ME4413_inClassExercise4_wsol
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Name: ______________________ Student ID no.: _______________ ME4413 Heat and Mass Transfer – Exercise 4 Date: 9 April 2015 1. What is the driving force for heat transfer, electric current flow, fluid flow, and mass transfer? (1 mark) Answer: Temperature difference is the driving force for heat transfer, voltage difference is the driving force for electric current flow, pressure difference is the driving force for fluid flow, and concentration difference is the driving force for mass transfer 2. Fick's law of diffusion is expressed on the mass and mole basis as diff,A = -ρADAB(dwA/dx) and diff,A = -CADAB(dyA/dx), respectively. Are the diffusion coefficients DAB in the two relations the same or different? (0.5 mark) Answer: In both relations, DAB are the same. 3. Determine the mole fraction of CO2 dissolved in water at the surface of water at 300 K. The mole fraction of CO2 in air is 0.005, and the local atmosphere pressure is 100 kPa. The saturation pressure of water at 300 K is 3.60 kPa. The Henry’s constant for CO2 in water at 300 K is 1710 bar. (1.5 marks) Solution:
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Transcript of ME4413_inClassExercise4_wsol
Name: ______________________
Student ID no.: _______________
ME4413 Heat and Mass Transfer – Exercise 4
Date: 9 April 2015
1. What is the driving force for heat transfer, electric current flow, fluid flow, and
mass transfer? (1 mark)
Answer:
Temperature difference is the driving force for heat transfer, voltage difference is the
driving force for electric current flow, pressure difference is the driving force for fluid
flow, and concentration difference is the driving force for mass transfer
2. Fick's law of diffusion is expressed on the mass and mole basis as mdiff,A =
-ρADAB(dwA/dx) and Ndiff,A = -CADAB(dyA/dx), respectively. Are the diffusion
coefficients DAB in the two relations the same or different? (0.5 mark)
Answer:
In both relations, DAB are the same.
3. Determine the mole fraction of CO2 dissolved in water at the surface of water at
300 K. The mole fraction of CO2 in air is 0.005, and the local atmosphere pressure
is 100 kPa. The saturation pressure of water at 300 K is 3.60 kPa. The Henry’s
constant for CO2 in water at 300 K is 1710 bar. (1.5 marks)
Solution:
