Thermal transport in metal foams has received growing attention in both academic research and industrial applications. In this paper the recent research progress of thermal transport in metal foams ...has been reviewed. This paper aims to provide the comprehensive state-of-the-art knowledge and research results of thermal transport in open celled cellular metal foams, which covers the effective thermal conductivity, forced convection, natural convection, thermal radiation, pool boiling and flow boiling heat transfer, solid/liquid phase change heat transfer and catalytic reactor. The forced convection and thermal conductivity have been extensively investigated, while less research were performed on two-phase (boiling and solid/liquid phase change heat transfer) and thermal radiation in metal foams. Also most research still treats the metal foam as one type of effective continuous porous media, very few researchers investigated the detailed thermal behaviours at the pore level either by numerical or experimental approaches.
► The latest developments in solar thermal applications are reviewed. ► Various types of solar collectors are summarised. ► Thermal energy storage approaches and systems are discussed. ► The current ...status of existing solar power stations is reviewed.
Thermal applications are drawing increasing attention in the solar energy research field, due to their high performance in energy storage density and energy conversion efficiency. In these applications, solar collectors and thermal energy storage systems are the two core components. This paper focuses on the latest developments and advances in solar thermal applications, providing a review of solar collectors and thermal energy storage systems. Various types of solar collectors are reviewed and discussed, including both non-concentrating collectors (low temperature applications) and concentrating collectors (high temperature applications). These are studied in terms of optical optimisation, heat loss reduction, heat recuperation enhancement and different sun-tracking mechanisms. Various types of thermal energy storage systems are also reviewed and discussed, including sensible heat storage, latent heat storage, chemical storage and cascaded storage. They are studied in terms of design criteria, material selection and different heat transfer enhancement technologies. Last but not least, existing and future solar power stations are overviewed.
Because the biological and/or pharmacological properties of a given molecule often depend on the absolute and relative configurations of the stereogenic centers, different diastereomers may exhibit ...totally different biological and/or pharmacological activities. Therefore, for compounds containing multiple stereogenic centers, the stereoselective asymmetric synthesis of all of the individual diastereomers, preferably using a catalytic method, is of great interest and importance in organic synthesis and drug discovery. In this context, the development of catalytic diastereodivergent methods is highly desirable, since it provides one of the most efficient ways to access multiple diastereomers from the same substrates. The current review attempts to summarize the developments in the field of asymmetric diastereodivergent catalysis.
Sustainability in chemical synthesis is a major aspect of the current synthetic endeavors and, therefore, mimicking the biological process in the laboratory nowadays has the highest priority. Towards ...achieving this goal, designing organic reactions in domino mode rather than the multistep synthetic pathways and using organocatalysis instead of metal catalysis have received a lot of attention due to the inherent advantages of these processes in terms of synthetic efficiency and sustainability. As a result, the field of asymmetric organocatalytic domino reactions has witnessed tremendous progress in recent years. This review attempts to summarize the latest developments in asymmetric organocatalyzed domino reactions since 2012, with the emphasis on the catalysts and reaction modes. Discussions on the reaction mechanisms and the applications of the developed domino reaction methods in the synthesis of biologically active molecules and natural products are also included when appropriate.
► Investigations on thermal energy storage with PCMs in building applications are reviewed. ► The technologies of PCMs, including selection criteria, measurement methods and heat transfer ...enhancement, are summarised. ► Impregnation methods of PCMs into construction materials and their applications are also discussed. ► Numerical studies on thermal performance of buildings with PCMs are evaluated.
Thermal energy storage with phase change materials (PCMs) offers a high thermal storage density with a moderate temperature variation, and has attracted growing attention due to its important role in achieving energy conservation in buildings with thermal comfort. Various methods have been investigated by previous researchers to incorporate PCMs into the building structures, and it has been found that with the help of PCMs the indoor temperature fluctuations can be reduced significantly whilst maintaining desirable thermal comfort. This paper summarises previous works on latent thermal energy storage in building applications, covering PCMs, the impregnation methods, current building applications and their thermal performance analyses, as well as numerical simulation of buildings with PCMs. Over 100 references are included in this paper.
The effects of metal foams on heat transfer enhancement in Phase Change Materials (PCMs) are investigated. The numerical investigation is based on the two-equation non-equilibrium heat transfer ...model, in which the coupled heat conduction and natural convection are considered at phase transition and liquid zones. The numerical results are validated by experimental data. The main findings of the investigation are that heat conduction rate is increased significantly by using metal foams, due to their high thermal conductivities, and that natural convection is suppressed owing to the large flow resistance in metal foams. In spite of this suppression caused by metal foams, the overall heat transfer performance is improved when metal foams are embedded into PCM; this implies that the enhancement of heat conduction offsets or exceeds the natural convection loss. The results indicate that for different metal foam samples, heat transfer rate can be further increased by using metal foams with smaller porosities and bigger pore densities.
► The effects of metal foams on heat transfer enhancement of thermal storage are investigated. ► The numerical investigation is based on the two-equation non-equilibrium heat transfer model. ► Heat can be transferred quickly through the foam structure to the whole domain of PCM. ► At the liquid zone, natural convection is suppressed by the metal foam structures, owing to the big flow resistance. ► Heat transfer rate can be further increased by using metal foams with smaller porosities and bigger pore densities.
Both enantiomers of cis‐ and trans‐fused 3,4,4a,8a‐tetrahydro‐2H,5H‐pyrano2,3‐bpyran‐7‐carboxylates have been obtained in high diastereoselectivities and enantioselectivities from the same starting ...materials using a tandem inverse‐electron‐demand hetero‐Diels–Alder/oxa‐Michael reaction catalyzed by modularly designed organocatalysts (MDOs). Diastereodivergence was achieved in these reactions through the direct control of the stereochemistry of the bridgehead atoms of the fused ring using new MDOs self‐assembled from both enantiomers of proline and cinchona alkaloid thiourea derivatives.
Designer cat.: Both enantiomers of the title compounds are obtained with high diastereo‐ and enantioselectivities from the same starting materials by using an inverse‐electron‐demand hetero‐Diels–Alder/oxa‐Michael reaction catalyzed by modularly designed organocatalysts (MDOs). Diastereodivergence was achieved using MDOs self‐assembled from both enantiomers of proline and cinchona alkaloid thiourea derivatives.
The use of latent heat storage, microencapsulated phase change materials (MEPCMs), is one of the most efficient ways of storing thermal energy and it has received a growing attention in the past ...decade. However, there is no complete overview of its utilization in thermal energy storage systems, and the information is widely spread in the literature. In this paper, a comprehensive review has been carried out for MEPCMs. Four aspects have been the focus of this review: fabrication and characterization of MEPCMs, applications of MEPCMs to the textile and building, fundamental properties of microencapsulated phase change material slurry (MPCS) and application of MPCS to the thermal energy storage system. Over 140 recent publications are referenced in this paper.
This paper presents an experimental study on heat transfer characteristics of PCMs embedded in open-cell metal foams and expanded graphite, respectively. In this study the paraffin wax RT 27 and ...calcium chloride hexahydrate are employed as the heat storage media and the transient heat transfer behavior is measured. The results indicate that the addition of porous materials, either open-cell metal foams or expanded graphite, can enhance the heat transfer rate of PCMs. Especially for metal foams, the results show that they can double the overall heat transfer rate during the melting processes. The effect of mass ratio of expanded graphite on heat transfer is examined.
► Heat transfer performance of PCMs embedded in porous materials is experimentally investigated. ► Addition of metal foams and expanded graphite can significantly enhance the heat transfer of PCMs. ► Metal foams can provide better heat transfer performance than expanded graphite due to their continuous structures.
In this paper the experimental investigation on the solid/liquid phase change (melting and solidification) processes have been carried out. Paraffin wax RT58 is used as phase change material (PCM), ...in which metal foams are embedded to enhance the heat transfer. During the melting process, the test samples are electrically heated on the bottom surface with a constant heat flux. The PCM with metal foams has been heated from the solid state to the pure liquid phase. The temperature differences between the heated wall and PCM have been analysed to examine the effects of heat flux and metal foam structure (pore size and relative density). Compared to the results of the pure PCM sample, the effect of metal foam on solid/liquid phase change heat transfer is very significant, particularly at the solid zone of PCMs. When the PCM starts melting, natural convection can improve the heat transfer performance, thereby reducing the temperature difference between the wall and PCM. The addition of metal foam can increase the overall heat transfer rate by 3–10 times (depending on the metal foam structures and materials) during the melting process (two-phase zone) and the pure liquid zone. The tests for investigating the solidification process under different cooling conditions (e.g. natural convection and forced convection) have been carried out. The results show that the use of metal foams can make the sample solidified much faster than pure PCM samples, evidenced by the solidification time being reduced by more than half. In addition, a two-dimensional numerical analysis has been carried out for heat transfer enhancement in PCMs by using metal foams, and the prediction results agree reasonably well with the experimental data.
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