Discussion Forum

Hi,

I think that depends on the properties of the solid material. If the droplet is wetting the surface my understanding would be that you just need continuity and assign the thermal material properties.

Cheers
Edgar

Hi Edgar,

thanks for your reply,

yes I agree with you, but in reality during the spreading of the drop on the solid surface there is a discontinuity in temperature at the interface due to the roughness of the solid surface (contact is not perfect).
that is why we have to integrate a thermal contact resistance to describe this discontinuity.

Well, then it is probably the thin thermally resistive layer you need. The challenge may then be to define the proper thermal resistance. And it is highly transient, a function of time, isn't it?
Just for my understanding: are you modelling the impingement process, i.e. the spreading of the droplet?

Cheers
Edgar

yes, I'm modeling the impingement process of a molten droplet on a solid surface taking onto account the thermal contact resistance ( a constant value for now)
So I will try "thin thermally resistive layer" but the problem is which layer thermal conductivity i have to use i e the conductivity of the air between the droplet and the solid surface or what?? Also I don't know which value I have to use for the layer thickness.

best regards
Soufiane

The conductivity in the resistive layer should be of the film material, i.e., air. It may be necessary to correct this if you have partial contact.

You might find this model interesting:
www.comsol.com/showroom/animations/1492/
kind regards
Niklas

yes, I'm modeling the impingement process of a molten droplet on a solid surface taking onto account the thermal contact resistance ( a constant value for now)
So I will try "thin thermally resistive layer" but the problem is which layer thermal conductivity i have to use i e the conductivity of the air between the droplet and the solid surface or what?? Also I don't know which value I have to use for the layer thickness.

best regards
Soufiane

The conductivity in the resistive layer should be of the film material, i.e., air. It may be necessary to correct this if you have partial contact.

You might find this model interesting:
www.comsol.com/showroom/animations/1492/
kind regards
Niklas

yes, I'm modeling the impingement process of a molten droplet on a solid surface taking onto account the thermal contact resistance ( a constant value for now)
So I will try "thin thermally resistive layer" but the problem is which layer thermal conductivity i have to use i e the conductivity of the air between the droplet and the solid surface or what?? Also I don't know which value I have to use for the layer thickness.

best regards
Soufiane

hi Niklas, thanks for your reply,

yes I have a partial contact and I don't know if you have any idea about the expression that i have to use to correct the conductivity.

best regards

I suggest to check this paper:

Xue, Heichal, Chandra, Mostaghimi:
Modeling the impact of a molten metal droplet on a solid surface using variable interfacial thermal contact
Journal of materials science [0022-2461] yr:2007 vol:42 iss:1 pg:9-18

The group has done a lot of work on the experimental and theoretical analysis of droplet impact with simultanous solidification. The thermal contact resistance between two metals is usually described with a thermal contact coefficient (just like a convective heat transfer coefficient) and the relative temperature between both surfaces, such as

dq/dt=h_contact*(T_1-T_2)

If you need more help on that topic, let me know.

Have you got a working droplet spreading model with the phase field or level set mode? I tried that some time ago, but then I figured out that mass conservation was poor even with a really fine mesh...