Performance Evaluation of a Small-Scale Latent Heat Thermal Energy Storage Unit for Heating Applications Based on a Nanocomposite Organic PCM

Maria K Koukou,Luis Coelho,Kostas Lymperis,Costas Prouskas,George Evangelakis,Vassilis Stathopoulos,John Konstantaras,Amandio Rebola,George Dogkas,Michail Gr Vrachopoulos,Christos Pagkalos

doi:10.3390/chemengineering3040088

Abstract

A small-scale latent heat thermal energy storage (LHTES) unit for heating applications was studied experimentally using an organic phase change material (PCM). The unit comprised of a tank filled with the PCM, a staggered heat exchanger (HE) for transferring heat from and to the PCM, and a water pump to circulate water as a heat transfer fluid (HTF). The performance of the unit using the commercial organic paraffin A44 was studied in order to understand the thermal behavior of the system and the main parameters that influence heat transfer during the PCM melting and solidification processes. The latter will assist the design of a large-scale unit. The effect of flow rate was studied given that it significantly affects charging (melting) and discharging (solidification) processes. In addition, as organic PCMs have low thermal conductivity, the possible improvement of the PCM’s thermal behavior by means of nanoparticle addition was investigated. The obtained results were promising and showed that the use of graphite-based nanoplatelets improves the PCM thermal behavior. Charging was clearly faster and more efficient, while with the appropriate tuning of the HTF flow rate, an efficient discharging was accomplished.

Highlights

The expansion of urban societies and the continuous growth of the human population result in an increase in buildings’ energy demands
The results presented are follow up of a previous work [18] where the unit operation was evaluated by the use of four different organic phase change material (PCM), including A44
From the experimental measurements using graphite-based nanoplatelets to produce the enhanced organic PCM, it is concluded that charging and discharging of the PCM when it is enhanced with nanoparticles are faster and more efficient

Summary

Introduction

The expansion of urban societies and the continuous growth of the human population result in an increase in buildings’ energy demands. Latent heat thermal energy storage (LHTES) units using PCMs that change from the liquid to solid phase are extensively used in practical applications [1,2,3,4,5,6,7,8]. Similar results regarding the use of natural convection as an additional heat transfer mechanism were presented by our group [18] after studying experimentally and computationally a staggered finned HE working with four organic PCMs with nominal melting temperatures between 40–53 ◦C. A commercial staggered finned tube HE was investigated as part of an LHTES unit that used the commercial organic PCM A44 for storing thermal energy targeting the needs for heating a building.

Nano-Enhancement of Organic Paraffin

Results and Discussion

Conclusions