Hydraulic design

For transport around a process plant, gravity flow, rather than pumping of fluids, is an attractive option. There is no pump to fail. There are some very simple options for control, for example by regulated overflow over an adjustable weir - an attractive control option in the case of very abrasive slurries. 

We have to repeat the refrain that this text does not set out to be a comprehensive guide to specialist subjects, in this case open-channel (or part-filled closed-channel) flow, but the following notes may assist the generalist to avoid some of the worst disasters, in particular, inadequate elevation. Especially in the case of slurry systems, any calculation methods and designs should be backed and supplemented by observation of whatever industry practice is available for the slurry under consideration. 

For standard flow calculations in open channels or partially filled pipes, we need to define an equivalent to pipe diameter for the case of a full pipe. There is approximate equivalence of flow conditions if the ratio of wetted perimeter to fluid cross-sectional area is the same, as flow is only opposed by shear at the enclosing wall. The hydraulic radius R is defined as 

Turbulent flow in open channels (or part-filled pipes) behaves approximately as flow in full, circular pipe flow of the same hydraulic radius. On this basis we can rearrange the Farming friction formula (see p. 157) into the format of the Chezy formula 

For example, consider the case of a launder 1.0 m wide, ruiming 0.5 m deep, with a water-borne slurry whose velocity V is 2.5 m/s. The equivalent full-flow pipe diameter r/e is given by 

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N. E. Todreas and M. S. Ka2imi, Nuclear Systems I Thermal Hydraulic Fundamentals, 1989, II Elements of Thermal Hydraulic Design, 1990, Hemisphere Publishing Corp., New York. 

Rukovena, F. and T. D. Koshy, Packed Distillation Tower Hydraulic Design Method and Mechanical Considerations, Ind. and Eng. Chem. Res., Vol. 32, No. 10 0993) p. 2400 (Used by permission. The American Chemical Society. All rights reserved.)... 

The gas compression in practically all commercial machines is polytropic. That is, it is not adiabatic or isothermal, but some form peculiar to the gas properties and the hydraulic design of the compressor. Actual machines may be rated on adiabatic performance and then related to polytropic conditions by the polytropic efficiency. Other performance rating procedures handle the calculations as polytropic. For reference, both methods are presented. 

HydrauUc Design. The numbers 1 through 9 in the third character of the fixed cutter classification code refer to the hydraulic design of the bit (Figure 4-160). 

Figure 4-160. Hydraulic design code for fixed-cutter bits [54]. (Courtesy SPE.)...

The hydraulic design is described by two components the type of fluid outlet and the flow distribution. A 3 x 3 matrix of orifice types and flow distributions defines 9 numeric hydraulic design codes. The orifice type varies from changeable jets to fixed ports to open throat from left to right in the matrix. The flow distribution varies from bladed to ribbed to open face from top to bottom. There is usually a close correlation between the flow distribution and the cutter arrangement. 

A special case is defined the numbers 6 and 9 describe the crowfoot/water course design of most natural diamond and many TSP bits. Such designs are further described as having either radial flow, crossflow (feeder/collector), or other hydraulics. Thus, the letters R (radial flow), X (crossflow), or O (other) are used as the hydraulic design code for such bits. 

Cutter/Body Type Bit Profile Hydraulic Design Cutter Size/Density... 

Figure 4-164 shows a steel body core bit with a long-taper, stepped profile fitted with impregnated natural diamond blocks as the primary cutting elements. The bit has no inner cone. Since there is no specific code for the natural diamond/steel body combination, the letter O (other) is used as the cutter type/ body material code. The profile code 3 is used to describe the long outer taper with little or no inner cone depth. The hydraulic design code 5 indicates a fixed... 

It is important to understand whether there will be two-liquid phases present in the column. If two-liquid phases form in a large part of the column, it can make the column difficult to operate. The formation of two-liquid phases also affects the hydraulic design and mass transfer in the distillation (and hence stage efficiency). If it is possible to avoid the formation of two-liquid phases inside the column, then such behavior should be avoided. Unfortunately, there will be many instances when two-liquid phases on some plates cannot be avoided. The formation of two-liquid phases can also be sensitive to changes in the reflux ratio. 

Enhancement of CHF subcooled water flow boiling was sought to improve the thermal hydraulic design of thermonuclear fusion reactor components. Experimental study was carried out by Celata et al. (1994b), who used two SS-304 test sections of inside diameters 0.6 and 0.8 cm (0.24 and 0.31 in.). Compared with smooth channels, an increase of the CHF up to 50% was reported. Weisman et al. (1994) suggested a phenomenological model for CHF in tubes containing twisted tapes. 

Akoski, J., R. D. Watson, P. L. Goranson, A. Hassanian, and J. Salmanson, 1991, Thermal Hydraulic Design Issues and Analysis for ITER Diverters, Fusion Technol. 79.-1729—1735. (4)... 

A hydraulically designed system is preferred over standardized approach for optimization of the firewater flows, water storage requirements and piping materials. In any case, the main header should not be less than 203 mm (8 in.) in diameter. Piping routed to hydrants, monitors, hose reels and other protective systems should be at least 152 mm (6 in.) in diameter. 

Pumps shall be capable of at least a 5 percent head increase at rated conditions by replacement of the impeller(s) with one(s) of larger diameter or different hydraulic design. 

A deluge sprinkler system is a sprinkler system designed to NFPA 13 with open sprinkler heads. A water spray system is hydraulically designed with open spray heads to protect a specific hazard. Water spray systems are discussed in Section 7.4.8. 

The second-stage (ammonia removal) effluent contained unacceptable levels of F and P and had to be subjected to third-stage lime treatment. This raises the pH from 8.5 to 11.4 and produces an effluent with concentrations of F and P equal to 25 and 2 mg/L, respectively. The hydraulic design parameters were a 15 min reaction time and a 265 gpd/ft (10.8 m /m /day) clarifier overflow rate. The resulting precipitated solids underflow concentration was 0.6% by wt. In all three stages, an anionic polymer was used to aid coagulation, solids settling, and effluent clarification. 

It is quite clear, then, that a very high viscosity index liquid is desirable from the hydraulic designer s point of view, the higher the better. 

In a two-part series. Zeme discusses the importance of good separator hydraulics. A poor hydraulic design can make a good separation scheme ineffective. Zemel provides the methods and procedures to run a tracer test to identify short-circuiting, stagnant-flow regions, and shear forces. Analysis of the residence-time distribution curve that results is presented. Actual tests run on separators indicate that the most successful separator was the sequential dispersed-gas flotation cell, which closely followed the tanks-in-serie< model. This is contrasted with the poor performance of a conventional 2, 006-hbl [3 0-ms] wash tank The tracer responses of a pressurized flotation cell, a 15j000-bbl [2400 mJj wash tank, and a horizontal free-water knockout with and without baffles are also discussed. 

HYDRAULIC characteristics are only die aspect of the design of a separator, but poor hydraulic design can pake a good separation scheme operate poorly. 

Baffle pitch, or distance between baffles, normally is 0.2-1.0 times the inside diameter of the shell. Both the heat transfer coefficient and the pressure drop depend on the baffle pitch, so that its selection is part of the optimization of the heat exchanger. The window of segmental baffles commonly is about 25%, but it also is a parameter in the thermal-hydraulic design of the equipment. 

Specifying the need for a tray-type column, the type of tray must be determined. Sieve trays are considered most appropriate for this application. They offer a simple and inexpensive construction with low pressure drop (if the hydraulic design is adequate). Bubble cap and valve-type trays offer advantages in controlling liquid droplet entrainment, but pose significant difficulties for installation of cooling coils. 

This efficiency term (C) is potentially very comprehensive as it accounts for the key factors in plate hydraulic design, e.g. hole diameter, liquid depth, vapour velocity and open area. 

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