Tube banks

For pressure drop inside tubes, d is 0.046 and F is the fluid-flow path length. Across tubes banks, a is 0.75 and F is the product of the number of tube rows and the number of fluid passes across the tube bank. The physical property term is again tabulated after being normalised so that the lowest value is approximately unity. 

The generated water vapor rises through a screen (demister) placed to remove entrained saline water droplets. Rising further, it then condenses on the condenser tube bank, and internal heat recovery is achieved by transferring its heat of condensation to the seawater feed that is thus being preheated. This internal heat recovery is another of the primary advantages of the MSF process. The energy performance of distillation plants is often evaluated by the performance ratio, PR, typically defined as... 

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. 

Fanning friction factor /i for inner wall and / 2 for outer wall of annulus /l for ideal tube bank sldn friction drag coefficient Dimensionless Dimensionless... 

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

Further information on liquid-metal heat transfer in tube banks is given by Hsu for spheres and elliptical rod bundles [Int. J. Heat Mass Transfer, 8, 303 (1965)] and by Kahsh and Dwyer for oblique flow across tube banks [Int. ]. Heat Ma.ss Transfer, 10, 1533 (1967)]. For additional details of heat transfer with liqmd metals for various systems see Dwyer (1968 ed., Na and Nak supplement to Liquid Metals Handbook) and Stein ( Liquid Metal Heat Transfer, in Advances in Heat Transfer, vol. 3, Academic, New York, 1966). 

Turbulent Flow The correlation by Grimison (Trans. ASME, 59, 583—.594 [1937]) is recommended for predicting pressure drop for turbulent flow (Re > 2,000) across staggered or in-hne tube banks for tube spacings [(a/Dt), (b/Dt)] ranging from 1.25 to 3.0. The pressure drop is given by... 

FK . 6-42 Upp er chart Friction factors for staggered tube banks with minimum fluid flow area in transverse openings. Lower chart Friction factors for staggered tube banks with minimum fluid flow area in diagonal openings. (From Gtimison, Trans. ASME, 59,. 5S3 [1.937],)... 

For turbulent flow through shallow tube banks, the average friction factor per row will be somewhat greater than indicated by Figs. 6-42 and 6-43, which are based on 10 or more rows depth. A 30 percent increase per row for 2 rows, 15 percent per row lor 3 rows and 7 percent per row for 4 rows can be taken as the maximum likely to be encountered (Boucher and Lapple, Chem. Eng. Prog., 44, 117—134 [1948]). 

For laminar flow of non-Newtouiau fluids across tube banks, see Adams and Bell Chem. Eng. Prog., 64, Symp. Ser, 82, 133-145 [1968]). 

Flow-induced tube vibration occurs at critical fluid velocities through tube banks, and is to be avoided because of the severe damage that can result. Methods to predict and correct vibration problems may be found in Eisinger Trans. ASME J. Pressure Vessel Tech., 102, 138-145 [May 1980]) and Chen J. Sound Vibration, 93, 439-455 [1984]). 

Findfrom the ideal-tube bank curve for a given tube layout at the calculated value of (NRe), using Fig. 11-9, which is adapted from ideal-tnbe-bank data obtained at Delaware by Bergehn et al. [Trans. Am. Soc. Mech. Ting., 74, 953 (1952) and the Grimison correlation [Tran.s. Am. Soc. Mech. Tng., 59, 583 (1937)]. 

Calculate the shell-side heat-tran.sfer coefficient for an ideal tube bank hi. 

FIG. 11-15 Correction of friction factors for ideal tube banks, (a) Triangular and rotated square arrays, (h) In-line square arrays. 

The use of multiple tube banks as a droplet collector has also been studied by Calvert (R-12). He reports that collection efficiency for... 

In AFBC units, heat is removed from the flue gas by a convection-pass tube bank. The particulates leaving the boiler with the flue gas consist of unreacted and spent sorbent, unburned carbon, and ash. Multiclones after the convection pass remove much of the particulate matter and recvcle it to the combustor, increasing the in-furnace residence time an improving combustion efficiency and sulfur retention performance. Bubbling PFBC units do not have convection-pass tube banks and do not recycle solids to the boiler. 

Coal is fed as a paste containing 25 wt % water, and sorbent is fed diy by a lock-hopper system with pneumatic conveying. The top size of each feedstock is 3 mm in). The latent heat lost evaporating the water fed with the paste is compensated by increased gas turbine power output resulting from the increased flue-gas mass flow rate. For the 80-MWe unit, there are six coal feed points (one per 4.5 m" [48 ft"]) and four sorbent feed points (one per 6.7 m" [72 ft"]), all entering beneath the tube bank along one wall. The bed depth is... 

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). 

For turbulent flow across tube banks, a modified Fanning equation and modified Reynold s number are given. 

The prineipal disadvantage of die tubular reaetor is die diffieulty in eontrolling die temperature within die reaetor. This often results in hot spots espeeially when die reaetion is exodiermie. The tubular reaetor ean be in die form of one long tube or one of a number of shorter reaetors arranged in a tube bank (Eigure 4-7). 

Short and Brown in reference 172 found no net penalty against the single tube coefficient in a single row 20 tubes high. Belh concurs that this is home out in industrial experience, and current design practice is to assume that the average coefficient for the entire tube bank is the same as for a single tube. ... 

Flow 92.3 lb gas mixture, per tube. Estimated tube bank 4.48 lb... 

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