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Research Papers

Performance of Rigid Porous Stratification Manifolds With Interpretation for Off-Design Operation

[+] Author and Article Information
Shuping Wang, Jane H. Davidson

Mechanical Engineering,
University of Minnesota,
111 Church Street S.E.,
Minneapolis, MN 55455

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received April 27, 2013; final manuscript received September 10, 2013; published online November 26, 2013. Assoc. Editor: Nathan Siegel.

J. Sol. Energy Eng 136(2), 021021 (Nov 26, 2013) (7 pages) Paper No: SOL-13-1124; doi: 10.1115/1.4025710 History: Received April 27, 2013; Revised September 10, 2013

Thermal stratification of solar water storage tanks improves collector efficiency and provides higher quality energy to the user. A crucial aspect of maintaining stratification is preventing mixing in the tank, particularly during solar charging and hot water draws. An effective and simple approach to flow control is an internal stratification manifold. In this paper, the performance of the rigid porous manifold, which consists of a series of vertical hydraulic resistance elements placed within a perforated tube, is considered for charging operation. A 1D model of the governing mass, momentum, and energy conservation equations is used to illustrate the procedure for designing a manifold and to explore its performance over a broad range of operating conditions expected in solar water storage tanks. A manifold performance indicator (MPI) is used to evaluate the effectiveness of the manifold relative to an inlet pipe positioned at the top of the tank. The rigid porous manifold improves the stratification in the tank over a wide range of operating conditions unless the inlet flow rate is significantly reduced from the design point.

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Figures

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Fig. 2

One-dimensional rigid manifold model domain

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Fig. 1

Sketch of the flow field in a rigid porous manifold at design and off-design operating conditions. Greyscale levels indicate the temperatures in the tank and in the manifold. The inlet fluid is at an intermediate temperature between TH and TC.

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Fig. 3

Tank temperature distribution approximated by a smooth step function at different relative thermocline thickness (4.6/a)

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Fig. 6

Manifold performance at the design point with a = 10, CF = Riin = 544, and CO = 10

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Fig. 4

Schematic of a half section of a rigid porous manifold in which perforated plates serve as hydraulic resistance elements within a perforated tube

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Fig. 5

Effect of CO on crossflow distribution at design point with zero thermocline thickness and CF = 544

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Fig. 7

MPI and Mcross* distributions at various inlet temperatures: (a) MPI versus Tin; (b) Mcross* versus Z*

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Fig. 8

MPI and Mcross* distributions at various inlet mass flow rates: (a) MPI versus m·in; (b) Mcross* versus Z*

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Fig. 9

MPI and Mcross* distributions at various top tank temperatures: (a) MPI versus TH; (b) Mcross* versus Z*

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