料的选择以及容积的确定；（3）编写正确的 PLC 程序，使烘干机能够自动进料与排出。解决方法：（1）根据计算与查阅资料选择合适的干燥机外形与大小，在此基础上选择适当功率的风机，提升机，输送机；（2）由于烘干过程中的高温与高压，故需选择冷轧加强钢板作为干燥室材料，并喷涂耐高温涂层；（3）查阅书籍，编写出初步的程序梯形图，请教老师后，5再在软件中模拟运行，在模拟运行中对不足进行改进。五、毕业设计（论文）工作进度计划第一周到第五周（2016.03.07-2016.04.10） 查阅文献资料，拟订方案，验证并确定方案，编写任务书及开题报告。第六周（2016.04.11-2016.04.17） 准备材料，进行开题答辩。第七周（2016.04.18-2016.04.24） 机械部分设计。第八周（2016.04.25-2016.05.01） 温度及体积规划。第九周（2016.05.02-2016.05.07） 可编程控制器的选择。第十周（2016.05.09-2016.05.15） 控制部分设计，梯形图编写。第十一周（2016.05.16-2016.05.22） 可编程控制电路外接电路设计。第十二周（2016.05.23-2016.05.29） 写说明书，按要求检查。第十三周（2016.05.30-2016.06.05） 编写 PLC 程序。第十四周（2016.06.06-2016.06.12） 绘制电路图。第十五周（2016.06.13-2016.06.19） 绘制机械装配图。第十六周（2016.06.20-2016.06.25） 完成对论文的检查工作，完成设计说明书、图纸打印装订，小组预答辩，公开答辩。7六、主要参考文献（或资料）1刘相东，于才渊，财德仁.常用工业干燥设备及应该用， 北京：化学工业出版社，20052王城芝.谷物干燥原理与谷物干燥机设计，哈尔滨：哈尔滨出版社.19963徐泽敏，殷勇光，吴文福，日本捣鼓干燥机械化发展研究，你哦个也机械化研究，2007（6）:210-2124李长发，赵华海.日本的谷物干燥技术发展趋向.中国你哦工业化，2007，（10）：39-415吴文福，郑先哲，马中苏.谷物干燥储藏理论与技术.长春：吉林科学技术出版社，2001。6张正荣编.传热学.高等教育出版社.1985. 7曹崇文.谷物干燥数学模拟.北京：农业工程大学学报.19868戴天红，曹崇文.谷物干燥研究中的模糊数学方法.农业工程学报，19859于才渊、王宝和、王喜忠干燥装置设计手册、北京化学工业出版社 200510Drying Technology, 2015, Vol.33 (11), pp.1350-135911Russian Agricultural Sciences, 2013, Vol.39 (1), pp.91-9412Pakistan Journal of Biological Sciences, 2003, Vol.6 (19), pp.167513Applied Biochemistry and Biotechnology, 2010, Vol.162 (2), pp.594-6068指导教师意见指导教师_签字年 月 日专业审查意见审查人_签字年 月 日7Vol.4, No.5B, 90-95 (2013) Agricultural Sciences doi:10.4236/as.2013.45B017 Design parameters for a small- scale batch in-bin maize dryer Fashina Adepoju Bola.1, Akande Fatai Bukola.1*, Ibrahim Saula Olanrewaju2, Sanusi Bashir Adisa21Agricultural Engineering Department, Ladoke Akintola University of Technology, Ogbomoso, Oyo State; *Corresponding Author: bola_fashina 2Agricultural Engineering Department, The Polytechnic, Ibadan, Oyo State; fbukkyakande, easyprogress Received 2013 ABSTRACT Early season maize is harvested with high moisture content that makes it impossible to store. The sale of early season maize in green form is uneconomical to the farmer. Experience had shown that farmers could hardly make the cost of production from their sales. Also, grain losses are high when maize is harvested green. To minimize grain losses and thereby increase value and the profit margin of the farmer, a grain dryer is necessary for wet grains. Therefore, this paper presents the design and development of a batch in-bin maize grain dryer. Some properties of maize such as moisture content and bulk density were determined to get information re-quired for design of the dryer. The dimension of drying chamber, amount of moisture to be re-moved in a batch, quantity of air required to ef-fect drying, volume of air required to effect dry-ing, blower capacity, quantity of heat required to effect drying and actual heat used to effect dry-ing were all designed for. A maize dryer was de- veloped with a batch size of 100 kg of threshed wet maize. The dryer can be used in laboratory for experimental purpose as well as on the farm for commercial purposes. The dryer can be used to measure drying rates of maize at different initial moisture contents, drying air tempera-tures, drying air velocities and grain beds. The effects of different drying temperature, air ve-locity, loading and agitating speed on the quality of dried maize can be investigated with the dryer. Keywords: Design and Development; In-bin Maize dryer; Fresh Maize Grain; Moisture Content; Heat Transfer; Drying Rate 1. INTRODUCTION Maize is an all-important crop which provides an avenue for making various types of foods. It also has some medicinal values and serves as raw-materials for many industries. Grain is the most important part of maize crop and is put to many uses. Maize (Zea mays L.), or corn, is the most important cereal crop in sub-Saharan Africa and, with rice and wheat, one of the three most important cereal crops in the world. Maize is high yielding, easy to process, readily digested, and relatively cheaper than other cereals. It is also a versatile crop; growing across a range of agro ecological zones. Every part of the maize plant has eco-nomic value: the grain, leaves, stalk, tassel, and cob can all be used to produce a large variety of food and non-food products. Maize grain could be processed into different forms, especially in the form of maize meal, which is an impor-tant food for large numbers of people in Africa, provid-ing significant amounts of nutrients, in particular calories and protein. 1 Showed that 22 of 145 developing coun-tries had a maize consumption of more than 100 g per person per day. In a dietary intake survey in South Africa, 2 found that maize meal was consumed by almost, all of the respondents, both males and females, in the rural, farm, informal settlement and middle class urban strata. In industrialized countries, maize is largely used as livestock feed and as a raw material for industrial prod-ucts, while in developing countries, it is mainly used for human consumption. In sub-Saharan Africa, maize is a staple food for an estimated 50% of the population. It is an important source of carbohydrate, protein, iron, vita-min B, and minerals. Africans consume maize as a starchy base in a wide variety of porridges, pastes, grits, and beer. Green maize (fresh on the cob) is eaten parched, baked, roasted or boiled; playing an important role in filling the hunger gap after the dry season. The harvesting of the early season maize in Nigeria is Copyright 2013 SciRes. Openly accessible at /journal/as/ F. A. Bola. et al. / Agricultural Sciences 4 (2013) 90-95 91usually between July and October when the rain is fully established. At this time, natural drying on the field is difficult due to low atmospheric temperature and high relative humidity. If the crop is left on the field to dry, it will continue to deteriorate because of the slow rate of drying. They are therefore harvested with the high mois-ture content and sold cheaply to be cooked or roasted for consumption. This decrease in farmers income can be averted, if after harvesting, the maize can be dried and stored. Drying is one of the oldest methods of food preserva-tion. It is the removal of moisture from an agricultural produce/biomaterial to moisture content in equilibrium with the surrounding air or to such moisture content that can decrease the moulds enzymic action and insects infestation. Food stuffs are usually dried to enhance their storability, transportability, texture and retainabil-ity. Drying reduces the amount of water contained in the crop after harvest to an acceptable level for marketing, storage or processing 3. Both grain temperature and moisture content are critical in maintaining quality. Mould and insect activities are greatly reduced below 15C safe moisture levels for storage. However, these depend on grain variety, length of storage, storage struc-ture, and geographical location. The major input in a drying process is the heat which raises the temperature of the inlet air which is blown through a static grain bulk to be dried. The wet grains can only be dried if the inlet air conditions are drier than the wet grain. This means that the moisture contained in the inlet air can be removed by raising its temperature, thus, increasing its ability to remove moisture from a wet grain. The exit air which leaves the dryer after passing through the wet bulk of grain could accumulate and sub-sequently condense within the dryer if there are no ade-quate exit channels and if the airflow rate is low 4. The cooking of the grains and stress cracking due to the de-velopment of high internal grains temperatures and pressures can be avoided if the condition of the inlet air introduced into the dryer systems is carefully selected. This will ensure the good quality of out-loaded grain bulk. Also, during drying, the conditions of grains near-est to the inlet are always different from those nearest to the outlet and continue along single line within the bulk. These differences may occur as temperature of the air voids between grains and as moisture content of the grain when the progression of the air fronts are not uniformly distributed. In Nigeria and other African countries, post-harvest losses of agricultural products are very high. This is due to the fact that each of the products has its season and it is mostly produced in excess of what is immediately needed. The losses are due to lack of appropriate preser-vation and storage facilities. These losses made the products unavailable throughout the year and where they are available there is a sharp difference in prices at har-vest and later after harvest. Therefore, the objective of this study is to design and develop a batch in-bin maize grain dryer for freshly harvested maize for on farm usage with a view to reducing the postharvest losses faced by farmers thereby increasing their income. 2. MATERIALS AND METHODS In order to develop an efficient batch in- bin dryer for maize, the following properties and parameters were determined. 2.1. Determination of Moisture Content The moisture content of the maize was determined to know the amount of moisture to be removed from the freshly harvested maize. The sample freshly harvest maize grain was weighed and dried in a ventilated elec-tric oven set at 65 for 24 hs when constant weight was obtained in accordance with 5. The sample was re-moved and allowed to air-cool. The weight of the dried sample was determined using a digital sensitive weighing balance of 0.01 g accuracy. The moisture content (% ) was computed using Eq.1. (1) 2.2. Determination of Bulk Density of Maize at Harvest 6 Developed an empirical formula which relates bulk density and moisture content for maize as stated in Eq. 2. (2) Maize harvested at maturity normally has an average moisture content of 32% (wb) 7. Substituting the value of Mwb = 32% (wb) into Eq.2 gives. TWm= 0.7019 + 0.01676 (32) 0.0011598 (32)2 + 0.00001824 (32)3 TWm= 0.6483 g/cm3 TWm= 648.3 kg/m32.3. Design Considerations In designing the dryer, the following considerations were made: To have a uniform dried product such that the tem-perature and moisture content are the same at every lev-els of the grain thickness, the inlet air would be directed as to span through the entire circular base of the dryer. Copyright 2013 SciRes. Openly accessible at /journal/as/ F. A. Bola. et al. / Agricultural Sciences 4 (2013) 90-95 92 To avoid accumulation of vapour, the upper lid of the dryer will be perforated so as to allow easy flow of va-pour picked by the heated air from the grains to the at-mosphere. To reduce the static pressure which the fan must over-come in order to supply the desired airflow, an agitator shaft was incorporated. A cylindrical shaped dryer is therefore considered for easy and uniform agitation. To reduce the heat loss due to conduction and to con-serve energy generated by the heaters, the drying cylin-der was lagged with glass fiber because of its effective-ness and availability. To ensure that the grains would not be contaminated, the inner wall, the agitation shaft and the perforated flour of the dryer were made of stainless steel-material and To ensure that the rate of drying of the grains is en-hanced, appropriate size of heater was considered to raise the temperature of the drying air. 2.3.1. Design of the Dryer The design of the maize dryer (Figure 1) was based on the following: amount of moisture to be removed, quan-tity of air required to effect drying, volume of air to ef-fect drying, blower design and capacity, quantity of heat required, heat transfer, actual heat used to effect drying, rate of mass transfer, thermal efficiency, and the drying rate. The design was based on ambient temperature (T1) of 32 ; this is applicable for steady flow systems as stated by 8. The initial humidity ratio (Hr1) is deter-mined to be 0.01 kg/kg dry air using the psychometric chart under normal temperature and 101.325 kPa baro-metric pressure. The safe drying temperatures (T2) re-quired for drying maize is 43 as stated by 9 2.3.2. Design of the Drying Chambers (Dimension) The dimension of the drying chamber was determined with the assumptions that, the configuration is cylindrical and mass of maize grain per batch is 100 kg. The bulk density of the maize grain depict that 6 482 kg of freshly harvested maize occupies 1 m3by volume, 1 kg of freshly harvested maize occupies 1/648.2 = 0.001542 m3100 kg will occupy 0.001542 100 m3= 0.1542 m3Since the dryer is cylindrical, assuming a diameter of 600 mm Volume = base area x height. 0.1542 = 0.32 height height = 0.1542/ 0.32= 0.5453 m. The dimension of the drying chamber was therefore determined to be 600 mm diameter and 546 mm height. 2.4. Amount of Moisture to be Removed Amount of moisture to be removed in kg (MR) is given in Eq.3 as: (3) Where, M is dryer capacity per batch (kg), Q1= initial moisture content of the maize to be dried 35%, Q2= maximum desired final moisture content, which is 13% based on experimental results 10. MRis therefore de-termined to be 25.29 kg. 2.5. Quantity of air Required to Effect Drying Quantity of air required to effect drying in kg (Qa). This can be calculated from Eq. 4 by 11 (4) where Hr1and Hr2are initial and final humidity ratios in kg/kg dry air respectively; and MR is as determined in Eq.3. The average ambient temperature and relative hu-midity are 31 for dry bulb temperature, 28 for wet bulb temperature and 35% for relative humidity. The initial humidity ratio Hr1is determined to be 0.01 kg/kg dry air using the psychometric chart under normal tem-perature and 101.325 kPa barometric pressure. After the heat has been supplied, the temperature of the product rises to 50 giving the final humidity ratio (Hr2) as 0.028 kg/kg dry air. Substituting these values of Hr1and Hr2,and Q1and Q2, into Eq.4 gives the quantity of air required to effect drying (Qa) as 1,405 kg. 2.6. Volume of Air to Effect Drying Volume of air to effect drying in m3(Va) can be deter-mined using Eq.5 by 11: (5) Figure 1. Exploded view of the dryer. Copyright 2013 SciRes. Openly accessible at /journal/as/ F. A. Bola. et al. / Agricultural Sciences 4 (2013) 90-95 93where, ais the density of air in kg/m3which is deter-mined at 0 to be 1.115 kg/m3based on properties of common fluids presented by 12. The volume of air to effect drying was therefore calculated to be 1,260.10 m32.7. Blower Design and Capacity The blower serves the purpose of transferring heated air from the heat exchanger to the dryer cabinet. The selection was based on the characteristics of centrifugal fan performance curve based on the Eqs.6-8: (6) (7) (8) where N is the speed (rpm) of the electric motor, H is the static pressure (Pa), q is the volumetric flow rate of air (m3/min), D is the diameter of the blower (m) and hp is the motor horse power. Based on the selection from the chart presented by 13 on the performance curve of a backward-curved centrifugal fan showing system char-acteristics, N1is 1000 rpm, D1is 0.46 m, H1is 1.41, H2is 1.09, q1is 226.4 m3/min, q2is 198.1 m3/min and hp1is 2.28. Based on Eq.6, N2is taken to be in 1000 rpm since an electric motor of 1000 rpm is selected. The value of D2, (m) is calculated based on Eq. 7 while hp2is calcu-lated from Eq. 8 for which a 2hp electric motor is se-lected. The Blower Capacity (BC) is calculated from Eq.9 14: (9) where Qa = Qm + Re + Zk and Qm = a q2= 1.115 kg/m3 198.1 m3/min = 220.88 kg/min; Re = 25% of Qm which is 55.22 kg/min; Zk = 1-2% of Qm which is 4.42 kg/min at 2%; and n= percentage safety factor that en-sures an adequate supply of air in all operating condi-tions at 15% but usually 10% - 20%. Substituting, BC is therefore calculated to be 322.6 kg/min. 2.8. Quantity of Heat Required for Effective Drying (Hr) in kJ The quantity of heat required for effective drying is as presented in Eq.10 (10) where M = dryer capacity per batch (kg) = 100 kg; Hk= CT (T2-T1), whereas CTis specific heat of maize = 1.8 kJ/kg ; and T2-T1= 50 - 32 , HL= latent heat of va-porization =1248.1 kJ/kg; and MR= amount of moisture was removed (kg) substituting these values into Eq.10, Hris calculated to be 31,888.50 kJ. 2.9. Heat Transfer Rate The heat transfer rate (Qht) can be determined from Eq.11 by 12 as: (11) where h = heat transfer coefficient = NuK/d and with Nu (Nusselt) = 121.3 = 0.13a0.33 with Ra= 109; K as thermal conductivity = 0.0305 kW/mK and d as diameter of the heat exchanger = 0.56 m, the value of h is 6.607 kW/m2oC; Ae= surface area of the heat exchanger = 0.7389 m2; and TB= temperature of hot air in the blower, . The value of heat transfer rate ( Qht) is therefore de-termined to be kJ. The quantity of heat that can be lost through the blower in the process is calculated from Eq.12 (12) where qL= quantity of heat lost (kJ); K = thermal con-ductivity of mild steel = 58 W/m.K; Ab= surface area of the blower = 0.88 m2; TBE= temperature difference between the hot air in the blower and the environment = T2-32 ; and k= distance = 1. The value of qLis therefore calculated in kJ. The net heat transfer rate (Qhtr) that will reach the cabinet is (Qht- qL) kJ. 2.10. Actual Heat used to Effect Drying (HD) The quantity of heat used in effecting drying HDcan be determined from Eq. 13 (13) where Ca= specific heat capacity of air = 1.005 kJ/kg ; MR= amount of moisture to be removed kg; and Tc= temperature difference in the dryer cabinet = T2-32 =50-32 . The quantity of heat is therefore calculated to be 457.50 kJ. 3. COMPONENT PARTS OF THE DRYER The component parts of the dryer are; frame, drying cylinder, agitating shaft, heat exchanger, air blower and electrical control panel. The components were fabricated and assembled according to design. The exploded view of the dryer is show in Figure 1. The dryer was fabricated using the following materi-als: (i) Stainless steel sheet: was used for lining the drying chamber of the dryer; (ii) Angle bar: was used for constructing the frame; (iii) Bearings: was used for holding the agitating shaft at both ends; (iv) Stainless steel rod: was used as the agitating shaft; (v) Mild steel sheet: was used as external cover for the drying chamber and the lid; Copyright 2013 SciRes. Openly
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