The study of the heat-transfer characteristics difference between considering and neglecting the heat radiation effect on a non-insulated and insulated circular duct

• Main Authors: Lin, Shu-Lian, 林淑聯
• Other Authors: King-Leung Wong
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/v4yy9r

碩士 === 崑山科技大學 === 機械工程研究所 === 97 === Non-insulated and insulated ducts are commonly used in many industries and various buildings. Since the equation of heat radiation contains the 4th order exponential of temperature, it becomes very complicate to solve such equation. Most heat transfer researchers argue that from their own experiences, the heat radiation effect can be ignored due to the small temperature difference between insulated and non-insulated surfaces and surrounding. This thesis focuses in detail on the impact of heat radiation effect on the accuracy of heat transfer characteristics of non-insulated and insulated ducts by comparing the results obtained by considering and neglecting heat radiation effect. A LabVIEW programming is developed in this thesis to calculate the heat transfer characteristics of non-insulated and one to three insulated layers insulated circular ducts with heat radiation effect taken into account. It is found that neglecting heat radiation effect is likely to produce large errors of non-insulated and thin-insulated ducts in cases of ambient air with low external convection heat coefficients and with larger surface emissivity, especially when the ambient air temperature is different from that of surroundings under conditions of large internal fluid convection coefficients. Another important finding in this thesis is that using ducts with greater surface emissivity can greatly improve the heat exchanger effect, and ducts with smaller insulated surface emissivity result in better insulation.