Pipe entrance

Entrance and Exit Effects In the entrance region of a pipe, some distance is required for the flow to adjust from upstream conditions to the fuUy developed flow pattern. This distance depends on the Reynolds number and on the flow conditions upstream. For a uniform velocity profile at the pipe entrance, the computed length in laminar flow required for the centerline velocity to reach 99 percent of its fully developed value is (Dombrowski, Foumeny, Ookawara and Riza, Can. J. Chem. Engr, 71, 472 76 [1993])... 

Friction in piping, entrance and exit head losses... 

In chromatography-FTIR applications, in most instances, IR spectroscopy alone cannot provide unequivocal mixture-component identification. For this reason, chromatography-FTIR results are often combined with retention indices or mass-spectral analysis to improve structure assignments. In GC-FTIR instrumentation the capillary column terminates directly at the light-pipe entrance, and the flow is returned to the GC oven to allow in-line detection by FID or MS. Recently, a multihyphenated system consisting of a GC, combined with a cryostatic interfaced FT1R spectrometer and FID detector, and a mass spectrometer, has been described [197]. Obviously, GC-FTIR-MS is a versatile complex mixture analysis technique that can provide unequivocal and unambiguous compound identification [198,199]. Actually, on-line GC-IR, with... 

Table 7-5 Loss Coefficients for Pipe Entrance and Exit...

The frictional loss term F in Equation 4-28 represents the loss of mechanical energy resulting from friction and includes losses resulting from flow through lengths of pipe fittings such as valves, elbows, orifices and pipe entrances and exits. For each frictional device a loss term of the following form is used ... 

For pipe entrances and exits Equation 4-38 is modified to account for the change in kinetic energy ... 

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,... 

K are the excess head loss terms, including pipe entrances and exits, pipe lengths, and fittings (unitless). 

Given y based on the type of gas pipe length, diameter, and type pipe entrances and exits total number and type of fittings total pressure drop upstream gas density. 

Assume fully developed turbulent flow to determine the friction factor for the pipe and the excess head loss terms for the fittings and pipe entrances and exits. The Reynolds number can be calculated at the completion of the calculation to check this assumption. Sum the individual excess head loss terms to get 2 Kf. 

Pipe entrance and exit pressure losses should also be calculated and added to obtain the overall pressure drop. The loss in pressure due to sudden expansion from a diameter dtl to a larger diameter dl2 is given by the equation... 

C correction factor for short-pipe entrance losses (equation 10a)... 

Second, the friction loss hL from pipe entrance to exit may also be expressed as foot-pounds per pound of flowing fluid. This term is more commonly referred to as the head loss in feet of fluid. It is loss, because the hydraulic grade line shown in Fig. 6.1 exhibits the hL loss. 

Pipe entrance loss K value for heat exchanger 1.0 = 1.00... 

Using references such as the Crane Technical Paper No. 410, other pipe-fitting values can be proportionally factored. For two-phase flow pipe entrance and exit, however, new, more accurate equations are presented in this book, as shown here ... 

It is logical to expect that enhanced mass transfer will occur at pipe entrances. Berger and Hae found the following relationship, where L is the length or distance from the entrance (4,16) ... 

It has been shown that the major source of Rn in the indoor environments is the subsoil region. From here, Rn can diffuse (or be convected) into the building through cracks, water pipe entrances etc. 

For the sudden contraction at the pipe entrance, note that the entrance cross section, 5], is essentially infinity. Therefore,... 

For part 2, the Bernoulli equation is now applied between points 1 and 2 in Figure 20. Contributions to the fnction loss are now included. Besides skin fnction, there are losses associated with the contraction at the pipe entrance and one 90° elbow ... 

The thermal driving forces, or the approaches, at the pipe entrance and exit are given by... 

Instruments IR-85 Fourier Transform infrared spectrometer, through an IBM GC-IR interface. The interface consisted of a gold-coated Pyrex light-pipe with potassium bromide windows. A scan rate of 6 scans/sec and a spectral resolution of 8 cm- - were used for data acquisition. Samples were introduced into the system via splitless injections. A fused silica capillary column, 30 m x 0.32 mm i d DB-WAX (dj 1.0 pm), was employed with the outlet end connected directly to the GC-IR light-pipe entrance. Helium was used as the carrier gas at an average linear velocity of 41.4 cm/sec (35°C). No make-up gas was employed in the system. The column temperature was programmed from 35°C to 180°C at 2°C/min. The GC-IR light-pipe assembly was maintained at 170°C. 

Although the potential energy provides the flowing fluid with kinetic energy at the pipe entrance, the kinetic energy is later recovered. This indicates that the measured pipe pressure will be lower than the calculated pressure by one velocity head. If the kinetic energy is not recovered at the pipe exit, the exit counts as a loss of one velocity head. Table 3-2 shows how K varies with changes in pipe size. 

Develop and implement safe work practices —lockout —confined space entry —opening process equipment or piping —entrance control Safe work practices shall apply to employees and oontraa employees (e) Develop and implement safe work practices —lockout —confined space entry —opening process equipment or piping —entrance control Safe work practices shall apply to emptoyees and contract employees... 

The definition of A" (i.e., Kj= 2efW) involves the kinetic energy of the fluid, V /2. For sections in which the flow area changes (e.g., pipe entrance, exit, expansion, contraction, etc.), the entering and leaving velocities will be different. Since the value of the velocity used with the definition of Kp is arbitrary, it is very important to know which velocity is implied when values of the loss coefQcient are used from various sources (e.g., handbooks, manuals, texts, etc.). In most cases it is the largest velocity, through the smallest flow area, but the values in Table 5.6 for contractions and expansions are all used with the upstream velocity. 

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