Variable gas velocity

The boundary layers for these three variables (gas velocity, temperature, and concentration) may sometimes coincide, although in slow reactions, the profiles of velocity and temperature may be fully developed at an early stage while the deposition reaction is spread far downstream the tube. 

Ideally, the axial velocity through the cross-flow unit should be greater than about 4-6 m/s to minimize the boundary layer of particles near the membrane surface. The wax permeate flow from the filter is limited by a control valve actuated by a reactor-level controller. Hence, a constant inventory of slurry is maintained within the SBCR system as long as the superficial gas velocity remains constant. Changes in the gas holdup due to a variable gas velocity are calculated... 

Model for a Nonisobaric Column with Variable Gas Velocity... 

Deckwer,W.-D. "Non-isobaric bubble columns with variable gas velocity". Chem.Engng.Sci. 31 0 976 ) 309. 

Due to the variable gas velocity and the nonlinear rate law the model equations represent a set of coupled nonlinear algebraic and differential equations of boundary value type which must be solved numerically. For this purpose the nonlinear equations are entirely linearized using the cjuasilinearization technique (12) and the linearized differential equations are solved using the orthogonal collocation method based on shifted Legendre polynomials (13). 

Symoniak, M.F., Correlation for sizing adsorption systems, Chem. Eng. (N.Y.), 6 October, 172-174 (1969). Zwiebel, 1., Fixed-bed adsorption with variable gas velocity due to pressure drop, Ind. Eng. Chem. Fund.. 8(4),... 

In order to demonstrate the effect of gas flow variations due to absorption and reaction. Fig. 5 compares the conversion of model <13> with constant and with variable gas velocity for various values of It is observed that the discrepancy between both models depends only in a small extent on the individual values of Da, Y> St, and m as long as cl 0.5. Therefore, the curves shown in Fig. 5 present average values. Only for c = -1 a larger difference was found. However, no clear dependence on the individual parameters could be discerned. Therefore, the area is shaded in... 

For the more general case with variable gas velocity due to the counteracting effects of absorption and expansion and vvith consideration of a fast reaction of order m in A and n in B the governing balance equation of the gas phase is given by... 

Deckwer, W.-D. Non-Isobaric Bubble Columns with Variable Gas Velocity Chem. Eng. Sci. 31 (1976) 309-317. 

The variation of the gas hold up and the interfacial area are taken into account by eqns (1) and (4), respectively. Assumption (8) accounts for a variable gas velocity. Therefore an additional relation is required. This is obtained from a balance on the inerts which yields ... 

Equation 7-22 can be used to predict the efficiency when the overall mass transfer coefficient for a given absorber is known. The overall mass transfer coefficient is experimentally determined from pilot plant and full-sized units. For the GEESI open spray tower, the overall mass transfer coefficient, K a, has been correlated to three variables gas velocity, liquid density, and inlet SO2 concentration ... 

Spray Correlations. One of the most important aspects of spray characterization is the development of meaningful correlations between spray parameters and atomizer performance. The parameters can be presented as mathematical expressions that involve Hquid properties, physical dimensions of the atomizer, as well as operating and ambient conditions that are likely to affect the nature of the dispersion. Empirical correlations provide useful information for designing and assessing the performance of atomizers. Dimensional analysis has been widely used to determine nondimensional parameters that are useful in describing sprays. The most common variables affecting spray characteristics include a characteristic dimension of atomizer, d Hquid density, Pjj Hquid dynamic viscosity, ]ljj, surface tension. O pressure, AP Hquid velocity, V gas density, p and gas velocity, V. ... 

P. Y. McCormick [Chem. Png. Prog., 58(6), 57 (1962)] compared all available data. The comparisons showed that flight geometry and shell speed should be accounted for in the value of K. He suggested that shell rotational speed and flight number and shape must affect the overall balance however, data for evaluating these variables separately are not available. Also, it is not beheved that the effect of gas velocity... 

Many experimental studies of entrainment have been made, but few of them have been made under actual distillation conditions. The studies are often questionable because they are hmited to the air-water system, and they do not use a realistic method for collecting and measuring the amount of entrainment. It is clear that the dominant variable affecting entrainment is gas velocity through the two-phase zone on the plate. Mechanisms of entrainment generation are discussed in the subsection Liquid-in-Gas Dispersions. ... 

Under controlled conditions (e.g., in the laboratory), the inherent collection efficiency of fabric filters approaches 100 per cent. In actual operation, it is determined by several variables, in particular the properties of the dust to be removed, choice of filter fabric, gas velocity, method of cleaning, and cleaning cycle. Inefficiency usually results from bags that are poorly installed, torn, or stretched from excessive dust loading and excessive pressure drop. 

Most of heat transfer correlations are based on data obtained in flow boiling from relatively large diameter conduits and the predictions from these correlations show considerable variability. Effects of superficial liquid and gas velocity on heat transfer in gas-liquid flow and its connection to flow characteristics were studied by Hetsroni et al. (1998a,b, 2003b), Zimmerman et al. (2006), Kim et al. (1999), and Ghajaret al. (2004). However these investigation were carried out for tubes of D = 25—42 mm. These data, as well as results presented by Bao et al. (2000) in tubes of L> = 1.95 mm and results obtained by Hetsroni et al. (2001), Mosyak and Hetsroni (1999) are discussed in the next sections to clarify how gas and liquid velocities affect heat transfer. Effects of the channel size and inclination are considered. 

One of the advanced concepts for capturing CO2 is an absorption process that utilizes dry regenerable sorbents. Pure sodium bicarbonate from Dongyang Chemical Company and spray-dried sorbents were used to examine the characteristics of CO2 reaction in a flue gas environment. The chemical characteristics were investigated in a fast fluidized reactor of 0.025 m i.d., and the effects of several variables on sorbent activity, including gas velocity (1.5 to 3.5 m/s), temperature (40 to 70 °C), and solid concentration (15 to 25 kg/m /s)], were examined in a fast fluidized-bed. Spray-dried Sorb NX30 showed fast kinetics in the fluidized reactor. 

The reactivities of pure NaHCOa solid. Sorb NHR, NHR5, and NX30 sorbents were examined in a fast fluidized bed reactor. The CO2 removal of the pure NaHCOa solid increased from 3 % to 25 % when the variables were altered. Removal increased as gas velocity was decreased, as the carbonation temperature was decreased, or as the solid circulation rate was increased. The CO2 removal of Sorb NHR and NHR5 was initially maintained at 100 % for a short period of time but quickly dropped to a 10 to 20 % removal. However, the Sorb NX30 sorbent showed fast kinetics in the fast fluidized reactor, capturing all of the 10 % of the CO2 in the flue gas within 3 seconds in the fast fluidized reactor. 

Now, from its essential notion, we have the feedback interconnection implies that a portion of the information from a given system returns back into the system. In this chapter, two processes are discussed in context of the feedback interconnection. The former is a typical feedback control systems, and consists in a bioreactor for waste water treatment. The bioreactor is controlled by robust asymptotic approach [33], [34]. The first study case in this chapter is focused in the bioreactor temperature. A heat exchanger is interconnected with the bioreactor in order to lead temperature into the digester around a constant value for avoiding stress in bacteria. The latter process is a fluid mechanics one, and has feedforward control structure. The process was constructed to study kinetics and dynamics of the gas-liquid flow in vertical column. In this second system, the interconnection is related to recycling liquid flow. The experiment comprises several superficial gas velocity. Thus, the control acting on the gas-liquid column can be seen as an open-loop system where the control variable is the velocity of the gas entering into the column. There is no measurements of the gas velocity to compute a fluid dynamics... 

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