Library Subscription: Guest
Home Archives Officers Future meetings Assembly for International Heat Transfer Conferences

Liquid Film Wave Patterns and Dryout in Microgap Channel Annular Flow

DOI: 10.1615/IHTC15.eec.009808
pages 1941-1955

Caleb A. Holloway
Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, USA

Avram Bar-Cohen
Laboratory of the Thermal Management of Electronics, Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455; and Defense Advanced Research Projects Agency (DARPA), Microsystems Technology Office, University of Maryland, College Park, MD

Darin Sharar
University of Maryland


KEY WORDS: Two-phase/Multiphase flow, Electronic equipment cooling, Flow Patterns

Abstract

Two-phase flow in microgap channels offers highly potent thermal management capability and is the foundation for the emerging “embedded cooling” paradigm of electronic cooling. While heat transfer and pressure drop in such flows are intimately tied to their distinct forms of vapor-liquid aggregation, insufficient attention has been paid to characterizing the wave patterns and dryout in high-quality microgap channel flow. The present visualization study focuses on adiabatic and diabatic two-phase flow of FC-72 in a 184μm microgap channel operating at a mass flux of 230 kg/m2-s. For the adiabatic conditions, flow qualities ranged between 27% and 81%, but rather than the anticipated smooth "annular" liquid film, widely spaced, 3D waves, with a wavelength that decreases with increasing flow quality, were observed on the liquid-vapor interface. Short wavelength waves with continuous spanwise fronts, similar in appearance to Tollmien-Schlichting waves, appeared at the largest flow quality of 81%. For the diabatic condition, the inlet flow quality was maintained at 36% and, with the addition of heat along the lower wall of the microgap channel, the exit flow quality varied between 36% and 104%. The liquid-vapor interface displayed 3D wave patterns for exit qualities larger than 40%, but at exit qualities greater than 76%, the evaporating liquid film experienced repeated cycles of local rupture and healing. Given the absence of film rupture for the adiabatic condition, this cyclic film rupture-healing process in the diabatic condition is attributed to the additional destabilizing forces imposed by evaporation and temperature gradients in the liquid film.

Download article Publication Ethics and Malpractice Recommend to my Librarian Bookmark this Page