An Experimental study of Fullerene (C60) Nano-fluids on Pool Boiling Conditions
Critical heat flux (CHF) is directly related to the performance of the system since CHF limits the heat transfer of a heat transfer system. Significant enhancement of CHF allows reliable operation of equipment with more margins to operational limit and more economic cost saving. The previous results show that the nano-fluids significantly enhanced pool boiling CHF compared to pure water. It was supposed that CHF enhancement was due to increased thermal conductivity of fluids, change of bubble shape and behavior, and nano-particle coating of the boiling surface. The previous researches also show that mainly the pool boiling experiment was employed metal particles. Fullerene (C60) is a novel carbon allotrope that was first discovered in 1985 by a winner noble “Sir Harold W.Kroto, Richard E. Smalley and Robert F.Curl Jr”. In this study we report the first CHF experiment in pool boiling conditions using Fullerene (C60) nanofluids.
2.1. Preparations of nanofluids
The C60 particles are nearly water insoluble in water, because of their strong hydrophobicity and van der Waals attractions. As a way alternative to such chemical synthesis, water dispersion of C60 itself has recently attracted increasing interest for practical applications. Some methods based on reprecipitation, solvent replacement, and ultrasonications have been introduced to prepare the dispersion, and surfactant, polymer, or other detergents are often added.
In this study we use acid treatment as our method to have water dispersible Fullerene (C60).The fullerene [C60] used in this work was 99.99% pure from Sigma Aldrich. All the solvents and chemical reagents were from Aldrich.
2.2. Zeta Potential Measurements
The dispersion and stability of fullerene (C60) nanofluids were checked by measuring zeta potential. Zeta potential is an abbreviation for electrokinetic potential in colloidal system. In other words, zeta potential is the potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed particle. The significance of zeta potential is that its value can be related to the stability of colloidal dispersions. The zeta potential of Fullerene nanofluids were found in the range of mV . The zeta potential of nanofluids was constant for more than one month .
3. Boiling experimental facility and procedure
The CHF of deionized pure water and nanofluids was measured in the apparatus , which basically consists of horizontal flat surfaces heater submerged in the test fluid at atmospheric pressure.
4. Results and Discussions
4.1. CHF with fullerene (C60) nanofluids
For the prediction of CHF of pure fluids, Zuber’s (1959) correlation, has been used widely for the past years. The CHF for flat plate is predicted as 1110 kW/m2 by Zuber’s model for water under atmospheric pressure. The results data for CHF of pure water was approximately 50% lower than Zuber prediction, however the main focus of this present work is to investigate CHF enhancement using nano-fluids relative to CHF of pure water, the experimental CHF value of pure water in present work can be used as standar for subsequent CHF comparisons of nano-fluids. It was also reported by N. Barkhu and J.H. Lienhard that the prediction of zuber equation is not valid.
Significant CHF enhancement is observed for all concentrations content Fullerene (C60) nanofluids compare to pure water. CHF enhancement as compared to pure water occurs up to 108% for 0.01vol% fullerene (C60) nanofluids, up to 46% for 0.001vol% fullerene (C60) nanofluids, and up to 22% for 0.0001vol% fullerene (C60) nanofluids.
4.2. Heat Transfer Coefficients with fullerene (C60) nanofluids
The boiling curves in Fullerene nanofluids are shifted to the left of boiling curve in water. Its means the heater surface boiling in Fullerene nanofluids will generally have a higher nucleation site density causing this shift to the left.
The critical heat flux in pool boiling conditions is experimentally evaluated for Fullerene (C60) nanofluids. It is found several significant findings such as:
1. The zeta potential of Fullerene nanofluids were in the range of 41 mV. The zeta potential of nanofluids was constant for more than one month. It concludes that the treatment has been succeeded produces water dispersible Fullerene (C60) nanofluids with good stability.
2. Enhanced (~108.9%) CHF was observed for solutions with Fullerene (C60) nanofluids with concentration 0.01%.
3. The pool boiling HTCs of Fullerene (C60) nanofluids are higher than those of pure water in the entire nucleate boiling regime.
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 N. Zuber, Hydrodynamic aspects of boiling heat transfer, AEC Report AECU-4439, Physics and Mathematics, 1959.
 J.H. Lienhard, A heat transfer textbook, Prentice-Hall, p. 404, 1981.
 U.S Choi, Developments and Applications of Non-Newtonian Flows, ASME FED-Vol. 231/MD, vol. 66, (1995), PP. 99-105.