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CBE 465 4/14/2017 Heuristics “Rules of Thumb”

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**Use of Experience-Based Principles to:**

Turton: Chapter 11 CBE 465 4/14/2017 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

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**Example of Heuristic Usage**

CBE 465 4/14/2017 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 ____?

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**Creation of Heuristics / Shortcuts**

CBE 465 4/14/2017 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.

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**Creation of Heuristics / Shortcuts**

CBE 465 4/14/2017 Let subscript 1 be old, 2 be new T Property 21 deg. C 93 deg. C Ratio (93o/21o) 𝝆 [𝒌𝒈/𝒎𝟑] 997.4 963.2 0.966 𝒌 [𝑾/𝒎𝒐𝑪] 0.604 0.678 1.12 𝑪𝒑 [𝒌𝑱/𝒌𝒈𝒐𝑪] 4.19 4.20 1.00 𝝁 [𝒌𝒈/𝒎/s] 9.8 x 10-4 3.06 x 10-4 0.312

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**Creation of Heuristics / Shortcuts**

CBE 465 4/14/2017 Property 21 deg. C 93 deg. C Ratio (93o/21o) 𝝆 [𝒌𝒈/𝒎𝟑] 997.4 963.2 0.966 𝒌 [𝑾/𝒎𝒐𝑪] 0.604 0.678 1.12 𝑪𝒑 [𝒌𝑱/𝒌𝒈𝒐𝑪] 4.19 4.20 1.00 𝝁 [𝒌𝒈/𝒎/s] 9.8 x 10-4 3.06 x 10-4 0.312 So for same diameter pipe; with water flowing; ignoring effects of T on

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Chapter 11 Heuristics CBE 465 4/14/2017

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4/14/2017 CBE 465

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4/14/2017 CBE 465

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4/14/2017 CBE 465

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4/14/2017 CBE 465

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4/14/2017 CBE 465

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Example CBE 465 4/14/2017

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**Estimate size of flash drum V-102**

Example CBE 465 4/14/2017 Estimate size of flash drum V-102

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4/14/2017 CBE 465

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4/14/2017 CBE 465

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CBE 465 4/14/2017 Heuristics “Rules of Thumb”

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**Estimate size of heat exchanger E-105**

Example CBE 465 4/14/2017 Estimate size of heat exchanger E-105

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4/14/2017 CBE 465

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4/14/2017 CBE 465

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**Estimate size of reboiler E-106**

CBE 465 4/14/2017 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

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4/14/2017 CBE 465

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**Homework: Problem 11.1 Turton**

CBE 465 4/14/2017 Heuristics?? Homework: Problem 11.1 Turton

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