[marcoac14]

Originally Posted by siavash_y

I have the same problem, did u find a solution marcoac?

Well, not a good one. I found workarounds, not real solutions.

As many users suggested, you can use design modeler to imprint planes along the channel and interpolate them. If you're working with parameters this is the best solution in my opinion because you can write an expression to give you the result right away. It will give you a fairly good idea of what's happening, but may not be as accurate as required.

Another solution is to export temperature and velocity as a csv file and use it in Mathematica (or similar) to interpolate over the domain and extract the results you need.

Regards,
Marco

[VIPIN KAKKAR]

Hi,
i am simulating natural convection heat transfer from perforated fin array and have solved the problem in CFX,but i am unable to find out Nusselt number of the fin array.
please tell me how to find out Nusselt number of fin array.

[VIPIN KAKKAR]

i am working on natural convection heat transfer of perforated fin array in CFX. i have solved it in CFX, now i need to find out Nusselt no. of fin array for that first of all i have to find out heat flux value of fin. The problem is with the post processing software as I don't really know it well enough. How do I extract the heat flux values for my FIN wall?

[singer1812]

Use variable "Wall Heat Flux". This of course assumes you didnt model the wall as adiabatic......

[VIPIN KAKKAR]

Originally Posted by singer1812

Use variable "Wall Heat Flux". This of course assumes you didnt model the wall as adiabatic......

sir,
may you explain me how to use "wall heat flux" variable. when i select wall heat flux in variable tab it shows value of min & max heat flux, whether this min & max value is for whole body?
i want to find out Average heat flux for a single body & single surface. Please tell me how to find out.

[ghorrocks]

The min and max refer to the object locator it is referring to.

Use the function calculator to calculate any function of any area.

[VIPIN KAKKAR]

Originally Posted by ghorrocks

The min and max refer to the object locator it is referring to.

Use the function calculator to calculate any function of any area.

sir,
i am finding heat flux using two expressions- areaAve(wall heat flux)@location and ave(wall heat flux)@location.
value for both the expressions is different.
what does function areaAve and ave mean?

[ghorrocks]

This is explained int he documentation, in the CFX reference guide. areaAve is the area weighted average and ave is just a simple arithmetic average.

[VIPIN KAKKAR]

Originally Posted by ghorrocks

This is explained int he documentation, in the CFX reference guide. areaAve is the area weighted average and ave is just a simple arithmetic average.

Thank you sir for your suggestion!
sir,please tell me one more thing what does areaAve(Temperature)@location
" area weighted average temperature" mean. Is it absolute temperature or relative temperature(difference of absolute and atmospheric temperature).
In my fin array problem when i gave heat flux 5900 W/m2 to fin base then areaAve(Temperature)fin shows 140 K.

[ghorrocks]

The temperature returned will be the temperature variable - that will be defined as C, F or K depending on your setup. And it is an absolute value, not a relative one.

If you have and areaAve(temperature) of 140K then your fin is really cold. This is 140K absolute, so 133K below the freezing point of water. I hope this is what you intended to do.

[VIPIN KAKKAR]

Originally Posted by ghorrocks

The temperature returned will be the temperature variable - that will be defined as C, F or K depending on your setup. And it is an absolute value, not a relative one.

If you have and areaAve(temperature) of 140K then your fin is really cold. This is 140K absolute, so 133K below the freezing point of water. I hope this is what you intended to do.

Thank you sir!
sir, in my problem of "natural convection heat transfer from perforated fin array", i can calculate heat flux and temperature at any face of fin array in CFX-post ,but how to calculate Nusselt Number of Fin Array in CFX-post

[VIPIN KAKKAR]

sir please tell me how to find wall heat transfer coefficient and wall adjacent temperature. what are expressions to find these variables.

[Thomas MADELEINE]

I don't understand your question...
you have the name of the variable so you can plot it in CFD-Post...
both of them are Wall variable so plot it on the Wall with a contour.
For better understanding use the CFD-Post Help on these variable and the CEL function...

[Pyotr]

Hi everyone,


I’ve been running a simulation of gas flowing through a multi hole heated solid body. I need to obtain data like Reynolds, Prandtl and Nusselt number along the channel.


In order to obtain data from various cross-sections along the channel, I’ve created a surface (Insert -> Location -> User Surface), Method -> Offset From Surface, which is parallel to the outlet surface. I just change the distance from the outlet and I get all the data in the new location. All the expressions contain a reference to this location.


I called the user surface “Data Collection” and the expressions are as follows:

ReDataCollection (Reynolds number):
sqrt(4*area()@Data Collection/pi)*areaAve(Velocity)@Data Collection*areaAve(Density)@Data Collection /areaAve(Dynamic Viscosity)@Data Collection

PrDataCollection (Prandtl Number):
areaAve(Specific Heat Capacity at Constant Pressure)@ Data Collection*areaAve(Dynamic Viscosity)@ Data Collection / areaAve(Thermal Conductivity)@Data Collection

TwallDataCollection (Temperature at the wall):
areaAve(Wall Adjacent Temperature)@Data Collection+(areaAve(Wall Heat Flux)@Data Collection/areaAve(Wall Heat Transfer Coefficient)@Data Collection)

TbulkDataCollection (Bulk Temperature):
areaAve(Temperature)@Data Collection

MyHTCDataCollection:
areaAve(Wall Heat Flux)@Data Collection/(TwallDataCollection- TbulkDataCollection)

NuDataCollection (Nusselt Number):
MyHTCDataCollection* sqrt(4*area()@Data Collection/pi)/ areaAve(Thermal Conductivity)@Data Collection

I got the diameter of the channel from sqrt(4*area()@Data Collection/pi), since the calculated area is not exactly what I expected from theory (just a minor difference), but to maintain the consistency, I chose to evaluate like this.

I managed to get results that seem to be reasonable, but I am still uncertain about the accuracy of expressions I used to obtain Nusselt Number.

Is it correct to use “areaAve(Wall Heat Flux)@Data Collection”, “areaAve(Wall Adjacent Temperature)@Data Collection”, and “areaAve(Wall Heat Transfer Coefficient)@Data Collection” in this context?

“areaAve(Wall Heat Flux)@Data Collection”, for example, gives me the heat flux in the specific cross-section I am working on?


Thanks!

[Antanas]

It seems to me that Wall Heat Flux is defined on wall, but not on cross-section.
Also keep in mind that locator based CEL functions use conservative values in calculations i.e. average over near wall control volume, but not boundary values.

[ghorrocks]

As Antanas states, wall heat flux is not defined on a flow cross section plane.

You will have to define a curve at the intersection of your plane "Data Collection" and the wall. You can do this by a polyline with the "Boundary Intersection" option. Then you can do lengthAve(Wall Heat Flux)@Line on the curve to get the average Wall heat flux at that countour.

[Pyotr]

Hi Antanas and Glenn,


I did what you suggested, and the data I extracted from the polyline are about 1.5% higher, on average, than the ones I got from areaAve(Wall Heat Flux) at the cross-section.


Thanks a lot!