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 0.406×2.032mm2 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 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. Features unique to two-phase micro-channel flow were identified and employed to validate key assumptions of an annular flow boiling model that was previously developed to predict pressure drop and heat transfer in two-phase micro-channel heat sinks. This earlier model was modified based on new findings from the adiabatic two-phase flow study. The modified model shows good agreement with experimental data for water-cooled heat sinks.

Two-Phase Microchannel Heat Sinks: Theory, Applications, and Limitations

“…Additionally, most investigators conclude that, while macrochannel flow regime maps do capture overall qualitative trends, they cannot be relied upon for quantitative predictions. Figure 16(a) shows a flow module that was constructed by Qu et al [115] to investigate adiabatic two-phase flow regimes in a horizontal 0.406 mm deep, 2.032 mm wide, and 12 cm long microchannel. Figure 16(b) depicts the construction of a mixer containing a 40 lm porous tube, which was used to bubble nitrogen gas from the core into a water stream passing through the annulus between the porous tube and housing.…”

“…This also requires the use of proper dimensionless groups in the transition models. As indicate by Qu et al [115], those should include at a minimum Phase Reynolds numbers: Phase Weber numbers:…”

“…(f) Comparison of flow regime map with macrochannel map of Taitel and Dukler[117]. (Adapted from Qu et al[115]).…”

The Effect of Hydraulic Diameter on Flow Boiling within Single Rectangular Microchannels and Comparison of Heat Sink Configuration of a Single and Multiple Microchannels

“…Literature reveals that previous experimental works who tried to identify and differentiate the transition limits between conventional tubes and micro-scale channels, in most cases, disagree in their findings. Some of these studies have concluded that the hydraulic diameter range for microchannels should be between 10 and 200 µm [1,2] while some other studies state that this range should be between 1 and 1000 µm [3][4][5]. Such separation is therefore only conventional, and we will conservatively consider only small channels below 200 µm.…”

Estudo do efeito da inclinação no escoamento bifásico em canal retangular com dimensões características da transição entre micro- e macro-escala

“…Com o decréscimo do diâmetro hidráulico a partir de uma determinada dimensão constatam-se desvios significativos do comportamento da perda de pressão, transição entre padrões de escoamento e fração de vazio. Qu et al (2004)…”