Analysis of Vibration Isolators for Hermetic Compressors

Nowadays, the customers of refrigerators and freezers have become more exigent in respect to the acoustic comfort of these home appliances. Among the noise sources, there are the refrigerant flow, the fans and the compressors. The compressors might be responsible for a part of the cabinet low frequency noise which could be generated either by the gas pulsation that excites the tubing or the compressor low frequency vibration that transfers energy to the cabinet base plate and tubing. The compressor low frequency vibration is a function of the mechanism loads and the gas pressure that acts on the piston and it is modulated by its running frequency and harmonics. Besides, at low frequencies, the compressor behaves as a rigid body assembled on isolators or grommets which link the compressor to the cabinet base plate. If one knows these rigid body natural frequencies, it’s possible to optimize the refrigerator project, providing a better acoustic performance for manufacturers and final customers. Based on this context, this paper aims to present a study of the compressor grommets, usually made in rubber. First of all, an investigation about the materials is carried out using a technique with a single degree-of-freedom system. In a second time, an analysis of the static behavior of an isolator using the rubber properties is done. Finally, a numerical model to predict the modal behavior of a compressor assembled on a rigid base is created and validated experimentally

Análise de isoladores de vibração usados em refrigeradores

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2013.Os consumidores de bens domésticos, tais como condicionadores de ar, aspiradores de pó, refrigeradores e máquinas de lavar, têm se tornado nos últimos anos mais exigentes no tocante ao conforto acústico. No mercado de refrigeração, fabricantes atualmente investem em projetos de controle do ruído dos seus produtos, seja para mitigar eventuais problemas de qualidade, ou para atender requisitos de legislação. Num refrigerador, a vibração de baixa frequência produzida pelo compressor é uma das principais responsáveis pelo ruído final. Esta é transmitida por vários caminhos até o seu respectivo gabinete, que por sua vez irradia ruído. O presente estudo analisou os isoladores de vibração utilizados entre a placa base do compressor e a do refrigerador, primeiramente caracterizando o material com o qual estes são constituídos. Utilizando-se das propriedades do material, criou-se um modelo em elementos finitos para análise do comportamento vibratório deste isolador. Com base na excitação imposta pelo mecanismo de um compressor recíproco, no modelo de corpo rígido do compressor, na resposta dinâmica de um isolador e nas impedâncias das tubulações, foi possível modelar um gabinete simplificado e otimizar o isolador de vibração de forma a reduzir o ruído de baixa frequência de um sistema de refrigeração.Abstract : Customers of domestic goods, such as air conditioners, vacuum cleaners, refrigerators and washing machines, have recently become more exigent in respect to the acoustic comfort. Nowadays, in the refrigeration market, manufacturers are investing in noise control for their products either to mitigate the quality problems or to respect the standards that the governments create. In a refrigerator, the low frequency vibration produced by the compressor is one of the main components of the final noise. This vibration is transmitted by several paths until it reaches the cabinet of the refrigeration system that radiates the noise. This study evaluated the vibration isolators used between the base plate of the compressor and the base plate of the refrigerator. Initially, the properties of these isolators were characterized. With these data, it was created a finite elements model to analyze the vibratory behavior of this component. Using the excitation imposed by the mechanism of a reciprocating compressor, the rigid body model of this compressor, the dynamic response of a vibration isolator and the impedances of the refrigerator tubing, it was possible to model a simplified refrigerator cabinet and to optimize the isolator in order to reduce the low frequency noise of this refrigerator

Acoustic Improvements for a New Generation of Variable Speed Compressor

Variable speed reciprocating compressors (VSRC) present some advantages comparing to single speed compressors, mainly in terms of energy consumption and noise. Once the acoustic performance is analyzed, it is verified that the compressor running most part of the time at frequencies lower than the ones of the electric nets imply lower sound level for VSRC and, therefore, many home appliances manufacturers direct their use in the premium refrigerator models. Following a general market trend for comfort items, home appliances noise is becoming more and more important nowadays, implying even VSRCs demand acoustic improvements in order to reduce the sound level of the refrigerators. In such a scenario, this paper presents numerical and experimental studies carried out in an existing platform of variable speed compressors, identifying some sources and transmission paths associated to the overall sound level of the compressor itself and a representative refrigerator model. Based on the foreseen opportunities, a design optimization focusing on sources and paths is presented and, as a result, the acoustic performance of the new generation is compared to the performance of the current version of this variable speed compressor platform

Noise Characteristics Improvements for a New Generation of Variable Capacity Compressor using Linear Motor Technology

The household appliances market noise levels requirements have rapidly increased in the last years. Despite the traditional approach for defining noise requirements focused on steady-state sound power levels, the transient noise is becoming a key factor in defining sound quality specification. Variable speed compressor technologies lead to a significant advantage on this aspect since in standard operation conditions the compressor runs at relatively low speeds for most of the time. Linear motor driven reciprocating compressors present great advantages since this technology allows dealing with cooling capacity variation without changing the motor speed. This allows also easier and more effective design of lower noise generation. This paper presents the benefits of the variable capacity, linear motor driven reciprocating compressors over rotary motor driven reciprocating compressors, either at variable capacity and fixed speeds. Emphasis is given to the physical phenomena and engineering advantages of the linear motor concept

The Effect of Biphasic Refrigerant Flow on Refrigerator Noise

Nowadays, the sound level and the sound quality are two very important buying criteria for the final users of a household or light commercial appliance. In order to assure good noise levels, the choice of a compressor with low noise at a specific condition is not the only point necessary to care. It is important to evaluate the transient noise, specially the one that depends on the state and the phases of the refrigerant. The goal of this paper is to present two studies, the first one showing how a biphasic flow in the suction line, close to the compressor in a drinking fountain can create transient noise due to the excitation of compressor gas cavity. The second case concerns the flow noise generated by the refrigerant in the capillary tube. In both cases, thermocouples are placed in different parts of the unit in order to better understand the behavior of the refrigerant flow. Different refrigerant charges are tested, verifying the thermodynamic and acoustic behavior of the units. Some different control techniques are also tried, aiming to avoid undesired noise (for example, pure tone) and reducing the overall levels. Finally, a proposed refrigerant charge is set, assuring a good trade-off regarding noise and thermodynamic performance