竖直矩形窄缝流道内强迫流动沸腾传热实验研究
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摘要
常压下在竖直矩形窄缝流道内，以纯净水作为实验工质，进行了强迫流动沸腾的流型特征、启动时壁面温度变化特性和沸腾传热特性的实验研究。实验段中的窄缝宽度为2mm，采用单侧蒸汽加热，另一侧可视化，可以直接观察到流道内的流型变化和发生沸腾的整个过程。
实验中对矩形窄缝流道中强迫流动沸腾换热过程进行了拍摄，发现矩形窄缝流道中流型的转变与一般管内的流型转变存在差异，出现有别于普通圆管内两相流的特殊流型。
在启动实验中，壁面温度变化经历了三个阶段，对应于三种不同的换热方式。加热功率、体积流量和入口过冷度对壁温变化、净蒸汽产生点及饱和沸腾滞后现象均有影响。
由实验观察发现当实验条件一定时，净蒸汽产生点的位置处于一种动平衡状态。经验证发现，Levy模型和Saha模型计算的净蒸汽产生点与实验结果相差甚远。在体积流量为60L/h情况下，用孙奇等人计算模型的计算值与实验值吻合较好，相对误差在±20％以内。
在饱和沸腾过程中，流动不稳定性、窄缝流道内汽液两相流动的对称性差等因素，对加热壁面和工质的温度波动有一定影响。体积流量仅在过冷沸腾区内对工质温度有显著影响。
Flow pattern characteristics of forced flow boiling heat transfer, characteristics of wall temperature variation and boiling heat transfer characteristics in vertical narrow rectangular channel under atmospheric pressure with pure water as experimental medium was investigated. The width of narrow channel in testing section was 2 mm, and single wall vapor heating and visualization were introduced in the experiments. The variation of flow pattern characteristics in channel and the procedure of boiling generating can be observed directly from one side, with the channel heated from the other one.
The variation procedure of forced flow boiling heat transfer in narrow rectangular channel was photographed in the experiment. There was difference between transition of flow pattern in narrow rectangular channel and transition of flow pattern in common tube.
Corresponding for three phases in variation of wall temperature in the experiment of start-up, there were three different modes of heat exchange. Heating power, volume flow rate and condensate depression in entrance all influenced the variation of wall temperature, OSV (initial point of net vapor generation) and hysteresis of saturated boiling.
According to the experiment observation, the position of OSV existed in state of dynamic balancing under definite experimental condition. By the verification, the position of OSV which calculated from model Levy and model Saha was far from the experimental one. While the conclusion drew from model SUNQI tally with experimental value preferably under condition that volume flow rate was 60L/h, with relative error less than±20 %.
In the process of saturated boiling, the instability of flow, the weak symmetry of vapor-liquid two-phase flow in narrow channel and other factors had some influence on temperature fluctuation of heating wall and medium. Volume flow rate had notable influence on the medium only in section of subcooled boiling.
实验中对矩形窄缝流道中强迫流动沸腾换热过程进行了拍摄，发现矩形窄缝流道中流型的转变与一般管内的流型转变存在差异，出现有别于普通圆管内两相流的特殊流型。
在启动实验中，壁面温度变化经历了三个阶段，对应于三种不同的换热方式。加热功率、体积流量和入口过冷度对壁温变化、净蒸汽产生点及饱和沸腾滞后现象均有影响。
由实验观察发现当实验条件一定时，净蒸汽产生点的位置处于一种动平衡状态。经验证发现，Levy模型和Saha模型计算的净蒸汽产生点与实验结果相差甚远。在体积流量为60L/h情况下，用孙奇等人计算模型的计算值与实验值吻合较好，相对误差在±20％以内。
在饱和沸腾过程中，流动不稳定性、窄缝流道内汽液两相流动的对称性差等因素，对加热壁面和工质的温度波动有一定影响。体积流量仅在过冷沸腾区内对工质温度有显著影响。
Flow pattern characteristics of forced flow boiling heat transfer, characteristics of wall temperature variation and boiling heat transfer characteristics in vertical narrow rectangular channel under atmospheric pressure with pure water as experimental medium was investigated. The width of narrow channel in testing section was 2 mm, and single wall vapor heating and visualization were introduced in the experiments. The variation of flow pattern characteristics in channel and the procedure of boiling generating can be observed directly from one side, with the channel heated from the other one.
The variation procedure of forced flow boiling heat transfer in narrow rectangular channel was photographed in the experiment. There was difference between transition of flow pattern in narrow rectangular channel and transition of flow pattern in common tube.
Corresponding for three phases in variation of wall temperature in the experiment of start-up, there were three different modes of heat exchange. Heating power, volume flow rate and condensate depression in entrance all influenced the variation of wall temperature, OSV (initial point of net vapor generation) and hysteresis of saturated boiling.
According to the experiment observation, the position of OSV existed in state of dynamic balancing under definite experimental condition. By the verification, the position of OSV which calculated from model Levy and model Saha was far from the experimental one. While the conclusion drew from model SUNQI tally with experimental value preferably under condition that volume flow rate was 60L/h, with relative error less than±20 %.
In the process of saturated boiling, the instability of flow, the weak symmetry of vapor-liquid two-phase flow in narrow channel and other factors had some influence on temperature fluctuation of heating wall and medium. Volume flow rate had notable influence on the medium only in section of subcooled boiling.
引文
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[2]IshibasM E, Nishilcaw K.Saturated Boiling Heat Transfer in Narrow Spaces. Int. J. Heat Mass Transfer. 1969. 12: 863-894P.
[3]孙淑凤．吴裕远．液氮在狭缝通道内受迫流动沸腾换热的实验研究．西安交通大学学报，2001，(35)5：450-454页．
[4]沈秀中．宫崎庆次．徐济鋆．在垂直环形窄缝流道中的沸腾传热特性研究．核科学与工程，2001，(21)3：244-251页．
[5]吴裕远．陈流芳．杜建通．潘春晖．杨东文．液氮在狭缝中热虹吸两相流传热的强化实验研究．西安交通大学学报，1994，28(9)：104-110页．
[6]夏春林．狭窄空间内沸腾传热机理．航空学报，1994，(15)7：274～279页．
[7]M D Diev. A I Leontiev. A study of liquid microlayer during boiling in narrow vertical slot channels. Experimental Heat Transfer, 1998,11(2): 101-120P.
[8]H Kusuda. M Monde. H Uehara. K Otubo. Bubble influence on boiling heat transfer in a narrow space(in a low heat-fiux region).Heat Transfer-Japanese Research, 1981,9(2):56-60P.
[9]E Ishibashi. Z H Liu. T Chirifu. N Murakami. Pool-boiling heat-transfer characteristics of the surface-worked heat-transfer tubes in narrow spaces under reduced pressure conditions. Heat Transfer-Japanese Research, 1993, 22(7): 703-715P.
[10]孙中宁．阎昌琪．杜泽．光管及窄环隙流道池沸腾换热实验研究．工程热物理学报，2001，22(4)：485-487页．
[11]张瑞．焦安军．弦月形狭缝通道内液氮受迫流动沸腾传热强化的研究．低温工程，2001，5：42-48页．
[12]高刚．吴洪涛．黄素逸．巴长喜．套管式蒸汽发生器沸腾传热实验研究． 核动力工程，1996，17(4)：332-336页．
[13]沈秀中．宫崎庆次．井村谕．徐济望．在双面加热的窄缝环形流道中流动沸腾换热研究．核动力工程，2001，22(2)：113-118页．
[14]潘良明．垂直矩形窄缝流动过冷沸腾时汽泡行为和换热．重庆大学博士论文．2002：33-47页．
[15]Gopinath R Warrier. Vijay K Dhir. Leslie A Momoda. Heat transfer and pressure drop in narrowrectangular channels. Experimental Thermal and Fluid Science, 2002,26:53-64P.
[16]Shi-Chune Yao, Yung Chang. Pooling heat transfer in a confined space. Int. J. Heat Mass Transfer. 1983,26(6): 841-848P.
[17]刘瑞兰．贾斗南．王增辉．苏光辉．秋穗正．环形狭缝通道内沸腾换热传热特性的实验研究．核科学与工程，2001，(21)3：238-243页．
[18]彭晓峰．王补宣．微型槽内流动沸腾的实验研究．工程热物理学报，1993，(14)3：281-286页．
[19]尤国春．张鹏．王如竹．多方位矩形窄缝中液氮沸腾传热特性实验研究．工程热物理学报，2004，(25)3：472-747页．
[20]吴云英．杨伟．葛根哈斯．缝宽2mm的矩形通道内流动沸腾传热的计算与关联．化工学报，1996，47(3)：367-370页．
[21]杨伟．吴云英．矩形窄缝通道内两相湍流蒸发的传热研究．内蒙古工业大学学报，1996，15(3)：48-52页．
[22]沈秀中．刘洋．张琴舜．适于窄缝流动沸腾传热的关系式．核动力工程，2002，23(1)：80-83页．
[23]苏顺玉．黄素逸．王小墨．环形窄缝中沸腾传热特性的研究．工程热物理学报，2004，(25)3：442-444页．
[24]浦鹏飞．潘良明．李午申．黄永军．竖直矩形狭缝通道内环状流沸腾换热分析模型．热科学与技术，2005，(4)3：208-212页．
[25]Levy S. Forced Convection Subcooled boiling of Vapor Volumetric Fraction. Int. J. Heat Mass Transfe 1967, 10: 951-965P.
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