Enshen Long

Solar radiation reflective coating material on building envelopes: Heat transfer analysis and cooling energy saving

Heat transfer through building envelopes constitutes the dominant part of indoor cooling load in summer. Coating building external walls with high reflectivity materials proves to be an effective way to reduce heat gains from solar radiation and save cooling energy consumption accordingly. In this paper, the transient heat transfer model of building external envelopes is established and validated through experiment, to investigate the thermal performance of building walls coated with retro-reflective materials. Moreover, taking an office building in Chengdu as an illustrative example, the cooling energy saving potential of such retro-reflective material coated building is evaluated in summer. The experiment results show that for the building box with retro-reflective coating materials (ru2009=u20090.59), the average indoor air temperature is about 2.4℃ lower than the reference box without coating materials, resulted from decreasing heat absorption of solar radiation for external walls. Furthermore, the illustrative example in Chengdu shows the cooling load can be reduced by about 9.1u2009W/m2, with such retro-reflective coating materials for building external walls, saving 15.2% electricity consumption in a whole summer. The incremental investment for coating can be paid back by 9.1 years for the studied case. Moreover, economic analysis and comparison indicate that such coating material is more applicable to southern cities in China, since the payback period is shorter due to more cooling energy saving for those with hot summer. This work can provide guidance for practical building envelope thermal design.

A Review on the Research of Promoting Biogas Fermentation Efficiency by Mixing

Mixed agitation can significantly improve the efficiency of anaerobic fermentation, which is shown by the remarkable improvement of biogas production and pollutant removal rate, so it has become an indispensable auxiliary process in modern biogas engineering. However, the internal mechanism of how agitation improves the fermentation efficiency is not clear, so it is difficult to find the best agitation form under complex conditions. However, in recent years, more research results have been obtained in this field. The effects of various agitation forms have been continuously verified on different feedstock characteristics under different fermentation and operating conditions, and the mechanism has been gradually clarified. The most important achievement is that in the 1990s it was clear that continuous agitation would impact the fermentation system, so batch agitation is the correct way to improve the fermentation efficiency. Since the 21st century, the latest research has focused on setting the operating parameters of batch agitation. Researchers have made greatly progress in all the aspects of medium, mode, power, speed and duration of agitation, and optimized the mixing scheme. Some studies have also revealed that stirring will affect the temperature field, impurity removal, toxicity accumulation and so on, and the optimal design of mixing scheme should take into account the comprehensive effects of all aspects. In this paper, the main worldwide research achievements in this field made in recent years are reviewed, and the internal mechanism that agitation can improve the anaerobic fermentation efficiency of biogas is clarified to a certain extent, and the suitable agitation forms under certain conditions are suggested.