Experimental investigation of condensation heat transfer characteristics and corrosion resistance on coated tube surfaces

Abstract

The condensation heat transfer characteristics and corrosion resistance of copper, Ni-P-Cu, polytetrafluoroethylene (PTFE), Ni-P, and Ni coated tube surfaces were investigated. The results indicate that condensation heat transfer coefficient of Ni-P-Cu, PTFE, Ni-P, and Ni coated tubes grows by 36.8%, 29.3%, 19.6%, and 7.5% than that of copper tubes, respectively. The phase structure of Ni, Ni-P, Ni-P-Cu, and PTFE coated tube surfaces is mixed crystal structure(nanocrystals-based), mixed crystal structure (amorphous-based), amorphous structure and crystal structure, respectively. Compared with Ni coating and Ni-P coated tube surfaces, the condensation droplets outside Ni-P-Cu and PTFE coated tubes are smaller in size, more densely distributed, and fall off more quickly, which can significantly promote dropwise condensation. The Ni-P-Cu coated tube surfaces achieve optimal condensation heat transfer. The corrosion speed of copper, Ni, Ni-P, Ni-P-Cu, and PTFE coated tubes are 86.5, 42.6, 18.2, 10.7, and 6.1 mg/dm2d per day, respectively. The PTFE coating tubes have the optimal corrosion resistance. The Ni-P-Cu, and PTFE coated tube surfaces have the best condensation heat transfer characteristics and corrosion resistance, and can be well used in the recovery of waste heat from low temperature flue gas. The multiple linear regression of the experimental data was carried out to obtain the experimental correlation formula for Nusselt number of convective condensation composite heat transfer for different coated tubes. The relative error between the predicted value and the experimental value is within ?15%.