Regular pressure drops

Usually, the general expression of the regular pressure drop is written as... 

The ratio Dj/L in the regular pressure drop coefficient accormts for the properly that the flow velocity depends on the pressure change between the inlet and the outlet in proportion to the length of the pipe. The same flow rate is obtained if the pressure change and the length of the pipe are simultaneously doubled. 

A common type of distillation contacting device used in refinery applications is the sieve tray. In the early 50 s and for many years before, the bubble cap tray was the mainstay of the distillation field. A sieve tray consists of a flat plate with regularly spaced holes, normally 1/2 to 1 inch in diameter. Liquid flows horizontally across the tray and into a channel, called a downcomer, which leads to the tray below. The sieve tray exhibits good capacity, excellent efficiency, low pressure drop, and good flexibility i.e., it will operate quite efficiently at tower loadings which are 1/2 to 1/3 of design values. 

Air cleaning (dust collection) can be cost effective for LVHV systems handling valuable dusts. Care must be taken when handling potentially toxic dusts from air cleaners. Regular, routine reconditioning of fabric filters (e.g., by automatic shaking or pneumatic pulsing) is impottant. This can be accomplished on a set maintenance schedule or as a function of pressure drop across the fabric filter. It is not recommended to recirculate airflow back to the workplace because of the low air volume and potential hazards in the event of filter failures. 

To ensnre reliahility, dry-type flame arresters shonld he inspected on a regular basis, as mentioned previously. Also, as discussed in Section 5.3.18, it is often the pracdce to provide pressure drop and temperatnre instm-mentadon to monitor the flame arrester condidon in service. This will provide indicadon of impending problems dial can affect the performance of the flame arrester. 

Fig. 3.17 Average pressure drop reduction as a function of flow rate for a series of different surfaces in a micro-channel having dimensions W = 2.54 mm, H = 127 pm, and L = 50 mm. The experimental data include a series of ultrahydrophobic surfaces with a regular array of square micro-posts with d = 30 pm with a spacing between micro-posts of w = 15 pm represented by triangles (A), <7 = 30 pm and w = 30 pm represented by squares ( ), J = 30 pm and w = 60 pm represented by circles ( ), and d = 30 pm and w = 150 pm represented by diamonds ( ). Reprinted from Ou et al. (2004) with permission...

Flow of trains of surfactant-laden gas bubbles through capillaries is an important ingredient of foam transport in porous media. To understand the role of surfactants in bubble flow, we present a regular perturbation expansion in large adsorption rates within the low capillary-number, singular perturbation hydrodynamic theory of Bretherton. Upon addition of soluble surfactant to the continuous liquid phase, the pressure drop across the bubble increases with the elasticity number while the deposited thin film thickness decreases slightly with the elasticity number. Both pressure drop and thin film thickness retain their 2/3 power dependence on the capillary number found by Bretherton for surfactant-free bubbles. Comparison of the proposed theory to available and new experimental... 

The main results of our first-order regular perturbation analysis are the expressions for the constant thin film thickness, hQ, and for the total hydrodynamic pressure drop across the entire... 

The first term in both Equations 17 and 18 is the constant surface-tension contribution and the second term gives the first-order contribution resulting from the presence of a soluble surfactant with finite sorption kinetics. A linear dependence on the surfactant elasticity number arises because only the first-order term in the regular perturbation expansion has been evaluated. The thin film thickness deviates negatively by only one percent from the constant-tension solution when E = 1, whereas the pressure drop across the bubble is significantly greater than the constant-tension value when E - 1. 

Work on the rate of dissolution of regular shaped solids in liquids has been carried out by Linton and Sherwood(1), to which reference is made in Volume 1. Benzoic acid, cinnamic acid, and /3-naphthol were used as solutes, and water as the solvent. For streamline flow, the results were satisfactorily correlated on the assumption that transfer took place as a result of molecular diffusion alone. For turbulent flow through small tubes cast from each of the materials, the rate of mass transfer could be predicted from the pressure drop by using the 1 j-factor for mass transfer. In experiments with benzoic acid, unduly high rates of transfer were obtained because the area of the solids was increased as a result of pitting. 

Figure 12. Pressure drop after regular intermittent compressions after film has been compressed beyond collapse point. From Thompson (101).

By computing the pressure drop in the static mixer and the pressure drop in the granulating head and adding this to the exergy requirements of the compressor, it is possible to compute the exergy input of the alternative scheme, and compare this with the regular extruder (Figure 11.7). 

Figure 2 shows the shape and size of the Monolith alumina supports. These are in the form of cylindrical segments of about 2.54 cm in length and about 1.0 cm in diameter. These have longitudinal and parallel channels along their length. The size, shape and thickness of the walls of the channels are also shown in Figure 2. The Monolith structure has about 60 to 80 percent of its cross-sectional area open. Therefore, a bed of regularly stacked Monoliths would offer significantly less pressure drop than that encountered in conventional packed beds. This has been observed by Satterfield and Ozel (1) for a water-air system.

For gas-phase applications, carbon adsorbents are regularly applied in the shape of hard granules, hard pellets, fiber, cloths, and monoliths since these prevent an extreme pressure drop [77,78],... 

Eqn (23) is a second order nonlinear difference equation the Jacobian of which is easily established as a regular tridiagonal matrix with a dominating diagonal, similar to system matrices found in the simulation of distillation columns. The analytical derivation of the Jacobian and the Newton-Raphson iteration is trivial. In figure 3 is shown an example where the intermediate pressures are plotted as functions of the total pressure drop across the line segment. The example is artificially chosen such that all e-parameters are the same, i.e. ... 

Such a comparison is given in Fig. 7 where the two heat transfer parameters X, and aw plus the external catalyst surface ap, the bed void fraction e and the pressure drop Ap are given for a selection of different random and regular catalyst packings in a tube of 50 mm internal diameter and a mass flow velocity of G. = 1 kg/(m2 s). 

Of the many experiments run in the PS micromodel, only Test 11-19A is described here (see Table II). It was a gas-drive of surfactant solution (GDS), in which the pressure drop across the micromodel was measured and analyzed in terms of the flow behavior recorded simultaneously on videotape. It was also of interest to examine bubble formation and breakup processes in the PS model, where the large and fairly regular pores might give a different behavior than the smaller, more variable pores of the RS model. The surfactant used in the PS model was an anionic-nonionic blend in a 10 wt.% (weight percent active) solution, and nitrogen was the gas used in the GDS test. Conditions were 1000 psi back pressure and ambient temperature. 

The parallel-passage and lateral-flow reactors arc reactors that feature a low pressure drop and the ability to handle gases containing dust. They owe these characteristics to the specific arrangement of the catalyst in regular structures Catalyst particles of a similar morphology as in traditional fixed beds are enclosed in geometric structures made of screens. 

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