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TRANSPORT PROPERTIES. Ch 30. Quantity. Gradiant. Laws. Temperature. Heat. HOT. - +. Electrons. Potential. - - - - -. - - - - -. - - - - -. Mass. Pressure. -- - - - - -. - - - - - - -. - - - - - --. Mass Concentration. Momentum Velocity.
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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 1 N C 6 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’ = # of molecules crossing the face in one second = If each carrier transports quantity ‘q’
T 2 HOT Z T 1 COLD T T1 T2 Potential Gradient in the System Z
Thermal Conductivity of an Ideal Gas – Part 1 Z Z+ C { Z T 1 3 N C T Z - B 1 Z 6 2 { Z- [ ] A T 1 3 N C T Z + k + From ‘A’ to‘B’ = 1 Z 6 2 T 1 3 N C [ ] Z 6 2 k From ‘C’ to ‘B’ = + [ ] - 2 = k - Since heat is a manifestation of K.E. and is transported via collisions between carriers, we shall consider gas collisions & mean free path ‘.’
Thermal Conductivity of an Ideal Gas – Part 2 [ ] - 2 k - Net Flux = = = = - T T 1 3 N C Z Z 6 2
Mean free path ‘’ Average distance traveled in 1s = If ‘Z’, = number collisions per s, = C 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 = A = 0 =2C =sqr2C Collision number = Mean free path = Relative Velocity
Diffusion:substances diffuse from a high concentration region to a low concentration region. Z Nz+ Nz Nz- x Net Flow Homework: Poizulle Formula & Viscosimeter