Experiment Study Of Heat Transfer Enhancement Of Nanofluids

In this paper, two kinds of nanofluids are prepared; equipments are established; the thermal conductivity and the convective heat transfer coefficient of the nanofluids prepared are measured by the equipments; their experimental result are analyzed according to the microcosmic mechanism of the heat transfer enhancement of nanofluids.Graphite/water nanofluids is prepared by two-step method. First, graphite nanoparticles are prepared by grinding/floatation method, and then let nanoparticles and liquid be mixed firsthand, the even distributed and stabilized suspensions are prepared by means of appending the different dosage of dispersant and using ultrasonic vibration. Fe₃O₄/water nanofluids are prepared by single-step method. The TEM photographs are given to illustrate the stability and evenness of suspensions.The transient hot-wire instrument for measuring the thermal conductivity of nanofluids is developed. The nanofluids prepared are measured. Their several characteristic behaviors have been found. First, the thermal conductivities of the two kinds of nanofluids increase linearly with the volume fraction increasing, and then when the volume fraction is equal to 1.0 %, the thermal conductivities of graphite/water nanofluids and Fe₃O₄/water nanofluids are respectively increased by 12% and 48%; finally, the experimental result is far better than that predicted by conventional theories.A set of equipment for measuring the convective heat transfer coefficient is developed. The nanofluids prepared are measured. Several characteristic behaviors of the nanofluids have been identified. First, the convective heat transfer coefficient of the two kinds of nanofluids increase linearly with the volume fraction increasing; secondly, when the Reynolds are between 3000-6500, their convective heat transfer coefficient increase linearly, but when the Reynolds is higher than 6500, they increases more rapidly; thirdly, the convective heat transfer coefficient of the graphite/water nanofluids at 35 amount to that of the Fe₃O₄/water nanofluids at 15; finally, when the volume fraction is 1.0%, they are increased by 90% comparing with water. Author find that nanofluids have temperature-dependent characteristic of nanofluids, but more study is needed to determine the extent.