scispace - formally typeset
Search or ask a question
Author

R. E. Powe

Bio: R. E. Powe is an academic researcher from Mississippi State University. The author has contributed to research in topics: Natural convection & Rayleigh number. The author has an hindex of 7, co-authored 11 publications receiving 360 citations.

Papers
More filters
Journal ArticleDOI
TL;DR: In this paper, the authors investigated the effect of the cubical enclosure shape on convection heat transfer between concentrically located isothermal spherical, cylindrical and cubical inner bodies and their isothermal cubical enclosures.

92 citations

Journal ArticleDOI
TL;DR: In this article, the characteristics of a natural convective oscillatory flow in horizontal, cylindrical annuli are described by giving amplitude, period, and wave length data as well as data showing when this type of flow has its inception from a previously stable flow at lower Grashof numbers.

65 citations

Journal ArticleDOI
TL;DR: In this article, the authors consider the natural convective flow phenomena which occur between a body of relatively arbitrary shape and its spherical enclosure and present new flow visualization results for eccentric spheres and for vertical cylinders inside the spherical enclosure.

28 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: In this paper, an experimental and theoretical-numerical investigation has been carried out to extend existing knowledge of velocity and temperature distributions and local heat-transfer coefficients for naturel convection within a horizontal annulus.
Abstract: An experimental and theoretical-numerical investigation has been carried out to extend existing knowledge of velocity and temperature distributions and local heat-transfer coefficients for naturel convection within a horizontal annulus. A Mach—Zehnder interferometer was used to determine temperature distributions and local heat-transfer coefficients experimentally. Results were obtained using water and air at atmospheric pressure with a ratio of gap width to inner-cylinder diameter of 0·8. The Rayleigh number based on the gap width varied from 2·11 × 104to 9·76 × 105. A finite-difference method was used to solve the governing constant-property equations numerically. The Rayleigh number was changed from 102 to 105 with the influence of Prandtl number and diameter ratio obtained near a Rayleigh number of 104. Comparisons between the present experimental and numerical results under similar conditions show good agreement.

716 citations

Journal ArticleDOI
TL;DR: In this article, the authors presented numerical solutions for natural convection heat transfer between a heated horizontal cylinder placed concentrically inside a square enclosure, where the governing elliptic conservation equations were solved in a boundary-fitted coordinate system using a control volumebased numerical procedure.
Abstract: Numerical solutions are presented for natural convection heat transfer between a heated horizontal cylinder placed concentrically inside a square enclosure. Three different aspect ratios (R/L 0.1, 0.2, and 0.3), and four different Rayleigh numbers (Ra = 10, 10, 10, and 10), are considered. The governing elliptic conservation equations are solved in a boundary-fitted coordinate system using a control volumebased numerical procedure. Results are displayed in the form of streamlines, isotherms, maximum stream function estimates, and local and average normalized Nusselt number values. At constant enclosure aspect ratio, the total heat transfer increases with increasing Rayleigh number. For constant Rayleigh number values, convection contribution to the total heat transfer decreases with increasing values of R/L. For convection-dominated flows, the average Nusselt number correlation is expressed as Nu = 0.92Ra(R/ L)*. Generated results are in good agreement with previously published experimental and numerical data.

236 citations

Journal ArticleDOI
TL;DR: In this paper, the vorticity-stream function formulation is used as the governing equation, and the coordinate transformation technique is introduced in the DQ computation, which is shown that the outer square boundary can be approximated by a super elliptic function.
Abstract: SUMMARY In this work, the natural convection in a concentric annulus between a cold outer square cylinder and a heated inner circular cylinder is simulated using the di;erential quadrature (DQ)method. The vorticity-stream function formulation is used as the governing equation, and the coordinate transformation technique is introduced in the DQ computation. It is shown in this paper that the outer square boundary can be approximated by a super elliptic function. As a result, the coordinate transformation from the physical domain to the computational domain is set up by an analytical expression, and all the geometrical parameters can be computed exactly. Numerical results for Rayleigh numbers range from 10 4 to 10 6 and aspect ratios between 1.67 and 5.0 are presented, which are in a good agreement with available data in the literature. It is found that both the aspect ratio and the Rayleigh number are

146 citations

Journal ArticleDOI
TL;DR: In this article, a numerical three-dimensional model based on the method of finite elements has been developed in order to point out the different types of evolution with time in natural convection in a saturated porous medium bounded by two concentric, horizontal, isothermal cylinders.
Abstract: The study of natural convection in a saturated porous medium bounded by two concentric, horizontal, isothermal cylinders reveals different types of evolution according to the experimental conditions and the geometrical configuration of the model. At small Rayleigh numbers the state of the system corresponds to a regime of pseudo-conduction. The isotherms are coaxial with the cylinders. At larger Rayleigh numbers a regime of steady two-dimensional convection sets in between the two cylinders. Finally, for Rayleigh numbers above the critical Rayleigh number Ra*c the phenomena become three-dimensional and fluctuating. The appearance of these different regimes depends, moreover, on the geometry considered and, in particular, on two numbers: R, the ratio of the radii of the cylinders, and A, the ratio of the length of the cylinders to the radius of the inner one. In order to approach these experimental observations and to obtain realistic theoretical models, several methods of solving the equations have been used.The perturbation method yields information about the thermal field and the heat transfer between the cylinders under conditions close to the equilibrium state.A numerical two-dimensional model enables us to extend the range of investigation and to represent properly the phenomena when steady convection appreciably modifies the temperature distribution and the velocities within the porous layer.Neither of these models allows account to be taken of the instabilities observed experimentally above a critical Rayleigh number Ra*c. For this reason, a study of stability has been carried out using a Galerkin method based on equations corresponding to an initial state of steady convection. The results obtained show the importance of three-dimensional effects for the onset of fluctuating convection. The critical transition Rayleigh number Ra*c is thus determined in terms of the ratio of the radii R by solving an eigenvalue problem.A numerical three-dimensional model based on the method of finite elements has thus been developed in order to point out the different types of evolution with time. Steady two-dimensional convection and fluctuating three-dimensional convection have been actually found by calculation. The solution of the system of equations by the method of finite elements is briefly described.The experimental and theoretical results are then compared and a general physical interpretation is given.

127 citations

Journal ArticleDOI
TL;DR: In this paper, the vorticity-stream function formulation is taken in the governing equation to take the global circulation flow into consideration, the pressure single value condition is applied, an explicit formulation is derived and the stream function value on the inner cylinder wall is updated from the values at all the interior points.

108 citations