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Re: [lammps-users] How to calculate viscous dissipation heat in pressure driven flow

Re: [lammps-users] How to calculate viscous dissipation heat in pressure driven flow

 From: Axel Kohlmeyer Date: Thu, 3 May 2018 12:49:08 -0400

```On Thu, May 3, 2018 at 10:14 AM, Jinhuan Pu <jinhuanpu@...24...> wrote:
> Hi everyone,
>
>
>
> I am using LAMMPS to simulation pressure driven flow in nanochannel flows.
> Initially, I use NVT ensemble to this system. Then I add a certain force to
> every fluid atom and give fluid just NVE ensemble, at the same time, the
> channel is set NVT ensemble to keep constant temperature as before.  After a
> period of time, this system get steady and there is a stable velocity
> profile. In addition, the fluid is heated due to viscous dissipation (fluid
> fiction). My question is that I want to calculate the viscous dissipation
> heat of the fluid. Or heat generation because of adding force to this
> system. If anyone have any idea about this? Thank you very much.

fix compute nvt should provide a global scalar property comprising the
amount of energy exchanged between the system and the heat bath.
for details, please check out the documentation for fix nvt (you may
have to dig around a little, there is a lot of information there.).
the difference of the value of that property between the beginning and
the end of a production run segment should be what you are looking
for, but only indirectly.

otherwise, you can do a compute ke/atom and compute pe/atom, define an
atom style variable that has the sum of the two. then do a compute
reduce sum over the atoms of interest and again, look at the
difference between the beginning of the run and the end (or progress
during) and you have the change in total energy of your atoms of
interest.

axel.

>
>
>
> Best regards,
>
> Jinhuan
>
>
>
>
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--
Dr. Axel Kohlmeyer  akohlmey@...24...  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.

```