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-   -   high LHTC values in Coolant jacket analysis (http://www.cfd-online.com/Forums/star-ccm/81665-high-lhtc-values-coolant-jacket-analysis.html)

rcm November 3, 2010 04:31

high LHTC values in Coolant jacket analysis
 
hello all,

I'm doing analysis of water jacket of crankcase and cylinder head of multicylinder diesel engine. i am using polyhedral cells with prism layer at wall. y+ is maintained between 10 to 125 .

The problem is i'm getting very high values of HTC's . it goes up to 60000 W/m2k in region where velocities are 4m/s to 6m/s . i am using realizable k-e all y+. i get same values when i use high y+ wall treatment.

has anyone come across such high values of HTC? or does anyone knows what could be the possible reason?

HTC in coolant jacket analysis should not exceed 20000 W/m2K

RobertB November 3, 2010 07:13

Do you have the heat transfer reference temperature set to something sensible?

I assume you have checked the fluid properties to make sure all the values are credible.

rabat November 4, 2010 02:43

high LHTC values in Coolant jacket analysis
 
Do you have locally high LHTC?
Normally I have by 5m/s ~ 25000W/m^2.K.
Are the residuals ok? 10^-4
Your calculation is isothermal or segragated fluid temperatur?

rcm November 7, 2010 22:46

Hi RobertB,
Thanks for reply
I'm checking only Local heat transfer reference temperature.. it doesnt require to set up the referance temperature.. anyways the heat transfer referance temperature is set to 90 deg C that is inlet temperature of coolant. fluid properties are also correct.

rcm November 7, 2010 23:09

Hi rabat,
Thanks for reply
velocities goes above 5m/s and they are up to 7m/s and at some small region it goes up to 8m/s. i have given fixed temperature at wall but i have segregated fluid temperature model on. when u do reset to restart in CCM+ resudual starts from 1 so i cant really tell whether its below 1e-4. its converged and residuals have constant value

abdul099 January 6, 2011 17:16

Not sure whether it's the same issue, but in external aero calculations, the Y+ range from lets say 5 to 25 should be avoided when possible. Even with the all Y+ turb model, because this is just blending the high Y+ model and the low Y+ model according to the Y+ value. It's better than using one of the two other models, but it will not create miracles.

rabat January 12, 2011 12:57

high LHTC values in Coolant jacket analysis
 
Hello,

I've never get high HTC, my quetions are:

How many prism layers do you have?
How wide the prism layer thickniss?

Rabat

MBA January 15, 2011 00:21

Hello ,

How did you calculate HTC?


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