Secondary circulation

Erosion in the nozzle or orifices is often associated with weepage of solids. This can be avoided by carefully designing a grid with the proper pressure drop criteria as presented in Sec. 3.2. Poorly designed bubble caps tend to have erosion problems due to the secondary circulation of solids. Therefore, bubble caps should be designed to minimize secondary circulation of solids. 

For each of the three particles sizes studied, the deposition efficiency in the trachea was much greater than predicted if uniform deposition is assumed. In each data set the ratio at the lower flow rate exceeded that at a higher flow. If the increase results from turbulence introduced by the larynx it might be expected to be more effective at the higher flow rate. The discrepency may result from the jet formed downstream of the larynx. The center line velocity substantially exceeds the mean velocity of the air stream and secondary circulation patterns are set up near the wall which can act as dead zones (Ultman, 1 985) ... 

Secondary Circulation Loop Temperature Control Systems... 

This is the simplest system for temperature control of a reactor only the jacket temperature is controlled and maintained constant, leaving the reaction medium following its temperature course as a result of the heat balance between the heat flow across the wall and the heat release rate due to the reaction (Figure 9.9). This simplicity has a price in terms of reaction control, as analysed in Sections 6.7 and 7.6. Isoperibolic temperature control can be achieved with a single heat carrier circuit, as well as with the more sophisticated secondary circulation loop. 

Figure 9.8 Heating cooling system with secondary circulation loop.

Figure 9.9 Isoperibolic temperature control with a secondary circulation loop.

Curved Pipes and Coils For flow through curved pipe or coil, a secondary circulation perpendicular to the main flow called the Dean effect occurs. This circulation increases the friction relative to straight pipe flow and stabilizes laminar flow, delaying the transition Reynolds number to about... 

The results are due to the difference in differential pressure behaviour at IHX. Figure 5 shows the influence of the isolation valves actuation sequence on the differential pressure behaviour at IHX, which is defined as a subtraction from secondary to primary coolant pressure. Though the profile of differential pressure behaviour at IHX is almost the same in all of the cases, occurrence time of the peaks and their intensity are different in each case because of the momentum change difference which are induced by the difference of isolation valves actuation time and occurrence time of secondary circulator trip. 

Kaloni used Oldroyd model, Schtimmer a fourth order fluid model, while Wissler a nonhnear Maxwell model Employing the perturbation method, the authors observed that the inclusion of second-order perturbation terms (which bring in the non-Newtonian effects) predicted velocity profiles with superimposed secondary circulation patterns. 

This ensures that most of the jet momentum is spread by entrainment and mixing the jet and bulk liquids, and that a reasonable secondary circulation is set up within the bulk liquid—the object of any design must be to produce liquid motion throughout the whole tank. 

Pressure drop in helical coils is dependent on whether the flow is laminar or turbulent. Typically flows are laminar at low fluid velocities and turbulent at high fluid velocities. In cuived pipes and coils a secondary circulation takes plac e called the double eddy or Dean Effect. VVliile this circulation increases the friction loss, it also tends to stabilize laminar flow, thus increasing the critical Reynolds number. 

The layout of underground cooling chamber needs to take high-low pressure heat exchanger and secondary circulating pumps into account. Secondary water is neither constant pressure device nor pump power distribution. 

Secondary circulating pumps are designed to be controlled by variable frequency and three pumps... 

Constant pressure water inlet device and filter device are built up at a time in secondary circulating water system. 

Figure 8.13 Secondary circulation in an anchor agitated tank. [Peters and Smith, 1967]...

The main vortex inside the fluid sphere is driven by the tangential stress exerted by the external flow downstream over a large part of the sphere. For high Reynolds numbers, the stress exerted by the circulation in the trailing vortex is sufficient to create a small secondary vortex inside the fluid sphere with a circulation in an opposite direction to that of the main vortex. For example, at Re = 300 and for K = 5,10, and 100 (Figure 5.5), the presence of negative values for the tangential velocity at the rear of the sphere indicates the presence of such a secondary circulation inside the fluid sphere. 

In certain regions, heavy rainfall is closely related to the low-level jet. For example, during the early summer rainy season in subtropical China and Japan, extremely heavy rainfall (at least 100 mm/day) is one of the most disastrous weather phenomena. As in other parts of East Asia, extremely heavy rainfall is also found by meteorologists in Taiwan to be closely associated with a low-level jet. For example, there was an 84% likelihood that a low-level jet of at least 12.5 m/sec would be present at 700 mb (about 3 km) 12 hr before the start of the rainfall event. They concluded that the low-level jet may form to the south of heavy rainfall as part of the secondary circulation driven by convective latent heating. 

The oscillating wind regimes depicted schematically in Fig. 16 (and from observations in Figs. 10 and 11) are accompanied by secondary circulations in the meridional plane, and by temperature anomalies in balance with the adiabatic heating and cooling associated with the secondary circulations. The magnitude of these anomalies can be estimated because, even in the tropics, the zonal-mean zonal wind and temperature are in thermal wind balance. Near the equator, Eq. (13) can be written as follows ... 

A shell and tube type IHX integrated with heat transfer tubes for the decay heat removal system is used Considering their contribution to the simplification of the head access area, sodium immersed EM pumps are employed as both primary and secondary circulating pumps Cold traps are integrated with the primary EM pumps... 

If it is undesirable to circulate the coolant at the regular rate when the tube is deenergized, a secondary circulating pump can be used to move the coolant at a lower rate to purge any air that might enter the system and to prevent stagnation. Typical recommended minimum circulation rates within the coolant Hnes are as follows ... 

Several designs have evolved, many with horizontal axes (i.e. both ends closed) with the outer cylinder rotating and the inner cylinder fixed, which provides best hydrodynamic stability. Some horizontal-axis Couette flocculators are flow-through designs, even with a tapered gap to provide taper flocculation However, horizontal-axis apparatuses suffer from end effects which cause secondary circulation, so only a limited central zone (about one quarter of the length) is in defined laminar flow. 

In the Messo turbulence crystallizer, a secondary circulation loop (see vortex) -driven by the primary circulation loop - is created in the outer suspension section. This secondary circulation loop serves the purpose of sorting out the coarser crystals from the inner draft tube recirculation process, concentrating them in an outer... 

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