2Use 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
3Example 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 ____?
4Creation 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.
5Creation 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
6Creation 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