Superficial mass velocity

Dp = particle diameter, Df = vessel diameter, (note that D /Df has units of foot per foot in the equation), G = superficial mass velocity, k = fluid thermal conductivity, [L = fluid viscosity, and c = fluid specific heat. Other correlations are those of Leva [Jnd. Eng. Chem., 42, 2498 (1950)] ... 

G mass flow rate, kg/s superficial mass velocity, Ib/hfft, kg/m2 s... 

Total pressure atm Superficial mass velocity (lb-moles/hr-ft2) Initial rate lb-moles S02 Temperature, T (°F) Grams catalyst... 

G = superficial mass velocity based on total cross-sectional area ... 

Notice that the superficial mass velocity G is constant throughout the bed, but that p will vary for compressible fluids. When the pressure drop is small compared with the absolute pressure, equation 12.7.4 may be used for gases by employing the arithmetic average of the inlet and... 

G is the superficial mass velocity in pounds mass per hour per square foot... 

This equation can also be rewritten in terms of the superficial mass velocity G, which does not vary along the length of the reactor. 

One of the first things that should be done in the analysis is to determine if pressure variations along the length of a reasonable-size reactor will be significant for the specified operating conditions. This will require a knowledge of the superficial mass velocity through the tubes. This quantity may be calculated from the tube dimensions and the inlet flow rate and... 

Perhaps the simplest classification of flow regimes is on the basis of the superficial Reynolds number of each phase. Such a Reynolds number is expressed on the basis of the tube diameter (or an apparent hydraulic radius for noncircular channels), the gas or liquid superficial mass-velocity, and the gas or liquid viscosity. At least four types of flow are then possible, namely liquid in apparent viscous or turbulent flow combined with gas in apparent viscous or turbulent flow. The critical Reynolds number would seem to be a rather uncertain quantity with this definition. In usage, a value of 2000 has been suggested (L6) and widely adopted for this purpose. Other workers (N4, S5) have found that superficial liquid Reynolds numbers of 8000 are required to give turbulent behavior in horizontal or vertical bubble, plug, slug or froth flow. Therefore, although this classification based on superficial Reynolds number is widely used... 

Note that while the fluid density may be a function of the pressure in the bed in a compressible flow, the superficial mass velocity is constant. The Ergun equation in the form given in eq. (3.450) is more convenient when analyzing the effects of pressure drop in the fluid density. 

Gfm = the superficial mass velocity based on the minimum fluidization velocity... 

G superficial mass velocity of gas (based on cross-sectional area of empty tower), lb/(hXf 2)... 

No good methods are available for calculating heat-transfer coefficients when appreciable subcooling of the condensate is required. A conservative approach is to calculate a superficial mass velocity assuming the condensate fills the entire tube and use the equations presented above for single-phase heat transfer inside tubes. This method is less conservative for higher condensate loads. 

In using this friction factor for a tubular reactor, the Reynolds number is evaluated at Borne estimated average condition, and then the corresponding friction factor is used for the whole bed. In calculating the axial pressure profile, the average composition and temperature in a cross section are used to estimate the density of the fluid, and this density is used with the average superficial mass velocity to estimate the axial derivative of pressure. 

G superficial mass velocity N parameter used in Barkelew s cri-... 

Here jh — ( ioo/Cph( ) (Cp(i/A )fand hioc is the local heat-transfer coefficient G is the superficial mass velocity the subscript f denotes properties evaluated at the film temperature Tt = i Ts + Ty,). Here Ts refers to the surface temperature and Th to the bulk fluid temperature. The quantity l/ is an empirical coefficient that depends on the particle shape, e.g., yp = 1.0 for spheres and yp = 0.91 for cylinders. Values of yp for other shapes are tabulated elsewhere (B2, B3). 

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