Elevation head

The fluid dehvery in an air-spray system can be pressure or suction fed. In a pressure-fed system, the fluid is brought to the atomizer under positive pressure generated with an external pump, a gas pressure over the coating material in a tank, or an elevation head. In a suction system, the annular flow of air around the fluid tip generates sufficient vacuum to aspirate the coating material from a container through a fluid tube and into the air stream. In this case, the paint supply is normally located in a small cup attached to the spray device to keep the elevation differential and frictional pressure drop in the fluid-supply tube small. 

FIG. 8-82 Installed flow characteristic as a function of percent of total system head allocated to the control valve (assuming constant head pump, no elevation head loss, and an R equal 30 equal-percentage inherent characteristic). 

Figure 10-32 shows the schematic of a pump, moving a fluid from tank A to tank B, both of which are at the same level. Tne only force that the pump has to overcome in this case is the pipe function, variation of which with fluid flow rate is also shown in the figure. On the other for the use shown in Figure 10-33, the pump in addition to pipe friction should overcome head due to difference in elevation between tanks A and B. In this case, elevation head is constant, whereas the head required to overcome fric tiou depends on the flow rate. Figure 10-34 shows the pump performance requirement of a valve opening and closing. 

Most mammals show one or more of the following elements in F. jaw opening (gape or yawn) plus an elevated head posture and a temporary stillness there may also be specific respiratory and tongue movements plus a degree of nostril closure. The repertoire of F. elements occurs in various combinations, and is conspicuous in Ungulate and Carnivore repertoires (Estes, 1972). One or more of the behaviour elements in F., as in Fig. 7.6(a) to (f) may be present in any one species their separate functions (if any) have not been examined in detail. 

The cause of flow between these points is the difference in elevation head between them, that is, (Z, - Z2), denoted as dh, which is contributed by the gravitational potential. If is the distance between the two points on the water table, then the djd ratio is known as the hydraulic gradient. 

For the confined aquifer, the pressure head becomes more important than the elevation head. As can usually be seen in an artesian aquifer condition, the groundwater may flow from a lower elevation to a higher elevation if the water pressure at the lower elevation is higher. 

This elevation head loss of 20 psig had the same effect on the condenser—and on the tower s pressure—as did the rat or Nat s frictional loss. 

When elevation head and work transfer are neglected, the mechanical energy balance equation (6.13) with the friction term of Eq. (6.18) become... 

Equation (5.52) is Bernoulli s theorem [16], an energy equation that is well known to be equal to the sum of the elevation head, the pressure head, and the velocity head. Here the elevation head has been left out because the fan suction air pressure and the exiting air pressure from the air cooler are both equal. 

In Eq. (10.7) every term represents a linear quantity. Thus p/w, called pressure head, is an equivalent height of liquid representing a pressure p in a fluid of specific weight w z is elevation head and V2/2g is velocity head. It is obvious that hf must be a linear quantity also it is called friction head or lost head. The sum of the first three is called total head and is denoted by H, where ... 

A generalized equation, describing the system curve of a process is P = H + Ff(Qx), where P is the required to pump discharge pressure, H is the static or elevation head, Ff is the friction factor, Q is the flow rate, and x is an exponent that varies between 1.7 and 2.0 usually, 2.0 is used. 

Figure 83 Different geologic and topographic conditions that can result in artesian groundwaters. Artesian conditions require that there be a confining bed and elevated heads elsewhere in a groundwater recharge zone, (a) Shows elements of a "classical artesian system within a syncline. Artesian wells are shown in (b) stabilized sand dunes, (c) crystalline rock, (d) folded and fractured sedimentary rocks, (e) flat-lying sedimentary rocks, and (f) glacial sediments. From S. N. Davis and R. J. M, DeWiest. Hydrogeology. Copyright 1966. Used by permission.

True grouting pressures are those at the elevation of the grouted stratum. Gages at the pump do not include the elevation head, nor can they account for friction losses in the piping system, or in the grouted strata. 

BERNOULLI S THEOREM - In stream of liquid, the sum of elevation head, pressure head and velocity remains constant along any line of flow provided no work is done by or upon liquid in course of its flow, and decreases in proportion to energy lost in flow. 

---