# REGARDING DPM

Member

WHY MASS FLOW RATE, DIMAETER AND VELOCITY ARE REQUIRED IN DPM INJECTIONS. I MEAN TO SAY THAT IF MASS FLOW RATE AND DIAMETER IS KNOWN THEN VELOCITY CAN BE EAISLY WORKED OUT AND VICE VERSA. SO WHY ALL THREE INPUTS ARE REQUIRED ?

IN PUBLISHED ARTICELS IF MASS FLOW RATE IS CALCULATED ON THE BASIS OF DROPLET VELOCITY THEN IT DOES NOT MATCH. WHY IS IT SO ?

PLEASE CLEARIFY WHAT IS DIFFERENCE AMONG THREE AND WHAT ARE THEIR SIGNIFICANCE ?

• Forum Coordinator

Hello,

Mass Flow Rate is needed to calculate the number of parcels in a standard way for transient tracking. Fluent does not track each individual particle, rather it tracks a representative collection of such particles known as parcels. The mass flow rate is needed to calculate this. For a steady state tracking, each parcel is representative of a fraction of the total continuous mass flow rate. This does not set any velocity to the particles.

Generally speaking , if you set the injection velocity to 0 and just specify the mass flow rates, the drag at the injection port will drive the particles, so eventually they will reach an equilibrium depending on the relaxation time of the particles.

But you can also set the velocity of injection which is independent of the mass flow rate. The droplets will then enter the domain with that velocity. So essentially , if the specified velocity is quite different from the existing flow velocity, considerable drag will ensue.

I hope this helps.

Regards,

Surya

• Morgantown, West VirginiaMember
edited October 8

DPM, as suggested by its acronym, injects a discrete mass flow rate (this is not equivalent to m_dot=rho*vel*Area). In Fluent the discrete mass flow rate of particles

is nothing but m_dot=# particles per sec [#/s] * mass of particle [kg]. The first item is known as the "strength" and is nothing but the reciprocal of your particle injection time step, this way you inject a single particle each time step, or better said, one parcel. Please note, there is no velocity here yet. So you need to further specify your injection velocity, and of course to specify your particle diameter or size distribution, density, etc..

Hope this helps

• Member

THANK YOU SDEB AND ALAINISLAS FOR YOUR RESPOSE

SO IF VELOCITY IS NOT PROVIDED TO PARTICLES AND ONLY MASS FLOW RATE IS GIVEN THEN IT CORRESPONDS TO ONE WAY COUPLING ?

OR HOW TO SET ONE WAY AND TWO WAY COUPLING ?

• Morgantown, West VirginiaMember
edited October 12

Please note that If you specify mass flow rate, you still need to input initial velocity (these are independent inputs). the coupling mechanism refers to the interaction between the phases. It is my understanding that one-way coupling accounts for the interaction of the fluid over the solid phase only and two-way coupling accounts for both interactions, e.g. fluid over solid phase & solid over fluid phase. Depending on you turbulence model, you may find these options in the DPM setup. I suggest you to read the theory guide.

• Member
edited October 13

I HAVE GONE THROUGH THE MANNUAL. AS PER MANNUAL, IN ONE WAY COUPLING FLUID PHASE INFLUENCE PARTICLE PHASE VIA DRAG AND TURBULENCE MOREOVER PARTICLE PHASE HAS NO INFLUENCE ON FLUID PHASE WHEREAS IN TWO WAY COUPLING BOTH PHASE INTERACT WITH EACH OTHER.

MY QUESTION IS IF I DID NOT PROVIDE VELOCITY TO PARTICLE (ONLY MASS FLOW RATE IS GIVEN) THEN THEY WILL FLOW IN THE DOMAIN DUE TO THE DRAG OF CONTINUOUS PHASE. IF NO HEAT TRANSFER IS CONSIDERED THEN IS IT A CASE OF ONE WAY COUPLING ?

• GermanyForum Coordinator

@prashant please do not use capital letters all the time: that is bad style. You need to specify the velocity of the particles entering the domain.

• Member
edited October 21

If I don't specify velocity then particle will flow as per the properties of continuous phase. Does such case corresponds to one way coupling ?

• UKForum Coordinator

If you don't give the particle an initial velocity it is assumed to enter the domain at rest. It'll then be accelerated & carried by the fluid.

Coupling refers to whether the particle influences the flow field (coupled, interaction with continuous phase is ticked in the DPM panel) or not (option is not ticked).

• Member

Thank you