共查询到20条相似文献,搜索用时 31 毫秒
1.
2.
This paper focuses on an analytical investigation of two-phase flow pressure-drop oscillations in a vertical heated tube with the two-fluid model employed in the computer code MINI-TRAC. Pressure-drop oscillation is an important phenomenon appearing in a two-phase flow channel with compressible volume existing in the upstream region. In a previous investigation, pressure-drop oscillations with superimposed density-wave oscillations were observed. In this work, numerical calculations have been carried out to predict the characteristics of pressure-drop oscillations and the range of instabilities. We also offer an application of the two-fluid model to the analysis of pressure-drop oscillations at low pressure in a heated channel with a small inner diameter. Good agreement between the simulations and experiments was obtained. © 1999 Scripta Technica, Heat Trans Jpn Res, 27(8): 597–608, 1998 相似文献
3.
ExperimentalInvestigationofForcedConvectiveBoilingFlowInstabilitiesinHorizontalHelicallyCoiledTubesL.J.Guo;Z.P.Feng;X.J.Chen(... 相似文献
4.
5.
《International Journal of Heat and Mass Transfer》2007,50(11-12):2078-2088
The present study explores experimentally the two-phase flow instability in a microchannel heat sink with 15 parallel microchannels. The hydraulic diameter for each channel is 86.3 μm. Flow boiling in the present microchannel heat sink demonstrates significantly different two-phase flow patterns under stable or unstable conditions. For the stable cases bubble nucleation, slug flow and slug or annular flows appear sequentially in the flow direction. On the other hand, forward or reversed slug/annular flows appear alternatively in every channel. Moreover, the length of bubble slug may oscillate for unstable cases with reversed flow demonstrating the suppressing effect of pressure field for bubble growth. It is found that the magnitude of pressure drop oscillations may be used as an index for the appearance of reversed flow. A stability map on the plane of inlet subcooling number versus phase change number is established. A very narrow region for stable two-phase flow or mild two-phase flow oscillations is present near the line of zero exit quality. 相似文献
6.
In parallel evaporative micro-channels, system instability may occur in terms of cyclical fluctuations at a long period. This is due to the co-existence of the liquid phase flow at high mass flux and the two-phase flow at a lower mass flux among different parallel channels under the same total pressure drop. For a system at constant flow rate pumping, with a pressure regulating tank and a constant heating pre-heater, alternations between these two states of boiling and non-boiling could happen with a period of minutes. This cyclical system instability has been modeled, where the liquid phase flow occurs at conditions of high inlet subcooling and low surface heat flux that the boiling inception is hard to initiate. The system instability criteria are established in terms of a system binary states parameter, S, and a non-dimensional surface heat flux. This model has been validated experimentally. 相似文献
7.
The earliest research in the field of two-phase flow was conducted by Lorentz (1909). The studies on the analysis of two-phase flow instabilities by Ledinegg (1938) created considerable interest concerning the phenomenon of thermally induced flow instability in two-phase flow systems. The objective of this review is to sum up the experimental and theoretical work carried out by various investigators over a period of several years, demonstrating and explaining three main instability modes of two-phase flow dynamic instabilities, namely, density-wave type, pressure-drop type and thermal oscillations, encountered in various boiling flow channel systems. The typical experimental investigations of these instabilities in tube boiling systems are indicated and the most popular models to predict the two-phase flow dynamic instabilities, namely the homogenous flow model and the drift-flux models are clarified with the solution examples and the validation of the model results with experimental findings are also provided. 相似文献
8.
LU Junfu YUE Guangxi YANG Hairui ZHANG Jiansheng YU Long ZHANG Man YANG Zhongming 《Frontiers in Energy》2008,2(2):134
The future of circulating fluidized bed (CFB) combustion technology is in raising the steam parameters to supercritical levels. Understanding the heat flux distribution on the water wall is one of the most important issues in the design and operation of supercritical pressure CFB boilers. In the present paper, the finite element analysis (FEA) method is adopted to predict the heat transfer coefficient as well as the heat flux of the membrane wall and the results are validated by direct measurement of the temperature around the tube. Studies on the horizontal heat flux distribution were conducted in three CFB boilers with different furnace size, tube dimension and water temperature. The results are useful in supercritical pressure CFB boiler design. 相似文献
9.
10.
Yukio Sudo 《亚洲传热研究》1997,26(1):16-29
A quantitative analysis of critical heat flux (CHF) under high mass flux with high subcooling at atmospheric pressure was successfully carried out by applying a new transition region model for a macro-water sublayer on heated walls to the existing model of a vapor blanket over the macro-water sublayer. The CHF correlation proposed in this study could predict well the experimental data obtained for water mass flux of 940 to 20,300 kg/m2s using circulate tubes 2 to 4 mm in diameter and 30 to 100 mm in length with inlet subcooling of 30 to 90 °C and rectangular channels heated from one side with gaps of 3 to 20 mm, length of 50 to 305 mm, and inlet subcooling of 30 to 77 °C and revealed a unique feature of CHF, namely, that the effects of wall friction of subcooled boiling flow and the velocity of the steam blanket above the macro-water sublayer at atmospheric pressure become the dominant factors while they were not dominant at higher pressures. © 1997 Scripta Technica, Inc Heat Trans Jpn Res, 26 (1): 16–29, 1997 相似文献
11.
H. Gürgenci T.N. Veziroglu S. Kaka 《International Journal of Heat and Mass Transfer》1983,26(5):671-679
A constant-property homogeneous-flow model is developed to generate the limit cycles of pressure-drop and density-wave oscillations in a single-channel upflow boiling system operating between constant pressures, with upstream compressibility introduced through a surge tank. In the model, thermodynamic equilibrium conditions are assumed and the effects of the wall heat storage and the variation of the fluid properties are neglected. Satisfactory agreement with the experimental cycles is noted for the pressuredrop oscillations. As for the density-wave oscillations, the agreement with the experiments is reasonably good regarding the periods of the oscillations, but not so good for the amplitudes. 相似文献
12.
This research has been conducted to investigate the effect of inlet subcooling on two‐phase flow instabilities in a horizontal pipe system with augmented surfaces. Five different inlet temperatures are used to study the effect of inlet subcooling for five different heat transfer surface configurations. All experiments are carried out at constant heat input, system pressure and exit restriction. The effect of inlet subcooling on the steady‐state characteristics and two‐phase flow instabilities are studied for each configuration. The bound aries for the appearance of pressure‐drop‐type and density‐wave‐type instabilities are found and the effect of the inlet subcooling on these oscillations is studied for each configuration. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
13.
Junfu Lu Long Yu Guangxi Yue Hairui Yang Jiansheng Zhang Man Zhang Zhongming Yang 《Frontiers of Energy and Power Engineering in China》2008,2(2):134-139
The future of circulating fluidized bed (CFB) combustion technology is in raising the steam parameters to supercritical levels.
Understanding the heat flux distribution on the water wall is one of the most important issues in the design and operation
of supercritical pressure CFB boilers. In the present paper, the finite element analysis (FEA) method is adopted to predict
the heat transfer coefficient as well as the heat flux of the membrane wall and the results are validated by direct measurement
of the temperature around the tube. Studies on the horizontal heat flux distribution were conducted in three CFB boilers with
different furnace size, tube dimension and water temperature. The results are useful in supercritical pressure CFB boiler
design.
__________
Translated from Journal of Power Engineering, 2007, 27(3): 336–340 [译自: 动力工程] 相似文献
14.
15.
16.
S.L. Qi P. Zhang R.Z. Wang L.X. Xu 《International Journal of Heat and Mass Transfer》2007,50(25-26):4999-5016
This paper is the first portion of a two-part study concerning the flow boiling of liquid nitrogen in the micro-tubes with the diameters of 0.531, 0.834, 1.042 and 1.931 mm. The contents mainly include the onset of nucleate boiling (ONB), two-phase flow instability and two-phase flow pressure drop. At ONB, mass flux drops suddenly while pressure drop increases, and apparent wall temperature hysteresis in the range of 1.0–5.0 K occurs. Modified Thom model can predict the wall superheat and heat flux at ONB. Moreover, stable long-period (50–60 s) and large-amplitude oscillations of mass flux, pressure drop and wall temperatures are observed at ONB for the 1.042 and 1.931 mm micro-tubes. Block phenomenon at ONB is also observed in the cases of high mass flux. The regions for the oscillations, block and stable flow boiling are classified. A physical model of vapor patch coalesced at the outlet is proposed to explain the ONB oscillations and block. Vapor generation caused by the flash evaporation is so large that it should be taken into account to precisely depict the variation of mass quality along the micro-tube. The adiabatic and diabatic two-phase flow pressure drop characteristics in micro-tubes are investigated and compared with four models including homogeneous model and three classical separated flow models. Contrary to the conventional channels, homogeneous model yields better prediction than three separated flow models. It can be explained by the fact that the density ratio of liquid to vapor for nitrogen is comparatively small, and the liquid and vapor phases may mix well in micro-tube at high mass flux due to small viscosity of liquid nitrogen, which leads to a more homogeneous flow. Part II of this study will focus on the heat transfer characteristics and critical heat flux (CHF) of flow boiling of liquid nitrogen in micro-tubes. 相似文献
17.
Deterioration in heat transfer of endothermal hydrocarbon fuel 总被引:5,自引:0,他引:5
Numerical studies under supercritical pressure are carried out to study the heat transfer characteristics in a single-root coolant channel of the active regenerative cooling system of the scramjet engine, using actual physical properties of pentane. The relationships between wall temperature and inlet temperature, mass flow rate, wall heat flux, inlet pressure, as well as center stream temperature are obtained. The results suggest that the heat transfer deterioration occurs when the fuel temperature approaches the pseudo-critical temperature, and the wall temperature increases rapidly and heat transfer coefficient decreases sharply. The decrease of wall heat flux, as well as the increase of mass flow rate and inlet pressure makes the starting point of the heat transfer deterioration and the peak point of the wall temperature move backward. The wall temperature increment induced by heat transfer deterioration decreases, which could reduce the severity of the heat transfer deterioration. The relational expression of the heat transfer deterioration critical heat flux derives from the relationship of the mass flow rate and the inlet pressure. 相似文献
18.
垂直并联多通道内高温高压汽-水两相流密度波型不稳定性的实验研究 总被引:1,自引:0,他引:1
在高压汽水两相流实验台上对垂直上升并联多通道中的汽 水两相流密度波型不稳定性进行了系统的试验研究,发现了并联多通道中汽液两相流密度波型不稳定性的主要特征,确定了系统压力、质量流速、入口过冷度、热负荷、进口及出口节流、可压缩容积等对该类不稳定性的影响;并将垂直并联多通道内高压汽液两相流的密度波型不稳定性与垂直并联双通道和单通道内的密度波不稳定进行了对比分析。所得结果可为大型直流锅炉和蒸汽发生器的设计提供依据。图13参10 相似文献
19.
Shahid Husain M. Altamush Siddiqui Suhail Ahmad Khan 《Numerical Heat Transfer, Part A: Applications》2019,75(11):776-793
Numerical studies on low flow rate convection boiling in a vertical annulus has been carried out to predict effects of inlet subcooling and mass flow rate. The aspect ratio of vertical annulus is 352 while the annular gap is 3.5?mm. RPI wall boiling model is used for the development of present code and the results are verified with those available in literature. The results show that onset of significant void (OSV) can be delayed to achieve maximum heat transfer by increasing the liquid subcooling and liquid mass flow rate. The average Nusselt number increases almost linearly with increase in the mass flow rate as well as the inlet subcooling. At high heat flux, very high wall temperatures are observed with low subcooling and low mass flow rates. This should be avoided for enhanced safety. 相似文献
20.
两相流密度波型脉动理论分析方法可以分为两大类:一类是数值解析法,另一类是近似分析法。数值分析法已经有很多学者进行了大量研究,而近似分析法研究相对少一些,特别是运用系统控制原理的方法来分析两相流密度波型脉动就更少,本文运用系统控制原理的方法来研究两相流密度波型脉动,提出了描述并联沸腾管内两相流密度波型脉动的线性分相模型,导出了描述系统稳定性的状态空间表达式,计算了质量流速、热负荷和系统压力的变化对系统特征方程式的特征根的影响。结果表明:各个参数对密度波型脉动界限值的影响规律与实验值是一致的。 相似文献