High-turbulent flow

The phase Doppler method utilizes the wavelength of light as the basis of measurement. Hence, performance is not vulnerable to fluctuations in light intensity. The technique has been successfully appHed to dense sprays, highly turbulent flows, and combustion systems. It is capable of making simultaneous measurements of droplet size, velocity, number density, and volume flux. 

So far as possible, components that operate in highly turbulent-flow conditions should be designed with a view to eliminating cavitation and/or impingement erosion attack. 

It was originally proposed (7 ) that, for polymerizations using soap concentrations near the CMC, the highly turbulent flow either prevented the coalescense of monomer drops or increased their number thus reducing the effective soap concentration. 

As will be shown later, the velocity profile for a Newtonian fluid in laminar flow in a circular tube is parabolic. When this is introduced into Eq. (5-38), the result is a = 2. For highly turbulent flow, the profile is much flatter and a 1.06, although for practical applications it is usually assumed that a = 1 for turbulent flow. 

The simplest and most common device for measuring flow rate in a pipe is the orifice meter, illustrated in Fig. 10-7. This is an obstruction meter that consists of a plate with a hole in it that is inserted into the pipe, and the pressure drop across the plate is measured. The major difference between this device and the venturi and nozzle meters is the fact that the fluid stream leaving the orifice hole contracts to an area considerably smaller than that of the orifice hole itself. This is called the vena contracta, and it occurs because the fluid has considerable inward radial momentum as it converges into the orifice hole, which causes it to continue to flow inward for a distance downstream of the orifice before it starts to expand to fill the pipe. If the pipe diameter is D, the orifice diameter is d, and the diameter of the vena contracta is d2, the contraction ratio for the vena contracta is defined as Cc = A2/A0 = (d2/d)2. For highly turbulent flow, Cc 0.6. 

At high OC1- concentrations, high temperature and high turbulent flow conditions, reduction of the CIO- becomes important. 

For orientation purposes, the pressure drop in steel pipes may be found by the rapid method of Table 6.3, which is applicable to highly turbulent flow for which the friction factor is given by von... 

TABLE 6.3. Approximate Computation of Pressure Drop of Liquids and Gases in Highly Turbulent Flow in Steel Pipes ... 

Energy demand High (turbulent flow) Low-moderate (laminar flow) Low... 

Plug Flow Reactor. A PFR is a continuous flow reactor. It is an ideal tubular type reactor. The assumption we make is that the reaction mixture stream has the same velocity across the reactor cross-sectional area. In other words, the velocity profile across the reactor is a flat one. In a PFR there is no axial mixing along the reactor. The condition of plug flow is met in highly turbulent flows, as is usually the case in chemical reactors. 

To enhance mass transfer to and from the wall surface, the tube is packed with inert pellets. Thus, plug-flow in the axial direction is assumed and only radial dispersion is considered, which are valid not only for highly turbulent flow but even for relatively low Reynolds number flow compared to the empty tube. 

The value of depends both on the fraction of the gas flow that bypasses the structure in the gap between the structure and the tube wall and on the flow regime therein. The larger the ratio of the gap to the hydraulic diameter of the channels of the structure, the higher the bypass stream velocity and the less effective the interaction with the well-mixed, highly turbulent flow in the structure. This in turn leads to substantially reduced heat transfer. 

The fluid particle fragmentation phenomena in a highly turbulent flow are related to the fact that the velocity in a turbulent stream varies from one point to another (i.e., validated by two-point measurements [99]). Therefore, different dynamic normal stresses will be exerted at different points on the surface of the fluid particle. Under certain conditions, this will inevitably lead to deformation and breakage of the fluid particle. 

For highly turbulent flow (i.e., constant Kfg), the required pump head is a quadratic function of the flow rate Q. This relation, which is superimposed on the pump characteristic curves (see line SI in Figure 5.9), is the operating line for the system. The actual pump head and the resulting flow rate are determined by the intersection of the operating line and the pump impeller characteristic curve. For the specified flow rate, the best (least cost) pump/impeller/motor combination that will provide this flow rate should be selected. 

What models should be used either for scaleup or to correlate pilot plant data Section 9.1 gives the preferred models for nonisothermal reactions in packed beds. These models have a reasonable experimental basis even though they use empirical parameters D, hr, and Kr to account for the packing and the complexity of the flow field. For laminar flow in open tubes, use the methods in Chapter 8. For highly turbulent flows in open tubes (with reasonably large L/dt ratios) use the axial dispersion model in both the isothermal and nonisothermal cases. The assumption D = E will usually be safe, but do calculate how a PFR would perform. If there is a substantial difference between the PFR model and the axial dispersion model, understand the reason. For transitional flows, it is usually conservative to use the methods of Chapter 8 to calculate yields and selectivities but to assume turbulence for pressure drop calculations. 

The same knowledge of velocity distribution is needed to calculate the value of V by Eq. (4.4). As shown in Chap. 5, a = 2.0 for laminar flow and is about 1.05 for highly turbulent flow. 

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