| An extensive experimental study of natural convection from an electrically heated vertical cylinder suspended in air was conducted. The study consisted of three parts: laminar steady state natural convection from the outer surface of the cylinder; transient natural convection from a cylinder; and suppression of natural convection from a cylinder using non- or poorly-conducting circular fines. Detailed review and analysis of approximate mathematical solutions to the vertical flat plate and cylinder are included in this work.; In the first part, three 316 SS test sections were used, with diameters ranging from 1.6 to 4.8 cm and lengths from 1.6 to 2.3 m. Vertical profiles consisting of temperature at thirteen locations along the test section were obtained using miniature thermocouples. Data were taken at six different power levels, producing convective heat transfer coefficients from 3–10 W/m 2·°C. The following correlation relating the local Nusselt number to the local modified Rayleigh number and the cylindrical diameter was developed: Nuy=1.2849Rayy */d0.1651 . ; The transient study was conducted on one of the three cylinders using thermocouples mounted at three elevations, and one power level was considered. Data were taken at 20 second intervals over 2200 second. The resulting correlation relates an average Nusselt number to the product of a Grashof number and non-dimensional time: Nu=33694GrRn t/R2 -0.4019. ; The suppression study was conducted on one test section using different numbers and diameters of non-conductive fins mounted on the test section along with the thermocouples. Tests are reported for two different power levels. The decelerating effect of the fins on the air flow reduced the heat transfer by up to 18% and probably more at unmonitored locations nearer to the leading edge. |
