Vaporization forced convection

Tank Cells. A direct extension of laboratory beaker cells is represented in the use of plate electrodes immersed into a lined, rectangular tank, which may be fitted with a cover for gas collection or vapor control. The tank cell, which is usually undivided, is used in batch or semibatch operations. The tank cell has the attraction of being both simple to design and usually inexpensive. However, it is not the most suitable for large-scale operation or where forced convection is needed. Rotating cylinders or rotating disks have been used to overcome mass-transfer problems in tank cells. An example for electroorganic synthesis is available (46). 

Klausner JF, Mei R, Bernard D, Zeng L (1993) Vapor bubble departure in forced convection boiling. Int J Heat Mass Transfer 36 651-661... 

Katto Y (1978) A generalized correlation for critical heat flux for the forced convection boihng in vertical uniformly heated round tubes. Int J Heat Mass Transfer 21 1527-1542 Khrustalev D, Faghri A (1996) Fluid flow effect in evaporation from liquid-vapor meniscus. ASME J Heat Mass Transfer 118 725-747... 

A correlation for the heat transfer coefficient in the region of forced-convection vaporization can be expressed in the form... 

The primary mode of heat transfer at the wall is forced convection of the vapor phase. As the liquid does not wet the heating surface during film boiling, heat transfer due to drop-wall collisions is relatively small, resulting in low wall-drop heat transfer (only a few percent of the total heat input). Most of the droplet evaporation occurs because of vapor-drop heat transfer. Just after dryout, the... 

Kast, W., 1964, Significance of Nucleating and Non-stationary Heat Transfer in the Heat Exchanger during Bubble Vaporization and Droplet Condensation, Chem. Eng. Tech. 36(9) 933-940. (2) Katto, Y., 1981, General Features of CHF of Forced Convection Boiling in Uniformly Heated Rectangular Channels, Ini. J. Heat Mass Transfer 24.14131419. (5)... 

Levy, S., 1966, Forced Convection Subcooled Boiling—Prediction of Vapor Volumetric Fraction, Rep. 

Schrock, V. E., and L. M. Grossman, 1959, Forced Convection Boiling Studies, Forced Convection Vaporization Project—Final Rep. 73308 UCX 2182, University of California, Berkeley, CA. (4) Schrock, V. E., and L. M. Grossman, 1962, Forced Convection Boiling in Tubes, Nuclear Sci. Eng. 12 474-480. (4)... 

Consider a tube heated uniformly at a heat flux q/A fed with saturated water at the base at a velocity Fo. For this velocity and heat flux, nucleate boiling will take place, and a temperature difference aTo will be established. At some distance up the tube vaporization will occur and increase the volumetric flow of material and hence the velocity to, say, Fi. The line for forced convective heat transfer meets the boiling curve below the heat flux of q/A and so nucleate boiling will still be the mode of heat transfer and the temperature difference AT, and hence the heat transfer... 

Our discussion of film condensation so far has been limited to exterior surfaces, where the vapor and liquid condensate flows are not restricted by some overall flow-channel dimensions. Condensation inside tubes is of considerable practical interest because of applications to condensers in refrigeration and air-conditioning systems, but unfortunately these phenomena are quite complicated and not amenable to a simple analytical treatment. The overall flow rate of vapor strongly influences the heat-transfer rate in the forced convection-condensation system, and this in turn is influenced by the rate of liquid accumulation on the walls. Because of the complicated flow phenomena involved we shall present only two empirical relations for heat transfer and refer the reader t.o Rohsenow [37] for more complete information. 

If boiling is maintained for a sufficiently long length of tube, the majority of the flow area will be occupied by vapor. In this instance the vapor may flow rapidly in the central portion of the tube while a liquid film is vaporized along the outer surface. This situation is called forced-convection vaporization and... 

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