Numerical Investigation On Combined Heat Loss Characteristics In Fully Open Cylindrical Cavity With Environmental Wind

Heat loss in a cavity can be found in many engineering application fields, such assolar energy power generation system, the breaking system of aircraft, energyconservation in architecture and so on. The research of heat loss characteristics in cavitycan not only fulfill the mechanism of heat loss in cavity, but also provide scientific basisfor the design of engineering applications.In the case of considering the variable properties of air, the combined heat loss(conduction, convection and radiation) characteristics of a fully open cylindrical cavitywas studied by3D numerical simulation, and the simulation process was validated withrelated experiment under the same condition. The research was performed in thefollowing two thermal boundary conditions: all wall heated (both bottom and side wallare heated with constant heat flux, Case1); only bottom heated (only bottom is heatedwith constant heat flux, Case2). Visualization results, i.e., temperature contours andvelocity vectors on the symmetric plane and velocity field on the aperture plane aregiven to reflect heat transfer characteristics in the cavity. Furthermore, the effects ofrelevant parameters, such as wind speed, wind incidence angle, tilt angel and heat fluxon combined heat loss characteristics have been analyzed in detail. Accordingly, Nusseltnumber correlations that can evaluate combined convection heat loss and radiation heatloss with reasonable accuracy in the given range are proposed under two differentthermal boundary conditions respectively.Results reveal that under the two different thermal boundary conditions,environmental wind can greatly influence heat transfer characteristics, thus thetemperature field and velocity field in cavity are quite different from that without wind.With environmental wind, average combined convection heat loss Nusselt number Nucare always larger than that of natural convection in no-wind environnment under thesame condition, while radiation heat loss Nusselt number Nurare always lower than thatof no-wind case. With environmental wind, average combined convection heat lossNusselt number Nucand radiation heat loss Nusselt number Nurare affected by windspeed, wind incidence angle, tilt angel and so on, which is distinguished from NucandNurvary monotonously with tilt angel in no-wind condition. Under some certain windconditions, for a given tilt angel, there exists a critical wind incidence angle whichmakes Nucmaximum and Nurminimum. Additionally, when φ=90°, Nucand Nurare dependent on wind speed.On the other hand, there are different points under two thermal boundaryconditions. When the wind incidence angle, wind speed, tilt angle and heat flux are allthe same, the average temperature of the inner cavity wall and the air speed at the sameposition of aperture plane under Case2are lower than those under Case1. Besides,under the same condition, percentage of convection heat loss in Case1is always lowerthat in Case2, while the percentages of conduction and radiation heat loss are alwayshigher in Case1.