Tube banks pressure drops

Tube banks, pressure drop in flow over 93,431... 

Low-fin tubes. The method presented above can be used to predict pressure drop for banks of low-fin tubes. For low-fin tubes, the pressure drop is calculated assuming that the tubes are bare. The mass velocity and tube diameter used for calculation are those for a bare tube with the same diameter as the fins of the low-fin tube. 

Banks of finned tubes. For fin tubes other than low-fin tubes, the pressure drop for flowing across banks of transverse fin tubes can be calculated from... 

For pressure drop inside tubes, d is 0.046 and F is the fluid-flow path length. Across tubes banks, a is 0.75 and F is the product of the number of tube rows and the number of fluid passes across the tube bank. The physical property term is again tabulated after being normalised so that the lowest value is approximately unity. 

APm.AP,., Pressure drop for ideal-tube-bank cross-flow and ideal window respectively AP for shell side of baffled exchanger kPa Itf ft ... 

Turbulent Flow The correlation by Grimison (Trans. ASME, 59, 583—.594 [1937]) is recommended for predicting pressure drop for turbulent flow (Re > 2,000) across staggered or in-hne tube banks for tube spacings [(a/Dt), (b/Dt)] ranging from 1.25 to 3.0. The pressure drop is given by... 

For banks of in-line tubes,/for isothermal flow is obtained from Fig. 6-43. Average deviation from available data is on the order of 15 percent. For tube spacings greater than 3D(, the charts of Gram, Mackey, and Monroe (Trans. ASME, 80, 25—35 [1958]) can be used. As an approximation, the pressure drop can be taken as 0.32 velocity head (based on V ) per row of tubes (Lapple, et al.. Fluid and Paiiicle Mechanics, University of Delaware, Newark, 1954). 

E/ig. Exp. Sta. Bull., 2 [1950]) recommend the following equations for pressure drop with laminar flow (Re, < 100) of liquids across banks of plain tubes with pitch ratios P/D( of 1.25 and 1..50 ... 

The arbor (wicket) heater is a substantially vertical design in which the radiant tubes are inverted Us connecting the inlet and outlet terminal manifolds in parallel. An overhead crossflow convection bank is usually included. This type of design is good for heating large gas flows with low pressure drop. Typical duties are 53 to 106 GJ/h (50 to 100 10 Btu/h). 

Figure 10-142. Pressure drop in fluid flowing across tube banks with segmental baffles. (Used by permission Buthod, A. P. Oil Gas Journal, V. 58, No. 3, 1960. PennWell Publishing Company. All rights reserved.)...

Bergelin, O. P, W. L. Lafferty,Jr., M. D. Leighton, R. L. Pigford, Heat Transfer and Pressure Drop during Viscous and Turbulent How across Baffled and UnbafUed Tube Banks, University of Delaware, Eng. Exp. Sta., Newark, Del. Bui. No. 4 (1958). 

Ishehara, K,J. W. Palen, andj. Taborek, Critical Review of Correlations for Predicting Two-Phase Flow Pressure Drop Across Tube Banks, Heat Trans. Eng.,Y. 1, No. 3,Jan.-March (1980). 

For flow at right angles to the axes of the tubes, the cross-sectional area is continually changing, and the problem may be treated as one involving a series of sudden enlargements and sudden contractions. Thus the friction loss would be expected to be directly proportional to the number of banks of pipes j in the direction of flow and to the kinetic energy of the fluid. The pressure drop - APf may be written as ... 

Using Tinker s approach, BELL(12, i22) has described a semi-analytical method, based on work at the University of Delaware, which allows for the effects of major bypass and leakage streams, and which is suitable for use with calculators. In this procedure, the heat transfer coefficient and the pressure drop are obtained from correlations for flow over ideal tube banks, applying correction factors to allow for the effects of leakage, bypassing and flow... 

The complex flow pattern on the shell-side, and the great number of variables involved, make it difficult to predict the shell-side coefficient and pressure drop with complete assurance. In methods used for the design of exchangers prior to about 1960 no attempt was made to account for the leakage and bypass streams. Correlations were based on the total stream flow, and empirical methods were used to account for the performance of real exchangers compared with that for cross flow over ideal tube banks. Typical of these bulk-flow methods are those of Kern (1950) and Donohue (1955). Reliable predictions can only be achieved by comprehensive analysis of the contribution to heat transfer and pressure drop made by the individual streams shown in Figure 12.26. Tinker (1951, 1958) published the first detailed stream-analysis method for predicting shell-side heat-transfer coefficients and pressure drop, and the methods subsequently developed... 

In Bell s method the heat-transfer coefficient and pressure drop are estimated from correlations for flow over ideal tube-banks, and the effects of leakage, bypassing and flow in the window zone are allowed for by applying correction factors. 

The pressure drop in the cross-flow zones between the baffle tips is calculated from correlations for ideal tube banks, and corrected for leakage and bypassing. 

A Pi = the pressure drop calculated for an equivalent ideal tube bank,... 

Any suitable correlation for the cross-flow friction factor can be used for that given in Figure 12.36, the pressure drop across the ideal tube bank is given by ... 

Most of the pressure drop will occur in the convection section. The procedures for estimating the pressure drop across banks of tubes can be used to estimate the pressure drop in this section, see Section 12.9.4 and Volume 1, Chapter 9. 

Briggs, D. E. and Young, E. H. (1963) Chem. Eng. Prog. Symp. Ser. No. 59, 61, 1. Convection heat transfer and pressure drop of air flowing across triangular pitch banks of finned tubes. 

A simpler method due to Kem (1950, pp. 147-152) nominally considers only the drop across the tube banks, but actually takes account of the added pressure drop through baffle windows by employing a higher than normal friction factor to evaluate pressure drop across the tube banks. Example 8.8 employs this procedure. According to Taborek (HEDH, 1983, 3.3.2), the Kern predictions usually are high, and therefore considered safe, by a factor as high as 2, except in laminar flow where the results are uncertain. In the case worked out by Ganapathy (1982, pp. 292-302), however, the Bell and Kem results are essentially the same. 

APj = ideal pressure drop across the tube bank jf = shell-side friction factor ... 

Pressure drop for flow of gases over a bank of tubes may be calculated with... 

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