Two-phase State Research Articles

Strong electrocaloric response with ultrawide working temperature span in lead-free BaTiO3-based ceramics by composition design

Solid-state refrigeration technology based on electrocaloric effect provides a cost-effective and convenient approach for microelectronic device cooling. However, the working temperature range of electrocaloric materials is often narrow and incommensurate with that required by many microelectronic devices including computer chips and CPUs. In this work, the working temperature span of electrocaloric response in BaTiO3 ceramics were tuned by the simultaneous introduction of Sr and Hf (abbreviated as BSHT). Through rational variation of Sr and Hf content, not only the Curie temperature is reduced to ∼80 °C, but also the room-temperature phase structure of the ceramics can be effectively tuned from a single rhombohedral phase to coexistence of rhombohedral + orthorhombic or orthorhombic + tetragonal phases. Relaxor behavior of BSHT ceramics is evident by the frequency-dispersion of dielectric permittivity and the increased relaxor diffuseness factor γ. Temperature-dependent Raman spectra confirm that Ba0.85Sr0.15Hf0.06Ti0.94O3 (0.6BSHT) sustain a two-phase coexistence state over a broad temperature range. 0.6BSHT ceramics render a large adiabatic temperature change ΔT of 0.91 K under 40 kV cm−1 with a broad temperature span of ∼57 °C, covering the working temperature window of most microelectronic devices. Moreover, the electrocaloric response of 0.6BSHT shows excellent fatigue endurance, i.e., the adiabatic temperature change shows a trivial degradation of <4.4 % after 106 cycles. This work demonstrates that BaTiO3-based ceramics remain one of the most promising electrocaloric candidates and compositional modification is an effective route to tune the electrocaloric response for fulfilling the requirements of practical applications.

New monoclinic ground state of FeSi

By means of ab initio techniques with the hybrid functional we show the existence of a new phase of FeSi with the monoclinic symmetry (space group P21) originated from the B20 cubic structure (space group P213) due to slight orthorhombic distortion, which is turned out to be the ground state. The monoclinic FeSi not only displays the minimum in the total energy, but it is also characterized by a phonon spectrum without imaginary frequencies and by conducting properties (contrary to semiconducting properties of cubic FeSi) with antiferromagnetic ordering and the magnetic moment of 2.3 μB for each Fe atom. These findings are supported by data of X-ray diffraction and high-resolution transmission electron microscopy of ultrathin FeSi films (∼3nm in thickness) grown on Si(111) by solid-phase epitaxy indicating the monoclinic symmetry to fit better the film structure as compared to the cubic symmetry, as well as by resistivity versus temperature measurements within a wide temperature range (2–300 K) pointing out bad metal properties. The analysis of field and temperature dependences of the magnetic moment of ultrathin FeSi films shows the presence of a ferromagnetic-antiferromagnetic two-phase state. We also discuss how our findings of the new phase of FeSi can interpret its known experimental data on electronic, transport and optical properties without involving the metal–insulator transition and Kondo-like effects.

Crystal structure of solid solutions 0.65BiFeO3–0.35Ba1-xSrxTiO3 in the region of morphotropic phase boundary

Solid solutions 0.65BiFeO3–0.35Ba1-xSrxTiO3 (0 ≤ x ≤ 1) with the compositions in the vicinity of the morphotropic phase boundary “rhombohedral-cubic” were synthesized by the Solid-state reaction method. The crystal structure and morphology of the ceramics 0.65BiFeO3–0.35Ba1-xSrxTiO3 were studied based on the data obtained by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, as well as energy-dispersive X-ray spectroscopy methods. It was determined that the chemical substitution of barium ions with strontium ions leads to a decrease in the magnitude of rhombohedral distortions, while the unit cell parameters decrease in the whole substitution concentration range. The solid solutions with x ≥ 0.25 are characterized by a single-phase structural state with a cubic unit cell; the average crystallite size decreases with increase of the dopant ions. The results of the structural studies carried out using Raman spectroscopy indicate the presence of rhombohedral distortions in the structure of all studied compounds, which is caused by the presence of nanosized clusters with rhombohedral symmetry. The obtained results made it possible to determine the sequence of the changes occurred in the phase state and the unit cell parameters in the region of the morphotropic phase boundary “rhombohedral -pseudocubic”; the concentration intervals corresponding to the single-phase and two-phase structural states of the compounds were determined. The region of concentration stability of the polar rhombohedral phase was clarified using the structural data obtained by local and microscopic research methods.

Model and Analysis of Pump-Stopping Pressure Drop with Consideration of Hydraulic Fracture Network in Tight Oil Reservoirs

The existing pump-stopping pressure drop models for the hydraulic fracturing operation of tight oil reservoirs only consider the main hydraulic fracture and the single-phase flow of fracturing fluid. In this paper, a new pump-stopping pressure drop model for fracturing operation based on coupling calculation of the secondary fracture and oil-water two-phase flow is proposed. The physical model includes the horizontal wellbore, the fracture network and the tight oil reservoir. Through the numerical simulation and calculation, the wellbore afterflow performance, the crossflow performance between the main hydraulic fracture and the secondary fracture, the fracturing fluid leakoff and the oil-water replacement after termination of pumping are obtained. The pressure drop characteristic curve is drawn out by the bottom-hole flow pressure calculated through the numerical simulation, and a series of analyses are carried out on the calculated pressure drop curve, which is helpful to diagnose the -oil-water two-phase flow state and the fracture closure performance under the control of the fracture network after hydraulic fracturing pumping. Finally, taking a multi-stage fractured horizontal well in a tight oil reservoir in the Junggar basin, China as an example, the pump-stopping pressure drop data of each stage after hydraulic fracturing are analyzed. Through the history fitting of the pressure drop characteristic curve, the key parameters such as fracture network parameters, which include the half-length of main hydraulic fracture, the conductivity of main hydraulic fracture and the density of secondary fracture, the fracture closure pressure are obtained by inversion, thus, the hydraulic fracturing effect of fractured horizontal well in tight oil reservoirs is further quantified.

Effect of inlet throttling on thermohydraulic instability in a large scale water-based RCCS: An experimental study

The objective of the present experimental study is to investigate the effect of inlet throttling on the thermohydraulic stability of a large scale water-based Reactor Cavity Cooling System (RCCS). The test was performed using the water-based Natural convection Shutdown heat removal Test Facility (NSTF) at Argonne, which represented a ½ axial scale and 12.5° sector slice of the full scale Framatome 625 MWt SC-HTGR RCCS concept. A two-phase steady state was first established through direct condensate refill, followed by increased inlet throttling over 10 stages, corresponding to a loss coefficient K over the range of 0.05–653. With the inlet throttling gradually increased, the system experienced a unique transition process between stabilization and destabilization. Through a stability analysis, three instability mechanisms were identified in the present test, including a compound mechanism due to both natural circulation oscillations (NCOs) and density wave oscillations (DWOs), Type-II DWOs, and geysering.

Dependence of Electrochemical Characteristics of a Biodegradable Fe-30Mn-5Si wt.% Alloy on Compressive Deformation in a Wide Temperature Range

Fe-30Mn-5Si alloy subjected to a compression test at various deformation temperatures ranging from 350 to 900 °C with a strain rate of 1 s−1 are studied. It was found that the Fe-30Mn-5Si alloy exhibits high resistance to the dynamic recrystallization process in a whole studied range of deformation temperatures. There are no differences in structure formation in the zone of action of tangential tensile stresses and peripheral and central zones of localized compressive stresses. The room-temperature X-ray diffraction study shows the presence of a single-phase state (FCC γ-austenite) after deformation temperature range from 350 to 700 °C and a two-phase state (FCC γ-austenite + HCP ε-martensite) after deformation test at 900 °C. The presence of a two-phase state provides a higher rate of biodegradation compared with a single-phase state. The changes in the biodegradation rate dependence on the structure change with an increase in the deformation temperature are explained. Favorable temperature regimes for subsequent thermomechanical processing are proposed based on the relationship between structure formation and biodegradation rate to obtain semi-products from the Fe-30Mn-5Si alloy.

Gas–Water Two-Phase Displacement Mechanism in Coal Fractal Structures Based on a Low-Field Nuclear Magnetic Resonance Experiment

In this paper, the gas–water two-phase seepage process under a real mechanical environment is restored by a nuclear magnetic resonance experiment, and the gas–water two-phase distribution state and displacement efficiency in coal with different porosity under different gas injection pressures are accurately characterized. The fractal dimension of liquid phase distribution under different gas injection pressures was obtained through experiments, and the gas–water two-phase migration law is inverted according to it. Finally, the gas–water two-phase migration mechanism inside the fractal structure of coal was obtained. The results are as follows: 1. Gas will first pass through the dominant pathway (the composition of the dominant pathway is affected by porosity) and it will continue to penetrate other pathways only when the gas injection pressure is high. When the gas injection pressure is low, the displacement occurs mainly in the percolation pores. With the increase in gas injection pressure, the focus of displacement gradually shifts to the adsorption pore. 2. As the gas injection pressure increases, the displacement efficiency growth rate is relatively uniform for the high-porosity coal samples, while the low-porosity coal samples show a trend of first fast and then slow growth rates. When the gas injection pressure reaches 7 MPa, the displacement efficiency of high-porosity coal samples exceeds that of low-porosity coal samples. 3. With the increase in gas injection pressure, the fractal dimension of the adsorption pore section and the seepage pore section shows an increasing trend, but the fractal dimension of the adsorption pore section changes faster, indicating that with the increase in gas injection pressure, gas–water two-phase displacement mainly occurs in the adsorption pore section.

Chloride ion transport in unsaturated ultra-high performance concrete cracks under high hydraulic pressures

The high strength, durability, and impermeability of ultra-high performance concrete (UHPC) make it a vital material for the construction of deep underground facilities, such as tunnels, nuclear waste repositories, and research laboratories. However, the presence of cracks and high hydraulic pressure in deep underground greatly accelerates the transport of chloride ions, which can shorten the service life of UHPC. Unfortunately, the underlying mechanism for this is still unclear. Here, we investigated the influence of hydraulic pressure and capillary force on chloride ion transport in cracked UHPC using a self-designed testing module. It was found that the presence of trapped gas creates a gas–liquid two-phase state within the cracks. Theoretical models were established using the Laplace equation, which effectively describe the hindrance of gas within cracks on the transport of chloride ions. Contrary to current understanding, the primary driving force for chloride ion transport within the crack is the capillary pores along the crack walls, rather than the capillary forces associated with the crack itself. In addition, the unhydrated regions within the UHPC interior expedite the adsorption of water molecules compared to ordinary concrete. Hydraulic pressure significantly accelerates the depth of chloride ion penetration. Subsequently, the visualization of the solution within cracks was carried out through the application of X-ray computed tomography (X-CT) and capillary tests, thereby providing a means to validate the accuracy of the model. This study contributes to the advancement of our knowledge regarding the influence of capillary force and high hydraulic pressure on the transport of chloride ions. The findings have important implications for the analysis of the durability of UHPC structures situated in deep underground environments.

Experimental study on catalyst-free high-temperature and high-pressure aluminum-water reaction characteristics using metal as energy carrier

Aluminum-water reaction have the potential for clean hydrogen production and power generation. In this work, the effects of reactions such as temperature, pressure, water-aluminum ratio, and water state of the high-temperature and high-pressure aluminum-water reaction are experimentally investigated. The findings demonstrate that the micron aluminum powder can produce 100% hydrogen in a catalyst-free neutral environment by enhancing the temperature and pressure. The aluminum-water interaction is favored by excess water and the gas-liquid two-phase state. The effects of Na+ and K+ ions within water in high-temperature and high-pressure reactions under neutral environments have a negligible effect, and the in-situ reaction with clean water has a high hydrogen yield. The high-temperature and high-pressure aluminum-water reactions consist of four stages. Hydrogen and heat are generated only when water molecules and activated aluminum are constant touch. He results provide the foundation for aluminum-water-based hydrogen cogeneration.

Effect of Gas Injection on the Enhancement of Condensate Recovery in a Gas Condensate Reservoir

So far, many methods have been used to increase production from gas condensate reservoirs, but in general, all these methods can be placed in two groups:1) Methods of maintaining pressure or preventing pressure drop; 2) Creating chemical changes in reservoir fluids to improve production mechanisms due to capillary forces.Also, many of the methods used have realized both of the above purposes and at the same time while maintaining the reservoir pressure (or preventing pressure drop) also change the chemical physical properties of the reservoir. One of these methods is gas injection. What causes severe changes in the performance of condensate gas reservoirs as soon as the pressure reaches the dew point pressure is the change of the reservoir fluid from a single-phase gas state to a two-phase gas condensate state. In order to accurately study the fluid behavior of one of condensed gas reservoirs, the reservoir fluid was simulated by software, four samples of nitrogen gas, carbon dioxide, methane and separator gas, were injected into the reservoir and then the effect of changing injection rate, injection pressure and injection duration on gas condensate recovery has been investigated by these injection gases.

Pore network simulation of loop heat pipe evaporator with different pore size distribution

To investigate the relationship between the loop heat pipe evaporator heat-transfer coefficient and wick pore size distribution, this work simulated the two−phase thermal hydraulics in the evaporator by pore network model in three dimensions. The simulation considered a liquid–vapor (L–V) two-phase state in the wick, which is induced by nucleate boiling and local pore-scale fluid dynamics. Some wick samples, while having the same macroscopic porous characteristics such as permeability, were created with different pore size distributions. Heat transfer and fluid flow of the evaporator were solved with ammonia and R134a as working fluids, along with stainless-steel and polytetrafluoroethylene (PTFE) porous materials. Each evaporator showed a different evaporator heat-transfer coefficient and maximum applied heat flux. Some characteristics with respect to the L–V phase distribution in the wick were selected to investigate their correlation with heat-transfer coefficients. As a result, the correlation coefficients with the three-phase contact line (TPCL) length ranged from 0.70 to 0.91. Only the TPCL showed a correlation with the heat-transfer coefficients in all conditions, as opposed to the vapor pocket maximum depth and liquid saturation. It was discovered that the TPCL length is proportional to the heat-transfer coefficients. In all cases, the TPCL length and heat-transfer coefficients reached a maximum at moderate pore size dispersion. In addition, The heat-transfer coefficients of the PTFE wick were more sensitive to the TPCL length than that of the stainless-steel one. The discovery helps enhance the thermal performance of the evaporator porous structural design by additive manufacturing.

Multimode OAM beam generation through 1-bit programmable metasurface antenna

modern wireless communication, the orbital angular momentum (OAM) beam is considered as an important technology. Some considerable efforts have been devoted to using this technology for channel capacity enhancement as much as possible. Nowadays, programmable metasurfaces provide an innovational scenario for generating multi-mode OAM beams due to their ability for digital electromagnetic waves modulation. However, the current programmable metasurfaces for generating OAM beams are typically based on reflective and transmissive modes, which have low aperture efficiency due to spillover and illumination effects. In this paper, a 1-bit programmable metasurface antenna is proposed with capability of producing highly efficient dynamic multi-mode OAM beams. The proposed structure is consisted of electronically reconfigurable meta-radiating elements loaded by PIN diodes to generate two-phase states of electric field. The designed Field Programmable Gate Array (FPGA) can assign a code sequence of 0 or 1 to the metasurface antenna in real-time to generate multi-mode OAM beams. Hence, a dynamical surface is obtained by switching PIN diodes to change the phase distribution on the surface. To verify the concept, the metasurface antenna is fabricated and measured with different OAM beam states, which are in agreement with the full-wave simulations, properly. The designed structure introduces a capable multi-mode OAM alternative for high throughput mm-wave communications.

Investigation on optimal selection of multi-nozzle spray dust suppression parameters for air-operated spraying system

To evaluate the granularity distribution pattern for multi-nozzle interference spray, the two-phase flow state inside the nozzle and the fragmentation process of the droplet particles in the eddy current field is studied, and the atomization characteristics of the multi-nozzle spray interference process is simulated based on CFD technology. The results indicate that the braking distance in the atomization field decreases with the increase of atomization pressure, and the decreasing speed is slower, in contrast, the atomizing angle increases with the rise in atomization pressure and the decrease of nozzle diameter. Compared with the single nozzle atomization field, the multi-nozzle atomization field has a more uniform distribution of droplet particles through collision, polymerization and rupture, which can achieve a better dust removal effect. By increasing the atomization pressure, the multi-nozzle interference atomization area can be formed faster, the droplet size is more refined, and the distribution is more uniform. Under the optimal parameters, practical testing indicates that the multi-nozzle air-operated atomization system makes the total dust and respirable dust concentrations at the various measuring points decrease rapidly, and the maximum suppression rates reach 95.52% and 96.84%, respectively.

Relationship between phase distribution and heat-transfer coefficient of loop heat pipe evaporator investigated by lateral observation of porous media

Loop heat pipes (LHPs) can be passively operated, require no electric power, and can be flexibly arranged, making them promising in thermal control systems for both terrestrial and aerospace applications. Understanding the two-phase state in the porous media of a capillary evaporator induced by nucleate boiling is key to enhancing the evaporator performance. This study visualized the liquid–vapor (L–V) phase distribution on the contact surface between the cylindrical evaporator casing and the wick to investigate the L–V phase distribution and to figure out its relationship with the evaporator heat-transfer coefficient. The visualization was successfully realized under conditions similar to those observed in a practical environment using a sapphire tube as the evaporator casing. The observation results showed that the wick underwent a phase transition from a liquid-saturated state to a two-phase state under the effect of nucleate boiling, and the evolution of the L–V phase distribution on the contact surface with varying heat load could be determined. The heat-transfer coefficient peaked immediately after the nucleate boiling and then decreased with increasing heat load. The three-phase contact line (TPCL) within the casing, liquid, and vapor phases showed a similar trend; however, the saturation on the contact surface was different, decreasing quickly after the nucleate boiling, followed by a gradual decrease. The correlation coefficients between the heat-transfer coefficient and the saturation/TPCL length were −0.61 and 0.83 under all heat load conditions, respectively. The characteristics of the heat-transfer coefficient as a function of the heat load were found to correspond to those of the TPCL length rather than the saturation. This finding can aid in the design of microscopically optimized porous media by additive manufacturing.

Study of the operating characteristics of a pump-driven thermosyphon loop with gas–liquid separation

Pump-driven thermosyphon loop (PDTL) is a highly efficient cooling method for air-conditioning systems in data centers. Typically, the refrigerant in gas–liquid two-phase state leads to significant pressure drop in pipes following evaporator, which results in more energy consumption for data centers cooling. This study proposes a novel PDTL with gas–liquid separation (PDTLGLS), aiming to separate the gas–liquid phase refrigerant into liquid phase and gas phase, to reduce pressure drop following evaporator and improve the PDTL performance using a gas–liquid separator. Driven by the pressure difference between the gas–liquid separator and the reservoir, the gas-phase refrigerant is condensed into liquid-phase refrigerant back to the reservoir and the liquid-phase refrigerant returns to a reservoir directly without heat exchanging. This paper firstly conducted a theoretical analysis of PDTLGLS. Then the experiments were conducted using R134a to investigate the influence of refrigerant flow rate and heating power on the performance of PDTLGLS. Furthermore, transient characteristics of the PDTLGLS were experimentally analyzed by varying the heating power. The experimental results show that the PDTLGLS achieves 36.8%-53.3% less heat dissipation temperature difference (from evaporator to condenser) and 28.3%–33.3% higher EER than traditional PDTL, and lower dryness could enlarge the PDTLGLS advantages. Furthermore, both analysis results and experimental results show that the PDTLGLS can adjust to diverse refrigerant mass flow and heating power via the self-regulation of the liquid height in the gas–liquid separator, which implies that the PDTLGLS is an effective way to enhance the traditional PDTL performance and could sustain stable operation across a broad spectrum of operating conditions.

Links between non-180° domain and heterophase structures in ferroelectric solid solutions: from stress relief to phase contents

A model of a heterophase sample with interlayers is applied to describe some two-phase states in ferroelectric 0.69BiFe1- x Ga x O3–0.31BaTiO3 solid solutions with x = 0 − 0.06. Features of a coexistence of the rhombohedral and pseudocubic phases are first analysed at variations of a unit-cell parameter of the pseudocubic phase aPC in heterophases with x = const. Conditions for the complete stress relief at planar interfaces hold in the presence of non-180° domains in the rhombohedral phase and at the aforementioned variations of aPC . Agreement between the calculated and experimental results on contents in 0.69BiFe1- x Ga x O3–0.31BaTiO3 at room temperature is achieved.

Mechanical energy conversion to electricity through periodically stress-induced martensitic transformation in Co-Ni-Ga

We anticipate and demonstrate experimentally the mechanical-to-electrical energy conversion through the variation of magnetization resulting from a periodical stress-induced martensitic transformation in the single crystalline Co-Ni-Ga ferromagnetic shape memory alloy. Dynamic loading in a stress-induced austenite-martensite two-phase state was performed with the peak-to-peak strain amplitude from 0.002 to 0.024 in a frequency range of 25 - 150 Hz. A reproducible superelastic behavior occurred at all frequencies. Alongside this remarkable result, we found that the electrical power output depends quadratically on the peak-to-peak strain. This study suggests a new route for the development of broad-band vibration energy harvesting devices.

Shock response of unidirectional carbon polymer composite up to pressures of 200 GPa

Carbon fiber reinforced composite materials are often used to protect spacecraft from hypervelocity impacts with micrometeoroids or space debris. Therefore, shock-wave properties of these materials at pressures corresponding to orbital impact velocities are of interest. Experimental studies of shock compressibility of unidirectional carbon fiber polymer composite with longitudinal and transverse fiber orientation relative to the direction of shock-wave propagation have been carried out in the pressure range of up to 200 GPa. Particle velocity profiles on the composite surface-water window interface were recorded with a multichannel laser interferometer. The formation of a two-wave structure with a precursor amplitude from 1.5 to 3 GPa was observed with longitudinally oriented fibers. We show that Hugoniot of the composite material almost does not depend on the orientation of the carbon fibers, except for low pressures, when the particle velocity does not exceed 1 km/s. The graphite/diamond phase transition and the destruction of epoxy resin result in a characteristic kink on the Hugoniot curve with a distinct two-phase state region in the 23–35 GPa pressure range.

The Investigation of Two-Phase Expansion Performance with Indicator Diagram in a Twin-Screw Expander

Volumetric expanders are proven to be more suitable for small-scale waste heat recovery applications because of their simplicity, reliability, lower rotational speed and lower cost. Unlike turbines, volumetric expanders can work in the two-phase fluid state, which broadens their application fields. To investigate the two-phase performance of volumetric expanders, a specific twin-screw expander was chosen and modeled. The leakage loss and the suction pressure loss were primary concerns in this research. The two-phase expansion process in the expander is presented in detail using the developed mathematical model with an indicator diagram. The influence of several factors, including inlet vapor quality, rotational speed and intake pressure, are investigated. The influence mechanism of the vapor phase and the liquid phase on expander performance is clarified. In brief, this paper presents an illustrative understanding of the two-phase expansion process in twin-screw expanders.

Experimental study of the effect of fastening bolts on PEMEC performance

The fastening bolt is one of the important parts of the stacked structure proton exchange membrane electrolyzer (PEMEC), and the bolt tightening behavior has a significant impact on the electrochemical performance of the PEMEC. In this paper, we use a transparent visualization system to explore the effect of tightening bolt behavior on the performance of PEMEC. Pressure sensitive paper was used to record the contact pressure distribution map of PEMEC under different bolt tightening methods, and a high-speed camera was used to record the state of gas-liquid two-phase flow inside PEMEC under different bolt tightening methods. Both of them are used to verify the effect of bolt tightening behavior on the performance of PEMEC. The experimental results show that the contact pressure of PEMEC increases with the increase of bolt torque, and the electrochemical performance first increases and then decreases with the increase of bolt torque. The optimum bolt torque is 3.5 N m for a square PEMEC with an end plate size of 100 mm × 100 mm and a membrane size of 50 mm × 50 mm × 0.17 mm. The PEMEC performance increases with the increase of bolt tightening steps, and the optimal tightening step for the system is three steps. In addition, symmetrical tightening of bolts is beneficial for improving electrochemical performance, and there is an optimal tightening sequence in the system. This paper illustrates the relationship between tightened bolts and PEMEC electrochemical performance, showing the relationship between bolt tightening and the gas-liquid two-phase flow state inside PEMEC. The research results can provide a reference for optimizing the assembly and installation process of PEMEC.