Study on preparation,structure and thermal energy storage property of capric–palmitic acid/attapulgite composite phase change materials

Fatty acid phase change materials (PCMs) have some advantages such as less corrosivity, no separation of subcooling phase and low price. In this paper, capric acid and palmitic acid are composited according to a certain mass ratio to prepare binary fatty acid. Capric–palmitic acid are absorbed into attapulgite by vacuum method to prepare capric–palmitic acid/attapulgite composite PCMs. Analysis methods such as differential scanning analysis (DSC), scanning electron microscope (SEM), Fourier transform infrared (FT-IR) and specific surface analysis (BET method) are used to test the thermal properties, structure and composition of the prepared composite PCM. The results indicate that the pore structure of the caplic–paltimic acid/attapulgite composite PCM is open-ended tubular capillary, which is beneficial to the adsorption. Capric acid and palmitic acid can be absorbed uniformly into attapulgite and the optimum absorption ratio of capric–palmitic binary fatty acid is 35%. There is no chemical reaction between the capric–palmitic acid and attapulgite. The phase change temperature of the capric–palmitic acid/attapulgite composite PCM is 21.71 °C and the latent heat is 48.2 J/g.     

Polyurethanes as solid–solid phase change materials for thermal energy storage

Polyurethane polymers (PUs) have been synthesized as solid–solid phase change materials for thermal energy storage using three different kinds of diisocyanate molecules and polyethylene glycols (PEGs) at three different molecular weights. PEGs and their derivatives are usually used as phase change units in polymeric solid–solid phase change materials due to the hydroxyl functional groups. 1000, 6000, and 10,000 g/mol number average molecular weight PEGs are used as working element as hexamethylene, isophorone, and toluene diisocyanates are used as hard segment at the backbone. The effects of molecular weight of PEG and type of diisocyanate on the thermal energy storage properties have been discussed. Only two of the produced polymers show solid–liquid phase change as the rest show solid–solid phase transitions. The produced PUs with a solid–solid phase transitions have potential to be used in thermal energy storage systems.     

Alanate–borohydride material systems for hydrogen storage applications

Alteration of the thermodynamic stability of selected borohydride/alanate systems, including the combination of LiBH₄ with NaAlH₄ and LiBH₄ with CaCl₂ and LiAlH₄, was investigated to determine the possibility of forming intermediate stability mixed AlH₄⁻–BH₄⁻ phase.     

The host hollow carbon nanospheres as cathode material for nonaqueous room-temperature Al–S batteries

Aluminum-ion batteries have attracted great attention in virtue of their reliable safety performance and cost-effective raw materials. The sulfur element with a high specific capacity gives great development space for aluminum-sulfur (Al–S) battery. However, the dissolution of sulfur in electrolyte hinders the application of Al–S battery. Carbon materials with porous structure has larger specific surface area for adsorption of sulfur, and the porous carbon for sulfur cathode provides a certain barrier for the shuttle effect during the charge-discharge process. In this work, hollow carbon synthesized by template method is applied to Al–S batteries. It is found that the cave-like porous carbon material provides space for storing sulfur and polysulfides, alleviating the sulfur shuttle effect in Al–S batteries. The specific capacity of the hollow carbon materials for Al–S batteries is 1027 mAh g^?1 at the first cycle and the rechargeable specific capacity achieves 378 mAh g^?1 after 28 cycle.     

Simulation and economic optimization of a solar assisted combined ejector–vapor compression cycle for cooling applications

This paper describes the hourly simulation and optimization of a thermally driven cooling cycle assisted by solar energy. The double stage solar ejector cooling cycle is modelled using the TRNSYS-EES simulation tool and the typical meteorological year file containing the weather data of Florianópolis, Brazil. The first stage is performed by a mechanical compression system with R134a as the working fluid, while the second stage is performed by a thermally driven ejector cycle with R141b. Flat plate collectors and an auxiliary energy burner provide heat to the ejector cycle. The thermo-economical optimization is carried out with respect to the intercooler temperature and the flat plate solar collector area, for given specific costs of the auxiliary energy and electric energy, the capital cost of the collectors, ejector cooler, and the capital cost of equivalent mechanical compression cooler.     

Design and optimization of an air heating solar collector with integrated phase change material energy storage for use in humidification–dehumidification desalination

Compared to solar water heaters, high-temperature solar air heaters have received relatively little investigation and have resulted in few commercial products. However, in the context of a humidification–dehumidification (HD) desalination cycle, air heating offers significant performance gains for the cycle. Heating at a constant temperature and constant heat output is also important for HD cycle performance. The use of built in phase change material (PCM) storage is found to produce consistent air outlet temperatures throughout the day or night. In this study, the PCM has been implemented directly below the absorber plate. Using a two dimensional transient finite element model, it is found that a PCM layer of 8 cm below the absorber plate is sufficient to produce a consistent output temperature close to the PCM melting temperature with a time-averaged collector thermal efficiency of 35%. An experimental energy storage collector with an 8 cm thick PCM layer was built and tested in a variety of weather and operating conditions. Experimental results show strong agreement with model in all cases.     

Thermal energy storage properties of the capric acid–stearic acid binary system and 48# paraffin–liquid paraffin binary system

In this paper, the phase change temperature, latent heat and thermal stability of the capric acid–stearic acid binary system and 48# paraffin–liquid paraffin binary system were experimentally studied. The experimental results showed that the phase change temperature and phase change latent heat change with the content of the component. The phase change temperature of binary mixtures changes in a wide range, so they can be used in different fields by adjusting mixing ratio. The phase change latent heat of fatty acid mixtures is higher than that of paraffin mixtures. The thermal stability of fatty acid mixtures is better than that of paraffin mixtures. The mixtures used in the phase change material (PCM) wall or the PCM floor as energy storage materials are given in the paper.     

Novel acid–base molecule-enhanced blends/copolymers for fuel cell applications

A series of acid–base molecule-enhanced composite membranes are successfully prepared. The composite membranes are composed of a sulfonated poly(aryl ether ketone) (6FSPEEK) as an acidic component, and of aminated poly(aryl ether ketone) containing a naphthyl group (AmPEEKK-NA) as a basic component. The composite membranes exhibit obviously improved thermal, oxidative and dimensional stability. Especially, these composite membranes possess excellent tensile properties both in the dry and wet state. The proton conductivities of these membranes are higher than 2.45 × 10⁻² S cm⁻¹ at room temperature and higher than 6.0 × 10⁻² S cm⁻¹ at 80 °C. The morphology of the membranes is studied in detail by SEM and AFM. All the data prove that both composite and aminated/sulfonated copolymer membranes may be potential proton exchange membrane for fuel cell applications.     

Preparation and performance of form-stable polyethylene glycol/silicon dioxide composites as solid–liquid phase change materials

This work mainly involved the preparation and characterization of form-stable polyethylene glycol (PEG)/silicon dioxide (SiO₂) composite as a novel solid–liquid phase change material (PCM). In this study, the polyethylene glycol/silicon dioxide composites as form-stable, solid–liquid phase change material (PCM) was prepared. In this new material, the polyethylene glycol acts as the latent heat storage material and silicon dioxide serves as the supporting material, which provides structural strength and prevents the leakage of the melted polyethylene glycol. Results indicated that the composite remained solid when the weight percentage of silicon dioxide was higher than 15%. Moreover, the polyethylene glycol was observed to disperse into the network of the solid silicon dioxide by investigation of the structure of the composite PCMs using a scanning electronic microscope (SEM). The properties of the porous materials and phase change materials were characterized using Fourier transformation infrared spectroscope (FTIR). The transition process was observed using polarizing optical microscope (POM) and dynamic thermo mechanic analysis (DMA). The melting temperatures and latent heats of the form-stable PEG/SiO₂ composite PCMs were determined using differential scanning calorimeter (DSC).     

Preparation and characterization of a new nanosized silicon–nickel–graphite composite as anode material for lithium ion batteries

A new type of nanosized silicon–nickel–graphite (Si–Ni–G) composite was prepared by high energy mechanical milling (HEMM) and pyrolysis using SiO as the precursor of Si for the first time. X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM) and scanning electron microscopy (SEM) were used to determine the phases obtained and to observe the microstructure and distribution of the composite. The composite powders consisted of Si, Ni, SiO₂, NiO and a series of Si–Ni alloys. The formation of the inactive SiO₂ and Si–Ni alloy phases could accommodate the large volume changes of the active particles during cycling. In addition, cyclic voltammetry (CV) and galvanostatic discharge/charge tests were carried out to characterize the electrochemical properties of the composite. The composite electrodes exhibited an initial discharge and charge capacity of 1450.3 and 956.4 mAh g⁻¹, respectively, maintaining a reversible capacity of above 900 mAh g⁻¹ for nearly 60 cycles.     

Microencapsulation of phase change material in water dispersible polymeric particles for thermoregulating rubber composites—A holistic approach

Summary To avoid the leakage of phase change materials (PCM) to its surrounding, microencapsulation of PCM in a polymeric shell is highly desirable. These microcapsules ideally should provide a platform to store and release latent heat of the PCM without undergoing any physicochemical transformation of core (PCM) as well as shell (polymer) materials. Several characteristics such as heat transfer efficiency, thermal conductivity, water dispersibility, and durability of the PCM capsules are dependent on the nature of shell materials. In the present study, a random copolymer of poly (methyl methcrylate-co-2-hydroxyethyl methacrylate) poly (MMA-co-HEMA) with an optimum ratio of 75/25 (methyl methacrylate (MMA)/2-hydroxyethyl methacrylate (HEMA)) was used as shell material to encapsulate paraffin wax (PCM), using emulsion solvent evaporation method. The microcapsules of ~5-μm size with a shell thickness of ~0.8 μm with high encapsulation efficiency (~92.34%) and thermal storage capability (99.85%) were fabricated. In addition to ease of water dispersibility, PHEMA (poly(2-hydroxyethyl methacrylate)) containing water absorbable shells also exhibit enhanced thermal conductivity from 0.1 to 0.49 W/(m·K) at 25°C in wet state compared with the dry capsule. The capsules show good durability by displaying no significant change in thermal properties and water dispersibility after running through 500 heating/cooling cycles. To test the feasibility of this novel water dispersible microencapsulated PCM, these were mixed with natural rubber latex at various blend ratios, and their thermal behaviour was evaluated. The obtained rubber composite showed good thermoregulation property with enhanced mechanical strength.     

Effect of internal void placement on the heat transfer performance – Encapsulated phase change material for energy storage

The effect of an internal air void on the heat transfer phenomenon within encapsulated phase change material (EPCM) is examined. Heat transfer simulations are conducted on a two dimensional cylindrical capsule using sodium nitrate as the high temperature phase change material (PCM). The effects of thermal expansion of the PCM and the buoyancy driven convection within the fluid media are considered in the present thermal analysis. The melting time of three different initial locations of an internal 20% air void within the EPCM capsule are compared. Latent heat is stored within an EPCM capsule, in addition to sensible heat storage. In general, the solid/liquid interface propagates radially inward during the melting process. The shape of the solid liquid interface as well as the rate at which it moves is affected by the location of the internal air void. The case of an initial void located at the center of the EPCM capsule has the highest heat transfer rate and thus fastest melting time. An EPCM capsule with a void located at the top has the longest melting time. Since the inclusion of a void space is necessary to accommodate the thermal expansion of a PCM upon melting, understanding its effect on the heat transfer within an EPCM capsule is necessary.     

Study of the KNO3–LiNO3 and KNO3–NaNO3–LiNO3 eutectics as phase change materials for thermal storage in a low-temperature solar power plant

For heat storage applications, the solid–liquid phase changes of the LiNO₃–KNO₃ and LiNO₃–KNO₃–NaNO₃ mixtures of eutectic compositions have been investigated by Differential Scanning Calorimetry (DSC) and with a home built calorimeter working on large samples – typically 500 g. The design of the new calorimeter matches at best the geometry and the thermal transfers in the industrial application. The kinetics of crystallization has been particularly studied. Density measurements of the salts in the liquid state allowed to calculate the volumetric storage capacity.     

Ni–P and Ni–Co–P coated aluminum alloy 5251 substrates as metallic bipolar plates for PEM fuel cell applications

This study is aimed to replace graphite bipolar plates in PEM fuel cells with surface modified aluminum alloy. To improve the surface characteristics of aluminum alloy 5251 (AA5251) substrate, Ni–P and Ni–Co–P coatings were deposited using electroless and electroplating deposition techniques [power supply and chronoamperometry]. Surface morphology and chemical composition of prepared coatings have been investigated using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques. The corrosion behaviour of Ni–P and Ni–Co–P coated AA5251 was studied in (0.5 M H₂SO₄ + 2 ppm HF) solution by potentiodynamic polarization technique. Lower corrosion current densities and more positive corrosion potentials were gained after coating AA5251 with Ni–P and Ni–Co–P deposits. Much better corrosion resistance was shown by coatings containing cobalt. Potentiostatic tests were carried out at +160 mV (MMS) in air-saturated solution to simulate cathode environment in PEM fuel cells. The current density of Ni–Co–P (1:1)/AA5251 was stabilized at a value lowered by 4 times relative to that at bare AA5251 substrate. Interfacial contact resistance values between coated substrates and carbon paper were measured. Ni–P and Ni–Co–P coatings prepared by electroless method showed ICR values, twice that at ones prepared by electroplating power supply technique.     

Characterisation of as cast model Mn–Si–Cr–Ni steels for reactor pressure vessel applications

Abstract

Initial results are reported from a study aimed to investigate the role and influence of the elements Cr, Ni, Mn and Si on the radiation stability of reactor pressure vessel steels. Twelve as cast model ferritic steels with basic composition typical of those used in Russian WWER-1000 and Western PWR reactor pressure vessel materials were subjected to Charpy impact, magnetic Barkhausen noise (MBN), Vickers hardness tests and SEM examination. Higher Cr content in model steels was found generally to give increased RMS values independent of Mn and Si contents. The ductile–brittle transition temperatures (DBTT) and hardness values of the model steels were found to be independent of composition. Two steels, with low concentration of Ni and high concentration of Cr or vice versa , showed high transition temperatures (?16 and ?42°C respectively). An additional heat treatment to improve the properties is being considered for these compositions. The correlation between DBTT and MBN results has potential for rapid determination of the effect of composition and irradiation on the steel properties. The next stage of the assessment will investigate the effect of irradiation of the model steels to accumulated neutron fluences of ～10¹⁹ cm^?2.     

Theoretical analysis of a CO2–NH3 cascade refrigeration system for cooling applications at low temperatures

As a result of environmental problems related to global warming and depletion of the ozone layer caused by the use of synthetic refrigerants (CFC’s, HCFC’s and HFC’s) experienced over the last decades, the return to the use of natural substances for refrigeration purposes, appears to be the best long-term alternative. In this paper, a cascade refrigeration system with CO₂ and NH₃ as working fluids in the low and high temperature stages, respectively, has been analysed. Results of COP and exergetic efficiency versus operating and design parameters have been obtained. In addition, an optimization study based on the optimum CO₂ condensing temperature has been done. Results show that following both method’s exergy analysis and energy optimization, an optimum value of condensing CO₂ temperature is obtained. The compressor isentropic efficiency influence on the optimum system COP has been demonstrated. A methodology to obtain relevant diagrams and correlations to serve as a guideline for design and optimization of this type of systems has been developed and it is presented in the paper.     

Nonlinear dynamic characteristics and bifurcation analysis of Ti–Zr–Ni quasicrystal as hydrogen storage material

In this article, the nonlinear dynamic characteristics and bifurcation of a Ti–Zr–Ni quasicrystal impacted by hydrogen atoms are studied. New nonlinear damping terms are proposed to express the delay characteristics of Ti–Zr–Ni quasicrystal, and the accurate natural frequency is obtained by the harmonic balance method. A new method based on the developed largest Lyapunov exponent is proposed to analyze the local stability of any point in the system, and the system's global stability is determined. Finally, a new way to realize the switch between hydrogen storage and release based on stochastic Hopf bifurcation is proposed. The results of theoretical analysis and numerical simulation show that the system's motion can be switched between a periodic orbit and a balanced point near the bifurcation boundary with little energy consumption, which is helpful for hydrogen storage and release.     

Synergistic Co–P bonding effect on hydrogen evolution reaction activity and supercapacitor applications of CoMoP material

Due to the synergistic effect between transition metals and hetero-atoms, transition metal-phosphide-based composites have been used as electrode materials for electrocatalytic hydrogen evolution reactions (HER) and supercapacitors, but their ideal performance has yet to be achieved. Herein, the binary transition metal phosphides, CoMoP and NiMoP, were grown on Ni-foam using a two-step hydrothermal approach and phosphorus deposition in a tube furnace. Both the CoMoP and NiMoP materials showed promising HER activity, displaying an overpotential of 137 mV and 144 mV @10 mA/cm², respectively. The theoretical studies demonstrated that the ΔG_H1 on CoMoP (?0.28 eV) was closer to zero than on NiMoP (?0.34 eV), due to the synergistic Co–P bonding, making it more accessible for H-adsorption, thereby endowing HER. In addition, the CoMoP and NiMoP materials exhibited 3507 F/g and 930 F/g energy storage capacities, respectively. Moreover, both samples had close to 100% Coulombic efficiency and about 50% capacitance retention. Based on these findings, it looks like CoMoP could be good for both the HER and supercapacitor electrodes.