Nomenclature For Chapter 15
a, = constant in Eq. (29) for evaluating outside film coefficient of heat transfer, dimensionless A = area of heat transfer, ft2; subscripts m designates mean area; subscript
0 designates outside area; subscript / designates film area b0 = constant in Eq. (32) for evaluating shell-side friction factor, dimension-less
Bj = correction factor in Eq. (30) to account for friction due to sudden contraction, sudden expansion, and reversal of flow direction, dimen-sionless
Ba = correction factor in Eq. (31) to account for friction due to reversal of flow direction, recrossing of tubes, and variation in cross section, dimensionless cc = constant, dimensionless; defined in Table 4 cp = heat capacity, BtU/(lbX°F); prime refers to process fluid CA = installed cost of heat exchanger per unit of outside-tube heat-transfer area, $/ft2
C, = cost for supplying 1 ft • lbf to pump the fluid through the inside of the tubes, $/ft ■ lbf
Ca = cost for supplying 1 ft ■ lbf to pump the fluid through the shell side of the exchanger, $/ft > lbf CT = total annual variable cost for heat exchanger and its operation, $/year Cu = cost of utility fluid, $/lb D = diameter or distance, ft D' = diameter, in.
Dc = clearance between tubes to give smallest free area across shell axis, ft De = equivalent diameter = 4 x hydraulic radius, ft E = power loss per unit of outside-tube heat-transfer area, ft • lbf/(hXft2); subscript i designates inside tubes, and subscript o designates outside tubes f(- = Fanning friction factor for isothermal flow, dimensionless f ' = special friction factor for shell-side flow, dimensionless Fa = correction factor for radiant heat transfer based on relative orientation of surfaces, dimensionless; defined by Eqs. (6) and (7) Fc = friction due to sudden contraction, ft • lbf/lbm Fe = friction due to sudden enlargement, ft 1 lbf/lbm
Fe = correction factor for radiant heat transfer based on emissivities and absorptivities of surfaces, dimensionless; defined by Eqs. (6) and (7) Fr = friction due to reversal of flow direction, ft • lbf/lbm Fs = safety factor in Eq. (29) to account for bypassing on shell side of exchanger, dimensionless Ft = correction factor on logarithmic-mean At for counterflow to give mean At, dimensionless; defined in Fig. 15-2 g = local gravitational acceleration, ft/(sXs)
gc = conversion factor in Newton's law of motion, 32.17 ft • lbm/(sXsXlbf) G = mass velocity inside tubes, lb/(hXft2)
Gs = shell-side mass velocity across tubes based on the minimum free area between baffles across the shell axis, lb/(hXft2) h = film coefficient of heat transfer, Btu/(hXft2X°F); subscript c indicates convection; subscript d represents dirt or fouling; subscript co indicates conduction hr = film coefficient for heat transfer by radiation, Btu/(hXft2X°F) Hy = hours of operation per year, h/year k = thermal conductivity, Btu/(hXft2X°F/ft); subscripts x, y, and z refer to direction of heat-flow path K — dimensional constant; defined in Table 4
Kc = constant in expression for evaluating friction due to sudden contraction, dimensionless
KF s= annual fixed charges including maintenance, expressed as a fraction of the initial cost for the completely installed unit, dimensionless K{ = constant for evaluation of B(, dimensionless; defined with Eq. (30) L = heated length of straight tube or length of heat-transfer surface, ft; if tubes in parallel are involved, L is the length of one tube n = constant, dimensionless tlb = number of baffle spaces = number of baffles plus 1, dimensionless n = number of tube passes, dimensionless
Nc = number of clearances between tubes for flow of shell-side fluid across shell axis, dimensionless NGt = Grashof number = L3p2g(3 At/fi2, dimensionless NPt = Prandtl number = cpix/k, dimensionless
Nr = number of rows of tubes across which shell fluid flows, dimensionless NRe = Reynolds number = DG/^l, dimensionless N, = total number of tubes in exchanger = number of tubes per pass Xnp, dimensionless
Ny = number of rows of tubes in a vertical tier, dimensionless heat-transfer equipment-design and costs <45
4 at rate of heat transfer, Btu/h
Q = amount of heat transferred in time, 6, Btu r = radius, ft
R = temperature ratio for evaluating FT, dimensionless; defined in Fig. 15-2
Rdw = combined resistance of tube wall and scaling or dirt factors, [Btu/(hXft2X°F)]_1; defined with Eq. (39).
5 = temperature ratio for evaluating FT, dimensionless; defined in Fig.
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