Flow Boiling of Carbon Dioxide in Horizontal Mini-Channel and Pattern Dynamics Approach to Study Flow Pattern

2009 ◽  
Author(s):  
Mamoru Ozawa
Keyword(s):  
Carbon Dioxide ◽  
High Pressure ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Flow Instability ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Bond Number ◽  
Pattern Dynamics ◽  
Mini Channels

This paper provides a brief review on experimental and numerical investigations of flow patterns, pressure drop, and heat transfer including critical heat flux (CHF) of flow boiling carbon-dioxide (CO2) at high pressure in mini-channels ranging 0.5mm to 3.0mm in diameter. The flow patterns of CO2 at high pressure with small density difference between vapor and liquid and low surface tension show a slightly different structure from so far observed in mini-channels with air and water. The phase mal-distribution, similar to conventional tubes, in the cross-section becomes rather significant beyond the critical Bond number, which leads to the intermittent dryout at the upper wall of the tube. So far proposed flow pattern transition criteria are ineffective there, and newly developed discrete bubble model demonstrates its high potential in predicting flow patterns. Conventional homogeneous flow model is still available in predicting pressure drop. Based on this fact, flow instability problems, which significantly affect CHF, is discussed focusing on high-pressure CO2 flow.

Flow Boiling Heat Transfer, Pressure Drop, and Flow Pattern for CO2 in a 3.5mm Horizontal Smooth Tube

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Chang Yong Park ◽  
Pega Hrnjak
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer

Abstract C O 2 flow boiling heat transfer coefficients and pressure drop in a 3.5mm horizontal smooth tube are presented. Also, flow patterns were visualized and studied at adiabatic conditions in a 3mm glass tube located immediately after a heat transfer section. Heat was applied by a secondary fluid through two brass half cylinders to the test section tubes. This research was performed at evaporation temperatures of −15°C and −30°C, mass fluxes of 200kg∕m2s and 400kg∕m2s, and heat flux from 5kW∕m2 to 15kW∕m2 for vapor qualities ranging from 0.1 to 0.8. The CO2 heat transfer coefficients indicated the nucleate boiling dominant heat transfer characteristics such as the strong dependence on heat fluxes at a mass flux of 200kg∕m2s. However, enhanced convective boiling contribution was observed at 400kg∕m2s. Surface conditions for two different tubes were investigated with a profilometer, atomic force microscope, and scanning electron microscope images, and their possible effects on heat transfer are discussed. Pressure drop, measured at adiabatic conditions, increased with the increase of mass flux and quality, and with the decrease of evaporation temperature. The measured heat transfer coefficients and pressure drop were compared with general correlations. Some of these correlations showed relatively good agreements with measured values. Visualized flow patterns were compared with two flow pattern maps and the comparison showed that the flow pattern maps need improvement in the transition regions from intermittent to annular flow.

Experimental Study of Flow Patterns, Pressure Drop and Flow Instabilities in Parallel Rectangular Minichannels

2004 ◽  
Author(s):  
Prabhu Balasubramanian ◽  
Satish G. Kandlikar
Keyword(s):  
Pressure Drop ◽  
High Speed ◽  
Flow Instability ◽  
Flow Boiling ◽  
Pressure Fluctuations ◽  
Flow Patterns ◽  
Flow Instabilities ◽  
Stable Operation ◽  
Phase System ◽  
High Heat Flux

The use of phase change heat transfer in parallel minichannels and microchannels is one of the solutions proposed for cooling high heat flux systems. The increase in pressure drop in a two phase system is one of the problems, that need to be studied in detail before proceeding to any design phase. The pressure drop fluctuations in a network of parallel channels connected by a common head need to be addressed for stable operation of flow boiling systems. The current work focuses on studying the pressure-drop fluctuations and flow instabilities in a set of six parallel rectangular minichannels, each with 333 μm hydraulic diameter. Demonized and degassed water was used for all the experiments. Pressure fluctuations are recorded and signal analysis is performed to find the dominant frequencies and their amplitudes. These pressure fluctuations are then mapped to their corresponding flow patterns observed using a high speed camera. The results help us to relate pressure fluctuations to different flow characteristics, and their effect on flow instability.

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

2004 ◽  
Vol 126 (3) ◽  
pp. 288-300 ◽  
Author(s):  
Weilin Qu ◽  
Seok-Mann Yoon ◽  
Issam Mudawar
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Heat Sinks ◽  
Phase Flow ◽  
Micro Channel ◽  
Two Phase

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.

Flow Pattern and Boiling Heat Transfer of CO2 at High Pressure in Horizontal Mini-Channels

2010 ◽  
Author(s):  
Takeyuki Ami ◽  
Noriko Nakamura ◽  
Hisashi Umekawa ◽  
Mamoru Ozawa ◽  
Masahiro Shoji
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Flow Pattern ◽  
Void Fraction ◽  
Boiling Heat Transfer ◽  
Flow Behavior ◽  
Nucleate Boiling ◽  
Flow Patterns ◽  
Heat Transfer Deterioration ◽  
Mini Channels

Experimental investigation was conducted with CO2 at high pressure, ranging 5.0 to 6.5 MPa, in horizontal mini-channels of 0.51, 1.0 and 2.0 mm in diameters. In smaller bores tube, e.g. 0.51 and 1.0 mm, the phase stratification is not serious and the flow pattern becomes quasi-axi-symmetric, while in 2.0 mm or larger tubes phase stratification becomes significant as in conventional sized tubes. This phase stratification, together with the intermittent flow behavior, causes the heat transfer deterioration at the upper wall. Existing criteria as a whole were insufficient in predicting flow patterns. In order to predict complicated two-phase flow behavior, including inherent void fraction fluctuation and flow patterns, the discrete bubble model based on a pattern dynamics approach was developed, so as to be applicable to the horizontal mini-channels. The simulated void fraction fluctuations successfully provided not only the flow pattern maps in terms of statistical properties, but also quantitative estimation of the heat transfer deterioration at the upper wall of the tube of 2.0 mm in diameter. Existing correlations were evaluated through the comparison with the present experimental data, and a nucleate boiling mode was found a dominant mode over the boiling heat transfer at high pressure in mini-channels.

scholarly journals Flow Pattern Map of Flow Boiling in a Rectangular Channel Filled with Porous Media

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2440
Author(s):  
Youngwoo Kim ◽  
Dae Yeon Kim ◽  
Kyung Chun Kim
Keyword(s):  
Porous Media ◽  
Flow Pattern ◽  
Flow Regime ◽  
Annular Flow ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Flow Patterns ◽  
Flow Pattern Map ◽  
Mist Flow ◽  
Churn Flow

A flow visualization study was carried out for flow boiling in a rectangular channel filled with and without metallic random porous media. Four main flow patterns are observed as intermittent slug-churn flow, churn-annular flow, annular-mist flow, and mist flow regimes. These flow patterns are clearly classified based on the high-speed images of the channel flow. The results of the flow pattern map according to the mass flow rate were presented using saturation temperatures and the materials of porous media as variables. As the saturation temperatures increased, the annular-mist flow regime occupied a larger area than the lower saturation temperatures condition. Therefore, the churn flow regime is narrower, and the slug flow more quickly turns to annular flow with the increasing vapor quality. The pattern map is not significantly affected by the materials of porous media.

Flow Patterns During Flow Boiling Instability in Silicon-Based Pin-Fin Microchannels

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Fayao Xu ◽  
Huiying Wu ◽  
Zhenyu Liu
Keyword(s):  
Single Phase ◽  
Flow Instability ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Pin Fin ◽  
Short Period ◽  
Pin Fins ◽  
Amplitude Mode

In this paper, the flow patterns during water flow boiling instability in pin-fin microchannels were experimentally studied. Three types of pin-fin arrays (in-line/circular pin-fins, staggered/circular pin-fins, and staggered/square pin-fins) were used in the study. The flow instability started to occur as the outlet water reached the saturation temperature. Before the unstable boiling, a wider range of stable boiling existed in the pin-fin microchannels compared to that in the plain microchannels. Two flow instability modes for the temperature and pressure oscillations, which were long-period/large-amplitude mode and short-period/small-amplitude mode, were identified. The temperature variation during the oscillation period of the long-period/large-amplitude mode can be divided into two stages: increasing stage and decreasing stage. In the increasing stage, bubbly flow, vapor-slug flow, stratified flow, and wispy flow occurred sequentially with time for the in-line pin-fin microchannels; liquid single-phase flow, aforementioned four kinds of two-phase flow patterns, and vapor single-phase flow occurred sequentially with time for the staggered pin-fin microchannel. The flow pattern transitions in the decreasing stage were the inverse of those in the increasing stage for both in-line and staggered pin-fin microchannels. For the short-period/small-amplitude oscillation mode, only the wispy flow occurred. With the increase of heat flux, the wispy flow and the vapor single-phase flow occupied more and more time ratio during an oscillation period in the in-line and staggered pin-fin microchannels.

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