Study on Critical Heat Flux in Rectangular Channels Heated From One or Both Sides at Pressures Ranging From 0.1 to 14 MPa

1996 ◽  
Vol 118 (3) ◽  
pp. 680-688 ◽  
Author(s):  
Y. Sudo
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Model ◽  
High Water ◽  
Experimental Results ◽  
Low Velocity ◽  
Two Phase ◽  
Flow Models ◽  
Rectangular Channels ◽  
Boiling Flow

In this study, a quantitative analysis of critical heat flux (CHF) in rectangular heated channels was carried out based on new flow models and the analytical results were compared with existing experimental results at pressures of about 0.1 to 14 MPa with a water mass flux of 3.9 to 28,000 kg/m2s and inlet water subcooling ranging from 0 to 328 K. The flow models proposed for CHF were a completely separated two-phase flow model with a macroliquid sublayer under conditions of comparatively low velocity and zero water subcooling at outlet of the channel and a subcooled boiling flow model with a macroliquid sublayer under the conditions of high water subcooling and high velocity, respectively. It could be shown that the analytical CHF results gave good predictions for over 800 existing experimental results, identifying the effects of predominant parameters as regards CHF.

scholarly journals A Separated-Flow Model for Predicting Flow Boiling Critical Heat Flux and Pressure Drop Characteristics in Microchannels

2012 ◽  
Author(s):  
Tie Jun Zhang ◽  
Siyu Chen ◽  
Evelyn N. Wang
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Critical Heat Flux ◽  
Flow Model ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Separated Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Microchannel Cooling

Two-phase microchannel cooling promises high heat flux removal for high-performance electronics and photonics. However, the heat transfer performance of flow boiling microchannels is limited by the critical heat flux (CHF) conditions. For variable heat inputs and variable fluid flows, it is essential to predict CHFs accurately for effective and efficient two-phase microchannel cooling. To characterize the CHF and pressure drop in flow boiling microchannels, a separated-flow model is proposed in this paper based on fundamental two-phase flow mass, energy, momentum conservation and wall energy conservation laws. With this theoretical framework, the relationship among liquid/vapor interfacial instability, two-phase flow characteristics and CHF is further studied. This mechanistic model also provides insight into the design and operational guidelines for advanced electronics and photonics cooling technologies.

scholarly journals Development and validation of two-phase flow models and critical heat flux prediction for the highly-scalable CFD code NEK-2P

2018 ◽  
Author(s):  
Adrian Tentner ◽  
Prasad Vegendla ◽  
Dillon Shaver ◽  
Ananias Tomboulides ◽  
Aleks Obabko ◽  
...  
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Models ◽  
Development And Validation

Advances in Modeling Critical Heat Flux in LWR Boiling Flows With the NEK-2P CFD Code

2018 ◽  
Author(s):  
Adrian Tentner ◽  
Prasad Vegendla ◽  
Ananias Tomboulides ◽  
Aleks Obabko ◽  
Elia Merzari ◽  
...  
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Vertical Channel ◽  
Nucleate Boiling ◽  
Heated Wall ◽  
Transfer Model ◽  
Axial Distribution ◽  
Two Phase ◽  
Wide Range ◽  
Boiling Flow

The paper focuses on the extension of the NEK-2P Wall Heat Transfer model, which was initially developed for the analysis of Critical Heat Flux (CHF) under Dryout (DO) conditions to the simulation of CHF under Departure from Nucleate Boiling (DNB) conditions. The paper presents results of recent NEK-2P analyses of several CHF experiments including both DO and DNB conditions. The CHF experiments analyzed have measured the axial distribution of wall temperatures in two-phase boiling flow in a vertical channel with a heated wall. The axial distribution of the calculated wall temperatures is compared with the corresponding experimental data. Reasonably good agreement with measured data is obtained in predicting the CHF location and post CHF wall temperature magnitudes illustrating the ability of the NEK-2P code and Extended Boiling Framework (EBF) models to simulate the CHF phenomena for a wide range of thermal-hydraulic conditions.

Critical Heat Flux on a Horizontal Cylinder in an Upward Subcooled and Low-Quality Two-Phase Crossflow

1986 ◽  
Vol 108 (2) ◽  
pp. 441-447 ◽  
Author(s):  
M. K. Jensen ◽  
M. Pourdashti
Keyword(s):  
Heat Flux ◽  
Experimental Investigation ◽  
Flow Regime ◽  
Critical Heat Flux ◽  
Horizontal Tube ◽  
Horizontal Cylinder ◽  
Regime Transition ◽  
Low Velocity ◽  
Two Phase ◽  
Flow Regime Transition

An experimental investigation has been conducted to determine the low-velocity critical heat flux (CHF) behavior on a single horizontal tube in a subcooled and low-quality two-phase crossflow of R-113. Data were obtained over a range of velocities (up to 0.3 m/s), subcooling (0 to 14 K), and qualities (0 < x < +30 percent) at two pressures. There was a linear decrease in the CHF with increasing quality up to about 10 percent quality; then, due to a flow regime transition, the CHF remained relatively constant. A correlation has been developed which predicted well the subcooled and low-quality region CHF condition in the linearly decreasing portion of the curve. Data from the literature are also predicted well.

Orientation Effects on Critical Heat Flux From Discrete, In-Line Heat Sources in a Flow Channel

1993 ◽  
Vol 115 (4) ◽  
pp. 973-985 ◽  
Author(s):  
C. O. Gersey ◽  
I. Mudawar
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Liquid Velocity ◽  
Heat Fluxes ◽  
Heat Sources ◽  
Low Velocity ◽  
Two Phase ◽  
Chip Surface ◽  
Horizontal Orientation ◽  
Limited Success

The effects of flow orientation on critical heat flux (CHF) were investigated on a series of nine in-line simulated microelectronic chips in Fluorinert FC-72. The chips were subjected to coolant in upflow, downflow, or horizontal flow with the chips on the top or bottom walls of the channel with respect to gravity. Changes in angle of orientation affected CHF for velocities below 200 cm/s, with some chips reaching CHF at heat fluxes below the pool boiling and flooding-induced CHF values. Increased subcooling was found to dampen this adverse effect of orientation slightly. Critical heat flux was overwhelmingly caused by localized dryout of the chip surface. However, during the low velocity downflow tests, low CHF values were measured because of liquid blockage by vapor counterflow and vapor stagnation in the channel. At the horizontal orientation with downward-facing chips, vapor/liquid stratification also yielded low CHF values. Previously derived correlations for water and long, continuous heaters had limited success in predicting CHF for the present discontinuous heater configuration. Because orientation has a profound effect on the hydrodynamics of two-phase flow and, consequently, on CHF for small inlet velocities, downflow angles should be avoided, or when other constraints force the usage of downflow angles, the inlet liquid velocity should be sufficiently large.

Computational Fluid Dynamics Modeling of Two-Phase Boiling Flow and Critical Heat Flux

2014 ◽  
Author(s):  
Adrian Tentner ◽  
Elia Merzari ◽  
Prasad Vegendla
Keyword(s):  
Fluid Dynamics ◽  
Heat Flux ◽  
Computational Fluid Dynamics ◽  
Critical Heat Flux ◽  
Wall Temperature ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Axial Distribution ◽  
Two Phase ◽  
Boiling Flow

This paper presents recent advances in the modeling of two-phase boiling flow and critical heat flux that have been implemented in the Extended Boiling Framework (EBF) [1, 2, 3]. The EBF code was developed as a customized module built on the foundation of the commercial Computational Fluid Dynamics (CFD) code STAR-CD, which provides general two-phase flow modeling capabilities, for the detailed analysis of the two-phase flow and heat transfer phenomena that occur in Boiling Water Reactor (BWR) fuel assemblies. These phenomena include coolant phase changes and multiple flow regimes that directly influence the coolant interaction with the fuel pins and, ultimately, the reactor performance. An effort to expand the EBF two-phase models and to explore their applicability to other CFD codes is currently underway. The paper presents results of recent CFD analyses of Critical Heat Flux (CHF) experiments that have measured the axial distribution of wall temperature in two-phase upward flow in a vertical channel with a heated wall. The experiments were designed to produce the onset of CHF in the upper half of the heated channel. The simulated axial distribution of wall temperature is compared with experimental data, illustrating the ability of the extended EBF model to capture the onset of CHF for a wide range of thermal-hydraulic conditions relevant for BWRs. The paper concludes with a discussion of results and plans for future work.

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