Low Temperature End Research Articles

Enhancing the performance of PVT-TEG power generation systems by heat pipes and Fe3O4 nanofluids

In recent years, enhancing the cooling of photovoltaic (PV) panels to improve overall energy efficiency has become a significant focus. In this study, we propose an improved power generation system integrating semiconductor thermoelectric generators (TEGs). The integration involves the installation of several heat pipes and serpentine copper tubes on the back of PV panels, with nanofluids flowing through the copper tubes as the working fluid, effectively cooling the PV panels. The copper tube is connected to the heat exchanger on the high-temperature side of the TEGs, forming a closed-loop circulation system. Consequently, the cooling fluid transfers heat to the hot surface of the TEGs, utilizing waste heat generated by the PV panels for electricity generation. The TEGs consist of 10 thermoelectric modules, with the low-temperature end in contact with the finned aluminum plate (TEGs radiator) and actively cooled by natural air cooling. Additionally, to validate the design rationale, multiple sets of comparative experiments were arranged. The experiments utilized nanofluids with volume fractions of 0.5 %, 1 %, 2 %, and 3 %, and water, as the cooling fluid. The experimental results demonstrated that the maximum operating temperature of the reference PV panel can reach 81.9 °C, and the average and maximum exergy efficiencies throughout a day are recorded at 16.91 % and 31.84 %, respectively. It’s noteworthy that the most significant cooling effect occurs when the nanofluid volume fraction is 2 %, reducing the maximum temperature of the PVT panel to 61.5 °C. Simultaneously, the average daily exergy efficiency and exergy efficiency of the PVT-TEG power generation system reached peak values of 21.06 % and 39.87 %, respectively. Compared to the reference PV panels, the output power of the PVT-TEG system increases by up to 30.51 %.

Thermo-economic examination of ocean heat-assisted pumped thermal energy storage system using transcritical CO2 cycles

In response to the challenges posed by the growth of renewable energy electricity to the security of the power grid, energy storage technology has rapidly developed in recent years. Pumped thermal energy has been recognized as an attractive massive energy storage technology with the superiority being independent of site. An ocean heat-assisted pumped thermal energy storage system using transcritical CO2 cycles is proposed in this study. State-of-the-art thermo-economic models are developed and described to simulate the system processes and conduct cost estimates. The originality of this system lies in the ability to effectively improve its efficiency by configuring seawater at different depths at the low temperature end of the system. Research has found that, if the seawater used in the charge process always comes from the surface of the ocean, the system efficiencies are 48.1 %, 61.3 % and 66.4 % respectively when the depth of seawater during the discharge process are 50 m, 100 m and 1000 m. When the seawater employed in the entire system comes from 1000 m underwater, the efficiency of the system is only 53.5 %. In addition, for the 50 MW/10 h system, the minimum value of levelized cost of storage is 0.143 $/kWh. The uncertainty analysis of cost for the proposed system is carried out using the Monte Carlo method. Results show that with the charge/discharge duration ratio rising from 4 h/10 h to 10 h/4h, the total capital cost falls from 245 ± 76 M$ to 102 ± 34 M$ and the levelized cost of storage reaches the minimum value when this ratio is 1. The larger the energy storage capacity, the lower the levelized cost of storage. In summary, the system has shown satisfactory results in both thermodynamics and economic performance, and further research is worthwhile in the future.

Voids size distribution in gelled waxy crude oil under dynamic and static cooling

Waxy crude oil is known for its high wax contents that can potentially result in gelling following sufficient cooling of the transportation line in the subsea bed at offshore fields. The gelling over the entire lines requires an accurately predicted restart pressure to restart the clogged and idle system. However, the common way of predicting the restart pressure has been reported to result in over-designed and predicted piping parameters. Recent research findings evidenced the formation of voids which would reduce the restart pressure significantly. The study conducted in this paper is aimed at investigating the voids size distribution in gelled crude oil across and along transportation pipelines. Sets of experiments simulating crude oil transportation during both static and dynamic cooling were conducted. The gelled crude oil below the pour point temperature was then scanned using a Magnetic Resonance Imaging (MRI) system to detect the voids formed. The resulting voids at each scanning cross-section were quantified, and their distributions were investigated. It was observed that dynamic cooling had minimal impacts on the voids size difference along the pipeline with the difference in voids areas within 10 mm2 to be twice and uniform for the entire flow rates tested. However, voids size in statically cooled waxy crude oil was found to be highly distributed with a maximum of 6 voids size distribution in 10 mm2 ranges. The low-end temperature had the highest size difference while the difference was decreasing with higher end temperatures. This study shows that the voids amount in dynamically cooled waxy crude oil could also be estimated with lower numbers of cross-sectional voids areas. However, the higher cross-sectional voids detection is recommended while estimating voids in statically cooled waxy crude oil.

Minute-cadence observations of the LAMOST fields with the TMTS – III. Statistical study of the flare stars from the first two years

ABSTRACTTsinghua University-Ma Huateng Telescopes for Survey (TMTS) aims to detect fast-evolving transients in the Universe, which has led to the discovery of thousands of short-period variables and eclipsing binaries since 2020. In this paper, we present the observed properties of 125 flare stars identified by TMTS within the first two years, with an attempt to constrain their eruption physics. As expected, most of these flares were recorded in late-type red stars with GBP − GRP >2.0 mag; however, the flares associated with bluer stars tend to be on average more energetic and have broader profiles. The peak flux (Fpeak) of the flare is found to depend strongly on the equivalent duration (ED) of the energy release, i.e. Fpeak∝ED0.72 ± 0.04, which is consistent with results derived from the Kepler and Evryscope samples. This relation is likely to be related to the magnetic loop emission, while, for the more popular non-thermal electron heating model, a specific time evolution may be required to generate this relation. We notice that flares produced by hotter stars have a flatter Fpeak - ED relation compared to that from cooler stars. This is related to the statistical discrepancy in light-curve shape of flare events with different colours. In spectra from LAMOST, we find that flare stars have apparently stronger H α emission than inactive stars, especially at the low-temperature end, suggesting that chromospheric activity plays an important role in producing flares. On the other hand, the subclass with frequent flares is found to show H α emission of similar strength in its spectra to that recorded with only a single flare but similar effective temperature, implying that chromospheric activity may not be the only trigger for eruptions.

Investigations on nonlinear processes of a Gifford-McMahon type orifice pulse tube refrigerator

The target of this investigation is to illustrate the nonlinear fluid flow, heat transfer, and vortex formation phenomena in an orifice pulse tube refrigerator by numerical simulation. Numerical results confirm that jet streaming is generated at the low-temperature end of the pulse tube in between the junction of U-shaped tube and pulse tube. The primary vortex, which is generated due to the minor loss, continuously grows because of velocity change and eventually leads to the formation of secondary eddy. Consequently, flow straighteners have been adopted at the hot side of the regenerator, hot heat exchanger, and both sides of U-shaped tube. It is noticed that, jet streaming has been suppressed at the cold end of the pulse tube. Nevertheless, the streaming effect generated due to the oscillating flow of the gas parcels within the pulse tube, and third type of streaming have not been suppressed with the flow-straightener. Additionally, the numerical simulation shows different gas flow behaviors within the pulse tube that occurs due to the oscillating pressure pulse. An experimental investigation is conducted to compare experimental results with the numerical results and a valid agreement is observed between them.

Pure Green Upconversion from a Multicolor Downshifting Perovskite Crystal

AbstractLanthanide‐doped halide perovskite has emerged as a promising phosphor for multimode luminescence. Here, a chloride‐based perovskite single crystal is reported, namely Cs2NaInCl6:Yb3+,Er3+, that is grown in a hydrothermal reactor. The as‐grown crystals feature two distinct luminescence behaviors under UV and 980 nm laser excitation, respectively. Under UV lamp excitation, the crystal shows a multicolor emission of sharp bands at 448, 550, and 660 nm, covering a wide color gamut in CIE diagram. In stark contrast, the crystal under 980 nm excitation exhibits a pure green upconversion with a green‐to‐red ratio up to 211. The universal green dominance is further demonstrated in many chlorides, including Cs2AgInCl6, Cs2NaBiCl6, and Cs2AgBiCl6. The strong green upconversion is used for optical thermometry, which demonstrates an unprecedented sensitivity up to 9.3% K−1 at the low temperature end. The work introduces a kind of new hosts for single‐band upconversion luminescence, opening up many possibilities in areas such as low‐threshold laser and pure‐green color converter.

Chemical vectoring in continental geothermal systems: Composition of altered rocks and illite as guides to magmatic degassing

The Taupō Volcanic Zone, New Zealand, is one of the most voluminous volcanic regions on Earth. Over the last 1.8 Myr, bimodal volcanism in this rifted-arc setting has been dominated by voluminous rhyolite ignimbrite eruptions (>6000 km3 cumulative) and minor arc-type andesite and dacite, underpinned by basaltic intrusions. The combination of the magmatism and extensionally thinned arc crust with high heat flow has resulted in more than 23 active geothermal fields in the region. The fluids sampled in the geothermal systems are dominated by dilute meteoric fluids that are low in components such as acids, alkalis, and some trace metals commonly ascribed to magmatic sources but can contain large amounts of deep sourced magmatic volatiles such as CO2.This study was designed to assess the long-term (>20,000yr) fluid and metal input into two Taupō geothermal systems, and the amount and proportion of magmatic-derived components in these fluids. We collected major and trace element compositions of hydrothermal altered whole rocks and clay minerals from two active geothermal systems and compared them with hydrothermally altered rocks of the fossil (0.6 Ma) Ngatamariki magmatic-hydrothermal system, which has a demonstrated large magmatic contribution. The Ohaaki and Rotokawa geothermal systems have both been drilled to a depth of 3000 m, with sampled reservoir fluids containing low concentrations of chloride (∼1000 mg/kg) but high levels of gas (CO2, N2) that have previously been interpreted to reflect subduction components derived from arc-type magmas. Whole-rock samples lack enrichment in chloride-transported metals such as Cu, Pb or Zn but have minor anomalies of bisulfide-complexed Au, Sb, and As in the uppermost 1500 m of the geothermal reservoirs. Hydrothermal water-rock interactions in the deep reservoirs of both geothermal systems at temperatures between 220 and 300 °C produced assemblages of illite + albite + adularia + calcite + pyrite that are in equilibrium with the observed neutral to slightly acidic pH (6 ± 1) of the present-day fluids. In the lower temperature end of this range, Mg and Fe increasingly enter the illite crystal lattice via Tschermak-type (phengite) substitution, whereas a few high-temperature (>300 °C) samples contain scarce muscovite compositions. The illites commonly have low contents of most trace metals, although minor amounts of Cs, Li, Cu, Sb and Sn occur in near-surface samples. Based on these data, over the >20,000-year lifetime of the Ohaaki and Rotokawa geothermal systems, fluids were dominated by chloride-poor meteoric water and contained little magmatic contributions other than conducted heat, some gases (CO2 - N2 ± H2S), and a small fraction of the total H2O of geothermal waters. Therefore, the inferred magma bodies of intermediate to silicic composition that lie at shallow depth beneath these geothermal systems currently are not, and likely have not been for >20,000 years, degassing significant water and chloride despite the high water and chloride contents of the magmas. By inference, the intermediate to silicic magmas at depth have not transferred large amounts of volatiles to the geothermal systems over this period, and rather are storing them in the magmatic bodies to be released in volcanic eruptions that are commonly explosive and pyroclastic in nature and highly hazardous.

Bending and Straightening of a Medium Carbon Steel Continuous Casting Slab with Low Temperature End Plastic Groove.

The high temperature brittleness range of medium carbon microalloyed steel under an actual continuous casting process was determined by the high temperature tensile test. The test results revealed that only a third of the brittle temperature range from 650–825 °C was due to intergranular ferrite in the experimental steel. In addition, it was found that the plastic recovery was fast and stable when the temperature was lower than 725 °C (the lowest plastic temperature). Bending/straightening operation in this temperature range was conducive to controlling the generation of corner cracks. In order to keep the corner temperature at the low temperature end of the plastic curve when the slab was bent/straightened, the cooling water scheme of the secondary cooling zone of the continuous caster was formulated by numerical calculation. By appropriately increasing the cooling water flow in the foot roll and the secondary cooling zones 1–5, the corner temperature of slab during bending operation was 600–700 °C, avoiding the brittle temperature range. The industrial test was then carried out. The results showed that after using the optimized water volume, the corner grains of the slab were uniform and the microstructure was mainly pearlite + ferrite. In addition, the abnormally large grain size was reduced, and a large amount of ferrite was generated inside the grain, which avoided stress concentration at the corner of the slab during bending/straightening operation, and basically eliminated the corner crack of the slab.

A Simple Model for Mixing and Cooling in Cloud–Wind Interactions

Abstract We introduce a simple entropy-based formalism to characterize the role of mixing in pressure-balanced multiphase clouds and demonstrate example applications using enzo-e (magneto)hydrodynamic simulations. Under this formalism, the high-dimensional description of the system’s state at a given time is simplified to the joint distribution of mass over pressure (P) and entropy (K = P ρ −γ ). As a result, this approach provides a way to (empirically and analytically) quantify the impact of different initial conditions and sets of physics on the system evolution. We find that mixing predominantly alters the distribution along the K direction and illustrate how the formalism can be used to model mixing and cooling for fluid elements originating in the cloud. We further confirm and generalize a previously suggested criterion for cloud growth in the presence of radiative cooling and demonstrate that the shape of the cooling curve, particularly at the low-temperature end, can play an important role in controlling condensation. Moreover, we discuss the capacity of our approach to generalize such a criterion to apply to additional sets of physics and to build intuition for the impact of subtle higher-order effects not directly addressed by the criterion.

Effects of Linear Calibration Errors at Low-Temperature End of Thermal Infrared Band: Lesson From Failures in Cloud Top Property Retrieval of FengYun-4A Geostationary Satellite

Cloud top properties (CTPs) are important satellite products. However, the failures of CTPs derived from the Advanced Geostationary Radiation Imager of FengYun-4A (FY-4A/AGRI) have been occasionally reported by users. To this end, the feasibility of the operational CTP algorithm has been reviewed. First, this study reveals the slight differences in brightness temperature (BT) maps of thermal infrared (TIR) bands between two different imagers. Further analyses found that the nonretrieved pixels of CTP products from FY-4A/AGRI usually have a negative value down to −13 K in 10.8–13.5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> BT difference (BTD <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{10.8-13.5\,\mu \text {m}}$ </tex-math></inline-formula> ), and the joint distribution related to BTD <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{10.8-13.5\,\mu \text {m}}$ </tex-math></inline-formula> and BTD <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{10.8-12\,\mu \text {m}}$ </tex-math></inline-formula> is well separated from those successfully retrieved ones. These findings are confirmed by the simulations of the radiative transfer forward model (approaching −12 K or lower) and the cross-validation between the products from AGRI/FY-4A and the Infrared Atmospheric Sounding Interferometer of Meteorological Operational Satellite Program-Satellite B. In essence, the bias at the 13.5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> band is mainly affected by the relatively low accuracy and stability at the low-temperature end. Based on these findings, we have proposed a novel method to estimate calibration-related measurement biases of TIR bands and track their in-orbit stability. The statistical study based on the FY-4A/AGRI observations reveals significant daily and diurnal variations in performance and provides an insight into its stability at the TIR band ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$13.5~\mu \text{m}$ </tex-math></inline-formula> ).

Shrinkage Behavior, Thermal Expansion Behavior, and Electrical Conductivity Study of Samarium Doped Ceria Electrolytes

Ceria-based electrolytes generally have high sintering temperatures (~1500 °C)1,2, which increases the cell fabrication cost and decreases the mechanical stability of the cell due to rapid grain growth. In this work, the Ce0.9Sm0.1O2 (SDC) electrolyte is synthesized by microwave-assisted co-precipitation method using ethanol as a solvent. The sintering behavior of the green compact is studied using a dilatometer. Linear shrinkage and shrinkage rate behavior study shows a low sintering end temperature (1200 °C) and a final relative density of ~92%. A maximum linear shrinkage of -15.70% is observed at 1200 °C. A uni-modal shrinkage rate curve is seen, which confirms uni-modal pore size distribution in the powder. After 1388 °C, a dedensification is observed (+ 0.29% linear shrinkage), which might be associated with the reduction of Ce4+ to Ce3+ (please see Figure 1). Initial sintering results suggest that the synthesis method used has significantly lowered the SDC electrolyte's sintering temperature. Although the densification is completed at 1200 °C, the microstructure may change with further increase in the sintering temperature, affecting electrical conductivity. Inspired by the initial results, a detailed study on the effect of sintering temperature (1200 °C to 1500 °C) on the microstructure and electrical conductivity of SDC will be carried out and presented in the paper. S. Medisetti et al., Nano-Structures & Nano-Objects, 11, 7–12 (2017) https://www.sciencedirect.com/science/article/pii/S2352507X16301275.G. Accardo et al., J. Appl. Biomater. Funct. Mater., 14, 35–41 (2016) https://journals.sagepub.com/doi/abs/10.5301/jabfm.5000265. Figure 1

Lithium in red giants: the roles of the He-core flash and the luminosity bump

ABSTRACT Lithium abundances for red giants in the GALAH DR3 survey are studied. The rare examples of Li-enriched stars with abundances A(Li) ≥1.5 are confirmed to be He-core burning stars belonging to or evolved from the red clump with similar masses and metallicity: M ≃ 1.1 ± 0.2 M⊙ and [Fe/H] ≃ −0.3 ± 0.3. Li enrichment over the Li abundance present in a star’s predecessor at the tip of the red giant branch likely occurs in all these red clump stars. Examination of the elemental abundances (C to Eu) in the GALAH catalogue shows no anomalous abundances in red clump giants and, in particular, no dependence on the Li abundance, which ranges over at least five dex. Lithium synthesis is attributed to the He-core flash occurring in stars at the tip of the red giant branch. Models from the Modules for Experiments in Stellar Astrophysics (MESA) match the observed evolution of these stars along the red giant branch and to the red clump but only at the low effective temperature end of the observed spread of red clump giants. Run of Li abundance on the red giant branch is fairly well reproduced by MESA models. A speculation is presented that the series of He-core flashes not only leads to 7Li synthesis from a star’s internal reservoir of 3He but also may lead to internal restructuring leading to the observed effective temperature spread of red clump stars at about a constant luminosity. Giants exhibiting marked Li enrichments are not found at other evolutionary phases and, in particular, not directly associated with the luminosity bump on the red giant branch for which the Li abundance increase does not exceed 0.3 dex.

An effectiveness analysis of the pulsed resonant fuel combustion in the processes of steel­casting ladle drying and warming

This paper reports a technique of the pulsed resonant fuel combustion in the processes of drying and heating steel-casting ladles, devised to save fuel. The research method is based on the initiation of pulsations when burning fuel at a frequency equal to the frequency of natural fluctuations within the working volume of the ladle, which leads to the resonance of pulsations. This study aimed to define a technique to effectively burn fuel and to confirm a decrease in fuel consumption in the process of the pulsed resonant combustion. The experimental and industrial studies involving 8 drying operations and 5 ladle heating operations have established the possibility to comply with the normative requirements in line with the technological instructions at the level of 80‒100 %. The possibility to search for the pulsed resonance frequencies under industrial conditions has been confirmed, despite the negative impact of high temperatures, acoustic interference, and inertia of the equipment. The feasibility of a pulsation unit has been determined, as well as the possibility to steadily maintain, during the drying process, the required resonance frequencies of gas pulsations. A more intensive course of the drying process has been observed, which makes it possible to shorten the process duration and, accordingly, to reduce fuel consumption. The high excitability of resonance frequencies in the ladle during heating has been detected, due to the short length and volume of the section of a gas pipeline between the pulsation unit and burner compared to the drying bench. The warm-up intensity was noticeably higher than that of drying due to the lower end temperature of the lining (777‒910 °C instead of 900‒1,120 °C) and the lack of moisture evaporation. Using the pulsed resonant fuel combustion mode at the posts of intensive heating of ladles for melting makes it possible to force the heating by the resonant pulsation of the torch. During pulsed resonant combustion, the usable utilization of fuel heat increases markedly, which leads to an increase in the drying and heating processes efficiency and corresponding fuel economy. The decrease in the consumption of natural gas when drying the ladles amounted to 2.7÷26.1 %; at the warm-up ‒ 19.5÷37.8 %. These data indicate the energy efficiency of the pulsed resonant combustion and the feasibility of implementing a burning technique in the processes of ladle drying and warming

Research progress of large diamond single crystals under high pressure and high temperature

Diamond has a series of extreme characteristics superior to other materials, and also very wide application scope. The large diamond single crystal can play a role in its functional characteristics, which has become a research hotspot. In this paper, we introduce the principle and process of synthesizing large diamond single crystal by temperature gradient method (TGM) under high pressure and high temperature (HPHT), and summarizes the research status and research directions of different types of and additives-doped large diamond single crystals respectively. The principle of the temperature gradient method is that the carbon source, driven by the temperature gradient, diffuses from the high concentration region at the high temperature end to the low concentration region at the low temperature end, and diamonds are grown on the seed crystal. The growth rate of diamond crystal is controlled by adjusting the axial temperature gradient at synthesis cell, and the shape growth of Ib-type large diamond is controlled by the distribution in the V-shaped growth area. We introduce different kinds of diamond large single crystals from five aspects. Firstly, the Ia-type diamond large single crystal can be obtained by the annealing treatment of Ib-type diamond under HPHT. The conversion rate of C centre to A centre for nitrogen in diamond is improved by optimizing the conditions of HPHT. Secondly, the Ib-type larger diamond is studied very much in the following areas: the analysis of its surface characteristic, the control of inclusions and cracks, the precipitation mechanism and the elimination measures of regrown graphite and the mass production technology of multiseed method. Thirdly, IIa-type large diamond single crystal is introduced in which the nitrogen getter is selected due to the ability Al and Ti (Cu) to getter nitrogen, the catalyst is selected because of its effect on the nitrogen content in the diamond synthesized with Fe or Ni based catalyst, and the elimination method of microcrystalline graphite precipitation is presented by analyzing its mechanism. Fourthly, the boron elements exist in IIb-type diamond and have influence on the growth characteristics of synthetic diamond. Fifthly, introduced is the research status of diamond synthesized with B, N, S, P doping elements, in which its individual substance or their compound is used as a doping source or boron and other elements with small radius are used as co-doping agent. Then S or P with B co-doping is more conducive to the improvement of the performance of n-type diamond large single crystal semiconductor. Therefore, it is proposed that the large diamond single crystal need strengthening in mass production of IIa-type large diamond single crystal, superconducting characteristics of IIb-type large diamond single crystal, and doping of n-type semiconductors.

Insights into the Reactions of Hydroxyl Radical with Diolefins from Atmospheric to Combustion Environments.

Hydroxyl radicals and olefins are quite important from a combustion and an atmospheric chemistry standpoint. Large amounts of olefinic compounds are emitted into the earth's atmosphere from both biogenic and anthropogenic sources. Olefins make a significant share in transportation fuels (e.g., up to 20% by volume in gasoline), and they appear as important intermediates during hydrocarbon oxidation. As olefins inhibit low-temperature heat release, they have caught some attention for their applicability in future advanced combustion engine technology. Despite their importance, the literature data for the reactions of olefins are quite scarce. In this work, we have measured the rate coefficients for the reaction of hydroxyl radicals (OH) with several diolefins, namely 1,3-butadiene, cis-1,3-pentadiene, trans-1,3-pentadiene, and 1,4-pentadiene, over a wide range of experimental conditions ( T = 294-468 K and p ∼ 53 mbar; T = 881-1348 K and p ∼ 1-2.5 bar). We obtained the low- T data in a flow reactor using laser flash photolysis and laser-induced fluorescence (LPFR/LIF), and the high- T data were obtained with a shock tube and UV laser-absorption (ST/LA). At low temperatures, we observed differences in the reactivity of cis- and trans-1,3-pentadiene, but these molecules exhibited similar reactivity at high temperatures. Similar to monoolefins + OH reactions, we observed negative temperature dependence for dienes + OH reactions at low temperatures-revealing that OH-addition channels prevail at low temperatures. Except for the 1,4-pentadiene + OH reaction, which shows evidence of significant H-abstraction reactions even at low-temperatures, other diolefins studied here almost exclusively undergo addition reaction with OH radicals at the low-temperature end of our experiments; whereas the reactions mainly switch to hydrogen abstraction at high temperatures. These reactions show complex Arrhenius behavior as a result of many possible chemical pathways in such a convoluted system.

Modeling water partition in composite gels of BSA with gelatin following high pressure treatment

Changes in the structural properties of hydrogels made with gelatin and bovine serum albumin mixtures were recorded following exposure to high pressure at 300 MPa for 15 min at 10 and 80 °C. Dynamic oscillation, SEM, FTIR and blending law modelling were utilised to rationalise results. Pressurization at the low temperature end yielded continuous gelatin networks supporting discontinuous BSA inclusions, whereas an inverted dispersion was formed at the high temperature end with the continuous BSA network suspending the discontinuous gelatin inclusions. Lewis and Nielsen equations followed the mechanical properties of the composites thus arguing that solvent partition between the two phases was always in favour of the polymer forming the continuous network. As far as we are aware, this is the first attempt to elucidate the solvent partition in pressurised hydrogel composites using blending law theory. Outcomes were contrasted with earlier work where binary mixtures were subjected only to thermal treatment.

Pyrolysis characteristics of cellulose derived from moso bamboo and poplar

To compare with pyrolysis characteristics of cellulose from moso bamboo and poplar, samples were pyrolyzed with different heating rates through thermogravimetric analysis (TG). The kinetics was calculated by Kissinger–Akahira–Sunose method. The results showed that pyrolysis process of moso bamboo and poplar fiber included three stages, and the main pyrolysis occurred in the second step. Moso bamboo fiber had a higher start temperature, a lower end temperature and a more mass loss at each heating rate in the main pyrolysis stage. With increase in heating rate, the temperature corresponding to the maximum of mass loss increased and the DTG curve shifted to higher temperature. The reaction rates varied at different heating rates. The activation energy of cellulose from moso bamboo was lower than poplar cellulose, indicating cellulose of moso bamboo was easier to be pyrolyzed. The results from this research will provide guidance to thermal conversion of moso bamboo and poplar.

Experimental study on a stove-powered thermoelectric generator (STEG) with self starting fan cooling

Abstract In order to obtain electricity in off-grid areas and in emergency conditions (earthquake, hurricane, tidal wave, military field, etc.), a prototype of stove-powered thermoelectric generator (STEG) without battery embedded was built and tested. A novel type of heat collector, i.e. two copper heat conducting flat plates installed oppositely, was designed to integrate a relative large number of thermoelectric (TE) modules (eight TE modules in the present work). The heat collector works with optimized heat sinks and cooling fans to maintain large temperature difference and low cold end temperature, and to insure the self startup of the STEG. Hard charcoal was used to test the performance of the STEG, including the startup performance, power load feature, response dynamics when adding a load and thermoelectric efficiency. Results showed that the STEG can be self startup. The measured maximum electricity power is 12.9 W, and the thermoelectric efficiency lies between 2.4% and 2.8% when the temperature difference ranges from 119 °C to 147 °C. The response time is short enough (several seconds) to stable the outputs, and the cold end temperature is low enough, i.e. less than 65 °C to install normal cooling fans.

Effect of feedstock and pyrolysis temperature on properties of biochar governing end use efficacy

The aim of this study was to systemically evaluate how feedstock characteristics and temperature influence biochar evolution during pyrolysis and to establish their relationships with biochar potential for soil amendments. We produced four biochar thermosequences from oak, pine, sugarcane and peanut shell at twelve temperatures (350–900 °C), and characterised them by yield, proximate analysis, elemental analysis, pH, electrical conductivity (EC) and carbon (C) functional groups using FTIR and solid-state 13C CPMAS NMR spectroscopy, along with principal component and cluster analyses. The results showed that not all biochar properties changed consistently with increasing pyrolysis temperature during slow pyrolysis. The significant increase in biochar pH with increasing pyrolysis temperature, was only observed between 350 and 500 °C (p < 0.05). Three principal components (PC) explained 88.9% of the variances in biochars. PC1 (ash, Mn, K, Fe, N, P and EC) and PC3 (Ca, Na and Mg) scores were essentially determined by feedstock type with notable influence of low pyrolysis temperatures. PC2 (O, H, C, volatile matter, fixed matter and pH) score was greatly influenced by pyrolysis temperature. Sugarcane derived biochars had high PC1 score but low PC3 score, while peanut shell derived biochars were contributed by both PC1 and PC3. The wood derived biochars had low scores of both PC1 and PC3, but the low temperature end of wood derived biochar thermosequences had significant higher PC2 scores than the high temperature end (p < 0.05). Understanding how biochar feedstock characteristics and pyrolysis temperature regulate biochar evolution will benefit tailored biochar manufacture.

Effects on the optical properties and conductivity of Ag–N co-doped ZnO

Nowadays, the studies of the effects on the optical bandgap, absorption spectrum, and electrical properties of Ag–N co-doped ZnO have been extensively investigated. However, Ag and N atoms in doped systems are randomly doped, and the asymmetric structure of ZnO is yet to be explored. In this paper, the geometric structure, stability, density of states, absorption spectra and conductivity of pure and Ag–N co-doped Zn[Formula: see text]Ag[Formula: see text]O[Formula: see text]N[Formula: see text]([Formula: see text]=0.03125, 0.0417 and 0.0625) in different orientations are calculated by using plane-wave ultrasoft pseudopotential on the basis of density functional theory with GGA[Formula: see text]U method. Results show that the volume, equivalent total energy and formation energy of the doped system increase as the concentration of Ag–N co-doped Zn[Formula: see text]Ag[Formula: see text]O[Formula: see text]N[Formula: see text] increases at the same doping mode. The doped systems also become unstable, and difficulty in doping. At the same concentration of Ag–N co-doped Zn[Formula: see text]Ag[Formula: see text]O[Formula: see text]N[Formula: see text], the systems with Ag–N along the [Formula: see text]-axis orientation is unstable, and doping is difficult. The optical bandgap of Ag–N co-doped systems is narrower than that of the pure ZnO. At the same doping mode, the optical bandgap of the systems with Ag–N perpendicular to the [Formula: see text]-axis orientation becomes narrow as the concentration of Ag–N co-doped Zn[Formula: see text]Ag[Formula: see text]O[Formula: see text]N[Formula: see text] increases. The absorption spectra of the doped systems exhibit a red shift, and this red shift becomes increasingly significant as the concentration of Ag–N co-doped Zn[Formula: see text]Ag[Formula: see text]O[Formula: see text]N[Formula: see text] increases. Under the same condition, the relative hole concentrations of the doped systems increases, the hole effective mass in valence band maximum decreases, the hole mobility decreases, the ionization energy decreases, Bohr radius increases, the conductance increases and the conductivity become better. Our results may be used as a basis for the designing and preparation of new optical and electrical materials for Ag–N co-doped ZnO applied in low temperature end of temperature difference battery.