Liquid side coefficient

U. Single water drop in air, liquid side coefficient / jy l/2 ki = 2 ), short contact times / J 1 lcontact times dp [T] Use arithmetic concentration difference. Penetration theory, t = contact time of drop. Gives plot for k a also. Air-water system. [lll]p.. 389... 

The liquid side coefficients are for straight mass transfer without chemical reaction and are therefore based on flow through the whole film of thickness Xq. 

The values of k a are practically independent of the gas velocity up to a critical value which depends on nozzle type, column diameter, and physical properties (P7, Mil) then increases with increasing gas velocity. Typical results are given in Fig. 24 for a shower nozzle. Moreover k a, kc, and a all increase as the gas velocity increases independently of the type of nozzle, the column size, the liquid flow rate, and probably the physical properties, as shown in Fig. 25. The interfacial area and true liquid-side coefficient increase with the liquid flow rate L (Fig. 24), owing to increased surface area, higher drop velocity, and increased circulation or... 

Values of the true liquid-side coefficient ki, are comparable to those in packed columns. 

A wall separates a gas from a liquid. The temperature of the gas, Tg, is different from that of the fluid, T,. It is proposed to increase the heat transfer between the gas and the liquid by adding fins to either the gas side or the liquid side. To which side must the fins be added for the best result Data Brass wall, k = 100 W/m-K, rectangular brass fins, 1 mm thick, 2.5 cm long, and spaced 2 mm apart. The gas-side and the liquid-side coefficients of heat transfer are hg = 10 and hi = 1,000 W/m2 K, respectively. 

Liquid-side coefficients. The liquid-side coefficient depends to a large extent on the velocity of the liquid over the heated surface. In most evaporators, and especially those handling viscous materials, the resistance of the liquid side controls the overall rate of heat transfer to the boiling liquid. In natural-circulation evaporators the liquid-side coefficient for dilute aqueous solutions is between 1500 and 3000 W/m -°C (300 and 600 Btu/ft -h- F). The heat flux may be conservatively estimated for nonfouling solutions from Fig. 15.13. 

Forced circulation gives high liquid-side coefficients even though boiling inside the tubes is suppressed by the high static head. The liquid-side coefficient in a forced-circulation evaporator may be estimated by Eq. (12.32) for heat transfer to a nonboiling liquid if its constant 0.023 is changed to 0.028. ... 

Many equations have been proposed for the mass transfer coefficients. For tht liquid side coefficient, Laurent and Charpentier [11] recommend Mohunta equation [13]. 

T. Single liquid drops in gas, gas side coefficient =2 + ANiS,Ni [E] Used for spray drying (arithmetic partial pressure difference). [88] p. 489... 

Liquid-Film Coefficients (Physical) and (Reactive) The gas-side resistance can be eliminated by employing a pure gas, thus leaving the liquid film as the only resistance. Alternatively, after the gas-film resistance has been found experimentally or from corre-... 

Sinek and Young present a design procedure for predicting liquid-side falling film heat transfer coefficients within 20% and overall coefficients within 10%. 

If the tube bundle is to be large in diameter, it is possible that the liquid head will suppress the boiling in the lower portion of the horizontal bundle thereby actually creating a liquid heating in this region, with boiling above this. Under such situations, the boiling in the unit cannot be considered for the full volume hence, there should be two shell-side coefficients calculated and the resultant areas added for the total. 

Here, kg and ki are the gas-side and liquid-side mass transfer coefficients. Their units are identical to those for Kg and Ki, m/s. Like the overall coefficients, they are usually measured and reported as the composite quantities kgAj and kiAi with SI units of s. ... 

The measurement of liquid side gas - liquid mass transfer coefficient kia, showed that the value of kia increase with increasing rotation speed (V) and gas flow rate (Qg). hi the present research, the effect of impeller rotation on mass transfer coefficient was more significant than the effect of gas flow rate. The following correlation was obtained kia =1.7 x 10 ... 

The molar transfer rate coefficient kG (gas side) or kL (liquid side) (m s-1) can be defined as the ratio between the intrinsic molecular diffusivity of the solute gas A in the gas or liquid matrix and the diffusion lengths dG or dL (Eqs. (2) and (3)). The diffusion lengths depend on the reactor flow and mixing properties. 

Introducing the solid-liquid partition coefficients Dt and expanding the left-hand side for constant M... 

The gas film coefficient is dependent on turbulence in the boundary layer over the water body. Table 4.1 provides Schmidt and Prandtl numbers for air and water. In water, Schmidt and Prandtl numbers on the order of 1,000 and 10, respectively, results in the entire concentration boundary layer being inside of the laminar sublayer of the momentum boundary layer. In air, both the Schmidt and Prandtl numbers are on the order of 1. This means that the analogy between momentum, heat, and mass transport is more precise for air than for water, and the techniques apphed to determine momentum transport away from an interface may be more applicable to heat and mass transport in air than they are to the liquid side of the interface. 

The values of the film coefficient for liquids without phase change are usually larger than those for gases, by one or two orders of magnitude. Nonetheless, the liquid-side heat transfer resistance may be the major resistance in an equipment heated by saturated steam. Film coefficient for liquids without phase change can be predicted by correlations such as those in Equations 5.8a, 5.12a, or 5.13. 

In cases where the major resistance is in the liquid phase, the ratio RL/ RT= 1 and the simplification can be made that the over-all coefficient is equal to the liquid film coefficient. Which resistance dominates has to be determined from the ratio kLa / (kGa Hc) (Table 3-3). For compounds with a low Hc such as semi-volatile organic compounds, both resistances can be important (Libra, 1993). In oxygen transfer the liquid-side resistance dominates and KLa = kLa. This is also true for most of the cases in ozone mass transfer, unless there is strong mass transfer enhancement by very fast or instantaneous reactions of... 

Fortunately changes in k,a due to mass transfer enhancement from ozone decay can be neglected, as Huang et al. (1998) showed by example of cyanide ozonation in strongly basic solutions (pH = 12-14) in a system where the value of the purely physical liquid side mass transfer coefficient was not too low (kL° > 0.03 cm s l). This is supported further by the results from several ozonation experiments, which showed that no ozone decay occurs in the liquid film at lower pH values (phenol, pH = 10 (Metha et ah, 1989) 4-nitrophenol, pH = 8.5 (Beltran et ah, 1992 a)). 

Finally, in Fig. 3.4-12 [24], a comparison is given for the overall, gas-based, mass transfer coefficient for several liquid-to-gas and solid-to-gas packed beds and column systems. In Fig. 3.4-12, for a given data point, the vertical distance up to the Tan et al. [27] correlation (which is for a solid-to-fluid boundary layer) would provide a measure of the liquid-side mass-transfer resistance associated with the liquid. This is so because amount of the large gas... 

The second section presents a review of studies concerning counter-currently and co-currently down-flow conditions in fixed bed gas-liquid-solid reactors operating at elevated pressures. The various consequences induced by the presence of elevated pressures are detailed for Trickle Bed Reactors (TBR). Hydrodynamic parameters including flow regimes, two-phase pressure drop and liquid hold-up are examined. The scarce mass transfer data such gas-liquid interfacial area, liquid-side and gas-side mass transfer coefficients are reported. 

The influence of pressure on the mass transfer in a countercurrent packed column has been scarcely investigated to date. The only systematic experimental work has been made by the Research Group of the INSA Lyon (F) with Professor M. Otterbein el al. These authors [8, 9] studied the influence of the total pressure (up to 15 bar) on the gas-liquid interfacial area, a, and on the volumetric mass-transfer coefficient in the liquid phase, kia, in a countercurrent packed column. The method of gas-liquid absorption with chemical reaction was applied with different chemical systems. The results showed the increase of the interfacial area with increasing pressure, at constant gas-and liquid velocities. The same trend was observed for the variation of the volumetric liquid mass-transfer coefficient. The effect of pressure on kia was probably due to the influence of pressure on the interfacial area, a. In fact, by observing the ratio, kia/a, it can be seen that the liquid-side mass-transfer coefficient, kL, is independent of pressure. 

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