Numerical Study Of Natural Convection Heat Transfer Characteristics Of Cu-water Nanofluids In Complex Cavity

As a new type of energy transport medium with high efficiency and high heat transfer performance,nanofluid has a wide range of applications in vehicle engineering,engine heat dissipation,biomedicine,nuclear energy and others.Recently,many scholars have carried out many theoretical and practical researches on the heat transfer characteristics of nanofluids,especially in the field of natural convection heat transfer of nanofluids,and have achieved fruitful results.In this paper,the natural convection heat transfer characteristics of Cu-water nanofluids in a two-dimensional complex closed cavity are studied numerically.The contents and conclusions are as follows:(1)Natural convection of Cu-water nanofluid in a cavity with a thermal insulation board with different length and location is investigated numerically.The left sidewall of the cavity is maintained at a constant hot temperature,while the opposite wall has a constant cold temperature.The top and bottom horizontal walls of the cavity are adiabatic.The effects of the length and location of insulation board,nanoparticles volume fraction and Rayleigh number on natural convection heat transfer are analyzed.The results show that the average Nusselt number decreases with an increase in the length of the insulation board.When the length of the insulation board is high,the heat transfer rate at low Rayleigh number is not sensitive to the change of Rayleigh number,and the average Nusselt number almost does not change with the increase of nanoparticles volume fraction.When the length of the insulation board is kept at the fixed value,the average Nusselt number increases with increasing Rayleigh number and nanoparticles volume fraction.It is also found that the isotherms and flow fields in the cavity are different with the change of the location of the insulation board.(2)Natural convection of Cu-water nanofluid in an inclined cavity with a partially heated wall is studied numerically.The central part of the left sidewall of the cavity is maintained at a constant hot temperature,while the right sidewall has a constant cold temperature.The other walls are adiabatic.The effects of the length of partially heated wall,inclination angle of the cavity,volume fraction of nanoparticles and Rayleigh number on the natural convection of nanofluids are analyzed.The results show that when the inclination angle increases from 0° to 30°,the average Nusselt number Nu increases with the increase of the inclination angle.When theinclined angle increases from 30° to 60°,the average heat transfer rate decreases with an increase in the inclination angle.When the inclined angle,Rayleigh number and nanoparticles volume fraction are kept at the fixed values,the average Nusselt number along the hot wall decreases with the increasing length B of partially heated source.This indicates that within a certain range,the average heat transfer rate increases with the decrease of the length of partially heated source.(3)Natural convection heat transfer of Cu-water nanofluid in an L-type cavity with an internal heating obstacle is studied numerically.The shape of the internal heating obstacle is rectangular,and its top wall and two sidewalls are maintain at a constant high temperature,and the two cold walls of the enclosure are equal in length and are perpendicular to each other.The effects of cold wall length,heat source size,heat source location,volume fraction of nanoparticles and Rayleigh number on natural convection are analyzed.The results show that when nanoparticles volume fraction and Rayleigh number are high,the average Nusselt number increases first and then decreases with the increase of cold wall length.When nanoparticles volume fraction and Rayleigh number are low,the average Nusselt number increases with the increase of the cold wall length.As the heat source height increases,the average Nusselt number increases first and then decreases.By comparing the average Nusselt number at different locations of heat source,it can be seen that the optimum location of the heat source can not be found easily.For example,when N/W= 0.6,the average Nusselt number for the heat source located in the right side of the cavity is higher than that for it located in the left side of the cavity.However,when N/W=0.2,the average Nusselt number for the heat source located in the left side is higher than that for it located on the right side.