Calculating piping losses

For estimating purposes in usual piping systems, the values of pressure drop across an orifice or nozzle will range from 2 to 5 psi. For more exact system pressure drop calculations, the loss across these devices should be calculated using some size assumptions. 

For dust extraction systems, the concentration of solids usually is quite low. For this reason, the methods employed to calculate pressure loss are based on air-only conditions. Comprehensive information is available (ASHRAE, 1985 ACGIH, 1992) to assist the designer in estimating the pressure loss caused by pipe branches, ducts, elbows, etc. 

The method of calculating frictional losses is described in Chapter 2. It may be noted here that losses occur as the fluid flows through the plain pipe, pipe fittings (bends, valves), and at expansions and contractions such as into and out of vessels. 

From Eq. (A-l), we can calculate the loss per set of pipes (10 pipes) connecting each absorber and stripper is... 

The installed SRV capacity should, however, always be calculated to ensure its flow is sufficient, with the correct inlet pressure losses being considered. For inlet piping loss calculations, see Section 6.1.1. 

Step 5 Calculate pipe straight segment friction pressure loss APf. 

Source Hooper, W. B., Calculate Head Loss Caused by Change in Pipe Size, ... 

Hooper, W. B., The 2-K Method Predicts Head Losses in Pipe Fittings, Chem. Eng., p. 97, Aug. 24 (1981). Hooper, W. B., Calculate Head Loss Caused by Change in Pipe Size, Chem. Eng., p. 89, Nov. 7 (1988). Hutchison, J. W., ISA Handbook of Control Valves, Instrument Society of America, Research Triangle Park,... 

In order to do the energy balance for the whole system, the temperature of flue gas was measured as well as the temperature of the surface of burner units and pipes. Compensation of temperature measurement due to radiation to the pipe walls was made in order to find the real exhaust gas temperature. Calculating energy loss with flue gas, Qpq. estimating surface losses, Q and having chemical energy of the fuel, Qp and thermal energy of the air, Q the efficiency of the system, t), was calculated. Equation 24.4... 

In most instances, we must multiply the calculated water horsepower by at least a factor of two or three to compensate for pump efficiency, gas engine inefficiency, and pipe losses. 

EXAMPLE 2.10-4. Trial-and-Error Solution to Calculate Pipe Diameter Water at 4.4°C is to flow through a horizontal commercial steel pipe having a length of 305 m at the rate of 150 gal/min. A head of water of 6.1 m is available to overcome the friction loss Fj. Calculate the pipe diameter. 

The design procedure requires trial and error calculations. Pipes are available in fixed sizes and so the procedure adopted here is to select a pipe size and determine the saltation velocity from Equation (8.1). The system pressure loss is then calculated at a superficial gas velocity equal to 1.5 times the saltation velocity [this gives a reasonable safety margin bearing in mind the accuracy of the correlation in Equation (8.1)]. The calculated system pressure loss is then compared with the allowable pressure loss. The pipe size selected may then be altered and the above procedure repeated until the calculated pressure loss matches that allowed. 

When using formula (VI.32) to calculate the loss of particles, one must know not only the values of the experimental coefficients (a and b) but also the values of Vay and v et > which vary with the diameter of the air pipe (see 31). According to formula (VI.32) a uniform removal of the adhering dust layer is assumed (loss rate constant). 

The Darcy-Weisbach Equation applies to a wide range of fluids, while the Hazen-Williams Equation is based on empirical data and is used primarily in water modeling applications. Each of these methods calculates friction losses as a function of the velocity of the fluid and some measure of the pipe s resistance to flow (pipe wall roughness). Typical pipe roughness values for these methods are shown in Table 3.3. These values can vary depending on the product manufacturer, workmanship, age, and many other factors. 

The Darcy-Weisbach Equation is a generally accepted method for calculating friction losses from liquids flowing in full pipes. It recognizes the dependence on pipe diameter, pipe wall roughness, liquid viscosity, and flow velocity. Darcy-Weisbach is a general equation that applies equally well at any flow rate and any incompressible fluid. 

To calculate head losses in piping systems with both pipe friction and minor losses use ... 

Hooper, W.B., Calculated head loss caused by change in pipe size. Chemical Engineering, November 7, 89-92, 1988. 

In order to select the pipe size, the pressure loss is calculated and velocity limitations are estabHshed. The most important equations for calculation of pressure drop for single-phase (Hquid or vapor) Newtonian fluids (viscosity independent of the rate of shear) are those for the deterrnination of the Reynolds number, and the head loss, (16—18). 

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. 

Losses 4 fof incompressible flow in sections of straight pipe of constant diameter may be calculated as previously described using the Fanning fric tion fac tor ... 

Example 6 Losses with Fittings and Valves It is desired to calculate the liquid level in the vessel shown in Fig. 6-15 required to produce a discharge velocity of 2 m/s. The fluid is water at 20°C with p = 1,000 kg/m and i = 0.001 Pa - s, and the butterfly valve is at 6 = 10°. The pipe is 2-in Schedule 40, with an inner diameter of 0.0525 m. The pipe roughness is 0.046 mm. Assuming the flow is tiirhiilent and taking the velocity profile factor (X = 1, the engineering Bernoulli equation Eq. (6-16), written between surfaces 1 and 2, where the... 

Example 8 Compressible Flow with Friction Losses Calculate the discharge rate of air to the atmosphere from a reservoir at 10 Pa gauge and 20 G through 10 m of straight 2-in Schedule 40 steel pipe (inside diameter = 0.0525 m), and 3 standard radius, flanged 90 elhows. Assume 0.5 velocity heads lost for the elhows. 

This formula is another variation on the Affinity Laws. Monsieur s Darcy and VVeisbach were hydraulic civil engineers in France in the mid 1850s (some 50 years before Mr. H VV). They based their formulas on friction losses of water moving in open canals. They applied other friction coefficients from some private experimentation, and developed their formulas for friction losses in closed aqueduct tubes. Through the years, their coefficients have evolved to incorporate the concepts of laminar and turbulent flow, variations in viscosity, temperature, and even piping with non uniform (rough) internal. surface finishes. With. so many variables and coefficients, the D/W formula only became practical and popular after the invention of the electronic calculator. The D/W forntula is extensive and eomplicated, compared to the empirieal estimations of Mr. H W. 

Last, we need to calculate the Hf losses through other connections in the piping... 

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