# Wall Transfer Coefficien - Heat Transfer Coefficient - CFX

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 Register Blogs Members List Search Today's Posts Mark Forums Read November 2, 2011, 17:49 Wall Transfer Coefficien - Heat Transfer Coefficient - CFX #1 New Member   Join Date: Oct 2011 Posts: 7 Rep Power: 12 Dear friends, I have simulated the flow in a simple geometry (like 2 paralel walls - "2,5D" case). My BC are (for laminar flow): In - low velocity and fixed temperature; Wall - no slip and fixed temperature; Out - Openning with static pressure. In CFX-Post: I have created a line in wall position, through the length. When I plot the variable (Wall Transfer Coefficien), the value found isn't the value hoped. 1) Why this happen? But when I take the Heat Flow "q" (in same line created) and temperature average of section "Tav" (with formulas in own CFX-Post)... I can obtain "h" correctly: q /(Tw-Tav) = h 2) Why "q" is correct, but "h" isn't? 3) How can I obtain "h" directly? 4) I have seen thread about that. Some users has talked about reference temperature.. But I don't understand that... Someone can explain it for me? and how can I change this reference temperature? I'm starting to study the CFD world... Thanks in advance everyone.   November 2, 2011, 20:58 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,170 Rep Power: 134    I would start by working through this FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F   November 2, 2011, 22:25 #3 New Member   Join Date: Oct 2011 Posts: 7 Rep Power: 12 First of all, thanks for answer. I liked the link! There are a lot of good things over there! but... don't worry... I have done all steps, mainly for to learn how the software works. My results aren't inaccurate. I'm using: RMS = 10^-09 and highresolution for advection and couple velocity-pressure. The simulation doesn't need great adjustments.. So highresolution scheme is good. I have problem just with Heat Transfer Coefficient, even the "q" seem is right. The manual doesn't let clear about "h". There said some thing about: "... using an external heat transfer coefficient, hc...". As am I getting the value of "q" correct, while the value of "h" seem being wrong? How can I obtain the truly value of "h"? *I did the same simulation on FLUENT software and I obtained the "h" correct there! Last edited by Gargioni; November 2, 2011 at 22:34. Reason: I forgot some things =/   November 2, 2011, 22:49 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,170 Rep Power: 134    There is more to accuracy than convergence tolerance and differencing scheme. h is referenced to a ambient temperature. By default CFX uses a function of the local fluid temperature which is usually quite different to the engineering definition (which is usually inlet temperature or far field temperature). To get h as engineers understand it have a look in the output file. There is a discussion in there about HTC reference temperatures and how to define your own temperature.   November 2, 2011, 23:25 #5 New Member   Join Date: Oct 2011 Posts: 7 Rep Power: 12 "There is more to accuracy than convergence tolerance and differencing scheme." I said just for let clear that I don't have problems with accuracy. May you help me to find this thread about HTC? Thanks in advance =]   November 2, 2011, 23:28 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,170 Rep Power: 134    It is in the output file. Have a look in your simulation. It is not a thread, but there are plenty of threads in the forum which have discussed the issue.   November 4, 2011, 15:34 #7 New Member   Join Date: Oct 2011 Posts: 7 Rep Power: 12 I changed the expert parameter tbulk for htc. And I think CFX considers the tbulk value like constant How I said: I have simulated the flow in a simple geometry, like 2 paralel walls - "2,5D" case. I have created a line in wall position, through the length, for captures the "h", however the value of "tbulk" is variable along the length. What can I do when the tbulk value isn't constant?   November 6, 2011, 04:57 #8 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,170 Rep Power: 134    If you have set the tbulk parameter then tbulk will be constant and the value you define, otherwise it will depend on local flow conditions. You can easily extract h for a constant tbulk anyway. The local tbulk temperature used is an available variable, so between that and the wall heat transfer variable you can calculate h based on any tbulk you like.   March 7, 2012, 00:19 #9 New Member   Join Date: Oct 2011 Posts: 7 Rep Power: 12 I solved my problem... doing a CEL routine. __________________ -- Gregory T. Gargioni ------><> E-mail: gargionis gmail "dot" com -------------------------------------   April 15, 2013, 07:46 #10 Member   Join Date: Nov 2011 Location: Germany Posts: 40 Rep Power: 12 maybe u can give a short summary of the steps which u made to help me?   October 24, 2017, 14:02 #11 New Member   Join Date: Oct 2011 Posts: 7 Rep Power: 12 !\$Tw=298.15; !\$Zposi = 0.4; !\$TBulkZ = \$Zposi*20; !\$a=0; !for (\$i=1; \$i<89; \$i++) { !\$a=\$a+0.005; !\$Xposi[\$i] = \$a; !} !for (\$i=1; \$i<89; \$i++) { PLANE: Teste.\$i Option = XY Plane Z = \$Xposi[\$i] Colour Mode = Variable Colour Variable = Temperature Range = Local END !\$Tbulk[\$i] = massFlowAve("Temperature","Teste.\$i"); !\$q[\$i] = massFlowAve("Wall Heat Flux","Teste.\$i"); !\$h[\$i]=(\$q[\$i]/(\$Tw-\$Tbulk[\$i])); !} !\$b=0; !for (\$i=1; \$i<41; \$i++) { !\$b=\$b+0.0001875; !\$Yposi[\$i] = \$b; !} !for (\$i=1; \$i<41; \$i++) { POINT: Point.\$i Option = XYZ Point = 0.0, \$Yposi[\$i], \$Zposi Colour Mode = Variable Colour Variable = Temperature Range = Global END !\$T[\$i] = maxVal("Temperature","Point.\$i"); !\$Tadm[\$i] = (\$Tw-\$T[\$i])/(\$Tw-\$Tbulk[\$TBulkZ]) !} \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm __________________ -- Gregory T. Gargioni ------><> E-mail: gargionis gmail "dot" com -------------------------------------   September 20, 2019, 06:23 #12
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 Originally Posted by Gargioni !\$Tw=298.15; !\$Zposi = 0.4; !\$TBulkZ = \$Zposi*20; !\$a=0; !for (\$i=1; \$i<89; \$i++) { !\$a=\$a+0.005; !\$Xposi[\$i] = \$a; !} !for (\$i=1; \$i<89; \$i++) { PLANE: Teste.\$i Option = XY Plane Z = \$Xposi[\$i] Colour Mode = Variable Colour Variable = Temperature Range = Local END !\$Tbulk[\$i] = massFlowAve("Temperature","Teste.\$i"); !\$q[\$i] = massFlowAve("Wall Heat Flux","Teste.\$i"); !\$h[\$i]=(\$q[\$i]/(\$Tw-\$Tbulk[\$i])); !} !\$b=0; !for (\$i=1; \$i<41; \$i++) { !\$b=\$b+0.0001875; !\$Yposi[\$i] = \$b; !} !for (\$i=1; \$i<41; \$i++) { POINT: Point.\$i Option = XYZ Point = 0.0, \$Yposi[\$i], \$Zposi Colour Mode = Variable Colour Variable = Temperature Range = Global END !\$T[\$i] = maxVal("Temperature","Point.\$i"); !\$Tadm[\$i] = (\$Tw-\$T[\$i])/(\$Tw-\$Tbulk[\$TBulkZ]) !} \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Tbulk \$q \$h \$Xposi \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm \$Yposi \$Tadm

Hi

How did you implement this code into CFX?
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best regards
pblasiak   September 23, 2019, 16:09 #13 Senior Member   Przemek Join Date: Jun 2011 Posts: 245 Rep Power: 14 Ok I found that it is in Reference guide in Power Syntax chapter __________________ best regards pblasiak  Tags heat transfer coefficient, wall transfer coefficien Thread Tools Search this Thread Show Printable Version Email this Page Search this Thread: Advanced Search Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are On Refbacks are On Forum Rules Similar Threads Thread Thread Starter Forum Replies Last Post Yr0gErG FLUENT 4 December 2, 2019 00:04 mullenc525 CFX 4 January 24, 2017 14:30 andred FLUENT 0 November 16, 2010 21:13 Gary Holland CFX 10 March 13, 2009 03:30 Miguel Baritto CFX 4 August 31, 2006 12:02

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