Allowing for Thermal Expansion

Referring to Fig. 26.1, we can see how a floating-head exchanger works. The tube-side flow enters the bottom of the channel head. This assumes the cold fluid to be on the tube side. The cold fluid may be on the shell side or the tube side of an exchanger. The convention is to put the 

Inside the exchanger s channel head, we have the pass partition baffle, which divides the chaiuiel head into two equal portions. This baffle forces the total flow only through the bottom half of the tubes. The tubes themselves are pipes of either 0.75 or 1 inch OD (outside diameter). The front end of each tube is slipped into a slightly larger hole drilled into the channel head tubesheet. This tubesheet is a disk about 2 inch thick, slightly larger than the inner diameter of the shell (shell ID). 

The tubes are firmly attached to the tubesheet by rolling. After a tube is pushed into the tubesheet, a tapered tool is inserted into the open end of the tube and forcefully rotated. The tube s diameter is thus slightly expanded. While rolling is quite effective in sealing the tube inside the tubesheet, rolls have been known to leak. 

The tube-side fluid now flows into the floating head, which acts as a return header for the tubes. The tube-side flow makes a 180° turn and flows back through the top half of the floating-head tubesheet. The floating head is firmly attached to the floating-head tubesheet. But why is it that one end of the tubes must be left free to float The reason is thermal expansion—or, more precisely, the differential rate of thermal expansion between the tubes and the shell. 

Not all shell and tube exchangers have a floating head. Many exchangers have individual U bends for each tube. In such cases, each of the U bends functions like a mini-floating head for each tube. 

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Heat Recovery and Seed Recovery System. Although much technology developed for conventional steam plants is appHcable to heat recovery and seed recovery (HRSR) design, the HRSRhas several differences arising from MHD-specific requirements (135,136). First, the MHD diffuser, which has no counterpart ia a conventional steam plant, is iacluded as part of the steam generation system. The diffuser experiences high 30 50 W/cm heat transfer rates. Thus, it is necessary to allow for thermal expansion of the order of 10 cm (137) ia both the horizontal and vertical directions at the connection between the diffuser and the radiant furnace section of the HRSR. 

Interna] Insulation The practice of insulating within the vessel (as opposed to applying insulating materials on the equipment exterior) is accomplished by the use of fiber blankets and hghtweight aggregates in ceramic cements. Such construction frequently incorporates a thin, high-alloy shroud (with slip joints to allow for thermal expansion) to protect the ceramic from erosion. In many cases this design is more economical than externally insulated equipment because it allows use of less expensive lower-alloy structural materials. 

Provide flexibility to allow for thermal expansion, or contraction, of pipework and connected equipment. 

It is still necessary to have a small relief system to allow for thermal expansion of a liquid-full system. This relief system is also necessary for handling hydraulic overfill and fire conditions, but the system is usually relatively simple. 

Supporting beams are used to stiffen the trays, and the trays must be fastened securely to prevent movement caused by gas surges. To allow for thermal expansion and to facilitate installation, slotted bolt holes should be provided in the supporting rings, and there should be adequate clearance between the tray and shell wall. 

Curved-blade impellers are generally used in CSTR pyrolysis vessels. Generally the gap between the scraper and the vessel wall is between 6-9 mm to allow for thermal expansion effects. 

Valves should be mounted vertically with their stems up, if possible. They should be accessible and well supported without strain, with suitable allowance for thermal expansion of the adjacent pipe. Room should be allowed for fully opening the valve and for repacking the stuflBng box. 

There is yet another expansion factor we can define, the I/O expansion factor, which we take as the ratio of the outlet flow rate to the inlet flow rate, allowing for the expansion in total flow. From the discussion preceding equation 5.59 we see that the outlet flow rate, allowing for thermal expansion as well as desorption is (Toa/T fo + kmVjT, while the expanded flow of sweeping gas alone at the outlet will be (Toa/Tj,). Hence the I/O expansion feet or is... 

The John Zink test facility has successfully used a horizontal TO system on top of a long metal plate to allow for easy modification of equipment configurations. The horizontal vessel connects directly to the stack and additional vessels and thermal expansion are accommodated by sliding the equipment on top of the metal plate. Flexible piping is used on all of the connections to the system to also allow for thermal expansion and modularity. 

A 500-mL round-bottomed flask is fitted with a 30-cm long tube for use as an air-cooled reflux condenser. This tube is closed by a stopcock fitted with a rubber breathing bag, allowing for thermal expansion of gases but maintaining the inertness of the atmosphere inside. 

Tray temperature often varies from one set of operating conditions to another (e.g., it is higher when a distillation column is pressured than when it is depressured). Often, the tray temperature is not the same as the shell temperature. Tray design should allow for thermal expansion of tray sections. Failure to do so may result in tray buckling or beam warping. 

Each component that is required in the calibration standard will need to have its weight calculated for the required amount of standard. The physical properties needed for these calculations can be obtained from the GPSA Engineering Data Book. Section 16, Physical Properties. When calcullating the amount required, it is advised to fill the cylinders only 80 percent full to allow for thermal expansion. 

All coils should be evenly supported at a minimum of three places. Supports should be evenly spaced and allow for thermal expansion of the coil. 

Sufficient endwise clearance, 3/8 in., between the end of the liner and the tank wall is provided to allow for thermal expansion 1/32 in. is allowed for radial expansion of the tube within the pilot ring.. ... 

There are 1/8 to 1/4 inch nominal gaps between the blocks to allow for thermal expansion and reduce fabrication tolerance requirements. The removal of a gunbarrel at the six old reactors will therefore permit that thermal shield block to drop. If too many blocks in a column drop, it may be difficult to get the top gunbarrel in because of misalignment and the weight of blocks above may prevent insertion of the bottom gunbarrel. This problem does not exist at the K Reactors because the keys span adjacent blocks and limit the total drop to a single gap width. 

Specification of the preferred or required means to allow for thermal expansion. Often expansion joints or bellows are considered impermissible on grounds of reliability, and the provision of inherently flexible piping design (incorporating sufficient bends) is specified. 

Estimation of costs for power poles to transmit electricity Protection of the pipelines from freezing in cold environments Allowance for water hammer and transients Allowance for thermal expansion in hot climates... 

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