Heat Preservation Process Research Articles

In-situ isothermal aging TEM analysis of a micro Cu/ENIG/Sn solder joint for flexible interconnects

Sn/ENIG has recently been used in flexible interconnects to form a more stable micron-sized metallurgical joint, due to high power capability which causes solder joints to heat up to 200 °C. However, Cu6Sn5 which is critical for a microelectronic interconnection, will go through a phase transition at temperatures between 186 and 189 °C. This research conducted an in-situ TEM study of a micro Cu/ENIG/Sn solder joint under isothermal aging test and proposed a model to illustrate the mechanism of the microstructural evolution. The results showed that part of the Sn solder reacted with Cu diffused from the electrode to form η´-Cu6Sn5 during the ultrasonic bonding process, while the rest of Sn was left and enriched in a region in the solder joint. But the enriched Sn quickly diffused to both sides when the temperature reached 100 °C, reacting with the ENIG coating and Cu to form (NixCu1-x)3Sn4, AuSn4, and Cu6Sn5 IMCs. After entering the heat preservation process, the diffusion of Cu from the electrode to the joint became more intense, resulting in the formation of Cu3Sn. The scallop-type Cu6Sn5 and the seahorse-type Cu3Sn constituted a typical two-layered structure in the solder joint. Most importantly, the transition between η and η’ was captured near the phase transition temperature for Cu6Sn5 during both the heating and cooling process, which was accompanied by a volume shifting, and the transition process was further studied. This research is expected to serve as a reference for the service of micro Cu/ENIG/Sn solder joints in the electronic industry.

Energy-saving production of high value-added foamed glass ceramic from blast furnace slag and hazardous wastes containing heavy metal ions

In this work, foamed glass ceramic (FGC) is prepared by using blast furnace slag (BFS), waste glass, and zeolite adsorbing heavy metal ions (HMI) as the raw materials. To conserve energy, the residual heat of BFS at low-temperature could be used as a heat source. In order to simulate the heating process, the green body is directly put into a hot tube furnace and heated during the cooling process without heat preservation process. The optimized FGC has an apparent density of 0.81 g cm−3, a compressive strength of 4.51 MPa, and a water absorption of 19.5%. The physical property of high value-added FGC meets the industry standard and it could be widely used in the field of building materials. The leaching efficiencies of Cu2+, Zn2+, and Cd2+ of FGC are as low as 0.76 mg L−1, 0.55 mg L−1, and 0.79 mg L−1, respectively. The HMIs are steadily stabilized in the FGC and have less impact on the environment. It is found that the newly formed columnar crystal has a great contribution to the improvement of compressive strength due to its pinning effect between the glass phase and crystalline phase. The newly formed lamellar crystal plays an important role in preventing HMI from escaping out into the environment. This study provides a reasonable method for converting solid waste into high value-added product, recycling industrial tail heat at low-temperature zone, and eliminating the harm of hazardous waste containing HMI to the environment.

Experimental study on thermal performance of a novel medium-high temperature packed-bed latent heat storage system containing binary nitrate

The packed-bed latent heat storage (PBLHS) system has received extensive attention due to its low investment cost and good application prospects. In the past, the research on this system mainly focused on the establishment of mathematical models and the structural optimization of the thermal energy storage (TES) tank. There are few experimental studies on the thermal performance of PBLHS systems under medium-high temperature conditions. In this work, a novel medium-high temperature PBLHS experimental system is designed and constructed. Based on binary nitrate NaNO3–KNO3 (55-45 wt%) as the phase change materials (PCM), a spherical encapsulated PCM suitable for the packed bed TES is prepared. The heat transfer characteristics of the charging process, the static heat preservation process, and the discharging process are experimentally studied, respectively. In addition, the influence of the temperature and flow rate of the heat transfer fluid on the pressure drop of the PBLHS system is also investigated. The results indicate that with the continuous increase of the average air temperature inside the TES tank, the temperature difference inside the tank shows a trend of first increasing and then decreasing. When the average air temperature is around 225–272 ℃, the temperature difference is almost at a stable stage, and the temperature difference is about 84 ℃ (±1 ℃). The temperature difference decreases slowly in the initial stage of the discharging process. The overall efficiency of the current PBLHS system based on binary nitrate is 79.3%. The results also indicate that the air temperature and flow rate have a significant effect on the pressure loss of the packed-bed system. The experimental results of this work can provide experimental data support for the structural optimization design and industrial application of the packed-bed TES system.

Enhanced precipitation strengthening of Mg-Al-Sn-Ca alloy by multidirectional rolling

The control of precipitation density has always been a difficult issue in the application of precipitation strengthening mechanism. Here we reported the precipitation of Mg2Ca in a novel Mg-2Al-0.8Sn-0.5Ca (wt. %, ATX2105) alloy promoted by multidirectional rolling. Microstructure characterization revealed that the dislocation density of the multidirectional rolling ATX2105 sample was 3.6×1013m−2 higher than that of unidirectional rolling sample after the second pass of rolling, which can effectively promote the precipitation of Mg2Ca during the heat preservation process between rolls. Benefiting from the combination of more precipitates and finer grains, the yield strength of the multi-directionally rolled ATX2105 was ∼41 MPa higher than its unidirectionally rolled counterpart. Eventually, the multidirectional rolling ATX2105 sample showed a good combination of strength and ductility, exhibiting an ultimate tensile strength of ∼302 MPa, a yield strength of ∼251 MPa, and an elongation of ∼23.4%. In this work, the role of multidirectional rolling in promoting precipitation is clarified for the first time, which may provide new ideas for improving the effectiveness of precipitation enhancement.

Investigation on battery thermal management based on phase change energy storage technology

Electric vehicles are gradually replacing some of the traditional fuel vehicles because of their characteristics in low pollution, energy-saving and environmental protection. In recent years, concerns over the explosion and combustion of batteries in electric vehicles are rising, and effective battery thermal management has become key point research. Phase change materials (PCM) can absorb or release a large amount of latent heat during the phase change process while maintaining a constant temperature (phase change temperature). In this paper, STAR-CCM+ software is used to carry out three-dimensional simulation of single cell and battery packs with PCM to investigate changing characteristics of battery temperature rise and temperature difference during the cooling and heat preservation process. At the same time, temperature rise and temperature difference of battery are analyzed under different ambient temperatures, convection heat transfer coefficients and phase change latent heats of PCMs. In summer, at an ambient temperature of 30 °C, when using PCM, the battery cell temperature can be reduced by 4 °C in 1800 s, which is about 8.6% lower than that without PCM. In winter, at an ambient temperature of −5 °C, the PCM with a melting point about 20 °C can keep the battery cell temperature drop of no more than 28% within 6700 s at a higher convection coefficient of 5 W/m2·K. Comparing the temperature of the battery pack with that of the battery cell, in the summer with an ambient temperature of 30 °C, the temperature of the battery pack decreased by 13.3 °C in 3600 s, while in the winter with an ambient temperature of −30 °C, the temperature of the battery pack increased by 14.3 °C in 5700 s. The use of phase change materials is conducive for batteries in electric vehicles to dissipate heat in summer and preserve heat in winter.

In-situ observation of grain growth and phase transformation in weld zone of Ti-6Al-4V titanium alloy by laser welding with filler wire

Through in situ observation at high temperature confocal laser scanning microscope, the microstructures and phase transformation of Ti-6Al-4V titanium alloy welded joint by laser welding with filler wire during heating, heat preservation and cooling process in simulating welding thermal cycle were studied. When the weld microstructure was heated to 380 °C, obvious grain growth was observed. After heating to 1 050 °C, weld microstructures were mostly composed of coarse β-columnar grains. During the heat preservation process of the weld metal, it could be found that the β phase boundary moved slowly. In the cooling process of weld microstructures, with the increase of the cooling rate, the transition temperature for new phase precipitation decreased gradually, and that for ending the precipitation increased gradually. The microstructures after cooling to room temperature at a rate of 0.5 °C/s and 5 °C s−1 were composed of α phases. At 20 °C s−1, acicular α′ martensite appeared in the microstructures. At 80 °C s−1, precipitated phases were all composed of acicular α′ martensite.The Ti-6Al-4V titanium alloy weld microstructure by laser welding with filler wire is completely hexagonal close packed (HCP) crystal structure.The hardness of the weld microstructures was improved with the cooling rate getting faster.

Nov model zapiranja votlin in razvoj novih pod vplivom različnih napetostnih stanj

Cavity defects including a shrinkage cavity, air hole and porosity are typical defects of an ingot, which are difficult to avoid. These defects can disappear during deformation at a reasonably high temperature and heat-preservation process so as to ensure the quality of forgings. However, the current understanding of the mechanism of the void closure is insufficient, and the models that can accurately predict the evolution of a void are relatively rare. Based on the representative-volume-element model, a theoretical analysis and numerical simulation, the influence of the Lode parameter and stress triaxiality on the void closure is expounded. Besides, based on the above research, a new void-evolution model considering all kinds of macro-stress states is proposed. The model can predict the closure degree of voids in different positions and various macro-stress states during the plastic deformation of ingots. Comparing the new void-evolution model with other models, numerical simulations and physical-simulation results, the accuracy of the proposed void-evolution model is verified.

Structure-related differential proteins identification for sous-vide cooking hairtail (Trichiurus lepturus) product.

Optimal heating parameters for sous-vide cooking hairtail (Trichiurus lepturus) were selected and the differential proteins related to texture change were clarified using proteomics. Heating under 68 °C for 20 min was chosen to be the desirable heating parameter. Texture profile analysis (TPA) showed the texture of hairtail changed more severely during heat-up process than heating preservation process. Most of the high-content proteins did not change much during heating preservation. 169 kinds of proteins were identified as differential expressed proteins. Actin cytoplasmic 1, myosin heavy chain 1 and myosin heavy chain were the most variable structural proteins during heat-up process, with the change fold of 32.4, 29.1 and 18.8, respectively, while the highest structure proteins changing fold during heat preservation process were 16.7, 4.7 and 3.9, respectively, much lower than that of heat-up process. The partial deformation of structure-related proteins under sous-vide cooking was a vital factor in reserving the texture of hairtail.

Grain Growth of AZ31 Magnesium Alloy Based on Three‐Dimensional Cellular Automata

Based on the thermodynamic conversion mechanism and energy transition principle, a three‐dimensional cellular automata model of grain growth is established from the aspects of grain orientation, grain size distribution, grain growth kinetics, and grain topology. Also, the effect of temperature on the three‐dimensional grain growth process of AZ31 magnesium alloy is analyzed. The results show that the normal growth of three‐dimensional grains satisfies the Aboav‐weaire equation, the average number of grain planes is between 12 and 14 at 420°C and 2000 CAS, and the maximum number of grain planes is more than 40. Grains of different sizes are distributed normally at different times, most of which are grains with the ratio of grain diameter to average grain diameter R/Rm ≈ 1.0, which meets the minimum energy criterion of grain evolution. The grain of AZ31 magnesium alloy increases in size with the increase of temperature, and the number of grains decreases with the increase in time. The angle between the two‐dimensional slices of three‐dimensional grains is approximately 120°, which is consistent with that of the traditional two‐dimensional cellular automata. The relative error of grain size before and after heat preservation is in the range of 0.1–0.6 μm, which indicates that the 3D cellular automata can accurately simulate the heat preservation process of AZ31 magnesium alloy.

Effect of moisture transfer on texture uniformity of cooked rice after heat preservation with electric rice cooker

The texture uniformity of rice cooked by electric rice cooker (ERC) will deteriorate during the heat preservation process. In this study, the uniformity of rice texture and water dynamic were investigated by means of physical property analyzer and low-field nuclear magnetic resonance technique. The water content, distribution and migration in rice were compared to illustrate the effect of heat preservation mode with different temperature at pot cover. The middle-upper layer of rice was drier and harder after 24 h of heat preservation in conventional mode, while the outer-upper layer of rice absorbed water, swelled or even broken. The difference of water content between the two parts was 6.55%, and the difference of hardness was 333.31 g. The relaxation signal indicated that the binding force between immobile water of the two parts and the rice matrix became weaker after heat preservation. By adjusting the heat preservation mode with higher temperature of the cover, the moisture content difference between the internal-upper layer and the peripheral upper layer was decreased to 0.39% after 24 h of heat preservation, and the hardness difference was reduced to 2.99 g. These mean that the texture uniformity of the whole pot rice after heat preservation was maintained.

Influence of Heat-Treatment on Enhancement of Yield Strength and Hardness by Ti-V-Nb Alloying in High-Manganese Austenitic Steel

To deal with the problem of poor yield strength and hardness in the initial use of high-manganese austenitic steel, we investigated the alloying design, microstructure, precipitates, mechanical properties, and comprehensive strengthening mechanism of high-manganese austenitic steel through two novel heat-treatment processes, namely continuous heating process (CHP) and segmented heat preservation process (SHPP). In this work, austenitic Fe-0.9C-17Mn-0.8Si-2.0Cr-0.3Ni-0.5Cu-0.7Mo steels alloyed with Ti, V, and Nb were designed. The grain size of SHPP steels was smaller than that of CHP steels due to the smaller size of precipitates. The results of mechanical experiments showed that the yield strength and impact toughness of SHPP steel were obviously higher than those of CHP steel, but the Brinell hardness of CHP steel was higher than that of SHPP steel. The higher Brinell hardness and poorer impact toughness of CHP steel were mainly due to the larger-sized precipitates. Finally, solid-solution strengthening played the most effective role of increasing the yield and tensile strengths of the two steels.

Thermal management of 48 V standby battery for outdoor base station at cold environment

The standby battery for outdoor base station could not function properly at cold environment for a long time. In order to improve its performance and lengthen its life time, it was necessary to heat the battery and keep warm. This dissertation presented the heating and heat preservation method of 48 V Lead-acid battery pack for base station based on the heating plate and phase change materials at cold environment. Then, the thermal management performances of this battery pack were simulated. The results showed that the uniformity of battery temperature field was increased and the heat preservation process was lengthened effectively. And the pack kept good working condition after continuous heating and heat preservation progress. The method was simple and practicable, and it could be used on the thermal management of lithium ion battery because of its good applicability

Interfacial Behaviors in Cu/Molten Sn–58Bi/Cu Solder Joints Under Coupling with Thermal and Current Stressing

The interfacial behaviors of Cu/molten Sn–58Bi/Cu solder joints under the coupling effect of a temperature gradient and the current stressing have been investigated. The most obvious change of the interfacial behaviors under the individual electromigration (EM) and thermomigration (TM) in molten solder was the asymmetrical growth of interfacial Cu–Sn intermetallic compounds (IMCs), which grew rapidly as the stressing time prolonged. The growth rates of the interfacial IMCs induced by TM under a temperature gradient of 40 °C/cm were slightly faster than EM under the current density of 0.5 × 104 A/cm2. However, the microstructure evolution and interfacial behaviors changed obviously when the thermal was distributed unevenly across the entire solder stripe under current stressing. It was found that there was a Bi-rich layer adhered to the anode side and a distributed Cu6Sn5 phase existed in the solder matrix when the anode and the cold end were at the same end. Additionally, a large number of Bi-blocks and Cu–Sn IMCs were dramatically observed in the solder matrix when the anode and the hot end were on the same side. The main reason for this result may be attributed to the significant change of the diffusion of Bi atoms under the thermo-electric coupling conditions. In the initial melting stage of solder, the Bi atoms in molten Sn–58Bi solder rapidly diffused to the anode and then began to be reversely dissolved into the solder matrix. The experimental results proved the additional temperature gradient played a positive or negative role on the reverse dissolution of Bi atoms in the heat preservation process.

Flow behavior and microstructure evolution of a TiBw/TA15 composite with network-distributed reinforcements during interrupted hot compression

Interrupted hot compression tests were performed on a TiBw/TA15 composite with network architecture to study its flow behavior and microstructure evolution during a two-step deformation process. The microstructure was observed by electron backscatter diffraction (EBSD) and the high-temperature β grain boundaries were reconstructed through several special misorientation angles. The fraction of the primary α (αp) phase declined during the heat preservation process. The flow stress exhibited a lower value due to softening upon reloading compared to that observed prior to the interruption. In addition, the hold time and deformation temperature were important factors influencing the composition of the matrix phase, and the αp phase disappeared with increasing hold time and temperature. The high-temperature β grains became longer with a larger average aspect ratio when the deformation temperature reached 1283 K. Both TiB reinforcement and the αp phase restrained the growth of β grains, preventing hot deformation at higher temperatures and resulting in longer inter-pass holding times due to the absence of the αp phase. The low strain rates resulted in a significant β phase grain growth because of sufficient time and the lack of constraints. The optimized process parameters, which can provide guidance to actual production, were obtained in this study.

Thermal management of standby battery for outdoor base station based on the semiconductor thermoelectric device and phase change materials

In order to extend the life span of standby battery for outdoor base station, a semiconductor thermoelectric device/phase change materials (PCMs) coupled battery thermal management system (BTMS), as well as the three-dimensional model of 48 V 80 Ah battery pack, was designed in this paper. The effect of various influencing factors, especially semiconductor thermoelectric device arrangement, temperature range of thermal management, cooling and heating power was investigated numerically. The results showed that the semiconductor thermoelectric devices were arranged at two flanks of minimum size direction could effectively improve the uniformity of battery module temperature field and prolong the heat preservation process. When the temperature difference between upper or lower limit of thermal management temperature range and the phase change temperature of PCMs (TPCM) was no more than 5 K, the maximum temperature difference (ΔTmax) of battery module during the cooling or heating process was lower than 5 K. Both the best choice of cooling and heating power was 200 W. What’s more, after 1 C discharging and 0.5 C charging process, the maximum temperature (Tmax) of battery module was restrained under the 312 K. During continuous cooling and heat preservation cycle, the cooling time and heat preservation time was about 14 h and 4.15 days, respectively, when the average ambient temperature was 323 K. The simulation results will be useful for the design of PCMs based battery thermal management system for outdoor base station battery.

Thermal Storage Characteristics of the Vertical Cylindrical Water Tank

AbstractThis study conducts experimental and numerical investigations on the thermal storage characteristics of the vertical cylindrical water tank in the heat preservation process. A new experimen...

Experimental Investigation on the Thermal-Energy Storage Characteristics of the Subcritical Water

This paper first proposes the concept of using subcritical water as a thermal energy storage (TES) material. Subcritical water has a maximum TES temperature of 330°C and an internal energy storage density as high as 977.75 MJ/m3, which is very suitable for industrial waste heat recovery. This paper investigates the TES characteristics of subcritical water in the heat preservation process. An experimental apparatus was set up, and experiments at different initial temperatures were performed. The experiments show that subcritical water has greater TES capacity than normal water because of its high section energy density. The water tank can be divided into three regions according to the section energy density. The section energy density rapidly increases in the lower head region, slowly increases in the transition region and remains stable in the isothermal region. The section energy density is distributed according to the tank shape and temperature distribution. When the initial temperature increases, the changing rate of the section energy density along the axial direction rapidly increases in the lower head region, slowly increases in the transition region and does not change in the isothermal region. The section exergy density has similar characteristics to the section energy density.

WITHDRAWN: Microstructure and properties of welded joint for T92 ferritic heat resistant steel

Abstract Three kinds of test welding wires were developed, and the effect of the proposed welding wires on the microstructure and properties of the T92 deposited materials were studied. The results showed that: the welding wires should be preheated with the temperature range 200–250 °C to prevent the crack occurring; By PWHT, the second phase precipitated at grain boundary and sub-grain boundary as well as inside grain. The precipitation at grain boundary and sub-grain boundary was mainly Cr 23 C 6 phase, and the precipitation inside grain was the diffuse point-like MX phase; When Ni content was greater than 1%, the point AC 1 decreased to be lower than the PWHT temperature. The austenite transformation happened in the tempering heat preservation process at a temperature above AC 1 , then, austenite changed into untempered martensite in the cooling stage, leading to the ununiformity of tempered structure and deteriorated properties as well as the reduction of toughness. As the impact toughness increased, the fraction of radial region and shear lips region reduced while fiber region enlarged. The shear fracture surface ratio for the proposed three deposited metals were 83%, 87% and 86%, respectively, and the fiber regions mainly consisted of the typical dimples.

Research on Grain Refinement Effect of Al-5Ti-C Alloy on Pure Aluminum and its Attenuation Mechanism

The texture feature and grain refinement effect of Al-5Ti-C alloy on pure aluminum were analyzed and its attenuation mechanism was discussed by using X-ray diffraction (XRD), scanning electron microscopy (SEM), optical microscopy (OM) and other experimental methods.The results show that: Al-5Ti-C alloy is composed of Al, TiAl3 and TiC. Al-5Ti-C alloy has a good grain refining capacity for commercially pure aluminum. During the heat preservation process, due to precipitation of titanium compound in the aluminum melt, refinement effect of Al-Ti-C alloy is declined.

Microstructure Evolution of Al/Fe Liquid/Solid Interface

The liquid/solid composite technology has wide range of applications in the preparation of Fe-Al composite materials and structures. The diffusion-reaction zone (DRZ) formed in the liquid/solid interface has a great influence on their properties. The Al-Fe diffusion couple was prepared by using the insert technology and treated at 700°C-900°C. The microstructure evolution and growth mechanism of the DRZ in the Al/Fe liquid /solid interface were investigated. The result shows that the microstructure of Al/Fe liquid/solid diffusion couple after heat treatment (HT) is (Al+FeAl3)/FeAl3/Fe2Al5/Fe; Fe2Al5 is the only new phase during the heat preservation process, FeAl3 is formed by desolventizing during the cooling process. The growth of the Fe2Al5 is controlled by the chemical reaction of the Al atoms and Fe atoms before the Fe2Al5 continuous single-phase layer is formed; Once the continuous Fe2Al5 single-phase layer is formed, the growth of the Fe2Al5 mainly depends on the diffusion of Al atoms in the solid phase Fe2Al5 layer, and the reaction occurs in the solid/solid interface of the Fe2Al5 layer and iron. Precipitate is not found in the iron while the needlelike and strip FeAl3 precipitates appear in the aluminum; the density and size of the FeAl3 precipitates decrease gradually from the vicinity of interface to the distant.