Experimental Investigation On Combined Heat Loss Characteristics Of A Cylindrical Cavity With Different Opening Ratios Under Environmental Wind Condition

The heat loss characteristics in an open cavity have a wide range of industrial applications such as solar cavity receiver, cooling of electronic components, the breaking device of aircraft and building energy conservation etc. An experimental investigation on the heat losses of a cylindrical cavity is performed to explore the effect of title angles, wind speeds, wind incidence angles and heat flux on the heat losses of the cavity with different opening ratios under environmental wind condition. The study uses electric heating method including all surfaces heated(both bottom and side surfaces) and only the bottom surface heated.Results reveal that, for all surfaces heated condition, the bottom wall temperatures change in a small range, while the side wall temperatures fluctuate sharply and the temperature gradient of the same cross section is greater with the increasing distance departure from bottom wall. For only bottom surface heated condition, the bottom wall temperatures keep basically unchanged, while the side wall temperatures also decrease sharply with the increasing distance departure from bottom wall, but the temperature gradient of the same cross section of the side wall has a little change.Under the two heating methods, the combined convection heat loss and radiation heat loss increase as opening ratio increases, while the conduction heat loss decreases for constant wind speed. When there is no wind, the convection heat loss decreases with increasing of opening ratio, but the varying patterns of the radiation heat loss and the conduction heat loss are same. Meanwhile, the conduction heat loss is more than the radiation heat loss at low opening ratio, which is opposite at high opening ratio. There is a critical opening ratio which is greater for the all surfaces heated condition than the only bottom surface heated. At fixed opening ratios, the radiation heat loss and the conduction heat loss decrease with wind speed increasing, while the combined convection heat loss increases.For different opening ratio cavities under windy environment in this thesis, the combined convection heat loss Nusselt number Nuc increases with the increasing of opening ratio and wind speed, while radiation heat loss Nusselt number Nur increases as the opening ratio increases but decreases with wind speed raising when other parameters are fixed. The changing characteristics of Nuc being affected by wind incidence angle and title angle are complex and Nur changes little, which illustrates that opening ratio is dominant influencing factor of Nuc and Nur.Besides, the empirical correlations of combined convection heat loss Nusselt number and radiation heat loss Nusselt number are obtained for different conditions using linear regression method. Moreover, the uncertainty in the experiment is analyzed in detail to test the reliability of the measurement results.