Discussion Forum

Hello.

I am trying to simulate heat deposition in side-pumped laser Nd:YAG rod. However, I am struggling a bit with it.

Rod is mounted in two copper heat sinks. There is an ideal heat contact between rod and a mount, however there is a thin layer of thermal grease (k = 2 W/mK). This setup is held in the air with T = T_amb = 25 degC (like in the example in manual).

Assumptions:

1) Nd concetration is defined as absorption coefficient alfa = 5 [1/cm]

2) Pump source emits radiation in a shape of rectangular area (see Fig.) of 3x11 [mm^2] with heat density of P = 1 [W/cm^2]. It creates a boundary heat source Q = P * exp(-alfa*x) [W/cm^2] - exponential part represents absorption in the medium.
I cannot directly choose a limited area of the rod's side-surface, so I drew a thin (0.1 mm), curved YAG-shape which is placed on the side-surface of the medium and as a boundary heat source, as seen in the figure. Is there a way to choose this small rod area directly in the heat source boundary selection field?

3) The initial temperature of air/copper/YAG is T_amb = 25 degC

4) Copper mounts temperature is constant T = 25 degC

5) There is a natural convection from uncovered rod's surface and facets to the air (T_amb). In previous versions I was able to select boundries which dissipated the heat through natural convection (add a node). Here however, I can't find this feature and aforementioned boundries are thermally insulated, which is not true. How can I select these rod surfaces to dissipate heat through convection?

6) There is a laminar air flow of air along the rod (like in manual) with U = 1 [cm/s]

7) I use time-dependent solver, from 0 to 60 s.

My model does not compute. I've attached MPH file.
I would appreciate any help.
Cheers.