Effective pipe-length

In fact the term gdz is usually small compared with dF, allowing the height term to be neglected in many cases if necessary, an approximate allowance can be made in the final calculation by adding an additional effective pipe-length to the friction term.)... 

Effectively an additional length of pipe has been added to the true length in order to find the effective pipe-length, 1, ... 

Half-inch copper tubing is commonly used for steam tracing. Three-eighths-inch tubing is also used, but the effective circuit length is then decreased from 150 feet to about 60 feet. In some corrosive environments, stainless steel tubing is used, and occasionally standard carbon steel pipe (one half inch to one inch) is used as the tracer. 

Figures 26-63 and 26-64 illustrate the significant differences between subcooled and saturated-liquid discharge rates. Discharge rate decreases with increasing pipe length in both cases, but the drop in discharge rate is much more pronounced with saturated liquids. This is because the flashed vapor effectively chokes the flow and decreases the two-phase density.

The following analysis enables one to calculate the diameter of a pipeline transporting any compressible fluid. The required inputs are volumetric flow rate, the specific gravity of the gas relative to air, flow conditions, compressibility factor Z where Z is defined by nZRT = PV, the pressure at the point of origin and the destination, the pipe length, and pipe constants such as effective roughness. The working equations have been obtained from the literature. Since the friction factor... 

The value of C3 is 0.011454 in USCS units and 20.178 x 10 in SI units. The inputs for the calculation are Q (bbl/hr or mVhr) and pipeline length (miles or km), viscosity U (Centistokes), pipe diameter D (inches or meters), effective pipe roughness e, and pipeline lengths (miles or km). The Fanning friction factor is... 

For deflagrations, the dependence of overpressure and its effect on a flame arrester do not scale in proportion to pipe length, pipe diameter, or pipe length to diameter ratio. 

We now have five remaining unknowns—Qm, pm, p, Lm and (AP)f— and only two remaining equations, so we still have three arbitrary choices. Of course, we will choose a pipe length for the model that is much less than the 700 miles in the field, but it only has to be much longer than its diameter to avoid end effects. Thus we can choose any convenient length that will fit into the lab (say 50 ft), which still leaves two arbitrary unknowns to specify. Since there are two fluid properties to specify (p and p), this means that we can choose (arbitrarily) any (Newtonian) fluid for the lab test. Water is the most convenient, available, and inexpensive fluid, and if we use it (p = 1 cP, p = 1 g/cm3) we will have used up all our arbitrary choices. The remaining two unknowns, Qm and (AP)f, are determined by the two remaining equations. From Eq. (2-12),... 

The K factors for the entrance and exit effects are determined using Equation 4-39. The K factor for the gate valve is found in Table 4-2, and the K factor for the pipe length is given by Equation 4-30. For the pipe entrance,... 

Introducing the general correlation for the friction factor suggested by Churchill (11), figure 2 shows how the choking conditions now depend on the pipe length for isothermal conditions and variable friction factor. As it is seen, the effect of the variable friction factor is negligible. 

In this flow range the inlet effects make themselves felt until d/1 <= 200 (pipe diameter d, pipe length 1)... 

The thermowell arrangements shown in Figure 7-108 present other methods that can be used in making the 1-inch connections in process piping. To evaluate each of the thermowell details shown, these are summarized and appraised in Table 7-16a. This table presents an analysis showing the active, effective thermal lengths inside the pipe and how they compare in speed of response, and to what instruments they are best applied. It also shows that it is not practical to use certain well arrangements for temperature instruments. 

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