超临界压力锅炉水冷壁倾斜并联内螺纹管内两相流不稳定性的试验研究

针对国产首台600 MW超临界机组在亚临界压力条件下的水动力特性,进行了倾斜并联内螺纹管内的汽液两相流不稳定性试验研究,观察到压力降型和密度波型两种类型的脉动。探讨了影响不稳定性的主要参数。并给出了发生不稳定性的阈值。试验表明:在超临界锅炉滑压运行设计参数条件下,水冷壁管内不会发生两相流不稳定性。图11表1参7     

600MW超临界CFB垂直并联内螺纹管两相流压力降不稳定试验研究

在600 MW超临界CFB水冷壁变负荷实际运行条件下,以水冷壁实际采用的Φ28.6×5.8 mm的4头内螺纹管为研究对象,在高压汽水两相流回路上对垂直并联管中汽液两相流压力降型不稳定进行了试验研究.确定了压力、质量流速、进口过冷度以及上游可压缩容积对垂直并联内螺纹管两相流压力降型脉动的影响.结果表明,随压力增大,发生脉动的临界热负荷增加,界限干度逐渐升高,系统稳定性增强,脉动周期先变长后变短,脉动的振幅逐渐减小.本试验中,当压力P＞6 MPa时,就不再有压力降脉动发生;随着质量流速的增加,脉动发生的界限热负荷升高,而脉动的周期减小;进口过冷度对密度波脉动呈现单值性影响,随进口过冷度增加,界限热负荷单调增加,界限干度的变化表现出不同的趋势,在较低的质量流速下,随着过冷度的增加,界限干度单调下降;在较高的质量流速下,随着过冷度的增加,界限干度单调上升;上游可压缩容积对界限热负荷的影响较小,随充气比的增大,脉动的周期和幅值逐渐增大.     

垂直并联内螺纹管水动力不稳定性试验研究

以东方锅炉（集团）股份有限公司自主开发的600MW超临界“w”火焰锅炉拟采用的031．8x6mm多头优化内螺纹管为研究对象,在多相流试验台上进行了锅炉水冷壁在低负荷条件下的水动力不稳定性试验研究,并对试验结果进行了初步分析,得出了水冷壁发生水动力不稳定的条件。试验表明：东方锅炉自主设计的600MW超临界“w”火焰锅炉水冷壁拟采用的多头内螺纹管在当压力〉6MPa时,试验就不再有密度波型脉动发生,当压力〉9MPa时,就不再有压力降型脉动发生。因此,根据东方锅炉超临界“w”火焰锅炉的设计特点及设计运行参数范围,锅炉运行不会出现水动力不稳定现象,水冷壁水动力是安全的、可靠的。     

超超临界锅炉水冷壁传热特性和温度偏差

叙述了变压运行超超临界锅炉水冷壁的运行特点,传热恶化、温度偏差与水动力稳定性的国内外研究结果,提出了对垂直内螺纹管水冷壁质量流速的选取和水动力不稳定性校核的看法.     

超临界锅炉垂直管屏水冷壁变压运行特性分析

针对1 000 MW超超临界机组锅炉内螺纹管垂直管屏水冷壁变压运行特性进行了理论分析.重点分析了低质量流速下的水冷壁热偏差对流量偏差的影响关系和内螺纹管传热特性以及直流锅炉水冷壁强制流动特性被自然循环特性部分低偿的流动特性.     

超超临界锅炉垂直水冷壁的结构特点和水动力特性

叙述了超超临界锅炉垂直水冷壁的结构特点和水动力特性,并介绍了内螺纹管垂直管圈水冷壁主要设计参数的选取原则和水动力稳定性的判别方法。     

600MW超临界压力直流锅炉启动工况水动力稳定性分析

文中介绍正在研制的国产600MW超临界变压运行直流锅炉水冷壁结构特点和启动过程。通过理论分析，得到了分析水冷壁水动力稳定性的准则方程式。根据锅炉的实际运行工祝，在高压汽水两相试验台上，进行了螺旋管圈水冷壁倾斜管中水动力不稳定性的试验研究。其参数为P＝2～4MPa，质量流速G＝600～1200kg/m2s，入口过冷度△tsub=10～120°C，热负荷0～650kw／m2，管径20×2mm，螺旋升角α＝14°。在上述参数范围内，研究了压力、质量流速、入口过冷度、热负荷及热负荷分布、进口和出口节流、可压缩容积对螺旋管圈水动力不稳定性的影响。由试验得出的计算公式，分析计算了锅炉水动力稳定性边界，在最小直流工祝时可能会出现压力降型脉动。     

亚临界及近临界压力区内螺纹管汽水两相流的传热

本文阐述了在西安交通大学高压汽水两相流实验回路上进行的垂直上升内螺纹管内汽水两相流传热特性的试验研究。试验管采用φ28×6mm的螺纹管,试验管材料为:12Cr1MoV。试验参数为压力P=13.0～22.0MPa,内壁热负荷q=200～800kW/m~2质量流速G=400～1800kg/m~2·s。试验确定了在上述参数范围内的壁温变化特性,得出了发生传热恶化的临界热负荷和界限质量流速。文中结论对采用内螺纹管的电站锅炉水冷壁的设计具有较高的价值。     

超临界W型火焰锅炉垂直水冷壁水动力特性研究

对超临界W型火焰锅炉垂直水冷壁的水动力特性进行研究,首先对锅炉应用的材料为SA-213T12的ф31.8mm×5.5mm四头优化内螺纹管在试验台进行阻力特性研究,得到摩擦阻力系数λ。根据摩擦阻力系数λ及运行参数,计算某电厂600 MW超临界机组直流锅炉炉膛垂直水冷壁的阻力特性、流量偏差及热负荷偏差,并对水冷壁的水动力特性进行分析研究。     

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

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     

Two－Phase Critical Discharge of Initially Saturated or Subcooled Water Flowing in Sharp－Edged Tubes at High Pressure

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Experimental Investigation of Two-Phase Flow Instabilities in Low-Mass-Flux Water Wall Tubes of Supercritical Circular Fluidized Bed Boilers

For the purpose of disclosing the hydrodynamic flow characteristics, under the low mass velocity conditions of the 600-MW supercritical circular fluidized beds boilers, experimental studies on instability of two-phase flow in parallel vertical internally ribbed tubes were conducted. Two kinds of oscillations, pressure-drop oscillation and density-wave oscillation, have been observed. In the range of test parameters the effects of pressure, mass flux, inlet subcooling, compressible volume, exit throttle, and asymmetric heat flux to the two-phase instability were explored and analyzed. Indications from experiment data are: To increase system pressure, mass flux and inlet subcooling will intensify the stability of water wall tubes. To increase exit throttle will intensify the instability of water wall tubes. The bounding pressure and bounding mass flux of density-wave oscillations and the bounding pressure of pressure-drop oscillation have been obtained. Based on the results of testing and using a homogeneous model, the threshold relational expressions of instability were obtained. The results may be used for the design and safe operation of parallel vertical rifled water wall tubes of supercritical circular fluidized beds boilers.     

Optimization of Venturi tube design for pipeline pulverized coal flow measurements

A Venturi flow meter was designed to accurately measure the mass flow rate of pulverized coal in power plant pipelines. Numerical simulations of the dilute turbulent gas-solid two-phase flow in a horizontal Venturi tube were used to study the effects of Venturi tube geometry on the pressure distribution in the mixture. The results show that Venturi tube geometry strongly influences the metering of the dilute gas-particle two-phase flow. The geometry can be optimized to improve the precision of the measurement and ensure stable measurements. Furthermore, the geometries of three types of Venturi tubes were optimized for an experimental study of pulverized coal mass flow rate measurements.     

MASS FLOW RATE DISTRIBUTION AND PHASE SEPARATION OF R-22 IN MULTI-MICROCHANNEL TUBES UNDER ADIABATIC CONDITION

The present study investigated mass flow rate distribution and phase separation of R-22 in multi-microchannel tubes under adiabatic condition. The test section consisted of inlet and outlet headers with the inner diameter of 19.4 mm and 15 parallel multi-microchannel tubes. Each microchannel tube had 8 rectangular ports with hydraulic diameter of 1.32 mm. The key experimental parameters were the orientation of the header (horizontal and vertical), flow direction of refrigerant into the inlet header (in-line, parallel and cross flow), and inlet quality (0.1, 0.2, and 0.3). The effect of inlet quality on the mass flow rate distribution and phase separation in the microchannel tubes was negligible. The effect of the orientation of the header on the mass flow rate distribution and phase separation was the largest among the test parameters. Horizontal header showed better mass flow rate distribution and phase separation characteristics than vertical header. Both parallel and cross-flow conditions showed better mass flow rate distribution and phase separation than in-line flow condition.     

Boiling curve in temperature wave region

Heat transfer was studied for the case of autowave transition from metastable to stable boiling regimes. The boiling curves classification was proposed in dependence on the direction of the vectorial parameters, such as temperature gradient, flow and temperature wave velocity. According to the proposed hypothesis, considerable changes in heat transfer relationships in the regions affected by temperature waves can be explained by local non-equilibrium near-to-wall layers.The experiments were conducted to study heat transfer in case of autowave change of boiling conditions in tubes in the pressure range from 3 to 10 MPa and in the broad range of steam quality and mass velocity. It was demonstrated that the change of boiling regimes in tubes in the form an autowave could be observed if the steam quality was less than its boundary value.The paper also discusses possible application of the obtained data for simulation of abnormal processes in the reactor core.     

A comparison of flow characteristics of refrigerants flowing through adiabatic straight and helical capillary tubes

This paper presents a numerical investigation of the flow characteristics of helical capillary tubes compared with straight capillary tubes. The homogenous two-phase flow model developed is based on the conservation of mass, energy, and momentum of the fluids in the capillary tube. This model is validated by comparing it with the experimental data of both straight and helical capillary tubes. Comparisons of the predicted results between the straight and helical capillary tubes are presented, together with the experimental results for straight capillary tubes obtained by previous researchers. The results show that the refrigerant flowing through the straight capillary tube provides a slightly lower pressure drop than that in the helical capillary tube, which resulted in a total tube length that was longer by about 20%. In addition, for the same tube length, the mass flow rate in the helical capillary tube with a coil diameter of 40 mm is 9% less than that in the straight tube. Finally, the results obtained from the present model show reasonable agreement with the experimental data of helical capillary tubes and can also be applied to predict the flow characteristics of straight capillary tubes by changing to straight tube friction factors, for which Churchill's equation was used in the present study.     

Evaporative characteristics of R-134a and R-600a in horizontal tubes with perforated strip-type inserts

Experimental heat transfer coefficients for R-134a and R-600a in horizontal tubes with vertically positioned perforated strip-type inserts are reported in this paper. Tests were conducted using a single-tube evaporator test facility. The test section used was 2000 mm long, 10.6 mm inside diameter, horizontal, smooth copper tube with perforated strip-type inserts made from the same material (copper). Test parameters were varied as follows: heat flux 9.1-31.2 kW/m²; mass velocity 82.3-603.3 kg/m² s; quality 0-0.85, and a saturation temperature of 6 °C. The flow pattern were identified for different test tubes and flow conditions. The heat transfer coefficients for R-600a were higher than those for R-134a. The heat transfer performance and pressure drop can be improved up to 2.5 and 1.5, respectively for a 96 perforated holes enhanced tube. All comparisons were based on the same nominal mass flow rate. Finally, an empirical correlation was developed.     

Investigations on heat and mass transfer characteristics of falling film horizontal tubular absorber

An experimental set-up is built incorporating only two principle components, viz, absorber and generator of vapor absorption refrigeration system (VARS) to investigate heat and mass transfer characteristics of absorber. The refrigerant, R134a (1,1,1,2-tetrafluroethane) is absorbed by R134a-DMAC (N,N-dimethylacetamide) solution flowing over the horizontal tubes arranged as tube bank. The effect of solution flow rate, coolant flow rate and temperature, heater load and concentration of R134a is studied. The performance parameters like solution exit temperature from tubes, state point temperatures, heat flux, mass flux, and overall heat and mass transfer coefficients are presented for different operating condition of absorber. For lower flow rate of the solution and higher flow rate of the coolant, the bulk solution temperature is found to decrease. The heat and mass transfer coefficients increase with mass flow rate of the solution. An increase in inlet temperature of coolant results into an increase in overall heat transfer coefficient and decrease in overall mass transfer coefficient.     

Performance of a split-type air conditioner matched with coiled adiabatic capillary tubes using HCFC22 and HC290

This paper experimentally investigated the system performance of a split-type air conditioner matching with different coiled adiabatic capillary tubes for HCFC22 and HC290. Experiments were carried out in a room-type calorimeter. The results have shown that (1) similar cooling effects can be achieved by matching various capillary tubes of different inner diameters; (2) parallel capillary tubes presented better system performance and flow stability with weaker inlet pressure fluctuations than the single capillary tube; (3) with the coil diameter of the capillary tube increasing from 40 mm to 120 mm, the mass flow rate tended to increase slightly. But the cooling capacity, input power and energy efficiency ratio (EER) did not show evident tendency of change; (4) the refrigerant charge and mass flow rate for HC290 were only 44% and 47% of that for HCFC22, respectively, due to the much lower density. And HC290 had 4.7–6.7% lower cooling capacity and 12.1–12.3% lower input power with respect to HCFC22. However, the EER of HC290 can be 8.5% higher than that of HCFC22, which exhibits the advantage of using HC290. In addition, the experimental uncertainties were analyzed and some application concerns of HC290 were discussed.     

Experimental study of operation performance for hydrocarbon fuel pump with low specific speed

In this paper,a small flow rate hydrocarbon turbine pump was used to pressurize the fuel supply system of scramjet engine.Some experiments were carried out to investigate the characteristics of turbine pump driven by nitrogen or combustion gas under different operating conditions.A experimental database with regard to the curves of the rotational speed,mass flow rate and net head with regard to centrifugal pump were plotted.These curves were represented as functions of the pressure and temperature at turbine inlet/outlet and the throttle diameter at downstream of centrifugal pump.A sensitivity study has been carried out based on design of experiments.The experimental was employed to analyze net head of centrifugal and throttle characteristics.The research results can accumulate foundations for the close loop control system of turbine pump.