Graduate Thesis Or Dissertation
 

An experimental study of the acoustical characteristics of dampers in air conditioning systems

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/zw12z8980

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  • The noise problem in air conditioning systems is receiving ever increasing attention because of the importance of noise on a comfortable human environment. Some work has been done on the solutions to the noise problem by an investigation of a few system elements. The acourstical characteristics of dampers become more important with the present tendency to use high air velocity in the air distribution system, but this element has not been investigated. The experimental study presented here concerns the attenuation characteristics of the duct section and damper, and noise generation characteristics of a conventional single -blade damper and two proposed airfoil dampers with solid and perforated surfaces respectively. Air velocity in the duct, degree of damping, size, and damper configuration were chosen as variables for this study. During the performance of this experiment, two important preliminary studies were done on the characteristics of an acoustic plenum chamber and microphone windscreens. Because of the limited fan capacity available, the construction of an acoustic plenum chamber with acceptable performance was necessary. Because of the importance of the wind noise effect on noise measurement, the construction of a satisfactory windscreen was needed. In the study of noise attenuation without air flow, perforated airfoil dampers were found to be most effective in general. But, as the flow damping increases, the effectiveness decreases at high frequencies. At high frequencies, the single -blade dampers were found most effective. Since high frequency noise control is much easier and more inexpensive than low frequency noise control, the airfoil damper is favorable as far as the attenuation without air flow is concerned. The attenuation spectrum did not change much at the middle frequency range regardless of the type of damper, and the degree of flow damping was found to be the most significant variable in changing the attenuation spectrum. The rate of change of attenuation with respect to damper position was not a linear function for any damper. The attenuation for the perforated airfoil damper was not sensitive to changes in damper position or configuration. The results on noise generation showed that increasing the flow damping causes high noise generation. This result was most evident for single -blade dampers. The increase in flow damping made the spectra smoother for all dampers tested. There existed a frequency range where the noise generation was most sensitive to the damper setting. The sound level distribution of the generated noise level was high at low frequency and low at high frequency, so the noise generation results in a problem of low frequency noise control. An increase in air velocity resulted in higher levels of noise generation, but this did not influence noise generation as strongly as the degree of damping. A result of this work showed that it might be possible to improve the acoustical characteristics of dampers by combining desirable property of both solid and perforated airfoil dampers. An airfoil damper with perforated surface on the upstream side and solid surface on the downstream side could show better acoustical properties. Further research on the acoustical properties of other types of dampers and other system elements should be done in the near future. The design criteria necessary to improve the aerodynamic air flow patterns should be a parallel study. Much research will be necessary to provide the engineering profession with the additional information needed to achieve a more comfortable human environment through better air conditioning design.
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file details YunKyungW1968.pdf 2017-08-23 Público Baixar