The condensation heat transfer characteristics and corrosion resistance of
copper, Ni-P-Cu, polytetrafluoroethylene, 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. 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?dm-2?d-1, respectively. PTFE
coating tubes have the optimal corrosion resistance. 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%.
Convective condensation heat transfer of R134a in tubes at different inclination angles