The use of paraffin, salts and salt hydrates as phase change materials (PCMs) have been researched extensively and used in a number of commercial applications. However, metals and metal alloys, which ...possess a high storage density on a volume basis as well as a substantially higher thermal conductivity, has received much less attention. This paper discusses the considerations for the use of metal and metal alloys as phase change materials for high temperature thermal storage applications, as well as summarises the literature on the limited research in this area. Although some pure metals and metal alloys present interesting thermal properties to be used as PCMs in thermal storage systems, there is a lack of understanding on the implications of the metallurgical aspects related to the melting and solidification of these materials under thermal cycling at high temperatures. The main issues to be considered include vapour pressure, undercooling, corrosion, segregation, changes in composition and microstructure, changes in thermal properties and undesired reactions. Further research is needed before these materials can be used as PCMs in thermal energy storage systems in industry.
This paper presents a review of the literature on low carbon and low embodied energy materials in buildings. Embodied energy is defined and discussed vs. operating energy of buildings and its growing ...importance due to the implementation of the Energy Building Performance Directive (EBPD) in Europe as example. The difficulty of measuring embodied energy and the difficulty in comparing published data are highlighted, showing an example of proposed new methodology found in the literature. Relationship between embodied energy and embodied CO2 or CO2 footprint is defined. Different materials defined in the literature as low carbon materials are referred, such as cement and concrete, wood, bricks, rammed earth and sandstone. The review shows the research efforts found in the literature to develop new materials with less embodied energy. Finally, the effect of material substitution in the embodied energy of a building is reviewed in the literature.
The use of adequate thermal energy storage (TES) systems is an opportunity to increase energy efficiency in the building sector, and so decrease both commercial and residential energy consumptions. ...Nano-enhanced phase change materials (NEPCM) have attracted attention to address one of the crucial barriers (i.e. low thermal conductivity) to the adoption of phase change materials (PCM) in this sector. In the present study two PCM based on fatty acids, capric and palmitic acid, were nano-enhanced with low contents (1.0 wt.%, 1.5 wt.% and 3.0 wt.%) of copper (II) oxide (CuO) nanoparticles. Copper (II) oxide (CuO) was synthesized via coprecipitation method obtaining 60⁻120 nm diameter sized nanoparticles. Thermal stability and high thermal conductivity were observed for the nano-enhanced phase change materials (NEPCM) obtained. Experimental results revealed remarkable increments in NEPCM thermal conductivity, for instance palmitic acid thermal conductivity was increased up to 60% with the addition of 3 wt.% CuO nanoparticles. Moreover, CuO nanoparticles sedimentation velocity decreases when increasing its content.
Human phonation is a highly non-linear process in which subglottal flow emanating from the lungs induces self-oscillations of the vocal folds. In normal conditions, this results in the generation of ...a regularly pulsating volume velocity that becomes the source of acoustic waves, which once modulated by the vocal tract, get emitted outwards as voice. However, vocal fold oscillations can become chaotic under many circumstances. For instance, even in the case of healthy symmetric vocal folds, an excess value of the subglottal pressure can trigger chaotic motion. In this paper, we derive a chaos control strategy for a two-mass model of the vocal cords to revert the situation and render the motion regular again. The approach relies on slightly altering the system energy to move it to a stable state. Given that no external control forces can be applied to the vocal cords, it is proposed to add a third mass to the original two-mass model, which is assumed to be made of an ideal smart material. The mass of the smart material is presumed negligible in comparison to the two masses of the vocal folds model, but its damping and stiffness can be tuned to evolve with time. For a fixed subglottal pressure for which the motion is chaotic, it is shown how periodicity can be recovered using adequate damping laws, by either attaching the smart material onto the larger vocal fold mass or onto the smaller one. For the latter, chaos control turns to be more difficult and the damping of the smart material has to quickly vary with time. On the other hand, given that the subglottal pressure would rarely be constant in a real situation, we also introduce a damping law to avoid chaotic motion as the subglottal pressure augments or diminishes. Finally, it is shown that control can not only be achieved by acting on the damping of the smart material but also on its stiffness. A stiffness law to prevent chaotic oscillations and get a healthy pulsating volume velocity is therefore implemented. A brief discussion on the mid-long term potential of the presented solution for practical cases is included.
•Healthy human phonation relies on regular self-oscillations of the vocal folds.•Excessive subglottal pressure can result in chaotic motion of the vocal cords.•Chaos control strategies are proposed for a symmetric vocal fold two-mass model.•The strategies consider a smart material with time depending damping and stiffness.•Control is attained for time varying subglottal pressure restoring normal phonation.
Today, one of the biggest challenges our society must face is the satisfactory supply, dispatchability and management of the energy. Thermal Energy Storage (TES) has been identified as a breakthrough ...concept in industrial heat recovery applications and development of renewable technologies such as concentrated solar power (CSP) plants or compressed air energy storage (CAES). A wide variety of potential heat storage materials has been identified depending on the implemented TES method: sensible, latent or thermochemical. Although no ideal storage material has been identified, several materials have shown a high potential depending on the mentioned considerations. Despite the amount of studied potential heat storage materials, the determination of new alternatives for next generation technologies is still open. One of the main drawbacks in the development of storage materials is their cost. In this regard, this paper presents the review of waste materials and by-products candidates which use contributes in lowering the total cost of the storage system and the valorization of waste industrial materials have strong environmental and societal benefits such as reducing the landfilled waste amounts, reducing the greenhouse emissions and others. This article reviews different industrial waste materials that have been considered as potential TES materials and have been characterized as such. Asbestos containing wastes, fly ashes, by-products from the salt industry and from the metal industry, wastes from recycling steel process and from copper refining process and dross from the aluminum industry, and municipal wastes (glass and nylon) have been considered. Themophysical properties, characterization and experiences using these candidates are discussed and compared. This review shows that the revalorization of wastes or by-products as TES materials is possible, and that more studies are needed to achieve industrial deployment of the idea.
•The use of Life Cycle Costing (LCC) at the solar energy sector is unveiled.•LCC evidences the economic feasibility of solar and hybrid systems.•Economic pillars of sustainability in renewable energy ...solutions are discussed.
This review focus on LCC Assessment (LCCA) and the adoption of this methodology for the economic pillar evaluation of the Sustainability Life Cycle in the Solar Energy sector. Research showed the effectiveness of this methodology as the main component for assessing sustainability in the economic domain, and the relationship with the primary methods of environmental and social areas. The energy industry has been responsible for a significant number of publications, and the use of LCCA for different scale solar energy solutions as vehicles, houses, buildings, highways, rural properties and power plants indicates the usefulness of this methodology. In the large-scale solar energy solutions, for Solar Photo Voltaic (SPV) and Concentrated Solar Power (CSP), the use of LCCA can upraise the advantages for choosing or integrating both solutions. Also clarifying the feasibility of their critical ancillary solutions, named Electrical Energy Storages (EES) and the Thermal Energy Storages (TES). In minor scale solar energy solutions where the crescent technological evolution of SPV Cells has resulted in higher energy efficiency rates, the use of the LCCA can demonstrate the sensitive reduction on the Levelled Cost of Energy (LCOE), reflecting on the feasibility of solutions as the Zero Energy Buildings (ZEB). These facts allied to the crescent number of studies and publications shows that LCCA is a promising field of studies and a powerful tool to achieve a most complete and reliable Life Cycle Sustainability Assessment of solar energy technologies and also the solar energy implementation projects, mainly in the design phase.
Highlighted experimental studies on nanofluids reveal an anomalous increment in the specific heat capacity (Cp) of these ionic systems when nanoparticles are added. This fact is really important due ...the applicability of nanofluids in concentrating solar power plants as heat transfer fluid and storage media. These are promising results for the development of high-temperature heat storage applications by enhanced storage capacity materials. The present work focuses on the study of this effect in NaNO3 molten salt doped with SiO2 nanoparticles by molecular dynamics (MD) simulations and Differential Scanning Calorimetry (DSC) experiments. The study shows that for nanoparticles’ concentrations around 1% wt. the Cp increases by 26% compared to pure NaNO3, whereas at higher concentrations the effect disappears. The results approach high agreement between experimental and simulation results and MD simulations reveal that the increase of Cp at low concentrations is explained by the formation of a semi ordered layer of ionic fluid. This layer is rich in Na+ cations, around the nanoparticles whereas the reduction of Cp at concentrations higher than 2% wt. is related to the aggregation of nanoparticles as revealed by Scanning Electron Microscopy (SEM). However, deep experimental results with other materials will be required in order to validate the layering effect.
Three mechanisms have been proposed as candidates to explain the unconventional Cp increment phenomenon in nanofluids. Adapted from Ref. (6). Mechanism I: The superficial atoms of the nanoparticles are less limited since they have a smaller number of bonds. Therefore, this superficial atom oscillates at lower natural frequencies and high amplitudes, resulting in a higher superficial energy. Mechanism II: The interaction of nanoparticle’s surface atoms with the ionic salt. Mechanism III: The presence of a semi-solid layer around the nanoparticles surface contributes to the Cp increment of the nanofluid. Display omitted
•NaNO3 based nanofluid has a limit concentration around 2%wt. for the Cp improvement.•MD results show similar trend than Cp measured with DSC of 5–15 nm nanoparticles.•Analysis of the ρ(r) shows a layer formation on the nanoparticle surface.•The semi-solid layering mechanism is observed to explain the non-conventional Cp.
Phase change materials (PCM) is one of the most interesting solutions to be used in thermal energy storage (TES) systems for direct steam generation (DSG) thermosolar facilities. Properties such as ...high energy density and energy storing/delivery at constant temperature bring PCM based systems in excellent candidates for DSG facility storage units. Accordingly, LiOH-KOH peritectic mixture, with a melting point of 315°C and an enthalpy change of 535kJ/kg, has been reported as attractive solution for the saturated storage module in DSG plants. A steam-PCM heat exchanger is the critical component to carry out the thermal transference between both substances. Although materials selection to be applied for steam applications is well known, lack of knowledge is detected in the field of high temperature hydroxides corrosion. Therefore, three metallic materials, A516 Gr70 carbon steel, A316L stainless steel and Inconel 625 Ni-base alloy, have been evaluated to determine their corrosion performance after hydroxides exposure. While A516 Gr70 was discarded for this application due to high corrosion rates, A316L and Inconel 625 displayed good corrosion resistance after 2640h. Finally, A316L stainless steel was selected as potential candidate for the construction of the steam-PCM heat exchanger considering cost and thermal efficiency optimization.
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•A516 Gr70, A316L and Inconel 625 corrosion by LiOH-KOH mixture has been evaluated.•Tests performed in closed autoclaves under N2 atmosphere. LiOH-KOH mixture at 360°C.•A516 Gr70 does not offer long term corrosion resistance.•Inconel 625 shows good corrosion performance but is discarded due to high cost.•A316L selected as potential candidate for the design of steam-PCM heat exchanger.
Thermal Energy Storage Materials (TESMs) may be the missing link to the “carbon neutral future” of our dreams. TESMs already cater to many renewable heating, cooling and thermal management ...applications. However, many challenges remain in finding optimal TESMs for specific requirements. Here, we combine literature, a bibliometric analysis and our experiences to elaborate on the true potential of TESMs. This starts with the evolution, fundamentals, and categorization of TESMs: phase change materials (PCMs), thermochemical heat storage materials (TCMs) and sensible thermal energy storage materials (STESMs). PCMs are the most researched, followed by STESMs and TCMs. China, the European Union (EU), the USA, India and the UK lead TESM publications globally, with Spain, France, Germany, Italy and Sweden leading in the EU. Dissemination and communication gaps on TESMs appear to hinder their deployment. Salt hydrates, alkanes, fatty acids, polyols, and esters lead amongst PCMs. Salt hydrates, hydroxides, hydrides, carbonates, ammines and composites dominate TCMs. Besides water, ceramics, rocks and molten salts lead as STESMs for large-scale applications. We discuss TESMs’ trends, gaps and barriers for commercialization, plus missing links from laboratory-to-applications. In conclusion, we present research paths and tasks to make these remarkable materials fly on the market by unveiling their potential to realize a carbon neutral future.
•Stress relaxation tests were conducted on seven laminated glass interlayers.•The master curves were obtained by using the t-T-P shifting (CFS) algorithm.•The stiffness of all tested interlayers ...decreased over time and temperature.•An equation to fit each relaxation master curve was represented by a Prony series.•The storage and loss modulus were obtained by using interconversion methods.
The mechanical behaviour of laminated glass is strongly affected by the polymeric interlayer placed between glass layers. In general, this interlayer is a viscoelastic material, and therefore it may experience creep and stress relaxation when subjected for an extended period to a constant stress or strain respectively. In this study, seven different commercial interlayer materials (EVALAM, EVASAFE, PVB BG-R20, Saflex DG-41, PVB ES, SentryGlas, and TPU) were evaluated with relaxation tests at different temperatures, in order to build the relaxation master curves through the time-temperature superposition principle. A generalized Maxwell model was chosen to describe the viscoelastic behaviour of the tested materials. This paper includes the coefficients of the Prony series that fit better the experimental results. This paper has two main goals. First, to present the Prony coefficients (ei and τi), which can then be used to create numerical models that take into consideration the time and temperature-dependant behaviour of the interlayer. Second, to provide the two components of the complex modulus (E*(ω)) of each material, the storage modulus (E’(ω)) and the loss modulus (E’’(ω)), which can be obtained from the relaxation modulus (E(t)) by using analytical interconversions.
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