CONVECTIVE HEAT TRANSFER FOR RADIAL FLOW BETWEEN A SEGMENTED PAIR OF PARALLEL DISKS

PHILIP HAROLD SNYDER, Purdue University

Abstract

An analytical and experimental study was performed in regard to heat transfer from a segmented pair of parallel disks in the presence of radial inflow or outflow. The parameters were chosen such that the developing boundary layers were turbulent over a large fraction of the flow passage. Experiments were conducted with a 22.5-degree segment of two closely-spaced parallel disks with an outer-to-inner diameter ratio of 2.0. This geometry and flow regime are applicable to the cooling of a 1200 KV shunt reactor which employs sulfur hexafluoride gas flow between the adjacent winding sections. Dimensional analysis was used to make the laboratory apparatus equivalent to the reactor system, and the experimental results are reported in terms of dimensionless parameters. The flow velocity was limited such that the Mach number was not a significant parameter. Air was used to simulate the sulfur hexafluoride in the experiments. The laboratory apparatus was scaled up by a factor of three relative to the envisioned equipment to be employed in the reactor application. A constant wall heat flux was imposed by the use of ribbon-foil electrical heaters. Wall temperatures were measured by foil thermocouples at 14 radial positions along each of four radial lines for Reynolds numbers at the inner diameter (based on two times the plate spacing) in the range of 8 x 10('3) to 1.5 x 10('5). In most of the experiments conducted the potential flow in the core gave way to the developing boundary layers, such that turbulent flow existed over the entire cross-sectional area well upstream of the exit. Experimental results obtained for both radially-inward and -outward flows are presented and compared with those predicted by means of an integral momentum equation solution for both developing and fully developed portions of the flow. Experimental results generally demonstrated good agreement with predicted values and trends. A nondimensional parameter whose value is dependent upon plate spacing, inner channel radius, and Reynolds number resulted from the integral momentum equation analysis and provided good correlation of both pressure coefficient and convective heat transfer results. Experimentally determined values of the heat transfer coefficient in some cases were found to be only one-third of the value predicted by the Dittus-Boelter relationship.

Degree

Ph.D.

Subject Area

Mechanical engineering

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