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

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

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

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 ____?

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.

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

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

Chapter 11 Heuristics CBE 465 4/14/2017

4/14/2017 CBE 465

4/14/2017 CBE 465

4/14/2017 CBE 465

4/14/2017 CBE 465

4/14/2017 CBE 465

Example CBE 465 4/14/2017

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

4/14/2017 CBE 465

4/14/2017 CBE 465

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

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

4/14/2017 CBE 465

4/14/2017 CBE 465

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

4/14/2017 CBE 465

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