Paperback. Pub Date :2012-09-01 Pages: 432 Publisher: basic information about the title of the chemical industry: food engineering unit operations original price: 58 yuan Author: Feng Biao. painted country the cloud editor of Press: Chemical Industry Publication Date :2012-9-1 00:00:00 ISBN: 9787122139887 Words: 743.000 yards: 432 Edition: 1 Binding: Paperback: 16 Weight: Editor's Summary This book combines the transfer principle expounded the basic principles of the common unit operation in .

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Title: Food engineering unit operations Feng Biao. Tu cloud 9787122139887(Chinese Edition)
Language: English
ISBN 10: 7122139883
ISBN 13: 9787122139887
Binding: paperback
Condition: New

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Synopsis

《食品工程单元操作》结合传递原理阐述了食品工业中常见单元操作的基本原理和主要应用，注重学生工程设计和实际操作能力培养，详细介绍了处理食品工程问题的常用方法，并配备了大量的例题和习题。考虑到教学中的实际需要，本书尽量以简洁的语言进行叙述，突出应用，简化理论推导。《食品工程单元操作》可作为高等院校食品科学与工程专业的教材或参考书，也可供从事食品、发酵、粮食加工、油脂、制糖及其他农产品加工工业的生产、设计、科研人员阅读。3.3.1乳化3.3.1.1乳化液的类型与稳定性食品乳化液通常有两种类型，即水包油型与油包水型。牛乳和冰淇淋为典型的水包油型乳化体系。黄油和人造奶油是典型的油包水型乳化产品。形成何种类型的乳化液，与组成物料的物性、两相的比例、乳化剂的类型及乳化液的制备方法等有关。乳化液分散相液滴的直径一般在0.1～10μm之间，工业化生产的食品乳化液中的脂肪球的直径范围通常在0.1～2.5μm之间，应用高效均质机生产的含乳型乳化制品（如冷冻甜食）中的脂肪球直径平均值可控制在0.5μm以下。乳化液的稳定性通常以乳化液分散相的上升（或沉降、絮凝）和聚合的速度来衡量。一般说来，乳化液的流动性受连续相液体支配。当连续相为水相时，乳化液的黏度通常较低，连续相为油相时，黏度通常较高。分散相的体积含量也是影响乳化液流动性的因素，分散相物质在乳化液中的体积含量升高会使乳化液的流动性降低。理论上说，乳化液的稳定性是相对的。由互不相溶的水和油两相用人工搅拌方式制成的乳化液，不论是油包水还是水包油型，都是不稳定的。分散相与连续相间存在密度差是分散相沉降或上浮，最终使乳化液分层的根本原因，两相的相对移动速度一般可以用斯托克斯定律描述。分散相的液滴始终存在着由小变大的趋势，分散相液滴聚结的原因是在两相的界面处存在着自由能，这种自由能与单位体积乳化液内两相间的界面积成正比，因而与分散相液滴的大小成反比。两相界面存在的能总是力图通过收缩界面使两相问保持最小的接触面积，从而降低自由能。分散相液滴趋于取球形体是这种作用的表现形式之一，液滴自发并合成大滴是这种收缩界面效应的另一表现形式。因此，为了获得稳定的乳化液，除了使分散相液滴的直径足够小以外，还必须消除两相间存在的界面张力，为此在配制乳化液时要加入乳化剂。乳化液两相的黏度也是其稳定性的重要因素。分散相液滴的黏度高时，可减慢液滴间的并合；而连续相黏度高时，分散相的上浮或沉降速度将减慢。连续相的黏度对分散相液滴并合的程度也起很大的影响。液滴并合是因液滴互相碰撞引起的，因此增大黏度对这种碰撞有阻碍作用。在乳化液中，以增加黏度为目的而加入的物质为增黏剂（或称增稠剂）。由于黏度与温度有关，一般温度越高黏度越低。因此，有些乳化产品，必须及时降温并在低温下保存，才能稳定。分散相液滴的带电状态也是乳化液稳定的一个因素。由于液滴带同种电荷，在液滴之间存在一种相互排斥作用，有阻止分散相并合的作用。使用离子型表面活性剂作乳化剂，或者使用食盐之类的电解质，对增加分散相液滴的带电性，促进乳化液的稳定性有显著的效果。绪论01食品工程与单元操作02单位、量纲和换算021物理单位的换算022经验公式的换算1流体流动和输送1

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