Outward phase change in a cylindrical annulus with axial fins on the inner tube
01 Dec 1986-International Journal of Heat and Mass Transfer (Pergamon)-Vol. 29, Iss: 12, pp 1855-1868
TL;DR: In this article, a theoretical analysis of the phase change process in a cylindrical annulus in which rectangular, uniformly spaced axial fins, spanning the annulus, are attached to the inner isothermal tube, while the outer tube is kept adiabatic.
Abstract: A theoretical analysis is presented for the phase change process occurring in a cylindrical annulus in which rectangular, uniformly spaced axial fins, spanning the annulus, are attached to the inner isothermal tube, while the outer tube is kept adiabatic. The model assumes conduction to be the only mode of heat transfer. The governing equations are solved by finite-difference methods. The time-wise evolution of the interface profile, phase-change fraction and energy stored/discharged and the effect of all the nine prescribable parameters are presented here. Based on the analysis a working formula VF = 1.1275 (FoSteTf)0.624 (N)0.028 (L)−1.385(W)−0.049 is suggested for engineering design purposes.
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TL;DR: In this paper, a review of the history of thermal energy storage with solid-liquid phase change has been carried out and three aspects have been the focus of this review: materials, heat transfer and applications.
Abstract: Thermal energy storage in general, and phase change materials (PCMs) in particular, have been a main topic in research for the last 20 years, but although the information is quantitatively enormous, it is also spread widely in the literature, and difficult to find. In this work, a review has been carried out of the history of thermal energy storage with solid–liquid phase change. Three aspects have been the focus of this review: materials, heat transfer and applications. The paper contains listed over 150 materials used in research as PCMs, and about 45 commercially available PCMs. The paper lists over 230 references.
3,637 citations
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TL;DR: In this paper, a review of the phase change materials (PCM) and their application in energy storage is presented, where the main advantages of encapsulation are providing large heat transfer area, reduction of the PCMs reactivity towards the outside environment and controlling the changes in volume of the storage materials as phase change occurs.
Abstract: Latent heat storage is one of the most efficient ways of storing thermal energy. Unlike the sensible heat storage method, the latent heat storage method provides much higher storage density, with a smaller temperature difference between storing and releasing heat. This paper reviews previous work on latent heat storage and provides an insight to recent efforts to develop new classes of phase change materials (PCMs) for use in energy storage. Three aspects have been the focus of this review: PCM materials, encapsulation and applications. There are large numbers of phase change materials that melt and solidify at a wide range of temperatures, making them attractive in a number of applications. Paraffin waxes are cheap and have moderate thermal energy storage density but low thermal conductivity and, hence, require large surface area. Hydrated salts have larger energy storage density and higher thermal conductivity but experience supercooling and phase segregation, and hence, their application requires the use of some nucleating and thickening agents. The main advantages of PCM encapsulation are providing large heat transfer area, reduction of the PCMs reactivity towards the outside environment and controlling the changes in volume of the storage materials as phase change occurs. The different applications in which the phase change method of heat storage can be applied are also reviewed in this paper. The problems associated with the application of PCMs with regards to the material and the methods used to contain them are also discussed.
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TL;DR: In this paper, the state of the art of phase change materials (PCMs) for storing solar energy is discussed. But, prior to the large-scale practical application of this technology, it is necessary to resolve numerous problems at the research and development stage.
Abstract: The continuous increase in the level of greenhouse gas emissions and the climb in fuel prices are the main driving forces behind efforts to more effectively utilise various sources of renewable energy. In many parts of the world, direct solar radiation is considered to be one of the most prospective sources of energy. However, the large-scale utilisation of this form of energy is possible only if the effective technology for its storage can be developed with acceptable capital and running costs. One of prospective techniques of storing solar energy is the application of phase change materials (PCMs). Unfortunately, prior to the large-scale practical application of this technology, it is necessary to resolve numerous problems at the research and development stage. This paper looks at the current state of research in this particular field, with the main focus being on the assessment of the thermal properties of various PCMs, methods of heat transfer enhancement and design configurations of heat storage facilities to be used as a part of solar passive and active space heating systems, greenhouses and solar cooking.
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Abstract: Materials with hierarchical porosity and structures have been heavily involved in newly developed energy storage and conversion systems. Because of meticulous design and ingenious hierarchical structuration of porosities through the mimicking of natural systems, hierarchically structured porous materials can provide large surface areas for reaction, interfacial transport, or dispersion of active sites at different length scales of pores and shorten diffusion paths or reduce diffusion effect. By the incorporation of macroporosity in materials, light harvesting can be enhanced, showing the importance of macrochannels in light related systems such as photocatalysis and photovoltaics. A state-of-the-art review of the applications of hierarchically structured porous materials in energy conversion and storage is presented. Their involvement in energy conversion such as in photosynthesis, photocatalytic H 2 production, photocatalysis, or in dye sensitized solar cells (DSSCs) and fuel cells (FCs) is discussed. Energy storage technologies such as Li-ions batteries, supercapacitors, hydrogen storage, and solar thermal storage developed based on hierarchically porous materials are then discussed. The links between the hierarchically porous structures and their performances in energy conversion and storage presented can promote the design of the novel structures with advanced properties.
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Abstract: In this paper, an updated review of the state of technology and installations of several energy storage technologies were presented, and their various characteristics were analyzed. The analyses included their storage properties, current state in the industry and feasibility for future installation. The paper includes also the main characteristics of energy storage technologies suitable for renewable energy systems.
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References
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31 Dec 1959
TL;DR: In this paper, a classic account describes the known exact solutions of problems of heat flow, with detailed discussion of all the most important boundary value problems, including boundary value maximization.
Abstract: This classic account describes the known exact solutions of problems of heat flow, with detailed discussion of all the most important boundary value problems.
21,797 citations
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TL;DR: In this article, a finned vertical tube with either conduction in the solid or natural convection in the liquid was used to study freezing on a paraffin phase change medium with a fusion temperature of 36.4°C.
Abstract: Experiments were performed to study freezing on a finned vertical tube when either conduction in the solid or natural convection in the liquid controls the heat transfer. Conduction is the controlling mode when the liquid is at its fusion temperature, whereas natural convection controls when the liquid temperature is above the fusion value. The phase change medium was a paraffin, 99% pure n-eicosane, with a fusion temperature of 36.4°C. Auxiliary experiments were also performed with an unfinned tube to obtain comparison data. For conduction control, the enhancement of freezing due to finning is less than the area ratio of the finned and unfinned tubes, whereas for natural-convection control the enhancement is very nearly equal to the area ratio. The liquid-solid interface is a thicket of whisker-like crystals when conduction controls but is straight (i.e. vertical). On the other hand, the interface is smooth but tapered when natural convection controls—yielding bottom-heavy frozen specimens. When conduction controls, freezing continues more or less indefinitely, whereas natural convection severely retards the freezing and ultimately terminates it altogether.
109 citations
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TL;DR: In this paper, a thermal storage system consisting of vertically arranged fins between a heated and cooled horizontal finned-tube arrangement is reported, where the high thermal expansion coefficient and low viscosity of paraffin wax, at temperatures above 50/sup 0/C, are utilized to induce natural convection in the liquid phase even at small thicknesses.
Abstract: Heat transfer enhancement in a thermal storage system consisting of vertically arranged fins between a heated and cooled horizontal finned-tube arrangement is reported. The high thermal expansion coefficient and low viscosity of paraffin wax, at temperatures above 50/sup 0/C, are utilized to induce natural convection in the liquid phase even at small thicknesses. The experimental data on the rate of production of liquid as a function of time and temperature of the hot surface is presented. The photographs of the melted zone indicate a naturally buoyant flow induced in the neighborhood of the vertical fins causes a rapid melting of the solid wax and a downdraft along the cooler solid phase surface. The heat transfer coefficient at the interface is calculated from experimentally determined instantaneous locations of the moving boundary.
87 citations
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TL;DR: In this paper, a simplified numerical model based on a quasi-linear, transient, thin fin equation was proposed to predict the fraction of melted phase change materials and the shape of the liquid-solid interface as a function of time with sufficient accuracy for engineering purposes.
Abstract: Phase-change energy storage devices have an inherent disadvantage due to the insulating properties of the phase-change materials (PCM's) used. Such systems are difficult to analyze theoretically due to the nonlinearities of the moving liquid-solid interface and the presence of natural convection as shown by several recent numerical and experimental investigations. Previous work has been unsuccessful in predicting the performance of phase-change devices in the presence of fins and natural convection. This study presents a simplified numerical model based on a quasi-linear, transient, thin fin equation, which predicts the fraction of melted PCM, and the shape of the liquid-solid interface as a function of time with sufficient accuracy for engineering purposes. Experimental results are compared in dimensionless form with model predictions, and show fairly good agreement. To achieve high heat-transfer rates with a fixed amount of PCM and metal fin material, the model indicates that melting the PCM in a pure conduction mode with closely spaced thin fins is preferable to melting PCM with thicker fins spread further apart, even in the presence of natural convection.
75 citations