The Influence of Non-Uniform Heating on Two-Phase Flow Instability in Parallel Channels

2013 ◽  
Author(s):  
Xiaodong Lu ◽  
Linglan Zhou ◽  
Hong Zhang ◽  
Yingwei Wu ◽  
Guanghui Su ◽  
...  
Keyword(s):  
Heat Flux ◽  
Two Phase Flow ◽  
Flow Instability ◽  
System Stability ◽  
System Control ◽  
Phase Flow ◽  
Uniform Heating ◽  
Two Phase ◽  
System Pressure ◽  
Parallel Channels

The two-phase flow instability in parallel channels heated by uniform and non-uniform heat flux has been theoretically studied in this paper. Based on the homogeneous flow model in two-phase region, the system control equations of parallel channels were established. Semi-implicit finite-difference method and staggered mesh method were used to discretize the system control equations and the difference equations were solved with a chasing method. The cosine profile and uniform constant heat flux represent the non-uniform and uniform heating condition, respectively. The marginal stability boundaries (MSB) of parallel channels and the three-dimensional instability spaces (or instability reefs) of different heat flux models were obtained. For cosine profile heating, the stability of parallel channels increases with the increase of the system pressure and inlet resistant coefficient. In high inlet subcooling region, cosine heat flux can strengthen the system stability. However, in low inlet subcooling region, the negative effect to system stability will be caused by non-uniform heating. The increase of inlet resistant coefficient will move the turning point of the MSB to high inlet subcooling number.

Theoretical investigations on two-phase flow instability in parallel channels under axial non-uniform heating

2014 ◽  
Vol 63 ◽  
pp. 75-82 ◽  
Author(s):  
Xiaodong Lu ◽  
Yingwei Wu ◽  
Linglan Zhou ◽  
Wenxi Tian ◽  
Guanghui Su ◽  
...  
Keyword(s):  
Two Phase Flow ◽  
Flow Instability ◽  
Phase Flow ◽  
Uniform Heating ◽  
Two Phase ◽  
Theoretical Investigations ◽  
Parallel Channels

The influence of non-uniform heating on two-phase flow instability in subchannel

2019 ◽  
Vol 345 ◽  
pp. 7-14
Author(s):  
Sipeng Wang ◽  
Bao-Wen Yang ◽  
Hu Mao ◽  
Yu-chen Lin ◽  
Guanyi Wang
Keyword(s):  
Two Phase Flow ◽  
Flow Instability ◽  
Phase Flow ◽  
Uniform Heating ◽  
Two Phase

Experimental Investigation and Flow Visualization of the Two-Phase Flow Instability at Low Vapor Quality in a Vertical Narrow Channel

2018 ◽  
Author(s):  
Liqiang Pan ◽  
Yang Liu ◽  
Weihua Li ◽  
Yefei Liu
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Test Section ◽  
Two Phase Flow ◽  
Flow Instability ◽  
Narrow Channel ◽  
Bubble Nucleation ◽  
Phase Flow ◽  
Vapor Quality ◽  
Two Phase

The two-phase flow instability of forced convection has been experimentally investigated in a vertical narrow channel with the hydraulic diameter of 2.857mm and aspect ratio of 20. Transparent, metallic and conductive films on external surfaces of the test section can provide visualization and uniform heating for deionized water. The heat flux is 6–18.2 kW · m−2. When the instability occurs at low vapor quality, a series of parameters are measured and visualized images are obtained by a high-speed camera. The results show that the large amplitude of pressure drop between the inlet and outlet in the test section is due to the elongated bubble, and the value of pressure drop is positively correlated with the volume of the bubble. The oscillation period of pressure drop decreases with the increase of heat flux, and the period can be determined by the method of the Fast Fourier Transform. The backflow phenomenon is analyzed, which has a greater effect on the oscillation of pressure drop than bubble nucleation, bubble growth, bubble coalescence and recoiling of bubble boundary.

Theoretical research on two-phase flow instability in parallel channels

2009 ◽  
Vol 239 (7) ◽  
pp. 1294-1303 ◽  
Author(s):  
Y.J. Zhang ◽  
G.H. Su ◽  
X.B. Yang ◽  
S.Z. Qiu
Keyword(s):  
Two Phase Flow ◽  
Flow Instability ◽  
Theoretical Research ◽  
Phase Flow ◽  
Two Phase ◽  
Parallel Channels

Numerical Research on Oscillation of Two-Phase Flow Under Rolling Motion

2010 ◽  
Author(s):  
Y. J. Zhang ◽  
G. H. Su ◽  
S. Z. Qiu ◽  
H. Li
Keyword(s):  
Two Phase Flow ◽  
Flow Instability ◽  
Control Volume ◽  
Stability Boundary ◽  
Marginal Stability ◽  
Rolling Motion ◽  
System Control ◽  
Phase Flow ◽  
Two Phase ◽  
High Equilibrium

Two-phase flow instability and dynamics of a parallel multichannel system has been theoretically studied under periodic excitation induced by rolling motion in the present research. Based on the homogeneous flow model considering the rolling motion, the parallel multichannel model and system control equations are established by using the control volume integrating method. Gear method is used to solve the system control equations. The influences of the inlet, upward sections, and heating power on the flow instability under rolling motion have been analyzed. The marginal stability boundary (MSB) under rolling motion condition is obtained. The unstable regions occur in both low and high equilibrium quality and inlet subcooling regions. The multiplied period phenomenon occurs in the high equilibrium quality region and the chaos phenomenon appears on the right of MSB. The concept of stability space is presented.

Effects of Non-Uniform Heating on Two-Phase Flow Through Microchannels

2013 ◽  
Author(s):  
Susan N. Ritchey ◽  
Justin A. Weibel ◽  
Suresh V. Garimella
Keyword(s):  
Heat Flux ◽  
Heat Sink ◽  
Two Phase Flow ◽  
Flow Regimes ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Microchannel Heat Sink ◽  
Uniform Heating ◽  
Two Phase ◽  
Local Flow

As size, weight, and performance demands drive electronics packages to become increasingly thinner and more compact, volume restrictions prevent the use of large intermediate heat spreaders to mitigate heat generation non-uniformities. Instead, these non-uniform heat flux profiles are imposed directly on the ultimate heat sink, either due to chip-scale variations or the desire to cool multiple discrete devices. A better understanding of the impacts of non-uniform heating on two-phase flow characteristics and thermal performance limits for microchannel heat sinks is needed to address these thermal packaging trends. An experimental investigation is performed to explore flow boiling phenomena in a microchannel heat sink with point hotspots, as well as non-uniform streamwise and transverse heating conditions across the entire heat sink area. The investigation is conducted using a silicon microchannel heat sink with a 5 × 5 array of individually controllable heaters attached to a 12.7 mm × 12.7 mm square base. The channels are 240 μm wide, 370 μm deep, and separated by 110 μm wide fins. The working fluid is FC-77, flowing at a mass flux of approximately 890 kg/m2s. High-speed visualizations of the flow are recorded to observe the local flow regimes. It is found that even though the substrate thickness beneath the microchannels is very small (200 μm), significant lateral conduction occurs and must be accounted for in the calculation of the local heat flux imposed. For non-uniform heat input profiles, with peak heat fluxes along the central streamwise and transverse directions, it is found that the local flow regimes, heat transfer coefficients, and wall temperatures deviate significantly from a uniformly heated case. These trends are assessed as a function of an increase in the relative magnitude of the nonuniformity between the peak and background heat fluxes.

Supercritical Flow Stability in Two Parallel Channels

2006 ◽  
Author(s):  
Vijay Chatoorgoon
Keyword(s):  
Analytical Study ◽  
Two Phase Flow ◽  
Flow Instability ◽  
Flow Stability ◽  
Phase Flow ◽  
Two Phase ◽  
Supercritical Flow ◽  
Light Water ◽  
Parallel Channels

An analytical study of supercritical flow stability in two parallel channels is reported here. This would be of immense value to new reactor designs that propose to use supercritical light water on the primary side. The finding is that two-phase flow instability and supercritical flow instability are not identical, as there are notable phenomenological differences as well as mathematical differences.

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