Emergence of rectangular shell shape in thermal energy storage applications: Fitting melted phase changing material in a fixed space
TL;DR: In this article, the effect of heat transfer fluid (HTF) tube position and shell shape on the melting time and sensible energy requirement for melting a phase change material (PCM) in a multitube latent heat thermal energy storage (LHTES) application was investigated.
Abstract: Here we document the effect of heat transfer fluid (HTF) tube position and shell shape on the melting time and sensible energy requirement for melting a phase change material (PCM) in a multitube latent heat thermal energy storage (LHTES) application. Tube location and shell shape are essential as the shape of the melted region, i.e. similar to the boundary layer, affects convective heat transfer performance. HTF tube total area is fixed in all cases to have the same amount of PCM. In order to eliminate the effect of heat transfer surface area variation, results of two- and four-tube configurations were compared within themselves. Liquid fraction, sensible enthalpy content, and latent/sensible enthalpy ratio relative to time were documented for two and four HTF configurations in various shell shape and tube locations. Results show that eccentric two tubes with rectangular shell decreases melting time and sensible energy requirement from 67 min to 32 min and from 161.8 kJ/kg to 136.3 kJ/kg for 72.3% liquid fraction, respectively, in comparison to the concentric tubes with the circular shell. When the number of HTF tubes increases to four, then the required melting time and sensible energy decrease 80% and 3.8%, respectively, for PCM to melt completely as the concentric tubes and circular shell is replaced with eccentric tubes and rectangular shell. Results of liquid fraction variation relative to time show that S-curve of melting becomes steeper if PCM distribution is such that the intersection of melted regions is delayed. Therefore, melted PCM regions could be packed into a shell that minimizes melting time and required sensible energy. Even rectangular shell shape increases the heat transfer surface (increased heat loss rate) because melting time has decreased greatly, total energy lost to the ambient from the surfaces of shell decreases. Eccentricity slows down the solidification process but due to increased heat loss rate from the surface, rectangular shell enables faster solidification than circular shell shape. There is a trade off in between solidification time and heat loss energy for rectangular channels which can be optimized by selecting proper insulation thickness. Overall, the results show that without any thermal conductivity enhancement (TCE) method, melting performance and latent heat storage capability can be significantly enhanced as decreasing the sensible heat storage by fitting the melted PCM regions into a fixed space for the applications where charging speed is lot faster than discharging.
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15 Jan 2002
TL;DR: The International Energy Agency (IEA) as mentioned in this paper is an autonomous agency that aims to promote energy security among its member countries through collective response to physical disruptions in oil supply and to advise member countries on sound energy policy.
Abstract: The International Energy Agency (IEA), an autonomous agency, was established in November 1974. Its mandate is twofold: to promote energy security amongst its member countries through collective response to physical disruptions in oil supply and to advise member countries on sound energy policy. The IEA carries out a comprehensive programme of energy cooperation among 28 advanced economies, each of which is obliged to hold oil stocks equivalent to 90 days of its net imports. The Agency aims to: n Secure member countries' access to reliable and ample supplies of all forms of energy; in particular, through maintaining effective emergency response capabilities in case of oil supply disruptions. n Promote sustainable energy policies that spur economic growth and environmental protection in a global context – particularly in terms of reducing greenhouse-gas emissions that contribute to climate change. n Improve transparency of international markets through collection and analysis of energy data. n Support global collaboration on energy technology to secure future energy supplies and mitigate their environmental impact, including through improved energy efficiency and development and deployment of low-carbon technologies. n Find solutions to global energy challenges through engagement and dialogue with non-member countries, industry, international organisations and other stakeholders. The European Commission also participates in the work of the IEA. Please note that this publication is subject to specific restrictions that limit its use and distribution. The terms and conditions are available online at Foreword Current trends in energy supply and use are patently unsustainable – economically, environmentally and socially. Without decisive action, energy-related emissions of CO 2 will more than double by 2050 and increased oil demand will heighten concerns over the security of supplies. We must – and can – change our current path; we must initiate an energy revolution in which low-carbon energy technologies play a lead role. If we are to reach our greenhouse-gas emission goals, we must promote broad deployment of energy efficiency, many types of renewable energy, carbon capture and storage, nuclear power and new transport technologies. Every major country and sector of the economy must be involved. Moreover, we must ensure that investment decisions taken now do not saddle us with sub-optimal technologies in the long term. There is a growing awareness of the urgent need to turn political statements and analytical work into concrete action. To spark this movement, at the request of the G8, the International Energy Agency (IEA) is developing a …
116 citations
TL;DR: In this paper , a novel triplex-tube latent heat thermal energy storage system is designed and the melting behavior of phase change materials is studied numerically, and the multi-parameter optimization design of the system is carried out by the response surface method.
20 citations
TL;DR: In this article , the effect of fin structures on the melting performance of phase change materials in a shell-and-tube heat exchanger was investigated, and it was found that fin structures in all cases performed better when located at the top of the heat transfer fluid tube, even though the literature considers that top-located fin inhibit natural convection circulations.
14 citations
TL;DR: In this paper , copper and nickel porous metal foams are applied in a PCM on hot side of a TEG to accelerate storage of fusion heat and power output of the TEG under transient boundary conditions.
13 citations
TL;DR: In this article , the effects of the bifurcated fins on melting and solidification are studied, and local and global entropy generation are discussed, and the radial lag time and the circumferential lag time were defined to evaluate thermal penetration and thermal uniformity.
Abstract: Latent heat thermal energy storage (LHTES) technology can alleviate the mismatch between the supply and demand of solar energy and industrial waste heat, but the low thermal conductivity of phase change materials (PCMs) is an issue that needs to be solved. In this work, the effects of the bifurcated fins on melting and solidification are studied, and local and global entropy generation are discussed. The radial lag time and the circumferential lag time were defined to evaluate thermal penetration and thermal uniformity. Subsequently, a novel arc-shaped fin configuration was proposed to further enhance the heat transfer. The results showed that attaching the bifurcated fins could effectively reduce the global entropy generation. Increasing the trunk fin length was beneficial to enhance the thermal uniformity and promote the melting process, while increasing the branch fin was more effective in the solidification process. Overall, thermal uniformity determined the phase change process. More importantly, the concentric arc-shaped fins significantly reduced the heat transfer hysteresis region, showed better thermal performance than straights fins, and the energy storage and release time were reduced by 52.7% and 51.6%, respectively.
4 citations
References
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TL;DR: In this article, an enthalpy formulation based fixed grid methodology is developed for the numerical solution of convection-diffusion controlled mushy region phase-change problems, where the basic feature of the proposed method lies in the representation of the latent heat of evolution, and of the flow in the solid-liquid mushy zone, by suitably chosen sources.
1,892 citations
TL;DR: In this paper, the phase change problem has been formulated using pure conduction approach but the problem has moved to a different level of complexity with added convection in the melt being accounted for, which makes it difficult for comparison to be made to assess the suitability of PCMs to particular applications.
Abstract: This paper reviews the development of latent heat thermal energy storage systems studied detailing various phase change materials (PCMs) investigated over the last three decades, the heat transfer and enhancement techniques employed in PCMs to effectively charge and discharge latent heat energy and the formulation of the phase change problem. It also examines the geometry and configurations of PCM containers and a series of numerical and experimental tests undertaken to assess the effects of parameters such as the inlet temperature and the mass flow rate of the heat transfer fluid (HTF). It is concluded that most of the phase change problems have been carried out at temperature ranges between 0 °C and 60 °C suitable for domestic heating applications. In terms of problem formulation, the common approach has been the use of enthalpy formulation. Heat transfer in the phase change problem was previously formulated using pure conduction approach but the problem has moved to a different level of complexity with added convection in the melt being accounted for. There is no standard method (such as British Standards or EU standards) developed to test for PCMs, making it difficult for comparison to be made to assess the suitability of PCMs to particular applications. A unified platform such as British Standards, EU standards needs to be developed to ensure same or similar procedure and analysis (performance curves) to allow comparison and knowledge gained from one test to be applied to another.
1,630 citations
TL;DR: In this paper, an experimental energy storage system has been designed using a horizontal concentric tube heat exchanger incorporating a medium temperature phase change material (PCM) Erythritol, with a melting point of 117.7°C.
456 citations
TL;DR: In this article, a numerical model is established to predict the phase change material (PCM) melting process in porous media, and the heat transfer enhancement technique using metal foam in a shell-and-tube type latent heat thermal energy storage (LHTES) unit is investigated.
275 citations
TL;DR: In this paper, an experimental energy storage system has been designed using an horizontal shell and tube heat exchanger incorporating a medium temperature phase change material (PCM) with a melting point of 117.7 °C.
269 citations