Moody’s diagram

In Equation 5, f, appears on both sides of the equation, and the solution can only be obtained by the use of iterative procedure. Friction factor can also be determined from a graph commonly known as Moody s diagram (Moody [47]). Barr [48] proposed the following equation... 

FIGURE 5.9 Moody s [58] friction factor diagram for fully developed flow in a rough circular duct [45]. 

First, assume / = 0.005 and use this to get NRe from Nc=fN 9. From NRe we find Z)ec, and thus s/Dtc. Then, using the Churchill equation or Moody diagram, we find a valyue for / and compare it with the assumed value. This is repeated until convergence is achieved ... 

The driving force (DF) is given by Eq. (7-45), in which the K- s are related to the other variables by the Moody diagram (or Churchill equation) for each pipe segment (Kpipe), and by the 3-K method for each valve and fitting (Kfit), as a function of the Reynolds number ... 

Assume velocity V, and calculate Reynolds number. From Reynolds number, calculate the friction factor from the Moody diagram shown in Figure 2.2, otherwise it can be obtained from the above-mentioned equations. Calculate the pressure drop and then compare the calculated result with the given value of pressure drop which is 118 kPa in the question of the example. Repeat until the desired pressure drop is reached. Polymath software can be used instead (Figure 2.19). The calculated velocity is 5.29 m/s as shown in Figure 2.20. 

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