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 Experimental Investigation and Prediction on Pressure Drop during Flow Boiling in Horizontal Microchannels

Micromachines ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 510
Author(s):  
Yan Huang ◽  
Bifen Shu ◽  
Shengnan Zhou ◽  
Qi Shi
Keyword(s):  
Pressure Drop ◽  
Flow Model ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Separated Flow ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Vapor Quality ◽  
Two Phase ◽  
Gas Flux

In this paper, two-phase pressure drop data were obtained for boiling in horizontal rectangular microchannels with a hydraulic diameter of 0.55 mm for R-134a over mass velocities from 790 to 1122, heat fluxes from 0 to 31.08 kW/m2 and vapor qualities from 0 to 0.25. The experimental results show that the Chisholm parameter in the separated flow model relies heavily on the vapor quality, especially in the low vapor quality region (from 0 to 0.1), where the two-phase flow pattern is mainly bubbly and slug flow. Then, the measured pressure drop data are compared with those from six separated flow models. Based on the comparison result, the superficial gas flux is introduced in this paper to consider the comprehensive influence of mass velocity and vapor quality on two-phase flow pressure drop, and a new equation for the Chisholm parameter in the separated flow model is proposed as a function of the superficial gas flux . The mean absolute error (MAE ) of the new flow correlation is 16.82%, which is significantly lower than the other correlations. Moreover, the applicability of the new expression has been verified by the experimental data in other literatures.

Pressure Drop of Two-Phase Flow Boiling with R-22 and R-290 in 7.6 mm Diameter Tube

2016 ◽  
Vol 818 ◽  
pp. 23-27
Author(s):  
Agus Sunjarianto Pamitran ◽  
Nasruddin ◽  
Helmi Dadang Ardiansyah ◽  
Muhammad Idrus Alhamid
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Phase Flow ◽  
Lower Mass ◽  
Two Phase ◽  
Experimental Pressure

The characteristics of two-phase flow boiling of R-290 are required for replacing R-22 that has been phased-out. The present study focuses on experimental pressure drop for R-22 and R-290. The experiment was run with heat flux of 5.09 kW/m2 to 19.03 kW/m2, mass flux of 114.91 kg/m2s to 751.74 kg/m2s and saturation temperature of 4.77°C to 18.12°C. The present result showed that pressure drop was affected by heat flux, mass flux and saturation temperature. Lower mass flux, heat flux and saturation temperature results in lower pressure drop. The pressure drop of R-290 is lower than that of R-22. Among the existing pressure drop prediction methods, Lokhart-Martinelli (1949) gives the best prediction for the present pressure drop data.

The Numerical Calculation of Two-Phase Pressure Drop During Flow Boiling in the Vertical Annular Channel

2008 ◽  
Author(s):  
Ruosu Wang ◽  
Changhong Peng ◽  
Tao Zhou ◽  
Shichao Wang
Keyword(s):  
Heat Flux ◽  
Numerical Calculation ◽  
Pressure Drop ◽  
Mass Flux ◽  
Flow Model ◽  
Flow Boiling ◽  
Annular Channel ◽  
Phase Flow ◽  
Two Phase ◽  
Phase Pressure

In this paper, according to a separated phase flow model for annular two-phase flow in the vertical annular channel, the liquid film thickness, void fraction and two-phase pressure drop along the flow channel are predicted. The calculated pressure drop values are compared with that measured in experiment in the range of mass flux from 38.8 to 163.1kg/m2s; pressure from 1.5 to 6.0 MPa; and heat flux from 4.9 to 50.7kW/m2 for inside tube and from 4.2 to 78.8kW/m2 for outside tube. It can be found that the model can predict the pressure drop well. With the mass flux increasing and the gap of the annular channel decreasing, pressure drop increases.

scholarly journals X-ray Imaging-Based Void Fraction Measurement in Saturated Flow Boiling Experiments with Seawater Coolant

2021 ◽  
Vol 5 (4) ◽  
pp. 31
Author(s):  
Seth Eckels ◽  
Zayed Ahmed ◽  
Molly Ross ◽  
Daniel Franken ◽  
Steven Eckels ◽  
...  
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Void Fraction ◽  
Test Section ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Tap Water ◽  
Phase Flow ◽  
Two Phase ◽  
X Ray

Recent studies have shown that the presence of dissolved salts in water can exhibit peculiar flow boiling and two-phase flow regimes. Two-phase flow and convective flow boiling are typically characterized with the help of void fraction measurements. To quantitatively improve our understanding of two-phase flow and boiling phenomenon with seawater coolant, void fraction data are needed, which can not be obtained from optical imaging. In this paper, we present experimental void fraction measurements of saturated flow boiling of tap water and seawater using X-ray radiography. X-rays with a maximum energy level of 40 KeV were used for imaging the exit region of the heated test section. At lower heat flux levels, the two phase flow in seawater was bubbly and homogeneous in nature, resulting in higher void fractions as compared to tap water. With an increase in heat flux, the flow regime was similar to slug flow, and void fraction measurements approached similarity with tap water. The predicted pressure drop using the measured void faction shows good agreement with the measured total pressure drop across the test section, demonstrating the validity of the measurement process.

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