Indexed on: 08 Mar '17Published on: 06 Mar '17Published in: Experimental Thermal and Fluid Science
In the present paper, a theoretical saturated flow boiling heat transfer coefficient correlation for nanofluid in minichannel has been proposed based on the contributions of convective boiling and nucleate boiling. For convective heat transfer, the absorbed heat amount of nanoparticles from fluid has been deduced by the fractal distribution theory. For nucleate boiling, the probability density equation of bubbles random growth is obtained on the basis of a Markov process. As a result, the nucleate flow boiling heat transfer coefficient formula is derived. In addition, three mass fractions for 0.2%, 0.5% and 1.0% Al2O3/H2O nanofluid are prepared by ultrasonic vibration and saturated flow boiling heat transfer coefficients in different rectangular minichannels with cross section 0.3×2 mm, 0.6×2 mm, 2×2 mm are experimentally investigated. The results show that the heat transfer performance is enhanced after adding nanoparticles in base fluid and the average saturated flow boiling heat transfer coefficients of 0.2 wt.%, 0.5 wt.% and 1.0 wt.% Al2O3/H2O nanofluid respectively increase by 11.2%, 15.4% and 18.7% compared with that of deionized water. Meanwhile, the average saturated flow boiling heat transfer coefficients for 1.0 wt.% Al3O2/H2O nanofluid are increased by 21.1%, 26.2% in channels with cross section 0.3 mm × 2 mm, 0.6 mm × 2 mm compared with the average heat transfer coefficients in channels with cross section 2 mm × 2 mm, which illustrates that the capillary effects are strengthened with the hydraulic diameter decreasing. Furthermore, a comparison is made between the experimental and theoretical data. The results show that the theoretical heat transfer model has a good universal prediction for nanofluid saturated flow boiling heat transfer in minichannel.