Pressure drop, estimation

For ordered, or structured, packings, pressure-drop estimation methods have been reviewed by Fair and Bravo [Chem. Eng. Progr, 86(1), 19 (1990)]. It is not common practice to use the packing factor approach for predicling pressure drop or flooding. For operation below the loading point, the model of Bravo et [Hydrocarbon... 

Loeb used Lapple s compressible flow work, techniques, and reasoning to develop graphs useful for direct calculations between tw o points in a pipe. Lapple s graphs were designed for pressure drop estimations for flow from a large vessel into a length of pipe (having static velocity in the reservoir). 

Hsu, Shih-liang, Packing Pressure Drop Estimated, Hydro. Processing, V. 64, No. 7 (1985) p. 89. 

In a similar way, the factor jf is obtained from Figure 9.82 and the pressure drop estimated from a modified form of equation 9.224 ... 

The details of the specific features of the heat transfer coefficient, and pressure drop estimation have been covered throughout the previous chapters. The objective of this chapter is to summarize important theoretical solutions, results of numerical calculations and experimental correlations that are common in micro-channel devices. These results are assessed from the practical point of view so that they provide a sound basis and guidelines for the evaluation of heat transfer and pressure drop characteristics of single-phase gas-liquid and steam-liquid flows. 

As can be seen, aZIPi = 0.1 seems to be an adequate upper limit to assume the error in the pressure drop estimation introduced by assuming constant fluid density to be negligible (%co is lower than about 0.64%). As has been analyzed previously, the limiting value of aZIPi is different (lower) in the case of a reacting system. This is why the analysis here is on the differences in pressure-drop estimation originating from the assumption of constant fluid density in a non-reacting system, while in reacting systems the analysis is on the effect of zero pressure drop assumption in the simplified models. 

The pressure drop across a steam control valve is a function of the valve design, size, and flow rate. The most accurate pressure-drop estimate that is usually available is that given in the valve manufacturer s engineering data for a specific valve size, type, and steam flow rate. Without such data, assume a pressure drop of 5 to 15 percent across the valve as a first approximation. This means that the pressure loss across this valve, assuming a 10 percent drop at the maximum steam flow rate, would be 0.10 x 80 = 8 psig (55.2 kPag). 

Generalized correlations for Rood point prediction have been based ou the early wort of Sherwood et aL19 Modifications of this wort have been made from time to time, with that of Eckert,20 mentioned eartier in connection with pressure drop estimation, being representative of those now in tise. The flood line is designated as the top curve of Fig. 5-8-12. Thus, as for pressure drop, the Eckert chart enables a quick estimate of the maximum allowable vapor flow through the packed bed in question. 

In Table 17.22, two correlations are presented for shellside two-phase flow pressure drop estimation, based on modifications of the internal flow correlations. The first correlation uses the modified Chrisholm correlation [69, 79], and the second one [80] employs the modified Lockhart-Martinelli correlation. The first correlation is for horizontal crossflow (crossflow in a baffled horizontal heat exchanger with horizontal or vertical baffle cuts). The second one is for vertical crossflow (upflow in a horizontal tube bundle). 

Figures 21 and 22 show the normalized pressured drop estimated by equation 128 for a packed D = 5.588 mm, ds = 3.040 mm, and e = 0.5916. The experimental data are taken from Fand and Thinakaran (92). We can observe that the approximate solution, equation 128, predicts fairly well the experimental results and is very good in representing the exact numerical solution of the governing equations. For clarity, Figure 21 is an expanded region for the small Rem values. Even with this scale, we observe that the approximate solution is very close to the exact numerical solution.

Equation (2-96) yields / = 0.00717, AP = 74 Pa. Notice the dramatic difference between this result and the pressure drop estimated for the packed bed ... 

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