Orifices, powder flow into

The measurement of apparent or bulk density of powders is covered in ISO 60 [17] and ISO 61 [18]. The first is a procedure for powders that can be poured from a funnel. A funnel of the form shown in Fig. 1 is mounted vertically with its lower end 20-30 mm above the top of a measuring cylinder of 100 ml capacity and internal diameter 40-50 mm. With the lower orifice closed, 110-120 ml of well-mixed powder is poured into the funnel, and then the powder is allowed to flow into the measuring cylinder, assisted if necessary by being loosened with a rod. When the cylinder is full, a straight bladed knife is drawn across the top of of the cylinder to remove excess, and then the contents are weighed. 

The flow coming out this vessel is sprayed into the expansion vessel (7) by means of a nozzle (6) (Spraydiy SK-SIY80-SKY16, orifice insert diameter 340 pm. Spraying System). The powder formed is collected in a porous bag made of PTFE fibres. Then, CO2 is depressurised (10) and can either be directed to the vent or purified and recycled. 

In case of use of pressure nozzles, the liquid feed is pumped through a small orifice under high pressure, typically 2-300 bars, and the liquid breaks up into droplets by friction with the atmosphere. Nozzles may produce powders with particularly narrow particle size distribution or relatively dense particles. The particle size from a given pressure nozzle is influenced by the feed rate. This is controlled by varying the feed pressure which again influences the flow capacity. Pressure nozzles are therefore less flexible than centrifugal atomizers with regard to ease of operation and control of product characteristics. 

R. Karuhn. R. Davies, B. H. Kaye, M. J. CUnch, Studies on the Coulter Counter, Part One Investigations into the Effect of Orifice Ceometry and Flow Direction on the Measurement of Particle Volume , Powder TechnoL (1975) 157—171 see also references 6 and 7. 

The SAS methods have been used for preparing a variety of particles and fine powders from proteins, pharmaceuticals, pigments, polymers, and even explosives. For example, Debenedetti and coworkers used a continuous-flow, supercritical antisolvent process to prepare fine powders of trypsin, lysozyme, and insulin proteins (58-60). In the preparation a protein solution in dimethyl-sulfoxide (DMSO) was sprayed through a small orifice into supercritical CO2. The particles had diameters ranging from 1 to 5 p,m. The biological activity of the micrometer-sized powders was nearly the same as that of the starting materials. The method has also been used in the processing of pharmaceutically important compounds, such as salmeterol xinafoate (61), sulfathiazole (62), and methylprednisolone and hydrocortisone acetate (41). Kitamura et al. used the... 

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