Dear Raza,

Patch an initial condition of zero absolute pressure in the volume where vaccum needs to be created

Syed Mughees Ali Thank you so much for your reply.

And what do I need to put in the thermophysical properties of that volume? And How should I declare this volume? as solid or as fluid?

OR I should do like this:

I declare the region as fluid(air), and then I put initial condition for pressure equals to zero, and then in thermophysical properties I put everything equals to zero (molecular weight, density, heat capacity etc)?

Thank you

Dear Raza,

You will run into problem, the time you define an absolute zero. By patching zero I mean a very small value. Think of a practical example of people conducting

rarified gas dynamics experiments. They define vaccum at very low pressure. Even the upper atmosphere is not absolute vaccum.

Also to answer the next question of thermophysical properties, kindly check some physical gas dynamic book, as I am not sure that continuum approximation will hold good in your case. Question that need to be asked is why you need these properties. These properties are used for mass, momentum and heat transfer in the fluid.

My recommendation to solve the problem.

As you are concerned only about heat transfer from radiation. Solve only radiation model, nothing else. Solve only energy equation with radiation terms. All the other terms will be zero. In that case you don't need to define pressure.

Read physical gas dynamics by Vincent and Chase and refer to lectures on radiation by C bajali.

In true vacuum there is no medium for the heat to travel through. Hence the only heat transfer is radiation. Hence, CFD does not really seem like the most obvious tool for your problem...