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

2. 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 m in,1 m in,2 m in,3 m out,1 m out,2.....

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

4. 1 st Law, Open Systems SISO = Single Inlet, Single Outlet At Steady-State nothing changes with respect to time m out m in.. Baratuci ChemE 260 April 15, 2005

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

6. MIMO Processes MIMO = Multiple Inlet, Multiple Outlet 1 st Law : 1 st Law, SS : m in,1. m in,2. m in,3. m out,1. m out,2. 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. Nozzles & Diffusers Common Assumptions: 1 st Law : Nozzle Diffuser Baratuci ChemE 260 April 15, 2005

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

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

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

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

13. 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: 1 st Law: Conservation of Mass: Mix Split Baratuci ChemE 260 April 15, 2005

14. Pipe Flow: Bernoulli Equation Assumptions: –Incompressible fluid: –No friction: 1 st Law: Bernoulli Equation : 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