Transient Leading to Periodic Fluid Flow and Heat Transfer in a Cavity Due to a Rotating Object

• Main Authors: Kuo-Hsuan Weng, 翁國軒
• Other Authors: 施陽正
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/897m92

碩士 === 國立臺北科技大學 === 冷凍空調工程系所 === 94 === In many engineering applications, there are a lot of equipments composed of the cavity, including mixing chamber, electronic cooling products, ventilation of buildings, collection of solar energy and heat storage system, etc. The complex flow field and heat transfer characteristics within the cavity are always attractive to the industry and researchers. In this study, the CFD software FLUENT is adopted to simulate the flow and temperature fields of various rotating objects (circle, square and equilateral triangle) with different sizes placed in the middle of a square cavity. The Prandtl number of the fluid within the cavity is set to be five and the flow is assumed to be laminar. Two kinds of thermal boundary conditions are considered in this study. One is the isothermal rotating object and the other is the adiabatic rotating object. The motionless object is set in rotation at time t=0 with a constant angular velocity. The effect of natural convection is neglected. According to the simulation results, the evolving flow field and the interaction of the rotating objects with the recirculating vortices at the four corners are elucidated. Moreover, similarity of the flow and thermal fields for various shapes is discussed. In the cases of both boundary conditions, the periodic oscillation of transient variations of the average Nusselt numbers on the surface of the rotating object and cavity walls becomes obvious as the Reynolds number decreases. However, periodic behavior does not appear in the cases of the circle object. For the cases of isothermal rotating objects, time-integrated average Nusselt number of the cavity is independent of shape of the object at higher Re. However, at lower Re, the triangle object clearly exhibits superior heat exchange capability followed by the square and circle objects. The phenomena found in the cases of isothermal objects also appear in the cases of adiabatic objects.