1. Introduction


  1. Theoretical Framework


Granular materials and fine powders are widely used in industrial applications. To control and to optimize processing methods, these materials have to be precisely characterized. The characterization methods are related either to the properties of the grains (granulometry, morphology, chemical composition, …) and to the behaviour of the bulk powder (flowability, density, blend stability, electrostatic properties, …). However, concerning the physical behaviour of bulk powder, most of the techniques used in R&D or quality control laboratories are based on old measurement techniques. During the last decade, we have updated these techniques to meet the present requirements of R&D laboratories and production departments. In particular, the measurement processes have been automatized and rigorous initialization methods have been developed to obtain reproducible and interpretable results. Moreover, the use of image analysis techniques improves the measurements precision.


A range of measurement methods has been developed to cover all the needs of industries processing powders and granular materials. However, in this application note, we will be focused on the GranuFlow instrument.



  1. GranuFlow


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).

与古老的霍尔流量计(ASTM B213, ISO4490) 或者与药典(USP1174)中描述的“通过孔口的流动”方法相比,GranuFlow是一个先进的流速计。

GranuFlow is a straightforward powder flowability measurement device composed of a silo with different apertures associated with a dedicated electronic balance to measure the flowrate. This flowrate 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 flowrate 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 (Cb, related to the powder flowability) and the minimum aperture size to obtain a flow (Dmin) (for theoretical background, user can refer to Appendix 1). The whole measurement is performed easily, fastly and precisely.


In this paper, we used a complete set of hole diameters: 4, 6, 8, 10, 12, 14 and 16mm.


The main purpose of this application note is to provide information regarding lactose analysis for the Pharmaceutical field.



  1. Lactose analysis


  1. Material


The powders used in this application are provided by Meggle Pharma. All these samples are made of lactose. They are called by the manufacturer Tablettose 70, Tablettose 80, Flowlac 90 and Flowlac 100. According to supplier’s data, the physico-chemical properties of these powders are described by the following table:

本应用中使用的粉末由Meggle Pharma提供。所有这些样品都是乳糖。他们被制造商称为Tablettose 70, Tablettose 80, Flowlac 90和Flowlac 100。根据供应商的数据,这些粉末的理化性能描述如下表:

Table 1: Lactose physico-chemical properties






Tablettose 70




Tablettose 80




Flowlac 90




Flowlac 100





SEM pictures have been made in order to have an information of the particle size distribution and particles shape:


The first observation concerns the particles shape, indeed, all Flowlac samples have spherical shape, while Tablettose samples have irregular one.


Then, with the help of ImageJ Software, the granulometric analysis of the four samples have been carried out (dpp is the mean primary particle diameter and σ the standard deviation):


Table 2: Lactose granulometric analysis.


  1. GranuFlow analysis


GranuFlow analysis were performed at 26°C and 40.0%RH (w = 8.5gH20/kgDryAir). Mass Flowrate was investigated for different hole size (from 4mm to 16mm). F is the powder flowrate (in g/s) and Cb the Beverloo parameter (in g/mm3). Dmin is the minimum aperture size to obtain a flow:

26°C40.00% RH(w = 8.5gH20/kg干燥空气)进行颗粒流分析。研究了不同孔径(4mm ~ 16mm)下的质量流量。F为粉末流量(单位为g/s) CbBeverloo参数(单位为g/mm3)Dmin是获得流量的小孔径尺寸:

Table 3: Raw data obtained with the GranuFlow instrument for the four lactose samples.


These results are really interesting, indeed by the look of Hausner ratio (cf. Table 1), we can see that the classical tap density test (“Densitap”) is unable to make differentiation between one sample to another (despite the high heterogeneity in terms of samples physico-chemical composition). However, GranuFlow allows to its user to make powder classification with great accuracy (with the help of Cb and Dmin parameters). Although Flowlac 90 and Tablettose70 have the same Cb parameter, Dmin information allows us to affirm that Flowlac90 has the best flowability from all samples and its followed by Tablettose70. Flowlac100 comes in third position, while Tablettose80 has the lower flowability. To prove these assumptions the following figure shows the mass flowrate according to hole diameter:

这些结果确实很有趣,从豪斯纳比(cf. Table 1)可以看出,经典的振实密度测试(“Densitap”)无法区分样品之间的差异(尽管样品的物理化学成分具有高度异质性)。然而,GranuFlow满足用户对粉末进行非常的分类(借助CbDmin参数)。虽然Flowlac90Tablettose70具有相同的Cb参数,但Dmin信息可以让我们确认Flowlac90在所有样本中流动性好,其次是Tablettose70Flowlac100排在第三位,而Tablettose80的流动性较差。为了证明这些假设,下图显示了根据孔直径的质量流量:

Figure 5: Mass flowrate versus aperture size for all lactose samples. Lines represent the Beverloo law.


This graph shows the good correlation between experimental data and modeled values (with Beverloo law). This fact is highly important, because with the Beverloo model, user can make data interpolation, and thus predicts the mass flowrate for different hole sizes.




GranuFlow allows to plot the full mass flowrate curve.


GranuFlow gives information about the Beverloo law (i.e powder flowability and minimum diameter for the powder to flow in silo configuration).


GranuFlow allows to classify powders in terms of flowability, even if the classical tap density test is unable to see Hausner ratio difference.




Appendix 1: GranuFlow theoretical background


The mass flowrate 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:


𝐹 = 𝜌 < 𝑣𝑜𝑢𝑡 >

𝜋 𝐷2 4


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. 𝑣𝑜𝑢𝑡 = √2 𝑔 𝛽 𝐷. This relation comes from the idea that the jamming mechanism is due to the formation of a semispherical arch before the orifice. If this arch has a typical size proportional to the aperture, we obtain 𝛽 = 0,5. To be more general, the parameter 𝛽 can be a free parameter.

Finally, the mass flowrate expression becomes:

颗粒自由落体,然后再通过孔,𝑣𝑜𝑢𝑡=√2𝑔𝛽𝐷。这种关系来自于这样一种观点,即堵塞机构是由于在孔口前形成半球形的拱。如果这拱具有典型的孔径大小成正比的,我们获得𝛽= 05。通常来讲,参数𝛽可以自由参数。



𝐹 =

𝜌 √2 𝛽 𝜋 4

 √𝑔 (𝐷 𝐷𝑚𝑖𝑛)2,5 = 𝐶𝑏𝑔 (𝐷 𝐷𝑚𝑖𝑛)2,5