Equivalent diameter, heat exchanger

Maxwell s law 594 Equivalent diameter, heat exchanger 528 Erosion 194... 

For rectangular ducts Kays and Clark (Stanford Univ, Dept. Mech. Eng. Tech. Rep. 14, Aug. 6, 1953) published relationships for headng and cooling of air in rectangular ducts of various aspect rados. For most noncircular ducts Eqs. (5-39) and (5-40) may be used if the equivalent diameter (= 4 X free area/wetted perimeter) is used as the characteristic length. See also Kays and London, Compact Heat Exchangers, 3d ed., McGraw-Hill, New York, 1984. 

Noncircular Ducts Equations (5-50 ) and (5-50/ ) may be employed for noncircular ducts by using the equivalent diameter D = 4 X free area per wetted perimeter. Kays and London (Compact Heat Exchangers, 3rd ed., McGraw-HiU, New York, 1984) give charts for various noncircular duels encountered in compact heat exchangers. 

When points for 20-ft-long tubes do not appear in Fig. 11-41, use 0.95 times the cost of the equivalent 16-ft-Iong exchanger. Length variation of steel heat exchangers affects costs by approximately 1 per square foot. Shell diameters for a given surface are approximately equal for U-tube and floating-head construc tion. 

Table 10-7 shows suggested tie rod count and diameter for various sizes of heat exchangers, as recommended by TEMA . Other combinations of tie rod number and diameter with equivalent metal area are permissible however, no fewer than four tie rods, and no diameter less than /g-in., should be used. Any baffle segment requires a minimum of three points of support. 

Figure 10-56. Equivalent diameter for tubes on shell side of exchanger taken along the tube axis, (a) Square pitch, (b) triangular pitch on 60° equilateral angles. (Used by permission Kern, D. Q. Process Heat Transfer, V Ed., 1959. McGraw-Hill, Inc. All rights reserved.)...

The outer and inner tubes extend from separate stationary tube sheets. The process fluid is heated or cooled by heat transfer to/from the outer tube s outside surface. The overall heat transfer coefficient for the O.D. of the inner tube is found in the same manner as for the double-pipe exchanger. The equivalent diameter of the annulus uses the perimeter of the O.D. of the inner tube and the I.D. of the inner tube. Kem presents calculation details. 

Steady two-phase flow. In rod (or tube) bundles, such as one usually encounters in reactor cores or heat exchangers, the pressure drop calculations use the correlations for flow in tubes by applying the equivalent diameter concept. Thus, in a square-pitched four-rod cell (Fig. 3.51), the equivalent diameter is given by... 

Calculate the equivalent diameter of the annular space of a double tube-type heat exchanger. The outside diameter of the inner tube d is 4.0 cm and the inside diameter of the outer tube is 6.0 cm. 

In the case where the fluid flow is parallel to the tubes, as in a shell-and-tube heat exchanger without transverse baffles, the equivalent diameter d of the shell side space is calculated as mentioned above, and h at the outside surface of tubes can be estimated by Equation 5.8a with the use of d. ... 

The alloy is failed during some cycles of hydrogen sorption - desorption and turns into powder with particles 3-4 microns. The specific surface of such powder can be estimated with assumption of their spherical shape a (1.5-2.0 microns) with equivalent diameter of a particle ded=4s/[ 0(l- )]=1.3-1.6 microns. These values can be used in calculations of gas dynamics of hydrogen flow and heat exchange in a layer. 

The equations presented here can also be used to predict heat-transfer coefficients for the shell side of shell-and-tube heat exchangers in which the baffles have been designed to produce flow parallel to the axis of the tube. For such cases, the diameter that should be used is the equivalent diameter... 

Several types of internals have been proposed so far. Some studies are presented by Volkct al. (VI2) and Grekelet al. (G15), who studied several arrangements of tubular internals and baffle trays. Volk suggested vertical tubes to increase the contact efficiency. For fluidized beds with diameter of 5-198 inches, conversions for beds of the same equivalent diameter (cf. Section I,C) were found equal. A large heat-exchange surface in the fluid bed is necessary for non-isothermal reactions, so the use of vertical tubes is quite practical. 

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