Interfacial reaction mechanism of TiBw/Ti6Al4V composites and Inconel 718 alloys by GTAW heat transmission

A good joint of Ti Bw/Ti6Al4V composites and Inconel 718 alloys was obtained by Gas Tungsten Arc Welding(GTAW) heat transmission. The interfacial reaction mechanism of joint was investigated and analyzed in details. Owing to the heat input applied on the surface of Ti Bw/Ti6Al4V composites, a solid-state reaction layer appeared at the interface of Ti Bw/Ti6Al4 V composites to Inconel 718 alloys. The thickness of the reaction layer was obviously increased with increasing heat input.Developing of reaction layer mainly depended on the diffusion of elements of Ti and Ni through the interface during welding to form solid solutions and intermetallic compounds(IMCs). The reaction layer can be divided into Ti-rich zone(layer 2) and Nirich zone(layer 1). In Ni-rich zone, relatively coarse dendrites were the predominant, however, more brittle IMCs like Ti2Ni were found in the Ti-rich zone. Micro hardness of reaction layer was much higher than that of base metal. While a slight decrease of hardness was found between Ti-rich zone and Ni-rich zone due to the formation of TiNi.

CFD-Based Optimization of a Shell-and-Tube Heat Exchanger

The main objective of this study is the technical optimization of a Shell-and-Tube Heat Exchanger(STHE).In order to do so,a simulation model is introduced that takes into account the related gas-phase circulation.Then,simulation verification experiments are designed in order to validate the model.The results show that the tem-peraturefield undergoes strong variations in time when an inlet wind speed of 6 m/s is considered,while the heat transfer error reaches a minimum of 5.1%.For an inlet velocity of 9 m/s,the heat transfer drops to the lowest point,while the heat transfer error reaches a maximum,i.e.,9.87%.The pressure drop increasesfirst and then decreases with an increase in the wind speed and reaches a maximum of 819 Pa under the 9 m/s wind speed con-dition.Moreover,the pressure drops,and the heat transfer coefficient increases with the Reynolds number.

Analysis on Transmission Heat Loss in Hot Water System of Residential Building

Based on the data of China Statistical Yearbooks, the current situation and development trend of the energy consumption of residential hot-water was discussed in this paper. Two hundred and sixty eight apartments were surveyed on the installation and operation situations of residential water heaters in five cities. Based on survey data, the proportion of pipeline heat loss was calculated in the energy consumption of a shower/bath. The influence factors of heat loss in residential hot-water pipeline network were discussed, and the measures were suggested for reducing the transport heat loss. The statistics and analysis conclusion have directive significance to reducing the transport heat loss.

Geothermal energy exploitation from depleted high-temperature gas reservoirs by recycling CO_(2): The superiority and existing problems

CO_(2) can be used as an alternative injectant to exploit geothermal energy from depleted high-temperature gas reservoirs due to its high mobility and unique thermal properties.However,there has been a lack of systematic analysis on the heat mining mechanism and performance of CO_(2),as well as the problems that may occur during geothermal energy exploitation at specific gas reservoir conditions.In this paper,a base numerical simulation model of a typical depleted high-temperature gas reservoir was established to simulate the geothermal energy exploitation processes via recycling CO_(2) and water,with a view to investigate whether and/or at which conditions CO_(2) is more suitable than water for geothermal energy exploitation.The problems that may occur during the CO_(2)-based geothermal energy exploitation were also analyzed along with proposed feasible solutions.The results indicate that,for a depleted low-permeability gas reservoir with dimensions of 1000 m×500 m×50 m and temperature of 150℃ using a single injection-production well group for 40 years of operation,the heat mining rate of CO_(2) can be up to 3.8 MW at a circulation flow rate of 18 kg s^(-1)due to its high mobility along with the flow path in the gas reservoir,while the heat mining rate of water is only about 2 MW due to limitations on the injectivity and mobility.The reservoir physical property and injection-production scheme have some effects on the heat mining rate,but CO_(2)always has better performance than water at most reservoir and operation conditions,even under a high water saturation.The main problems for CO_(2) circulation are wellbore corrosion and salt precipitation that can occur when the reservoir has high water saturation and high salinity,in which serious salt precipitation can reduce formation permeability and result in a decline of CO_(2) heat mining rate (e.g.up to 24%reduction).It is proposed to apply a low-salinity water slug before CO_(2)injection to reduce the damage caused by salt precipitation.For high-permeability gas reservoirs with high water saturation and high salinity,the superiority of CO_(2) as a heat transmission fluid becomes obscure and water injection is recommended.

Structural Modification of Al65Cu16.5Ti18.5 Amorphous Powder through Annealing and Post Milling： Improving Thermal Stability

To improve thermal stability of the Al65Cu16.5Ti18.5 amorphous powder,structural modification of the amorphous powder was performed through annealing and post milling.Annealing above the crystallization temperature（Tx） not only induced nanoscale intermetallics to precipitate in the amorphous powder,but also increased Cu atomic percentage within the residual amorphous phase.Post milling induced the amorphization of the nanocrystal intermetallics and the formation of Cu9Al4 from the residual amorphous phase.Thus,a mixed structure consisting of amorphous phase and Cu9Al4 was obtained in the powder after annealing and post milling（the APMed powder）.The phase constituent in the APMed powder did not change during the post annealing,which exhibited significantly improved thermal stability in comparison with the as-milled amorphous powder.