Tube bundles, tubes

P,P Center-to-center spacing of tubes in tube bundle (tube pitch) for tube pitch normal to flow Pp for tube pitch parallel to flow m ft... 

Figure 10-137. Heating and cooling in tube bundles—tube-side friction factor. (Used by permission Kern, D. Q. Process Heat Transfer, 1 Ed., p. 836, 1950. McGraw-Hill, Inc. All rights reserved. Using nomenclature of Standards of Tubular Exchanger Manufacturers Association.)...

Figures 5.4 and 5.5 show typical elevation and plot plan section sketches of horizontal air-cooled exchangers. The essential components are one or more tube sections, called tube bundles, and one or more axial flow fans, all enclosed in a structural module made to anchor footings into concrete or to stand on an offshore platform. As shown, one fan may serve more than one tube bundle. A bay may be made up of multiple tube bundles and may also be served by one or more fans. Most important is the fact that one exchanger may be composed of any number of tube bundles. Tube bundles may be arranged in series or in parallel, just like shell/tube bundles.

Leaks erosion/corrosion/vibration/improper tube finishing/cavitation/lack of support for tube bundle/tube end fatigue. 

Tube bundle Removable on all sizes if required. Standard design of size "A and B units may not have a removable tube bundle. TUbes are normally 1 in (25.4 mm)... 

Remick and Geankoplis made flux measurements for both species in the isobaric diffusion of nitrogen and helium through their tube bundle. Pressures spanned the interval from 0.444 nim, Hg to 300,2 ram Hg, which should cover the whole range between the limits of Knudsen streaming and bulk diffusion control. Then, since K and K, are known in this case, the form of the proposed flux relations could be tested immediately by plotting the left hand side of equation (10.15) against... 

Translate the heat-transfer area deterrnined in steps (8) or (9) into corresponding tube bundle dimensions (ie, number of tubes, diameter, and tube length). 

Translate the heat-transfer area deterrnined above into corresponding tube bundle dimensions. If different from those assumed in step (2), repeat steps (2) through (8) until satisfactory agreement is reached. The method caimot be appHed to cases in which U varies along the tube length or the stream... 

Fypass Flow Effects. There are several bypass flows, particularly on the sheUside of a heat exchanger, and these include a bypass flow between the tube bundle and the shell, bypass flow between the baffle plate and the shell, and bypass flow between the shell and the bundle outer shroud. Some high temperature nuclear heat exchangers have shrouds inside the shell to protect the shell from thermal transient effects. The effect of bypass flow is the degradation of the exchanger thermal performance. Therefore additional heat-transfer surface area must be provided to compensate for this performance degradation. 

Entrance andExit SpanXireas. The thermal design methods presented assume that the temperature of the sheUside fluid at the entrance end of aU tubes is uniform and the same as the inlet temperature, except for cross-flow heat exchangers. This phenomenon results from the one-dimensional analysis method used in the development of the design equations. In reaUty, the temperature of the sheUside fluid away from the bundle entrance is different from the inlet temperature because heat transfer takes place between the sheUside and tubeside fluids, as the sheUside fluid flows over the tubes to reach the region away from the bundle entrance in the entrance span of the tube bundle. A similar effect takes place in the exit span of the tube bundle (12). 

This implies that the LMTD or M I D as computed in equations 20 through 26 may not be a representative temperature difference between the two heat-transferring fluids for aU tubes. The effective LMTD or M ID would be smaller than the value calculated, and consequentiy would require additional heat-transfer area. The tme value of the effective M I D may be determined by two- or three-dimensional thermal—hydrauUc analysis of the tube bundle. Baffle—Tube Support PlateXirea. The portion of a heat-transfer tube that passes through the flow baffle—tube support plates is usuaUy considered inactive from a heat-transfer standpoint. However, this inactive area must be included in the determination of the total length of the heat-transfer tube. 

Miscellaneous Effects. Depending on individual design characteristics, there are other miscellaneous effects to consider in the determination of the final sizing of a heat exchanger. These include effects of flow maldistribution of both the sheUside and tubeside fluids, stagnant or inactive regions in the tube bundle, and inactive length of the tube in tubesheets. These effects should be individuaUy assessed and appropriate additional areas should be provided. 

Inorganic membranes (29,36) are generaUy more stable than their polymeric counterparts. Mechanical property data have not been definitive for good comparisons. IndustriaUy, tube bundle and honeycomb constmctions predominate with surface areas 20 to 200 m. Cross-flow is generaUy the preferred mode of operation. Packing densities are greater than 1000 /m. Porous ceramics, sintered metal, and metal oxides on porous carbon support... 

Recirculating Ste m Generator. The corrosion performance of many RSGs in commercial power stations in the United States has been marginal (2). Many tube bundles have had to be replaced. Many tubes have been plugged or sleeved with inserts as a result of excessive corrosion on the secondary side. 

The other space-saving approach is to use the Kobe (Kobe Steel) type of channel enclosure, which does not have all the external head bolts of typical TEMA Type B or Type C head enclosures. These exchangers require special tools to remove the tube bundles and trained maintenance personnel to do the work. These exchangers should never be located in stmctures because of the need to be able to access the channel from grade as it is difficult to remove the channel cover plate by using special equipment. 

Galvanic corrosion can be controlled by the use of sacrificial anodes. This is a common method of controlling corrosion in heat exchangers with Admiralty tube bundles and carbon steel tube sheets and channel heads. The anodes are bolted direcdy to the steel and protect a limited area around the anode. Proper placement of sacrificial anodes is a precise science. 

Circulating fluidized-beds do not contain any in-bed tube bundle heating surface. The furnace enclosure and internal division wall-type surfaces provide the required heat removal. This is possible because of the large quantity of soflds that are recycled internally and externally around the furnace. The bed temperature remains uniform, because the mass flow rate of the recycled soflds is many times the mass flow rate of the combustion gas. Operating temperatures for circulating beds are in the range of 816 to 871°C. Superficial gas velocities in some commercially available beds are about 6 m/s at full loads. The size of the soflds in the bed is usually smaller than 590 p.m, with the mean particle size in the 150—200 p.m range (81). 

The cod wound heat exchanger consists of multiple tubes heHcally wound on a mandrel, usually with spacers between each tube layer. The tubes are inserted into tube sheets at both ends of the tube bundle, with separate tube sheets to accommodate each tube circuit. The tube bundle is enclosed ia a sheU with inlet and outlet no22les for the sheUside fluid. This type of heat exchanger is usually constmcted of aluminum or stainless steel. Large aluminum... 

Improved and redesigned rotors of modem compressors save considerable power. The ethylene fractionator and the propylene refrigeration condensers can be replaced with extended surface tube bundles instead of conventional tube bundles. 

These equations apply to single tubes or to flat surfaces in a large pool. In tube bundles the equations are only approximate, and designers must rely upon experiment. Palen and Small [Hydrocarbon Process., 43(ll), 199 (1964)] have shown the effect of tube-bundle... 

For nonisothermal flow of liquids across tube bundles, the fric tion factor is increased if the liquid is being cooled and decreased if the liquid is being heated. The factors previously given for nonisotherm flow of liquids in pipes ( Tncompressible Flow in Pipes and Channels ) should be used. 

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