Presentation on theme: "1 Heuristics “Rules of Thumb”. 2 Turton: Chapter 11 Check new process designs Provide equipment size and performance estimates Help with troubleshooting."— Presentation transcript:
2 Turton: Chapter 11 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 Use of Experience-Based Principles to: 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 21 O C and a velocity of 1.83 m/s. Now, you need to estimate a heat transfer coefficient when the water temperature is 93 O C 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 Property21 deg. C93 deg. CRatio (93 o /21 o ) 997.4963.20.966 0.6040.6781.12 4.194.201.00 9.8 x 10 -4 3.06 x 10 -4 0.312
6 Creation of Heuristics / Shortcuts So for same diameter pipe; with water flowing; ignoring effects of T on Property21 deg. C93 deg. CRatio (93 o /21 o ) 997.4963.20.966 0.6040.6781.12 4.194.201.00 9.8 x 10 -4 3.06 x 10 -4 0.312