DPM Particle Types in ANSYS Fluent 2024 R1

#+CATEGORY: cfd

#+TAGS: DPM Fluent particle types inert droplet combusting multicomponent

#+MATURITY: growing

DPM Particle Types :: Complete Reference for ANSYS Fluent 2024 R1

This page covers all five particle types Fluent ships, what physics each enables, and how to pick the correct one. Target application: shisha PM2.5 simulation.

Particle Type Decision Matrix

Massless Particle

The simplest DPM particle type. A Massless particle:

• Has zero diameter and zero mass
• Experiences no drag (moves at the local fluid velocity exactly)
• Does not interact with the continuous phase (zero source terms)
• Cannot evaporate or combust

Use cases:

• Flow visualization (streamline-like, but Lagrangian)
• Residence time distribution: track how long fluid elements stay in the domain
• Debugging: check that the flow field is reasonable before activating real particles
• Passive scalar transport (tracer gas) without diffusion

How to set up:

• Select Massless in the injection panel
• Diameter field is ignored
• No material properties needed (no density, no specific heat)

Not for shisha PM2.5: massless particles do not model real physics. Use Inert for smoke.

Inert Particle

The workhorse type for solid particles and non-evaporating aerosols. An Inert particle:

• Has a fixed diameter and density
• Experiences drag (Stokes, Schiller-Naumann, or any other law)
• Can exchange heat with the gas (if heat transfer is enabled), but does not change phase
• Can experience additional forces (Saffman, virtual mass, thermophoresis, Brownian via UDF)

Required material properties:

Create a material: Materials > Create/Edit > Fluent Database > copy air > rename to "pm25_soot"

• Set density = 1200 kg/m^3
• Set specific heat = 1200 J/(kg K)
• Set thermal conductivity = 0.5 W/(m K)

*For shisha PM2.5: this is the correct particle type. Smoke particles are:

• Solid carbonaceous aerosol (inert)
• Non-evaporating at operating temperature
• Diameter 0.1--2.5 \mu m
• Density ~ 1200 kg/m^3

Droplet Particle

Adds phase-change physics to the inert particle. A Droplet particle:

• Everything an inert particle does
• Evaporates according to Law 2 (convective vaporization)
• Boils according to Law 3 (when T\_p reaches T\_boiling)
• Can form a wall film (semi-reflect BC)
• Can break up (TAB, Wave models)

When to use:

• Fuel injection (diesel, gasoline spray)
• Water mist (humidifier, spray cooling)
• Pesticide droplets

Not for shisha: smoke is not a liquid spray. Inert is the correct choice.

Evaporation sequence: 1. Droplet heats up (Law 1: sensible heating) 2. Surface evaporates (Law 2: vapor mass flux = f(T, p, d)) 3. Diameter shrinks 4. If T\_p reaches T\_boiling: violent boiling (Law 3) 5. Droplet disappears

*Multicomponent Droplet :PROPERTIES: :ID: cfd_dpm-particle-types--multicomponent :CUSTOM_ID: cfd_dpm-particle-types--multicomponent :END:

A droplet made of multiple liquid species. Each species evaporates at its own rate, with the more-volatile species evaporating first.

Required setup:

• Define each species in the mixture
• Set initial mass fraction of each species in the injection
• Define boiling point and latent heat for each

Use case:

• Fuel blends (gasoline = multiple hydrocarbons)
• Multicomponent aerosol where composition matters

Not for shisha: smoke is single-phase inert.

Combusting Particle

The most complex type. A Combusting particle: 1. Heats up (Law 1) 2. Devolatilizes: releases volatile gases (Law 4--8 model) 3. Char burns: solid carbon oxidizes (Law 9--10 model) 4. Leaves ash residue

Devolatilization models:

Char combustion models:

Use case:

• Pulverized coal combustion
• Biomass burning
• Solid-fuel particles

Not for shisha: smoke is not burning.

Comparison Table

Custom Particle Types (UDF)

If none of the five types fits, you can extend Inert with a UDF that:

• Adds custom body forces (DEFINE_DPM_BODY_FORCE)
• Adds custom heat-transfer laws (DEFINE_DPM_HEAT_MASS)
• Modifies particle diameter on the fly (DEFINE_DPM_EROSION hooks)
• Controls injection properties (DEFINE_DPM_INJECTION_INIT)

See also: DPM UDF Programming

Shisha PM2.5 Particle Type Selection

Setup steps: 1. =Models > Discrete Phase > Injections > Create > = select Inert 2. Materials > Create/Edit > New material "shisha_pm25":

• Density: 1200 kg/m^3
• Specific heat: 1200 J/(kg K)
• Thermal conductivity: 0.5 W/(m K)

3. Assign material to the injection 4. Set diameter: log-normal, d\_g = 1.0 \mu m, sigma = 1.5 5. Set temperature: 320--350 K (smoke from bowl)

--- :PROPERTIES: :seeAlso: cfd_dpm-setup-activation, cfd_dpm-injection-types, cfd_dpm-heat-mass-transfer, cfd_dpm-shisha-pm25, cfd_dpm-udf :END: