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The air supply terminal located at the floor level attached to side-wall is widely used in large space buildings, leading to potential energy saving as well as significant vertical thermal stratification. The cooling load calculation of such system is challenging, especially the calculation of the load gained from unoccupied zone. This paper adopts experiment and computational fluid dynamics (CFD) methods to study the heat transfer upward and downward across the stratified surface in large space building with floor-level side wall air-supply system. Five experimental cases with different heat source power and exhaust airflow ratios are performed to study their effects on the indoor thermal environment. We investigate the same cases in CFD and verify the result of vertical temperature distribution and cooling load components. As a critical parameter in evaluating the thermal stratification environment of large space building, the inter-zonal heat transfer coefficient Cb is emphatically discussed. By comparing the Cb value obtained through the two methods, the accuracy of the microscopic method is verified by the heat balance method. The results show that the Cb value is mainly affected by the zonal division and air distribution, but less prominently by exhaust airflow ratio and heat source in the occupied zone.

This research revisited the preparation of the pure titanium dioxide. Through the aerosol-assisted technology and our self-made setup, a kind of titanium dioxide with higher activity than commercial product P25 was successfully fabricated, while this aerosol-assisted process takes only about 10 s. By adjusting the operation temperature, the obtained titanium dioxide nanoparticles have different crystalline sizes and phase compositions, which are two major factors determining the catalytic activity of the materials. The results show that the optimum temperature was 600 °C, and the AST-600 particle prepared under this condition has the rate constant at 1.49 in the removal of methyl orange, which is 2.36 times that of Degussa P25. Although the AST-600 particle could only be activated by UV light similar to P25, the efficiency of AST-600/g-C3N4 is higher than that of P25/g-C3N4 under the visible condition. Meanwhile, the as-prepared titanium dioxide particles have been thoroughly characterized by TEM, SEM, XRD, PL, XPS, DRS, Raman and nitrogen adsorption in the study. Hence, we prepared a pure titanium dioxide with higher catalytic activity than P25, but the process is still very convenient, low cost and easy to scale up, holding great potential as an alternative to commercial product P25.

Friction plug welding (FPW) experiments were performed on 8-mm-thick 2219-T87 FSW welds to investigate the weld formation, microstructure, hardness distribution, mechanical property, and fracture behaviors of FPW joint. The main findings are as follows: geometric size of supporting plate hole and welding force exert great effect on weld formation and mechanical property. Recrystallized zone (RZ) with varied width is observed on the bonding interface between the plug and base metal due to huge friction heat and deformation. Softening is found near the bonding interface due to the disappearance of cold working and transformation of constituent particles. The ultimate tensile strength (UTS) and elongation of FPW joint can reach 336.3MPa and 8%, respectively. The initial fracture of tensile specimen is prone to locate at the lower part of RZ. The tensile fracture morphology of FPW joint is characterized by dimples.

The modified 9Cr–1Mo steel was selected to conduct friction stir welding experiment. Defect-free welded joints were successfully obtained with the welding parameters of 300 rpm–50 mm/min and 400 rpm–50 mm/min. The microstructures of the welded joint were observed by scanning electron microscopy, electron backscatter diffraction and transmission electron microscope. The main microstructural characteristics of the weld zone (WZ) and the high-temperature heat affected zone are the formation of fresh quenched martensite, dissolution of M23C6 carbides, grain refinement and increase in kernel average misorientation. The WZ is significantly hardened, and the maximum hardness of this region is about twice that of the base material (BM). The ultimate tensile strength of the welded joint is up to 98% that of BM. The absorbed impact energies of the SZ and HAZ reach 77.8% and 87.4% that of the BM, respectively. Besides, the influence of post weld heat treatment on the microstructure and mechanical properties of the welded joint was also investigated.

Microstructure and mechanical properties of underwater wet friction taper plug-welded API X52 pipeline steel with 6500–7500-rpm rotational speed at 30–45-kN axial force have been investigated, and the defect-free friction taper plug-welded joints were obtained. It was found that the microstructure in welded joint was remarkably inhomogeneous and very different from the X52 base metal. The weld region could be divided into forged zone (FZ), final frictional plane (FFP), shear deformation zone (SDZ), bonding zone (BZ), and heat-affected zone (HAZ). The HAZ has the coarsest grain and mainly consists of martensite and bainite, and the FZ and SDZ are mainly characterized by a mixture of martensite, bainite, and various shapes of ferrites. The BZ is represented by the banding pattern of fine equi-axed grain ferrites because of local decarbonization around frictional interface in wet welding condition. The axial force has a greater impact on microstructure of welded joint as compared with rotational speed. The hardness profiles measured on cross section of welded joints are severely non-uniform, ranging from 200 to 400 HV1, due to the inhomogeneity of microstructures. The impact absorbed energy of bonding interface sites in welds was considerably lower than that of base metal (about 20% of parent metal) because of the local obviously coarse grain, Widmanstatten ferrites, and banding ferrite defects. The principle of “close mode” friction welding is illustrated, and the microstructural characteristics and mechanical properties of welds can be predicted by judging the type of friction welding.

The present work reports the influence of thermal process on microstructure and mechanical behavior for friction taper plug welding (FTPW) in structural steel S355. The results indicate that there is a significant decrease in total energy input and cooling time in temperature interval from 800 to 500 °C (Δt8/5) with increasing the axial force. However, the varying axial force has little effect on the peak temperature. The microstructure of weld zone contains acicular ferrite, polygonal ferrite, grain boundary allotriomorphic ferrite, and lath bainite. With decreasing total energy input and Δt8/5, the formation of lath bainite is promoted as well as the precipitation and growth of grain boundary allotriomorphic ferrite is inhibited. The hardness tends to increase with decreasing total energy input and Δt8/5. Charpy impact energy at the bonding line is almost 35 J ± 7 J for all specimens. On the other hand, Charpy impact energy at the weld zone increases gradually with decreasing total energy input and Δt8/5.

In the present study, a number of joints were fabricated successfully on DH36 marine steel sheet in underwater wet based on friction taper plug welding (FTPW). The influences of the plug and hole geometry parameters combination on the quality of welded joint forming were first investigated. It was found that tapered holes and plugs were the preferred choice and a suitable cone angle range was obtained. Using the preferred hole and plug designed further expand the range of welding parameters to explore process parameters influence on the welding quality. Bonding mechanism and microstructural evolution to FTP welds were investigated with multiple observations. Mechanical properties of the obtained joints were also evaluated with tensile and Charpy impact tests by reference to AWS D3.6 Underwater Welding Code. The best result is found as the joint welded with 7500 rpm and 40 kN which has 535.6 MPa ultimate tensile strength, 22.5 % elongation, and 42.5 J impact energy at bonding line.

The Q235 and X65 steel tapered plugs were used to perform friction taper plug welding (FTPW) on X65 pipeline steel in underwater wet condition. The work concentrates on defect formation, torque variation, energy input during FTPW, and also the weld microstructures and hardness. Energy input is proportional to torque-time integration under constant rotating speed and is critical to realize metallurgical bonding between the hole and plug. Increasing burn-off can prolong welding time, thus enhancing energy input, so that defect can be eliminated. Using X65 plug can produce defect-free welds since the energy input is adequate. However, when Q235 plug is used, lack of bonding is commonly found as a kind of root defect in friction taper plug (FTP) weld owing to the insufficient energy input. The weld zone microstructure mainly consists of upper bainite in X65 plug weld, but Widmanstatten structure in Q235 weld. In heat-affected zone, the microstructure is found as upper bainite in both X65 and Q235 plug welds.

Fatigue properties of FS welds with a kissing bond (bonded welds) were studied by comparing the test results of bonded welds with those of sound welds. The fatigue life of bonded welds is 21∼43 times shorter than that of sound welds under the stress ratio R = 0.1, and the fatigue characteristic values of each welds have decreased from 100.24 MPa for sound welds to 65.57 MPa for bonded welds at 2 × 106 cycles. At the macroscopic level there is no evidence of failure by shear. The fatigue fracture revealed cracks initiated from the root tip of kissing bond.