Impellers rotational speed

Blend time tb, the time required to achieve a specified maximum standard deviation of concentration after injection of a tracer into a stirred tank, is made dimensionless by multipfying by the impeller rotational speed ... 

Head (h) varies as square of the impeller rotational speed. 

The shear rate calculated from impeller rotational speed is used to identify a viscosity from a plot of viscosity versus shear rate determined with a capillaiy or rotational viscometer. Next Nr is calculated, and Np is read from a plot like Fig. 18-17. 

Impeller Reynolds Number a dimensionless number used to characterize the flow regime of a mixing system and which is given by the relation Re = pNDV/r where p = fluid density, N = impeller rotational speed, D = impeller diameter, and /r = fluid viscosity. The flow is normally laminar for Re <10, and turbulent for Re >3000. 

Characteristic length [Eq. (121)] L Impeller diameter also characteristic distance from the interface where the concentration remains constant at cL Li Impeller blade length N Impeller rotational speed also number of bubbles [Eq, (246)]. N Ratio of absorption rate in presence of chemical reaction to rate of physical absorption when tank contains no dissolved gas Na Instantaneous mass-transfer rate per unit bubble-surface area Na Local rate of mass-transfer per unit bubble-surface area Na..Average mass-transfer rate per unit bubble-surface area Nb Number of bubbles in the vessel at any instant at constant operating conditions N Number of bubbles per unit volume of dispersion [Eq. (24)] Nb Defined in Eq. (134)... 

This research used mechanically agitated tank reactor system shown in Fig. 1. The reactor, 102 mm in diameter and 165 mm in height, was made of transparant pyrex glass and was equipped with four baffles, 120 mm in length and 8 mm in width, and six blades disc turbine impeller 45 mm in diameter and 12 mm in width. The impeller was rotated by electric motor with digital impeller rotation speed indicator. Waterbath thermostatic, equipped with temperature controller was used to stabilize reactor temperature. Gas-liquid mass transfer coefficient kia was determined using dynamic oxygenation method as has been used by Suprapto et al. [11]. 

The evaluation of acetaldehyde oxidation process was carried out by aeration of acetaldehyde solution and analyzing the concentration of acetic acid using gas chromatography HP 5890 with detector FID equipped with PEG Column in 15 minutes time interval. The gas flow rate Qg), impeller rotation speed N) and temperature (7) were varied. 

In the range of 500 to 900 rpm, Fig. 3 and 4 showed that impeller rotation speed does not affect significantly on reaction conversion for relatively long reaction time (above 60 minutes). Apparently, the hydrodynamic condition of liquid in the reactor was sufficiently turbulent by aeration. 

Increasing of temperature and gas flow rate can enhance the selectivity, however the selectivity decrease with increasing impeller rotation speed (Fig. 5 and 6). In general, increasing selectivity was followed by decreasing of conversion, as shown in Fig. 7. 

Liquid phase oxidation reaction of acetaldehyde with Mn acetate catalyst can be considered as pseudo first order irreversible reaction with respect to oxygen, and the reaction occurred in liquid film. The value of kinetic constant as follow k/ = 6.64.10 exp(-12709/RT), k2 = 244.17 exp(-1.8/RT) and Lj = 3.11.10 exp(-13639/RT) m. kmor. s. The conversion can be increased by increasing gas flow rate and temperature, however the effect of impeller rotation on the conversion is not significant. The highest conversion 32.5% was obtained at the rotation speed of 900 rpm, temperature 55 C, and gas flow rate 10" m. s. The selectivity of acetic acid was affected by impeller rotation speed, gas flow rate and temperature. The highest selectivity of acetic acid was 70.5% at 500 rpm rotation speed, temperature of 55 C... 

It is known that the power required to drive a fan depends upon the impeller diameter (D), the impeller rotational speed (co), the fluid density (p), and the volume flow rate (0. (Note that the fluid viscosity is not important for gases under normal conditions.)... 

Tank diameter D Impeller rotational speed N Fluid viscosity p. 

The variables involved in the performance of a centrifugal pump include the fluid properties (p, and p), the impeller diameter (cl), the casing diameter (/)), the impeller rotational speed (N), the volumetric flow rate of the fluid (0, the head... 

Kramers et al. (1953) were among the first to study mixing times as a function of baffle position and impeller rotational speed. Results of several experimental studies have been combined into empirical correlations relevant to industrial applications (Prochazka and Landau, 1961 Hoogendoorn and Den Hartog, 1967 Sano and Usui, 1985 Grenville, 1992 Ruszkowski, 1994 Nienow, 1997). Grenville and Nienow (2004) present a concise review as to such correlations. 

Impeller design, number of impellers, rotation speed. 

Nomenclature d =tube diameter, D = impeller diameter, L = plate coil height, N = impeller rotational speed, nb = number of baffles or of vertical tubes acting as baffles, T = tank diameter, Z = liquid height... 

A cylindrical tank (1.22 m diameter) is filled with water to an operating level equal to the tank diameter. The tank is equipped with four equally spaced baffles, the width of which is one tenth of the tank diameter. The tank is agitated with a 0.36 m diameter, flat-blade disk turbine. The impeller rotational speed is 4.43 rps. The air enters through an open-ended tube situated below the impeller and its volumetric flow rate is 0.0217 m3/s at 1.08 atm and 25°C. Calculate ... 

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