Learning Forum

[Amir]

I am using EWF model to simulate condensation of humid air. What are the ways to calsulate the net amount of heat absorbed/passed by film to the walls at the end of simulation?

[Rob]

Are you looking for the energy passed into the film from the flow, or from the film to the "outside" or flow to wall? Is at the end for the instantaneous value on completion of the run, or are you wanting an integral over the run? For the latter you need to save monitor data during the run, it's not available in the final data file. 

[Amir]

Rob, I am looking for the (1)Energy passed from the flow to the wall, and (2)Energy passed from the wall to the outside, and (3) Energy passed from flow into the film, and (4)Energy passed from the film into the wall.

I have tried:

Flux report -->> "Total heat transfer rate" and BC chosen as walls and I am attaching the result.

Is this showing the rate of heat transfer from the walls to the outside of the domain? And will the area below the curve be the total amount of energy passed from the wall to the outside [number2 as mentioned abow]?

[Rob]

The Flux report is energy passing through the wall(s), so if it's external it's the loss to "outside". Yes, it'll be the area under the graph, but given the sharp jump at the beginning and flat profile it's looks like you've reached a near steady solution. 

[Amir]

Thanks Rob,

What advantages would "reaching near steady solution" give to us? Does it mean that we can predict the behaviour of flow and field variables for longer physical times?[without actually running a simulation for that time? and saving time and computational cost?]

 

[Rob]

That's for you to decide. If the solution has stopped changing, then it's not unreasonable to assume you've got an equilibrium condition. Whether that holds indefinitely is for you to check. Most/all engineering is based on an assumption somewhere: the reason we spend so long at Uni is to help us determine which assumption we can use, and whether it's valid for whatever we're doing.