Counter-flow classifiers

Two instruments have been developed for on-line measurement of flowing powders coarser than 100 pm in size [23-26]. In the first instrument a side stream of solid particles from a process line is fed into an air elutriator that separates it into an oversize and undersize stream. The particle flow rate into the elutriator is measured and the cut size for the elutriator adjusted so that the flow of oversize particles out equals 50% of the inlet flow. The elutriator cut size is then equal to the average size of the powder. In the second instrument the flow rate is varied and the signal ratio of the two 

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Classifiers may be divided into two categories, counter-flow equilibrium and cross-flow separation. 

Counter-flow equilibrium classifiers in a gravitational field-elutriators... 

In practice, we encounter three types of heat exchangers, classified according to the flow of one fluid relative to that of the other. In a parallel-flow heat exchanger both fluids flow in the same direction in a counter-flow heat exchanger the fluids flow in opposite directions and in a cross-flow heat exchanger the fluids flow at right angles... 

Cosio et al. (2006) used an electronic tongue system based on flow injection analysis (FIA) with two amperometric detectors, together with the use of an electronic nose, in order to classify olive oil samples on the basis of their geographical origin. Counter-propagation maps were used as classification tools. 

An attractive property of monolithic reactors is their flexibility of application in multiphase reactions. These can be classified according to operation in (semi)batch or continuous mode and as plug-flow or stirred-tank reactor or, according to the contacting mode, as co-, counter-, and crosscurrent. In view of the relatively high flow rates and fast responses in the monolith, transient operations also are among the possibilities. 

On-line detection can be classified as either homogeneous or heterogeneous. In the homogeneous system, the effluent is mixed with a liquid scintillation cocktail before passing through a flow cell that is positioned in a scintillation counter. In the heterogeneous system, the effluent passes through a flow cell packed with a solid scintillator. 

Particle size distribution and classifier selectivity have been determined, using kernel density estimations, to data from (two) classifier flow streams. The procedure has been applied to hydrocyclones using platey particles whose sizes were determined with a Sedigraph 5100 and spheroidal particles whose size distributions were determine using the Malvern Mastersizer and the Coulter Counter [8] Svarovsky s equation was used [9,10]. 

Pacific Scientific Met One 210 Liquid Particle Counter is used to measure particles in clean fluids used in electronic, pharmaceutical and other manufacturing processes. It classifies particles in six size ranges in the 0.4 to 25 pm size range using laser diode based forward light scattering. Maximum count rate is 8000 particles per minute at a fluid flow rate of 100 ml min. ... 

Each technique has advantages and disadvantages. Packed columns are flexible as the packing can be easily modified for optimisation of each recovery process, but they are best suited to small scale operations. Tray columns are used for large scale, low to medium flow rate applications involving non-corrosive materials. Spray systems are used almost entirely for applications where pressure drop is critical such as flue gas treatment. Types of equipment classified as spray columns include cyclone and venturi systems. Bubble column equipment is a low cost, low maintenance option however back mixing can occur which reduces the counter-current flows required for optimum absorption. 

Figure 2 shows a schematic view of a typical simple three-dimensional electrode with its main components porous cathode, current feeder, counter electrode, and membrane or separator. Regarding the constructive aspects, the three-dimensional electrode can be classified as flow-through or flow-by, depending on the relative direction of current and electrolyte flow, as illustrated in Fig. 2. The flow-though configuration is convenient in many cases only for laboratory studies, since electrode thickness is limited by the irregular potential and current distribution which make scale-up difficult. Moreover, the flow-by configuration can also proportionate long residence times and high conversions per electrolyte pass [2].

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