Falling-film flows, heat transfer, and potential advances in solar desalination

A liquid film falling between horizontal tubes is known to manifest three main flow regimes or modes. In the droplet mode, liquid falls from the tubes as droplets impinging on the tubes below. At increased flow rates, the liquid departs from regularly spaced sites as a continuous, steady flow, forming the jet or column mode. At the highest flow rates, the liquid typically falls as a continuous film spanning the inter-tube space, in the sheet mode. The flow regime has important implications on heat transfer and the operation of falling-film heat exchangers. The intermittency of the droplet mode can raise concerns about surface de-wetting, but the large flow rates of the sheet mode are associated with a thicker film, both tend to decrease heat transfer. A discussion of these flows and a basis for interpreting mode transitions will be followed by an exploration of opportunities arising from new manufacturing methods and surface enhancement for solar desalination applications.

After completing a doctorate at Purdue University, Anthony Mark Jacobi joined the Johns Hopkins University. In 1992, he moved to the University of Illinois at Urbana-Champaign, where from 1997 to 2015 he served as Associate Director and then Co-Director of the Air Conditioning and Refrigeration Center (an NSF-founded I/UCRC). He is currently Kritzer Distinguished Professor and Head of Mechanical Science and Engineering, and Fellow of ASME and ASHRAE.