超临界水在大型换热器中的流动与传热强化研究
发布时间：2019-06-30 21:51
【摘要】：超临界水在锅炉或反应堆等大型换热设备中的应用能够大幅提高其出口工质热力参数,从而提高发电设备的整体经济性。然而超临界水在大比热区的特殊热物理性质及其在高焓值区较低的吸热能力使得其高温条件下的应用受到了一定的限制,因此对超临界水在大型换热器中,尤其是高温条件下的传热强化的研究十分重要。本文以超临界锅炉水冷壁及反应堆堆芯为对象,利用商业CFD软件对超临界水在内螺纹和定位格架等扰流部件影响下的流动和传热强化特性进行了数值研究,重点分析了受热面内冷通道中工质流动及传热在径向及周向分布特性,并揭示了其相关机理。针对内螺纹管的数值研究表明,内螺纹的导流作用在垂直于主流的方向造成了较强的二次流场,而主流焓值的变化对二次流场的基本结构几乎没有什么影响。局部传热在内螺纹管周向和径向分布不均,超临界水在螺纹顶部区域的换热效果远好于螺纹底部。在螺纹顶部表面形成的单个旋涡产生一个压力相对较低的区域,使得这个该区域传热得到强化。在大比热区,由于流体热物性急剧变化,换热的不均性更加显著。螺纹底部是换热的薄弱点,内螺纹管结构优化的重点应集中在该区域。针对装配有定位格架的反应堆堆芯的数值结果表明,由于流动阻塞效应的影响,高温条件下燃料棒包壳表面温度周向分布不均,中心区最低而窄缝区最高。在标准型定位格架的下游,严重的抑流作用使得窄缝区的周向温差增加,传热效果减弱；带有交错叶片的定位格架的下游,包壳周向流动与传热特性差异很大,在下游小部分区域传热性能有所增强,但是由于旋流作用的影响,周向大部分区域的传热减弱,因此旋流不利于超临界水在高焓值区的传热,定位格架下游的换热弱化现象或许是超临界反应堆紧凑型堆芯的特有现象,须在堆芯设计中加以重视。
[Abstract]:The application of supercritical water in large-scale heat exchange equipment such as a boiler or a reactor can greatly improve the heat parameters of the working medium of the outlet, so as to improve the overall economy of the power generation equipment. However, the special thermal physical properties of the supercritical water in the large specific heat area and the lower heat absorption capacity in the high specific heat area are limited, so the research on the heat transfer enhancement of the supercritical water in the large-scale heat exchanger, in particular at high temperature, is very important. In this paper, the flow and heat transfer enhancement characteristics of the supercritical water under the influence of the internal thread and the positioning grid are numerically studied by using the commercial CFD software as the object of the water-cooled wall and the reactor core of the supercritical boiler. In this paper, the characteristics of the flow and heat transfer of the working medium in the cold channel in the heated in-plane are analyzed, and the related mechanism is also revealed. The numerical study on the internal thread tube shows that the flow-guiding effect of the internal thread causes a stronger secondary flow field in the direction perpendicular to the main flow, and the change of the main flow value has little influence on the basic structure of the secondary flow field. And the heat exchange effect of the supercritical water on the top area of the thread is far better than the bottom of the thread. A single vortex formed on the top surface of the thread creates a relatively low pressure zone such that the heat transfer in this region is enhanced. In the large specific heat area, the non-uniformity of heat exchange is more significant due to the rapid change of the thermal physical properties of the fluid. The bottom of the thread is the weak point of heat exchange, and the optimization of the internal thread pipe structure should be focused on the area. The numerical results of the reactor core with the positioning grid show that the surface temperature of the fuel rod can be distributed unevenly in the condition of high temperature due to the influence of the flow blocking effect, and the central area is the lowest and the narrow slit area is the highest. in the downstream of the standard type positioning grid, the severe flow-inhibiting effect is such that the circumferential temperature difference of the narrow-seam zone is increased, the heat transfer effect is weakened, the downstream of the positioning grid with the staggered blades, the difference between the circumferential flow of the cladding and the heat-transfer characteristic is large, and the heat transfer performance of the downstream small-part region is enhanced, However, due to the influence of the swirl effect, the heat transfer in most regions of the circumferential direction is weakened, so that the swirling flow is not favorable for the heat transfer of the supercritical water in the high-flow-value region, and the heat exchange weakening phenomenon downstream of the positioning grid may be a unique phenomenon of the compact core of the supercritical reactor, and it is necessary to attach importance to the core design.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TK172
本文编号：2508287
[Abstract]:The application of supercritical water in large-scale heat exchange equipment such as a boiler or a reactor can greatly improve the heat parameters of the working medium of the outlet, so as to improve the overall economy of the power generation equipment. However, the special thermal physical properties of the supercritical water in the large specific heat area and the lower heat absorption capacity in the high specific heat area are limited, so the research on the heat transfer enhancement of the supercritical water in the large-scale heat exchanger, in particular at high temperature, is very important. In this paper, the flow and heat transfer enhancement characteristics of the supercritical water under the influence of the internal thread and the positioning grid are numerically studied by using the commercial CFD software as the object of the water-cooled wall and the reactor core of the supercritical boiler. In this paper, the characteristics of the flow and heat transfer of the working medium in the cold channel in the heated in-plane are analyzed, and the related mechanism is also revealed. The numerical study on the internal thread tube shows that the flow-guiding effect of the internal thread causes a stronger secondary flow field in the direction perpendicular to the main flow, and the change of the main flow value has little influence on the basic structure of the secondary flow field. And the heat exchange effect of the supercritical water on the top area of the thread is far better than the bottom of the thread. A single vortex formed on the top surface of the thread creates a relatively low pressure zone such that the heat transfer in this region is enhanced. In the large specific heat area, the non-uniformity of heat exchange is more significant due to the rapid change of the thermal physical properties of the fluid. The bottom of the thread is the weak point of heat exchange, and the optimization of the internal thread pipe structure should be focused on the area. The numerical results of the reactor core with the positioning grid show that the surface temperature of the fuel rod can be distributed unevenly in the condition of high temperature due to the influence of the flow blocking effect, and the central area is the lowest and the narrow slit area is the highest. in the downstream of the standard type positioning grid, the severe flow-inhibiting effect is such that the circumferential temperature difference of the narrow-seam zone is increased, the heat transfer effect is weakened, the downstream of the positioning grid with the staggered blades, the difference between the circumferential flow of the cladding and the heat-transfer characteristic is large, and the heat transfer performance of the downstream small-part region is enhanced, However, due to the influence of the swirl effect, the heat transfer in most regions of the circumferential direction is weakened, so that the swirling flow is not favorable for the heat transfer of the supercritical water in the high-flow-value region, and the heat exchange weakening phenomenon downstream of the positioning grid may be a unique phenomenon of the compact core of the supercritical reactor, and it is necessary to attach importance to the core design.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TK172
【共引文献】
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3 刘小龙;超临界W型火焰锅炉水冷壁的热应力分析[D];华中科技大学;2013年
4 邓彦翔;超临界直流锅炉水冷壁流动阻力研究[D];华中科技大学;2012年
5 唐丽君;超临界压力下低温甲烷在肋片冷却圆管中的强化传热的数值模拟研究[D];浙江大学;2014年
6 周昭勇;超临界甲烷/氢混合工质冷却换热特性研究[D];上海交通大学;2014年
7 张婧雍;基于CFD的超临界水棒束内流动传热研究[D];上海交通大学;2014年
8 魏婷;超临界水冷固态增殖包层热工设计准则的初步研究[D];上海交通大学;2014年
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