Tube-bank arrangements

Correlations for forced convection over tubes in crossflow are complicated by the effect of the tube bank arrangement. For the range of Reynolds numbers likely to be encountered in industrial boilers the following equations may be used ... 

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. 

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). 

Pierson, O.L. Trans. Am. Soc. Mech. Eng. 59 (1937) 563. Experimental investigation of influence of tube arrangement on convection heat transfer and flow resistance in cross flow of gases over tube banks. 

The basic construction consists of a rectangular or cylindrical steel chamber, lined with refractory bricks. Tubes are arranged around the wall, in either horizontal or vertical banks. The fluid to be heated flows through the tubes. Typical layouts are shown in Figure 12.69a, b and c. A more detailed diagram of a pyrolysis furnace is given in Figure 12.70. 

Air at 1 atm and 10°C flows across a bank of tubes 15 rows high and 5 rows deep at a velocity of 7 m/s measured at a point in the flow before the air enters the tube bank. The surfaces of the tubes are maintained at 65°C. The diameter of the tubes is 1 in [2.54 cm] they are arranged in an in-line manner so that the spacing in both the normal and parallel directions to the flow is 1.5 in [3.81 cm]. Calculate the total heat transfer per unit length for the tube bank and the exit air temperature. 

A tube bank uses an in-line arrangement with S = Sp = 1.9 cm and 6.33-mm-diameter tubes. Six rows of tubes are employed with a stack 50 tubes high. The surface temperature of the tubes is constant at 90 C, and atmospheric air at 20°C is forced across them at an inlet velocity of 4.5 m/s before the flow enters the tube bank. Calculate the total heat transfer per unit length for the tube bank. Estimate the pressure drop for this arrangement. 

A more compact version of the tube bank in Prob. 6-66 can be achieved by reducing the Sp and S dimensions while still retaining the same number of tubes. Investigate the effect of reducing Sp and S in half, that is, Sp = S, = 0.95 cm. Calculate the heat transfer and pressure drop for this new arrangement. 

An in-line tube bank is constructed pf 2. 5-cm-diameter tubes with 15 rows high and 7 rows deep. The tubes are maintained at 90°C, and atmospheric air is blown across them at 20°C and u. = 12 m/s. The arrangement has Sp = 3.75 and S = 5.0 cm. Calculate the heat transfer from the tube bank per meter of length. Also calculate the pressure drop. 

As the fluid enters the tube bank, Ihe flow area decreases from A, = SfL to Af- Sj- — /T)/, between the tubes, and thus flow velocity increases. In staggered arrangement, the velocity may increase further in Ihe diagonal region if the tube rows are very close to each other. In tube banks, the flow characteristics are dominated by the maximum velocitiy Kp, that occurs within Ihe lube bank rather than the approach velocity V. Therefore, the Reynolds number is defined on the basis of maximum velocity as... 

Arrangement of the tubes in in-line and staggered tube banks (Ai, Aj-, and Ad aru flow areas at indicated locations, and L is the length of the tubes). 

Flow through tube banks is studied experimentally since it is loo complex to be treated analytically. We arc primarily interested in (be average heat transfer coefficient for the entire tube bank, which depends on the number of tube rows along (lie flow as well as the arrangement and the size of the tubes. 

In an industrial facility, air is to be preheated before entering a furnace by geo-u thermal water at 120°C flowing through the tubes of a tube bank located in a S duct. Air enters the duct at 20°C and 1 atm v/ith a mean velocity of 4.5 m/s, H and flows over the tubes in normal direction. The outer diameter of the tubes is 1.5 cm, and the lubes are arranged in-line with longitudinal and transverse pilches of Sr = Sf = 5 cm. There are 6 rows in the flow direction with 10 tubes i in each row, as shown in Fig. 7-28. Determine the rate of heat transfer per unit 3 length of the tubes, and the pressure drop across the tube bank. 

For this square in-line tube bank, the friction coefficient corresponding to Reo = 5086 and SJD = 5/1.5 = 3.33 is, from Fig. 7-27a. f 0.16. Also, X = 1 for the square arrangements. Then the pressure drop across the tube bank becomes... 

Air is to be heated by passing it over a bank of 3-m-long tubes inside which steam is condensing at 100°C. Air approaches the tube bank in the normal direction at 20 C and I aim with a mean velocity of 5.2 m/s. The outer diameter of the tubes is 1.6 cm, and die lubes are arranged staggered with longitudinal and transverse pitches of = Sj = 4 cm. There are 20 row.s in the flow direction with 10 tubes in each row. Determine (a) the rate of heat transfer, (f ) and pressure drop across the tube bank, and (c) the rate of condensation of steam inside the tubes. 

In this equation, N is the nnmber of major restrictions in the tube bank (i.e., the nnmber of times the flow reaches its maximnm velocity in flowing throngh the tube bank). In the 30° and 90° arrangements, N is equal to the number of tube rows crossed in the bank for the 45° and 60° layonts, N is one less than the number of rows crossed. The term Ap is the frictional pressure drop across the tube bank. 

Forced Convection Tube Banks (30,31,32) Figure shows tube arrangements in a bank. )... 

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