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Analysis of the root causes of refrigerant-induced noise in refrigerators
Abstract and Figures
Refrigerant-induced noises, which occur irregularly at special thermodynamic cycle conditions, are frequently cited by residential
customers who use refrigerators. However, these noises are very difficult to resolve and their root causes cannot usually
be exactly identified. In this research, the root causes of the irregular refrigerant-induced noise are estimated through
the theories of two-phase flow and bubble dynamics. Also, by using refrigerant-supplying equipment that can continuously supply
refrigerant to the test unit at typical cycle conditions, the flow patterns of the evaporator in vertical and horizontal pipes
are inspected and their noises are simultaneously measured. Through the observation of the relationship between the flow pattern
and the refrigerant-induced noise, the root causes of this irregular refrigerant noise can be identified and verified.
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... The strainers installed near the electronic expansion valve (EEV) help convert slug flow into bubble flow, creating a more uniform two-phase flow and thereby reducing noise levels. In evaporator inlets, Han et al. 10,11 found that the transition from intermittent flow to wavy flow and annular flow can lead to reduced flow-induced noise. Removing unnecessary vertical pipes and adjusting mass flux, vapor quality, and pipe diameter could help reduce noise by controlling flow patterns. ...
Refrigerant-induced vibration and noise near thermal expansive valve (TXV) in automobile air conditioning has gradually disturbed the driver and negatively affected the passenger experience. Nevertheless, the effect of environmental thermal load on vibration and noise is unclear and flow pattern identification of refrigeration needs to be accurate but low cost. In this paper, an experimental setup is conducted so as to investigate the effect of thermal load on flow patterns, vibration, and noise near TXV. Both vibration and noise are closely related to the flow pattern conversion during the starting process under different thermal loads. Besides, the vibration characteristics are analyzed on the frequency spectrum at different positions and axes. Increasing thermal load can raise the amplitude of vibration peaks but almost not affect the peak distribution. Finally, according to the connection of time-varying vibration signals and flow patterns, statistical features of triaxial vibration are used to train multilayer perceptron to identify flow patterns in TXV-inlet tube and TXV-outlet tube. The highest average accuracy for all flow patterns is found to be 99.8% (inlet) and 98.2% (outlet) for the test set. Besides, the specific accuracy for each flow pattern is found to be above 99% (inlet) and 96% (outlet), illustrating the model is capable of identifying flow patterns with few samples. The ensemble features of triaxial vibration can more accurately reflect the flow pattern transition compared with single-axis vibration. As seen in the above results, the specific flow patterns inducing larger vibrations can be avoided by adjusting thermodynamic parameters and redesigning refrigeration equipment in future designs.
... The noise was excited by pressure pulses arising in intermittent flow and strongly correlated with the vapor velocity of two-phase flow during the nonintermittent flow. Han et al. [29][30][31] found that the intermittent flow and slug flow led to the irregular refrigerant-induced noise in the condenser outlet tube and evaporator inlet tube. The horizontal tube, small inner diameter tube, and additional strainer were applied to reduce the noise by prompting the transition from intermittent flow to other steady flow patterns. ...
In recent years, the flow-induced vibration and noise in automotive refrigerant system gradually become the main factor affecting driving comfort. However, the relationship of flow pattern, vibration, and noise is not clear, and pattern identification is not easy but necessary. In this paper, a series of experiments are conducted to investigate the relationship of flow pattern, flow-induce vibration, and noise near the thermal expansion valve in an automobile refrigerant system. The flow pattern, vibration, and noise are closely related to startup processes. Mist flow, which contains more mist two-phase mixture than transition flow and wispy-annular flow, leads to the largest amplitude of vibration and strong broadband hiss noise. Moreover, the increase in compressor speed promotes the pattern transition and the vibration amplitude in time domain but has no effect on the distribution of vibration peaks in frequency spectrum. Finally, a short-time Fourier transform and convolutional neural network combined method for flow pattern identification is developed based on the relationship of flow pattern and flow-induced noise. After using transfer learning and data augmentation, four trained network architectures show relatively high accuracy above 94% for test set. Among them, ResNet34 not only has the highest accuracy of 98.8% but also can recognize each type of flow pattern. The generalization of this method can help engineers to recognize flow patterns in air conditioning without flow visualization but only need to measure sound signals.
... They determined that intermittent flow produces fluctuating non-stationary noise due to pressure pulses, whereas in nonintermittent flow, uniform noise is associated with vapor velocity in two-phase flows. Hartmann and Melo 28 and Han et al. 29 independently verified that noise within capillary tubes originates from the presence of bubbles and flow non-uniformities. As noted above, while studies on the generation of noise by single and multiphase flows have been conducted extensively, there is still a lack of systematic research on the occurrence and variation of noise, particularly regarding multiphase flows and flow patterns. ...
This study investigates the numerical exploration of acoustic noise generated by different flow patterns within a horizontal circular pipe, employing validated numerical methods such as large eddy simulation, continuous surface model, and the Ffowcs Williams–Hawkings acoustic model for simulating a complex three-dimensional multiphase fluid flow and acoustic noise. The research mainly focuses on the significant influence of flow patterns on acoustic noise generation through detailed analyses of pressure, velocity, and turbulent kinetic energy across three distinct source regions within the flow. Three flow patterns are examined. The stratified flow is characterized by the complete segregation of the two phases. The plug flow is defined by large, elongated bubbles typically moving in the axial direction with a periodic nature. The slug flow is characterized by the rapid formation of large, elongated gas bubbles separated by liquid phases. In the stratified flow, noise generation primarily stems from pressure fluctuations near phase interfaces. Plug flow exhibits noise due to bubble–surface interactions, particularly near the outlet. Slug flow generates noise from interactions between liquid waves and the pipe surface. Comparing sound pressure levels across flow patterns reveals higher noise levels in the plug and slug flows compared to the stratified flow, attributed to their disruptive nature. Total sound pressure level analysis indicates slug flow as the highest noise producer, highlighting phenomena such as interface breaking. The present study will contribute to effective mitigation strategies in engineering applications by providing an understanding of flow dynamics and noise generation mechanisms.
... kHz, the two-phase flow of refrigerant causes the noise is reduced by about 25 dB. Based on the twophase flow theory, Han et al. 22 found that one of the reasons for inducing the irregular noise of refrigerant is the existence of two-phase flow. He et al. 23 studied the noise spectrum characteristics of hydraulic press by wavelet transform. ...
Electronic expansion valves are widely used in refrigeration systems. However, the two-phase flow-induced noise is often produced during operation. In this paper, the two-phase flow-induced noise characteristics of electronic expansion valves are investigated by means of a combination of numerical calculations and experimental studies. The numerical results show that the noise distribution in the flow field is closely related to the valve opening. As the valve opening increases, the noise in the flow field begins to develop in the downstream region. The experimental results showed a gradual increase in the refrigerant flow rate of the experimental system as the valve opening was increased from 60 to 200 pulses (tested at 10-pulse intervals). The flow-induced noise increases first and then decreases and then increases. With the increase in valve opening, the cavitation phenomenon after valve throttling becomes more and more serious. By processing the noise signal, it is found that the flow-induced noise is distributed in wide frequency. When the valve opening is 60–100 pulse, the noise is mainly concentrated in 10–20 kHz. When the valve opening is 110–150 pulses, the noise concentrated in the high band gradually spreads to the low band. When the valve opening is 160–200 pulses, the noise at low frequency and high frequency increases significantly with the increase in valve opening. After adding a groove structure on the valve core, the noise of the electronic expansion valve decreased by 1.75 dB.
The refrigerant flowing through an electronic expansion valve (EEV) of a multi-split air conditioner is usually in two-phase state which may generate more severe flow noise than that in sub-cooled state. The purpose of this paper is to experimentally investigate the influences of the two-phase R410A operation conditions on the flow noise characteristics in the EEV, including listening sense forms, frequency distributions and sound pressure levels (SPLs). The experimental conditions cover the refrigerant mass flow rate ranging from 30 to 90 kg h–1 and the refrigerant quality ranging from 0.02 to 0.4. The results show that low mass flow rate facilitates the reduction of noise frequency, and the peak noise frequency was reduced by up to 32% as the mass flow rate decreased. Low refrigerant quality helps to reduce the SPL of flow noise, and the average SPL decreased by 6 dB as the refrigerant quality decreased. The guidance of inlet flow pattern by transforming the churn flow to the annular flow helps to simultaneously reduce the noise frequency and SPL, and the peak noise frequency as well as the averaged SPL decreased by 47% and 4 dB, respectively. Moreover, the hissing noise and the gurgling noise are the only two kinds of listening sense forms of flow noise detected in the present experiment, and the peak frequency and the average SPL of hissing noise are both higher than those of gurgling noise.
Presently, from the viewpoint of comfort in air conditioning, noise reduction is being a matter of importance. This study focuses on the problem of noise in indoor air conditioners caused by the refrigerant flowing through the expansion valve. We investigated a method by which to reduce the low-frequency intermittent flow noise. It is supposed that this intermittent flow noise is related to the flow pattern of the refrigerant through the expansion valve. We carried out an experimental investigation to establish a correlation between flow pattern of refrigerant and consequent noise. It is shown that the noise is reduced if the flow of refrigerant at the inlet area of the expansion valve is made continuous both in gas and liquid phases.
Presently, in our quest to develop low-noise air conditioning equipment, it is important to reduce the refrigerant flow noise. To date, this problem has been investigated on the basis of trial and error. Fundamental cause and mechanism of the flow noise must be analyzed before a drastic reduction of noise can be achieved. In this study, air-water two-phase flow was used to create a slug flow with single large gas bubble for the purpose of modeling the problem. We investigated the relations among gas bubble state, static pressure pulsation and flow noise caused by single gas bubble passing through the orifice, In the results, it is shown that the noise level increases twice while the gas bubble passes through the orifice and that there exist correlations among flow state, static pressure pulsation and flow noise.
Noise problems caused by two-phase flows in tubes connected to air-cooled heat exchangers have become more serious, since the level of air conditioner fan noise has decreased. In particular, when a slug flow occurs, the noise level greatly increases. In this study, an air-water two-phase flow was used to create a slug flow through a capillary tube in order to investigate the mechanism of the noise. We also investigated the relationship between the gas bubble state and the pressure pulsation by changing the void fraction. The results show that the pressure pulsation level, which is proportional to the noise level, is determined by the magnitude and the density of the impact pressure pulsation caused by the expansion of the gas at the end of the capillary tube.
Gas bubbles, when entrained in water or other liquid, can generate high sound pressures in the liquid. Significant sound pressures are associated only with volume pulsations of the bubble, whereas oscillations in the shape of the bubble do not result in appreciable sound. Calculations have been made of the sound pressures resulting from excitation of volume pulsations by the following mechanisms: by bubble formation,coalescence, or division; by the motion of a free stream of liquid containing entrained bubbles past an obstacle; and by the flow of liquid containing entrained bubbles through a pipe past a constriction. The calculation of the sound pressuregenerated by bubble formation has been verified by measurements with bubbles formed at a nozzle.
Transitions for vertical upflow of gas-liquid systems are modeled. A
method for predicting transitions is soundly based on the results of the
work. With the initial conceptual studies of the transient flow regime
behavior complete in this report, it will be possible to write computer
programs to explore the ideas in the second report of the study.
Two‐phase gas‐liquid flow has been investigated in a 1‐inch internal diameter vertical tube coil containing two risers and a downcomer all connected by “U” bends. Flow pattern data were obtained in the three vertical tubes, each 17.30 ft. long, for five different air‐liquid systems at about 25 psia over flow ranges of 0–700 lb m air/min‐ft ² and 140–25300 lb m liquid/min‐ft ² . Liquid phase viscosities ranged from 1 to 12 cp.
A flow pattern classification with six regimes including coring‐bubble, bubbly‐slug, falling film, falling bubbly‐film, froth and annular flow regimes was established for downflow. Flow patterns in the bends were also classified.
Data from the present investigation were used to formulate an empirical flow pattern graphical correlation for both upflow and downflow which is based upon the coordinates (R v ) 1/2 and Fr TP /A, where R v is the delivered gas‐to‐liquid volume ratio, Fr TP is the mixture Froude number, and A = μ s /(S L σ s ³ ) 1/4 in which μ s , S L , σ s are specific viscosity, specific density and specific surface tension respectively of the liquid with reference to water. The correlation was satisfactorily tested with independent literature data for upflow systems, including air‐water, steam‐water at various pressures, nitrogen‐mercury and air‐heptane, and data from flowing gas‐oil wells. No independent literature data appear to be available for testing the correlation for downflow systems, but it is anticipated that the correlation will prove to be generally applicable.
The coring phenomenon in downward bubble flow was examined by means of high speed motion photography and is explained by the development of a lift force on a bubble.
Study of Noise Reduction of Refrigerant for Capillary Tube in the Refrigerator, 32nd Conference Journal of Refrigeration and Air-Conditioning Association
- S Hirakuni
- Y Smida
- H Yamamoto
- S. Hirakuni
S. Hirakuni, Y. Smida and H. Yamamoto, Study of
Noise Reduction of Refrigerant for Capillary Tube
in the Refrigerator, 32nd Conference Journal of Refrigeration and Air-Conditioning Association. 4
(1998) 22-24.