• International Journal of Air-Conditioning and Refrigeration
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• v.17 no.2
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• pp.37-44
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• 2009

It is well known that a refrigerant-induced noise is caused by two-phase flow in the indoor unit of a heat pump air-conditioner. Especially when the flow pattern in a pipe is intermittent flow, the irregular noise occurs frequently. But it is very difficult to avoid this kind of the noise for the application of air-conditioner. Therefore, in this research, the flow patterns at two-phase flow state in a pipe of the indoor unit for the air-conditioner are researched using cycle simulator at typical cycle conditions. In order to find the relationship between refrigerant-induced noise and flow pattern, the noise patterns are investigated with respect to the estimated flow pattern from the various flow pattern maps. Base on the estimations of the flow patterns by those maps, the refrigerant-induced noise is evaluated as decreasing tube diameter, which can transit the flow pattern from slug to annular flow.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.208-211
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• 2006

Flow resistance induced by each element in suction nozzle of a vacuum cleaner with a rotary fan is investigated numerically and its relation with flow-induced noise is examined. Flow resistance and vorticity in suction nozzle are calculated and it is found that they are closely related with flow-induced noise. From numerical results, it is suggested that reduction of flow resistance effectively increases all-suction performance and decreases sound pressure level of noise generated in the suction nozzle.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2632-2637
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• 2007

Rotary performance and flow resistance induced by each element in suction nozzle of a vacuum cleaner with a double-blade rotary fan are investigated numerically and its relation with flow-induced noise and rotary performance is examined. Flow resistance and vorticity in suction nozzle are calculated and it is found that they are closely related with flow-induced noise. Gap between double blades, adoption of cross-flow fan, enlargement of flow inlet area, and optimization of blade number are tested for noise reduction. Finally, the effects of each method are verified experimentally. It is found that several combinations of the proposed methods can be adopted for noise reduction although the degree of reduction is not much.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.935-938
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• 2007

In suction nozzle of a vacuum cleaner, where flow-induced noise is generated mainly by flow resistance, several ideas to reduce noise are investigated. To increase fan performance, blade number is optimized and a centrifugal fan is replaced by a cross-flow fan, In addition, gear ratio of fan to drum brush is changed. It is found that fan performance is increased by adopting these methods. Next, the blade height of the fan is decreased to reduce sound pressure level, which causes inevitably decrease in fan performance. Eventually, flow-induced noise is reduced by 6.3 dBA in its overall level with the fan performance maintained.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.7
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• pp.621-626
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• 2001

The flow induced noise of the cross-flow fan with uniform/random pitch blades is predicted by computational methods. With the time dependent surface pressure data obtained by solving the incompressible Navier-Stokes equations in moving coordinates, the acoustic pressure is predicted by the Ffowcs Williams-Hawkings equation. The positions of the blade noise source are identified through an investigation of the acoustic pressure history induced by one blade, and it is confirmed that the dominant noise source is near the stabilizer. Since the acoustic pressure of the random pitch fan fluctuates according to the blade passin, the dominant BPF noise of the uniform pitch fan is modulated into some reduced discrete noises which have multiples of a 50Hz difference from BPF.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.957-963
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• 2008

The refrigerant-induced noise of the air conditioner is one of the irregular noises which occurs at the indoor unit. Because the air-conditioner makers are always trying to reduce the sound pressure level radiated from indoor unit, reducing the refrigerant-induced noise at low cooling mode is very important problem. But it is very difficult to estimate whether the refrigerant-induced noise occurs or not before it becomes problem. In this paper, a method to predict the refrigerant-induced noise is suggested using flow pattern map. It is estimated that the irregular noise from the refrigerant comes from the slug flow in a pipe.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.78-83
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• 2003

General algorithm is developed for the prediction of internal flow-induced noise. This algorithm is based on the integral formula derived by using the General Green Function, Lighthills acoustic analogy and Curls extension of Lighthills. Novel approach of this algorithm is that the integral formula is so arranged as to predict frequency-domain acoustic signal at any location in a duct by using unsteady flow data in space and time, which can be provided by the Computational Fluid Dynamics Techniques. This semi-analytic model is applied to the prediction of internal aerodynamic noise from a throttle valve in an automotive engine. The predicted noise levels from the throttle valve are compared with actual measurements. This illustrative computation shows that the current method permits generalized predictions of flow noise generated by bluff bodies and turbulence in flow ducts.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.810-815
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• 2003

Flow-induced noise propagated from flow over a sphere is numerically investigated for laminar flow at Re = 300 and 425, and for turbulent flow at Re = 3700 and $10^4$, where the Reynolds number is based on the freestream velocity and the sphere diameter. The numerical method used for obtaining the flow over a sphere is based on an immersed boundary method in a cylindrical coordinate system. The Curle’s solutions of the Lighthill’s acoustic analogy with and without the far-field and compact-source approximation are used in order to investigate the noise field from flow over a sphere. Since the drag and lift forces change irregularly in time at Re = 425, 3700 and $10^{4}$, the noise propagates in a complicated manner. At Re = 300, 425 and $10^{4}$, the noise from dipole sources is much larger than that from quadrupole sources. On the other hand, at Re = 3700, the quadrupole source becomes dominant. The temporal variation of the flow-induced noise around a sphere is obtained at some observation points, which shows that the peak frequency corresponds to the Strouhal number associated with the wake instability.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.3 s.108
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• pp.240-246
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• 2006

In the air-conditioner, refrigerant induced noise and vibration can be increased when the airflow rate is reduced in order to decrease the noise at the low mode. Through the test and analysis of this kind of noise, it can be verified that the main reasons of refrigerant induced noise are the velocity and flow Induced force of the refrigerant at the inlet of the evaporator, So, in order to reduce this velocity, quality at the evaporator inlet should be minimized. And, in order to reduce flow induced force of the refrigerant, sudden change of fluid flow must not be occurred. So, in this paper, we will review the characteristics of refrigerant cycle and find how the quality and flow induced force can be minimized.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.10
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• pp.1012-1020
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• 2009

This research is focused on the experimental study of the noise induced by two-phase refrigerant flow in the evaporator. The two-phase flow in the evaporator has various flow patterns. The effects of two-phase flow pattern's characteristics on the noise of the evaporator are investigated experimentally. The experimental data shows that the generated noise is mainly related to the layout of the pipe and the certain two-phase flow patterns such as the churn and slug flow. Based on these results, we removed the unnecessary vertical pipe and changed the pipe diameter of the evaporator - inlet into small one in order to avoid the intermittent flow condition. The noise level of newly-designed inlet-pipe of the evaporator was measured experimentally by refrigerant-supplying equipment and compared with that of conventional one.