Equivalent length method

The value K = 0.05 for gate valve from Table 6.5 appears to be low Chemical Engineering Handbook, for example, gives 0.17, more nearly in line with that from Table 6.6. The equivalent length method of Table 6.4 gives high pressure drops although convenient, it is not widely used. 

Regarding the equivalent length method. Hooper (1992) wrote ... 

Constant friction method. The principle is that the friction losses per meter run of the duct are taken as being constant. Values in the 1 to 5 Pa/m range are typical. The friction losses of connecting elements are expressed as an equivalent length of the straight ductwork runs. This is a simple method. It is ideally suited as a preliminary design method where it is combined with another approach. 

For pipe fittings, valves, and other flow obstructions the traditional method has been to use an equivalent pipe length Lequiv in Equation 4-30. The problem with this method is that the specified length is coupled to the friction factor. An improved approach is to use the 2-K method,s-6 which uses the actual flow path length in Equation 4-30 — equivalent lengths are not used — and provides a more detailed approach for pipe fittings, inlets, and outlets. The 2-K method defines the excess head loss in terms of two constants, the Reynolds number and the pipe internal diameter ... 

Alternatively, equation (9.10) (jives an approximate value for the correction factor. For the ERM, Fauskef17] gave a Table of friction correction factors as a function of the equivalent length to diameter ratio. These are given inTable5.1 and tend to be quite conservative compared with values estimated using the Omega method. 

In the velocity head method of accounting for fitting losses, a multiplicative coefficient is found empirically by which the velocity head term (v)2/2g is multiplied to obtain the fitting loss. This term is then added to the regular velocity head losses in Eq. (63). Extensive tables and charts of both equivalent lengths and loss coefficients and formulas for the effect of flow rate on loss coefficients... 

Analytical methods. After the reactor operation the fibers were cut into 10 cm segments and dried in an oven at 90°C for 72 hours. The dry mass density was obtained by taking the difference between the dry mass of the cut fiber and that of an empty one of equivalent length. This difference corresponds to the biomass accumulated in the interstitial space between the inner and outer fibers. Glucose was determined by glucose analyzer (YSI model 23 A, Yellow Springs, OH) and rifamycin B was measured spectrophotometrically at A25 nm. 

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