A study on the acoustics and heat transfer in cooling systems' heat exchangers

A study on the heat transfer at the heat exchangers of conventional and an alternative refrigeration system was conducted for improved performance. Studies were carried out at the evaporator of conventional refrigeration systems on flow-induced noise reduction. In addition, thermoacoustic refrigeration system was studied as an alternative cooling technology.; Several flow regulators were constructed and tested at the evaporator exit region. Out of several prototypes tested, the results from the ribbed-tube evaporator were used in the final analysis as it yielded increased efficiency and reduced flow-induced noise. The ribbed-tube evaporator and a smooth-tube evaporator were compared in terms of heat exchanger effectiveness, overall coefficient of performance (COP), run-time ratio and pressure drop. The heat exchanger effectiveness of the ribbed-tube evaporator was found to be 7% higher compared to the smooth-tube evaporator. The COP value of the system employing the ribbed-tube evaporator was also found to be higher. Although the pressure drop for the ribbed-tube evaporator was found to be slightly higher than that for the smooth-tube evaporator, the compressor used in the two systems was able to overcome this increase in pressure drop.; For the noise reduction study, a general model was defined taking frequency, temperature and pressure values into account. For each frequency band in the range of interest, a correlation was formed. These correlations can be used for other refrigerators as the relations of the identified parameters are universal.; Regarding the thermoacoustic refrigeration studies, experimental investigations on the oscillatory flow of gas and the heat transfer at the warm side heat exchanger were performed. An empirical correlation for this heat transfer was developed in terms of Nusselt, Reynolds and Prandtl numbers. The heat transfer correlations were based on the oscillatory flow conditions unlike some previous studies in the literature performed based on straight flow conditions. Factors that influence the heat transfer and construction of the system were identified. Results also showed the relationship between the oscillatory heat transfer coefficient at the heat exchangers, the mean pressure and frequency.