High Temperature Side Research Articles

On the decrease of entropy on cooling polymer melts and an orientationally-disordered crystal

The heat capacity, Cp, measured on heating a glass in adiabatic and scanning calorimetry experiments generally shows an overshoot peak before the liquid state is reached. We argue that when estimates of Sliq, the entropy of a liquid, inadvertently include part of the Cp on the high temperature side of this peak, the decrease of Sliq with T is greater than the true decrease, and the downward curvature of the Sliq - T plot is, as an artefact, greater. This affects the super-linear extrapolation of Sliq to T below the glass to liquid transition temperature, which is basis of the theory for thermodynamic origin of glass formation. The artefact may be avoided by, (i) using the heat capacity of a liquid, Cp,liq, measured during cooling in a scanning calorimetry experiment and (ii) by directly determining the ratio, (Cp,liq /T) = (∂Sliq /∂T)P. As examples, we analyze the Cp,liq data of two polymers measured during cooling of the melt and heating of the glass, the latter on the same time scale as used in adiabatic calorimetry, and compare the results against those obtained from dynamic measurements. We similarly analyze the Cp of an orientationally-disordered crystal. F. Simon (Z. Anorg. Allg. Chem. 203 (1931) 219–227) had provided a sigmoid shape extrapolation of Cp and sublinear extrapolation of Sexc (= Sliq – Scryst) of glycerol down to T = 60 K. We discuss it in terms of (Cp,exc /T) = (∂Sexc /∂T)P. Features of the (Cp,exc /T) against T plot agree with Simon's Sexc against T plot within experimental and analytical errors.

Performance optimization on the irreversible regenerative Ericsson refrigeration cycle using electrocaloric materials as the working medium

A regenerative Ericsson refrigeration cycle using electrocaloric (EC) materials as the working medium is established. In accordance with the thermodynamic properties of EC materials, the mathematical expressions of the coefficient of performance (COP) and cooling rate of the regenerative EC Ericsson refrigeration cycle are derived. The cooling rate is selected as an objective function and optimized with respect to one of the two isothermal process temperatures in the Ericsson refrigeration cycle, Subsequently, the optimal ranges and bounds of the COP and dimensionless cooling rate are determined. Furthermore, the impacts of the heat leakage, finite heat capacities of heat reservoirs at high and low temperature sides, the Curie temperature of EC materials, the electric field intensity difference in the EC Ericsson refrigeration as well as the regenerator efficiency, internal irreversibility resulting from the thermal hysteresis of EC materials, etc. on the optimal performance of the regenerative EC Ericsson refrigeration cycle are revealed. The conclusions obtained are beneficial to the optimal parameter design of EC refrigerators.

Three electrodes analysis of a 3 V-class all-solid-state lithium-ion battery based on garnet-type solid electrolyte Li6.4La3Zr1.4Ta0.6O12

At present, fabrication of all-solid-state lithium-ion batteries using garnet-type electrolytes is still challenging due to issues with interfacial stability and interfacial impedance caused by the high-temperature sintering process. In this work, we employ Li2CO3 as additive to mitigate high-temperature side reactions and prepare an all-solid-state battery LNM|LLZT|LTO using spinel-structured LiNi0.5Mn1.5O4 (LNM) and Li4Ti5O12 (LTO) as electrodes and garnet-type Li6.4La3Zr1.4Ta0.6O12 (LLZT) as the electrolyte. The battery voltage reaches beyond 3 V and can be charged and discharged for 5 cycles at a rate of C/10. The three-electrode setup of the battery allows the separation of positive and negative electrodes in their voltage profiles and impedance responses during cycling. Our results suggest that the high-voltage electrode LNM can work with LLZT in a solid-state-battery configuration and the negative electrode is the performance-limiting component.

Charge-density-wave Amplitude in Quasi-one-dimensional Halogen-bridged Palladium Complex, [Pd(15N-en)2Br](Suc-C5)2·H2O (Suc-C5 = Dipentylsulfosuccinate), Estimated by 15N Solid-state NMR

Abstract Temperature dependency of the 15N CP-MAS NMR spectrum were examined in quasi-one-dimensional bromo-bridged palladium compound [Pd(en)2Br](Suc-C5)2·H2O (Suc-C5 = dipentylsulfosuccinate), which shows mixed-valence (MV) to averaged-valence (AV) phase transition. Single and double peaks were observed at lower and higher temperature sides from the phase transition temperature, reflecting that they are AV and MV states, respectively. Peak-to-peak interval in the spectra steadily decreased upon cooling, showing the charge-density-wave (CDW) amplitude decreased accompanied by approaching the AV state.

Liquid–liquid transition in elemental liquids investigated by sound velocity measurements: trends in the periodic table

Abstract The velocity of sound has been measured as a function of temperature to investigate structural changes in the molten As–Sb alloy. The overall profile of temperature dependence of the sound velocity changes smoothly from Sb to As. The results indicate that a tendency to change structures in the supercooled state develops with increasing As fraction, and confirm the previous conclusion that molten As changes rapidly its structure in the undercooled state and is already in the high-temperature side of an assumed liquid – liquid transition at the melting point. By confirming the structural transition in molten As, it is possible to mark the elements in the periodic table that undergo a crossover liquid –liquid transition around the melting point under the saturating vapor pressure. Observed trends for liquid – liquid transitions are discussed on the basis of the Peierls distortion mechanism.

INVESTIGATION ON STRUCTURAL, MORPHOLOGICAL, THERMAL AND OPTICAL PROPERTIES OF BLEND PPY- PVA THIN FILMS DOPED WITH NANO TiO2 PARTICLES

Poly Vinyl Alcohol (PVA), Poly Pyrrole (PPY), and PPY-PVA blend thin films loaded with varying concentrations of nano TiO2 particles were prepared by using the in-situ chemical oxidative polymerization technique. Prepared films have undergone several characterization techniques i.e., XRD, UV- Spectroscopy, SEM, and DSC to study their structural, morphological, optical, and thermal properties. SEM images revealed that the surface morphology of PPY has been significantly modified upon the addition of PVA and nano TiO2 particles and observed the presence of pores on the surface. XRD spectra disclose that the amorphous nature of PPY whereas semi-crystalline nature of PVA and the amorphous nature of PPY-PVA blend thin film, also revealed that the concentration of dopant imparts the crystallinity to the nanocomposite thin films. The DSC thermographs confirmed that the shifting of melting temperature towards the higher temperature side in PPY-PVA blend thin film compared to pure PPY and PVA and the addition of dopant has changed melting points towards slightly lower temperature side. Direct band gap values of prepared thin films have been calculated by plotting UV graphs, and these were diminished as rising in the concentration of dopant which supports the conductivity level of thin films.

Heat transport by thermoacoustically generated steady flow

Conventional heat exchangers for thermoacoustic engines have limited heat transfer area and may not utilize heat effectively. A self-circulating heat exchanger proposed by Backhaus and Swift is a looped tube that connects a heat source and a high-temperature heat exchanger, a steady flow is generated in the looped tube due to a thermoacoustic spontaneous acoustic oscillation taking place in a thermoacoustic engine and heat is transported from the heat source to the high-temperature heat exchanger by the steady flow. The purpose of this study is to confirm the heat transport by the acoustically generated steady flow. A standing-wave thermoacoustic engine was constructed with a looped tube connected to the high-temperature side heat exchanger. The relationship between the ratio of the lengths of the thermoacoustic engine and the loop tube and the pressure amplitude was measured. The pressure amplitude became zero when the length of the loop tube was about one times the length of the thermoacoustic engine. Furthermore, the streaming flow was confirmed indirectly by measuring the temperature inside the loop tube. The temperature field of the loop tube implied to the generation of the acoustically generated steady flow.

Pyroelectric power generation in PLZST material by temperature dependent phase transformation

Efforts are being made to increase the efficiency of energy consumption by effectively using the dissipated heat as a source of renewable energy. Herein, we focused on a heat source wherein the temperature varies with time and recovers electrical energy from thermal energy by the pyroelectric effect. Further, we evaluated the net power density of the (Pb, La) (Zr, Sn, Ti)O3 material that is produced by its phase transformation as a result of increase in temperature. It was measured by the Sawyer-Tower circuit that was installed a diode and switch. The results showed that when the low or high temperature side of the measurement environment is in the antiferroelectric phase, the net power density decreased or became negative. Additionally, we estimated the range of temperature wherein a high-power density could be attained by examining the changes in it due to phase transformation.

Reverse heat flow with Peltier-induced thermoinductive effect

The concept of “thermal inductance” expands the options of thermal circuits design. However, the inductive component is the only missing components in thermal circuits unlike their electromagnetic counterparts. Herein, we report an electrically controllable reverse heat flow, in which heat flows from a low-temperature side to a high-temperature side locally and temporarily in a single material by imposing thermal inertia and ac current. This effect can be regarded as an equivalent of the “thermoinductive” effect induced by the Peltier effect. We derive the exact solution indicating that this reverse heat flow occurs universally in solid-state systems, and that it is considerably enhanced by thermoelectric properties. A local cooling of 25 mK is demonstrated in (Bi,Sb)2Te3, which is explained by our exact solution. This effect can be directly applicable to the potential fabrication of “thermoinductor” in thermal circuits.

Alternative positions of internal heat exchanger for CO2 booster refrigeration system: Thermodynamic analysis and annual thermal performance evaluation

• Three CO2 booster systems with different locations of IHX are proposed. • Thermodynamics models of booster systems are developed and annual performance is studied. • S1 is the optimal solution system to improve COP, which is enhanced by 0.6% - 6.36%. • By adding IHX, the APF of CO2 booster system can be improved significantly. • IHX can improve annual performance in subtropical and tropical climatic regions. Refrigeration systems running on transcritical CO 2 cycle are considered an alternative to phase-down the use of hydrofluorocarbons (HFCs) in response to the Kigali Amendment. Responding to the need to improve the efficiency of CO 2 booster systems and to identify optimum system designs, thermodynamic models of three booster systems are proposed with the use of an internal heat exchanger (IHX). Findings from this study suggest that placing the IHX with a low-temperature fluid side at the suction line of high pressure stage compressor and high-temperature fluid side at the outlet of gas cooler represents the most optimal approach in improving the coefficient of performance (COP) of the booster system. When operating in the transcritical conditions, the COP values can be improved by 6.35% at the IHX thermal effectiveness of 0.8 and by 6.48% at the ratio of medium temperature load to low temperature load of 6. Using IHX can significantly reduce the compressor discharge pressure, which can be reduced by 0.55 MPa at the ambient temperature of 40 °C. Furthermore, by adding IHX, the annual performance factor of CO 2 system can be improved significantly by 1.68% and the annual total power consumption can be decreased by 6.48% in the tropical climate. It can be concluded that IHX can improve the COP values of a booster system when operating in the subtropical and tropical regions.

Experimental Investigation of the Heat Transfer Characteristics of Plate Heat Exchangers Using LiBr/Water as Working Fluid

In this study, the heat exchange characteristics of water–LiBr solutions used as working fluid in a plate heat exchanger (PHE) were experimentally investigated at various concentrations. To analyze the heat transfer characteristics under LiBr/water conditions, a brazing type plate heat exchanger was installed, and the LiBr concentration on the high-temperature side was controlled at 56%, 58%, 60% and 60%. The results showed that the average heat transfer rate under water/water conditions was higher than that under LiBr/water conditions and the average heat transfer rate decreased as the LiBr concentration on the hot side increased. In addition, under both water/water and LiBr/water conditions, the average heat transfer rate and overall heat transfer coefficient increased as the mass flow rate of the working fluid on the hot side increased. When LiBr was used, the Reynolds number (Re) of LiBr on the hot side was more than nine times lower than that of water at the same mass flow rate owing to the influence of the increased viscosity. Based on the data obtained from the water/water and LiBr/water experiments, a correlation for predicting the Nusselt number (Nu) on the hot side in a wide range was developed.

Mechanical behaviors of tunnel lining in uneven temperature field of high geothermal surrounding rock

Because of large temperature difference between inside and outside of tunnel lining in high ground temperature environment, thermal stress is easy to occur in the structure, which affects the stability of tunnel lining. In this paper, a three-dimensional thermo-mechanical coupled numerical model of rock stratum-tunnel is established based on a tunnel project with high geo-temperature, and the stress of tunnel lining under high geo-temperature environment is calculated and analyzed, the influence of temperature distribution on lining stress is analyzed. The results show that the principal stress and surrounding rock pressure increase with the increase of temperature at the initial stage of lining. When the temperature field is not uniform, the stress concentration is easier at the corner of the initial support of the high temperature side. When the temperature difference between the left and right sides of the lining is constant, the surrounding rock pressure ratio between the high temperature side and the low temperature side is basically the same. However, the pressure difference of surrounding rock increases with the increase of the initial temperature value. Therefore, the unfavorable temperature field distribution of surrounding rock should be carefully handled in tunnel design and construction. The research results of this paper will provide some reference value for the design and construction of similar tunnel with temperature and heat damage in highland.

Structural and Electrical Behavior of (0.70)BiFe1−xCoxO3–(0.30)PbTiO3 Solid Solutions Prepared by Simple Sol-Gel Route

Several compositions of the (0.70)BiFe1−xCoxO3 – (0.30)PbTiO3 system for x = 0.00, 0.03, 0.06, 0.09, 0.12 dubbed (0.70)BFCO − (0.30)PT were prepared by sol-gel route. Raman analysis confirmed the coexistence of two phases (rhombohedral and tetragonal) up to x = 0.06 and almost a single tetragonal phase for 0.09 and 0.12 revealed by X-ray diffraction analysis. The effect of Co substitution in BFO-PT in the electrical properties has been discussed. The dielectric permittivity and dielectric loss were improved by the Co substitution in the BFO-PT ceramic. A broad hump was observed for x = 0.0 around the Nèel temperature, disappearing for higher x compositions and it is followed by a low-temperature hump for x = 0.09 and 0.12. A systematic and detailed study on the ac conductivity determines the nature of the conduction mechanisms based on the activation energy values in different temperature regions. These results show that an Arrhenius type of thermally activated process occurs in the low-temperature regime, a small polaron hopping in the intermediate regime and an oxygen vacancy-based mechanism takes place in the high-temperature side. Fourier transform infrared spectra show a strong band corresponding to the Fe–O stretching and O–Fe–O bending vibrations.

High-pressure magnetic properties of antiferromagnetic samarium up to 30 GPa using a SQUID-based vibrating coil magnetometer

Samarium (Sm) has antiferromagnetic (AFM) ordering at the hexagonal site at ${T}_{\mathrm{N}}(\text{hex})=106$ K, and at the cubic site at ${T}_{\mathrm{N}}(\text{cub})=14$ K at ambient pressure. The structural transition from the so-called Sm-type structure to the double hexagonal close-packed (dhcp) structure occurs at approximately 6 GPa. According to electrical resistance measurements, the shift of ${T}_{\mathrm{N}}$(hex) toward the low-temperature side occurs simultaneously with the shifting of ${T}_{\mathrm{N}}$(cub) toward the high-temperature side with increasing pressure. We conducted dc magnetic measurements on Sm at high pressure up to 30 GPa using a SQUID-based vibrating-coil-magnetometer to pursue ${T}_{\mathrm{N}}$(cub) at high pressure: The magnetic measurements revealed stepwise anomalies below 2 GPa. A ferromagnetic (FM) anomaly was observed in the dhcp structure, suggesting that spins at both structural sites formed the FM magnetization. In the face-centered cubic (fcc) structure at above 12 GPa, a reduction in the magnetic signal occurred. In the distorted fcc structure at above 20 GPa, sufficient suppression of the FM moment was observed and afterward the diamagnetic signal suggesting the possibility of superconductivity was observed.

Effects of grain refinement on the microstructures and damping behaviors of a Cu–Al–Ni–Mn–Ti shape memory alloy

Grains of a Cu–Al–Ni–Mn–Ti shape memory alloy (SMA) were remarkably refined by the Al–La–B inoculant. Evolution of microstructures and changes of both martensitic transformation (MT) temperatures and damping property of the Cu–Al–Ni–Mn–Ti SMA were also systematically investigated. It was found that with increasing the adding amount of inoculant, the grain size decreased first and then increased, whereas the damping increased first and then decreased. When the adding amount of inoculant reached 2.5 wt%, the smallest grains and the highest damping could be obtained. The improvement of damping could be attributed to the increased density of interfaces between matensite lamellae and between twins. Moreover, with increasing the adding amount of inoculant, all characteristic temperatures of both reverse and forward MT shift to high temperature side. This could be ascribed to the decreased Al content in the Cu–Al–Ni–Mn–Ti SMA due to the formation of Al11La3 phase. In addition, this is also related to the changes of the density of grain boundaries and the order degree of the Cu–Al–Ni–Mn–Ti SMA.

Electrolyte Design for Lithium Metal Anode-Based Batteries Toward Extreme Temperature Application.

Lithium anode‐based batteries (LBs) are highly demanded in society owing to the high theoretical capacity and low reduction potential of metallic lithium. They are expected to see increasing deployment in performance critical areas including electric vehicles, grid storage, space, and sea vehicle operations. Unfortunately, competitive performance cannot be achieved when LBs operating under extreme temperature conditions where the lithium‐ion chemistry fail to perform optimally. In this review, a brief overview of the challenges in developing LBs for low temperature (<0 °C) and high temperature (>60 °C) operation are provided followed by electrolyte design strategies involving Li salt modification, solvation structure optimization, additive introduction, and solid‐state electrolyte utilization for LBs are introduced. Specifically, the prospects of using lithium metal batteries (LMBs), lithium sulfur (Li‐S) batteries, and lithium oxygen (Li‐O2) batteries for performance under low and high temperature applications are evaluated. These three chemistries are presented as prototypical examples of how the conventional low temperature charge transfer resistances and high temperature side reactions can be overcome. This review also points out the research direction of extreme temperature electrolyte design toward practical applications.

Thermal and kinetic analyzing of pyrolysis and combustion of self-heating biomass particles

As a renewable fuel, the application of biomass fuel gets more and more attention. Fire and explosion are the main safety problems in the biomass fuel storage process. The characteristic parameters and kinetic analysis of pyrolysis and combustion are significant to guide the safe storage of biomass fuel. In this work, the thermogravimetric analysis (TGA) was used to obtain the pyrolysis and combustion characteristics of corn straw powder, poplar wood chip and rice husk in nitrogen and air, respectively. The Thermogravimetry-Differential Thermogravimetric (TG-DTG) profile shows that the pyrolysis process of these biomass includes three stages of drying, pyrolysis and carbonization, while the combustion process includes three stages of drying, devolatilization and coke combustion. The main reaction stage of biomass pyrolysis and combustion are roughly between 170∼400 °C and 180∼530 °C, respectively. With the increase of the heating rate, TG and DTG profiles shifts to the high temperature side. Furthermore, the kinetic analysis was performed by using Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO), Friedman, and Coats-Redfern (CR) methods, based on the thermogravimetric experimental data. The activation energy of biomass pyrolysis is shown to be between 70∼100 kJ/mol. For the activation energy of biomass combustion, the calculated value from isoconversional methods is between 140∼180 kJ/mol. The calculated value from CR method is between 80∼150 kJ/mol, and the activation energy of the coke combustion stage is greater than that of the devolatilization stage. Finally, the auto-ignition experiment of biomass particles was designed and conducted, indicating that the corn straw powder is more prone to spontaneous combustion, followed by rice husk and poplar wood chip, which corresponds to the results of activation energy. And the fire hazard of the biomass particles was analyzed according to the characteristic parameters. This work provides fundamental data to promote the development of storage techniques and facilitate the safe production of biomass particles.

Synthesis and dielectric relaxation behavior of 55B2O3–15SiO2– 30Na2O: WO3 glass system

55 B2O3 – 15 SiO2 – 30 Na2O: x WO3, (x ranging from 0 to 5 wt%) glass composites were prepared according to the melt-quenching procedure. The prepared samples were characterized via X-ray diffraction and broad band dielectric spectroscopy (viz., dielectric constant (ε1), tanδ and AC conductivity (σAC) over a wide range of frequency and temperature). No sharp peaks were shown in the XRD pattern and is evidence of the amorphous nature of the samples. It turns out that the values of ε1 and ε2 are increasing at higher temperatures particularly at lower frequencies. The energy barrier height, WM values decreased as 0.27, 0.25 and 0.22 while showed value of 0.29 eV for 5.0 wt% WO3. In the dielectric modulus plots, two relaxation processes are found especially on the higher temperature side. It also shifted a higher frequency with increasing temperature. The values of exponent s have been found to lie between 0.48 and 0.74, which confirms that the conduction mechanism in the glass samples follows the correlated barrier hopping model. By calculating the activation energy associated with the relaxation processes and DC conductivity, it was found that the values are close, which indicates that the same charges contribute to the two processes.

An experimental and modeling study of autoignition characteristics of two real low-octane gasoline fuels in a heated rapid compression machine at elevated pressures

Gasoline compression ignition (GCI) has received much attention due to its high efficiency and low emissions. The low-octane gasoline can be applied to extend the GCI operating range. However, there is limited knowledge of the autoignition chemistry for the low-octane gasoline. In this study, the ignition delay times (IDTs) of two real distillate gasoline fuels with research octane numbers (RON) of 72 and 83, denoted as G72 and G83 respectively, were measured in a heated rapid compression machine (RCM) over wide ranges of pressures (10, 15 and 20 bar), temperatures (670–940 K), equivalence ratios (0.5, 1.0 and 2.0), and diluted conditions. Both G72 and G83 exhibit apparent two-stage ignition characteristics with negative temperature coefficient (NTC) behavior in the low-to-intermediate temperature region. Considering the effects of exhaust gas recirculation (EGR) technology on GCI combustion, ignition characteristics of low-octane gasolines under simulated-EGR conditions were also studied by varying the N2/O2 ratio while fixing the fuel mole fraction. It is found that the NTC region moves towards the higher temperature side as the oxygen concentration decreases. Moreover, two six-component surrogates were formulated for G72 (28.4% n-pentane, 3.5% n-heptane, 24.5% 2-methylhexane, 26.3% 2,2,4-trimethylpentane, 13.8% cyclopentane, and 3.3% toluene, by mol.), and G83 (16.5% n-pentane, 10.6% n-heptane, 5.6% 2-methylhexane, 37.4% 2,2,4-trimethylpentane, 10.2% cyclopentane and 19.7% toluene, by mol.). Kinetic modeling was then conducted using a published kinetic model coupled with proposed surrogates. Sensitivity analysis results further revealed that compared with isooctane, cycloalkane chemistry is more important in the overall autoignition behavior at low temperatures.

Understanding of intriguing metal to semiconductor transition in Ni0.5Zn0.5Fe2O4 nanoparticulates

Temperature-dependent electrical transport characteristics of un-milled and high-energy ball-milled samples (3 h (70 nm), 6 h (55 nm) and 9 h (45 mm)) of Ni0.5Zn0.5Fe2O4 spinel ferrite were explored. A well-defined metal to semiconductor transition exhibited by all the samples has been construed in view of direct and superexchange cationic interactions and delocalization to localization of charge carriers on increasing temperature. The peak temperature (Tmax) was found to shift towards a higher temperature side on milling principally governs by the lattice vibration scattering and intrinsic excitation. The crystallite size reduction, enhancement in strain and sudden decrease in the formation and octahedral site occupancy of Fe 2+ ions on milling found responsible for the prodigious rise (~ 250 times) in normalized resistivity values for the sample comminuted for 9 h. The spectrum of energies corresponds to charge trapping centers that cause small bump (3 h milled sample) and sharp cusp (9 h milled sample) for T>Tmax. These materials may be found suitable for thermal cutoff switching applications.