Acoustophoretic Radiation Force
Use the Acoustophoretic Radiation Force node to exert forces on small particles due to acoustic radiation. To be subjected to this force, particles must be in a region where the acoustic pressure or acoustic velocity is not spatially uniform.
In addition, the Acoustophoretic Radiation Force is only applied if the acoustic pressure or acoustic velocity has already been computed in a Frequency Domain study type. This is because the magnitude of the acoustophoretic force depends on the angular frequency.
Supported formulations:
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Newtonian,
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Newtonian, first order, and
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Newtonian, ignore inertial terms.
Radiation Force Model
This section determines how the equation for the acoustophoretic radiation force is defined. It also determines what inputs will be shown in subsequent sections.
Select an option from the Particle type list: Solid particle (the default) or Liquid droplet.
Select an option from the Thermodynamic loss model: Ideal (the default), Viscous, or Thermoviscous. The Thermoviscous loss model is the most detailed of the three but requires the most in-depth knowledge of the particle and fluid material properties.
Acoustic Fields
Enter a value or expression for the following:
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Pressure p (SI unit: Pa). This should be computed from another physics interface using a Frequency Domain study type.
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Acoustic velocity u (SI unit: m/s). Similarly, this should be solved for in another physics interface such as the Pressure Acoustics, Frequency Domain interface.
Particle Material Properties
Most of the required particle material properties are specified in the Additional Material Properties section for the Particle Properties node, with the exception of the following.
If Solid particle is selected from the Particle type list, enter values or expressions for the:
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Pressure-wave speed cp,p (SI unit: m/s, default 2,400 m/s), and
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Shear-wave speed cs,p (SI unit: m/s, default 1150 m/s).
If instead Liquid droplet is selected, just enter the Adiabatic speed of sound cp (SI unit: m/s, default 1445 m/s).
Surrounding Fluid Properties
All of the inputs in this section are domain material properties that can either be taken From material or given a User defined expression. The defaults given below are shown by first selecting User defined.
For any Thermodynamic loss model, enter the:
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Density ρ (SI unit: kg/m3, default 995 kg/m3), and
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Speed of sound c (SI unit: m/s, default 1500 m/s).
If the Thermodynamic loss model is Viscous or Thermoviscous, also enter the Dynamic viscosity μ (SI unit: Pa·s, default 8.4 × 10-4 Pa·s).
If the Thermodynamic loss model is Thermoviscous, also enter the:
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Bulk viscosity μB (SI unit: Pa·s, default 2.4 × 10-3 Pa·s),
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Heat capacity at constant pressure Cp (SI unit: J/(kg·K),
default 4.18 × 103 J/(kg·K)),
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Isobaric coefficient of thermal expansion αp (SI unit: 1/K, default 2.75 × 10-4 1/K),
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Ratio of specific heats γ (dimensionless, default 1.01), and
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Thermal conductivity k (SI unit: W/(m·K), default 0.61 W/(m·K)). The thermal conductivity is always assumed to be a scalar for the purpose of computing the acoustophoretic radiation force.
Advanced Settings
Select the Use piecewise polynomial recovery on field check box to smooth the radiation pressure using piecewise polynomial recovery. This can give a much more accurate representation of the radiation pressure because it uses information on adjacent mesh elements to reconstruct the field. If a coarse mesh is used to compute the field then this option can be especially useful.
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Studies and Solvers and Frequency Domain in the COMSOL Multiphysics Reference Manual
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Acoustophoretic Radiation Force in the theory section.