2 Use of Experience-Based Principles to: Turton: Chapter 11CBE 4654/14/2017Use of Experience-Based Principles to:Check new process designsProvide equipment size and performance estimatesHelp with troubleshooting problems with existing systemsVerify computer simulations and resultsProvide initial estimates for simulator inputsUse as a starting place for initial designsDeveloping preliminary process layoutsTurton indicates that heuristics:Don’t guarantee a solutionMay contradict other heuristicsCan reduce the time to solve problemsDepends on the context in which it is used
3 Example of Heuristic Usage CBE 4654/14/2017What 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 CBE 4654/14/2017Turton suggests a 3 step process:PredictAuthenticate/AnalyzeReevaluate/Rethink:Example: suppose you calculated a turbulent heat transfer coefficient insidea 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 CBE 4654/14/2017Let subscript 1 be old, 2 be new TProperty21 deg. C93 deg. CRatio (93o/21o)𝝆 [𝒌𝒈/𝒎𝟑]997.4963.20.966𝒌 [𝑾/𝒎𝒐𝑪]0.6040.6781.12𝑪𝒑 [𝒌𝑱/𝒌𝒈𝒐𝑪]4.194.201.00𝝁 [𝒌𝒈/𝒎/s]9.8 x 10-43.06 x 10-40.312
6 Creation of Heuristics / Shortcuts CBE 4654/14/2017Property21 deg. C93 deg. CRatio (93o/21o)𝝆 [𝒌𝒈/𝒎𝟑]997.4963.20.966𝒌 [𝑾/𝒎𝒐𝑪]0.6040.6781.12𝑪𝒑 [𝒌𝑱/𝒌𝒈𝒐𝑪]4.194.201.00𝝁 [𝒌𝒈/𝒎/s]9.8 x 10-43.06 x 10-40.312So for same diameter pipe; with water flowing; ignoring effects of T on