Constant number Parcel method

Lao · August 6, 2014, 12:01

Hi everyone,
I try to understand how the constant-number method works. In fact, I see that Fluent adjusts the number of parcels injected when I fix the number of particle per parcel, in order to satisfy the mass flow rate I set, in the injection point properties.

But I cannot find the equations to link the number of stream, mass flow rate, time step,the number of particle per parcel and finally the number of parcels injected when the calculation runs.

More precisely,

I have dt=0.001s
number of time steps=100
mass flow rate=4.639e-4kg/s (particle of titanium, and diameter=10e-5m)
1 particle per parcel
and I see: ''183 particle parcels injected with mass=4.64e-7''

Please help,

Cheers,

Lao

Clarence91 · August 20, 2014, 19:10

Dear Lao,

could you fix this problem?

Lao · August 25, 2014, 06:19

hi Clarence,

No, I am still searching.

Can you help?

Thanks

Clarence91 · August 25, 2014, 13:13

Not yet. Still working on the same but couldnt fix it.

I dont understand one thing, when the number of particles in each parcel is greater than 10 then it should mean that the particle diameter is smaller than the parcel diameter right? But in my case I am not able to see that.

I think if i can fix the parcel diameter then i can calculate the rest.

Clarence91 · August 25, 2014, 13:14

As far as I know, constant mass/diameter is something like, if you enter some value then fluent will make sure that its not going to exceed that limit.

Lao · August 26, 2014, 05:42

But how do you know the parcel diameter?

Clarence91 · August 27, 2014, 18:32

RESULTS-->GRAPHICS AND ANIMATIONS-->PARTICLE TRACKS-->((color by - particle variables-->parcel diameter))

Lao · August 28, 2014, 06:02

First,you can use constant-diameter or constant-mass to ensure that the parcel diameter does not exceed the size of the smallest cells in the computational mesh.

Assuming that the parcel is a virtual concept, I mean It is a representative particle, so it doesnt have an exact shape. So I think that the concept of ''parcel diameter'' is not really diameter.And for me, if I amn not wrong, the particle diameter is always smaller than the parcel one.

I dont know if you understand my point. ^^

Lao · August 28, 2014, 06:06

In the help documentation, they said:

The concept of parcels is particularly important in the Discrete Element Method, where parcels occupy a finite volume and obstruct other DEM parcels The volume occupied by a parcel is calculated directly from the mass that it represents (so that a realistic density is created when parcels pack together) The equivalent ‘parcel diameter’ is used for calculating parcel-parcel contacts and forces However, for trajectories through fluid, it is still the ‘particle diameter’ that is used.

Clarence91 · August 28, 2014, 18:07

I understand the concept of DEM and parcel too.

I tried with const-diameter and constnt mass also, it dint work.
When I increased the fluid flow time step and keeping PARCEL RELEASE METHOD as STANDARD then i can see the right value for parcel diameter (I mean- parcel diameter to be greater than particle diameter) but thats not the correct way as our time step should be as much as low in order to get accurate results.

Lao · August 29, 2014, 06:08

but the thing is that I dont understand the concept of ''parcel diameter'' because for me, the parcel does not have shape (cylindric or circle,...) It is like a ramdom group of particles.

So I dont see how fluent calculate this parcel diameter.

Clarence91 · August 29, 2014, 12:55

radius of the dem parcel is that of a sphere whose volume is the mass of entire parcel divided by particle density.

August 6, 2014, 12:01	Constant number Parcel method	#1
Lao New Member Join Date: Aug 2014 Posts: 8 Rep Power: 12	Hi everyone, I try to understand how the constant-number method works. In fact, I see that Fluent adjusts the number of parcels injected when I fix the number of particle per parcel, in order to satisfy the mass flow rate I set, in the injection point properties. But I cannot find the equations to link the number of stream, mass flow rate, time step,the number of particle per parcel and finally the number of parcels injected when the calculation runs. More precisely, I have dt=0.001s number of time steps=100 mass flow rate=4.639e-4kg/s (particle of titanium, and diameter=10e-5m) 1 particle per parcel and I see: ''183 particle parcels injected with mass=4.64e-7'' Please help, Cheers, Lao

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August 20, 2014, 19:10		#2
Clarence91 Member MarkClarence Join Date: Jul 2014 Posts: 32 Rep Power: 12	Dear Lao, could you fix this problem?

August 25, 2014, 06:19		#3
Lao New Member Join Date: Aug 2014 Posts: 8 Rep Power: 12	hi Clarence, No, I am still searching. Can you help? Thanks

August 25, 2014, 13:13		#4
Clarence91 Member MarkClarence Join Date: Jul 2014 Posts: 32 Rep Power: 12	Not yet. Still working on the same but couldnt fix it. I dont understand one thing, when the number of particles in each parcel is greater than 10 then it should mean that the particle diameter is smaller than the parcel diameter right? But in my case I am not able to see that. I think if i can fix the parcel diameter then i can calculate the rest.

August 25, 2014, 13:14		#5
Clarence91 Member MarkClarence Join Date: Jul 2014 Posts: 32 Rep Power: 12	As far as I know, constant mass/diameter is something like, if you enter some value then fluent will make sure that its not going to exceed that limit.

August 26, 2014, 05:42		#6
Lao New Member Join Date: Aug 2014 Posts: 8 Rep Power: 12	But how do you know the parcel diameter?

August 27, 2014, 18:32		#7
Clarence91 Member MarkClarence Join Date: Jul 2014 Posts: 32 Rep Power: 12	RESULTS-->GRAPHICS AND ANIMATIONS-->PARTICLE TRACKS-->((color by - particle variables-->parcel diameter))

August 28, 2014, 06:02		#8
Lao New Member Join Date: Aug 2014 Posts: 8 Rep Power: 12	First,you can use constant-diameter or constant-mass to ensure that the parcel diameter does not exceed the size of the smallest cells in the computational mesh. Assuming that the parcel is a virtual concept, I mean It is a representative particle, so it doesnt have an exact shape. So I think that the concept of ''parcel diameter'' is not really diameter.And for me, if I amn not wrong, the particle diameter is always smaller than the parcel one. I dont know if you understand my point. ^^

August 28, 2014, 06:06		#9
Lao New Member Join Date: Aug 2014 Posts: 8 Rep Power: 12	In the help documentation, they said: The concept of parcels is particularly important in the Discrete Element Method, where parcels occupy a finite volume and obstruct other DEM parcels The volume occupied by a parcel is calculated directly from the mass that it represents (so that a realistic density is created when parcels pack together) The equivalent ‘parcel diameter’ is used for calculating parcel-parcel contacts and forces However, for trajectories through fluid, it is still the ‘particle diameter’ that is used.

August 28, 2014, 18:07		#10
Clarence91 Member MarkClarence Join Date: Jul 2014 Posts: 32 Rep Power: 12	I understand the concept of DEM and parcel too. I tried with const-diameter and constnt mass also, it dint work. When I increased the fluid flow time step and keeping PARCEL RELEASE METHOD as STANDARD then i can see the right value for parcel diameter (I mean- parcel diameter to be greater than particle diameter) but thats not the correct way as our time step should be as much as low in order to get accurate results.

August 29, 2014, 06:08		#11
Lao New Member Join Date: Aug 2014 Posts: 8 Rep Power: 12	but the thing is that I dont understand the concept of ''parcel diameter'' because for me, the parcel does not have shape (cylindric or circle,...) It is like a ramdom group of particles. So I dont see how fluent calculate this parcel diameter.

August 29, 2014, 12:55		#12
Clarence91 Member MarkClarence Join Date: Jul 2014 Posts: 32 Rep Power: 12	radius of the dem parcel is that of a sphere whose volume is the mass of entire parcel divided by particle density.