Investigation Of Flow And Heat Transfer Characteristics In Partitioned Thermal Convection Using Lattice Boltzmann Method

The partitioned thermal convection system is a novel structure that can substantially improve the heat transfer in thermal convection system.The similar geometric structures are widely used in heat exchangers and heat sinks.In this thesis,we use the lattice Boltzmann method(LBM)to simulates of the partitioned thermal convection system.The local grid refinement method is used to capture the flow field information more accurately in the region of complex flow.Compared with traditional computational methods,LBM has the advantages of clear physical background and excellent parallelism,etc.Firstly,the internal flow and heat transfer characteristics of partitioned thermal convection are investigated by LBM in this thesis.We mainly focus on effects of gap length,partition walls thickness and Ra number.The streamline,temperature and heat flux distributions were analyzed to reveal the internal flow and heat transfer characteristics of the partitioned thermal convection system.The numerical simulation results show that the presence of leakage vortices and heat transfer peaks in partitioned thermal convection.The presence of leakage vortices is closely related to the partition walls thickness.The heat transfer peaks mainly appear in the gap and channel inlet areas.It is found that the gap length and partition thickness significant effect for internal flow and heat transfer at Ra=10~8,when0.004<D~*<0.006 and 0.02<S~*<0.035 the Nusselt number(Nu)is maximum.The different optimal gap and optimal partition thickness exist in partitioned thermal convection when the Rayleigh number(Ra)is different.The numerical simulation results show that the optimal gap length decreases and the optimal partition thickness increases with the increase of the Ra number.The increase Ra number improves the heat transfer of the partitioned thermal convection system.Moreover,we use the water as the working fluid to investigate the partitioned thermal convection system forRa=10~9,and focus on the effects of gap length an partition wall thickness on the thermal boundary layer.By analyzing the streamline and temperature distribution characteristics,the definition of thermal boundary layer thickness is extended to make it more applicable to the partitioned thermal convection.The spatial nonuniformity of the thermal boundary layer in system is revealed by analyzing the time evolution of the temperature profile and the thermal boundary thickness.The numerical simulation results show that the gap length has a significant effect on the thermal boundary layer and Nu number.The thermal boundary layer thickness increases with the increasing gap length and the Nu number decreases with the increasing gap length at the range of0.005≤D~*≤0.03.The gap length and partition wall thickness have a coupled effect on the thermal boundary layer and Nu number.The effect of partition wall thickness on the thermal boundary layer and Nu number is stronger at D~*=0.01 and weaker at D~*=0.02.In addition,the thermal boundary layer distribution is divided into“m-type”and“n-type”according to the shape of the thermal boundary layer distribution with different gap lengths.Our investigation provides theoretical basis for enhancing heat transport and understanding the effect of partitions on the thermal boundary layer in thermal convection.It is important to guide similar geometries structure in engineering applications.