A study is made of unsteady natural convection in a square cavity of a fluid with a temperature-dependent viscosity. The flow is driven by instantaneously raising the temperature at one vertical wall and lowering the other. The viscosity variation is modeled by an exponential form, ν/$ν_o$=exp(-CT). Two boundary conditions at the horizontal walls are used : insulating walls and highly conducting walls. Numerical solutions to the governing time-dependent equations at large reference Rayleigh numbers are acquired. The evolutions of the flow patterns and isotherms are presented under various parameter settings. When the viscosity variations are large, convective activities are facilitated in the region of low viscosity and suppressed in the region of high viscosity. The global impact is to enhance the flow and heat transfer in the cavity. A representative time history of the velocities is shown. A heatup time scale is corroborated. The transient behavior of the Nusselt number at the walls is scrutinized. During the transient phase, the effect of a variable viscosity is such that the heat inflow to the cavity exceeds the heat outflow from the cavity. In effect, the cavity acts as a receiver of net heat input during the transient process.
열전달 문제를 취급할 때 나타나는 유체의 물성치는 정도의 차이는 있으나 모두 온도의 함수로 주어진다. 특정한 유체의 동점성계수는 온도에 아주 민감한 반응을 보이며, 따라서 물리적 현상을 정확하게 해석하기 위해서는 온도의 변화에 따른 동점성계수의 변화를 고려하여야 한다.
본 연구에서는 동점성계수가 온도의 함수로 주어질 때 밀폐공간내의 자연대류 열전달에 관한 유동특성과 열전달 현상을 수치적으로 해석하였다.
기준 온도에서의 동점성계수의 값이 일정하면, 최소값에 대한 최대값의 비가 클수록 고온면에서 운동량 전달 및 열전달이 활발해진다.
