ENHANCED POOL BOILING OF REFRIGERANTS FROM PLASMA-SPRAY COATED SURFACES

Kurzfassung

Coating characteristics effects on boiling performance of refrigerants are analysed for surfaces treated by radio frequency plasma sprayed copper and Inconel. The experimental results show substantial heat transfer improvement for the coated surfaces to those of bare surfaces. They also demonstrate that the thicker layer for the copper coatings, the higher heat transmission would be. Nonetheless for the Inconel coatings, instead the heat transfer coefficient decreases as the thickness of coating layer increases from 175.7 to 193.5 mm. This study therefore endeavours to explore phenomena that may influence such behaviour as well as to utilise neural network architectures to predict heat transfer coefficients. The data bank contains measurements for a wide range of operating conditions for different porosities, coating thicknesses and thermal conductivities. The independent parameters are in terms of dimensionless groups such as boiling number (BO), Prandtl number (Pr), and conductivity ratio. A comparison between the experimental and predicted results shows an overall average error of 4.6%. The accuracy of the network improves as heat flux increases. In addition, the trend of both predicted results and experimental data are qualitatively consistent.