Liquid process analytical systems

This section describes the phase change process for a single component on a molecular level, with both vaporization and condensation occurring simultaneously. Molecules escape from the liquid surface and enter the bulk vapor phase, whereas other molecules leave the bulk vapor phase by becoming attached to the liquid surface. Analytical expressions are developed for the absolute rates of condensation and vaporization in one-component systems. The net rate of phase change, which is defined as the difference between the absolute rates of vaporization and condensation, represents the rate of mass... 

Vol. 66 Solid Phase Biochemistry Analytical and Synthetic Aspects. Edited by William H. Scouten Vol. 67 An Introduction to Photoelectron Spectroscopy. By Pradip K. Ghosh Vol. 68 Room Temperature Phosphorimetry for Chemical Analysis. By Tuan Vo-Dinh Vol. 69 Potentiometry and Potentiometric Titrations. By E. P. Serjeant Vol. 70 Design and Application of Process Analyzer Systems. By Paul E. Mix Vol. 71 Analysis of Organic and Biological Surfaces. Edited by Patrick Echlin Vol. 72 Small Bore Liquid Chromatography Columns Their Properties and Uses. Edited by Raymond P.W. Scott... 

Of the analytical techniques available for process analytical measmements, IR is one of the most versatile, where all physical forms of a sample may be considered - gases, liquids, solids and even mixed phase materials. A wide range of sample interfaces (sampling accessories) have been developed for infrared spectroscopy over the past 20 to 30 years and many of these can be adapted for either near-lme/at-lme production control or on-line process monitoring applications. For continuous on-line measurements applications may be limited to liquids and gases. However, for applications that have human interaction, such as near-line measurements, then all material types can be considered. For continuous measurements sample condition, as it exists within the process, may be an issue and factors such as temperature, pressure, chemical interfer-ants (such as solvents), and particulate matter may need to be addressed. In off-line applications this may be addressed by the way that the sample is handled, but for continuous on-line process applications this has to be accommodated by a sampling system. 

True process analytics are based on automated systems. Automated instruments must be smaller, more rapid and robust than laboratory instruments and designed for unattended operation. Those most commonly used are based on spectroscopic, separation and electrochemical analytical techniques. Many of these are incorporated into or combined with flow injection analysis (FIA) systems in order to work well. Not all analytical methods lend themselves to automation. Analyses involving gases and liquids are most successfully automated while those using solid samples are most difficult to automate. And there will always be certain assays that are too complex or too costly to automate. 

These various simultaneous heat flow processes produce a dynamic, or transient, response in the temperatures of the container wall and the pressurizing gas, both of which also must be considered to be spacially dependent. This paper examines this transient process analytically and presents a solution for the temperatures of both the wall and pressurizing gas as continuous functions of space and time. These results are then compared with some experimental measurements on a liquid nitrogen system pressurized and discharged at 50 psia with gaseous nitrogen at various temperatures. 

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