Solar Thermal Energy Storage with Phase Change Material - Heat Exchanger Design and Heat Transfer Analysis
01 Jan 2017-pp 370-372
TL;DR: In this paper, a phase change material (PCM) heat exchanger with a helical coil tube was designed and fabricated for solar thermal energy storage, and was tested on a solar thermal experimental apparatus.
Abstract: Solar energy is clean and sustainable but intermittent in nature. Efficient storage of solar thermal energy is critical for its wider applications. This paper presents design and research on a thermal energy storage unit using phase change material (PCM). Aprototype of PCM heat exchanger with a helical coil tube was designed and fabricated for solar thermal energy storage, and was tested on a solar thermal experimental apparatus. This paper discusses the design concepts, selection of materials, as well as heat transfer analysis with the CFD tool Ansys Fluent. Keywords-Thermal; Energy Storage; Heat Exchanger; Design; Phase Change Material; Heat Transfer; Simulation; Testing.
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TL;DR: In this article, a phase change material (PCM) heat exchanger with a helical coil tube is designed, fabricated, and experimentally analyzed for its thermal storage performance under different operational conditions.
Abstract: Latent heat energy storage systems have superior features over conventional sensible storage systems. With a large latent heat of fusion, a phase change material (PCM) can absorb and release a great amount of thermal energy at nearly a constant temperature. This improves the capacity and efficiency of the energy storage unit while extending the service time. In this study, a prototype PCM heat exchanger with a helical coil tube is designed, fabricated, and experimentally analyzed for its thermal storage performance under different operational conditions. Paraffin wax is used as PCM and Ethylene glycol (EG)-water mixture is used as heat transfer fluid (HTF). Different HTF inlet temperatures, flow directions, and flow rates were tested to find out the effects of these parameters on the performance, including charging and discharging time, of the thermal storage unit. It was found that the most significant factor during charging is the HTF inlet temperature. The experimental results showed that increasing the HTF inlet temperature from 70 °C to 75 °C shortened the charging time by 35% while charging time was reduced up to 21% with increasing flow rate from 0.5 to 4 L/min. The discharging time, however, did not change substantially with flow rates. It was also found that higher flow rate leads to higher recovery efficiency. The flow direction of the HTF was found to have an insignificant effect on the total charging and discharging time but showed effects on the temperature variations of PCM in the energy storage unit.
48 citations
TL;DR: In this paper, a comparison of the thermal performance of two medium temperature sugar alcohol based PCMs of erythritol (C4H10O4) and xylitol (C5H12O5) was presented.
Abstract: Phase change material (PCM) based thermal energy storage systems decrease fossil fuel consumption and can help to reduce environmental impacts. However, extensive application of PCMs are hindered owing to their low thermal conductivity, causing slow charging and discharging processes. In the present work, a comparison of the thermal performance of two medium temperature sugar alcohol based PCMs of erythritol (C4H10O4) and xylitol (C5H12O5) in a vertical double spiral coil unit is presented. Effects of the operating parameters such as volume flow rate and inlet temperature of the heat transfer fluid (HTF) Therminol-55 on the phase change behavior of the PCMs were investigated. Temperature variation of PCMs at different locations of the storage unit, melt fraction and heat storage/discharge rate were obtained. Melting of PCMs was a faster process owing to the impact of natural convection. Furthermore, the double spiral coil storage unit provided suitable thermal performance, achieving high PCM melting rate. Quantitatively, erythritol stored 790 kJ of heat in 60 min for an HTF inlet temperature of 155 °C. For the same flow rate and HTF temperature difference, xylitol stored 450 kJ of heat in 35 min. Therefore, erythritol exhibited superior charging characteristics than xylitol; however, subcooling obstructed the discharging performance of erythritol. On the other hand, no subcooling effect was noticed during the discharging of xylitol.
28 citations
TL;DR: In this paper, a spiral coil thermal storage unit was investigated to analyze the impact of operating parameters such as inlet temperature and flow rate of the heat transfer fluid and explain the physics of heat transfer during the phase change process of xylitol.
21 citations
TL;DR: In this paper , a review of low temperature phase change materials for thermal energy storage, important properties and applications of low-temperature phase change material have been discussed and analyzed, as well as various techniques to improve the heat transfer characteristics of TES systems using low temperature Phase change materials have also been discussed.
5 citations
References
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TL;DR: This Perspective provides a snapshot of the current energy landscape and discusses several research and development opportunities and pathways that could lead to a prosperous, sustainable and secure energy future for the world.
Abstract: Access to clean, affordable and reliable energy has been a cornerstone of the world's increasing prosperity and economic growth since the beginning of the industrial revolution. Our use of energy in the twenty–first century must also be sustainable. Solar and water–based energy generation, and engineering of microbes to produce biofuels are a few examples of the alternatives. This Perspective puts these opportunities into a larger context by relating them to a number of aspects in the transportation and electricity generation sectors. It also provides a snapshot of the current energy landscape and discusses several research and development opportunities and pathways that could lead to a prosperous, sustainable and secure energy future for the world.
7,721 citations
TL;DR: The use of a latent heat storage system using phase change materials (PCMs) is an effective way of storing thermal energy and has the advantages of high energy storage density and the isothermal nature of the storage process.
Abstract: The use of a latent heat storage system using phase change materials (PCMs) is an effective way of storing thermal energy and has the advantages of high-energy storage density and the isothermal nature of the storage process. PCMs have been widely used in latent heat thermal-storage systems for heat pumps, solar engineering, and spacecraft thermal control applications. The uses of PCMs for heating and cooling applications for buildings have been investigated within the past decade. There are large numbers of PCMs that melt and solidify at a wide range of temperatures, making them attractive in a number of applications. This paper also summarizes the investigation and analysis of the available thermal energy storage systems incorporating PCMs for use in different applications.
4,482 citations
"Solar Thermal Energy Storage with P..." refers background in this paper
...The disadvantages of inorganic PCMs are the sub- cooling issue, as well as corrosion of the containment material [6,7]....
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TL;DR: In this paper, the authors determined the proper amount of paraffin ( n -docosane) absorbed into expanded graphite (EG) to obtain form-stable composite as phase change material (PCM), examination of the influence of EG addition on the thermal conductivity using transient hot-wire method and investigation of latent heat thermal energy storage (LHTES) characteristics of Paraffin such as melting time, melting temperature and latent heat capacity using differential scanning calorimetry (DSC) technique.
793 citations
"Solar Thermal Energy Storage with P..." refers background in this paper
...To overcome these problems, phase change materials (PCMs) have been proposed to store thermal energy [2, 3]....
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TL;DR: In this paper, a tube-in-shell thermal energy storage system with three kinds of paraffin with different melting temperatures is analyzed experimentally, and the effects of the Reynolds number and the Stefan number on the melting and solidification behaviors are determined.
160 citations
"Solar Thermal Energy Storage with P..." refers background in this paper
...To overcome these problems, phase change materials (PCMs) have been proposed to store thermal energy [2, 3]....
[...]
TL;DR: In this paper, a direct-contact heat exchanger using erythritol (melting point: 391 K) as a phase change material (PCM) and a heat transfer oil (HTO) for accelerating heat storage is described.
75 citations
"Solar Thermal Energy Storage with P..." refers background in this paper
...Many types of phase change energy storage systems have been studied [4,5]....
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