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TECHNICAL BRIEFS

On the Effectiveness of Baffles in Indirect Solar Storage Systems

[+] Author and Article Information
F. A. Kulacki

Department of Mechanical Engineering,  University of Minnesota, Minneapolis, MN 55455kulacki@me.umn.edu

Jane H. Davidson

Department of Mechanical Engineering,  University of Minnesota, Minneapolis, MN 55455jhd@me.umn.edu

M. Hebert

Department of Mechanical Engineering,  University of Minnesota, Minneapolis, MN 55455

J. Sol. Energy Eng 129(4), 494-498 (Feb 20, 2007) (5 pages) doi:10.1115/1.2770757 History: Received July 16, 2006; Revised February 20, 2007

Parameters that control heat transfer and mixing in energy extraction from indirect solar storage tanks that employ an immersed heat exchanger with a straight baffle beneath are identified and estimated. The analysis of flow in the baffle is based on boundary layer theory and provides insight into the effectiveness of a baffle in controlling growth of the thermal plume from the heat exchanger. The important physical mechanisms are the restricted entrainment and heat transfer to the storage fluid. For an adiabatic baffle as a base case, key design factors are the point of attachment of the plume on the baffle and the width of the baffle relative to that of the heat exchanger.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Conceptual sketch of an indirect storage tank with an immersed heat exchanger for discharge. A shroud and straight baffle are intended to prevent mixing of the cool fluid falling from the surface of the heat exchanger with the bulk storage fluid.

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Figure 2

Estimated Nusselt numbers for an immersed heat exchanger tube, D=2.86cm

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Figure 3

Model of the falling buoyant plume in a straight baffle of width equal to diameter of cylinder, DB=D

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Figure 4

Initial plume thickness (solid line) and maximum velocity (dashed line) for D=2.86cm

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Figure 5

Baffle flow with DB=D=2.86cm: (a) plume thickness, (b) plume centerline velocity. Dashed line denotes plume attachment to baffle of width DB=D.

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Figure 6

Velocity profile at attachment (dashed line) and fully developed profile (solid line) in a straight baffle of width D=DB. The Gaussian profile is given by Eq. 5 and altered by the plume spread, δ(x).

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