Pressure drop or friction loss

K Empirical proportionality constant for cyclone pressure drop or friction loss Dimensionless Dimensionless ... 

Empirical proportionally constant for cy clone pressure drop or friction loss, dimensionless Constant for stationary vane separators, based on design... 

The viscous or frictional loss term in the mechanical energy balance for most cases is obtained experimentally. For many common fittings found in piping systems, such as expansions, contrac tions, elbows and valves, data are available to estimate the losses. Substitution into the energy balance then allows calculation of pressure drop. A common error is to assume that pressure drop and frictional losses are equivalent. Equation (6-16) shows that in addition to fric tional losses, other factors such as shaft work and velocity or elevation change influence pressure drop. 

System components, such as pumps, valves and gauges, create both turbulent flow and high friction components. Pressure drop, or a loss of pressure, is created by a combination of turbulent flow and friction as the fluid flows through the unit. System components that are designed to provide minimum interruption of flow and pressure should be selected for the system. 

Pressure drop or head loss in a piping system is caused by fluid rising in elevation, friction, shaftwork (e.g., from a turbine) and turbulence due to sudden changes in direction or cross-sectional area. Figure 3-2... 

Friction loss or drag is synonymous with the dissipationof energy. For flow in a pipe, the rate of energy dissipation per unit mass of fluid can be expressed in terms of the mean- flow velocity and either the wall stress, pressure drop, or Fanning friction factor, as follows ... 

Operating Pretturet The proper operating pressures within single-effect and multi-effect evaporators must be maintained to enhance thermal efficiency and capacity. The pressures can be affected by loss of vacuum and line restrictions. As frictional pressure drops or vapor pressure within each effect increases, the boiling point of the liquor is higher and additional steam at a higher pressure is needed to maintain capacity and the achievable heat transfer AT s of each effect. 

Pressure Drop. The prediction of pressure drop in fixed beds of adsorbent particles is important. When the pressure loss is too high, cosdy compression may be increased, adsorbent may be fluidized and subject to attrition, or the excessive force may cmsh the particles. As discussed previously, RPSA rehes on pressure drop for separation. Because of the cychc nature of adsorption processes, pressure drop must be calculated for each of the steps of the cycle. The most commonly used pressure drop equations for fixed beds of adsorbent are those of Ergun (143), Leva (144), and Brownell and co-workers (145). Each of these correlations uses a particle Reynolds number (Re = G///) and friction factor (f) to calculate the pressure drop (AP) per... 

Pressure Drop. The pressure drop across a two-phase suspension is composed of various terms, such as static head, acceleration, and friction losses for both gas and soflds. For most dense fluid-bed appHcations, outside of entrance or exit regimes where the acceleration pressure drop is appreciable, the pressure drop simply results from the static head of soflds. Therefore, the weight of soflds ia the bed divided by the height of soflds gives the apparent density of the fluidized bed, ie... 

There are economic and operational reasons for considering an additional stage of compression. The addition of a stage of compression requires an additional scrubber, additional cylinder or case, and more complex piping and controls. In addition, there are some horsepower losses due to additional mechanical friction of the cylinder or rotating element and the increased pressure drop in the piping. This horsepower loss and additional equipment cost may be more than offset by the increased efficiency of compression. 

The basis for single-phase and some two-phase friction loss (pressure drop) for fluid flow follows the Darcy and Fanning concepts. The exact transition from laminar or dscous flow to the turbulent condition is variously identified as between a Reynolds number of 2000 and 4000. 

The total piping system pressure drop for a particular pipe installation is the sum of the friction drop in pipe valves and fittings, plus other pressure losses (drops) through control valves, plus drop through equipment in the system, plus static drop due to elevation or pressure level. For example, see Figure 2-2. 

Rather than assuming a pressure drop across the control as 25%, 33%, or 40% of the other friction losses in the system, a logical approach [9] is summarized here. The control valve pressure drop has nothing to do with the valve size, but is determined by the pressure balance (See Equation 2-59 [9]). 

For good control by the valve, the pressure drop across (or through) the valve must always be greater than the friction losses of the system by perhaps 10% to 20% (see [9]). 

Note that this control valve loss exceeds 60 percent of this system loss, since the valve must take the difference. For other systems where this is not the situation, the system loss must be so adjusted as to assign a value (see earlier section on control valves) of approximately 10 to 20 psi or 25 to 60 percent of the system other than friction losses through the valve. For very low pressure systems, this minimum value of control valve drop may be lowered at the sacrifice of sensitive control. 

The values of friction loss (including entrance, exit losses, pressure drop through heat exchangers, control valves and the like) are hjL and h L. The total static head is D — Sl, or [(D -f D ) — (—Sl)] if siphon action is ignored, and [(D + D ) — (S l)] for worst case, good design practice. 

The number of turbulence or pressure drop producing fittings in the pump suction line should be kept to a minimum. Because of the excessive turbulent and friction loss that they produce, globe valves should not be used in the pump suction line. When NPSH or turbulence is a problem, a turbulence-reducing device should be used. This device should be located as near the pumps suction flange as possible. 

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