Study on Heat Transfer Characteristics of Gaseous Flows in Micro Channels

小型器件的制造增加了对微观几何结构中流体流动和换热的了解的需要。由于摩擦损失，微通道内流体流动的压力降很大。在气态流动的情况下，气体沿通道膨胀，并在通道中加速流动。这导致温度下降，因为从内能到动能的能量转换。微通道内气体流动的换热特性可能不同于不可压缩流动。然而，目前还没有关于微通道内气体流动换热特性的参数研究。这就是本研究的动机。本研究的目的是：1.获得微通道内气体流动的换热特性。2.对前述研究中数值得到的通道出口气体温度进行了验证：(1)对热流密度在10^2~10^4W范围内恒定壁温的通道进行了计算。通道高度范围为10到100μm，通道高度和长度的纵横比固定为200。得到了微通道内气体流动的换热特性。将微通道内的壁温和本体温度与常规尺寸的平行板通道中不可压缩流动的壁温和体温进行了比较。利用激光诱导荧光法对微管出口气体温度进行了测量，并与前面的数值计算结果进行了比较。并讨论了激光诱导荧光法用于温度测量的可行性。

Fabrication of small devices has increased the need for understanding of fluid flow and heat transfer in micro geometries. The pressure drop of fluid flow in a micro channel is quite large because of the friction loss. In case of gaseous flows, gas expands along the channel and flow is accelerated in the channel. This results in temperature fall due to the energy conversion from the internal energy to the kinetic energy. Heat transfer characteristics of gaseous flow in a micro channel might differ from that of incompressible flows. However, there is no parametric study on the heat transfer characteristics of gaseous flow in micro-channels. This is the motivation of the present study. Objectives of the present study are; 1. To obtain the heat transfer characteristics of gaseous flow in micro channels. 2. Verification of the gas temperature at the channel exit that has been numerically obtained in a foregoing research.(1) The computations are performed for channels with constant heat flux which ranges from 10^2 to 10^4W m^<-2> and with the constant wall temperarure. The channel height ranges from 10 to 100μm and the aspect ratio of the channel height and length is fixed at 200. The heat transfer characteristics of gaseous flow in a micro channel is obtained. The wall and bulk temperatures in micro-channels are compared with that of the incompressible flow in the conventional sized parallel plate channel. The heat transfer characteristics of a micro tube is also obtained.(2) The gas temperature at the exit of a micro tube was measured by a laser-induced fluorescence method and the comparisons were made with numerically obtained temperature in a foregoing research. And the availability of the laser-induced fluorescence method for temperature measurements is discussed.