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Research Papers

The Effects of Boundary Design on the Efficiency of Large-Scale Hot Water Heat Stores

[+] Author and Article Information
Varghese Panthalookaran

 Rajagiri School of Engineering and Technology (RSET), Rajagiri Valley P.O., Kakkanad Kochi-682039, Kerala, Indiavarghese@rajagiritech.ac.in

Wolfgang Heidemann

 Institute of Thermodynamics and Thermal Engineering (ITW), University of Stuttgart, Pfaffenwaldring 6, Stuttgart D-70550, Germanyheidemann@itw.uni-stuttgart.de

Hans Müller-Steinhagen

 Technische Universität Dresden, Helmholzstrasse 10, Dresden D-01069, Germanyrektor@tu-dresden.de

J. Sol. Energy Eng 133(4), 041007 (Oct 11, 2011) (8 pages) doi:10.1115/1.4004472 History: Revised June 06, 2010; Received July 16, 2010; Published October 11, 2011; Online October 11, 2011

Boundary design of stratified hot water heat stores is important not only to minimize the thermal losses to the ambient but also to preserve the thermodynamic quality of the stored energy. A new method of characterization, which equivalently accounts for both these concerns, is applied in this paper to investigate into the boundary design of large-scale hot water heat stores. A variety of concepts related to general design of the containments, namely, the effects of the thermal conductivity and thickness of the container wall, are numerically analyzed. The design insights provided by the analysis are in good agreement with the corresponding experimental results for small-scale hot water heat stores found in the literature. Different ways of insulation application, differential application of the external insulation, and insulation of the top walls are further investigated to obtain ideas for the efficient use of the insulation material. The new characterization scheme proves to be an efficient tool to rank the performance of different boundary designs during storing process of large-scale stratified hot water heat stores and to provide valuable design insights.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

General layout of hot water heat store for the numerical experiments

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Figure 2

The initial temperature profiles within the hot water seasonal heat store, as used for the numerical experiments

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Figure 3

Transient evolution of ηSEN2 for hot water seasonal heat stores with different wall materials

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Figure 4

Transient evolution of Nusselt number (Nu) at the interior surfaces of hot water seasonal heat stores with different wall materials. The initial minimum temperature of the store (333.15 K) is used as the reference temperature (Tref ) in the calculation of the heat transfer coefficient, and unit length (1 m) is used as the characteristic length in the calculation of the Nu.

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Figure 5

Temperature profiles inside the heat store after 2 h of storing for different wall materials

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Figure 6

Time-averaged ηSEN2 as a function of the effective thermal conductivity (λ) of the composite wall material

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Figure 7

Time-averaged ηSEN2 as a function of wall thicknesses

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Figure 8

Transient evolution of Nusselt number at the interior side walls of hot water seasonal heat store, for different wall thicknesses (Nusselt numbers are evaluated as in Fig. 4)

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Figure 9

Time-averaged ηSEN2 for different installation options of the insulation

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Figure 10

Transient evolution of ηSEN2 for different installation options of the insulation

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Figure 11

Sketch of different patterns for external insulation (a) constant (b) variable insulation volumes

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Figure 12

Time-averaged ηSEN2 for different patterns of external insulation with constant total volume of insulation (see Fig. 1)

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Figure 13

Time-averaged ηSEN2 for different patterns of external insulation with variable volume of insulation (see Fig. 1)

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Figure 14

Time-averaged ηSEN2 for different effective thermal conductivities (λ) of the top boundary

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Figure 15

Magnitude of vorticity developed near the interior of the top surface of the hot water seasonal heat store as a function of the effective thermal conductivity (λ) of the top walls

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