Potential head

H = total potential head during flotv, ft P = power, ft-lb/sec W = impeller blade widtii, ft p = viscosity, Ib/ft-sec p = density, pounds/cu ft Ns = revolutions/sec... 

H = Total potential head during flow, ft of liquid Hp = Motor, horsepower... 

Orifice meters, Venturi meters and flow nozzles measure volumetric flow rate Q or mean velocity u. In contrast the Pitot tube shown in a horizontal pipe in Figure 8.7 measures a point velocity v. Thus Pitot tubes can be used to obtain velocity profiles in either open or closed conduits. At point 2 in Figure 8.7 a small amount of fluid is brought to a standstill. Thus the combined head at point 2 is the pressure head P/( pg) plus the velocity head v2/(2g) if the potential head z at the centre of the horizontal pipe is arbitrarily taken to be zero. Since at point 3 fluid is not brought to a standstill, the head at point 3 is the pressure head only if points 2 and 3 are sufficiently close for them to be considered to have the same potential head... 

Bernoulli s law slates that in steady flow, the lotal head is a constant at any poinl and equal lo the sum of the pressure head, p/u>. the velocity head, ir/2g. and the potential head C. Since there is actually a loss of head between any two points due to friction, die difference between the total heads ai any two points must equal the friction head when the flow is steady. 

From Eq. (63), the mechanical energy equation in head form, it is seen that, in the absence of a pump head, losses in a pipe system consist of pressure head changes, potential head changes, and velocity head changes. When fittings or changes in pipe geometry are encountered, additional losses occur. 

The simulation will be done in a zone of 200 m between an infiltration well and a pumping well. This zone shows a kf value of 5TO"5 m/s along the fracture and 10 8 m/s within the pores (those kf values are only for orientation and are not needed directly for the modeling). The flow velocity is 10 m/day due to the potential head. 

Mooney EE, Dodd LG, Otrry TD, et al. Middle ear carcinoid an indolent tumor with metastatic potential. Head Neck. 1999 21(l) 72-77. 

The spatial distribution of the potential head was calculated based on geostatistics from thematic point information and measurements from observation wells (Hutchinson, 1989). The potential head was used to define the groundwater divides, the P and 2" order boundary conditions and the initial conditions of the groimdwater modelling. 

The spatial distribution of the hydraulic head was calculated based on measurements and a digitized map of the groimdwater contour lines. The hydraulic head of the groundwater was used to define the P and the potential head of the ditch as boundary condition 3 order. For calibration the exfiltration rate (Q) is determined by run off measurements ... 

Pump manufacturers have established guidelines to ensure each pump they supply is not exposed to conditions that result in cavitation. The design standard is called NPSHR or net positive suction head required. The NPSHR takes into account any potential head losses that might occur between the pump s suction nozzle and impeller thereby ensuring the liquid does not drop below its vapour pressure (bubble point). The NPSH is a measure of the proximity of a liquid to its vapour pressure, and must exceed the pump manufacturer s pump NPSHR. There are two process variables that can be adjusted, in case the available NPSH is less than the NPSHR raise the static head and lower friction losses. Conversely, the NPSHR can be reduced by using a larger, slower speed pump, a double suction impeller, a larger impeller inlet area, an oversized pump and a secondary impeller placed ahead of the primary impeller. 

Martin s (1972) was the first investigation that attempted to understand the process of gas induction. This was based on Equation 9.1. For a 1-1 type impeller, the potential head of the gas in the hollow pipe can be neglected in comparison to the static liquid head on the orifice. Equation 9.1 further implies that the viscous dissipation in gas flow through the pipe is negligible (viscosity, /flow past a cylindrical body (most first-generation impellers were cylindrical in shape), Martin (1972) derived an equation for the pressure on the surface of the cylinder at a point located at an angle 0 from the axis of the cylinder ... 

Since the three terms in the left-hand side of Eqs. (5) and (6) have the dimensions of height, they are respectively called the velocity head, the pressure head, and the potential head. In other words, the first term and the second term correspond to the heights of fluid required to maintain the flow velocity u at the static pressure, p. 

The basic law concerned with flow is that enunciated by Darcy (1856), which states that the rate of flow, v, per unit area is proportional to the gradient of the potential head, /, measured in the direction of flow, k being the coefficient of permeability ... 

Employees must wear head protection whenever there are head hazards or potential head hazards that are, or could be, present. 

This is the mechanical-energy loss due to skin friction for the pipe in N m/kg of fluid and is part of the F term for frictional losses in the mechanical-energy-balance equation (2.7-28). This term (Pi—Pz)/ for skin friction loss is different from the (p, — Pz) term, owing to velocity head or potential head changes in Eq. (2.7-28). That part of F which arises from friction within the channel itself by laminar or turbulent flow is discussed in Sections 2.10B and in 2. IOC. The part of friction loss due to fittings (valves, elbows, etc.), bends, and the like, which sometimes constitute a large part of the friction, is discussed in Section 2.10F. Note that if Eq. (2.7-28) is applied to steady flow in a straight, horizontal tube, we obtain (pi — Pz)/p = F. 

The most common instrument used for viscosity measurements in low-viscosity liquids is the capillary viscometer. In this instrument, a liquid is made to flow under its own potential head through a narrow capillary with a weU-defined length and cross section. The volumetric flow rate Qota simple Newtonian liquid undergoing laminar flow in a capillary of diameter d and length / is given by Poiseuille s equation ... 

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