Numerical studies on the heat transfer characteristics of falling film evaporation on a horizontal elliptical tube for seawater desalination

• Published in: Desalination and water treatment 2021-01, Vol.210, p.31-43
• Main Authors: Balaji, D., Velraj, R., Murthy, M.V. Ramana
• Format: Article
• Language: English
• Subjects: Elliptical tubes; Ellipticity; Film heat transfer co-efficient; Fully developed thermal region
• ISSN: 1944-3986; 1944-3986
• DOI: 10.5004/dwt.2021.26596

This paper discusses the effect of elliptical tube geometry on the heat transfer performance of falling film evaporation over the horizontal heated plain tubes in comparison with circular tubes for seawater desalination. To study this, a two-dimensional CFD model was developed, compared and validated with published data available in the literature. A CFD simulation was carried out for varying liquid load, ellipticity (E) and corresponding changes in the film heat transfer co-efficient (HTC), liquid film thickness were recorded and analysed. Also novelty in finding the commencement of the fully developed thermal region over the tube from current simulation model is discussed. An attempt was also made to measure the thickness of the film around the tubes from the CFD model. Mechanisms that influences enhancement in heat transfer using the elliptical tubes were numerically investigated and discussed in the present work. Outputs from simulation model indicated that low value of liquid film thickness appears approximately at the angular position of the range between 90° and 110°. Also this study revealed that liquid film thickness decreases and HTC increases with the increase of ellipticity of the tube. Commencement angle of fully developed thermal region from top of tube shifted downward with the increase of the liquid load. For the same operating conditions, the elliptical tube gives 24%–26% more HTC and 8%–18% thinner film thickness compared with the circular tubes indicating better suitability of elliptical tubes for seawater desalination.