Ezperimental Investigation of the Crystallization Process of Nanofluid with a DSC Technique
The appearance of a high supercooling degree during solidification process of water in an ice storage system will lower evaporating temperature, which cuts down EER (Energy Effect Ratio) of ice-storage equipment. As we know, when a solution contains other particles, nucleation is facilitated and heterogeneous nucleation can occur under a smaller degree of supercooling as water freezes. In this paper, water-TiO2 nanofluid with weight fraction of 5％, average particle size of 75nm was used to investigate the effect of titanium dioxide nanoparticles on the crystallization behavior of deionized water by means of differential scanning calorimetry (DSC) at four different cooling rates, 3℃/min, 5℃/min, 7℃/min and 9℃/min. Some useful parameters such as the transformation temperature and time, latent heat were obtained from the DSC spectra for the crystallization and melting analysis. On the basis of these data, the overall crystallization and melting rate, the heat of crystallization and melting, and supercooling degree of water-TiOz nanofluid were compared with deionized water. The DSC experimental results show that, with the increase of cooling rate, the supercooling degree and the crystallization rate of both deionized water and water-TiO2 nanofluid become greater and faster, respectively. Moreover, water-TiO2 nanofluids have lower supercooling degree and larger crystallization rate than pure deionized water at any cooling rate ranging from 3℃/min to 9℃/min. The influence of titanium dioxide nanoparticles on the supercooling degree of deionized water get stronger as the cooling rate increase, whereas get weakened on the crystallization rate. For the melting process, the rapid cooling rate can strongly decrease the peak melting temperature but has little effect on the onset melting temperature for both deionized water and water-TiO2 nanofluid. The melting temperature and melting rate of water-TiO2 nanofluid are lower and higher than those of deionized water, respectively, that is, the faster the cooling rate is, the easier the melting process is. It is also found that the latent heat of water-TiO2 nanofluid is lower than that of deionized water. Water-TiO2 nanofluid can enhance the crystallization process because titanium dioxide nanoparticles are useful for nucleation. As the enhancement on the supercooling degree and the crystallization rate get more and less significant with the increase of cooling rate, respectively, it is necessary to choose the proper cooling rate with the tradeoff analysis methods of the supercooling degree and the crystallization rate in practical applications.
Water-TiO2 nanofluid Nucleation Supercooling degree DSC
Ying Chen Lisi Jia
Faculty of Material and Energy Engineering,Guangdong University of Technology,Guangzhou,China
国际会议
The 6th International Symposium on Heating,Ventilating and Air Conditioning(第六届国际暖通空调学术会议)
南京
英文
2061-2068
2009-11-06（万方平台首次上网日期，不代表论文的发表时间）