## Fluids

#### Boundary condition error

• kaniz
Subscriber

I am working on a model where a single liquid water droplet will impinge on a semi-infinite cold substrate. The initial temperature of the droplet and air is at 2C and the substrate is at -25C. When the droplet will impinge on the substrate it will solidify on the surface. However, I would like to capture the transient thermal distribution inside the substrate. Based on this description, I set-up the boundary condition and run the simulation. However, when I run it gives me few errors. Is someone could assist me on that issue. Thanks.

• Raef.Kobeissi
Subscriber

Hello Kaniz,

You mentioned that the droplet will solidify, have you used the solidification & Melting model? what type of model have you used and which ANSYS package did you use?

Subscriber

Hi
I'm looking for advice about how to run a very simple transient heat conduction model without going through a huge learning curve with ANSYS, since I do not have engineering background.  In the biology sphere there are some situations where you need a slow controlled freezing of a small patch of water or animal tissues. (Note: the aim is not just snap-freezing). In practice I see these techniques being done poorly because of misconceptions about the physics. As a retired person who does some unpaid teaching of students who will be later using these techniques, I want get a more quantitative idea of what's happening.

The simple model I want to investigate is a cold (< 0 deg C) cylindrical metal rod, one end of which is placed in contact with some high-water-content gel (ie, allowing heat conduction but no convection). The rod is held stationary until the water starts to freeze. The aim is to see how long it takes to reach the freezing point at various distances (in depth and sideways) from the end of the rod. This is a 2D problem as the geometry is axially symmetric.  The heat flow is from the water into the rod, and to keep the model very simple I want to ignore other effects (eg, heat released by the phase-change during freezing, transfer of heat from the surrounding air to the rod, and radiative transfers). The result I want is just a contour plot of temperatures in the gel (around the end of the rod) vs time.  The parameters needed are very few: the starting temperatures of the rod and the gel, rod dimensions, water volume, thermal conductivities and specific heat of the 2 materials.

So, a simple problem for an engineer!  As a non-engineer, I am finding it hard to even get started on this model in Ansys (Student ed).  Basically I just want to specify the above parameters re shape and materials involved, and hope that all the mesh generation and setting up the maths is done for me. I know there are tutorials by the dozen to allow me to self-educate about using Ansys. From my point of view that's not a good use of time, as I don't really need understanding of the program, just some results to use in optimising the techniques mentioned.  Are there are some similar scenarios already worked up as examples?  If so, I'd be grateful if anyone can point me to them.

Thanks

• Raef.Kobeissi
Subscriber
Hello This is not a simple simulation to carry out without some understanding of the software’s basic features and components. Your problem could be solved using the melting/solidification model with the energy equation on. You need to read about this model to carry out the simulation. I will also try to find you a proper tutorial and post it here.
Cheers