Bend loss coefficient

Fig. 7. (a) Configuration for flow turning. The frictional resistance resulting from the bend length must be added (b) pressure—loss coefficient, K, for 90°... 

Miller Internal Flow Systems, 2d ed.. Chap. 13, BHRA, Cranfield, 1990) gives the most complete information on losses in bends and curved pipes. For turbulent flow in circular cross-seclion bends of constant area, as shown in Fig. 6-14 7, a more accurate estimate of the loss coefficient K than that given in Table 6-4 is... 

Because most applications for micro-channel heat sinks deal with liquids, most of the former studies were focused on micro-channel laminar flows. Several investigators obtained friction factors that were greater than those predicted by the standard theory for conventional size channels, and, as the diameter of the channels decreased, the deviation of the friction factor measurements from theory increased. The early transition to turbulence was also reported. These observations may have been due to the fact that the entrance effects were not appropriately accounted for. Losses from change in tube diameter, bends and tees must be determined and must be considered for any piping between the channel plenums and the pressure transducers. It is necessary to account for the loss coefficients associated with singlephase flow in micro-channels, which are comparable to those for large channels with the same area ratio. 

You have probably noticed that when you turn on the garden hose it will whip about uncontrollably if it is not restrained. This is because of the unbalanced forces developed by the change of momentum in the tube. If a 1/2 in. ID hose carries water at a rate of 50 gpm, and the open end of the hose is bent at an angle of 30° to the rest of the hose, calculate the components of the force (magnitude and direction) exerted by the water on the bend in the hose. Assume that the loss coefficient in the hose is 0.25. 

A 90° horizontal reducing bend has an inlet diameter of 4 in. and an outlet diameter of 2 in. If water enters the bend at a pressure of 40 psig and a flow rate of 500 gpm, calculate the force (net magnitude and direction) exerted on the supports that hold the bend in place. The loss coefficient for the bend may be assumed to be 0.75 based on the highest velocity in the bend. 

Water flows through a 45° expansion pipe bend at a rate of 200 gpm, exiting into the atmosphere. The inlet to the bend is 2 in. ID, the exit is 3 in. ID, and the loss coefficient for the bend is 0.3 based on the inlet velocity. Calculate the force (magnitude and direction) exerted by the fluid on the bend relative to the direction of the entering stream. 

FIG. 6-14 Loss coefficients for flow in bends and curved pipes (a) flow geometry, (b) loss coefficient for a smooth-walled bend at Re= 106, (c) Re correction factor, id.) outlet pipe correction factor. (From D. S. Miller, Internal Flow Systems, 2d ed BHRA, Cranfield, U.K., 1990.)... 

The flow in pipe fittings, e.g. bends and valves, is generally too complex to determine theoretically. For turbulent flow, these minor losses are approximately equal to the square of the flow velocity. Thus, we define a loss coefficient, K,... 

Bends in the pipes may produce significantly greater head loss than the straight pipes. This type of loss results from the boundary separation and the swirling secondary flow. The boundary separation happens near the inside of the bend. The swirling secondary flow occurs due to the imbalance of centripetal forces as a result of the curvature of the pipe centreline, and this results in energy losses. The loss coefficient (KL) is mainly dependent on the ratio of R/D as shown in Figure... 

Table 7.1 Loss coefficients for bends and fittings in turbulent How...

Pigott [39] tabulated the loss coefficient, K, for elbows and bends from literature and established relationship of K with D /D, and friction factor. 

Attenuation The combination of optical energy losses from a light pulse traversing a length of optical fiber resulting from absorption and scattering, typically referred to as intrinsic attenuation, and bending losses, typically referred to as extrinsic attenuation, expressed in dB. However, attenuation is often used as a synonym for attenuation coefficient, expressed in dB/km. 

For turbulent flow through fittings, with the exception of bends, the loss coefficient is independent of the Reynolds number because inertia forces dominate. Experimental work showed that this is true for Newtonian fluids (Miller, 1978, Crane, 1999) and non-Newtonian fluids (Edwards et al., 1985, Ma 1987, Turian et al., 1998). 

The calibration of the model is simple in using two constant coefficients to fit the model to the experimental data across a wide range of flow conditions (air velocity and suspension density) for any one particulate solid. This suggests that it should be both simple to use, and effective, for prediction of bend losses from limited experimental data. 

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