A Numerical Simulation Of Laminar Mixed Convective Flow Pattern And Heat Transfer In A Horizontal Rectangular Channel

Mixed convection widely exists in natural and industrial fields,such as chemical vapor deposition(CVD),the cooling of electronic components and flat plate heat exchangers.The study of laminar mixed convection in the horizontal channel has many advantages,especially for the rational design and improvement of the heat exchanger and the material preparation process.In mixed convection,forced flow in the horizontal direction and natural convection driven by buoyancy or Marangoni force affect the flow together.Based on the finite volume method,this paper uses FLUENT software to simulate the laminar mixed convection in a horizontal rectangular channel.The model adopted is a rectangular horizontal channel and the internal flow of the fluid in closed channel(heated from below and cooled from above both with a constant temperature)and open channel(heated from below with a constant temperature and the upper surface is a free surface in contact with air)are discussed respectively.The text is conducted in the range of 10 ? Re ? 20,5000 ? Ra ? 32600,10 ? Bi ? 30,and 250 ? Ma ? 2000,respectively.Firstly,the two mechanisms of the formation of longitudinal rolls in closed channel are analyzed.The first one,called sidewall roll initiation mechanism,is triggered by the sidewall effect,and two longitudinal rolls are first initiated at the sidewalls of the channel and then propagate gradually to the core of the downstream direction.The second one,namely combined initiation mechanism,is caused by the sidewall effect and the supercritical vertical thermal gradient at the lower wall,and almost all longitudinal rolls appear simultaneously just in the entrance downstream region of the channel.Secondly,the relevant parameters affecting the flow pattern and heat transfer in the closed channels is discussed,which include Reynolds number,Rayleigh number,the aspect ratio and the temperature of channel sidewalls.Then we studied the flow pattern and formation mechanisms of the longitudinal rolls in the open horizontal channel,and the difference between the closed channel and the open channel.Finally,the effects of the dimensionless numbers such as Reynolds number,Biot number,and Marangoni number on the flow pattern and heat transfer in the open horizontal channel are discussed.