Granular material flowmeter
Semi-automated measurement of powder flow rates through apertures
GranuFlow is a semi-automated powder flow tester able to measure quickly and precisely the mass flow rate of granular material passing through holes of various diameters.
Flow rates can be analysed versus the holes diameters in agreement with Beverloo’s law to determine the minimal diameter of flow for a granular material.
The measurement of mass flow through the various holes does not require any disassembling or cleaning of the instrument.
The configuration of GranuFlow can be adapted to meet a wide range of cell capacities (from milliliters to liters).
Through the simplicity of its design, Granuflow maximizes uptime.
It is made out of modules, each of them can be swapped to avoid extensive diagnostics.
Granuflow combines a stainless steel cell of 500ml capacity and a rotating plate with 7 different holes with diameters from 4 to 34 mm. Holes diameters are manually increased while the measurement takes place.
GranuFlow is an improved laboratory silo compared to the ancient Hall Flow Meter (ASTM B213, ISO4490) and compared to the “Flow Through An Orifice” method described in the Pharmacopea (USP1174).
GranuFlow is a straightforward powder flowability measurement device composed of a silo with different apertures associated with a dedicated electronic balance to measure the flow rate. This flow rate is computed automatically from the slope of the mass temporal evolution measured with the balance. The aperture size is modified quickly and easily with an original rotating system. The measurement and the result analysis are assisted by software. The powder flow rate is measured for a set of aperture sizes to obtain a flow curve.
Finally, the whole flow curve is fitted with the well-known Beverloo theoretical model to obtain a flowability index and the minimum aperture size to obtain a flow. The whole measurement is performed easily, fastly and precisely.
In addition to the acquisition, the software creates a database with the measurements and allows comparing the results.
The mass flow rate F through a circular orifice of diameter D is given by the product of the mean speed of the grains <vout>, the aperture area and the bulk density ρ. One has the general expression,
The Beverloo’s law is based on two hypotheses
The flow is blocked when the orifice diameter is below a threshold Dmin.
The grains experience a free fall before passing through the orifice, i.e.
This relation comes from the idea that the jamming mechanism is due to the formation of a semi-spherical arch before the orifice. If this arch has a typical size proportional to the aperture, we obtain To be more general, the parameter can be a free parameter.
Finally, the mass flow rate expression becomes