Hydraulic head

The constant K, which maintains the equaUty, has been termed the hydraulic conductivity, permeabiUty, or simply conductivity. The permeabiUty is generally accepted to be a constant for a saturated soil, except for very small gradients (2—4). Here represents the hydraulic head at location whereas A/is the hydraulic length between points 1 and 2. is an area perpendicular to the discharge vector. In differential form... 

Judging from the hydraulic heads, the vertical flow across the semipermeable interface 1 is in a downward direction, whereas across the semipermeable interface 2 it is in an upward direction. Therefore, unit 2 is being fed by fluid from the phraetic aquifer above it and the confined aquifer below. 

Residue Disposal. The major environmental problem in the Bayer process is disposal of bauxite residue which is effected by marine disposal, lagooning, use of underdrain lakes, or semidry disposal. Marine disposal in oceans or rivers, diluting the alkaline residue by large quantities of water, is environmentally unacceptable. Lagooning behind retaining dikes built around clay-sealed ground is commonly used, but there have been isolated leaks into aquifers. This has motivated installation of underdrains between the residue and clay-sealed, plastic-lined, lake bottom. This design removes the hydraulic head from the lake bottom and improves consoHdation of the residue. 

Use a close coupled ell for drawoff from gravity separators to eliminate backup of hydraulic head. 

Go to a standard handbook like Perry s Chemical Engineer s Handbook and obtain several hydraulic conductivities (say for sand, crushed stone, gravel, diatomaceous earth, other). Assume a constant head of fluid over a bed of each material, and apply Darcy s law to calculate flowrates and compare the results. Try several hydraulic head calculations and plot the results. Which of the materials studied shows the highest hydraulic resistance ... 

The hydraulic effects for the submerged portions of the vessel or system can be ignored w hen the total static head on the submerged portion is not greater than 0.53 times atmospheric pressure plus the hydraulic head [22], i.e., P ... 

It is quite desirable to place water into an open-hole section prior to running a casing or liner siring and cementing. The water will provide a hydraulic head to hold back any formation gas in the open-hole section that could cause a fire hazard at the rig floor. 

Whatever automatic start-up method is adopted, steam will only flow into the mains and discharge air from the air vents at a pressure at least a little above atmospheric. It then reaches the pipe and condenses on the cold metal, and at first the condensate temperature will be well below 100°C (212°F). This means that the steam traps will have a greater capacity than their normal rating when handling saturated condensate. If the traps are fitted to a collecting leg, at about 700 mm below the main, then filling of the collecting leg will provide a hydraulic head of about 0.07 bar or 1 Ib/in in addition to the line pressure. 

Condensate from the low-pressure coil together with that from the flash vessel will then drain to a collecting tank, or direct to a condensate pump, for return to the boiler plant. If the pressure of the flash steam is left to find its own level it will often be sub-atmospheric. As the condensate must then drain by gravity through the steam traps these also must be sufficiently below the condensate drain points to provide an appropriate hydraulic head, and a vacuum breaker fitted above the coil. The alternatives are to allow the condensate to drain directly to a condensate pump, or to supply additional low-pressure steam through a pressure-reducing valve, to maintain a positive pressure in the coil and flash vessel. 

Understanding the basic hydraulic mechanisms for synthetic liners and clay liners is very important in appreciating the advantages of a composite liner. Clay liners are controlled by Darcy s law (Q = kiA). In clay liners, the factors that most influence liner performance are hydraulic head and soil permeability. Clay liners have a higher hydraulic conductivity and thickness than do synthetic liners. Additionally, leachate leaking through a clay liner will undergo chemical reactions that reduce the concentration of contaminants in the leachate. 

Leakage through a synthetic liner is controlled by Fick s first law, which applies to the process of liquid diffusion through the liner membrane. The diffusion process is similar to flow governed by Darcy s law except that it is driven by concentration gradients and not by hydraulic head. Diffusion rates in membranes are very low in comparison with hydraulic flow rates even in clays. In synthetic liners, therefore, the factor that most influences liner performance is penetrations. Synthetic liners may have imperfect seams or pinholes, which can greatly increase the amount of leachate that leaks out of the landfill. 

Let ccij and friction head loss per unit length of size j pipe in branch i. Then the actual hydraulic head at any node k must not be less than a specified minimum head h(k), that is... 

Packed fractional distillation columns run in the batch mode are often used for low-pressure drop vacuum separation. With a trayed column, the liquid holdup on the trays contributes directly to the hydraulic head required to pass through the column, and with twenty theoretical stages that static pressure drop is very high, e.g., as much as 100-200 mm Hg. 

Aw is the width of the stream tube, and Ah is the change in hydraulic head over the incremental flow path, AL. 

Darcy s law can be written in an alternative form in terms of hydraulic head h (cm), the height to which water would rise above sea level if free to flow into a well, and hydraulic conductivity Kx, Ky (cm s-1) of the sediment. In this case, groundwater flows from high head to low, at a discharge given by,... 

Changes in hydraulic head reflect variation in the hydraulic potential, according to d = pg dh, and hydraulic conductivity is proportional to permeability,... 

The water table in the ARS is elevated compared with the aquifer hydraulic heads. This would promote the transport of As from the ARS into the aquifer by advection. Given the higher concentration of As in the ARS compared to the aquifer, As transport could also occur by diffusion through the clayey soil. 

Surface and groundwater flow within the Canada Creek watershed is SE from the high level of the mill and ARS to the low lying NATA then north through the wetlands (Fig 3). This path is based on local topography, core log data, and hydraulic head values for the confined aquifer. Hydraulic heads show groundwater in the Canada Creek... 

A- CONTACTOR REACTOR SHELL B- TUBE BUNDLE ASSEMBLY C- HYDRAULIC HEAD D- MOTOR E- IMPELLER F- CIRCULATION TUBE... 

Two hydraulic head gradients determined from wells or piezometers are shown in Figure 3.15. Piezometers are basically pipes or wells put in the ground which are... 

FIGURE 3.24 Groundwater conditions near the ground surface. Saturated and saturated zones (a), profile of moisture content vs. depth (b), pressure head and hydraulic head relationships insets = water retention under pressure heads less than (top) and greater than (bottom) atmospheric (c), profile of pressure head vs. depth (d), and profile of hydraulic head vs. depth (e). (After Freeze and Cherry, 1979.)... 

The permeability of concrete is a guide to its durability (Section 1.5.2) but it can also be relevant to the design of structures which are intended to withstand a hydraulic head of water or other liquid. Extreme porosity is usually... 

Results of the test showed that trichloroethylene (TCE) and perchloroethylene (PCE) concentrations in the water declined by more than 90% to below 2 parts per billion (ppb). All of the wells showed significant decreases in contaminants in less than 1 month. In four of the five piezometers (specialized monitoring wells whose primary purpose is the measurement of hydraulic head), TCE and PCE concentrations declined from as high as 10,000 parts per million... 

GeoSiphon has several potential limitations and will not be applicable at all sites. Groundwater at a site must demonstrate a difference in hydraulic head in order for the system to operate. In addition, fluctuations in the water table may inhibit the system s performance. The technology may not be applicable at sites with deep contamination and nonsurficial aquifers. When iron is used as the reactive media, performance may also be limited by factors such as pH and high nitrate levels in groundwater. 

The physics of thermal conduction and storage are, in fact, directly analogous to those of groundwater flow. Thermal conductivity (kT) and hydraulic conductivity (k) are analogous, as are heat capacity and storage coefficient and temperature (7) and hydraulic head (h). Indeed, heat flow (H) is estimated by an analogous equation to Darcy s Law ... 

---