# Steps for analysis of a flow

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 January 26, 2011, 10:55 Steps for analysis of a flow #1 Member   Join Date: Jan 2011 Posts: 37 Rep Power: 14 Hi guys, I am very new to CFX modeling so hello fellos. And right now i am using ANSYS Workbench 13.0 to model a gas flow of a impingement plate with neumann boundary conditions and varying the design I have a gas flow that is running through an impingement jet(from top to bottom) with a diameter of 0.0006(set as one of the design parameter) and a length of 0.00425(from top to bottom) with a static pressure of 1.95kPa and Static Temperature of 450°C at the top(colder side) and 1250°C at the bottom surface(hotter side). I have the results of simulations for different design variations(like platedepth,inlet,outlet diameter) So can anyone suggest me few steps that are generally done in a flow process analysis? Thanks a lot in advance Krishna

 January 26, 2011, 19:29 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,267 Rep Power: 136 Do the CFX tutorials, they are a good start. Have a look at the tutorials on the CFX-Community website as well. Do a literature search for similar applications to get a feel for how other people have done this sort of model.

 January 27, 2011, 04:46 Shear stress transport model #3 Member   Join Date: Jan 2011 Posts: 37 Rep Power: 14 I am using a shear stress transport model...so for solving the problem theoretically what kind of equations do i have to solve??

 January 27, 2011, 17:20 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,267 Rep Power: 136 What do you mean"theoretically"?

 January 28, 2011, 06:20 theoretically how to predict the Cooling efficiency?? #5 Member   Join Date: Jan 2011 Posts: 37 Rep Power: 14 The thing is i have all the post process results...including heat flux and heat transfer coefficient and Reynolds number and the give ngeometrical and fluid parameters...Can you tell me theoretically how to predict the Cooling efficiency

 January 28, 2011, 06:32 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,267 Rep Power: 136 You have the parameters from your simulation so you can work out the cooling performance from that. Or are you asking what is the expected cooling efficiency? In that case go to any heat transfer textbook and they should cover heat transfer from impinging jets.

 January 28, 2011, 07:35 #7 Member   Join Date: Jan 2011 Posts: 37 Rep Power: 14 yup thanks man...experimentally i can figure out the cooling efficiency ...But theoretically i need to know the expected cooling efficiency..Can you please tell me which text book is good for that. Thanks, Krishna

 January 28, 2011, 08:03 #8 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,267 Rep Power: 136 I go back to my original question - what do you mean by "theoretically"? I do not know of any theory which will tell me this, only empirical models and simulation results.

 January 28, 2011, 10:14 #9 Member   Join Date: Jan 2011 Posts: 37 Rep Power: 14 Ok i am really sorry....can u please tell me how to experimentally determine the Cooling efficiency of a SST model with Thermal energy conditions as i said above using the post processing simulation results of CFX?...the last time i typed the message i have typed it by mistake..sry

 January 28, 2011, 16:19 #10 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,267 Rep Power: 136 Nothing to be sorry about, it just seems you don't know what some of the terms you are using mean and imply. Here's some definitions: Simulation = a numerical model of a physical process Numerical Model = an approx answer to an analytical mathematical model of a physical process Experiment = Measurements of a physical process Empirical Model = A curve fit onto experimental results, with no reference to the underlying theory of the process. Theoretical model = A mathematical model which describes the underlying physical process In complex flows like impinging jets you usually only get empirical models and simulation results. Both are only approximations. So is your question - Are you trying to measure the modelled heat transfer from a impinging jet simulation?

 January 29, 2011, 11:50 #11 Member   Join Date: Jan 2011 Posts: 37 Rep Power: 14 hi, yes exactly...so let mw know how to do this please...thaks

 January 30, 2011, 05:35 #12 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,267 Rep Power: 136 OK, now that I know what you are asking I can answer you Easy: areaInt(Wall Heat Flux)@Surface should do it. Either put this CEL expression on a monitor point or in the CFD-Post function calculator for post-processing.

 January 31, 2011, 05:13 #13 Member   Join Date: Jan 2011 Posts: 37 Rep Power: 14 Thanks you man, It was bugging me since a week.Now I will try it tomorrow.Since i am outside today and do not have access to work. And one more thing is this gives me the heat flux at any point right. And mine is a thermal energy transfer SST model. So is there anything like Is entropic efficiency or anything that i can find??

January 31, 2011, 07:21
#14
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Glenn Horrocks
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Quote:
 this gives me the heat flux at any point right.
No. Read the documentation - the function I gave integrates the Wall Heat Flux over the wall boundary called "Surface 1".

Define a CEL expression for the entropic efficiency, that's all you need do.

 February 1, 2011, 09:23 entropic efficiency? #15 Member   Join Date: Jan 2011 Posts: 37 Rep Power: 14 does anyone know the expresion for the entropic efficiency in CFD Post?

 February 1, 2011, 12:08 #16 Member   Join Date: Jan 2011 Posts: 37 Rep Power: 14 I have one more question...Mine is a heat exhanger.. with impinging jets...So does anyone know hwo do you calculate the cooling efficiency using mass flow, Specific heat,Temperature ,pressure ??