[RabiArya]

I want to learn how to calculate the volumetric heat generation rate of a normal computer in a office. Also if someone could give some previously calculated value. It's okay if the value is for only monitor, or cpu or combined.

[flotus1]

There are many ways to model this, but a specific heat source (i.e. W/m³) is probably one of the more convoluted approaches. Depending on which scale you are looking at. But still, total heat sources (i.e. W) are probably what you want.

The most straightforward modelling approach that springs to mind:
The computer is modeled as a separate volume within the air volume that makes up the office. Then you can assign a total heat source (unit: W) to this volume.
Depending on whether you choose to model the computer volume as a fluid or solid box, you can also add momentum sources to model how the fans inside the PC exhaust hot air.
A variant of this would be to exclude the volume inside the computer, and just add the total heat source (unit: W) as a boundary condition.
Other variants are possible, depending on the exact scope of this simulation.

As for the amount of heat transferred:
A typical monitor is around 30W-50W. Lower for small monitors, larger for big monitors, much larger for big monitors with high refresh rates.
PCs have a larger range. From 10W for a thin client -which would probably be negligible- up to 600W or more for a large workstation PC. A typical semi-modern office PC is in the same ballpark as a monitor.