Type Of Phase Change Research Articles

Effects of Near-Critical Condensation and Cavitation on the Performance of S-CO2 Compressor

The supercritical carbon dioxide (S-CO2) Brayton cycle efficiency increases as the compressor inlet condition approaches the critical point. However, the thermodynamic properties of CO2 vary dramatically near the critical point, and phase change is most likely to happen. Both cavitation and condensation bring about significant adverse effects on the performance of compressors. In this paper, the quantitative effects of nonequilibrium condensation and cavitation on the performance of an S-CO2 centrifugal compressor with different inlet-relative entropy values are investigated. The properties of CO2 were provided by the real-gas property table, and the nonequilibrium phase-change model was adopted. The numerical simulation method with the nonequilibrium phase-change model was validated in the Lettieri nozzle and Sandia compressor. Furthermore, simulations were carried out in a two-stage centrifugal compressor under conditions of various inlet-relative entropy values. The type of nonequilibrium phase change can be distinguished by inlet-relative entropy. Cavitation makes the choke mass flow rate decrease due to the drop in the speed of sound. Condensation mainly occurs on the leading edge of the main blade at a large mass flow rate, but cavitation occurs on the splitter. The condensation is more evenly distributed on the main blade, but the cavitation is mainly centered on the leading edge.

Amplitude and phase changes in TESS photometry of five short period weak-lined T Tauri stars

ABSTRACT The statistical technique ‘Complex Demodulation’ (CDM) is used to track the amplitude and phase changes of periodicities in five naked T Tauri stars. The periodicities are most likely caused by dark spots on the stellar surfaces, which are rotated into and out of view. Two of the stars (CD-56 1438, CD-72 248) show two independent periodicities, probably due to being binary weak-lined T Tauri stars. Two different low-pass filters, operating, respectively, in the frequency and time domains, are used as part of the CDM methodology. Statistical aspects of the estimated amplitudes and phases are investigated in some detail: in particular, expressions are derived for standard errors and for possible biases. A large variety of different types of amplitude and phase changes are found, including approximately linear or quadratic, abrupt level shifts, pulses, and oscillatory. Long term changes in amplitudes are aperiodic, but mimic long-term cycles.

Study on design, preparation, and performance of low‐temperature rising concrete with energy storage aggregate

AbstractAlleviating cracks induced by the temperature rise in mass concrete has always been a research hotspot and engineering problem. In this study, a type of energy storage phase change low‐temperature rising concrete was designed and prepared to reduce the cracking risk of mass concrete. First, a type of energy storage coarse aggregate (ESA) was prepared using a semi‐dry method with cement and fly ash as matrix materials, mixed with carbon black (CB), carbon fiber (CF), and phase change material (PCM). Furthermore, the influence of these materials on the mechanical properties, microstructure, and pore structure of the ESA was studied. Subsequently, ESA was used to prepare phase change low‐temperature rising concrete, and its mechanical properties, thermal conductivity (TC), and internal temperature rise were investigated. The research results show that, except for the compressive strength of PCM‐15‐ESA, which is only 7% lower than that of the control, PC‐P0, other samples have no mechanical property deterioration. The double‐layer protection measures can effectively avoid the mechanical property deterioration of concrete induced by PCM leakage. The maximum internal temperature rise of concrete is reduced by 9.8°C, which greatly reduces the risk of cracking of concrete.

Effects of different binder systems on the reaction mechanism, microstructure and mechanical properties of PcBN composites

In this paper, PcBN composites were prepared with cBN, Al and Ti micropowders under high temperature and ultra-high pressure. The phase and microstructure of PcBN were analyzed, and the possible reactions in different systems were deduced. The synthesis process of PcBN under high pressure (5.5 GPa) and different temperature (950–1550 °C), and the influence of sintering temperature on the hardness and flexural strength of PcBN were studied. The results show that cBN in cBN-Al and cBN-Ti systems has reacted with Al and Ti respectively at 950 °C. In the cBN-Al-Ti system, cBN does not react with Al and Ti alone, but Al and Ti react to form a series of intermetallic compounds. With the increase of temperature, the type and mass of phase change constantly, and tend to be stable at 1350 °C. The binder has an obvious chemical reaction at the edge of the cBN particle, and the new phase is generated to firmly bond the internal particles together. The mechanical properties of PcBN sintered by cBN-Al-Ti system are the best.

Smart coating in protective clothing for firefighters: An overview and recent improvements

Recently, new developments in the design and performance optimization of smart mechanisms associated with natural and man-made hazards have progressed considerably. This is mainly owing to advances in smart sensing mechanisms including communication and data technologies. This work provides a detailed overview of existing improvements on smart hazard monitoring equipment and materials applied in textile sensing systems. Given that fire is one of the most common disasters in many countries such as Australia, and every year many firefighters are affected by these unfortunate incidents, the focus of this study is on firefighters' protective clothing Fire Fighter Protective clothing. This review provides a unique opportunity to study smart sensing systems in coating technologies, potentially provides more effective techniques for training and better safety protocols of fire fighters. It aims to revisit the existing advances and address recent challenges and opportunities for improvement in the domain of smart coating and fire protective wearables. The goal of this review is to provide information about smart coating in protective clothing for firefighters. The capability of some of these clothing in managing thermal stresses, responding to humid environment, monitoring some critical parameters and adapting to the size of the wearers (clothes fabricated with phase change and shape memory substances) made them attractive choice in adjusting specific design features of industrial textiles. Various types of phase change and shape memory substances are defined and a combination of these substances within the structure of fabrics are presented. This paper also provides a detailed review on the heat exposure and capability of the shape memory substances (SMM) and phase change materials (PCM) to delay the heat transfer through fire fighter protective clothing. Referring to the former research, several issues have been detected using such substances. For instance, combination of phase change and shape memory materials needs fundamental improvements with regards to assessment techniques and testing criteria. Additionally, recent improvements in the domain of PCM and SMM including modifying mechanical features, functionality, and durability under different conditions have been informed. It has been suggested that the major problem in developing fabric-Phase Change Materials (PCMs) and Shape memory material (SMM) systems is their usage methods. At last recent developments on wearable monitoring systems applied in the firefighters’ protective gear. Wearable sensors are usually used directly on the body or located on wearable items to monitor information related to firefighters’ safety.

Ethanol Phase Change Actuator Based on Thermally Conductive Material for Fast Cycle Actuation.

Artificial muscle actuator has been devoted to replicate the function of biological muscles, playing an important part of an emerging field at inter-section of bionic, mechanical, and material disciplines. Most of these artificial muscles possess their own unique functionality and irreplaceability, but also have some disadvantages and shortcomings. Among those, phase change type artificial muscles gain particular attentions, owing to the merits of easy processing, convenient controlling, non-toxic and fast-response. Herein, we prepared a silicon/ethanol/(graphene oxide/gold nanoparticles) composite elastic actuator for soft actuation. The functional properties are discussed in terms of microstructure, mechanical properties, thermal imaging and mechanical actuation characteristics, respectively. The added graphene oxide and Au nanoparticles can effectively accelerate the heating rate of material and improve its mechanical properties, thus increasing the vaporization rate of ethanol, which helps to accelerate the deformation rate and enhance the actuation capability. As part of the study, we also tested the performance of composite elastomers containing different concentrations of graphene oxide to identify GO-15 (15 mg of graphene oxide per 7.2 mL of material) flexible actuators as the best composition with a driving force up to 1.68 N.

The effect of expanded graphite on the performance of paraffin phase change materials used in thermal energy storage

Paraffin is the most commonly used phase change type of material for thermal energy storage but the main drawback is it has very low thermal conductivity. This study aims to enhance the thermal conductivity of the base PCM through the use of expanded graphite as supporting material. The expanded graphite at different percentage 3wt%, 6wt%, 9wt%, 12wt%, 15wt% is mixed with paraffin and five samples are prepared. Experimental results obtained on the samples clearly show that the thermal properties of samples are improved when compare to that of pure paraffin. It is found that both thermal conductivity and thermal diffusivity are increasing rapidly. Melting temperature is standard there is no change for all the compositions. Specific heat gradually started increasing during the initial time and then it started decreasing as the expanded graphite percentage increased. The latent heat value of this composition has decreased a lot when compared to pure paraffin.

A prospective observational study testing liquid crystal phase change type thermometer placed on skin against oesophageal/pharyngeal placed thermometers in participants undergoing general anesthesia

sBackgroundPatient outcomes are influenced by intraoperative temperature management. Oesophageal/pharyngeal temperature monitoring is the standard of care at our institute but is not well tolerated in awake patients. Many non-invasive temperature monitors have been studied. Only the TraxIt® Wearable Children’s Underarm Thermometer which contains liquid crystals that undergo phase changes according to temperature is available at our institution. We tested these non-invasive monitors against our standard of care which is the oesophageal/pharyngeal temperature monitor.MethodsWe conducted a prospective observational study of 100 patients receiving general anaesthesia for elective surgery. Patients were eligible for inclusion if they were ≥ 18 years old, were planned to have a general anaesthetic > 60 min during which no body cavity (chest or abdomen) would be opened. Patient temperature was measured with an oesophageal/pharyngeal thermistor probe and skin surface temperature monitors placed over the forehead, in the axilla, over the sternum, and behind the ear (over major vessels to the brain). Temperatures were recorded and then analysed using Altman-Bland plots. Pre-determined clinically relevant limits of agreement were set at −/+ 0.5 °C.ResultsFrom the 100 patients we collected 500 data points for each monitor with an average monitoring time of 102 min (30–300 min) across a range of surgical procedures. None of the skin surface temperature monitors achieved the pre-determined limits of agreement and results were impacted by the use of a forced air warmer.ConclusionThe TraxIt® Wearable Children’s Underarm Thermometers are not suitable for temperature monitoring during general anaesthesia.

Review of magnetic refrigeration system as alternative to conventional refrigeration system

The refrigeration system is one of the most important systems in industry. Developers are constantly seeking for how to avoid the damage to the environment. Magnetic refrigeration is an emerging, environment-friendly technology based on a magnetic solid that acts as a refrigerant by magneto-caloric effect (MCE). In the case of ferromagnetic materials, MCE warms as the magnetic moments of the atom are aligned by the application of a magnetic field. There are two types of magnetic phase changes that may occur at the Curie point: first order magnetic transition (FOMT) and second order magnetic transition (SOMT). The reference cycle for magnetic refrigeration is AMR (Active Magnetic Regenerative cycle), where the magnetic material matrix works both as a refrigerating medium and as a heat regenerating medium, while the fluid flowing in the porous matrix works as a heat transfer medium. Regeneration can be accomplished by blowing a heat transfer fluid in a reciprocating fashion through the regenerator made of magnetocaloric material that is alternately magnetized and demagnetized. Many magnetic refrigeration prototypes with different designs and software models have been built in different parts of the world. In this paper, the authors try to shed light on the magnetic refrigeration and show its effectiveness compared with conventional refrigeration methods.

Multi‐decadal evolution characteristics of global surface temperature anomaly data shown by observation and CMIP5 models

ABSTRACTBased on methods of statistical analysis, the time series of global surface air temperature (SAT) anomalies from 1860 to 2014 has been defined by three types of phase changes that occur through the division of temperature changes into different stages. The characteristics of the three types of phase changes simulated by Coupled Model Inter‐Comparison Project (CMIP5) models were evaluated. The conclusion is as follows: the SAT from 1860 to 2014 can be divided into six stages according to trend differences, and this subdivision is proved to be statistically significant. Based on trend analysis and the distribution of slopes between any two points (two points' slope) in every stage, the six stages can be summarized as three phase changes of warming, cooling, and hiatus. Between 1860 and 2014, the world experienced three heating phases (1860–1878, 1909–1942, and 1975–2004), one cooling phase (1878–1909), and two hiatus phases (1942–1975 and 2004–2014). Using the definition method, whether the next year belongs to the previous phase can be estimated. Furthermore, the temperature in 2015 was used as an example to validate the feasibility of this method. The simulations of the heating period by CMIP5 models are well; however, the characteristics shown by SAT during the cooling and hiatus period cannot be represented by CMIP5 models. As such, the projections of future heating phases using the CMIP5 models are credible, but for cooling and hiatus events they are unreliable.

Magnetic refrigeration: an eco-friendly technology for the refrigeration at room temperature

Magnetic refrigeration is an emerging, environment-friendly technology based on a magnetic solid that acts as a refrigerant by magneto-caloric effect (MCE). In the case of ferromagnetic materials MCE is a warming as the magnetic moments of the atom are aligned by the application of a magnetic field, and the corresponding cooling upon removal of the magnetic field. There are two types of magnetic phase changes that may occur at the Curie point: first order magnetic transition (FOMT) and second order magnetic transition (SOMT). The reference cycle for magnetic refrigeration is AMR (Active Magnetic Regenerative cycle) where the magnetic material matrix works both as a refrigerating medium and as a heat regenerating medium, while the fluid flowing in the porous matrix works as a heat transfer medium. Regeneration can be accomplished by blowing a heat transfer fluid in a reciprocating fashion through the regenerator made of magnetocaloric material that is alternately magnetized and demagnetized. In this paper, attention is directed towards the near room-temperature range. We compare the energetic performance of a commercial R134a refrigeration plant to that of a magnetic refrigerator working with an AMR cycle. Attention is devoted to the evaluation of the environmental impact in terms of a greenhouse effect. The comparison is performed in term of TEWI index (Total Equivalent Warming Impact) that takes into account both direct and indirect contributions to global warming. In this paper the AMR cycle works with different magnetic refrigerants: pure gadolinium, second order phase magnetic transition (Pr0.45Sr0.35MnO3) and first order phase magnetic transition alloys (Gd5Si2Ge2, LaFe11.384Mn0.356Si1.26H1.52, LaFe1105Co0.94Si110 and MnFeP0.45As0.55). The comparison, carried out by means of a mathematical model, clearly shows that GdSi2Ge2 and LaFe11.384Mn0.356Si1.26H1.52 has a TEWI index always lower than that of a vapor compression plant. Furthermore, the TEWI of the AMR cycle working with FOMT materials is always better than that of SOMT materials. Gd5Si2Ge2 is the best FOMT material.

기-액 상변화 열전달식 고온 히터 플레이트의 작동 특성과 성능에 관한 연구

The experimental study for the temperature uniformity on the wafer using liquid-vapor phase heat transfer mechanism is performed. For the experiment, the heater plate which is consist of stainless steel container, working fluid and electrical heater is designed, manufactured and tested at the range of 600 to <TEX>$850^{\circ}C$</TEX>. The results showed that the phase change type heater plate was much more uniform and stable temperature on the heater plate surface and wafer than the uniform heat flux type heater plate at the atmospheric condition. Also, the results of 300 mm outer diameter of heater plate showed that the same temperature uniformity compared with 230 mm.

イオン液体界面研究の進歩と展開

It is quite important to analyze and design interface between ionic liquid and other materials due to further development of functional interface. In the present study, physicochemical properties of mixtures containing ionic liquids are discussed. In the former part, interests are focused on the dynamic phase change of ionic liquid/water mixtures. Some ionic liquids show lower critical solution temperature type phase change after mixing with water. Component ions required for the realization of this type of phase change are proposed related to the water content. In the latter part, dimension control of ionic liquids is summarized considering the marriage of liquid crystals and ionic liquids. Through these results, importance of interface concerning ionic liquids has been mentioned.

Safety evaluation of superheated perfluorocarbon nanodroplets for novel phase change type neurological therapeutic agents

Sonothrombolysis using diagnostic ultrasound (US) in combination with microbubble (MB) contrast agents is an attractive trial. Superheated perfluorocarbon nanodroplet (SPN), which can turn into MBs upon US trigger, may have advantages in sonothrombolysis. As a preliminary investigation of SPN-assisted sonothrombolysis, we performed a safety evaluation in vivo . Twenty male rabbits (2.59 ± 0.14 kg) were assigned to three groups: the Control group ( n = 6), 2.2 mL/kg of physiological saline intravascular (i.v.) injection into auricular vein; the PL group ( n = 8), 25 mg/kg of phospholipid-coated SPN i.v.; and the AA group ( n = 6), 25 mg/kg of SPN coated with poly aspartic acid derivative i.v. Rectal temperatures were maintained at 39.08 ± 0.98 °C. Neurological evaluation and biochemical blood examinations were performed at pre-injection, 1, 4, and 7 days after injection. Organ samples including heart, lungs, liver, spleen and kidneys were harvested after euthanasia. Within an hour after administration of SPNs, both the PL and AA groups showed a reversible change in respiration. One animal in the AA showed transient nystagmus about 20 min after administration; however, there was no pathological damage. One animal in the PL died 2 days after. No histological damage was found in any organ sample from any of the animals. Moreover, no significant differences were found in the biochemical blood examination between the PL, AA, and Control groups. No neurological damage or histological change was found with two SPNs. We will further investigate the SPN-assisted sonothrombolysis based on the 500-kHz US exposure with bubble liposome acceleration of rt-PA efficacy.

Polymorphism, polar morphology and absolute structure determination of 4-iodo-4′-nitrobiphenyl (INBP)

4-Iodo-4′-nitrobiphenyl (INBP), a typical nonlinear optical molecule, features three polymorphs: Fdd2 as known before and two new forms, P2/c and P2. Monopolar crystals of the Fdd2 structure express a polar morphology and allowed an absolute structure determination. Iodo substituents cover the (001) and related faces. A negative pyroelectric coefficient was observed. The P2/c form was obtained from sublimation. Heating INBP (Fdd2) in the range of 150 to 180 °C ended in a second polar form (P2). DSC and dielectric measurements allowed us to assume a diffuse type of phase change from Fdd2 into P2. Lattice energy calculations for Fdd2 and P2/c yielded very similar energies. The twinning state observed for crystals not expressing polar symmetry is explained as a 50 : 50 % intergrowth of Fdd2 and P2/c. Periodic fragments allowed the close packing mode of all three polymorphs to be understood. A Hirshfeld surface analysis makes evident that apart from a strong linear synthon (I⋯NO2) other interactions in all three forms are very similar.

Quadruple-Layer Write-Once Disk for Blue Laser Based on Te–O–Pd Recording Films

The excellent performance of a 100-GB-capacity write-once disk was demonstrated. The disk has quadruple recording layers, i.e., Layer 3, 2, 1, and 0 (from the laser-incident side of the disk) based on the 4× Blu-ray disc (BD) format. Each layer is provided with a phase-change type memory film of Te–O–Pd, whose thickness was 20 nm for Layer 0, and only 6 nm for Layers 1, 2, and 3 in order to obtain high transmissivity. Additionally, for Layers 2 and 3, a metallic reflection layer was not needed and an AlN film with high thermal conductivity was formed next to each recording film. The AlN film suppressed the heat-induced damage of thin recording films. Consequently, the high transmissivities of 64% (Layer 1), 75% (Layer 2), and 81% (Layer 3) were achieved so that a quadruple layer disk with high quality was realized. The experimental disk showed tolerance to a wide range of writing speeds from 1× (36 Mbps) to 4× (144 Mbps). Good jitter values for each layer within an available maximum laser power of 27 mW on the disk were demonstrated. The acceleration test for lifetime using the Arrhenius plots showed that this write-once disk has an estimated lifetime of more than 100 years at 30 °C and 85% relative humidity (RH).

Neutral model analysis of landscape patterns from mathematical morphology

Mathematical morphology encompasses methods for characterizing land-cover patterns in ecological research and biodiversity assessments. This paper reports a neutral model analysis of patterns in the absence of a structuring ecological process, to help set standards for comparing and interpreting patterns identified by mathematical morphology on real land-cover maps. We considered six structural classes (core, perforated, edge, connector, branch, and patch) on randomly generated binary (forest, non-forest) maps in which the percent occupancy (P) of forest varied from 1% to 99%. The maps were dominated by the patch class for low P, by the branch and connector classes for intermediate P, and by the edge, perforated, and core classes for high P. Two types of pattern phase changes were signaled by abrupt transitions among the six structural classes, at critical P thresholds that were indicated by increased variance among maps for the same P. A phase change from maps dominated by the patch class to maps dominated by the branch and connector classes was related to the existence of a percolating cluster of forest, and the P threshold varied depending on the co-existence of the core class. A second phase change from the edge class to the perforated class was related to the existence of a percolating cluster of non-core (including non-forest) and represents a change of context from exterior to interior. Our results appear to be the first demonstration of multiple phase changes controlling different aspects of landscape pattern on random neutral maps. Potential applications of the results are illustrated by an analysis of ten real forest maps.

Phase Change Mechanisms in Pulsed Laser-Matter Interaction

ABSTRACTLaser micro-machining is finding many applications in materials processing and manufacturing. Various laser techniques are being used to fabricate micro-electronics, optics, and medical components. This paper will mainly deal with the fundamental issues involved in laser-matter interaction. Our studies are focused on laser induced thermal and thermomechanical phenomena and phase change mechanisms that determine the materials removal process during laser micro-machining. It is shown that during nanosecond laser machining, explosive phase change could occur, during which the liquid is superheated to close to the thermodynamic critical point, followed by an explosive, homogeneous phase transformation. On the other hand, it is observed in the experiment that the time needed for nucleation during laser induced phase explosion is on the order of one nanosecond. Thus, when a laser with a pulsewidth of the order of picosecond or less is used, it is likely that the material can be heated above the critical point, and another type of phase change, spinodal decomposition is possible. Molecular dynamics studies showed that with the use of a femtosecond laser pulse, it is possible to superheat the material to above the critical point, and spinodal decomposition is the dominant mechanism for materials removal.

A phase-change type micropump with aluminum flap valves

In this paper, a phase-change type micropump is presented. This micropump consists of a pair of aluminum flap valves and a phase-change type actuator. The actuator is composed of a heater, a silicone rubber diaphragm and a working fluid chamber. The diaphragm is actuated by the vaporization and the condensation of the working fluid. The micropump is fabricated by the anisotropic etching, the boron diffusion and the metal evaporation. The dimension of the micropump is 8.5 mm × 5 mm × 1.7 mm. The forward and the backward flow characteristics of the flap valve illustrate the appropriateness as a check valve. The flow rate of the micropump is measured for various voltages, frequencies and duty cycles of the square-wave input. When the square-wave input voltage of 10 V is applied to the heater, the maximum flow rate of the micropump is 6.1 μl min−1 at 0.5 Hz and the duty ratio of 60% for zero pressure difference. The maximum backward pressure when the flow rate is zero is 10 mm H2O.

Study of Phase Change Steam Accumulator and Application to Solar Rankine Cycle System.

Since fossil fuel like petroleum, coal, and natural gases will sooner or later run out in this or next century, natural energy like solar, wind, and biomass will rise as one of alterative energy sources. Most of the conventional solar thermal electric systems utilize high-temperature difference. In the present paper, an advanced solar Rankine cycle system with CPC (Compound Parabolic Concentrator) collector and steam accumulator of phase-change type is newly proposed. The phase-change steam accumulator with high temperature phase change material (PCM) is designed and evaluated both experimentally and theoretically. And this paper reports experimental results of the proposed system under actual solar radiation and under heat stored accumulator condition.