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Technical Briefs

Comparison of Stratification in a Water Tank and a PCM-Water Tank

[+] Author and Article Information
A. Castell, C. Solé, M. Medrano, M. Nogués

Departament d’Informàtica i Enginyeria Industrial, Universitat de Lleida, Pere de Cabrera s/n, 25001 Lleida, Spain

L. F. Cabeza

Departament d’Informàtica i Enginyeria Industrial, Universitat de Lleida, Pere de Cabrera s/n, 25001 Lleida, Spainlcabeza@diei.udl.es

J. Sol. Energy Eng 131(2), 024501 (Mar 25, 2009) (5 pages) doi:10.1115/1.3097277 History: Received July 06, 2007; Revised December 09, 2008; Published March 25, 2009

Most of the thermal energy storage systems available on the market use water as a storage medium. The improvement of the storage efficiency results in a higher performance of the whole system, and thermal stratification is commonly used for this purpose. On the other hand, in applications with small temperature changes, phase change materials (PCMs) provide high energy density since the latent heat is much larger than the sensible heat. This is the case of stratified hot water tanks, where the temperature change in the top layer is small as it is held close to the usage temperature. The benefits of using PCMs in a water tank, in terms of energy storage density, have been demonstrated before. The time with available hot water is increased because of the energy stored in the PCMs. The aim of this work is to demonstrate that the use of PCMs in the upper part of a water tank holds or improves the benefit of the stratification phenomenon. Two tanks with the same dimensions were compared during charging and discharging processes. One of them is a traditional water tank and the other is a PCM-water tank (a water tank with a phase change material placed at the top).

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Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 5

Richardson number for charging and discharging processes

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Figure 4

MIX number for charging and discharging processes

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Figure 3

Temperature profile for charging and discharging processes

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Figure 2

Temperature probes’ device and stratifier

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Figure 1

PCM location and geometry, and position of Pt-100 inside the tank

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