Two-Phase Flow and Heat Transfer in Rectangular Micro-Channels

Abstract

Knowledge of flow pattern and flow pattern transitions is essential to the development of reliable predictive tools for pressure drop and heat transfer in two-phase micro-channel heat sinks. In the present study, experiments were conducted with adiabatic nitrogen-water two-phase flow in a rectangular micro-channel having a 0.406 × 2.032 mm cross-section. Superficial velocities of nitrogen and water ranged from 0.08 to 81.92 m/s and 0.04 to 10.24 m/s, respectively. Flow patterns were first identified using high-speed video imaging, and still photos were then taken for representative patterns. Results reveal that the dominant flow patterns are slug and annular, with bubbly flow occurring only occasionally; stratified and churn flow were never observed. A flow pattern map was constructed and compared with previous maps and predictions of flow pattern transition models. Annual flow is identified as the dominant flow pattern for conditions relevant to two-phase micro-channel heat sinks, and forms the basis for development of a theoretical model for both pressure drop and heat transfer in micro-channels. Features unique to two-phase micro-channel flow, such as laminar liquid and gas flows, smooth liquid-gas interface, and strong entrainment and deposition effects are incorporated into the model. The model shows good agreement with experimental data for water-cooled heat sinks.

Stability of stratified two-phase flows in horizontal channels

“…The above results can be presented in a form of general expressions for the critical channel height and the corresponding maximum critical gas superficial velocity: - (27), implying that the range of gas flow rates for which stratified flow with a smooth interface can be maintained in field operations, which are associated with large channel sizes and elevated pressures, is much smaller than that obtained in lab scale experiments. Similarly, the range of stable (smooth) stratified flow when downscaling to micro channels significantly diminishes, which is in a general agreement with experimental findings (e.g., Kawahara et al, 2002, Qu et al, 2004, Ide et al, 2007.Note that the critical Fr and Re are however dependent on the viscosity ratio and should be identified for the particular gas-liquid system under consideration.…”

Theoretical model for fast bubble growth in small channels with reference to startup of capillary pumped loops used in spacecraft thermal management systems

“…Classical descriptions of the latter point to nucleation of a number of bubbles that grow, depart, and coalesce with one another, resulting in a several possible flow regimes, bubbly, slug, churn, and annular. However, in small channels, a nucleating bubble can quickly grow to engulf the entire cross-sectional, and as the heat flux is increased, a slug flow pattern evolves as the initial bubble grows axially by evaporation [14,15]. Fig.…”

The influence of channel wettability and geometry on water plug formation and drop location in a proton exchange membrane fuel cell flow field

“…Flow field flooding occurs at relatively low air/H 2 stoichiometry, for which a plug/slug flow regime has been observed in operating fuel cells [6e9]. From microscale two-phase flow studies [10,11] performed in semi-triangular and rectangular microchannels having a hydraulic diameter of 1 mm, it can also be concluded that a plug/slug flow regime is most likely to occur at low gas flow rates that correspond to low stoichiometry ( 2). Twophase flow regimes in the gas channels and their relevance for the PEM fuel cell operation was reviewed by Anderson et al [1], who concluded that more optimization work is still needed.…”