Traditional static anaerobic digestion technology presents the disadvantages of a low gas production rate and long digestion cycle, which is not conducive to the treatment of livestock manure. A 12 m3 multiphase flow anaerobic digester (MFD) was developed in this study to improve the biogas production rate and maintain constant temperature digestion during winters. Full-scale field experiments were conducted on the biogas production rate at different temperatures, the dynamic digestion effects, and the dynamic heating digestion effects of the system at Sichuan, China. A comparison of the dynamic and static digestion results of 50 days indicated that the biogas production for the dynamic digestion (DD) group was 115.22 m3 or 127.1% higher than that of the static digestion (SD) group with the same digestion temperature. The results of the heat transfer performance experiment revealed that the heat transfer rate of the system increased significantly, and the temperature of the biogas slurry increased rapidly. The optimization analysis of the system was based on the experimental results of the relationship between the slurry temperature and biogas production rate, and the economical digestion temperature of the system was proposed and calculated. Different insulation materials or insulation thicknesses have an influence on the economical digestion temperature. Additionally, the economical digestion temperature of the system in which the polystyrene insulation layer with a thickness of 90 mm was used, was found to be 27.2 °C. When digestion temperature was 22.3 °C, the energy efficiency ratio (EER) of dynamic anaerobic digestion system is 1. The advantages of MFD are low biogas production unit cost and high heat and mass transfer rate. However, the disadvantage of high operation energy consumption needs further improvement. And additional energy was required when system digestion temperature below 22.3 °C. The proposed MFD and dynamic anaerobic digestion system can play a significant role in using biomass resources and promoting the development of biogas projects.
The heating system combining solar air collector with hollow ventilated interior wall (SAC-HVIW) can effectively extend the heating time. However, due to the large wall-window ratio of buildings on Tibetan Plateau, the strong solar radiation irradiating on the interior wall may influence the thermal performance of HVIW. In this paper, an experimental room is constructed to study the influence of external solar heat gain on the thermal performance of HVIW. Steady-state measurements are carried out by considering different ventilation rates, supply air temperatures and heat gains. Results show that the external heat gain has almost no effect on U-value, but it increases the heating capacity by increasing the logarithmic mean temperature difference (LMTD). For all cases, the heating capacity of HVIW is related to LMTD and supply air velocity, and U-value mainly increases with supply air velocity. Heat transfer of the interior surface of HVIW is dominated by forced convection which increases linearly with supply air velocity. The radiant heat transfer coefficient of the exterior surface of HVIW is not affected by the external heat gain with the mean value of 5.65W/(m2.K), while the convective heat transfer coefficient increases logarithmically with the external heat gain. The proportion of radiant heat transfer decreases as a power function with the increase of the exterior surface temperature. Measurements in this paper are used to evaluate the influence of external heat gain on the heating performance of HVIW, which is beneficial to the design of HVIW.
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