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Heuristics

Heuristics. “Rules of Thumb”. Turton : Chapter 11. Use of Experience-Based Principles to:. Check new process designs Provide equipment size and performance estimates Help with troubleshooting problems with existing systems Verify computer simulations and results

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Heuristics

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  1. Heuristics “Rules of Thumb”

  2. Turton: Chapter 11 Use of Experience-Based Principles to: • Check new process designs • Provide equipment size and performance estimates • Help with troubleshooting problems with existing systems • Verify computer simulations and results • Provide initial estimates for simulator inputs • Use as a starting place for initial designs • Developing preliminary process layouts • Turton indicates that heuristics: • Don’t guarantee a solution • May contradict other heuristics • Can reduce the time to solve problems • Depends on the context in which it is used

  3. Example of Heuristic Usage • What is the density of water in SI units? In English units? • What does a gallon of milk weigh? What about 4 gallons of milk? • What does a cubic meter of air weigh? • The ratio of is approximately ____?

  4. Creation of Heuristics / Shortcuts • Turton suggests a 3 step process: • Predict • Authenticate/Analyze • Reevaluate/Rethink: Example: suppose you calculated a turbulent heat transfer coefficient inside a 1.5” pipe as: , for water at 21OC and a velocity of 1.83 m/s. Now, you need to estimate a heat transfer coefficient when the water temperature is 93OC and a velocity of 3.05 m/s. Solution: assume still turbulent flow and that the viscosity and density of water may change significantly over this temperature range. So find appropriate equation for calculation of Nusselt number.

  5. Creation of Heuristics / Shortcuts Let subscript 1 be old, 2 be new T

  6. Creation of Heuristics / Shortcuts So for same diameter pipe; with water flowing; ignoring effects of T on

  7. Chapter 11 Heuristics

  8. Example

  9. Example Estimate size of flash drum V-102

  10. Heuristics “Rules of Thumb”

  11. Example Estimate size of heat exchanger E-105

  12. In Class Exercise Estimate size of reboiler E-106 • Given: • mps (medium pressure steam) = 10 barg • T-101 operates at 3 bar • From simulation, reboiler duty = 2,512,500 W

  13. Heuristics?? Homework: Problem 11.1 Turton

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