This study focuses on a single-stage axial flow fan, investigating the effect of three kinds of wave leading edge stator blades on its noise reduction. The DDES method and the duct acoustic analogy theory based on the...This study focuses on a single-stage axial flow fan, investigating the effect of three kinds of wave leading edge stator blades on its noise reduction. The DDES method and the duct acoustic analogy theory based on the penetrable data surface were used for noise prediction. The results showed that the three kinds of wave leading edge blades were effective in reducing the rotor-stator interaction tonal noise and also have a certain inhibitory effect on broadband noise. The A10W15 stator blade can effectively reduce broadband noise in the frequency range of 2200 - 4200 Hz. When the amplitude is increased to 20, the noise reduction effect is further enhanced. However, when the amplitude is increased to 30, the broadband noise reduction effect is no longer significant. Further research shows that the wave leading edge stator blades can significantly change the pressure fluctuation distribution on the leading edge and suction surface, which control the modal energy distribution. Finally, this paper analyzed multiple factors affecting the broadband noise reduction, such as the noise source cut-off and cut-on effect and correlation. The purpose of this paper is to explore the laws of the influence of wave leading edge blades on the duct noise of real fan, and to reveal its noise control mechanism. .展开更多
Curtain-sided barns with circulation fans above stall are commonly used to house dairy cows in China.Many farms equipped with circulation fans are unable to provide appropriate cooling,especially for the naturally ven...Curtain-sided barns with circulation fans above stall are commonly used to house dairy cows in China.Many farms equipped with circulation fans are unable to provide appropriate cooling,especially for the naturally ventilated shed,which can result in decreasing feed intake and milk production.For alleviating heat stress and improving animal comfort,a system consisting of an air cooler and a 30 m perforated air duct(PAD)was integrated to evenly distribute cooling air.The air was cooled by underground water and delivered to targeted zones above stall bed.The system was evaluated in an open sided dairy barn in Tianjin,China.For the stalls equipped with PAD system,air velocity reached above 1.1 m/s at 0.5 m height plane of the stall space,and was more uniformly distributed.Compared to the stalls equipped with circulation fans,the PAD system lowered air temperature by 1.5℃,and increased relative humidity by 8.1%.On average,Temperature Humidity Index(THI)and Equivalent Temperature Index(ETI)were decreased by 0.5 and 0.6,respectively.After a 15 days’operation of the system,rectal temperatures of the treated dairy cows were significantly lowered.The results also showed that the cows under PADs had a higher milk production.These findings suggest the PAD can be an effective cooling alternative for naturally ventilated dairy barns to alleviate heat stress.展开更多
Due to the large degree of freedom in terms of design and installation, flexible ventilation ducts are commonly used in ventilation systems. However, excessive use of flexible ducts may lead to greater pressure drop a...Due to the large degree of freedom in terms of design and installation, flexible ventilation ducts are commonly used in ventilation systems. However, excessive use of flexible ducts may lead to greater pressure drop and higher energy consumption. This study conducted experimental measurements to characterize the pressure drop in flexible ventilation ducts with different compression ratios and bending angles. This investigation first measured the pressure drop in straight flexible ducts with four compression ratios under various airflow rates. The calculated friction factor for the straight flexible ducts was negatively associated with the compression ratio. Next, the pressure drops in single-bend flexible ducts with various bending angles from 30° to 150° were measured under various airflow rates. The calculated loss coefficient of the bend increased with the bending angle for single-bend flexible ducts. Finally, the influence of the intermediate duct length on the pressure drop across two bends was experimentally investigated. When the length of the intermediate duct was greater than eight times the inner diameter, the pressure drop across a double-bend flexible duct could be calculated from the friction factors and loss coefficients with a relative error less than 1%. The data obtained in this study can be used to calculate the total pressure loss in flexible ventilation ducting systems in buildings.展开更多
文摘This study focuses on a single-stage axial flow fan, investigating the effect of three kinds of wave leading edge stator blades on its noise reduction. The DDES method and the duct acoustic analogy theory based on the penetrable data surface were used for noise prediction. The results showed that the three kinds of wave leading edge blades were effective in reducing the rotor-stator interaction tonal noise and also have a certain inhibitory effect on broadband noise. The A10W15 stator blade can effectively reduce broadband noise in the frequency range of 2200 - 4200 Hz. When the amplitude is increased to 20, the noise reduction effect is further enhanced. However, when the amplitude is increased to 30, the broadband noise reduction effect is no longer significant. Further research shows that the wave leading edge stator blades can significantly change the pressure fluctuation distribution on the leading edge and suction surface, which control the modal energy distribution. Finally, this paper analyzed multiple factors affecting the broadband noise reduction, such as the noise source cut-off and cut-on effect and correlation. The purpose of this paper is to explore the laws of the influence of wave leading edge blades on the duct noise of real fan, and to reveal its noise control mechanism. .
基金This study was funded by National High Technology Research and Development Program(2013AA10230602)China Agricultural Research System(CARS-36).A special thank for all the help from Hailin Dairy Farm,Tianjin,China,where the field evaluation was conducted.
文摘Curtain-sided barns with circulation fans above stall are commonly used to house dairy cows in China.Many farms equipped with circulation fans are unable to provide appropriate cooling,especially for the naturally ventilated shed,which can result in decreasing feed intake and milk production.For alleviating heat stress and improving animal comfort,a system consisting of an air cooler and a 30 m perforated air duct(PAD)was integrated to evenly distribute cooling air.The air was cooled by underground water and delivered to targeted zones above stall bed.The system was evaluated in an open sided dairy barn in Tianjin,China.For the stalls equipped with PAD system,air velocity reached above 1.1 m/s at 0.5 m height plane of the stall space,and was more uniformly distributed.Compared to the stalls equipped with circulation fans,the PAD system lowered air temperature by 1.5℃,and increased relative humidity by 8.1%.On average,Temperature Humidity Index(THI)and Equivalent Temperature Index(ETI)were decreased by 0.5 and 0.6,respectively.After a 15 days’operation of the system,rectal temperatures of the treated dairy cows were significantly lowered.The results also showed that the cows under PADs had a higher milk production.These findings suggest the PAD can be an effective cooling alternative for naturally ventilated dairy barns to alleviate heat stress.
基金This work was partially supported by the Early Career Scheme of Research Grants Council of Hong Kong,China(No.24208518,No.25210419)and the National Natural Science Foundation of China(No.51708474).
文摘Due to the large degree of freedom in terms of design and installation, flexible ventilation ducts are commonly used in ventilation systems. However, excessive use of flexible ducts may lead to greater pressure drop and higher energy consumption. This study conducted experimental measurements to characterize the pressure drop in flexible ventilation ducts with different compression ratios and bending angles. This investigation first measured the pressure drop in straight flexible ducts with four compression ratios under various airflow rates. The calculated friction factor for the straight flexible ducts was negatively associated with the compression ratio. Next, the pressure drops in single-bend flexible ducts with various bending angles from 30° to 150° were measured under various airflow rates. The calculated loss coefficient of the bend increased with the bending angle for single-bend flexible ducts. Finally, the influence of the intermediate duct length on the pressure drop across two bends was experimentally investigated. When the length of the intermediate duct was greater than eight times the inner diameter, the pressure drop across a double-bend flexible duct could be calculated from the friction factors and loss coefficients with a relative error less than 1%. The data obtained in this study can be used to calculate the total pressure loss in flexible ventilation ducting systems in buildings.
