Effect of Physical and Geometrical Parameters on Nuselt Number

The results of this study show that the Nusselt number decreases with the increase of the dimensionless thermal conductivity and the Prandtl, Froude numbers. The increased Reynolds, Jacob numbers and the dimensionless thickness of porous layer leads to an increase the Nusselt number.

Numerical and theoretical investigations of heat transfer characteristics in helium-xenon cooled microreactor core

Helium-xenon cooled microreactors are a vital technological solution for portable nuclear reactor power sources.To exam-ine the convective heat transfer behavior of helium-xenon gas mixtures in a core environment,numerical simulations are conducted on a cylindrical coolant channel and its surrounding solid regions.Validated numerical methods are used to determine the effect and mechanisms of power and its distribution,inlet temperature and velocity,and outlet pressure on the distribution and change trend of the axial Nusselt number.Furthermore,a theoretical framework that can describe the effect of power variation on the evolution of the thermal boundary layer is employed to formulate an axial distribution cor-relation for the Nusselt number of the coolant channel,under the assumption of a cosine distribution for the axial power.Based on the simulation results,the correlation coefficients are determined,and a semi-empirical relationship is identified under the corresponding operating conditions.The correlation derived in this study is consistent with the simulations,with an average relative error of 5.3%under the operating conditions.Finally,to improve the accuracy of the predictions near the entrance,a segmented correlation is developed by combining the Kays correlation with the aforementioned correlation.The new correlation reduces the average relative error to 2.9%and maintains satisfactory accuracy throughout the entire axial range of the channel,thereby demonstrating its applicability to turbulent heat transfer calculations for helium-xenon gas mixtures within the core environment.These findings provide valuable insights into the convective heat transfer behavior of a helium-xenon gas mixture in a core environment.

Heat Transfer in Flue Gas with Vapor Condensation

This paper combines the film model with Nusselt's condensation theory to analyze the effects of water vapor condensation on the heat transfer performance of flue gas flowing through a vertical tube. The analysis compares the condensation and convective heat transfer rates. For the concentration range investigated, the water vapor condensation transfers more energy than the flue gas convection, but the convective heat transfer can not be neglected. The heat transfer intensification due to the condensation increased as the water vapor fraction increased. The theoretical results compared well with experimental data.

火电厂烟气水分及余热陶瓷膜法回收实验

火力发电是高耗能、高耗水行业,回收火电厂烟气中水分及余热能起到显著的节能、节水效果。通过单根20 nm孔径陶瓷膜进行烟气中水分及余热回收实验,研究不同烟气流量(4～18L/min)、烟气温度(50～70℃)、烟气相对湿度(40%～100%)和冷却水流量(0.5～2.0 L/min)对回收性能的影响。结果表明:水回收速率随烟气流量、烟气温度、烟气相对湿度增加而上升;水回收效率随烟气温度、烟气相对湿度增加而上升,随烟气流量增加而下降;冷却水流量变化对水回收速率和效率没有影响;烟气对流凝结努塞尔数(Nuf)用于评价烟气在陶瓷膜内的传热性能,其随烟气流量、烟气相对湿度、冷却水流量增加而升高;大烟气流量工况时Nuf随烟气温度增加而升高,小烟气流量时Nuf随烟气温度增加呈先升高后降低趋势。研究结果对于陶瓷膜在火电厂烟气中实际应用具有理论指导意义。

陶瓷膜组件回收烟气水分及余热性能实验研究

利用陶瓷膜组件回收烟气中水分及余热有望成为火电厂节能节水的一条有效途径。为了探究陶瓷膜组件回收水分及余热的性能,本文采用孔径2μm的陶瓷膜管组成的陶瓷膜组件进行了烟气中水蒸气及余热的回收实验,研究了不同烟气温度(40～100℃)、烟气流量(320～440 m3/h)、冷却水温度(11～15℃)和冷却水流量(0.62～0.72 m3/h)对陶瓷膜组件回收水与余热性能的影响。实验结果表明:回收水速率随烟气温度及烟气流量的升高而增大,随冷却水温度的增大而降低,而冷却水流量对回收水速率影响不大;烟气平均对流凝结努塞尔(Nu)数和Zhukaukas关联式所得Nu数均随烟气温度、烟气流量的升高而增大,且烟气平均对流凝结Nu数始终大于Zhukaukas关联式所得Nu数;热回收效率随烟气温度及冷却水流量的增大而提高,随冷却水温度的增大而降低,而随着烟气流量的增大,热回收效率先提高后降低。该研究结果可为陶瓷膜组件在火电厂实际应用提供了借鉴。

烟气在陶瓷膜管内对流凝结换热实验研究

为了研究烟气中水蒸气在陶瓷膜管内的热、质传递规律,通过烟气在单根陶瓷膜管内的对流凝结换热实验,研究了不同烟气参数(流量、温度和相对湿度)和冷却水流量对烟气对流凝结Sherwood数、烟气对流凝结Nusselt数和烟气显热、潜热换热量的影响。实验结果表明:烟气对流凝结Sherwood数、Nusselt数随烟气流量、温度和相对湿度的增加而上升,Sherwood数随冷却水流量增加基本不变,Nusselt数随冷却水流量增加显著上升;烟气潜热换热量与烟气对流凝结Sherwood数呈相同变化趋势,烟气显热换热量随烟气相对湿度、冷却水流量增加而上升,烟气流量大于10 L/min时,烟气显热换热量增长趋于平缓,烟气温度对烟气显热换热量没有影响。研究结果对于陶瓷膜在电厂实际烟气中应用具有指导意义。