## Fluids

#### Insulated Boundary layer causing heat outflow issue

• ianster1
Subscriber

I am working on a simulation with two heated plates (25 cm long) separated by a small non-heated insulated gap (2 cm).  I am running into an issue where energy is leaving the simulation through this gap causing a temperature decrease.  I need this gap to be perfectly insulative so the temperature remains constant.  With a heat flux of zero, shouldn't this gap remain constant temperature?  Is there a boundary condition I am fogetting to use?  Initially I though it was a mesh refinement issue, however, the mesh density is very high with 60 elements in the downsteam direction for the gap and 500 elements for the heated plates.  I attached an image from the results.  The first heated plate is set to a heat flux of 130 w/m^2, the gap 0 w/m^2, and the second heating plate at 125 w/m^2.

• Nikhil Narale
Ansys Employee

Hello,

How are you maintaining the temperature in the gap? Are you initializing the domain with a temperature value? If that is the case, heat-flux = 0 seems logical. However, if you want the energy to flow from the 1st plate towards the gap, setting heat-flux = 0 won't serve the purpose.

"The first heated plate is set to a heat flux of 130 w/m^2, the gap 0 w/m^2, and the second heating plate at 125 w/m^2."

I am finding it difficult to understand the logic behind this setup, can you please explain the objective of your simulation?

Thank you.

• Nikhil Narale
Ansys Employee

To add, if you are anticipating heat outflow issue, I would recommend you to first check Flux Reports. Temperature profiles may not show the correct picture.

• ianster1
Subscriber

The purpose of this simulation is to mimic a experimental solution.  The experiment is comprised of two heated plates separated by a small gap.  Due to experimental factors, the heating plates are not necessarily delivering the same power output so that is why they are slightly different.  Only temperature data was provided by the experiment so that is the only variable that we can compare our results to.  Since there is still technically some heat transfer between the plates and gap, I ran the sim one using coupling for the gap, however, the results were still the same.  For all of the simulations, the inlet temperature and velocity was initialized using a standard initialization.

I ran a heat flux report and I do not see any heat outflow.

Is the only way to maintain temperature over the gap to define the temperature?  I am hesitant on doing this as we are testing multiple different heat fluxes and the temperature downstream the first plate will not be the same.  Is there a way for fluent to maintain a constant temperature over the gap without specifying a specific temperature?

• Swathi V. V.
Ansys Employee

Hi,

You can fix the temperature of the gap region in cell zone option, go to cell zone --> fixed values --> temperature. If this gas is not a separate cell zone try cell register to split cell zone and then apply fixed temperature.