Due to the critical role of vapor confinement in establishing distinct flow and heat transfer characteristics in microchannels (as distinct from those in larger channels), the conditions under which such confinement occurs in microchannels are of great interest. It is shown in the present work that channel dimensions and flow properties alone, as proposed in past studies, are insufficient for d...

In this paper the heat transfer characteristics of a two-phase closed thermosyphon over a wide range of heat transfer rates, system pressure, aspect ratios and filling ratios were studied. The experiments focused on the boiling and condensation heat transfer characteristics of a thermosyphon with a copper tube having 25 and 32 mm inside and outside diameters. Distilled water was used as the wor...

Liquid metal MHD (Magneto-Hydro-Dynamic) systems can be employed to produce electricity from a wide range of heat resources. In such a system, a low-boiling organic fluid and a high-temperature liquid metal fluid mix. The former evaporates, and carries the latter to flow through an MHD channel, where the electricity is generated. The mixing process and the gas-liquid flow characteristics will h...

High-speed video and infrared thermometry were used to obtain timeand space-resolved information on bubble nucleation and heat transfer in pool boiling of water. The bubble departure diameter and frequency, growth and wait times, and nucleation site density were directly measured for a thin, electrically-heated, indium-tin-oxide surface, laid on a sapphire substrate. These data are very valuabl...

Critical heat flux (CHF) was measured and examined with high-speed video for subcooled flow boiling in micro-channel heat sinks using HFE 7100 as working fluid. High subcooling was achieved by pre-cooling the working fluid using a secondary low-temperature refrigeration system. The high subcooling greatly reduced both bubble departure diameter and void fraction, and precluded flow pattern trans...

Due to the lack of understanding in the literature of channel height effects on forced-convection boiling and critical heat flux (CHF) in rectangular channels, experiments were performed with FC-72 at 1.36 bar for channel heights of 2, 5, and 10 mm. Boiling heat transfer from a linear array of nine discrete heat sources simulating microelectronic chips was investigated for velocity and liquid s...

We present new laboratory observations of an advancing boiling front radiating from an injection point in a simulated geothermal reservoir. The Berea sandstone model is a 26 cm cube that is either heated to a dry 125°C, or saturated with 145°C steam in two separate testing configurations. Cool water is applied at the sample center, and the advancing boiling front is identified by a radial array...