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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 05:31

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 08:13

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 03:43

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 23:46

Hi RobertB,
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 8, 2010 00:09

Hi rabat,
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 18:16

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 13:57

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 01:21

Hello ,

How did you calculate HTC?

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