cheme140-fall04-mt1-Reimer-soln

cheme140-fall04-mt1-Reimer-soln - MIDTERM #1 EXAMINATION...

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1 MIDTERM #1 EXAMINATION – October 1, 2004 Chemical Engineering 140 Fall 2004 Professor Jeffrey Reimer Last Four Digits of Your SID #:__ SOLUTIONS ________ INSTRUCTIONS Read over the whole exam before beginning to write anything. Choose the problem or question that seems easiest to you and do it first. Continue to do the problems in order of increasing difficulty. Stay in motion. Show your work. There is plenty of extra paper, as well as the reverse sides of each sheet PLEASE DO NOT UNSTAPLE THE PAGES!!! Keep your work legible. If you don't understand a question, ask the instructor/proctor for help. Don't panic. If you have time at the end, check your solutions. Hand in your paper when time is called.
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2 1. (8 points) Circle the quantities that are conserved in engineering analyses: Mass Volume Concentration Dimensionless Numbers Moles Density Energy Temperature 2. (6 points) List 3 things wrong with the following flow sheet. 1.__ Not all streams are labeled ________________________________________ 2. __ Streams cross _________________________________________________ 3. __ Mass is accumulated (air enters melter but does not exit) _______________ 4. __ Too many arrows (water vapor stream from evaporator) ________________ 3. (6 points) Fick’s second law is as follows: = = dx dC dx d D dx C d D dt dC 2 2 Where: = D Diffusivity = t Time = x Distance = C Concentration [ ] volume mol = What are the dimensions of D ? Show your work. Define dimensions as follows: t = Time L = Length M = mass First rewrite Fick’s Law to solve for diffusivity, then rewrite in terms of dimensions: 2 2 2 VL M Vt M dx C d dt dC D = = salt water ice water 10ºC 1 atm air 25ºC 1 atm ice water purge water (80%) salt (20%) 100ºC 1 atm water 95% salt 5% 100 kg/hr 100ºC 1 atm Evaporator 100ºC Chiller 0ºC Melter 10ºC
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3 Cancel quantities to solve for the units of diffusivity: t L D 2 = 4. (60 points) A process employs a continuous stirred-tank of volume
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cheme140-fall04-mt1-Reimer-soln - MIDTERM #1 EXAMINATION...

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