An experimental study on CHF enhancement using nanofluids

Abstract

The critical heat flux (CHF) is one of the most important thermal hydraulic parameters in heat transfer sys-tem design and safety analyses. CHF enhancement allows higher limits of operational conditions such that heat transfer equipment can be operated safely with greater margins and better economy. Nanofluid is an engineered colloidal suspension of nano-sized particles in a base fluid. The application of nanofluids is thought to have strong potential for enhancing the CHF. Many researchers have studied CHF enhancement by using nanofluids since the work conducted by You et al. was reported. While numerous studies on CHF enhancement using nanofluids in pool boiling have been reported, there is little data about CHF in flow boiling using nanofluids. Various hypotheses have been proposed to explain the CHF enhancement. Among them, a decrease of the contact angle by the deposition of nanoparticles on the heater surface during boiling of nanofluids explains the CHF enhancement quite well. However, in light of counterexamples, this does not comprehensively explain the CHF enhancement. Therefore, a new mechanism to explain the CHF enhancement occurring with the use of nanofluids is required. In the present study, two kinds of experimental works were conducted and CHF enhancement mechanism of nanofluids was described. First, flow boiling CHF experiments using Al2O3 nanofluid and Al2O3 nanoparticle deposited tubes were conducted to find the primary reason of CHF enhancement. The flow boiling CHF of Al2O3 nanofluid with a plain tube (NFPT) and de-ionized water with an Al2O3 nanoparticle deposited tube (DWNT) were enhanced up to about 80% for all experimental conditions. There was no big difference in the CHF results between NFPT and DWNT; these results indicate that the CHF enhancement of Al2O3 nanofluid is surely caused by deposition of nanoparticles on the test section tube inner surface. After the flow boiling CHF experiments, the inner surfaces of the test section ...