Through design purposes

Cyclone Pressure Drop. Typical cyclone pressure drops range from 250 to 2000 Pa. Most data are reported for clean air flowing through the cyclone and these data are conservative for design purposes. Many investigators have unsuccessfully attempted to relate pressure drops to inlet and oudet dimension ratios. Manufacturers caUbration curves or experimental measurements on cyclones of similar dimension should be used where possible. If a rehable experimental measurement is available, however, the pressure drop at other conditions can be estimated by first evaluating the constant i in equation 17. 

Exit air usually is maintained far from saturated with moisture and at a high temperature in order to prevent recondensation of moisture in parallel current operation, with a consequent lowering of thermal efficiency. With steam heating of air the overall efficiency is about 40%. Direct fired dryers may have efficiencies of 80-85% with inlet temperatures of 500-550°C and outlet of 65-70°C. Steam consumption of spray dryers may be 1.2-1.81bsteam/lb evaporated, but the small unit of Table 9.19(b) is naturally less efficient. A 10% heat loss through the walls of the dryer often is taken for design purposes. Pressure drop in a dryer is 15-50 in. of water, depending on duct sizes and the kind of separation equipment used. 

We have introduced many practical software based numerical procedures to solve physico-chemical models for simulation and design purposes. Therefore, we hope that our readers now feel comfortable and ready to handle more complex industrial problems from the modeling stage through the numerical solution and model validation stages on her/his own. 

Equations (24) through (26) do not include any effects due to liquid viscosity or liquid flow rate. Consequently, the equations are most useful when experimental data for the packing are available at known L/G ratios and liquid viscosities. For design purposes, liquid-viscosity effects can be assumed negligible if the viscosity is under 2 centipoises. Because of errors that may be introduced by neglecting the influence of the liquid rate, use of Eq. (25) or (26)... 

The use of Fig. 13.36 requires a value of the packing factor i, which may be taken from Table 13.13 or 13.15. The abscissa term is the same as that for tray columns. It is sensible to use a value of about 80% of the maximum curve (equivalent to 1.5 in. H20/ft, or 125 mm Fl20/m) for design purposes. The corresponding ordinate term then allows deduction of the value of Cs, defined as Cs = Us[pg/(pL - Pg)]°, where Us is the allowable superficial velocity of vapor or gas through the column. Also, v = liquid kinematic viscosity = centistokes (centipoises/density, gm/ml). Example 13.16 shows how Fig. 13.36 is used. 

The reason that kbOt, is higher than calculated from Eq. (6-12) may be explained qualitatively by three effects (1) splitting, coalescence, and rupture of bubbles (T18, T20) (2) direct contact of gas and particles in the transition zone from dense phase to dilute phase (F18) (3) the influence of the particle capacitance effect (M21, M22) as a result of a small steady interchange of particles between the bubble void and the emulsion. An example of this is the case where particles are raining through the bubble (D18, R8, Wl) and (4) asphericity of the bubbles (D18). If the particle capacitance effect (discussed in the next section) is responsible for high experimental values for kb b. such values should not be applied to the usual catalytic reactions, where m is on the order of unity and particle capacitance has little effect on kbOt,. For design purposes it is normally better to use experimental mass-transfer coefficients obtained by a properly sized fluid bed for the reaction system of interest. 

Overall, food quality may be considered in terms of taste, textme, mouthfeel and other sensorial attributes or in terms of macro- and micronutrient content. For any concept of visual quality, colour acts as a very useful and intuitive indicator. Colour can be assessed at various times during the lifetime of a food product - from raw materials, e.g., the quality of flour for baking, through processing, e.g., monitoring roasting of coffee beans, and at the end point where a finished product needs to be confirmed as suitable for its designed purpose,... 

---