Session: 08-09-01: Thermal Energy Storage

Paper Number: 99377

99377 - Shape Stable Polymer Composites for Medium Temperature Thermal Storage: Detailed Heat Transfer and Scale Up 

Thermal storage is likely to be an important component of efficient energy management in the future. Many thermal storage approaches have been investigated. Latent heat storage systems provide excellent performance in terms of energy density and exergetic efficiency. However, there are challenges associated with the changing material properties accompanying the change of phase.

We consider the use of polymer composites as shape stabilized phase change storage media.  We have previously developed fiber reinforced and partially encapsulated high-density polyethylene (HDPE) composites for medium temperature (e.g., 125 °C) storage applications. We also discussed a bench-scale thermal energy storage (TES) system using these composites. These composites have high thermal capacity and the TES system can discharge above 350 kJ/kg of thermal energy (sensible and latent combined) under an hour when operating between 140 °C and 125 °C. These composites are also compatible with direct contact heat transfer approaches that minimize thermal resistance in charge/discharge and lower system cost. Such systems can be charged and discharged at rates exceeding 100 W/kg.

Here we consider the detailed thermal transport within the system and the mechanisms contributing to performance, including: convection with the media bed, conduction within the media itself, and melting/solidification kinetics. A detailed model is introduced for temperature evolution with the bed. This model is compared to experimental observations for a small (~3.6 kg) system. The heat transfer performance has significant consequences for the exergetic efficiency, which represents a significant potential advantage of latent heat storage systems. We consider the influence of system design and operational parameters on overall system exergetic performance.  For the small system, we demonstrate relatively high exergetic efficiencies exceed 80% at practical operational conditions.

We also consider the scale up of the system presented to larger (e.g., 1000 kg) implementations. We present a modular design using off the shelf containment options. Alternative composite formulation and bulk manufacturing approaches for the composite are demonstrated. Manufacturing complexity associated with fiber reinforced high-density polyethylene and the requirement for mixing them using a high shear mixer, is reduced. This new media has improved manufacturability and also lower cost of components. A strategy for in-house production of the composite and its installation in a media containment vessel is introduced and discussed. The simple construction also leads to a compact system for easy transportation and installation on site. The performance of full-scale systems aimed at industrial heat storage are modeled and shown to be promising for a range of applications. 

Presenting Author: Souvik Roy University of California, Merced

Presenting Author Biography: Souvik Roy is a PhD candidate in Mechanical Engineering at University of California, Merced. His current research involves developing and characterizing phase change material composites for latent heat thermal energy storage. His research also includes designing, developing and characterizing latent heat thermal energy storage systems using these composites for medium temperature applications.

Authors:

Souvik Roy University of California, Merced
James Palko University of California, Merced
Gerardo Diaz University of California, Merced
Roland Winston University of California, Merced