Search

Rebun is a small island located northwest of Hokkaido Island where hunter-fisher-gatherer cultural traditions continued until the 19th century CE. In this study, we quantified polycyclic aromatic hydrocarbons (PAHs), pentacyclic triterpene methyl ethers (PTMEs), n-fatty acids, and glycerol dialkyl glycerol tetraethers (GDGTs) in sediments from Lake Kushu in northern Rebun Island to reconstruct changes in limnology, the local environment and local to regional fire activities during the past 17,000 years (i.e., 17 ka). The PAH concentration increased from 11 to 10 cal ka BP. PAH and PTME compositions indicate that this change was associated with an increase of fire activity at proximal locations (i.e., the vicinity of Lake Kushu) and a change in the composition of grasses growing around the lake. A peak in PAH concentrations at 6.6–6.0 cal ka BP likely indicates intensive fire activity on Rebun Island. The PAH composition after 6 cal ka BP mainly reflected the combustion of conifers near the lake. The GDGTs, n-fatty acids, perylene, and PTME concentrations were higher around 10 cal ka BP and after 6 cal ka BP compared to the remaining periods, suggesting better preservation of those compounds under lake conditions marked by lower oxygen concentrations.

In recent years, phase change material emulsions (PCMEs) with enhanced energy storage capacities and good flow characteristics have drawn significant attention. However, due to the thermodynamically unstable nature and tiny particle confinement, the nanomaterial modification strategies at PCM/water interface to improve stabilities and reduce supercooling of nano-sized PCMEs (NPCMEs) are very limited and challenging. Herein, we report a facile strategy for constructing MXene-decorated NPCME with good stability, little supercooling, and high thermal conductivity by self-assembly of MXene nanosheets at PCM/water interface. The concentrations of MXene have great influences on the average droplet diameters, stabilities, and thermophysical properties of the NPCMEs. The results show that the PCMs have been well dispersed into the water in the form of quasi-spherical droplets, with average droplet diameters of 242–805 nm. The thermal conductivity of 10 wt% n-tetradecane/water NPCME containing 9 mg ml-1 MXene is 0.693 W m-1·K-1, achieving an enhancement by 15.5%, as compared to that of water. Besides, the MXene-decorated paraffin/water NPCMEs exhibit little supercooling and enhanced heat storage capacities. More importantly, this facile self-assembly strategy opens a new platform for preparing high-performance NPCMEs, which can be used as novel heat transfer fluids for thermal energy storage systems.

Phase change material emulsion (PCME) is a latent functionally thermal fluid prepared by dispersing a phase change material into a carrier fluid with the aid of surfactants. The PCME has a high specific heat capacity and enhanced heat transfer performance in the phase change region, and it shows great potential as a novel heat transfer fluid in air-conditioning systems and solar thermal systems. There have been few literature reviews on PCMEs. In this paper, a comprehensive summary of the research on PCMEs, including the fabrication process, thermophysical properties, rheological behavior, heat transfer performance, and applications in solar thermal systems, is presented. Additionally, directions for further studies and applications of PCMEs are proposed.

Carbon nanomaterials decorated phase change material emulsions (PCMEs) are promising working fluids for direct absorption solar collectors (DASCs). Aiming at realizing an optimization, eleven PCMEs with different mass fractions of graphite nanoplatelets (GNPs) (0.04%, 0.055%, 0.07%, 0.085% and 0.10%) and paraffin (15%, 20% and 25%) were prepared, and their thermophysical characteristics, optical absorption properties, and photo-thermal conversion performance were investigated systematically. It is shown that the thermal conductivity and optical absorption of the GNPs decorated PCMEs increase with the mass fraction of the GNPs, but show a reverse trend as the mass fraction of the paraffin is increased. The viscosity increases with the increase of the paraffin mass fraction at the same temperature, and gradually decreases along with the temperature increases. The photo-thermal conversion performance of the 0.04% GNPs decorated PCMEs is inferior to that of the ones at higher loadings of the GNPs; while, at high loadings of the GNPs, an interaction between the effect of the GNPs and that of the paraffin should be considered. It is revealed that thermal conductivity is an important factor influencing the temperature distributions within the PCMEs. And to avoid the evaporation of the water included in a PCME to weaken the incident light consequently, its optical absorption property should match with its thermal conductivity. The 0.07% GNPs decorated 20% PCME possesses the best photo-thermal conversion performance, and the relative heat storage capacity is 1.64 times as higher as that of distilled water. The 100 heating-cooling cycles test indicates that the 0.07% GNPs decorated 20% PCME exhibits good thermal reliability, making it show great potentials for use in DASCs.

The self-floating Ti3C2 MXene-coated polyurethane sponge (MXene@PU module) was prepared via the simple coating operation for thermal activation of peroxydisulfate (PDS) and production of clean water. Coating MXene on the surface of PU significantly improved the degradation of model pollutant carbamazepine (CBZ) compared with PU alone under simulated solar radiation. Because of the excellent photothermal conversion performance of Ti3C2 MXene and the unique double-deck structure of MXene@PU module, the interfacial temperature of MXene@PU module reached about 140 °C, far higher than that of PU (about 82 °C). Radical identification experiments demonstrated that both hydroxyl radical and sulfate radical contributed to the degradation of organic pollutant. Addition of Cl−, HPO42−, HCO3− and natural organic matter in solution generated inhibitory effect on CBZ degradation. The prepared MXene@PU module exhibited excellent stability after long-time experiment. Importantly, the interfacial evaporation process produced abundant recycled water and no pollutant was detected in recycled water. This study provides a feasible way to utilize the renewable solar energy for removal of organic pollutants and production of clean water.

A mixed polymeric emulsifier consisting of polyvinyl alcohol (PVA) and polyethylene glycol-600 (PEG-600) was explored for preparing high-performance phase change material emulsions (PCMEs) containing the paraffin with a melting point of 62–64 °C. After the effects of the mass ratio of PVA to PEG-600, the mass ratio of the mixed emulsifier to the paraffin and the homogenization rate on the size distribution, viscosity and dispersion stability of the PCMEs containing 20 wt% paraffin were systematically investigated, the optimal emulsifying process parameters have been determined to be the mass ratio of PVA to PEG-600 of 50:50, the mass ratio of the mixed emulsifier to paraffin of 1:5 and the homogenization rate of 10,000 rpm. Accordingly, the PCMEs with the paraffin mass fractions varying from 10 wt% to 30 wt% were prepared. It is found that the paraffin has been well dispersed in water in the form of sphere-like droplets with average diameters ranging from 3 µm to 11 µm in the obtained PCMEs. Significantly, the PCMEs with different mass fractions of the paraffin exhibit no supercooling, owing to the function of the mixed polymeric emulsifier as a nucleating agent. The apparent specific heat of PCMEs are 1.51–2.18 times as high as that of water at the phase transition temperature region, due to the existent of the paraffin in them. Their apparent thermal conductivity gradually decreases with an increase in the mass fraction of the paraffin, while the viscosity increases significantly with mass fraction of the paraffin at the same temperatures. Furthermore, the pumping power consumption of the PCMEs shows a drastic reduction as compared to that of water at the same heat storage capacity. It is revealed that the PCMEs show great potential for use as a novel heat transfer fluid (HTF) in thermal energy storage (TES) systems.

A simple and general vacancy defects anchoring strategy was developed for the synthesis of single atom metals, which exhibited excellent performance for peroxymonosulfate (PMS) activation. Production of Ti vacancy defects, conversion of metal ions to metal atoms, anchoring of single atom metals and construction of two-dimensional (2D) MXene structure on the eco-friendly Ti2AlN ceramic substrate were accomplished in one step using the molten transition metal salts. Complete removal of model pollutants including carbamazepine (CBZ), sulfamethoxazole (SMX) and 2,4-dichlorophen (2,4-DCP) was achieved within less than 2 min in PMS/single atom Co process. Hydroxyl radical ( OH), sulfate radical (SO4 -) and nonradical oxidation jointly contributed to pollutants degradation. More importantly, the exposed Ti atoms with strong reducibility of MXene substrate triggered the Co(III)/Co(II) cycle and thus accelerated PMS activation. The single atom Co catalyst exhibited excellent performance even under alkaline condition or in actual river water.

Graphite nanoparticles used as a nucleating agent have been dispersed into a phase change emulsion containing 30 wt% of OP10E, aiming at eliminating its supercooling and improving its thermal conductivity. Based on the optimizations using surface response methodology, the stable OP10E emulsion with small droplets can be prepared with the aid of the emulsifier with a HLB value of 8.9 at a loading of 5 wt%. It is found that the degree of supercooling for the emulsion decreases from 9.9 °C to almost 0 °C after the dispersion of the graphite nanoparticles at an optimal concentration of 2 wt%, suggesting a complete elimination in supercooling. The addition of the graphite nanoparticles has no effect on latent heat of the OP10E/water emulsion. The thermal conductivity of the emulsion containing 2 wt% graphite is 0.578 W m−1 K−1, achieving an enhancement by 88.9% as compared to the one without graphite. The viscosity of the emulsion containing 2 wt% graphite is lower than 11.5 mPa s, meeting the transportability requirements for pumping in practical applications. No distinct changes in these properties have been observed for the emulsion after being stored for 30 days or being experienced 300 heating-cooling cycles test, implying its good dispersion stability and thermal reliability. The high energy storage capacity, little supercooling, enhanced thermal conductivity, excellent thermal reliability and good fluidity make the graphite nanoparticles-dispersed OP10E/water emulsion show great potential for use as a novel cool storage fluid for high efficiency cool storage device.

In this paper, graphite nanoparticles have been dispersed into a paraffin/water emulsion with the purpose of improving the thermal conductivity and photothermal conversion performance of the emulsion. The melting enthalpy and apparent specific heat of 20 wt% paraffin/water emulsion is 39.2 J g−1 and 9.105 J g−1 K−1 and its melting and freezing temperatures are very close to those of paraffin. Moreover, the 300 heating–cooling cycles test indicates that the paraffin/water emulsions containing 0.1 wt% graphite exhibits good thermal reliability. The viscosities of all samples are lower than 0.0750 Pa s, meeting the transportablilty requirements in pump systems for applications. In addition, the thermal conductivity of the emulsion containing 0.1 wt% graphite increases by 20.0% as compared to the base fluid and its receiver efficiency is higher than 86.0% as the temperature ranges from room temperature to 80 °C. As a result, the paraffin/water emulsion containing graphite with high energy storage capacity, enhanced thermal conductivity and excellent photo-thermal performance, good thermal reliability and good fluidity shows great potential for use as advanced heat transfer fluid (HTF) in the low temperature applications of direct absorption solar collector (DASCs).

Thermal management systems (TMSs) are indispensable for practical applications of lithium-ion battery packs. In this study, phase change material (PCM) nano-emulsions with enhanced energy storage capacity, excellent dispersion stability, low viscosity and good thermal reliability were employed as coolants for high-performance liquid cooling thermal management systems (LCTMSs) for the first time. The maximum temperature (Tmax) and maximum temperature difference ( Δ Tmax) in a 5S4P battery pack were measured to evaluate the thermal management performance of these coolants. When a 10 wt% OP28E nano-emulsion was used at a flow rate of 200 mL min−1, Tmax and Δ Tmax were 1.1 °C and 0.8 °C, respectively, lower than those based on water, at a discharge rate of 2C. The increase in OP28E mass fraction of the nano-emulsion led to a gradual decrease in Tmax and Δ Tmax at identical discharge rates. Simulation studies were also conducted and validated by comparing with the experimental results. It was revealed that, Tmax and Δ Tmax decreased with increasing flow rate of the coolants, and the thermal management performance of the 10 wt% OP28E nano-emulsion was always better than that of water. This work sheds light on improving the performance of LCTMSs by using PCM nano-emulsions.

Passive thermal management systems using phase change materials (PCMs) provides an effective solution to the overheating of lithium ion batteries. But this study shows heat accumulation in PCMs caused by the inefficient cooling of air natural convection leads to thermal management system failures: The temperature in a battery pack operating continuously outranges the safety limit of 60 °C after two cycles with discharge rate of 1.5 C and 2 C. Here a hybrid system that integrates PCMs with forced air convection is presented. This combined system successfully prevents heat accumulation and maintains the maximum temperature under 50 °C in all cycles. Study on airspeed effects reveals that thermo-physical properties of PCMs dictate the maximum temperature rise and temperature uniformity in the battery pack, while forced air convection plays a critical role in recovering thermal energy storage capacity of PCMs. A numerical study is also carried out and validated with experiment data, which gives theoretic insights on thermo-physical changes in this hybrid battery thermal management system.