Particle diameter unit operation

Example 7.4 A round jet impactor is operated such that the jet Reynolds number is 3000. Using Fig. 7.36, find the particle diameter (unit-density sphere) that will be collected with 50 percent efficiency if the jet diameter is 0.3 cm. 

Cleaners are most efficient on relatively large particles, 80—300 pm in diameter (see Fig. 1). Flat toner ink particles can fragment during processing, therefore it is probably best to locate mechanical cleaners early in the sequence of office paper deinking unit operations (40). 

Cyclone filters are effective at removing larger particles and can operate over a wide range of temperatures, limited primarily by the material of construction. Cyclone filters are often designed as multiple units in series (multi-clones). They can remove >90% of particulates above about 5 microns in diameter at minimal pressure drops of 0.01 atm. Partial removal of material in the 1.5 micron range is also possible, but cyclonic filters become ineffective with sub-micron particles. 

Equations (29) and (30) allow us the calculation of column performance as a function of the particle diameter when the columns >are operated at minimum inlet pressure. We find that the pressure gradient is inversely proportional to the cube of the particle diameter and the number of plates generated per unit time is inversely proportional to the sc uare of the particle diameter. j... 

In the operation of preparative columns, it is necessary to obtain the maximum mass throughput per unit time and, at the same time, achieve the required resolution. Consequently, the column will be operated at the optimum velocity as in the case of analytical columns. Furthermore, the D Arcy equation will still hold and the equation for the optimum particle diameter can be established in exactly the same way as the optimum particle diameter of the analytical column. The equation is fundamentally the same as that given for the optimum particle diameter for a packed analytical column, i.e. (18) In chapter 12, except that (a) and (k ) have different meanings. 

From the view point of the assessment, the quality of an HPLC separation in response to changes in different system variables, such as the stationary phase particle diameter, the column configuration, the flow rate, or mobile phase composition, or alternatively, changes in a solute variable such as the molecular size, net charge, charge anisotropy, or hydrophobic cluster distribution of a protein, can be based on evaluation of the system peak capacity (PC) in the analytical modes of HPLC separations and the system productivity (Peff) parameters in terms of bioactive mass recovered throughput per unit time at a specified purity level and operational cost structure. The system peak capacity PC depends on the relative selectivity and the bandwidth, and can be defined as... 

As far as the dimensions of the chambers are concerned, they are imposed by the hydrodynamics of the drying process as illustrated in Figure 3.12. It is seen that in order to achieve the particle size (around 70 pm) of interest in FCC catalysts, the drying chamber diameter is between 3-4 meters. Such dimensions make the spray drying process difficult to downscale for a detailed study and modeling of this unit operation. 

To approach physical stability problems of suspensions, effectiveness and stability of surfactants as well as salt concentrations must be checked with accelerated aging. In addition, unit operations affecting particle size distribution, surface area, and surfactant effectiveness should be approached, taking into account that different types of distributions, for instance, volume or number weighted, give a different average diameter for an equal sample [43],... 

For the operation of the cold model ambient air was chosen as fluidising gas for the riser, and in order to match the required density ratio the gasifier was fluidized with a gas mixture of 55 45 % helium to air. Sj erical bronze particles with a density of 8900 kg/m and a mean particle diameter of 180 pm were chosen as bed material. The geometric scale factor between the two units was five and the normalised particle size distributions of the bronze particles and the sand used on the plant were comparable. The one scaling parameter it was not found possible to match was the particle shape factor 4). In the cold model the particles were spherical (( p1) w4iereas sand particles are normally considered to be broken solids for which ( 0.63 (6) in option in the CFB however attrition will be likely to increase this to nearer unity. 

The dimensions of a bag in a filter unit are 8 in. in diameter and 15ft long. Calculate the filtering area of the bag. If the filtering unit consists of 40 such bags and is to treat 480,000 ft /h of gas from an open-hearth furnace, calculate the effective filtration velocity in feet per minute and acfin per square foot of filter area. Also calculate the mass of particles collected daily if the inlet loading is 3.1 gr/ft and the unit operates at 99.99-b% collection efficiency. 

Many unit operations of chemical engineering deal with particles for which consideration of the particle diameter—particle characteristic dimension—is a fundamental design parameter. Table 9.2 lists several unit operations and the corresponding design parameter for which the particle diameter is required. 

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