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Heuristics - PowerPoint PPT Presentation

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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Presentation Transcript

“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

• 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

• Can reduce the time to solve problems

• Depends on the context in which it is used

• 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 ____?

• 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.

Let subscript 1 be old, 2 be new T

So for same diameter pipe; with water flowing; ignoring effects of T on

Estimate size of flash drum V-102

“Rules of Thumb”

Estimate size of heat exchanger E-105

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

Homework: Problem 11.1 Turton