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ChemE 260 Conservation of Mass & Energy, Steady-State Processes

ChemE 260 Conservation of Mass & Energy, Steady-State Processes. Dr. William Baratuci Senior Lecturer Chemical Engineering Department University of Washington TCD 5: A - C CB 4: 3 & 4. April 15, 2005. m out,1. m in,1. m in,2. m out,2. m in,3. Conservation of Mass.

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ChemE 260 Conservation of Mass & Energy, Steady-State Processes

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  1. ChemE 260 Conservation of Mass & Energy,Steady-State Processes Dr. William Baratuci Senior Lecturer Chemical Engineering Department University of Washington TCD 5: A - CCB 4: 3 & 4 April 15, 2005

  2. . . mout,1 min,1 . min,2 . . mout,2 min,3 Conservation of Mass • Mass is neither created nor destroyed • Integral Mass Balance on an Open System • Differential Mass Balance on an Open System Baratuci ChemE 260 April 15, 2005

  3. Flow Rates and Velocity • Specific Volume: or: • Therefore: • Volumetric Flow Rate: • Where: <v> = average fluid velocity Across = cross-sectional area for flow • Conclusion: Baratuci ChemE 260 April 15, 2005

  4. . mout . min 1st Law, Open Systems • SISO = Single Inlet, Single Outlet • At Steady-Statenothing changes with respect to time Baratuci ChemE 260 April 15, 2005

  5. Pout Pin Flow Work • Three main types of work in this course: • Wb is boundary work • Ws is shaft work • Associated with the rotating shafts in fluid processing equipment • Wflow is flow work or inection work • Work done to force fluid to flow into and out of the system • Evaluating Net Flow Work • 1st Law : Baratuci ChemE 260 April 15, 2005

  6. . . mout,1 min,1 . min,2 . . mout,2 min,3 MIMO Processes • MIMO = Multiple Inlet, Multiple Outlet • 1st Law : • 1st Law, SS : Baratuci ChemE 260 April 15, 2005

  7. Steady-State Processes • In the real world, the goal is usually to operate flow processes at steady-state. • Common steady-state flow processes: • Nozzles & Diffusers • Turbines • Pumps and Compressors • Throttling Devices • Heat Exchangers • Mixing Chambers • Pipes Baratuci ChemE 260 April 15, 2005

  8. Nozzle Diffuser Nozzles & Diffusers • Common Assumptions: • 1st Law : Baratuci ChemE 260 April 15, 2005

  9. Turbine Turbines • A turbine is a device which converts the energy of a flowing fluid into shaft work. • Common Assumptions: • 1st Law : Baratuci ChemE 260 April 15, 2005

  10. Compressor Pump Pumps & Compressors • Pumps cause liquids to flow by raising the pressure • Compressors cause gases to flow by raising the pressure • Common Assumptions: • 1st Law : Baratuci ChemE 260 April 15, 2005

  11. Valve Throttling Devices • A common throttling device is a partially closed valve • Other throttling devices include capillary tubes and porous plugs. • Common Assumptions : • 1st law : Baratuci ChemE 260 April 15, 2005

  12. Process HEX Utility HEX Heat Exchangers • Common Assumptions: • 1st law • Hot Side: • Cold Side: • Overall: Baratuci ChemE 260 April 15, 2005

  13. Mix Split Mixers, Splitters • Mixers and Splitters are tees in a pipe where streams join and mix or split, depending on the direction of flow into and out of the tee. • Common Assumptions: • 1st Law: • Conservation of Mass: Baratuci ChemE 260 April 15, 2005

  14. Pipe Flow: Bernoulli Equation • Assumptions: • Incompressible fluid: • No friction: • 1st Law: • BernoulliEquation : Baratuci ChemE 260 April 15, 2005

  15. Next Class … • Prepare for Test #1 • TCD Chapters 1 – 4 • CB Chapters 1 – 3 , 4.1 & 4.2, Supplements • Transient Mass Balances • Ordinary differential equations • Not too difficult. • Transient Energy Balances • Ordinary differential equations • WAY too difficult ! • Simplifying assumptions let us solve some special problems • General case requires numerical solution by a computer • We won’t do these in this course !  Baratuci ChemE 260 April 15, 2005

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