Baffle banks

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

The addidon of a second bank of similar coils for additional heat transfer area, either outside or inside the first bank of coils will not provide twice the transfer of heat but the effecdveness is estimated to be 70%-90% of the first bank of duplicate coils (assuming the same heat transfer area per bank) [29]. The additional coils will provide additional baffling therefore, the need for the dimension of the vertical baffles is reduced, or they might be removed entirely. 

The results of Petree and Small are summarized in [29]. These coils present a solid vertical face, with the coils vertical but impressed in the plates for flow of the heating or cooling medium. They take the place of vertical baffles, and are more solid obstructions to through flow in die vessel than individual vertical coils. Usually four or six banks are used. 

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). 

The production of benzylpenicillin is very sensitive to temperature. A lot of metabolic heat is generated and the fermentation temperature has to be reduced by controlled cooling. This heat transfer is achieved by circulating chilled water through banks of pipes inside the vessel (which also serve as baffles) or through external limpet coils on the jacket of the vessel. These coils consist of continuous lengths of pipe welded in a shallow spiral round the vessel. This cooling water system is also used to cool batched medium sterilized in the vessel prior to its inoculation. 

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. 

Froth baffles are placed between each unit mechanism to prevent migration of froth as the liquid flows along the tank. The liquor level is controlled at the end of each bank... 

Effectiveness of Internals in Controlling foam. Originally, the separators contained limited internals—an inlet disengaging device, surge baffles, an anti-foam baffle, and a demister at the outlet. After severe foaming occurred, however, a bank of parallel plates (Dixon plates) was filled in each separator on one of the Ninian and one of the Brent trains The plates provide a large surface area and are sloped so that the separated oil flows dow n to the surface of the liquid. The installation is illustrated m Ftg S. The parallel plates arc 4 in. apart and extend from near the top of the vessel in the vapor space down to the normal liquid level. 

Preheater vibration. Air preheaters or any type of waste-heat recovery device designed for horizontal flow across vertical tubes, may be subject to vibration produced by the velocity of gas across the tube banks. The velocity produces a vortex-shedding wave pattern that could correspond to the natural harmonic frequency of the tube bank. If the natural harmonic frequency is reached, excessive vibration of the tubes will occur. Redesign of the internal baffle system by inserting dummy baffles can stop the vibration. 

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. 

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. 

In this application, the portable camera is capable of imaging motion over the full width of the fluidised bed but not the full height. Because the main aim of the work was to quantify circulation, it was decided to form the camera elements up into lower and upper banks, intended to follow the flows under and over the baffle, respectively. 

Frictional pressure drop for tube banks may be calculated as follows For intermediate baffle... 

Bundles with tubes omitted from baffle windows. Frequently, tubes are omitted from the baffle-window areas. For this configuration, maldistribution of the fluid as it flows across the bank of tubes may occur as a result of the momentum of the fluid as it flows through the baffle window. For this reason, baffle cuts less than 20 percent of the shell diameter should only be used with caution. Maldistribution will normally be minimized if the fluid velocity in the baffle window is equal to or... 

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