水平圆管蓄热器的传热及非线性特性研究

Study on Heat Transfer and Nonlinear Characteristics of Horizontal Circular Tube Regenerator

利用Fluent软件对水平圆管外石蜡受热融化的相变蓄热过程进行数值模拟,采用基于焓法的凝固/融化模型,考虑自然对流,建立圆管外石蜡融化模型,其左右壁面冷却温度为293 K,上、下壁面为绝热边界条件,中间加热管壁温度为363 K,矩形腔宽为60 mm,分别取30,60和120 mm底边长作为特征尺寸,中间圆管直径为20 mm,分析圆管外石蜡受热融化后液相区石蜡的非对称流动特性。结果表明:当瑞利数Ra=5.27×10^(6)时数值解的轨迹在相空间中呈现一个不动点,表明是一个稳定定态解;当Ra=4.22×10^(7)时数值解的轨迹在相空间中为一封闭曲线,表明解是周期振荡解;在Ra=3.38×10^(8)时数值解的轨迹在相空间中没有确定的周期,解是随机的;数值结果揭示了在相同的冷却和加热温度下,改变模型的特征尺寸,融化过程的解不止一个定态。

Fluent software was used to numerically simulate the phase change heat storage process of paraffin melted by heat outside the horizontal circular tube.The solidification or melting models based on enthalpy method were used to consider the effect of natural convection.A paraffin melting model outside the circular tube was established,in which the cooling temperatures of the left and right wall surfaces were 293 K,the upper and lower wall surfaces were adiabatic boundary conditions,the wall temperature of the middle heating tube was 363 K,the width of the rectangular cavity was 60 mm,the bottom side lengths of 30 mm,60 mm and 120 mm were taken as the feature sizes respectively,and the diameter of the middle circular tube was 20 mm.The asymmetric flow characteristics of paraffin in the liquid phase region were analyzed after the paraffin was melted by heat outside the circular tube.The research results show that when Ra is 5.27×10^(6),the trajectory of the numerical solution presents a fixed point in the phase space,which indicates that it is a stable steady state solution;when Ra is 4.22×10^(7),the trajectory of the numerical solution is a closed curve in the phase space,which indicates that the solution is a periodic oscillation solution;when Ra is 3.38×10^(8),the trajectory of the numerical solution has no definite period in the phase space,and the solution is random.The numerical results reveal that there is more than one steady state solution in the melting process by changing the feature sizes of the model at the same cooling and heating temperatures.