Measurement of Liquid Film Thickness around Horizontal Tube Bundle by Optical Technique for Optimizing Evaporator Design and Manufacturing

Abstract

This paper proposes the improvement of design and manufacturing of Falling Film Horizontal Tube Evaporators (FFHTE) through optimizing different parameters such as tubes pitch, tubes diameter and material and liquid film flow rate. These design and operational parameters have a significant influence on the hydrodynamic of the liquid film (eg: wetability of the tubes, scale deposition, heat transfer coefficient, etc.). Due to the complexity of the liquid film flow around the horizontal tube bundle, the experimental approach is preferred than modeling because it gives a better understanding of the phenomena occurring in the heat exchanger. In this paper one experiment was carried out to investigate liquid film flow around a single horizontal tube. A particular attention was taken for the measurement of liquid film thickness around the tube using a novel optical technique based on light reflection. The influence of the tubes pitch, tube diameter, height of the liquid distribution system and the liquid mass flow on the transitions between falling-film modes and film thickness is investigated and the results are compared to other data obtained from the literature. It was found that tubes wetability and heat transfer increased with increasing the vertical tube pitch. To account for fouling and heat transfer performance, a tube spacing value of 1.3 was recommended.