This research explored different types of two-phase flow patterns that influenced heat transfer rate by assessing rectangular two-phase closed thermosyphon (RTPCT) made from glass with the sides of equal length of 25.2 mm, aspect ratio 5 and 20, evaporation temperature of 50, 70, and 90 °C, working substance addition rate of 50% by volume of evaporator, and water inlet temperature at condensation of 20 °C. Upon testing with aspect ratios 5, three flow patterns emerged which were: bubble flow, slug flow and churn flow respectively. As per the aspect ratio 20, four flow patterns were discovered which were: bubble flow, slug flow, churn flow and annular flow, respectively. Aspect ratio 5 pertains characteristic which resulted in a shorter evaporation rate of the RTPCT than that of the aspect ratio 20, thus, a shorter flow distance from the evaporator section to heat releaser was observed. Therefore, flow patterns at aspect ratio 5 exhibited a faster flow velocity than that of the aspect ratio 20. Furthermore, changes of flow pattern to the one that is important for heat transfer rate can be easily achieved. Churn flow was the most important type of the flow for heat transfer, followed by slug flow. Moreover, with aspect ratio 20, annular flow was the most important flow for the heat transfer, followed by churn flow, respectively. Throughout the test, average heat flux as obtained from the aspect ratio 5 were 1.51 and 0.74 kW/m2 which were higher than those of the aspect ratio 20. The highest heat flux at the operating temperature of the evaporator section was 90 °C, which was equivalent to 2.60 and 1.52 kW/m2, respectively.
Mining the lower seams in a sequence of shallow, closely spaced coal seams causes serious air leakage in the upper goaf; this can easily aggravate spontaneous combustion in abandoned coal. Understanding the redevelopment of fractures and the changes in permeability is of great significance for controlling coal spontaneous combustion in the upper goaf. Based on actual conditions at the 22307 working face in the Bulianta coal mine, Particle Flow Code (PFC) and a corresponding physical experiment were used to study the redevelopment of fractures and changes in permeability during lower coal seam mining. The results show that after mining the lower coal seam, the upper and lower goafs become connected and form a new composite goaf. The permeability and the number of fractures in each area of the overlying strata show a pattern of „stability-rapid increase-stability“ as the lower coal seam is mined and the working face advances. Above the central area of goaf, the permeability has changed slightly, while in the open-cut and stop line areas are significant, which formed the main air leakage passage in the composite goaf.
Energy storage technology (EST) is an effectiveway to improve the power quality of renewable energy generation (such as solar energy and wind energy), but a single energy storage system (ESS) is difficult to meet the demand for the safe operation of the grid. According to the structure and operation characteristics of the existing battery/super-capacitor hybrid energy storage system (HESS), a battery/super-capacitor HESS is proposed. The working principle and three working modes (the super-capacitor pre-charging cold stand-by mode, the boost mode and buck mode) of the HESS are analyzed in detail. The state equations of the boost mode and buck mode are derived. The state space average method is used to establish the small signal equivalent model under the buck/boost mode. More-over, the charge and discharge control strategy of the HESS is obtained by combining the voltage closed-loop control. The simulation model is built in Matlab/Simulink to verify the effectiveness of the proposed HESS and its control strategy. The results show that the HESS and its control strategy can ensure the DC bus voltage has good stability and superior anti-interference, and it can simultaneously provide large current, increase the battery life, and improve the technical economy of energy storage.
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