Tube bank, horizontal

Internal Regenerator Bed Colls. Internal cods generate high overall heat-transfer coefficients [550 W / (m -K)] and typically produce saturated steam up to 4.6 MPa (667 psi). Lower heat fluxes are attained when producing superheated steam. The tube banks are normally arranged horizontally in rows of three or four, but because of their location in a continuously active bubbling or turbulent bed, they offer limited duty flexibdity with no shutdown or start-up potential. 

Vei tical cylindrical cross-tube convection heaters are similar to the preceding type except for a horizontal convective tube bank above the combustion chamber. The design is economical with a high efficiency and is usually selec ted for higher-duty applications 11 to 210 GJ/h (10 to 200 10 Btu/h). 

Honzontal-tube cabin heaters position the tubes of the radiant-section-coil horizontally along the walls and the slanting roof for the length of the cabin-shaped enclosure. The convection tube bank is placed horizontally above the combustion chamber. It may be fired From the floor, the side walls, or the end walls. As in the case of its vertical cylindrical counterpart, its economical design and high efficiency make it the most popular horizontal-tube heater. Duties are 11 to 105 GJ/h (10 to 100 10 Btu). 

In the horizontal-tube box heater with side-mounted convection tube bank, the radiant-section tubes run horizontally along the walls and the flat roof of the box-shaped heater, but the convection section is placed in a box of its own beside the radiant sec tion. Firing is horizontal from the end walls. The design of this heater results in a relatively expensive unit justified mainly by its abihty to burn low-grade high-ash fuel oil. Duties are 53 to 210 GJ/h (50 to 200 10 Btu/h). 

Whitehead (1978) found patterns of bubble tracks in a large 1.2 m square bed similar to Werther preferred bubble tracks near the walls and comers of a shallow open bed and merging of bubbles toward the bed center at higher elevations. Nguyen, Potter, and Whitehead (1979) also found that a horizontal tube bank in the large bed caused smaller bubbles which appeared in more random locations across the upper surface of the bed. This work was carried out for fine solids at low superficial velocity, 15 cm/sec, and modest bed depths. 

Bock, H. J., and Schweinzer, J., Heat Transfer to Horizontal Tube Banks in a Pressurized Gas Solid Fluidized Bed, German Chem. Eng., 9(1) 16-23 (1986)... 

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. 

Figure 8.4. Example of tubular heat exchangers (see also Fig. 8.14). (a) Double-pipe exchanger, (b) Scraped inner surface of a double-pipe exchanger, (c) Shell-and-tube exchanger with fixed tube sheets, (d) Kettle-type reboiler, (e) Horizontal shell side thermosiphon reboiler, (f) Vertical tube side thermosiphon reboiler, (g) Internal reboiler in a tower, (h) Air cooler with induced draft fan above the tube bank, (i) Air cooler with forced draft fan below the tube bank.

FIG. 14-116 Experimental results showing effect of gas velocity and liquid load on entrainment from (a) vertical tube banks with horizontal gas flow and (b) horizontal tube banks with upflow. To convert meters per second to feet per second, multiply by 3.281. (Calvert, Yung, and Leung, NTIS Publ. PB-248050.)... 

The onset of liquid reentrainment from tube banks can be predicted from Fig. 14-116. Reentrainment occurred at much lower velocities in vertical upflow than in horizontal gas flow through vertical tube banks. While the top of the cross-hatched line of Fig. 14-116a predicts reentrainment above gas velocities of 3 m/s (9.8 ft/s) at high liquid loading, most of the entrainment settled to the bottom of the duct in 1 to 2 m (3.3 to 6.6 ft), and entrainment did not carry significant distances until the gas velocity exceeded 7 m/s (23 ft/s). 

For two-phase gas/liquid horizontal cross flow through tube banks, the method of Diehl and Unruh (Pet. Refiner, 37[10], 124-128... 

EXAMPLE 10-7 Condensation of Steam on Horizontal Tube Banks... 

Killion, J. D., and Garimella, S. (2003) Gravity-Driven Flow of Liquid Films and Droplets in Horizontal Tube Banks, International Journal of Refrigeration, Vol. 26(5), pp. 516-526. 

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