Mixing pumping rate

The bulk fluid velocity method relates a blending quaUty Chemscale number to a quaUtative description of mixing (Table 3). The value of is equal to one-sixth of the bulk fluid velocity defined by pumping rate divided by cross-sectional area of the tank (4). 

Not only is the type of flow related to the impeller Reynolds number, but also such process performance characteristics as mixing time, impeller pumping rate, impeller power consumption, and heat- and mass-transfer coefficients can be correlated with this dimensionless group. 

The combination of HP and rpm that corresponds to a particular superficial velocity depends on the size of the tank, the size of the impeller, and certain characteristics of the system. Tables 10.3, 10.4, and 10.5 are abbreviated combinations of horsepower and rpm that are suitable at particular pumping rates for the three main categories of mixing. More complete data may be found in the literature cited with the tables. 

Chou and Wollast (1984) used a fluidized bed reactor to study albite weathering. An illustration of their device is shown in Fig. 3.5. The flow needed to maintain the feldspar particles in suspension is provided by the pumping rate Plt while P2 is the rate of addition of fresh solution P2 is also the rate of output of the reacted solution. By changing the rate of renewal of P2 one can vary the residence time of the fluid in the reactor. To maintain a small difference in concentration between the input at the bottom of the fluidized bed and the output at the top of the bed, P2 must be small in comparison to Pi. Chou and Wollast (1984) maintained the renewal rate P2 between 3 and 6% of the mixing rate Pi. 

Solution If power scales as NjDj, then power per unit volume scales as NjDj. To maintain constant power per unit volume, IV/ must decrease upon scaleup. Specifically, Nj- must scale as DJ2 3. When impeller speed is scaled in this manner, the mixing time scales as D2J3and the impeller pumping rate scales as D7/3. To maintain a constant value for t, the throughput Q scales as Dj = S. Results for these and other design and operating variables are shown in Table 4.1. 

In these types of considerations the presentation of measured parameters as a function of both time and cumulative discharge is most useful. In the example of Fig. 4.16 the salty water broke through after pumpage of 3000 m3 in 12 hours. Hence, the routine pumping rate should be significantly lower if only fresh water is wanted, and abstraction may be closer to the break-through value if water quantity is of prime importance and the quality of the mixed waters is acceptable. 

The space velocity in cocurrent upflow, e.g., in the froth reactor, can be controlled within large areas by the pumping rate. There is an upper velocity limit for formation of small bubbles in the glass frit, and the very high back-mixing in the monolith indicates that draining of the monolith down to the inlet area can be a problem at low velocities. The residence-time distribution in the monolith froth reactor has been studied by Patrick et al. [36] and Thulasidas et al. [37]. 

An agitated tank is often used as an example of a first-order lag process. However, mixing in real tanks falls far short of the ideal well-mixed tank. Real tanks have composition responses that are a combination of a first-order lag and deadtime. If the pumping rate of the agitator Fa) is known, the deadtime (T ) of the real tank may be estimated by the following equation Tj = V/ F - - Fa), where V is the volume of the tank and F is the flow through it. 

Grouting mixes, pressures, the pumping rate and the sequence in which the holes are drilled and grouted will be determined in the field and shall be as directed. 

Soil is mixed with an equal amount (by weight) of quartz sand and placed In a glass funnel fitted with a 10- to 16- m glass filter plate. The solution U distributed over the surface of the soil column by means of a perforated pinie at the top of the funnel and glass beads on top of the soil. The initial pumping rate is 25 mL min L The solution in the vessel is mixed by a magnetic stirrer. 

In the volumetric metering approach, the quantities are determined through the pumps used to send them to the mixing lines. Densities of all raw materials must be known under the particular conditions of temperature and formulation, and the accuracy of the pumping rate regularly checked to get the right mass flow rate from the volumetric flow rates. 

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