Re: Models For Flowability
Intuitively,
1. Round particles flow more freely than non-round and cubical shapes flow more freely than slabby or splinter shaped particles
2. Particles of a consistent size will flow more freely than highly consolidated particles such as the case with the mix of fine and coarse ( ie more surface area in contact and surface asperity)
3. The coordination number should be minimized for free flowing action
4. The above assumes the smallest sizes and percentage do not introduce Van der Wahl and Einstein force interactions.
5. What about moisture?
Lawrence Nordell
Conveyor Dynamics, Inc. ■
Re: Models For Flowability
Even for narrow size distributions, particle size itself can also have an effect on flowability. For example, Fowler and Glastonbury reported that for sand flowing from a hopper, there was an optimum size of 65 mesh Tyler that gave maximum flowability and that there was much reduced and erratic flow below this size.
They reported a limiting size for all the materials they tested, below which flowability decreased. This point effectively marks the transition from granular to powder flow.
Fowler R T and Glastonbury J R, The flow of granular solids through orifices, Chem Eng Sci, 1959, Vol 10, pp 150-156 ■
Re: Models For Flowability
Thank you for the answers.
You confirm that theoretical models do not exit, or they are not at our knowledge.
I agree with the consideration of
Lawrence, while it is interesting the indication of Peter about Fowler R T and Glastonbury J R
Also in my experience the parameters that increase flowability are:
- size ( larger size increases flowability);
- shape (higher roundness increases flowability);
- roughness;
- moinsture (lower moinsture increases flowability);
- electrical or magnetic charges on the particle surface.
About size distribution, in the case of continuous distribution, the behaviour is more complex and it is not so easy have always gold rulas. I have studied the influence of size distribution on flowability in the case of granulated for tile ceramic and an easy trend it is not visible.
However I want increase my knowledge about this topic so any suggestion or collaboration are the welcome!
Prof. Marcello Romagnoli
University of Modena and Reggio Emilia - Italy ■
Flowability
A number of publications by Jerry Johanson and John Carson highlight the influence of void pressure and permeability on the flow rate of fine powders. Carson and Ploof discuss a tester to measure the relative flowability of powders in the Chicago Conference, Powder and Bulk Solids Proceedings – 1996, pp. 379 -396 With regard to moisture content it is well established that there is optimum liquor content for the worst flow condition. This is generally of the order of 10 to 12% for fine coal. The sensitivity of flow to various interacting factors precludes the creation of a simple predictive model. It may be more promising to consider the threshold at which specific factors become significant to solids flow. Some care is necessary when referring to particle size, as for examples clay particles that are shaped like plates are difficult to compare with more rounded fractions. They’re anisotropic nature introduces a fundamental difference in relation to packing state, with its variable influence on density, porosity, shear strength and flowability for a given condition of stress. ■
Flowability Model
Some months ago I have request informations about models to describe the flowability of powders.
In particular I was interested about mathematical equations that links size distribution with this parameters.
Recently I have applied DOE technique with differents materials and size distribution and I have obtained mathematical models that can determine the flowability of the system in function of size distribution and morphology of particles.
The approch works in a promising way.
Best regards
Marcello Romagnoli
University of Modena and Reggio Emilia - Italy ■
Models for flowability
Some model exit to define the best size distribution to obtain the best packing. Now I do not know if models exit to shape the best size distribution for the best flowability for a powder.
As you know this parameter is strongly influenced by size distribution and particle shape.
Do you know some theory or paper about this topics?
Thank in advance
Marcello Romagnoli
University of Modena and Reggio Emilia - Italy ■