[sortik]

Hello everyone how can one calculate total heat loss by object that is cooled down due to natural convection. I have simple square box with temperature set to 60C. it is in air enclosure with no flow and temperature of 22C. Simulation itself is ok and results also seems ok but I can't figure how can I determine how much heat in watts the object lost. I can tell the heat that is generated in every step with

areaInt(wall heat flux)@boundary

but its just the actual amount in actual step.

Is it possible to tell that the object lost X watts from the beggining till the end? And would this also be possible to compute in steady state simulation?

I am just starting doing simulations and for sure I am not expert in thermodynamics so please be gentle Thank you very much

[ghorrocks]

You will need to get the time history of the wall heat flux and then integrate it over time. To do this:
* Define a monitor point with the areaInt(wall heat flux)@boundary expression
* Run the simulation
* When completed, in solver manager make a plot monitor of that expression and export it to a CSV file
* Import the CSV file into your choice of mathematical software (matlab, python, excel) and do the time integration of the function. I trust you have some basic numerical mathematics background so you can do simple integrations like this.

[sortik]

Thank you for your reply. I have a polypropylene box that weights 0.52kg. It is cooled down from 60C to 22C. With basic math I get that it should lost 10.15 watts of heat. If I set up my monitor variable of integer of wall heat flux I get numbers from 27 watts to 0 with timestep of 10 seconds. If I integrete these values I will get high number is it because i have to put timesteps into hours because integral of wall heat fluxg gives value of watts/h?



Thank you again

[ghorrocks]

If you integrate Watts in time you get Watt.seconds, which is Joules.

You will need to convert hours to seconds - but I trust you already knew that.