摘要
在热流密度q=0-25kW／m^2、质量流速G=10-262kg／（m^2·s）及入口压力Pin=8～9MPa的实验参数范围内，研究超临界压力C02在螺旋管中上升流动的传热特性，分析质量流速、热流密度及人口压力对换热系数的影响规律。结果表明，沿程换热系数总体呈先上升后下降的趋势，极大值发生在主流平均温度小于准临界温度而壁温大于准临界温度条件下；在换热系数上升段，沿程近壁区流体比热容增加引起的单位体积流体换热能力增强以及粘度减小引起的热边界层减薄是传热强化的主要因素；当近壁区C02发生类液态到类气态的转变时，其比热容和导热系数减小是换热系数下降的主导因素。对于物性变化剧烈的超临界流体传热，Nu数仅作为对流与导热相对大小的度量，其数值大小不能客观反映实际换热能力的强弱。
Heat transfer characteristics of supercritical CO2 flowing upward through a uniform-heated helicallycoiled tube were experimentally investigated under the conditions of q=0-25 kW/m^2, G=10--262 kg/（m^2.s） and Pro=8-9 MPa. Effects of mass flux, heat flux and inlet pressure on the longitudinal heat transfer performance were analyzed. It was found that the heat transfer coefficients first increased and then decreased. The maximum values of heat transfer coefficients always occurred at the temperature range of Tb〈Tpc〈Tw. For the heat transfer coefficients ascent stage, the heat transfer capability enhancement per unit volume caused by the increased heat capacity, together with the thinner thermal boundary layer induced by the decreased viscosity, dominated the heat transfer performance at the near-wall region. While for the stage that CO2 experienced the state transition from quasi-liquid to qusi-vapour, the sharp decreases of heat capacity and thermal conductivity became the dominant factor for the heat transfer deterioration. For the transcritical convective heat transfer with large physical property variations, the Nusselts number, standing for the ratio of heat convection to conduction, could not represent the real heat transfer capacity any more.
出处
《核动力工程》
EI
CAS
CSCD
北大核心
2014年第1期28-31,共4页
Nuclear Power Engineering
基金
国家自然科学基金青年科学基金项目(51006035)
国家自然科学基金重大国际合作项目(51210011)
教育部留学回国人员科研启动基金
中央高校科研业务费专项资金(12MS35)
关键词
超临界压力CO2
螺旋管
对流换热
准临界温度
Supercritical CO2, Helically coiled tube, Convective heat transfer, Qusi-critical temperature
