Low Temperature Side Research Articles

Multiple Recycling of Wood–Plastic Recycled Composite (WPRC): Developing a Method to Evaluate the Degree of Degradation of Used WPRC

Wood–plastic recycled composite (WPRC) are composites obtained by heating and mixing the main raw material, wood flour, with thermoplastic resin, containing at least 40% by mass of recycled material in the raw material. In order to promote the multiple-recycling of WPRC to reduce greenhouse gas emissions and ensure the sustainability of resources, three types of WPRC decking materials with different exposure conditions (outdoor-exposed product, unexposed product and product stored in the factory for a long time) and samples after accelerated weathering tests (WPRC and recycled plastics from raw materials) were evaluated and compared by a TG-DTA in order to develop a method for evaluating the degree of degradation of used WPRC. Exothermic behavior with weight loss was observed in the temperature range of 30–500 °C for the WPRC product in two temperature ranges. In order to focus on the change in the first exotherm by oxidative degradation, where the rapid weight loss begins, this paper will focus on the exothermic behavior that develops in the temperature range of 150–300 °C on the lower temperature side. The results obtained are as follows. (1) Initial oxidation temperature (IOT) measurement from DTA behavior suggested that it is possible to evaluate the degree of degradation of WPRC. (2) On the exposed surface of WPRC exposed outdoors for more than 9 years and 8 months, significant decreases in the IOT were observed up to 1 mm from the surface, and a slight decrease in the IOT was observed between 1 and 2 mm from the surface. On the other hand, for the indoor long-term storage of 11 years and 6 months, there were almost no changes in the IOT with respect to the depth from the surface. Regarding the outdoor long-term-exposed WPRC, significant decreases in the IOT were observed not only on the exposed surface but also on the hollow and ribbed surfaces up to a depth of 1 mm from the surfaces. (3) A similar decrease in the IOT with increasing accelerated degradation time was observed for the WPRC and raw recycled plastic samples after accelerated weathering tests as for outdoor exposure. Furthermore, FTIR-ATR spectra also revealed that accelerated degradation caused oxidative degradation of the plastic. Therefore, it is thought that the decrease in the IOT can be used as an indicator to evaluate the degree of degradation of the plastic raw material in WPRC.

An investigation on thermoluminescence properties and kinetic parameters of Çankırı rock salt

This study investigates the thermoluminescence (TL) dosimetric properties and kinetic parameters of natural salt samples sourced from the Çankırı rock salt cave in Turkey using β irradiation. Obvious effective TL maximum observed at around 85 and 230°C. A preheat condition was determined to apply a thermal cleaning for the lower temperature side of TL spectrum. Dose sensitivity, linearity and reusability characteristics were investigated for effective TL maximum on the high temperature side of the spectrum. TL kinetic parameters were determined via various heating rates (VHR) experiment, and whole TL glow curve was studied via Tm−Tstop experiment and glow curve deconvolution. General order kinetics approach was utilized for glow curve deconvolution analysis. Kinetic parameters were determined for at least eight electron trap levels which has activation energies in the range of 0.8–1.53 eV.

Optimal intermediate temperature of two-stage cascade heat pump with non-azeotropic refrigerants for simultaneous heating and cooling

This paper presents a model for finding the optimal intermediate temperature to achieve the highest coefficient of performance of the standard two-stage cascade heat pump with non-azeotropic refrigerants for simultaneous heating and cooling. The optimal intermediate temperature remains unaffected by the pinch point temperature at the cascade heat exchanger, though this temperature does impact heat pump performance. The optimal intermediate temperature rises with increasing high-side condensing and low-side evaporating temperatures and the value is deviating from the average temperature between the condensing and evaporating temperatures of the high and low-temperature sides of the cascade heat pump, respectively by a correction factor. The factor is found to be dependent on the critical temperature ratio of the working fluids in the low-temperature side and high-temperature side including the condenser temperature of the high-temperature side of the cascade heat pump cycle. A developed model consisting of the average temperature with the correction factor for estimating the optimal intermediate temperatures were examined with a set of non-azeotropic refrigerants with different compositions at different high-side condensing (65–95 °C) and low-side evaporating (5–15 °C) temperatures and pinch point (2–11 °C) temperatures. The results on the optimal intermediate temperatures and the maximum COPs agreed very well with those calculated from the enthalpy method within ±7 % and ±3 % deviations, respectively.

Phase equilibria and crystallographic structure of clathrate hydrate formed with carbon dioxide and cyclohexanone

This paper reports the phase equilibrium and crystallographic data of the hydrate formed in the CO2 + cyclohexanone + water system. We measured the phase equilibrium condition and conducted the powder X-ray diffraction measurements. The formation of the structure II hydrate in the system of CO2 + cyclohexanone + water was observed at the temperature from 270.0 K to 275.6 K, under the pressure from 0.62 MPa to 1.70 MPa.At 270.0 K – 275.6 K and 0.62 MPa – 1.70 MPa, the structure II hydrate formed, and the phase equilibrium condition alleviated in the system of CO2 + cyclohexanone + water, while the hydrate formed at 276.5 K - 280.7 K and 2.02 MPa – 3.33 MPa, displayed structure I and cyclohexanone acted as an inhibitor. Equilibrium conditions were measured using the isochoric method, revealing different p-T slopes at high and low temperatures. The high-temperature slope closely resembled that of structure I CO2 hydrate reported previously. We continuously monitored temperature and pressure during the structural phase transition, resulting in a slope change. To directly determine the hydrate structure, PXRD measurements were conducted on two samples: one from the high-temperature side and the other from the low-temperature side. The sample from the high-temperature side exhibited structure I with a lattice constant of 11.8749 (9) Å at 153 K, while the low-temperature sample displayed structure II with a lattice constant of 17.443(1) Å at 153 K.

Development and characterization of thermosensing color indicator by pH changes using a temperature-responsive polymer

Poly(NIPAM-co-AAC) (P(NI-AC)) was synthesized by changing the polymerization conditions using poly(N-isopropylacrylamide) (NIPAM) as temperature-responsive polymer and acrylic acid (AAC). Thermosensing color indicators, that changes color depending on the external temperature, were fabricated using P(NI-AC), a pH indicator, and agar. The pH of the P(NI-AC) aqueous solution increased above the lower critical solution temperature (LCST, 34°C), and a gradual pH rise and the shrinkage of aggregate diameter continued up to 70 °C under conditions with high AAC polymerization ratio. The LCST of P(NI-AC) aqueous solution with glucose decreased, and the discoloration temperature range of the thermosensing color indicator with glucose shifted to lower temperature side from 37 to 30°C. The LCST of polymer synthesized with NIPAM, AAC, and N,N-dimethylacrylamide (DMA) increased, and the discoloration temperature range of the thermosensing color indicator shifted to higher temperature side from 39 to 50°C. These results indicated that the discoloration temperature range was successfully adjusted by as much as 20 °C.

The Nucleated Poly(L-lactic acid): The Role of a Phenylacetic Hydrazide Derivative

The melt-crystallization, cold-crystallization, melting behaviors, thermal stability, and optical properties of poly(L-lactic acid) (PLLA) nucleated by a phenylacetic hydrazide derivative (DAPH) were investigated. The melt-crystallization confirmed DAPH’s heterogeneous nucleation role in improving PLLA’s poor crystallization capability, concurrently DAPH loading, cooling rate and final melting temperature were three key factors affecting PLLA’s melt-crystallization behaviors. The results from cold-crystallization indicated that the addition of DAPH could accelerate PLLA’s cold-crystallization via cold-crystallization peak’s shift toward the lower temperature side as DAPH loading increased. Through analysis of PLLA/DAPH’s multiple melting behaviors after melt-crystallization, it was found that DAPH loading, the previous melt-crystallization and heating rate determined PLLA/DAPH’s melting processes after melt-crystallization; and PLLA/DAPH’s melting processes after isothermal crystallization depended on the previous crystallization temperature. A drop in thermal decomposition temperature for 5 wt.% mass loss suggested that pure PLLA has better thermal stability compared with PLLA/DAPH. Additionally, the introduction of DAPH could not improve PLLA’s transparency, in contrast, the haze of PLLA was increased greatly owing to the existence of DAPH.

Thermal performance of cavity masonry wall structures in the solar rich areas of Western China

Air cavities can effectively improve the thermal performance of building envelope. A cavity masonry wall (CMW) is a common and suitable envelope in the solar rich areas of Western China for integrating thermal insulation and heat storage. However, suitable structures for CMWs have not been obtained for different indoor and outdoor climates, which hinders the realization of near-zero energy buildings. In the present study, thermal performance was analyzed for different CMW structures to obtain the design method of the CMW structure. A mathematical model of CMWs was established and validated based on experiments. This model was used to analyze the effects of different structures for CMWs, and suitable structures were determined. Climate adaptability characteristics were analyzed for the suitable structures. Finally, the energy performance of buildings with CMWs was analyzed. A climate index for CMW structure design comprising the ratio of cooling relative to heating (RCH) was proposed to divide the outdoor climate, with winter heating when RCH ≤0.17, and winter heating and summer cooling when RCH >0.17. The suitable structures were obtained in different indoor and outdoor climates, where the closed air cavity was preferably placed on the low temperature side of the construction. The suitable structures exhibited better heat transfer attenuation delay characteristics to adapt to indoor and outdoor climates. It had a significant impact on the heating load compared with buildings with masonry walls, and a saving of above 10%. The design method of CMW structure proposed in this study can provide guidance for the application.

P-GaN gate power HEMT heterostructure as a versatile platform for extremely wide-temperature-range (X-WTR) applications

In this work, we manifest that the epitaxial structure for p-GaN gate high-electron-mobility transistor is a versatile platform to develop electronics for operating in an extremely wide temperature range (X-WTR) from 2 to 675 K, with comprehensive X-WTR studies on device operation and circuit behaviors. The key enabler for the high-temperature operation is the wide bandgap that substantially suppresses the thermal excitation of the intrinsic carrier. However, for the low-temperature side, the two-dimensional electron and hole gas (2DEG and 2DHG) channels at the heterojunctions are formed by the temperature-insensitive polarization fields, which free the carriers from freezing out. The monolithically integrated GaN n-FET, p-FET, and the resultant complementary circuits are, therefore, shown to operate in X-WTR.

Minimum entropy generation paths for generalized radiative heat transfer processes with heat leakage

Heat transfer processes (HTPes) with generalized radiative heat transfer law (HTL) [q∝Δ(Tn)] and heat leakage (HL) are optimized. With net amount of heat transferred (NAHT) of working fluid at low-temperature side and given process period, optimal path, that is, optimal temperature configuration of reservoir (TCR), for entropy generation minimization (EGM) of HTP is derived. Universal result for optimal path is provided, and results for four special HTLs, that is, Newtonian, radiative, linear phenomenological, and mixed HTLs, are further provided. Optimal path with EGM is compared with traditional ones of constant heat flux rate (CHFR) and constant reservoir temperature (CRT). Effects of HL and NAHT on optimal results are analyzed. Results show that ratio of heat flux rates between reservoir and working fluid to (n1+1)/2 power of reservoir temperature for EGM of HTPes without HL is a constant, but the optimal relationship between temperatures of working fluid and reservoir with HL is significant different. The differences among TCRs with different heat transfer paths increase with increases of HL and NAHT. The path of CHFR is very close to that of EGM, and the two paths are superior to that of CRT.

Temperature dependent structural properties of Mn1.90M0.10O3 (M = Cr and Fe)

The polycrystalline samples of Mn1.90Cr0.10O3 (MCO) and Mn1.90Fe0.10O3 (MFO) have been investigated for their temperature dependent magnetic and structural properties. The Cr and Fe substitutions have significant effect on the magnetic and structural properties of Mn2O3. Like pristine Mn2O3, the Cr and Fe substituted samples MCO and MFO also exhibit two antiferromagnetic transitions; one at ∼77 K, ∼80 K, respectively and another at ∼40 K. Our room temperature synchrotron x-ray powder diffraction (SXRD) results confirm that both the MCO and MFO samples crystallize in cubic symmetry. The temperature dependent SXRD results demonstrate the cubic to orthorhombic structural transition for the studied samples. The pristine Mn2O3 shows cubic to orthorhombic transition around 310 K, whereas this structural transition shifted towards lower temperature side with these substitutions i.e. around 240 K for MCO and 260 K for MFO. Interestingly, the centrosymmetric Pcab to non-centrosymmetric Pca21 change in symmetry is also resolved at the ferroelectric ordering temperature for MCO.

On paradoxical phenomena during evaporation and condensation between two parallel plates.

Kinetic theory has long predicted that temperature inversion may happen in the vapor-phase for evaporation and condensation between two parallel plates, i.e., the vapor temperature at the condensation interface is higher than that at the evaporation interface. However, past studies have neglected transport in the liquid phases, which usually determine the evaporation and condensation rates. This disconnect has limited the acceptance of the kinetic theory in practical heat transfer models. In this paper, we combine interfacial conditions for mass and heat fluxes with continuum descriptions in the bulk regions of the vapor and the liquid phases to obtain a complete picture for the classical problem of evaporation and condensation between two parallel plates. The criterion for temperature inversion is rederived analytically. We also prove that the temperature jump at each interface is in the same direction as externally applied temperature difference, i.e., liquid surface is at a higher temperature than its adjacent vapor on the evaporating interface and at a lower temperature than its adjacent vapor on the condensing interface. We explain the interfacial temperature jump and temperature inversion using the interfacial cooling and heating processes, and we predict that this process can lead to a vapor phase temperature much lower than the lowest wall temperatures and much higher than the highest wall temperature imposed. When the latent heat of evaporation is small, we found that evaporation can happen at the low temperature side while condensation occurs at the high temperature side, opposing the temperature gradient.

Temperature-gradient investigation of phase transitions in ferroelectrics using cooling and heating stage

A cooling and heating stage has been developed to investigate the properties of materials under temperature gradients. We utilized the ferroelectric material BaTiO3 to show the coexistence of cubic and tetragonal crystal structures within a single crystal at the high-temperature and low-temperature sides, respectively, under the temperature gradient around 403 K. Through the Raman mapping and synchrotron X-ray diffraction mapping, we successfully visualized the coexisting crystal structures along with the boundary. Additionally, using Raman mapping, we also visualized the coexistence state of the higher-temperature-tetragonal and lower-temperature-orthorhombic phases. Our developed stage demonstrated its capability as a means to continuously vary the temperature direction in the composition-temperature phase diagram, providing valuable insights into the phase transitions.

Cationic redistribution induced magnetic properties of Zn2+ substituted MgFe2O4 spinel ferrite

The effect of Zn incorporation on the cationic redistribution and consequent magnetic properties of Mg1-xZnxFe2O4 (0.0 ≤ x ≤ 0.8) spinels are reported. The X-ray photoelectron spectroscopy and X-ray diffraction studies reveal mixed spinel structures with cations occupying both octahedral and tetrahedral sublattices. Raman measurements show increased structural disorder with increasing Zn-content and A1g mode splitting attributed to peaks of Zn2+, Mg2+, and Fe3+ ions. The isothermal magnetization data reveal a maximum of 102 emu/g at x = 0.4, accompanied by a minimum in the coercivity (∼28 Oe) and a downward shift of the transition in temperature for x > 0.4. The temperature-dependent dc-magnetic susceptibility analysis shows a shifting of the transition region from the paramagnetic phase into the ferrimagnetic phase towards the lower temperature side with increasing Zn concentration. These materials synthesized by the low-cost solid-state method might revisit understanding Zn2+-induced cationic exchange in MgFe2O4 and find applications as a potential soft-magnetic material.

Study on heat transfer failure time effect energy of lithium heat pipe

Studying the efficiency of lithium heat pipe above 1000K in case of problems is of considerable value for mastering and controlling its safety. We use COMSOL software to model and calculate a single element above 1000 K, and calculate and analyze its various parameter changes under fault conditions. According to different situations that should be classified and discussed, the cold end fluid temperature and corresponding heat transfer coefficient in the lower temperature area, as well as the temperature situation at the other end, should be separately considered. Based on the calculated results, it is discussed that they all undergo linear and proportional changes with the target parameters, and the fluid situation on the lower temperature side has the smallest impact on these target results. The maximum temperature of the module will reach 1900K, and materials that can withstand 1900K need to be selected during design.

Influence of non-magnetic Cu on structural, magnetic and magnetocaloric properties on NiMnIn bulk Heusler alloys

The structural, magnetic, and magnetocaloric characteristics of bulk Cu-doped Ni47Mn40-sCusIn13 Heusler alloys (s = 0 and 1) were investigated. Temperature-dependent magnetizations for Ni47Mn40-sCusIn13(s = 0 and 1) were performed under a magnetic field (H) 0.05 T. The substitution of Copper (Cu) for Manganese (Mn) reduces the structural as well as magnetic phase transition temperatures. At room temperature (RT), PXRD pattern of Ni47Mn40-sCusIn13 (s = 0 and 1) bulk Heusler alloys shows that both samples have a cubic structure. The copper substitution in the Mn-site shifts the martensitic transformation temperature to the low temperature side as valence electron concentrations (e/a) decrease [MS = 288 K for s = 0 and MS = 251 K for s = 1]. The isothermal magnetization [M(H)] curve in the vicinity of the martensitic transition for s = 1 alloy exhibits the typical metamagnetic behavior that is not present for s = 0 Heusler alloys. The alloys reveal positive magnetic entropy changes (ΔSM) for s = 0 and 1 respectively. A maximal ΔSM of 10 J.kg-1K−1 at a temperature of 248 K has been obtained in the s = 1 compare than ΔSM of 1.27 J.kg-1K−1 (s = 0) alloys for a field change of 0–5 T.

Experimental study of an optical concentrated solar thermoelectric power generator

The commercial thermoelectric modules become more and more efficient in terms of mechanical reliability, cooling capacity (in Peltier mode), power generation (in Seebeck mode), tolerable thermal conditions and so on. In this paper a portable optical concentrated solar thermoelectric generator is proposed, designed, tested, and evaluated based on a single UTX15-288-F2 module in both transient and steady-state conditions. A 30 cm diameter optical concentrator is employed to concentrate the solar power on one side of thermoelectric. Due to the low scale of the generated power, the active cooling methods for the other side of the module is not desirable and economical. That is why the boundary condition of the other low temperature side of thermoelectric is just natural convection by a heatsink under shadow condition. The aim of this case study is to clarify the UTX15-288-F2 module behavior under the mentioned conditions for possible portable micropower applications. Generated power, solar radiation, temperature of both side of the module and ambient conditions are measured during the experiments, reported, discussed, and analyzed.

Tritium and deuterium release behavior of Li2TiO3-0.5Li4SiO4–Pb ceramic

The neutron multiplier lead (Pb) containing Li2TiO3-0.5Li4SiO4–Pb was prepared, which aimed at the improvement of the tritium release performance of the lithium ceramic without an increase in lithium density. Li2TiO3-0.5Li4SiO4–Pb and that without Pb were irradiated at Kyoto University Research Reactor (KUR) with the thermal neutron flux of 5.5 × 1012 n s−1 cm−2 and the fast neutron flux of 1.2 × 1012 n s−1 cm−2. Fast neutrons can trigger the Pb (n, 2n) reaction. The tritium release experiments were conducted using the tritium thermal desorption spectroscopy (tritium-TDS) system. Compared with Li2TiO3-0.5Li4SiO4, the tritium release rate at the lower temperature range was higher than that for Li2TiO3-0.5Li4SiO4–Pb. The tritium-TDS spectrum was also shifted to the lower temperature side. The isothermal heating experimental results confirmed that tritium in the form of gas species (HT) was controlled by the diffusion process, while the trapping and de-trapping process contributed to the total tritium release. Further, 3 keV D2+ implantation with the fluence of 2.0 × 1022 D m−2 and subsequent TDS measurements were performed. It was shown that the D2 release at the lower temperature side was increased for Li2TiO3-0.5Li4SiO4–Pb. Meanwhile, HD and HDO release at higher temperature side was significantly decreased.

Tunable magnetism and large inverse magnetocaloric effect in Shastry-Sutherland compounds Tb2Be2Si1-xGexO7 (0 ≤ x ≤ 1)

The structure, magnetism and magnetocaloric effect (MCE) have been systematically investigated on the series of Tb2Be2Si1-xGexO7 (0 ≤ x ≤ 1) compounds, where the magnetic Tb3+ ions are located on the quasi-two-dimensional Shastry−Sutherland-Lattice (SSL). The X-ray diffraction measurements reveal that all compounds crystallize into the tetragonal structure with space group P4¯21m, the lattice parameters and nearest neighbor Tb-Tb distances increase monotonically with the variation of doping content x. All samples show the antiferromagnetic (AFM) ordered ground state and field (μ0H) induced spin-flop (SP) transitions below Néel temperature (TN). Moreover, the constructed field-temperature (μ0H−T) phase diagrams of Tb2Be2Si1-xGexO7 (0 ≤ x ≤ 1) reveal that the AFM phase shifts to the low temperature and low field sides with increased x. Below TN, we can observe a crossover behavior of MCE from the low-field (Δμ0H<2.58 T) inverse MCE (IMCE) to the CMCE at high fields (Δμ0H>2.58 T). Among these serial compounds, Tb2Be2SiO7 exhibits the maximal IMCE with a value of 8.30 J kg−1 K−1 under Δμ0H= 0.7 T and 2 K, comparable to the MCE (8.6 J kg−1 K−1) of the benchmark material Tb3Ga5O12 at Δμ0H = 2 T. Additionally, it has a slightly better MCE performance than the materials RE3Ga5O12 (RE = Dy, Tb, Gd) under Δμ0H = 2 T. The realization of large IMCE performance for Tb2Be2SiO7 provides an alternative route for magnetic refrigeration at low field and liquid Helium temperatures.

Polymorphism of Cis-Unsaturated Fatty Acid Amide: Oleamide

The polymorphism of oleamide, an amide derivative of oleic acid, the most abundant naturally occurring cis-unsaturated fatty acid, was studied mainly by differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD) using a high-purity sample. The melt-crystallized sample showed two reversible solid-state phase transitions, revealing three crystalline phases, A–C, in order from the low-temperature side. The three solid phases gradually transformed to another solid phase, D, by holding them below 35 °C; D reverted only to C when heated above 45 °C. The B → C reversible transition was accompanied by a large transition enthalpy amounting to about one-third of the heat of fusion of the C phase. A low-purity oleamide showed no polymorphism. The XRD profiles in the long-spacing region suggested that all four phases formed the segregated lamellar structure, in which the methyl and amide groups were separated.

Single Crystallization of Cs4PbBr6 Perovskite from Supersaturated Organic Solutions Optimized Through Solubility Studies.

We demonstrate the fabrication of millimeter-sized single crystals of 0D-Cs4PbBr6 grown in a supersaturated solution consisting of organic solvents without HBr (aq). One of the precursors, CsBr, was dissolved in ethylene glycol (EG) mixed with dimethyl sulfoxide, which is a good solvent for the other precursor, PbBr2. At a solvent ratio of 20 vol % EG, the solubility of cesium bromide decreased and the title compound, Cs4PbBr6, was selectively formed, whereas, with an EG ratio of 80 vol %, 3D-CsPbBr3 was formed. A phase diagram (solubility curve) of Cs4PbBr6 in the mixed solvent containing 20 vol % EG was obtained by visually observing dissolution and crystal precipitation while changing the temperature. Because the solubility was proportional to the temperature, the solubility curve demonstrated an upper critical solution phenomenon. The solubility near the boiling point of the solution (150 °C) was approximately 0.14 M. A single crystal of Cs4PbBr6 was formed by growing a seed crystal in a supersaturated solution on the low-temperature side of the solubility curve. X-ray analysis established the crystal structure; a fluorescence emission at 520 nm with a full width at half maximum of 20 nm confirms the composition of the single crystal to be Cs4PbBr6.