Thermal conductivity enhancement of nanostructure-based colloidal suspensions utilized as phase change materials for thermal energy storage: A review
TL;DR: A review of studies focused on enhancing the thermal conductivity of phase change materials (PCM) for thermal energy storage upon introduction of nanostructures is presented in this article.
Abstract: A review of studies focused on enhancing the thermal conductivity of phase change materials (PCM) for thermal energy storage upon introduction of nanostructures is presented. These emerging materials have only been studied since 2005 and represent a clear departure from previous/existing practices of utilizing fixed, stationary high-conductivity inserts/structures into PCM. Carbon-based nanostructures (nanofibers, nanoplatelets and graphene flakes), carbon nanotubes, both metallic (Ag, Al, C/Cu and Cu) and metal oxide (Al 2 O 3 , CuO, MgO and TiO 2 ) nanoparticles and silver nanowires have been explored as the materials of the thermal conductivity promoters. Emphasis of the work so far has been placed on the dependence of the enhanced thermal conductivity on mass fraction of the nanostructures and temperature for both liquid and solid phases, however issues related to modifications of the degree of supercooling, melting temperature, viscosity, heat of fusion, etc. are also reported. In general, carbon-based nanostructures and carbon nanotubes exhibit far greater enhancement of thermal conductivity in comparison to metallic/metal oxide nanoparticles due to the high aspect-ratio of these nanofillers. Utilizing a figure of merit for the observed thermal conductivity enhancement, the majority of 340+ measured data points in both liquid and solid phases are summarized.
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TL;DR: The International Nanofluid Property Benchmark Exercise (INPBE) as discussed by the authors was held in 1998, where the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or "nanofluids" was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady state methods, and optical methods.
Abstract: This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.
881 citations
TL;DR: In this article, a comprehensive list of different organic, inorganic and eutectic phase change materials appropriate for passive cooling in buildings is reviewed, and full-scale testing and numerical modeling are found to be the most popular investigative methods used for experimental and theoretical analysis of PCMs.
Abstract: The most significant threat that mankind faces in the 21th century is global warming. Buildings, which account for 40% of global energy consumption and greenhouse gas emissions, play a pivotal role in global warming. Estimates show that their destructive impact will grow by 1.8% per year through 2050, which indicates that future consumption and emissions will be worse than today. Therefore, the impact of cooling systems cannot be ignored, as they, along with ventilation and heating systems, account for 60% of the energy consumed in buildings. Passive cooling techniques are a promising alternative to conventional cooling systems. Of the various passive cooling strategies, thermal energy storage by means of latent heat is an efficient way to increase the thermal inertia of building envelopes, which would reduce temperature fluctuations, leading to the improved thermal comfort of occupants. Phase change materials (PCMs) with high density for thermal energy storage can be efficiently employed to this purpose. This paper reviews recent studies of the application of PCMs for passive cooling in buildings. From the literature, a comprehensive list of different organic, inorganic and eutectic PCMs appropriate for passive cooling in buildings are reviewed. Full-scale testing and numerical modeling were found to be the most popular investigative methods used for experimental and theoretical analysis of PCMs. The combination of these two methods can provide a detailed and valid technique for PCM investigations. Finally, incorporating PCMs into building walls with macro encapsulation was also a dominant interest in previous studies.
651 citations
TL;DR: In this article, a summary of various solar thermal energy storage materials and TES systems that are currently in use is presented and the properties of solar thermal storage materials are discussed and analyzed.
Abstract: Usage of renewable and clean solar energy is expanding at a rapid pace Applications of thermal energy storage (TES) facility in solar energy field enable dispatchability in generation of electricity and home space heating requirements It helps mitigate the intermittence issue with an energy source like solar energy TES also helps in smoothing out fluctuations in energy demand during different time periods of the day In this paper, a summary of various solar thermal energy storage materials and thermal energy storage systems that are currently in use is presented The properties of solar thermal energy storage materials are discussed and analyzed The dynamic performances of solar thermal energy storage systems in recent investigations are also presented and summarized
608 citations
TL;DR: In this article, a review of thermal energy storage using phase change materials (PCMs), mainly using liquid-solid transition to store latent heat, allows a more compact, efficient and therefore economical system to operate.
563 citations
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TL;DR: In this article, the authors focused on the classification of various paraffins and salt hydrates, and provided an understanding on how to maximize thermal utilization of PCM and how to improve the phase transition rate, thermal conductivity, latent heat storage capacity and thermo-physical stability.
484 citations
References
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01 Jan 1873
TL;DR: The most influential nineteenth-century scientist for twentieth-century physics, James Clerk Maxwell (1831-1879) demonstrated that electricity, magnetism and light are all manifestations of the same phenomenon: the electromagnetic field as discussed by the authors.
Abstract: Arguably the most influential nineteenth-century scientist for twentieth-century physics, James Clerk Maxwell (1831–1879) demonstrated that electricity, magnetism and light are all manifestations of the same phenomenon: the electromagnetic field. A fellow of Trinity College Cambridge, Maxwell became, in 1871, the first Cavendish Professor of Physics at Cambridge. His famous equations - a set of four partial differential equations that relate the electric and magnetic fields to their sources, charge density and current density - first appeared in fully developed form in his 1873 Treatise on Electricity and Magnetism. This two-volume textbook brought together all the experimental and theoretical advances in the field of electricity and magnetism known at the time, and provided a methodical and graduated introduction to electromagnetic theory. Volume 2 covers magnetism and electromagnetism, including the electromagnetic theory of light, the theory of magnetic action on light, and the electric theory of magnetism.
9,565 citations
TL;DR: In this article, a methodology is introduced for predicting the effective thermal conductivity of arbitrary particulate composites with interfacial thermal resistance in terms of an effective medium approach combined with the essential concept of Kapitza thermal contact resistance.
Abstract: A methodology is introduced for predicting the effective thermal conductivity of arbitrary particulate composites with interfacial thermal resistance in terms of an effective medium approach combined with the essential concept of Kapitza thermal contact resistance. Results of the present model are compared to existing models and available experimental results. The proposed approach rediscovers the existing theoretical results for simple limiting cases. The comparisons between the predicted and experimental results of particulate diamond reinforced ZnS matrix and cordierite matrix composites and the particulate SiC reinforced Al matrix composite show good agreement. Numerical calculations of these different sets of composites show very interesting predictions concerning the effects of the particle shape and size and the interfacial thermal resistance.
1,638 citations
TL;DR: In this article, a modification of the original theories of Rayleigh and Maxwell permitted the deriva tion of expressions for the effective thermal conductivity of composites consisting of a continuous matrix phase with dilute concentrations of dispersions with spherical, cylin drical and flat plate geometry with a thermal barrier resistance at the interface between the components.
Abstract: A modification of the original theories of Rayleigh and Maxwell permitted the deriva tion of expressions for the effective thermal conductivity of composites consisting of a continuous matrix phase with dilute concentrations of dispersions with spherical, cylin drical and flat plate geometry with a thermal barrier resistance at the interface between the components.
1,185 citations
TL;DR: A review of experimental/computational studies to enhance the thermal conductivity of phase change materials (PCM) that were conducted over many decades is presented in this paper, where the authors focus on studies that concern with positioning of fixed, stationary high conductivity inserts/structures.
Abstract: A review of experimental/computational studies to enhance the thermal conductivity of phase change materials (PCM) that were conducted over many decades is presented. Thermal management of electronics for aeronautics and space exploration appears to be the original intended application, with later extension to storage of thermal energy for solar thermal applications. The present review will focus on studies that concern with positioning of fixed, stationary high conductivity inserts/structures. Copper, aluminum, nickel, stainless steel and carbon fiber in various forms (fins, honeycomb, wool, brush, etc.) were generally utilized as the materials of the thermal conductivity promoters. The reviewed research studies covered a variety of PCM, operating conditions, heat exchange and thermal energy storage arrangements. The energy storage vessels included isolated thermal storage units (rectangular boxes, cylindrical and annular tubes and spheres) and containers that transferred heat to a moving fluid medium passing through it. A few studies have focused on the marked role of flow regimes that are formed due to the presence of thermally unstable fluid layers that in turn give rise to greater convective mixing and thus expedited melting of PCM. In general, it can be stated that due to utilization of fixed high conductivity inserts/structures, the conducting pathways linking the hot and cold ends must be minimized.
1,028 citations
TL;DR: In this article, the authors provide a detailed literature review and an assessment of results of the research and development work forming the current status of nanofluid technology for heat transfer applications.
Abstract: This study provides a detailed literature review and an assessment of results of the research and development work forming the current status of nanofluid technology for heat transfer applications. Nanofluid technology is a relatively new field, and as such, the supporting studies are not extensive. Specifically, experimental results were reviewed in this study regarding the enhancement of the thermal conductivity and convective heat transfer of nanofluids relative to conventional heat transfer fluids, and assessments were made as to the state-of-the-art of verified parametric trends and magnitudes. Pertinent parameters of particle volume concentration, particle material, particle size, particle shape, base fluid material, temperature, additive, and acidity were considered individually, and experimental results from multiple research groups were used together when assessing results. To this end, published research results from many studies were recast using a common parameter to facilitate comparisons of data among research groups and to identify thermal property and heat transfer trends. The current state of knowledge is presented as well as areas where the data are presently inconclusive or conflicting. Heat transfer enhancement for available nanofluids is shown to be in the 15-40% range, with a few situations resulting in orders of magnitude enhancement.
1,023 citations