Heat transfer mechanism, pressure drop and flow patterns during FC-72 flow boiling in horizontal and vertical minichannels with enhanced walls

2013 ◽  
Vol 66 ◽  
pp. 472-488 ◽  
Author(s):  
Magdalena Piasecka
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Transfer Mechanism ◽  
Heat Transfer Mechanism

Study on onset of nucleate boiling with screw tube for fusion reactor application

2021 ◽  
Author(s):  
Ji Hwan Lim ◽  
Minkyu Park
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
High Heat ◽  
Transfer Mechanism ◽  
High Heat Flux ◽  
Heat Transfer Mechanism ◽  
System Parameters ◽  
Smooth Tubes

Abstract The onset of nucleate boiling (ONB) is the point at which the heat transfer mechanism in fluids changes and is one of the thermo-hydraulic factors that must be considered when establishing a cooling system operation strategy. Because the high heat flux of several MW/m2, which is loaded within a tokamak, is applied under a one-side heating condition, it is necessary to determine a correlative relation that can predict ONB under special heating conditions. In this study, the ONB of a one-side-heated screw tube was experimentally analyzed via a subcooled flow boiling experiment. The helical nut structure of the screw tube flow path wall allows for improved heat transfer performance relative to smooth tubes, providing a screw tube with a 53.98% higher ONB than a smooth tube. The effects of the system parameters on the ONB heat flux were analyzed based on the changes in the heat transfer mechanism, with the results indicating that the flow rate and degree of subcooling are proportional to the ONB heat flux because increasing these factors improves the forced convection heat transfer and increases the condensation rate, respectively. However, it was observed that the liquid surface tension and latent heat decrease as the pressure increases, leading to a decrease in the ONB heat flux. An evaluation of the predictive performance of existing ONB correlations revealed that most have high error rates because they were developed based on ONB experiments on micro-channels or smooth tubes and not under one-side high heat load conditions. To address this, we used dimensional analysis based on Python code to develop new ONB correlations that reflect the influence of system parameters.

Heat Transfer and Pressure Drop for Flow Boiling of Water in Narrow Vertical Rectangular Channels

2003 ◽  
Author(s):  
Jianyun Shuai ◽  
Rudi Kulenovic ◽  
Manfred Groll
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Boiling ◽  
Bubbly Flow ◽  
High Heat ◽  
Flow Patterns ◽  
Industrial Applications ◽  
Heat Fluxes ◽  
Experimental Conditions ◽  
Rectangular Channels

Flow boiling in small-sized channels attracted extensive investigations in the past two decades due to special requirements for transfer of high heat fluxes from narrow spaces in various industrial applications. Experiments on various aspects of flow boiling in narrow channels were carried out and theoretical attempts were undertaken. But these investigations showed large differences, e.g. up till now the knowledge on the development of flow patterns in small non-circular flow passages is very limited. This paper deals with investigations on flow boiling of water in two rectangular channels with dimensions (width×depth) 2.0×4.0 mm2 and 0.5×2.0 mm2 (corresponding hydraulic diameters are 2.67 mm and 0.8 mm). The pressure at the test section exit is atmospheric. For steady-state experimental conditions the effects of heat flux, mass flux and inlet subcooling on the boiling heat transfer coefficient and the pressure drop are investigated. Flow patterns and the transition of flow patterns along the channel axis are visualized and documented with a video-camera. Bubbly flow, slug flow and annular flow are distinguished in both channels. Preliminary flow pattern maps are generated.

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.

Contribution of Microlayer Evaporation During Flow Boiling Inside Microchannels

2008 ◽  
Author(s):  
A. Mukherjee
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Transfer Mechanism ◽  
Heat Transfer Mechanism ◽  
Cross Sectional ◽  
Thin Film Evaporation ◽  
Nucleate Boiling Heat Transfer ◽  
Microlayer Evaporation

Flow boiling through microchannels is characterized by nucleation and growth of vapor bubbles that fills the entire channel cross-sectional area. As the bubble nucleates and grows inside the microchannel, a thin film of liquid or a microlayer gets trapped between the bubble and the channel walls. The heat transfer mechanism present at the channel walls during flow boiling is studied numerically. These mechanisms are compared to the heat transfer mechanisms present during nucleate boiling and in a moving evaporating meniscus. It is shown that the thermal and the flow fields present inside the microchannels around the bubbles are fundamentally different compared to nucleate boiling or in a moving evaporating meniscus. It is explained that how thin film evaporation is responsible for creating an apparent nucleate boiling heat transfer mechanism inside the microchannels.

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.

scholarly journals Flow patterns and heat transfer mechanism of circular closed thermosyphons.

1988 ◽  
Vol 54 (499) ◽  
pp. 681-687
Author(s):  
Hideaki YAMAGISHI ◽  
Ryoji ISHIGURO ◽  
Toshiaki KUMADA ◽  
Yoichi MARUKO ◽  
Hiromu SUGIYAMA
Keyword(s):  
Heat Transfer ◽  
Flow Patterns ◽  
Transfer Mechanism ◽  
Heat Transfer Mechanism

Heat Transfer Mechanism and Flow Pattern During Flow Boiling of Water in a Vertical Narrow Channel: Experimental Results

2006 ◽  
Author(s):  
Ewelina Sobierska ◽  
Rudi Kulenovic ◽  
Rainer Mertz
Keyword(s):  
Heat Transfer ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Transfer Mechanism ◽  
Phase Flow ◽  
Fluid Temperature ◽  
Heat Transfer Mechanism ◽  
Two Phase ◽  
Mass Fluxes

Experimental investigations on flow boiling phenomena in a vertical narrow rectangular microchannel with the hydraulic diameter dh = 0.48 mm were carried out. The experiments were performed under fluid-inlet subcooling conditions with deionised and degassed water for different mass fluxes. Investigations on pressure drop and heat transfer during single-and two-phase flow have been carried out. Moreover, flow visualisation of the two-phase flow patterns along the channel was performed using a digital high-speed video camera. The present work outlines local heat transfer coefficients for three mass fluxes (200, 700 and 1500 kg/m2s) and heat fluxes (30–110, 35–150 and 65–200 kW/m2, respectively) during two-phase flow. The fluid temperature at the inlet was about 50 °C what corresponds to inlet subcooling, depending on flow pressure conditions, from 34 °C to 57 °C. The visual observations were used to obtain a better insight about the heat transfer mechanism.

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