DPM Spray: Particle Type, Direct Injection Type Setup

DPM Spray Introduction

In this article, the types of injections in Fluent software are given, and each one is explained. To simulate such problems, which usually have solid and gas particles or liquid and gas particles as input simultaneously, we use the discrete phase model method in the software. There are two different approaches to Euler-Lagrange and Euler-Euler to model multiphase flow.

According to the density and fraction of airborne particles, the volume fraction of airborne particles can be obtained equal to 1.5e-8. Given that this fraction is less than 0.1, the Euler-Lagrange perspective should be used to solve the two-phase current. Also, due to the low volume fraction of particles, the effect of the discrete phase, i.e., particles, on the continuous phase, i.e., air, is neglected. In this view, the fluid phase is considered continuously by solving Navier-Stokes equations with time averaging, while the dispersed phase is solved by tracking the path of a large number of particles, bubbles, or droplets inside the fluid field.

The dispersed phase can exchange mass, momentum, and energy with the fluid phase. In fact, in this view, the path of each particle is determined.

The basic assumption in this model is that the dispersed phase involves a small volume fraction even if the dispersed phase mass flow rate is greater than the fluid mass flow rate.

Because particle paths are known, this view is suitable for modeling spray dryers, liquid fuel combustion, and particulate streams, But it is not suitable for modeling liquid-liquid mixtures, fluidized substrates, or any other application where the secondary phase volume fraction cannot be neglected.

In this article, we describe In detail the following :

• Particle Type
• types of injections
• Atomizer Models
• Inputs for Atomizer Model
• And governing equations

DPM Spray Particle Type

This section defines the particle type and the physical models of each particle. To access the window related to this section, we do the following:

Models>>discrete phase>>injection>>create>>particle type

The type of particles is given in the following tables, each of which is briefly described :

Massless

As the name implies, it has no mass (there is no heat transfer) since it has no mass, related physical properties, and no force is applied to it. The physical models related to this part have also been disabled, and we can only track the particles when using this type.

Inert

Inert follows the force balance, the particles that we want to inject and enter the computational domain, we want to have heat transfer. We can use Inert (the particles have heat transfer). Industrial applications used in this method include particle injection in cyclones, intra-volume particle spraying, etc.

Droplet

Droplet also follows the balance of force, and we use them when we want to check evaporation or boiling, and it is used in issues related to corona, sneezing, etc.

Combusting

The particle must be solid for using this type, which follows the force balance. It is used for DPM combustion projects.

Multicomponent

This is used when several types of particles are injected.

 

ANSYS Fluent software provides types of injections that we can use depending on the kind of injection:

 

 Direct Injection Type Setup

single

Particle flow injected from a point is also shown in the figure below:

Release features can be set from the window that appears below, which can be accessed in Fluent software, each of which is described:

The point properties section should specify the injection start and stop times for transient problems and detect transient particles. If we set the value to zero for the start and end of the injection, they are injected only at starting.

The animation related to this work can be seen below, and the settings of this animation are given in the figure above; as you can see, the stream starts to injection from a point:

In this animation, the particle residence time is shown that the first injected particle has a longer residence time than the other particles.

 

Group

Particle streams that are injected in groups, first in Ansys Fluent software, we enter the section related to this injection and set its inputs:

In this type of injection, we must first specify the first and stop points and then Ansys Fluent software using the linear relationship . Paying attention to the number of points, i.e., the value of N determines the value of each parameter at the desired injection point. How to assign the first and last point is shown in the following figure:

Thus, for example, if your group consists of 5 particle streams and you define a range for the initial x location from 0.2 to 1 meters, the initial x  location of each stream is as follows:

• Stream 1: x = 0.2 meters
• Stream 2: x = 0.4 meters
• Stream 3: x = 0.6 meters
• Stream 4: x = 0.8 meters
• Stream 5: x =     1 meters

In the following figures, several different modes are given in Fluent software, each of which is briefly explained:

This figure is based on the simulated particle diameter, and its input settings are also given:

As you can see, the more we move to the left, the larger the diameter points will be. In the simulation, the larger diameter particles will be faster than the smaller diameter particles, as shown in the figure. And the related animation can be seen in the following figure:

The following figure, which has different velocities and is shown based on the residence time, and as we can see, the velocity changes according to the said linear relationship:

The animations for this mode and the corresponding window changes are given in the following shapes:

As you can see, we first marked the first and stop points, and then by specifying the Number Of Stream, the particles began to inject. The Number Of Streams indicates the number of particle flows in the group or cone injection. (This does not appear for single, surface, or file injections.) And we can specify the number of particle flows through the window that appears below:

Cone

This type is defined for three-dimensional problems; we can specify its kind from the cone type section. The types of conical shapes are point, hollow, ring, solid, each explained in order according to the simulations that have been done; the animation of each one is given separately:

• Point type

As the name implies, the coordinates of the point that propagates conically are given. The characteristics of this type of injection can be specified as follows:

• cone angle

This angle can be seen in the following figure:

The following figure is an example of a simulation that has already been done, and animation has been taken in this field, which is given in the following order:

The following animation settings are shown in Figure 6.

ring cone

The next type of cone subset is called the ring cone, which, as its name suggests, is published as a ring, which has the following specifications:

The following figure is an example of a case study:

In the following figure, we can see the inner and outer radius:

The animation settings are shown in Figure 7, and the animation can be seen below to understand this type of injection better:

Solid/hollow cone

Subsequent injections, which are made of cones, are propagated in the solid cone, i.e., solid cones and hollow cones, which are solid and hollow cones, respectively, which are as follows for both types of injections:

Adjust the velocity magnitude fraction to enter the current’s rotating component in the Swirl Fraction section. The direction of the rotation component is defined using the law to the right of the axis (a negative value for the rotation fraction can be used to reverse the direction of rotation).

The settings for the hollow-cone and solid-cone animations are shown in Figures 8 and 9, respectively. The inputs are fully defined, and below are the animations:

According to the hollow cone animation and as it is known, the particles are injected in the form of hollow cones.

In contrast to the solid cone, it is clear that the injection of the defined particles is as solid cones.

Surface

Particle streams are injected from a surface. And is injected from the same area as follows:

As shown from the figure, for this type of injection to be done well, we must first create a surface according to the current geometry and then adjust the specifications and features of the desired surface as shown below, each of which is described in the parameters:

No coordinates are required in this type of injection, and the boundary page is set as the input page.

The following is an animation of this previously simulated work:

Solid-cone DPM injection Tips

Tips on Solid-cone injection

In this article, tips on solid-cone injection have been investigated.

In addition to simple injections, ANSYS FLUENT offers more complex sprays injections that describe the initial break-up phenomena. For most injections, you must provide the particles’ initial diameter, position, and velocity. However, models for predicting droplet size and velocity distribution for sprays are used.

All atomization models use physical atomizer parameters such as diameter orifice and mass flow rate to calculate the initial drop’s size, velocity, and position.

The droplets must be randomly distributed to simulate an atomizer, both spatially through the scattering angle and release time. For other types of injections in ANSYS FLUENT (Non-Atomizer), all droplets are released in fixed paths at the beginning of the time step. Atomizer models use random path selection and staggering to achieve a random distribution.

• Half-cone angle

Determined by jet atomization. This angle can be seen in the following figure:

It is a function of the injector geometry, injection pressure, and environmental conditions shown in the figure below: