食品工程与装备技术

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1、DryingMembers：贾 燕 11811505 孙婵婵 11811503 王子健 11811502 张立辰 11811501Major：农产品加工及贮藏工程11 Basic drying theoryv1.1 The definition of dryingvDrying of foods implies the removal of water from the foodstuff.In most cases,drying is accomplished by vaporizing the water that is contained in the food.v干燥的定义食品干燥，去

2、除食品的水分。在大多数情况下，干燥是通过蒸发而除去食品中的水。21.2 Three States of WatervPure water can exist in three states,solid,liquid and vapour.The state in which it is at any time depends on the temperature and pressure conditions and it is possible to illustrate this on a phase diagram,as in 3Figure 1.1 Phase diagam for w

3、ater4vIf we choose any condition of temperature and pressure and find the corresponding point on the diagram,this point will lie,in general,in one of the three labelled regions,solid,liquid,or gas.This will give the state of the water under the chosen conditions.v如果我们选择任何温度和压力条件，并在图上找到对应点，这一点在于，在一般情

4、况下，在标记的三个地区，固体，液体或气体之一。所选择的条件下，这将使水的状态。52 Drying EquipmentvIn an industry so diversified and extensive as the food industry,it would be expected that a great number of different types of dryer would be in use.vNext several typical of the dryer will be introduced:v6v2.1 Tunnel DryersvThese may be reg

5、arded as developments of the tray dryer,in which the trays on trolleys move through a tunnel where the heat is applied and the vapours removed.In most cases,air is used in tunnel drying and the material can move through the dryer either parallel or counter current to the air flow.Sometimes the dryer

6、s are compartmented,and cross-flow may also be used.78v2.2 Spray DryersvIn a spray dryer,liquid or fine solid material in a slurry is sprayed in the form of a fine droplet dispersion into a current of heated air.Air and solids may move in parallel or counterflow.Drying occurs very rapidly,so that th

7、is process is very useful for materials that are damaged by exposure to heat for any appreciable length of time.The dryer body is large so that the particles can settle,as they dry,without touching the walls on which they might otherwise stick.Commercial dryers can be very large of the order of 10 m

8、 diameter and 20 m high.910v2.3 Vacuum DryersvBatch vacuum dryers are substantially the same as tray dryers,except that they operate under a vacuum,and heat transfer is largely by conduction or by radiation.The trays are enclosed in a large cabinet,which is evacuated.The water vapour produced is gen

9、erally condensed,so that the vacuum pumps have only to deal with non-condensible gases.Another type consists of an evacuated chamber containing a roller dryer1112v2.4 Freeze DryersvThe material is held on shelves or belts in a chamber that is under high vacuum.In most cases,the food is frozen before

10、 being loaded into the dryer.Heat is transferred to the food by conduction or radiation and the vapour is removed by vacuum pump and then condensed.In one process,given the name accelerated freeze drying,heat transfer is by conduction;sheets of expanded metal are inserted between the foodstuffs and

11、heated plates to improve heat transfer to the uneven surfaces,and moisture removal.The pieces of food are shaped so as to present the largest possible flat surface to the expanded metal and the plates to obtain good heat transfer.A refrigerated condenser may be used to condense the water vapour.1314

12、3 Unit operations and processesvThe drying process including the following unit operations：vFluid flow process,including liquid transportation and solid transportation etc.vHeat transfer process,including heat conduction,convection and evaporation and condensation,etc.vMass transfer process,the mate

13、rial of transmission,including gas absorption and drying etc.vThermal process,the temperature and pressure change process,including liquefaction,frozen etc.154 The application of dryingvDrying is one of the oldest methods of preserving food.Primitive societies practised the drying of meat and fish i

14、n the sun long before recorded history.Today the drying of foods is still important as a method of preservation.Dried foods can be stored for long periods without deterioration occurring.The principal reasons for this are that the microorganisms which cause food spoilage and decay are unable to grow

15、 and multiply in the absence of sufficient water and many of the enzymes which promote undesired changes in the chemical composition of the food cannot function without water.165 The domestic and overseas manufacturersv5.1 The domestic manufacturers vFor example:v上海奕晟矿山机械有限公司v四川望昌干燥设备有限公司v常州市中通干燥设备有限公司v成都九鼎干燥设备有限公司v常州市干燥设备厂有限公司17v5.2 The foreign manufacturersvFor example:vSharpenn Technologies Pvt.Ltd.vKilburn Engineering Ltd.vSanjivani Phathopharma Pvt.Ltd.vOld Carolina Brick Company vSuntrack Energy Systems Pvt.Ltd.18v谢谢大家19