BRIEFS Summary of papers published in this month’s research quarterly, I@EC Process Design and Development DYNAMICS OF A RADIANT DRYER WITH COUNTERCURRENT AIR FLOW
Dynamic response to heat input changes in an infrared dryer with countercurrent air flow was studied. A semiempirical relationship between the empirical Ziegler-Nichols constants and the drying variables was obtained. In responding to heat changes in any one of three sections, dead time corresponded to the transport time from the section exit to the measuring point plus a constant. The experimental time constants were related best with two pseudo-time constants calculated for each run, one for single sections and another for all sections possibly affected. Both were based on deviations with time from the original moisture-position profile. A “weighted” combination of these values gave the best estimates obtained.
M . E. Findley and M . W. Maloney, Auburn University,Auburn, Ala. IND.ENG.CHEM.PROCESS DESIGN DEVELOP. 3,89-96( 1964) A MODIFIED MOVING BED GRAIN DRYER
A method for optimal design of a modified moving bed grain dryer based on a discrete version of the Maximum Principle. Uniform distribution of the air across the complete length of a conventional moving bed dryer is generally a difficult task. Therefore, it is proposed to modify it by dividing the air supply channel in several equally divided sections so that the air supply rate to each section can be independently manipulated to achieve the optimal use of the air, First a set of general recurrence equations which relate the optimal operating conditions and control actions is established. The equations are applied to a specific example of designing a three-stage sorghum grain dryer.
Y. K. Ahn, H. C. Chen, L. T. Fan, and C. G. Wan, Kansas State University, Manhattan, Kan. IND.ENG.CHEM.PROCESS DESIGNDEVELOP. 3,96-100 (1964) NEW METHOD FOR SIMULATION OF MULTICOMPONENT DISTILLATION
A new method for the simulation of multicomponent petroleum distillation columns takes advantage of the power of mathematical programming techniques for computing the equilibrium states of physicochemical processes. The procedure is general and is able to incorporate changes of phase, external sources or sinks of mass or energy, and differential equations which describe system dynamics if they are relatively slow with respect to the chemical dynamics. By use of the Gibbs theorem, a chemical equilibrium may be defined in terms of the thermodynamic free energy of the components, the total free energy being minimized at equilibrium. A (nonlinear) free energy function is defined and then minimized under the natural physical (linear) restraints of the system. O n the analog computer, the solution method is by steepest descent. A digital solution has also been programmed.
E. C. Deland and M . B. Wolf, The RAND Corp., Santa Monica, Calif. IND.END.CHEM.PROCESS DESIGN DEVELOP. 3,100-106 (1964) A STATISTICAL CORRELATION OF THE EFFICIENCY OF PERFORATED TRAYS
The efficiencies of perforated trays were determined for the system methanol-air-water at atmospheric pressure. The effects of gas mass velocity, liquid mass velocity, hole diameter, weir height, and tray length upon Murphree tray efficiency were determined in a series of statistically designed experiments. Tray hydraulic data were also determined for use in a model to be utilized in the scale-up of small column data for commercial design. This model relates operating and design variables to the residence times of gas and liquid upon the tray by means of a two-constant equation.
Ray N. Finch and Matthew Van Winkle, The University of Texas, Austin 7.2, Tex.
IND.END.CHEM.PROCESS DESIGN DEVELOP. 3,106-116 (1964)
HEAT TRANSFER THROUGH LOW-DENSITY CELLULAR MATERIALS
Commercial acceptance of rigid foams blown with fluorocarbons is motivated largely by their superior thermal insulating characteristics. However, because the conductivities of such materials tend to increase, long-term performance of foam-containing products has been defined only by experience. An obvious need for a predictive function led to the synthesis of the model proposed here, which describes foam conductivity in terms of its complex fundamentals. Potential refinements are anticipated, since detailed confirmation awaits the further development of foam technology. In its present form, the model can be used to evaluate product designs empirically.
R. H. Harding, Union Carbide Corp., South Charleston, W. Va. IND.END.CHEM. PROCESS DESIGN DEVELOP. 3,117-125 (1964) POLARIZATION CHARACTERISTICS OF ELECTRODIALYTIC DEMINERALIZATION
The study of polarization characteristics as a function of velocity, direction of flow of the brine stream, and feed concentration was undertaken. New correlations between the limiting current density and product normality were established for both NaCl and diluted San Francisco Bay water feeds. A new phenomenon, termed “false polarization,” was observed while operating a nonstaged pilot-plant-size stack. The findings described are aimed to help to understand the different factors involved in polarization. This phenomenon, at present, is one of the limiting factors in the desalination of brackish waters by electrodialysis.
Susan A . Weiner, Pascal M . Rapier, and Walter K. Baker, Sea Water ConversionLaboratory, Universitv of California,Berkeley, Calif. IND.ENG.CHEM.PROCESS DESIGNDEVELOP. 3, 126-129 (1964) VARIABLE DENSITY EFFECTS AND AXIAL DISPERSION IN CHEMICAL REACTORS
The effects of variable density on conversion in chemical reactors with axial dispersion have been considered for laminar and turbulent flow models. For the turbulent flow case the density effects tend to cancel if ratios with respect to piston flow are used. This is not true of the results for the laminar flow model.
J . M . Douglas, The Atlantic Rejining Co., Glenolden, Pa., and K. B. Bischoff, The University of Texas, Austin, Tex.
IND.ENG.CHEM.PROCESS DESIGN DEVELOP. 3, 130-133 (1964) HYDROMECHANICAL METHOD TO INCREASE THE EFFICIENCY OF ALGAL PHOTOSYNTHESIS
Results of some experiments on a method to increase the efficiency of light utilization by dense algal cultures are given. The method involves subjecting an algal cell suspension to a time-dependent pattern of light and dark, so that advantage is taken of “flashing light effects.” Theoretical studies show that controlled patterns of light and dark are needed to yield appreciable increases in efficiency. Algal cell suspensions were placed in the annular space between two concentric cylinders ; the inner cylinder was rotated and the outer cylinder was fixed. The resulting fluid motion-Taylor vortices-and the inhomogeneous light field in dense suspensions provided the controlled, time-dependent pattern of light and dark. Experiments indicated that rate of photosynthesis increases with increasing rotor speed, and that flashing light effects rather than enhanced mass transfer rates cause the observed increase. Highest efficiencies were found at high suspension densities, low incident light intensity, and high rotor speeds.
R. L. Miller, A. G. Fredrickson, A. H. Brown, and H. M . Tsuchiya, University of Minnesota, Minneapolis, Minn. IND.ENG.CHEM.PROCESS DESIGN DEVELOP. 3,134-143 (1964) (Continued on page 79)
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