Identification of crack noises in household refrigerators

The crack noises propagating from a refrigerator disturb residents in a household; however, the reasons behind the mechanisms of such noises have not been identified yet. In this study, the crack noises in modern household refrigerators are identified and their root causes are explored. The appropriate parameters for overall and Fourier analyses are first determined and the noise characteristics of typical household refrigerators under various conditions are presented. Then, a special test rig providing remote control of the subcomponents including the compressor, fan and heater is designed and structural acceleration and sound pressure measurements inside and outside the test rig in a quiet room are performed. The acoustic and vibration measurements are conducted under various conditions by separately controlling each subcomponent. The crack noises in typical household refrigerators are identified and their root causes are explored by using the results of the overall and Fourier analyses. Some solutions to minimize the crack noises in household refrigerators are also summarized.WOS:000346546300025Scopus - Affiliation ID: 60105072Science Citation Index ExpandedQ2ArticleUluslararası işbirliği ile yapılmayan - HAYIRMart2015YÖK - 2014-1

Quantification of the flow noise in household refrigerators

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

Noise Generation in Household Refrigerators: An Experimental Study on fluid Borne Noise

The oscillatory pressure disturbance created by the refrigerant flow through pipes and components is one of the main sources of noise in household refrigerators. This type of excitation is transmitted to the pipes and travels through the structure reaching the cabinet and other parts exposed to the air, where audible airborne sound waves are created. In order to get a better understanding of this type of noise a household refrigerator was especially instrumented with thermocouples, absolute and dynamic pressure transducers and accelerometers. Tests were carried out at different operating conditions, when it was found that the compressor was the main source of excitation, practically affecting the entire refrigeration loop. It was also found that the flow velocity at the outlet of the capillary tube was high enough to induce significant vibrations in the evaporator. Finally, it was found that the entrance of vapor bubbles in the capillary tube produces sporadic and strong excitations. However those excitations do not travel very far along the flow, being attenuated by the condenser and the evaporator, but can nevertheless be transmitted to the pipes. In view of the collected database, comments and suggestions concerning the design of household refrigerators are presented and discussed

An Experimental Study on the Capillary Tube Flow and its Effect on the Acoustic Behavior of Household Refrigerators

Since the beginning of the “artificial” refrigeration era, a great deal of effort has been applied on the development of high efficient systems. The efforts were primarily focused on the compressor, bringing its efficiency to record-high values. Simultaneously, the compressor noise was brought down to almost inaudible levels. As a consequence, sources of noise that were previously unnoticeable became audible and started to play a major role among refrigerator manufacturers. One of those new sources of noise, generally known as fluid borne noise, is now a growing field of interest in engineering. The aim of this work is to study the relationship between the capillary tube flow and the acoustic behavior of household refrigerators by investigating a particular type of fluid borne noise that only occurs during the freezer mode of dual-evaporator appliances, known as fluctuating noise. To this end a household refrigerator was carefully instrumented and firstly tested in a reverberant chamber. Very heavy sound power level oscillations were found, even with the system in thermodynamic steady-state conditions. Acceleration measurements were also taken at the inlet pipe of the evaporator showing that the refrigerant flow in that region is highly pulsating, i.e., that the refrigerant flow pattern at the discharge of the capillary tube is not steady, in contrast to the indications of the thermodynamic readings. Visualizations studies of the flow pattern at the inlet of the capillary tube were also carried out, showing the presence of vapor bubbles – caused by an unbalance between the compressor and capillary tube mass flow rates – for most of the time. A needle valve was then installed in series with the freezer capillary tube in order to increase restriction and match the compressor and the capillary tube mass flow rates. The restriction provided by the optimum pair needle valve-capillary tube was converted into an equivalent I.D. capillary tube. The original freezer capillary tube was replaced by a same length smaller I.D. capillary tube, and another appliance tests were carried out. It was found that the higher restriction capillary tube attenuate the pulsating characteristic of the refrigerant flow, almost averting the disturbing fluctuating noise

Restart Test Design For Inverter Compressors

When a short power cut or electricity failure occurs on an electric supply system, which the household refrigerator is connected to, the suction and discharge pressures of the system become unbalanced, and the compressor exposes to higher loads than rated conditions. If the power recovers very quickly before the pressures get balanced, the compressor may not overcome the load and fails to start up. If the inverter control of the compressor has Class B protection software instead of mechanical overload protector; the inverter software forms a fault signal, cuts the energy through the compressor and waits for a while that provides pressure balancing before the next compressor start up trial. Provided that the compressor starts up, or the inverter control cuts energy by a fault signal, the compressor periodically tries running in an infinite loop. This situation prevents compressor running and cooling of the refrigerator. In order to prevent this, the inverter board and the control software should be controlled at every load condition if it works properly or not. Generally, a standard restart test is done to refrigerators by cutting the electricity off and energizing after a few seconds in order to check if the compressor starts up or a fault signal occurs. This test only checks one load condition and every different suction-discharge pressure value after power cut cannot be simulated that can occur in the field. Simulation of all loads on the refrigerator is a hard situation because providing variable suction-discharge pressure values on the refrigerator system is impossible and waiting for pressure balancing takes a long time for every load condition. For this paper; a compressor restart test is studied without a refrigerator and an array of suction-discharge pressures that can occur against the compressor is determined in case of a short power off-on situation in order to check all load conditions of the refrigerator. The test is carried out by compressor-electronic control pairs on a cooling system simulator. The compressor test results are verified by testing the same compressors on the refrigerator

Non-adiabatic capillary tubes in high efficiency household refrigerator: an experimental study

El tubo capilar con intercambio de calor líquido-succión (CT-LSHX) es un componente ampliamente utilizado en refrigeradores domésticos. Trabajos recientes han indicado que la entrada del tubo capilar era bifásica, aunque condiciones subenfriadas estaban medidas a la salida del condensador. El objetivo de esta tesis doctoral es examinar las condiciones reales a la entrada del tubo capilar de un refrigerador doméstico mediante el uso de un banco de pruebas innovador. Se instalaron tubos transparentes a la salida del condensador y a la entrada del tubo capilar con el fin de visualizar el flujo. La campaña de visualización experimental revela que el flujo a la entrada del tubo capilar era bifásico a pesar de la medición de un cierto subenfriamiento, independientemente de la posición del filtro instalado a la entrada del capilar (horizontal o vertical), la dirección del flujo (hacia arriba o hacia abajo) y la carga de refrigerante. Este estudio demuestra también que el filtro no estaba actuando como un acumulador ya que el nivel de líquido del capilar siempre siguió la entrada del tubo capilar, independientemente de la longitud del tubo capilar dentro del filtro. Se plantearon dos hipótesis para explicar el fenómeno: una condición de no equilibrio del refrigerante y/o un desequilibrio entre el caudal másico del compresor y del capilar, es decir, el sistema estaría equipado con un capilar no bastante restrictivo en comparación con las necesidades del compresor. El condensador original refrigerante-aire fue reemplazado por un condensador refrigerante-agua para evaluar, a partir del balance de calor en el condensador de agua, las condiciones del refrigerante a la salida del condensador y, por lo tanto, a la entrada del tubo capilar. Las mediciones indican un flujo bifásico no equilibrado compuesto de vapor y líquido subenfriados a la entrada del tubo capilar. Para verificar si la presencia de flujo bifásico se debía a un desequilibrio entre el caudal másico del compresor y del capilar, el diseño del banco de prueba se modificó utilizando un diámetro de tubo capilar más pequeño y aumentando la velocidad del compresor. Con esta nueva configuración, se alcanzó a llenar de líquido el filtro y, por lo tanto, tener condiciones exclusivamente líquidas a la entrada del tubo capilar. Se realizó una comparación de prestaciones entre un flujo bifásico y un flujo únicamente líquido a la entrada del capilar. Los resultados revelan que el COP fue mayor cuando la entrada del capilar era sólo líquida.El tub capil·lar amb intercanvi de calor líquid-succió (CT-LSHX) és un component àmpliament utilitzat en refrigeradors domèstics. Treballs recents han indicat que l'entrada del tub capil·lar era bifàsica, encara que condicions sub-refredades estaven mesurades a l'eixida del condensador. L'objectiu d'aquesta tesi doctoral és examinar les condicions reals a l'entrada del tub capil·lar d'un refrigerador domèstic mitjançant l'ús d'un banc de proves innovador. Es van instal·lar tubs transparents a l'eixida del condensador i a l'entrada del tub capil·lar amb la finalitat de visualitzar el flux. La campanya de visualització experimental revela que el flux a l'entrada del tub capil·lar era bifàsic malgrat el mesurament d'un cert sub-refredament, independentment de la posició del filtre instal·lat a l'entrada del capil·lar (horitzontal o vertical), la direcció del flux (cap amunt o cap avall) i la càrrega de refrigerant. Aquest estudi demostra també que el filtre no estava actuant com un acumulador ja que el nivell de líquid del capil·lar sempre va seguir l'entrada del tub capil·lar, independentment de la longitud del tub capil·lar dins del filtre. Es van plantejar dues hipòtesis per a explicar el fenomen: una condició de no equilibri del refrigerant i/o un desequilibri entre el cabal màssic del compressor i del capil·lar, és a dir, el sistema estaria equipat amb un capil·lar no bastant restrictiu en comparació amb les necessitats del compressor. El condensador original refrigerant-aire va ser reemplaçat per un condensador refrigerant-aigua per a avaluar, a partir del balanç de calor en el condensador d'aigua, les condicions del refrigerant a l'eixida del condensador i, per tant, a l'entrada del tub capil·lar. Els mesuraments indiquen un flux bifàsic no equilibrat compost de vapor i líquid sub-refredats a l'entrada del tub capil·lar. Per a verificar si la presència de flux bifàsic es devia a un desequilibri entre el cabal màssic del compressor i del capil·lar, el disseny del banc de prova es va modificar utilitzant un diàmetre de tub capil·lar més xicotet i augmentant la velocitat del compressor. Amb aquesta nova configuració, es va aconseguir omplir de líquid el filtre i, per tant, tindre condicions exclusivament líquides a l'entrada del tub capil·lar. Es va realitzar una comparació de prestacions entre un flux bifàsic i un flux únicament líquid a l'entrada del capil·lar. Els resultats revelen que el COP va ser major quan l'entrada del capil·lar era només líquida.Capillary tube with liquid-to-suction heat exchanger (CT-LSHX) is a component widely used in household refrigerators. Recent works have indicated that even when measuring subcooled conditions at the condenser outlet, the actual capillary tube inlet is two phase-flow. The aim of this PhD thesis is to examine the actual conditions at the capillary tube inlet of a household refrigerator by using an innovative test bench. Transparent tubes were set up at the condenser outlet and capillary tube inlet. The experimental visualisation campaign reveals that the capillary tube inlet was two-phase flow despite the measurement of a certain subcooling, regardless of the filter position (horizontal or vertical), flow direction (upward or downward) and refrigerant charge. This study also demonstrates that the filter was not acting as an accumulator since the liquid level of the capillary always followed the capillary tube entrance, regardless of the capillary tube length inside the filter. Two hypotheses were then posed to explain the phenomenon: a non-equilibrium condition of the refrigerant and/or an unbalanced matching between compressor and capillary tube, that is, the system would be equipped with a capillary tube with a notably large expansion capacity compared to the needs of the compressor. The original refrigerant-to-air condenser was replaced by a refrigerant-to-water condenser to assess, from the heat balance at the water condenser, the refrigerant conditions at the condenser outlet and therefore, at the capillary tube inlet. Measurements indicate a non-equilibrium two-phase flow composed of subcooled vapour and liquid at the capillary tube inlet. To verify if the presence of two-phase flow was due to unbalanced matching between the capillary tube and compressor, the test bench design was modified by using a smaller capillary tube diameter and increasing compressor speed. Fully liquid conditions at the capillary tube inlet were reached with this new configuration. A performance analysis comparison between a capillary tube inlet composed of vapour and liquid and a capillary tube inlet composed of only liquid was also performed. Results reveal that COP were higher in cases of fully liquid conditions at the capillary tube inlet.Bardoulet, LV. (2018). Non-adiabatic capillary tubes in high efficiency household refrigerator: an experimental study [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/113170TESI

Noise reduction in commercial refrigerators - a practical approach

An Adande refrigeration unit originally designed for use in the commercial catering industry was redesigned for use in households. This sector is more sensitive to refrigeration noise, following the introduction of the EU noise labelling directive. A practical noise control ap-proach was taken consisting of benchmarking the existing commercial unit, diagnosing the primary noise sources, redesigning the system components without affecting the refrigera-tion performance and assessing improvements. The aim was to reduce noise emissions and improve sound quality to those of frost free household refrigerators. Value engineering was used to optimise the performance gains such that the new unit suitable for the domestic mar-ket would be also used in the commercial sector. The sound power reduction achieved was greater than 4 dB. The sound quality of both the existing standard refrigerator and the opti-mised prototype unit were evaluated by a jury in a real living environment. The subjective exercise showed that the optimised prototype was perceived as being quieter and of im-proved sound quality compared to the standard refrigerator

Statistical energy analysis model for sound pressure level prediction on refrigerators

The final publication is available at Springer via http://dx.doi.org/10.1007/s40857-020-00188-0A Statistical Energy Analysis (SEA) model of a 510 liter capacity refrigerator is used to calculate the Sound Pressure Level (SPL) generated in a reverberation room. This is a reliable indicator of the vibroacoustic performance of the refrigerator and it is in some countries as a pre-commercialization test. The main contributions of the SEA model are, the characterization of the refrigerator structure (three-layer: HIPS, polyurethane foam and steel), and the modeling of important components such as internal chambers or ventilation gratings. The simulation results are successfully compared with laboratory measurements. The SEA model is then used to understand the vibroacoustic behavior of the refrigerator and to establish the most critical transmission paths and radiation mechanisms.Peer ReviewedPostprint (author's final draft

Non-Condensable Gases and their Effect on the Dynamic Behavior of Domestic Refrigerators

The aim of this work was to experimentally investigate the effect of non-condensable gases on the thermal acoustic behavior of domestic refrigerators under dynamic conditions. To this end, an acrylic made filter dryer was installed in the system for a proper visualization of the refrigerant flow at the capillary inlet. An accelerometer was also installed at the evaporator inlet to capture vibrations/noise signals, caused by the refrigerant pattern at the inlet of the expansion device. During the experiments the energy consumption was measured with the system systematically doped with precise amounts of nitrogen. It has been found that the energy consumption increases by 13%, when a mass fraction of 0.43% of N2 is added to the system. Moreover, it has been found that the energy consumption increases almost linearly with the N2 mass fraction. Pull-down tests were also carried out, showing a clear relationship between the N2 amount and the power and mass flow rate oscillations, soon after the compressor start-up, caused by the unbalance between the compressor and capillary tube mass flow rates. It was also observed that the noise level is higher when liquid refrigerant enters the capillary, thus increasing the corresponding mass flow rate