Thermal Cycle Characteristics Research Articles

Solidification/melting enhancement in ice thermal energy storage by synergistic effect of metal foam and carbon nanotube under magnetic field

In this work, water-based magnetic Multi-walled Carbon Nanotube Phase Change Material and Copper Metal Foam (MWCNT PCM-CMF) were combined to improve the performance in ice thermal energy storage. The effect of concentration of magnetic MWCNT, porosity and pore density of CMF and magnetic field intensity on the thermal cycle characteristics including supercooling degree, solidification/melting time, cold storage/release capacity and cold storage/release rate were studied. The results indicated that the optimal magnetic field intensity corresponding to the optimal thermal cycle characteristics decreases with the increased concentration of magnetic MWCNT. Moreover, the addition of magnetic MWCNT-CMF significantly accelerates the solidification process, which is dominated by heat conduction. Although the cold storage capacity of composites was ∼ 94% of pure water, the time required for cold storage was ∼ 52% of pure water as well as the cold storage rate was improved by ∼ 80%. The melting behavior is further improved by arranging gradient CMF. As a result, the combination of 0.04 wt% magnetic MWCNT under 75 mT magnetic field and CMF with 10/5 pore per inch (PPI) gradient pore density at 95% porosity has 86.8% reduction in supercooling degree, 39.8% advance in complete cycle time and the mean rate of energy storage/release is 1.52 times than pure water.

Analysis of variable cycle engines performance in cruising using GasTurb11

Variable cycle engines (VCE) have always been a hot topic in aircraft engine research. Because of its variable thermal cycle characteristics, it has a wide range of optimum operating conditions (altitude, flight Mach number). In this paper, a typical double bypass variable cycle engine is used as the object of study, and the Gasturb11 software is used to simulate the engine in two main modes at different altitudes and Mach numbers, to observe the engine operation performance, as well as the relationship between the range and endurance from the derivation of cruise equation. The results show that VCE has a best thermal cycling pattern for a given altitude and Mach number, and for a range of lift-to-drag ratios, resulting in the longest range or endurance of the aircraft. This paper investigates the relationship between range, endurance and thrust of a variable cycle engine and altitude and Mach number to help make the VCE better suited to the needs of an aircraft with multiple missions, long range and high endurance.

Thermal cycles, microstructures and mechanical properties of AA7075-T6 ultrathin sheet joints produced by high speed friction stir welding

0.5 mm thick AA 7075-T6 ultrathin sheets were butt jointed by conventional friction stir welding (C-FSW) and high speed friction stir welding (HS-FSW) under a constant rotational speed ( ω )/welding speed ( v ) ratio of 6.67 rad/mm using a pinless tool. In this study, the conventional ω of 2000 rpm and conventional v of 300 mm/min were adopted by C-FSW, and the high ω of 8000 rpm and high v of 1200 mm/min were adopted by HS-FSW. Compared with C-FSW, HS-FSW presented a fast heating and cooling rate thermal characteristic with a slightly higher peak temperature and significantly shorter elevated-temperature exposure time. Kissing bond defect was appeared in the weld bottom for C-FSW. While, no obvious defect was found in the weld obtained by HS-FSW. Compared with C-FSW, the proportion of deformed grains in the center of nugget zone (NZ) fabricated by HS-FSW was increased. For the joint fabricated by HS-FSW, the upper NZ was dominated by recrystallized grains, and the lower NZ was dominated by deformed grains. The ultimate tensile strength of the joint fabricated by HS-FSW can reach 87% of base metal (BM), and its elongation, yield strength and ultimate tensile strength were increased by 58.8%, 23.3% and 22.8% respectively compared with C-FSW. Both the joints fractured in the center of the NZ. The joint fabricated by C-FSW broke due to the kissing bond defect. While the joint fabricated by HS-FSW may be broken due to the weld thickness reduction. • The thermal cycle characteristics of HS-FSW were revealed. • The effect of the thermal cycle on microstructure was revealed. • The microstructures of the joint produced by HS-FSW were investigated by EBSD. • The tensile properties of the joint produced by HS-FSW were superior to by C-FSW.

Influence of secondary-pass laser treatment on retained ferrite and martensite in 44MnSiVS6 microalloyed steel

Overlapping regions of laser surface treatment are necessary features when processing large surface areas or cylindrical specimens. However, complex microstructural changes that appear in the regions with multiple heat treatment can affect their mechanical properties. Therefore, this study focuses on examining thermal cycle characteristics and resulting microstructures, particularly martensite and retained ferrite structures, to better understand the correlation between experienced thermal cycles and resulting microstructures. Laser surface hardening experiments on 44MnSiVS6 microalloyed steels together with thermal diffusion simulations were conducted to relate microstructures after the secondary pass of the laser treatment to the local thermal cycles experienced during the process. The amount of retained ferrite was calculated and compared to the respective thermal cycle characteristics. Regions which experienced thermal cycles below Ac3 temperature showed microstructures similar to those after tempering. The sizes of retained ferrite structures were found to decrease as the total holding time increases regardless of how the holding time is distributed in multiple laser treatments. However, the size of retained ferrite structures were constant in the region where tempering effect occurred. This shows that the amount of retained ferrite can be tailored by modifying the experienced total holding time and a reduction of retained ferrite structure happens only if the secondary thermal cycle is above Ac3 temperature.

Mechanical Properties of SiC Whisker-Reinforced Aluminum Matrix Composite Wheel

Carbon fiber composite has advantages such as high specific heat capacity, low coefficient of thermal expansion and low elastic modulus. The SiC whisker-reinforced aluminum (SiCw-Al) matrix composite wheel has been developed to address the thermal fatigue failure of wheels caused by the braking heat. This paper studied the thermal cycle characteristics, crack propagation and fracture mechanism of SiCw-Al matrix composite wheel. Using finite element simulation technology, it compared the fatigue life of both the SiCw-Al matrix composite wheel and the traditional steel wheel. According to the findings, during braking, the wheel made of SiCw-Al matrix composites has 20.1% lower maximum temperature than the ordinary steel wheel; Its maximum safety factor (yield strength/maximum stress) has increased by 1.08, and its fatigue life is significantly longer. The SiCw-Al matrix composites show excellent mechanical properties and is thus widely used.

Microstructure and mechanical properties of a novel Cu-reinforced maraging steel for wire arc additive manufacturing

In this study, a novel Cu-reinforced SHER120-G maraging steel was developed for the wire arc additive manufacturing (WAAM) process. The microstructural evolution, mechanical properties, and Ɛ-copper particle-strengthening mechanisms of the samples were investigated. The content of δ-ferrite and austenite increases with the increase of deposition height due to the unique thermal cycle characteristics of WAAM process. High-resolution transmission electron microscopy (HRTEM) images of the age hardened specimens clearly exhibit that there is a small amount of fine Ɛ-copper particles in the as-deposited sample due to the transient ageing effect. After direct ageing, a uniform and dense distribution of Ɛ-copper particles with the size about 6 nm formed in the martensite matrix. The yield strength and microhardness were significantly increased owing to the Orowan bypass mechanism and strain strengthening. The ultimate tensile strength, elongation and impact toughness reach 1221 MPa, 11.76% and 63 J, respectively. Additionally, improvements in the elongation and impact toughness characteristics were caused by the finer lath martensite, the disappearance of δ-ferrite, and the formation of higher content of reversed austenite during ageing.

Design and analysis of energy-efficient solar panel cooling system using computational fluid dynamics

This paper highlights the design of an effective liquid cooling system that utilizes the heat generated from the solar panel as a cooling medium to maintain the optimal desired temperature of the solar panel. The coolant for this finned cooling system is selected based on its vaporizing temperature range and thermal cycle characteristics. For analysis purposes, a CAD model is generated in Solidworks CAD package, and further meshing and numerical simulations are performed using Ansys Fluent software. Flow and heat transfer characteristics of the cooling system are investigated by plotting stream functions, velocity, and temperature distributions inside the system. Probing of variations in temperature, pressure and turbulent kinetic energy along vertical as well as longitudinal direction is graphically analysed. Thus, elucidating characteristic of parametric conditions under observation. This study’s results can be the potential background for designing an efficient solar panel cooling system with superior thermal performance.

Research on Cooling Method in Surfacing Repair Process of Aero Compressor Blade

For the cooling method in surfacing repairing, most of the research focuses on the method based on the fixture structure. However, due to the low thermal conductivity and ultrathin alloy blade, the heat transfer speed from the molten pool to fixture is slow. When the heat is transferred to the fixture, most of the molten pool has solidified and absorbed or segregated out some impurities. Therefore, how to cool the welding area directly is more critical. For this reason, the thermal cycle characteristics of typical points of the blade and the heat transfer process of the key area of the fixture are analyzed, the original cooling time is calculated, and two innovative cooling methods based on lateral forced convection cooling and vertical jet impact forced convection cooling are proposed. For lateral forced cooling, with “AF-field” lateral convection cooling modeling, the cooling effects of characteristic points and sections under different flow velocities are calculated. For vertical jet impact cooling, the pressure, flow rate, and convective heat flux distribution on the wall under different impact heights and nozzle diameter are calculated. The influence of different inlet flow rates on cooling performance is influenced, based on the analysis results of impact modeling, the moving heat sink model is established, and the cooling effect under different heat sink-source distances is calculated. The heat transfer rules of two methods are analyzed in detail through modeling and simulations. The results show that both methods can improve the cooling effect and the vertical jet impact cooling method has an effect that is more obvious. When the nozzle radius is 2 mm, the impact height is 4d, the inlet flow velocity is 35 m/s, and the distance is 7 mm, and the cooling time under the vertical jet impact method is shortened by 12.5%, which can achieve better cooling effect. The experiment further validates the effectiveness of the modeling and simulations.

Process Parameters Optimization of Friction Stir Welding of 6005A-T6 Aluminum Alloy Using Taguchi Technique

The control factors including rotating speed, welding speed and plunge depth of 6005A-T6 aluminum alloy friction stir welding were optimized by Taguchi method, and the combined effects of these factors were comprehensively investigated. Statistical results were analyzed by the analysis of variances and signal-to-noise ratios. The results show that the rotating speed is the most dominant factor in determining the joint tensile strength; and the plunge depth and welding speed are the second and third effective parameters, respectively. Under the optimum process parameters, the joint maximum tensile strength reaches 239.6 MPa which is 84% of that of the base material. The relationships between the main control factors, thermal cycle, formation, microstructure, mechanical properties and fracture characteristics were investigated.

Thermal-mechanical Coupling Numerical Simulation of Steel Pillar Girth Weld in Architectural Engineering

The heat transfer control equations of steel pillar girth weld in architectural engineering is obtained according to the analytical method, which is discretized by using Taylor series expansion method, and the one dimensional weld welding thermal cycle characteristics of different node are analyzed. Based on the software ABAQUS, the weld joint thermodynamic properties are obtained by thermal-mechanical coupling numerical simulation, including the field variables and process the output characteristics, of which results shows that the joint change trend of strain and temperature are consistent and the stress yield phenomenon is obvious under the effect of heat flux of continuous welding, while the residual stress is large, temperature falls and strain remains during the free cooling stage.

Numerical analysis of thermal cycle characteristics and prediction of microstructure in multi-pass UWW

Underwater wet welding process has been widely used in assembling and maintaining marine structures, due to its economy and versatility. However, it is difficult to understand the physical phenomenon during wet welding, especially when water environment makes this fleeting process even more complicated. It is necessary to get a deeper understanding of wet welding process by numerical analysis and thus provide theoretical references for process selection. A customized experiment platform was set up for multi-pass wet welding of the grooved butt joint of E36 steel. Besides, a hybrid heat source consisting of double ellipsoid heat source and Gaussian heat source was selected for numerical analysis of multi-pass underwater wet welding. This paper introduced the pool boiling heat transfer theory in numerical simulation of underwater wet welding process and proved to be applicable. The results of numerical analysis show that the profiles of calculated molten pools match well with those obtained by the experiment. A notable effect of water environment on thermal cycle characteristics is especially demonstrated by the comparison of cooling time t 8/5. In this study, the calculated t 8/5 values near the fusion zone are lowered so markedly that a result of full martensite transformation can be expected in E36 steel, which coincides well with the actual microstructure in its heat-affected zone.

Microstructures and mechanical properties of metal inert-gas arc welded Mg–steel dissimilar joints

The joining of Mg alloy to steel was realized by metal inert-gas arc welding, and the weld thermal cycle characteristics and Mg–steel joints were investigated. The results show that the temperature distribution in the joints is uneven. Mg alloy welds present a fine equiaxed grain structure. There exists a transition layer consisting mainly of AlFe, AlFe3 and Mg(Fe, Al)2O4 phases at Mg/steel interface, and it is the weakest link in Mg–steel joints. The welding heat input and weld Al content have the significant effect on the joint strength. The joint strength increases with increasing the heat input from 1680 J/cm to 2093 J/cm, due to promoting Mg/steel interface reaction. When weld Al content is increased to 6.20%, the joint strength reaches 192 MPa, 80% of Mg alloy base metal strength. It is favorable to select the suitable welding heat input and weld Al content for improving joint strength.

Development of Al2O3/glass-based multi-layer composite seals for planar intermediate-temperature solid oxide fuel cells

In this paper, the novel multi-layer composite seals for planar solid oxide fuel cells are studied. The composite seals with sandwiched structure include Al2O3-based tape as support and glass-ceramic slurry as binder connecting the interface of the neighboring components. The result finds out that glass-ceramic slurry with 20 wt% Al2O3 has the suitable strength and deformability. The thermal cycle characteristics are greatly improved by using the multi-layer composite seals, and the corresponding leakage rates are lower than 0.025 sccm cm−1 for 20 thermal cycles at the inlet pressure ranging from 0.5 psi to 2 psi. SEM investigations show a very compact and good adhesion between the neighboring components, which can minimize the leakage paths. Single cell testing is used to examine the performance of the seals. The value of open circuit voltage is 1.17 V. At the constant discharge current density of 0.37 A cm−2, the voltage is stabilized at about 0.85 V for 50 h. The results demonstrate that the novel multi-layer composite seals are good candidate for SOFC application.

Thermal Cycle Characteristics of AM 50 Magnesium Alloy Welded by FSW

By means of Friction stir welding (FSW), as-cast AM50 magnesium alloys were welded with travel speed of 50 mm/min and rotating rate of 1200 r/min. The thermal cycle was investigated by thermocouples and a paperless recorder. The results show that phenomenon of dual peaks and hysteresis exist in temperature curves of featured points at the starting part while only hysteresis in the middle part. The finishing part has the highest peak temperature while the starting part corresponds to the lowest one. Featured points for different depths in the same place share the same shape of temperature curves but with different peak temperature. The retaining time over recrystallization temperature at middle part is double that at finishing part.

Optimization of Segmented-in-series Tubular SOFCs with an (La, Sr)CoO3 System Cathode and the Generation Characteristics under Pressurization

We studied the application of LaCoO3 system cathode to improve the performance of segmented-in-series tubular type solid oxide fuel cells (SOFCs) operating at high temperature (1173 K). (La1−xSrx)CoO3 (LSC, x=0.2 or more) was chosen to take advantage of two of its properties: high electric conductivity and favorable behavior of element diffusion to a cathode interlayer (CIL) of (Sm0.2Ce0.8)O2 (SDC20). The cell stack performances were compared using LSC and (La0.5Sr0.25Ca0.25)MnO3 (LSCM) to cathode current collection layer (CCCL). The modification of cell stack structure composed of effective generation part and interconnector part was also examined. The area specific resistance (ASR) of the overall cell stack resistance with LSC modifying a stack structure decreased 18% than that of the stack using LSCM with conventional structure at atmospheric pressure. In a pressurized test of the cell stack fabricated with LSC, an increase of pressure resulted in a decrease of the ASR. As a result of comparing the pressurized performances of LSCM CCCL/(LSCM-10YSZ) CIL, LSCM/SDC20 and LSC/SDC20, the effect of ASR decrease by pressurization fell as the cell stack performances improve. We also found, however, that the cell stack fabricated with LSC will require improvements in long-term durability and thermal cycle characteristics.

Thermal cycle characteristics of PTCR ceramic thermistors

Thermal cycle treatment was performed in BaTiO 3 and (Ba, Pb)TiO 3 PTCR ceramic thermistors. When the treatment temperatures were higher than the Curie points, the room-temperature resistivities decreased at the initial thermal cycle stage, and then increased further with the thermal cycles. When the treatment temperatures were lower than Curie points, the room-temperature resistivities increased monotonously with the number of thermal cycle. The PTCR effects were also affected by the thermal cycle treatment. The oxygen absorption and oxidation were proposed for the monotonously increasing resistivity. Domain alternation and defect mechanisms were suggested to be the major cause for the resistivity decrease at the initial thermal cycle stage.

Thermal cycle characteristics of PTCR ceramic thermistors

Thermal cycle treatment was performed in BaTiO 3 and (Ba, Pb)TiO 3 PTCR ceramic thermistors. When the treatment temperatures were higher than the Curie points, the room-temperature resistivities decreased at the initial thermal cycle stage, and then increased further with the thermal cycles. When the treatment temperatures were lower than Curie points, the room-temperature resistivities increased monotonously with the number of thermal cycle. The PTCR effects were also affected by the thermal cycle treatment. The oxygen absorption and oxidation were proposed for the monotonously increasing resistivity. Domain alternation and defect mechanisms were suggested to be the major cause for the resistivity decrease at the initial thermal cycle stage.

Improvement of thermal cycle characteristics of a planar-type solid oxide fuel cell by using ceramic fiber as sealing material

The objective of this paper is to improve the endurance of solid oxide fuel cell (SOFC) against thermal cycles by reducing the stress caused by the difference in thermal expansion coefficients of alloy separator and electrolyte. The thermal cycle characteristics were improved by using a ceramic fiber for the sealing material. The ceramic fiber seemed to play the role of suppressing electrolyte-cracking by relaxing the stress set up during thermal cycles. The appropriate structure for the sealing material was investigated with 200 mm×150 mm×4 combined-cell single-layer modules. The glass was arranged around the internal manifold to suppress gas leakage, and the ceramic fiber was arranged around the electrolyte to prevent the glass from contacting the electrolyte. It was confirmed that the thermal cycle characteristics can be improved and that good cell performance can be maintained by adopting this gas seal structure.