EXPERIMENTAL INVESTIGATIONS ON THE COMBINED EFFECT OF NANOFLUID AND ULTRASONIC FIELD ON AMMONIA BUBBLE ABSORPTION

This article investigates the enhancement effect of nanofluid and ultrasonic fields separately and simultaneously on ammonia bubble absorption in the absorber for improving the efficiency of the absorption refrigeration system. Ammonia bubble absorption experiments are carried out in a visualized absorber. Three nanofluids (Al2O3, Fe2O3, and multiwalled carbon nanotubes LMWNTs]) at different concentrations and ultrasonic fields of single frequency (20 kHz, 28 kHz, and 40 kHz) and mixed frequency (20-28 kHz, 20-40 kHz, 28-40 kHz, and 20-28-40 kHz) are studied as enhancement factors. The absorption amount of ammonia and the effective absorption ratio, with and without enhancement factors, are obtained during the experiments. The bubble behaviors during the absorption process are observed: occurs, grows, detaches, diffuses, transforms, and vanishes. The results show that the addition of nanofluids enhances the heat and mass transfer process in the absorber. This enhancement ability follows Fe2O3 > Al2O3 > MWNTs. The effective absorption ratio achieves 1.16 enhanced by Fe2O3 nanofluid of 0.020 wt%. For the ultrasonic field of single frequency, the higher the frequency, the higher the effective absorption ratio. The mixed ultrasonic field results in better effects than the single ultrasonic field. Under the mixed ultrasonic field of 20-28-40 kHz, the effective absorption ratio reaches 1.11. Finally, the effect of combined actions of nanofluid and ultrasonic field are tested. The effective absorption ratio is 1.22 with the ultrasonic field of 20-28-40 kHz and nanofluid of 0.020 wt% Fe2O3.