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New data have been obtained on vaporization of water from rippling and nonrippling films in a countercurrent wetted-wall tower. Other similar data in the literature have been analyzed, and an effect of liquid Reynolds number on gos phase mass transfer has been shown to exist. Discrepancies in much of the literature data can be explained on this basis.The data on vaporization of water from rippling films have been correlated. The data on nonrippling films were correlated when the gas Reynolds number was calculated relative to the water surface.Attempts to correlate data on vaporization of pure liquids in a wetted-wall tower brought to attention various discrepancies in the available literature. Data obtained in this laboratory on vaporization of water into air flowing countercurrently indicated that the gas phase mass transfer coefficient was affected by liquid flow rate. In most pre- indicated that liquid flow conditions affect surface area and gas phase pressure drop and therefore might be expected to influence the gas mass transfer process.Hydrodynamic studies related to wetted-wall columns are well summa- Theoretical derivations (7, 2 2 ) , predict a ratio of 1.5 for surface velocity to average velocity when the liquid film is in true laminar flow with no gas flow. Jackson, Johnson, and Ceaglske The first comprehensive study of vaporization in a wetted-wall tower was made by Gilliland and Sherwood ( 1 2 ) who obtained data on both parallel and counterflow vaporization. Although the volumetric flow rate of the liquid was maintained approximately constant in all of this work and was well into the rippling range for the various liquids, the N R~~ varied considerably owing to differences in viscosity and density. In correlating their data Gilliland and Shenvood found a dependence on the direction of gas flow when N ' R~~ was used. However when gas Reynolds number calculated relative to the pipe wall was used, both parallel and counterflow data could be represented by the same correlation. This was the basis for the use of N R e g by later workers correlating this type of data.An

A total of 15 bileaflet mechanical heart valves were studied in a pulse duplicator at the Helmholtz Institute (Aachen, Germany) under conditions approximating first, a physiological pressure curve and subsequently, a sinusoidal pressure curve. In this study Edwards-Duromedics valves of the modified specification were compared with the earlier version of the Edwards-Duromedics valve as well as with St. Jude Medical valves. Each valve was tested at a series of nine (9) conditions. At each condition, without altering the valve installation or the systemic conditions, each valve was filmed by two separate video systems: the Helmholtz Institute strobe light system and a high speed video recording system. All data, as recorded by each system, was then independently analyzed by both of the two contributing groups and subsequently compared. In this manner, it was possible to objectively verify not only the consistency of the data obtained, but to also determine the relative reliability of the methods for cavitation threshold detection.

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