The effect of nanofluid stability on critical heat flux using magnetite-water nanofluids

Abstract

In nuclear safety, the critical heat flux (CHF) is a very important value that can determine the limit of the safety design. To prevent a minor nuclear accident from mitigating into a severe accident, the coolants should have a higher CHF value. Among the strategies to improve the CHF, many feasibility studies using several kinds of nanofluids were performed as an alternative coolant because of the abnormally CHF enhancement with a very small volume fraction of nanoparticles. Although many researches have tried to apply nanofluids into a real system as a coolant, there are some problems left to solve. In particular, it is necessary to understand the characteristics of nanopartide stability in the base fluid in order to guarantee the thermal performance of the nanofluids. In this study, three kinds of effects were considered to clarify the relation between nanofluid stability and CHF improvement: the effect of sonication, dilution, and storage time. The effect of sonication in the manufacturing process of the nanofluids should be considered. A two-step method is the most popular for manufacturing nanofluids. Based on the results of the present study, nanofluids made through a two-step method should be initially sonicated to guarantee their CHF enhancement. In the process of dilution, the limitation of nanoparticle concentration exists in the process of dilution to guarantee CHF enhancement. Finally, CHF enhancement using a nanofluid made by a two-step method can be guaranteed for at least a year. In addition, we also proved that CHF using nanofluids can be decreased according to the preservation time.