Entry pressure loss

Referring to the terminology in Fig. 5.9 and using analysis similar to that for the coni-cylindrical die, it may be shown that the shear, extensional and die entry pressure losses are given by... 

The NPSHr of reciprocating pumps is usually calculated for incipient cavitation conditions from the maximum entry pressure losses [18, 19], which are largely dictated by the characteristics of the suction check valve. The manufacturer s NPSHr data are in general based on these fluid mechanical effects. Typical values for the NPSHr range between 1 and 3 m for liquid CO2 (this corresponds to a pressure requirement of between 0.1 and 0.3 bar). 

Figure 9.18 Cavitation due to entry pressure losses and increasing fluid temperature (and hence vapor pressure) as fluid passes through the pump chamber. Pa, pv working chamber pressure and fluid vapour pressure pas, working chamber pressure at suction Ape, entry pressure loss I-III,...

In this case there will also be a pressure loss due to flow convergence at the die entry. This may be obtained from (5.47). 

The pressure loss associated with this type of exhaust opening is the sum of two pressure losses. The slot hood is usually thought of as a sharp-edged orifice and the duct entry (from the slot plenum) is a flanged opening. The rec ommended hood entry loss is given by Eq. (10.56) - ... 

The study found that the slot-type inlet at the bottom of the cabinet door resulted in higher pressure losses (lower CJ than the diffuser or perforated plate inlet. The exhaust configuration had little effect on Q or tracer gas clearance time. The study also concluded that an exhaust rate 0.118 m s for a two-cylinder cabinet was sufficient as little improvement was seen with an increase to 0.165 m s F" The slotted inlet took longer to clear a leak than either the perforated plate or diffuser inlet. Measured coefficients of entry for a two-cylinder gas storage cabinet are shown in Table 10.9. 

In addition to the irreversibilities associated with these components, pressure losses (Ap) may occur in various parts of the plant (e.g. in the entry and exit ducting, the combustion chamber, and the heat exchanger). These are usually expressed in terms of non-dimensional pressure loss coefficients, Ap/(p) N, where (/ )in is the pressure at entry to the duct. (Mach numbers are assumed to be low, with static and stagnation pressures and their loss coefficients approximately the same.)... 

Figure 26.3 shows the relationship between port diameter and fluid velocity at 4 and 7 m/s and highlights the nominal maximum velocities for various plates. As the flow through the machine increases, the entry and exit pressure losses also increase. The nominal maximum flow rate for a plate heat exchanger limits these losses to an acceptable proportion of the total pressure losses, and is therefore a function not only of the port diameter but... 

The design of the ductwork must ensure that the plant is both effective and efficient. Sharp bends and abmpt entries of branches into mains cause unnecessary pressure losses. Incorrectly sized ducts result in high pressure losses or blockages due to fallout from velocities being too low. 

Primary zone size is important with regard to efficiency and limits also. Within practical limits, a larger primary zone cross-sectional area will provide the best performance 138). Possible reasons arc lower velocities, less wall impingement by fuel, larger zone of low velocity, and less wall quenching of chemical reactions. The best axial distribution of open area of a combustor will depend on required operating conditions, the pressure loss characteristics, and the shape of the air entry ports. It will also depend on fuel-injection and fuel-volatility characteristics, as these factors will affect the amount of vapor fuel present at any location. If proper burning environment is to be obtained, these factors must be matched, and compromises in performance must be expected. 

These are the pressure losses created by the fluid prior to entry into a nozzle. They depend gready on the type of nozzle (Ke coefficient). See Section 6.1 for typical types of nozzle entries. An empirical equation is presented for the computation of entrance pressure losses ... 

Each of these pressure losses is given derived equations, and each is a separate entry to be added as an algebraic sum for the total pressure loss. This of course is similar to Eqs. (6.14) and (6.15). 

The viscous contribution to the total entrance pressure loss is very small. [C. D. Han, Influence of the Die Entry Angle in the Entrance Pressure Drop, Recoverable Elastic Energy and Onset of Flow Instability in Polymer Melt Flow, AIChE. J., 17, 1480 (1970).]... 

Total pressure loss from plenum to combustor exit at the end of cylindrical chamber was measured throughout the range of these experiments and varied with ER and flameholder version. The total range observed was from 5-8% of plenum pressure. For overall configuration C, the pressure loss was 7% at ER = 0.38. The quoted pressure losses include the losses at the bell-mouthed entry to the mixing section. 

As mentioned earlier, calculations from measurements are always made on the basis of Newtonian behaviour. This results in apparent quantities which have to be corrected. These corrections are necessary because of the reduced wall adhesion of many polymers (especially with a large filler content), and to this end the Rabinowitsch correction is applied to the shear rate. Also, owing to pressure losses on entry into the capillaries (when measuring with a capillary viscometer), the Bagley correction is applied to the shear stress T. 

The capillary dies must be very smooth, accurately machined, and hard. They are often made of tungsten carbide. Accuracy is especially critical. In a round-hole capillary, for example, the shear rate is a function of the radius cubed [see Eq. (7)]. A 1% error in the radius will result in a 3% error in the shear rate determination. Some dies have entry angles machined into their entrance to ease the abruptness of the transition from barrel to die and reduce the entrance pressure losses (see Bagley correction). Typical dies have diameters in the range of 0.5 to 2 mm, but specialty dies are available in almost any practical dimension. Depending on the piston speed and die selection, a wide range of shear rates can be achieved on capillary rheometers (see Fig. 9). 

The hydrodynamic entry length is usually taken as the distance from the tube entrance where the friction factor (pressure loss coefficient, see Section 3.4.1.1) reaches within 2% deviation the fully developed value. In laminar flow, the hydro-dynamic entry length is (Cengel, 2002) ... 

The additional pressure losses between (A) and (B) include the friction losses and pressure losses in all the pipe fittings such as valves, elbows, expansions, contraction branches, and bypasses. Pressure is also lost at entry and exit as well. Such pressure losses are expressed in terms of the Darcy-Weisbach equation and in terms of pressure loss factors for each fitting. 

CW = the pressure losses due to conduits and fittings between the tank (A) and the pump, including entry loss... 

Govier and Aziz (1972) indicated that once the initial period of stabilization is reached, the general form of pressure loss equations are the same as for time-independent non-Newtonian fluids. At the entry to a pipe, the flow may be laminar, but at a certain distance, once the entrance effects are overcome, the flow can transit to turbulence. 

Several barrier elements have been devised having tapered inlet and exit channels such that their cross sections will be in proportion to the amount of material passing through at any particular point [8, 9]. A 38 mm element made to the drawing in Figure 7.14 increased loss in output rate by a further 7.5%, compared with the Maddock element and increased entry pressure from 7 to 9 MPa. 

A low-pressure-loss type separator [IX-8] is mounted above the internal upper entry CRD as shown in Fig. IX-1. This new type separator, under development in a joint study by the Japanese BWR utilities and makers could decrease pressure losses by approximately 20% compared with the separator of a conventional type and effectively promotes natural circulation. 

The net suction lift possible with a pump amounts to the barometric pressure less the following items (1) true vapor pressure of liquid at the pumping temperature, (2) pressure caused by weight and spring of suction valve, and (3) entry friction losses. Should this computation come out to be negative it means that a net positive suction head is necessary, that the pump can produce no lift. Centrifugal pumps should always be provided with a flooded suction (positive head), because there is no convenient way to prime or fill them with liquid and they cannot operate without liquid in the case. 

Values of these hot spot factors are Fsa - 1.1672, foh = 1.2119, fAm = 2.3920 and fd = 1.4213. The same hotspot factors are also used for transient calculation. Pressure drop (in m of sodium column) values considered in the analysis at nominal power and flow conditions are core pressure drop of 64 m, standpipe entry pressure drop of 2 m, primary pipe pressure drop of 2 m, grid plate pressure drop of 4.5 m and IHX pressure drop of 1.5 m. Pressure drop at the ruptured end of the primary pipe is modeled by using unity veloeity head loss eoefficient. 

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