1、Chapter 11 Mass Transfer,College of Nuclear Science and Technology,1,Mass Transfer,Contents,11-1 Introduction 11-2 Ficks Law of Diffusion 11-3 Diffusion in Gases 11-4 Diffusion in Liquid and Solids 11-5 The Mass-Transfer Coefficient,Chapter 11 Mass Transfer,College of Nuclear Science and Technology,
2、2,11-1 Introduction,The transfer process of the compoments of mixture resulting from concentration gradient.,Whats mass Transfer?,Chapter 11 Mass Transfer,College of Nuclear Science and Technology,3,Mass transfer,Mass diffusion, the mass transfer process resulting from molecules motion.,Mass convect
3、ion, the mass transfer process resulting from convective mixing.,Chapter 11 Mass Transfer,College of Nuclear Science and Technology,4,11-2 Ficks Law of Diffusion,Consider the system in Fig.11-1.A thin partition separates the two gases A and B.When the partition is removed,the two gases diffuse throu
4、th each other until equabrium is established.The diffusion rate is given by Ficks Law of Diffusion.,Chapter 11 Mass Transfer,College of Nuclear Science and Technology,5,D,the ability of mass diffusion,Chapter 11 Mass Transfer,College of Nuclear Science and Technology,6,the Comparision of three trans
5、fer processes,Chapter 11 Mass Transfer,College of Nuclear Science and Technology,7,11-3 Diffusion in Gases,Two typical Mass Diffusion Processes,Equimolal counter dissuson,Single direction diffusion,Chapter 11 Mass Transfer,College of Nuclear Science and Technology,8,Equimolal counter dissuson,Defini
6、tion,Opposite direction,Chapter 11 Mass Transfer,College of Nuclear Science and Technology,9,Single direction diffusion,As the water evaporates,it will diffuse upward through the air,while the air can not reach the water surface.,Definition,Chapter 11 Mass Transfer,College of Nuclear Science and Tec
7、hnology,10,11-4 Diffusion in Liquid and Solids,Ficks law of diffusion can also be used in liquid and solid diffusion.,But diffusion in solids is complex because of the strong influence of molecular force fields on the process.,The numerical value of the diffusion coefficient for liquids and solids i
8、s much smaller than for gases,primarily because of larger molecular force fields.,Chapter 11 Mass Transfer,College of Nuclear Science and Technology,11,11-5The Mass-Transfer Coefficient,Mass convection,Chapter 11 Mass Transfer,College of Nuclear Science and Technology,12,Define a mass-transfer coefficient in a manner similar to that used for defining the heat-transfer coefficient.,Chapter 11 Mass Transfer,College of Nuclear Science and Technology,13,Comparison of heat convection and mass convection,Chapter 11 Mass Transfer,College of Nuclear Science and Technology,14,Thank you!,
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