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International Conference on Innovative Applied Energy    

E-Proceedings ISBN: 978-1-912532-05-6

St Cross College, University of Oxford, United Kingdom

  


 

Numerical study and LCA of an innovative PCM-Metal Foam thermal storage system for Solar Domestic Water Heating Systems

 


 

Raffaello Cozzolino, Stefano Guarino, Simone Venettacci and Vittorio Villani

University “Niccolò Cusano”, Engineering Department, Italy

 

  

Paper Abstract

Solar Domestic Water Heating Systems (SDWHS) are an interesting alternative to traditional heating systems that offer low emissions and could increase the energy efficiency of a building. A SDWHS requires a Thermal Energy Storage (TES) system that should satisfy hot water requirements when the sun power is not available. Today TES generally use water to store sensible heat. A more efficient way of accumulating thermal energy implies the usage of PCM (Phase Change Materials) to store energy by latent heat.

In this paper it is illustrated the design and numerical optimization of a TES system using paraffin wax as PCM. Paraffin waxes are organic PCM that have high latent heat (210 000 J/kg). The main drawback of paraffin waxes for TES application is their low thermal conductivity (about 0.3 W/(mK)). This value can be increased using a conductive matrix inside the wax. Open-cell aluminum metal foams are high conductive materials that can be used for this purpose. 0.95 porosity foam is used for this application. 

Numerical studies are implemented to evaluate the behavior of the metal foam – wax composite material. Assumptions used in the numerical simulation to maintain adequate accuracy while providing acceptable solution times are the absence of convective motion and the utilization of homogeneous properties for the composite material. The first assumption is justified by the fact that the metal matrix limits the motion of the wax. The second assumption implies that the metal foam and the wax are modelled numerically as a single material with properly averaged properties. Experimental analyses are implemented to determine the averaged properties of the metal foam – wax. 

2D preliminary studies are executed in COMSOL software to verify the precision of the numerical hypothesis in a case that can be solved analytically, known as “Stefan Problem”. 2D studies analyze the behavior of the solidification/fusion front, investigating the effect of the “mushy zone”, region where solid and fluid states are both present. 

3D studies on the TES geometry are completed to analyze how the paraffin wax melts and solidifies. The geometry of the TES, designed to store about 20 kWh of energy in 0.4 m3 of volume is obtained iteratively optimizing the shape factor, the number and the disposition of the pipes and the disposition of internal aluminum fins. 

Experimental analysis show that the compound material obtained combining aluminum foam with paraffin wax has a thermal conductivity almost 10 times greater than the wax alone (about 2.7 W/(mK)). 2D studies are validated thus the analytical model. 3D optimization can provide a TES design that meets the requirements of the SDWHS in terms of stored energy and peak power demands.

Finally, a Life Cycle Analysis (LCA) was performed to compare the PCM-aluminum foam based thermal storage system and a traditional one, in order to assess the environmental impact and to validate the innovative technological solution developed 

Paper Keywords
Phase Change Materials, Thermal Energy Storage, Life Cycle Assessment, Open-Cell Aluminum Foams.
Corresponding author Biography

TBA.

The International Conference on Innovative Applied Energy (IAPE’18)