Baffle cut

It is assumed that process conditions and physical properties are known and the following are known or specified tube outside diameter D, tube geometrical arrangement (unit cell), shell inside diameter D shell outer tube limit baffle cut 4, baffle spacing and number of sealing strips N,. The effective tube length between tube sheets L may be either specified or calculated after the heat-transfer coefficient has been determined. If additional specific information (e.g., tube-baffle clearance) is available, the exact values (instead of estimates) of certain parameters may be used in the calculation with some improvement in accuracy. To complete the rating, it is necessary to know also the tube material and wall thickness or inside diameter. 

Baffle cuts are expressed as the ratio of segment opening height to shell inside diameter. Cross-flow baffles with horizontal cut are shown in Fig. 11-36 7, c, andf. This arrangement is not satisfactoiy for horizontal condensers, since the condensate can be trapped between baf-... 

FIG. 11 -40 Baffle cuts, (a) Baffle cuts for single segmental baffles, (h) Baffle cuts for double segmental baffles, (c) Baffle cuts for triple segmental baffles. 

Dummy tubes or tie rods with spacers may be located within the pass partition lanes (and between the baffle cuts) in order to ensure maximum bundle penetration by the shell-side fluid. 

Industry sets limits that bound our degrees of freedom and thus tend to shorten our design case study load. We are all aw are of such limits and this last category is included primarily for completeness. Examples include minimum industrial thickness for carbon steel plate, and maximum baffle cut for shell and tube heat exchangers. 

The baffle cut determines the fluid velocity between the baffle and the shell wall, and the baffle spacing determines the parallel and cross-flow velocities that affect heat transfer and pressure drop. Often the shell side of an exchanger is subject to low-pressure drop limitations, and the baffle patterns must be arranged to meet these specified conditions and at the same time provide maximum effectiveness for heat transfer. The plate material used for these supports and baffles should not be too thin and is usually minimum thick-... 

Kern s correlation checks well for the data of Short, Bowman, and Tinker for a wide variety of baffle cuts and spacing for segmental baffles with and without leakage as summarized by Donohue. Short s data for disc and doughnut baffles is better calculated by ... 

For longer units requiring support plates for the tubes, the pressure drop will still be very small or negligible and can be estimated by Figure 10-140 using the appropriate baffle cut curve to match the tube support cut-out of about 50%. Kem recommends that the flow be considered similar to an annulus of a double pipe and treated accordingly. 

This drop is usually very small unless the baffle cut has been limited to a low value. ... 

N = number of tubes in bundle Bog = baffle cut area, expressed as fraction, representing opening as percent of shell cross-section area. 

Shell-side jh and j f factors for use in this method are given in Figures 12.29 and 12.30, for various baffle cuts and tube arrangements. These figures are based on data given by Kern (1950) and by Ludwig (2001). 

For the calculated Reynolds number, read the value of jh from Figure 12.29 for the selected baffle cut and tube arrangement, and calculate the shell-side heat transfer... 

DT = design temperature MOP = maximum operating pressure MOT = maximum operating temperature 3.40% baffle cut = 40% open area is a good rule-of-... 

Baffle cut. Baffles are used to direct the fluid stream across the tubes. The baffle cut is the height of the segment removed to form the baffle as a fraction of the baffle disc diameter. Baffle cuts from 0.15 to 0.45 are used. In conceptual design, a value of 0.25 can be assumed. 

I o = outside (tube-side) volumetric flowrate Bc = baffle cut Ds = shell diameter... 

The constants in the heat transfer and pressure drop correlations are functions of the fluid physical properties, volumetric flowrate, tube size and pitch. In preliminary design, it is reasonable to assume either 20 mm outside diameter tubes with a 2 mm wall thickness or 25 mm outside diameter tubes with 2.6 mm wall thickness. The tube pitch is normally taken to be pj = l.25do- A square tube pitch configuration can be assumed as a conservative assumption. Baffle cut can be assumed to be 0.25 in preliminary design. 

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