ISSN Online: 2379-1748
ISBN Flash Drive: 978-1-56700-472-4
ISBN Online: 978-1-56700-471-7
3rd Thermal and Fluids Engineering Conference (TFEC)
A COMBINED EXPERIMENTAL AND COMPUTATIONAL STUDY OF THE HEAT TRANSFER CHARACTERISTICS OF FALLING LIQUID-FILMS
Abstract
An optical technique that combines planar laser-induced fluorescence (PLIF), particle tracking velocimetry
(PTV) and infrared thermography (IR) was applied for the investigation of the hydrodynamic and heat transfer
characteristics of harmonically-excited liquid films falling under the action of gravity over an inclined, electrically
heated glass-substrate. PLIF was used to recover film-height data, PTV to recover two-dimensional
(2D) velocity-field data, and IR to recover the temperature of the gas-liquid interface. The experiments were
complemented by direct numerical simulations (DNSs) that provide additional information on the liquid viscosity,
temperature and velocity distributions between the flow inlet and the downstream location where the
optical measurements were collected. By adoption of this synergistic approach we recover a wealth of information,
including novel results on the spatiotemporal evolution of the interface topology, and the flow and
temperature fields underneath the wavy interface. Based on this data we also deduce local and instantaneous
heat transfer coefficients (HTCs), and focus our efforts towards the investigation of two HTC-enhancement
mechanisms; the observation of "hot-spots" as precursors to the formation of thermal rivulets, which can
result in local enhancements in excess of 50%, and the presence of large velocity components in the crossstream
direction of the flow, which promote mixing and are shown to improve heat transfer by up to ~ 7%
compared to flow regions of the same height.