An intrusive method for film thickness measurement on smooth horizontal tubes for subcooled water

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

Falling film evaporation technique is widely used in different applications such as in heat exchangers in desalination devices, absorption/desorption-type chillers, OTEC (ocean thermal energy conversion primer), petrochemical, and chemical process industries, just to mention a few industries. However, in spite of numerous studies the complete understanding is not totally clear yet, even some basic phenomena such as the behavior the film thickness and its relationship with the heat and mass transfer coefficients. The objective of the present work is present the study of an intrusive method for measuring a descending film thickness employing subcooled water as the working fluid at atmospheric conditions. The method used a novel configuration (leverage effect) in which a micrometer reading has its precision improved. As a needle tip touches the liquid film, an electrical current flows in signalizing the tip position and, consequently, the film thickness. The current proposal presents an accuracy 22% when compared with the theoretical result of Nusselt.