fix bubble/breakup command

Warning

This is an experimental feature. It may produce unexpected results, and its behaviour may change without announcement in a future version

Warning

GPU support for this command has not been tested and may not work as expected.

Syntax

fix ID group-ID buoyancy keyword value ...

  • ID, group-ID are documented in fix command

  • buoyancy = style name of this fix command

  • zero or more keyword/value pairs may be appended to args; the dim keyword must be used

  • keyword = density or dim or level or region

rho value = rho-value
  rho-value = liquid density in mass/length^3 units
WeCrit value = WeCrit-value
  WeCrit-value = value for critical Weber number (dimensionless)
region value = region-ID
  region-ID = ID of region atoms must be in to experience break-up

Examples

fix breakup bubble bubble/breakup rho 1000 WeCrit 0.5

Description

Break up gas-bubbles in a gas-liquid system if a certain criterion is fulfilled. To ensure numerical stability, the break-up is performed in a way that initially a set of daughter bubbles of equal size are inserted, which are slowly grown over time to reach their final radius.

According to (Lau), the break-up criterion can be defined as follows, using the critical Weber Number, i.e. break-up if We > We_crit:

We = rho*u_rel^2*d/surfaceTension

where rho is the liquid density, d the bubble diameter and surfaceTension is the surface tension. According to (Lau), the bubble size distribution can be modelled uniformly. u_rel is the relative velocity between liquid and gas.

The optional region keyword can be used to restrict the break-up to a defined geometrical region

The following material properties have to be defined, using multiple fix property/global commands:

fix id all property/global surfaceTension scalar value
    (value=value for the surface tension (in force / length units))

Restart, fix_modify, output, run start/stop

No information about this fix is written to binary restart files. No fix_modify option applies to this fix. This fix computes a a global 3-vector of the total buoyancy force, which can be accessed by various output commands. No parameter of this fix can be used with the start/stop keywords of the run command.

Restrictions

Currently, the absolute velocity of the gas bubbles (rather than the the relative velocity between liquid and gas) is used

Coarse-graining information:

Using coarsegraining in combination with this command might lead to different dynamics or system state and thus to inconsistencies.

Default

none

References:

(Lau) Lau, Deen and Kuipers, Chemical Engineneering Science, 108, p 9 (2014).