The flow noise in household refrigerators is quantified in this study. First, the sound pressure measurements in a quiet room using typical household refrigerators are conducted and the noise characteristics of the refrigerators are presented. Then, the flow noise in household refrigerators is quantified using the results of the overall analysis and Fourier transform of the measured sound pressure data. After that, the flow noise in household refrigerators is quantified using the sound pressure measurements conducted using a specially designed test rig. The frequency characteristics of the flow noise in household refrigerators are also explored and the contribution of the flow noise is identified

Ahmet Arisoy

Hasan Koruk

Necati Bilgin

English

Journal of Vibroengineering

  © JVE INTERNATIONAL LTD. JOURNAL OF VIBROENGINEERING. NOV 2014, VOLUME 16, ISSUE 7. ISSN 1392-8716 3557 
1441. Quantification of the flow noise in household 
refrigerators 
Hasan Koruk1, Ahmet Arisoy2, Necati Bilgin3 
1MEF University, Mechanical Engineering Department, Istanbul, 34396, Turkey 
2Istanbul Technical University, Mechanical Engineering Department, Istanbul, 34437, Turkey 
3INDESIT Company, Manisa, 45030, Turkey 
1Corresponding author 
E-mail: 1hasan.koruk@mef.edu.tr, 2arisoyah@itu.edu.tr, 3necati.bilgin@indesit.com 
(Received 22 July 2014; received in revised form 8 September 2014; accepted 13 September 2014) 
Abstract. The flow noise in household refrigerators is quantified in this study. First, the sound 
pressure measurements in a quiet room using typical household refrigerators are conducted and 
the noise characteristics of the refrigerators are presented. Then, the flow noise in household 
refrigerators is quantified using the results of the overall analysis and Fourier transform of the 
measured sound pressure data. After that, the flow noise in household refrigerators is quantified 
using the sound pressure measurements conducted using a specially designed test rig. The 
frequency characteristics of the flow noise in household refrigerators are also explored and the 
contribution of the flow noise is identified. 
Keywords: flow noise, household refrigerator, overall analysis, frequency characteristics. 
1. Introduction 
Refrigerators operate all day and propagate noise [1-4]. Most of the inhabitants are annoyed 
by refrigerator noise [3-4]. It should be noted that there are different sound sources including the 
compressor, fan and flow noises in household refrigerators [4-7]. However, identification and 
quantification of the flow noise in household refrigerators is difficult as it is not easy to distinguish 
the flow noise from other sound sources in refrigerators. Furthermore, the flow noise in 
refrigerators may be relatively high and such noises may affect the sound quality of the product 
[8-9]. Especially, during sleeping hours, the noise propagated by a refrigerator could be very 
annoying because of the decrease of the background noise at night. Therefore, there is a need for 
the quantification of the flow noise in household refrigerators. 
There have been some studies on the root causes of the flow noise in the literature [10-13]. 
The shapes and layouts of the capillary tube, evaporator inlet pipe, capillary outlet pipe and the 
outlet section of the heat exchanger as well as the speed and type of the refrigerant affect the flow 
noise [10-13]. In this case study, the flow noise of a modern household refrigerator is quantified 
via an effective experimental approach. First, the sound pressure measurements in a quiet room 
(representing a kitchen of a typical house) using the sample household refrigerator are conducted 
and the noise characteristics of this typical household refrigerator are presented. Then, the flow 
noise in the refrigerator is quantified using the results of the overall analysis and Fourier transform 
of the measured sound pressure data. After that, the flow noise in the household refrigerator is 
quantified using the results of the sound pressure measurements conducted using a specially 
designed test rig. The frequency characteristics of the flow noise in the refrigerator are also 
explored and the contribution of the flow noise is identified.  
2. Methodology 
The schematic of the experimental test setup used to present the noise characteristics of 
household refrigerators and quantify the flow noise is shown in Fig. 1(a) where ݌ଵ and ݌ଶ are the 
sound pressures measured inside and outside the refrigerator, respectively. The distances of the 
microphone ݌ଶ  from the refrigerator and the ground are 30 and 70 cm, respectively. A quiet 
acoustic space is created by placing some panels whose inner surfaces are covered by sound 
1441. QUANTIFICATION OF THE FLOW NOISE IN HOUSEHOLD REFRIGERATORS.  
HASAN KORUK, AHMET ARISOY, NECATI BILGIN 
3558 © JVE INTERNATIONAL LTD. JOURNAL OF VIBROENGINEERING. NOV 2014, VOLUME 16, ISSUE 7. ISSN 1392-8716  
absorbing materials around the test refrigerator. The properties of the refrigerator under 
investigation are listed in Table 1. The sound pressure measurements are performed after the test 
refrigerator reaches to the steady state conditions (i.e., after the refrigerator operates for  
ݐ = 24 hours). A special test rig providing remote control of the subcomponent including the 
compressor and fan is also designed to quantify the flow noise in household refrigerators. The 
unnecessary components creating difficulty to identify the flow noise are excluded from the test 
rig. Overall, the test rig includes mainly half of the refrigerator airframe, compressor, fan, heater, 
evaporator and cooling pipes. The schematic of the test rig is shown in Fig. 1(b) where ݌ଵ and ݌ଶ 
are the sound pressures measured inside and outside the cabinet, respectively. The temperature ܶ 
on the surface of the inner panel is also measured. 
 
a) 
 
b) 
Fig. 1. The schematics of a) the household test refrigerator and b) the designed test rig 
Table 1. Properties of the household refrigerator under investigation. 
Dimensions Main Functions Volume Performance 
Height (mm): 1900 Cooling system: No-frost Total (lt): 475 Energy efficiency class: A+ 
Width (mm): 700  Super cooling function: + Cooler (lt): 360 Season class: T  
Depth (mm): 750 Super freezing function: + Freezer (lt): 115 Freezing capacity (kg/24 h): 6 
The sound pressure signals are first recorded with a high sampling rate ( ௦݂ = 32.8 kHz) and 
then the overall and Fourier analyses of the signals are performed [14-16]. The overall value of a 
time-domain sound pressure signal based on exponential averaging (with time weighting ߬) at any 
time ݐ is determined as follows: 
݌ఛሺݐሻ = ඩ
1
߬ න ݌
ଶሺߞሻ݁ିሺ௧ି఍ሻ ఛ⁄ ݀ߞ
௧
ିஶ
, (1)
where ݌ఛሺݐሻ  is the instantaneous time varying sound pressure and ߞ  is a dummy variable of 
integration. The overall sound pressure level for a given ߬ value as a function of time ݐ is finally 
determined as follows: 
ܮ௣,ఛሺݐሻ = 10log ቈ
݌ఛଶሺݐሻ
݌଴ଶ
቉, (2)
where ݌଴ = 20 μPa is the value of the reference sound pressure. The Fourier Transform (FT) of 
the time domain ݌ሺݐሻ signal is conducted as follows [16]: 
ܲሺ݂ሻ = ܨܶሾ݌ሺݐሻሿ = න ݁ି௝ଶగ௙௧
ஶ
ିஶ
݌ሺݐሻ݀ݐ, (3)
1441. QUANTIFICATION OF THE FLOW NOISE IN HOUSEHOLD REFRIGERATORS.  
HASAN KORUK, AHMET ARISOY, NECATI BILGIN 
 © JVE INTERNATIONAL LTD. JOURNAL OF VIBROENGINEERING. NOV 2014, VOLUME 16, ISSUE 7. ISSN 1392-8716 3559 
where ݂ represents the frequency and ݆ = √−1. The overall analyses are conducted with ߬ = 1/4 s 
and the FT signal processing parameters are ∆݂ = 4 Hz and averaging time ݐ = 0.5 s (the overlap 
is 66.7 % and the number of averages is 6) in this study. The frequency range is selected to be 
quite wide (i.e., ݂ = 1 Hz-12.8 kHz).  
Overall, the main objectives of this study are as follows: 1) Present the characteristics of typical 
household refrigerators; 2) quantify the flow noise in household refrigerators; 3) quantify the flow 
noise using the designed test rig; 4) explore the frequency characteristics of the flow noise; and 
5) identify the contribution of the flow noise in household refrigerators. 
3. Noise characteristics of household refrigerators 
Here, the temperatures of the freezer and cooler of the test refrigerator are set as ܶ = –22°C 
and ܶ = +4°C, respectively. The overall sound pressure levels ܮ௣ for a duration of ݐ = 12000 s 
(or 3 hours 20 minutes) are plotted in Fig. 2. One of the cycles of the refrigerator operation in 
Fig. 2 (i.e, the data from ݐ = 2880 to 3600 s) is re-produced in Fig. 3. The FT of the data in Fig. 3 
is also plotted in Fig. 4. 
 
Fig. 2. Overall sound pressure levels measured inside (݌ଵ) and outside (݌ଶ) the refrigerator 
 
Fig. 3. Overall sound pressure levels measured inside (݌ଵ) and outside (݌ଶ) the refrigerator  
for one cycle of the refrigerator operation 
It is seen that there are mainly four regions labelled as A, B, C and D in Fig. 3. The region A 
corresponds to the background noise where ܮ௣ ≈ 18 dBA. The compressor and fan are on in the 
region B and the measured sound pressure levels are quite high in this region (i.e., ܮ௣ଵ,஻ > 60 dBA 
and ܮ௣ଶ,஻ > 40 dBA). The fan is off and the compressor operates with a small power to provide 
the flow circulation of the refrigerant in the region C. Therefore, the flow noise is dominant in the 
region C. Specifically; there are some crack noises in the region D, which is outside the scope of 
1441. QUANTIFICATION OF THE FLOW NOISE IN HOUSEHOLD REFRIGERATORS.  
HASAN KORUK, AHMET ARISOY, NECATI BILGIN 
3560 © JVE INTERNATIONAL LTD. JOURNAL OF VIBROENGINEERING. NOV 2014, VOLUME 16, ISSUE 7. ISSN 1392-8716  
this paper. The results in Figs. 3-4 show that the sound pressure levels in the region C are lower 
than those in the region B and higher than those in the region A. 
 
a) 
 
b) 
Fig. 4. The FT results of the data measured inside – ݌ଵ a) and outside – ݌ଶ b) the refrigerator  
for one cycle of the refrigerator operation 
4. Quantification of the flow noise in household refrigerators 
 
Fig. 5. Overall sound pressure levels measured inside (݌ଵ) and outside (݌ଶ) the refrigerator 
 
Fig. 6. The FT results of the data measured inside (݌ଵ) and outside (݌ଶ) the refrigerator  
for the region B where the compressor and fan are on 
The region where the flow noise is dominant in Figs. 3-4 (i.e, the data for ݐ = 3340-3520 s) is 
re-produced in Fig. 5. It is seen that the sound pressure levels are about ܮ௣ଵ,஻ = 62 dBA and 
1441. QUANTIFICATION OF THE FLOW NOISE IN HOUSEHOLD REFRIGERATORS.  
HASAN KORUK, AHMET ARISOY, NECATI BILGIN 
 © JVE INTERNATIONAL LTD. JOURNAL OF VIBROENGINEERING. NOV 2014, VOLUME 16, ISSUE 7. ISSN 1392-8716 3561 
ܮ௣ଶ,஻ = 40 dBA for the region B and ܮ௣ଵ,஼ = 40 dBA and ܮ௣ଶ,஼ = 28 dBA for the region C. It 
should be noted that the background noise is about 20 dBA. It is seen that the sound pressure 
levels when the compressor and fan are on (the region B) are at least 10 dB greater than those 
where the flow noise is dominant (the region C).  
The FT of the data in the region B in Fig. 5 is plotted in Fig. 6. As seen, the sound pressure 
levels are higher at some specific frequencies (corresponding to the compressor and fan rotating 
speeds) as expected. The FT of the data in the region C in Fig. 5 together with background noise 
are also plotted in Fig. 7. It is seen in Fig. 7 that the flow noise is dominant for a wide frequency 
range; specifically the sound pressure levels being high between ݂ = 100-500 Hz and  
݂ = 2-4 kHz.  
 
Fig. 7. The FT results of the data measured inside (݌ଵ) and outside (݌ଶ) the refrigerator  
for the region C where the flow noise is dominant and the background noises measured inside (݌ଵ,஻ீ)  
and outside (݌ଶ,஻ீ) the refrigerator 
5. Quantification of the flow noise using the special test rig 
The compressor and fan in the designed test rig in Fig. 1(b) are first operated for a while and 
they are then off; this repeats three times. The scenario of the test is presented in Table 2. The 
temperature and sound pressure levels for this scenario are plotted in Fig. 8. It is seen that the 
temperature varies between ܶ = –35°C and –15°C. As seen, the test rig including the 
measurements system and acoustic room is quite repeatable. One of the cycles in Fig. 8 (i.e., the 
data for ݐ = 2640-3600 s) is re-produced in Fig. 9. The FT of the region where the flow noise is 
dominant (i.e., the region C) is also plotted in Fig. 10. It is seen that the overall sound pressure 
levels and the frequency spectrums of the sound pressure data obtained here are quite similar for 
those obtained using the household refrigerator presented in Section 4. 
Table 2. Scenario of the experiment conducted using the designed test rig 
ݐ (s) Compressor Fan 
0-240 On On 
240-1560 Off Off 
1560-2160 On On 
2160-2760 Off Off 
2760-3360 On On 
3360-3600 Off Off 
The results in Fig. 9 show that the sound pressure levels are about ܮ௣ଵ,஻ =  60 dBA and  
ܮ௣ଶ,஻ = 50 dBA for the region B. The sound pressure levels vary from ܮ௣ଵ,஼ = 40 to 50 dBA and 
ܮ௣ଶ,஼ = 25 to 40 dBA in the region C. It is seen that the flow noise is at least 10 dB lower than 
those for the region B. It is also seen in Fig. 10 that the flow noise is dominant for a wide frequency 
range; specifically the noise magnitudes being high between ݂ = 100-500 Hz and ݂ = 2-4 kHz as 
1441. QUANTIFICATION OF THE FLOW NOISE IN HOUSEHOLD REFRIGERATORS.  
HASAN KORUK, AHMET ARISOY, NECATI BILGIN 
3562 © JVE INTERNATIONAL LTD. JOURNAL OF VIBROENGINEERING. NOV 2014, VOLUME 16, ISSUE 7. ISSN 1392-8716  
similar to the results presented in Section 4. 
 
Fig. 8. The temperature (ܶ) measured on the surface of the inner panel and overall sound pressure levels 
measured inside (݌ଵ) and outside (݌ଶ) the test rig. 
 
Fig. 9. Overall sound pressure levels measured inside (݌ଵ) and outside (݌ଶ) the test rig 
 
Fig. 10. The FT results of the data measured inside (݌ଵ) and outside (݌ଶ) the refrigerator  
for the region C and the background noises measured inside (݌ଵ,஻ீ) and outside (݌ଶ,஻ீ) the test rig 
1441. QUANTIFICATION OF THE FLOW NOISE IN HOUSEHOLD REFRIGERATORS.  
HASAN KORUK, AHMET ARISOY, NECATI BILGIN 
 © JVE INTERNATIONAL LTD. JOURNAL OF VIBROENGINEERING. NOV 2014, VOLUME 16, ISSUE 7. ISSN 1392-8716 3563 
6. Conclusions 
The flow noise in a typical household refrigerator is quantified in this case study. Specific 
contributions of this paper include the following. The noise characteristics of the refrigerator are 
presented and the flow noise in the household refrigerator is quantified using the results of the 
overall and Fourier transform of the measured sound pressure data. The flow noise in the sample 
household refrigerator is also quantified using the sound pressure measurements conducted by 
using a specially designed test rig. The frequency characteristics of the flow noise are explored 
and the contribution of the flow noise is identified.  
The results show that the flow noise is dominant for a wide frequency range; the noise 
magnitudes are specifically high between 100-500 Hz and 2-4 kHz. However, the contribution of 
the flow noise compared to the compressor and fan noises is negligible. Similar noise 
characteristics are obtained using both the designed test rig and the household refrigerator. It 
should be noted that the results presented in this study are obtained for a sample case. It can be 
considered that piping system of the sample refrigerator is designed properly.  
Acknowledgements 
The authors would like to thank to Indesit Company for supporting this study. The authors also 
specifically thank to Mechanical Engineer Onur Akaydin from Pro-Plan Ltd., Mechanical 
Engineer Murat Alparslan and Prof. H. Temel Belek from EDA Ltd. for their assistance. 
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1441. QUANTIFICATION OF THE FLOW NOISE IN HOUSEHOLD REFRIGERATORS.  
HASAN KORUK, AHMET ARISOY, NECATI BILGIN 
3564 © JVE INTERNATIONAL LTD. JOURNAL OF VIBROENGINEERING. NOV 2014, VOLUME 16, ISSUE 7. ISSN 1392-8716  
 
Hasan Koruk received Ph.D. degree in Mechanical Engineering Programme, Graduate 
School of Science Engineering and Technology from Istanbul Technical University, 
Istanbul, Turkey, in 2013. Now he works as an Assistant Professor at Mechanical 
Engineering Department, MEF University, Istanbul, Turkey. His current research interests 
include acoustics and noise control, mechanical vibrations, modal testing, finite element 
method, signal processing and vibration damping. 
 
Ahmet Arisoy received Ph.D. degree from Istanbul Technical University (ITU), Istanbul, 
Turkey, in 1979. He works as a faculty member at ITU Mechanical Engineering 
Department. He has worked mainly on the combustion, heat transfer, fluid mechanics and 
the HVAC area.   
 
Necati Bilgin received M.Sc. degree in Mechanical Engineering Department from Izmir 
Institute of Technology, İzmir, İstanbul, in 2010. He works as R&D Engineer at Indesit 
Company, Manisa, Turkey. His research interests are heat transfer, refrigeration cycle and 
electronic cooling 
 


Quantification of the flow noise in household refrigerators

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Quantification of the flow noise in household refrigerators

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