- - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - - - - -- TRANSPORT PROPERTIES Ch 30 Quantity Gradiant Laws Temperature Heat HOT - + Electrons Potential - - - - - - - - - - - - - - - Mass Pressure -- - - - - - - - - - - - - - - - - - -- Mass Concentration Momentum Velocity Flux = Jz = amount transported across unit area per s

Flux- Gases Transport is by discrete carriers and each carrier transports a finite amount In 1 second 1/6th of all molecules present in the box of dimensions will pass through the shaded area C z # of molecules traveling along ‘Z’ = 1 6 # of molecules crossing the face in one second = N C If each carrier transports quantity ‘q’

Potential Gradient in the System HOT COLD T 2 1 T2 T1 Z T Z

Thermal Conductivity of an Ideal Gas – Part 1 Since heat is a manifestation of K.E. and is transported via collisions between carriers, we shall consider gas collisions & mean free path ‘ .’ Z C B A {  Z+ Z- From ‘A’ to‘B’ = 1 6 N C  3 2 k [ T +  Z -  ] From ‘C’ to ‘B’ = 1 6 N C  3 2 k [ T +  Z  ] - 1 6 N C  3 2 k [   T Z ] =

Thermal Conductivity of an Ideal Gas – Part 2 [ - Net Flux = = 1 6 N C  3 2 k   T Z ] =   T Z = -

 = 0 =2C =sqr2C Mean free path ‘ ’ Average distance traveled in 1s = If ‘Z’, = number collisions per s,  = Consider a cylinder of radius,  , length In 1s, molecule will travel from one end to the other # collisions made by one molecule per s = But average relative velocity = = 0 =2C =sqr2C Relative Velocity Collision number = Mean free path =

Diffusion: substances diffuse from a high concentration region to a low concentration region. Nz+ Nz Nz- Z x Net Flow Homework: Poizulle Formula & Viscosimeter