Ideal tube bank

Fanning friction factor /i for inner wall and / 2 for outer wall of annulus /l for ideal tube bank sldn friction drag coefficient Dimensionless Dimensionless... 

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

Findfrom the ideal-tube bank curve for a given tube layout at the calculated value of (NRe), using Fig. 11-9, which is adapted from ideal-tnbe-bank data obtained at Delaware by Bergehn et al. [Trans. Am. Soc. Mech. Ting., 74, 953 (1952) and the Grimison correlation [Tran.s. Am. Soc. Mech. Tng., 59, 583 (1937)]. 

Calculate the shell-side heat-tran.sfer coefficient for an ideal tube bank hi. 

FIG. 11-15 Correction of friction factors for ideal tube banks, (a) Triangular and rotated square arrays, (h) In-line square arrays. 

It is shown in Section 9.9.5 that, with the existence of various bypass and leakage streams in practical heat exchangers, the flow patterns of the shell-side fluid, as shown in Figure 9.79, are complex in the extreme and far removed from the idealised cross-flow situation discussed in Section 9.4.4. One simple way of using the equations for cross-flow presented in Section 9.4.4, however, is to multiply the shell-side coefficient obtained from these equations by the factor 0.6 in order to obtain at least an estimate of the shell-side coefficient in a practical situation. The pioneering work of Kern(28) and DoNOHUE(lll who used correlations based on the total stream flow and empirical methods to allow for the performance of real exchangers compared with that for cross-flow over ideal tube banks, went much further and. 

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 ... 

The shell side with a number of segmental baffles presents more of a problem. It may be treated as a series of ideal tube banks connected by window zones, but also accompanied by some bypassing of the tube bundles and leakage through the baffles. A hand calculation based on this mechanism (ascribed to K.J. Bell) is illustrated by Ganapathy (1982, pp. 292-302), but the calculation usually is made with proprietary computer programs, that of HTRI for instance. 

Select the appropriate heat-transfer coefficient equation. Heat-transfer coefficients for fluids flowing across ideal-tube banks may be calculated using the equation... 

Findj i from the ideal-tube bank curve for a given tube layout at... 

FIG. 11-9 Correlation ofj factor for ideal tube bank. To convert inches to meters, multiply by 0.0254. Note thatp and D, have units of inches. 

Find/t from the ideal-tube-bank friction-factor curve for the given tube layout at the calculated value of (N ) using Fig. 11-15a for triangular and rotated square arrays and Fig. ll-15b for in-line square arrays. These curves are adapted from Bergelin et al. and Grimison (loc. cit.). 

Heat-transfer coefficient for cross flow over an ideal tube bank Fouling coefficient on outside of tube Heat-transfer coefficient in a plate heat exchanger Shell-side heat-transfer coefficient Heat transfer coefficient to vessel wall or coil Heat transfer factor defined by equation 12.14 Heat-transfer factor defined by equation 12.15 Friction factor... 

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