The airlift external circulation membrane bioreactor (AEC-MBR) is a new MBR consisting of a separated aeration tank and membrane tank with circulating pipes fixed between the two tanks. The circulating pipe is called a H circulating pipe (HCP) because of its shape. With the complex configuration, it was difficult but necessary to master the AEC-MBR's hydraulic characteristics. In this paper, simulation and optimization of the AEC-MBR was performed using computational fluid dynamics. The distance from diffusers to membrane modules, i.e. the height of gas-liquid mixing zone (h m ), and its effect on velocity distribution at membrane surfaces were studied. Additionally, the role of HCP and the effect of HCP's diameter on circulation were simulated and analyzed. The results showed that non-uniformity of cross-flow velocity existed in the flat-plate membrane modules, and the problem could be alleviated by increasing h m to an optimum range (h m /B 0.55; B is total static depth). Also, the low velocity in the boundary layer on the membrane surface was another reason for membrane fouling. The results also suggested that HCP was necessary and it had an optimum diameter to make circulation effective in the AEC-MBR.
The asphalt pavement is exposed to the natural environment, which is affected by Climate change such as temperature, rain, ultraviolet, and other environmental conditions. This study aimed to establish the asphalt binder performance of Yemen so that the asphalt pavement can be designed to resist the distresses of rutting and cracking that occurred due to seasonal temperature changes and rainfall. The first step of determining the binder performance is to establish high and low temperatures, as well as rainfall because the asphalt binder is a temperature and rainfall sensitive viscoelastic material. To study the climatic zoning of asphalt pavement in Yemen, the data of temperature and rainfall in 19 provinces of Yemen in the past 10 years were collected and comprehensively analyzed, and the variations laws of them were analyzed. According to the Chinese approach, the climatic zoning of Yemen's asphalt pavement was divided. The moisture temperature coefficient was introduced, and its probability distribution state was also analyzed. The standard of the moisture temperature coefficient was suggested and the asphalt pavement climate zones based on the moisture temperature coefficient were determined. The results indicated that the main influencing factors of asphalt pavement in Yemen were the temperature rise and rainfall, and the climate zones of asphalt pavement were divided into different zones such as 1-2-1, 2-2-2, 1-2-2, and 3-1-2. According to the principle of equal probability, the moisture temperature coefficient was found to be 18, and the asphalt pavement climate zoning map was drawn. The findings of this study are highly significant and provide valuable decision support for pavement management and improve the transportation system. Doi: 10.28991/cej-2020-03091613 Full Text: PDF
Background: The asphalt binder is considered a temperature-sensitive viscoelastic material. Temperature can cause some common distress of asphalt pavement, such as rutting (permanent deformation), which correlated with high-temperature environments, and thermal cracking, which correlated with low-temperature environments. Objective: This study aimed to establish asphalt binder Performance Grades (PGs) in the Yemeni region to ensure that the asphalt pavement design can effectively resist the distresses of rutting and cracking that occurred due to seasonal temperature changes. Methods: In order to determine the performance grades, the temperature zoning was performed by obtaining the last 10 years temperature data of 19 cities in Yemen gathered by the Yemeni Meteorological Authority. The collected data were analyzed based on the trend and statistical reliability. Three air-pavement temperature prediction models of Superpave, LTPP, and Oman model were used to predict air pavement temperatures. The local performance grades were computed using reliability levels of 50% and 98%. Since the dependent variables of latitude in the Superpave equation can more reflect the geographical locations of Yemeni regions rather than the other models, this study strongly approved the SHARP Superpave model to be used to determine the performance grades. Results: Based on the Superpave model with reliability analyses, performance grade maps were drawn. The most common performance grades recommended in this study for low traffic volume roads were PG64-10, and PG52-10. Conclusion: The findings of this study are highly significant and provide valuable decision support for pavement management and improve the transportation system in the Republic of Yemen.
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