Free Convective Flow Patterns in Cylindrical Annuli

Abstract

The results of nil available experimental investigations into the characteristics of free convective flow of air between horizontal isothermal concentric cylinders are reviewed and several discrepancies are pointed out. An experimental study is described which was directed at resolving these discrepancies and categorizing the several flow patterns which have been observed.Using six different cylinder sets and varying both the annulus pressure and temperature difference between the cylinder surfaces, a range of Grashof numbers (based on annulus width) from 300 to 3.4 X /0 6 was achieved.The resulting air flow patterns were made visible with the use of tobacco smoke and are documented by written descriptions, photographs, motion pictures, and quantitative data. One steady and three unsteady flow patterns were observed and comparison with the results of other investigators is presented.A chart is presented which allows prediction of the type of unsteady flow that will occur for a wide range of cylinder combinations and annulus operating conditions..1 comparison with cylinders in forced crossflow is used to satisfactorily predict the onset of one of the unsteady flow patterns. Also, the flow patterns observed experimentally are compared lo those predicted by an available analytical solution.

A numerical and experimental investigation of stability of natural convective flows within a horizontal annulus

“…In the present numerical studies, the annulus radius ratios were selected to permit comparison of the numerical solutions with experimental results. The value of R l 1.6 employed in the moderate gap numerical study was also used in the experiments by Powe et al (1969). The radius ratio R l 2.2 was chosen for investigation of a large-gap annulus since it is close to the values R l 2.18 and R l 2.3 at which benchmark comparisons of the numerical solutions and experimental results are made.…”

“…The classification of the annulus geometry considered in the present study as either moderate gap or large gap, depending on the radius ratio R, is based on the flow map of Powe, Carley & Bishop (1969) for air. Their experiments and compilation of experimental results from other investigators indicate that flow in large-gap annuli (R 1.71) remains stable up to much higher Rayleigh numbers than in moderate gap annuli (1.24 R 1.71).…”

“…Other studies revealed different convective regimes, especially that of Grigull & Hauf (1966), who used a Mach-Zehnder interferometer for their visualizations. Powe et al (1969) showed the existence of four convective regimes in an annulus containing air : a unicellular twodimensional steady regime for small Rayleigh number and any value of R, a multicellular regime for higher Rayleigh numbers and R 1.24, a spiral flow regime for R between 1.24 and 1.71, and an oscillating regime for very high Rayleigh number and R 1.71. A multicellular regime was previously observed for R l 1.15 by Liu et al (1961).…”

Use of the Schlieren Method to the Convection Analysis in the Steel Charge of Mixed Porosity / Wykorzystanie Metody Schlierena Do Analizy Zjawiska Konwekcji W Przypadku Wsadu Stalowego O Porowatości Mieszanej

“…The results of theoretical analysis [7,8], experimental studies [9,10,11] and numerical calculations [12,13,14] of natural convection in this type of systems indicate that the main factors determining the intensity of fluid motion are: the geometry of the area and the temperature distribution on its edges. Therefore, in order to obtain possibly the widest range of the analyzed subject, the samples made of different elements were tested.…”

Effects of slotted structures on the nonlinear characteristics of natural convection in a cylinder with an internal concentric slotted annulus

“…Bishop [13] and Powe et al [14] experimentally studied the natural convection in a closed helium filled annular space. Yoo [15] reported that when Rayleigh number was greater than a critical value, the stable solution was observed.…”