Experimentally study of the convective heat transfer from the surface of the sky lanterns with different shapes

• Main Authors: Chia-long Hsu, 徐嘉隆
• Other Authors: Yuan-Tang Lin
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/52445842071728605425

碩士 === 逢甲大學 === 機械工程學所 === 96 === The density of the hot air within the sky lantern lower than those of the cold air outside the lantern, it makes the lantern rise and float in the air. The convective heat transfer from the surface of the sky lantern indicate the transfer rate vary with the lantern shape. This paper focus on the study of the convective heat transfer of the sky lanterns with different shapes of cone, cylinder, gyratory and sphere. The surface temperature increase with the height of the lantern due to the rising hot air inside the lantern, the surface temperature distribute over the upper section of the cone shape lantern the highest surface temperature, so as the thermal boundary layer , the lantern will burn out because of this high temperature. Cylindrical lantern remove much more heat from the large upper surface, it will not fire because of the lower surface temperature. The upper area of the spherical lantern is smaller than the cylindrical lantern the upper surface temperature of the spherical lantern is higher than the conic lantern but which is lower than the cylindrical lantern the upper surface temperature of the gyratory lantern is similar to the conic lantern because of the same conic shape on the upper section. Results show that the convective heat transfer coefficient and Nusselt number decrease with the height of the lantern, it reveals that the convective heat transfer rate decrease with the height the lanterns. The conic and gyratory lantern have poor convective heat transfer because of the lower coefficient and Nusselt number; cylindrical lanterns have better convective heat transfer because of the higher coefficient and Nusselt number. Spherical lanterns have the less transfer rate because of the lowest convective heat transfer has the best result; the heat transfer coefficient and Nusselt number. The conic lantern have the advantage of fast rising and slowly descending; but poor in convective heat transfer on the upper surface. the cylindrical lantern transfer much heat from the upper surface cause it descends quickly, the advantage is not burn out easily. don''t burn out easily but have slowly; the gyratory lantern transfer less heat on the upper surface than on the middle surface, but it can lift off quickly and stay longer in the air. The uniform distribution of the surface temperature profile of the spherical lantern make it transfers less heat from the surface, this is the reason why the spherical lantern can float in the air longer than other lanterns.