The thickening of condensed liquid film outside heat-exchange pipes and the pipe bundle effect can significantly degrade the heat transfer efficiency, thus restricting the vacuum phase-change heating furnace from achieving its rated thermal efficiency of over 90%. In this work, a heat transfer enhancement method coupling simple harmonic vibration with non-circular pipes was proposed. A CFD model describing the heat transfer process of horizontal pipes under vibratory conditions was established and stepwise validated against experimental data from published literature and the Nusselt analytical solution. Taking a 50 mm steel circular pipe as the reference, numerical simulations were performed to investigate the effects of structural parameters of oval and droplet-shaped pipes on the near-wall velocity, temperature, wall shear stress, and heat transfer coefficient under horizontal simple harmonic vibration. The results demonstrate that simple harmonic vibration can induce oblique cross-flow outside the pipes, enhance flow field disturbance, and disrupt the liquid film stability, thereby providing a crucial flow field regulation mechanism for vibration-enhanced external condensation heat transfer. An increase in the aspect ratio of droplet-shaped pipes intensifies the wall contraction effect, promotes the formation of continuous small-scale vortices near the pipe wall, and significantly improves the time-averaged heat transfer coefficient. The heat transfer performance of oval pipes is slightly superior to that of circular pipes; among them, oval pipe 2 achieves a dynamic balance between shear driving force and liquid film resistance through the synergistic matching of velocity, temperature, and viscosity, thus exhibiting the optimal wall shear stress among the oval pipe series. Under dynamic conditions, the time-averaged heat transfer coefficients of non-circular pipes are consistently higher than those of circular pipes. Moreover, the inconsistency between the heat transfer coefficient and wall shear stress distributions reveals the multi-mechanism synergy characteristics of external condensation heat transfer on non-circular pipes. This study provides core theoretical support for the engineering design of vibration-enhanced heat transfer technologies in vacuum phase-change heating furnaces.

Heavy oil is characterized by high viscosity. High viscosity makes it challenging to recover and transport. HZSM-5, MoO₃/HZSM-5, ZrO₂/HZSM-5 and MoO₃–ZrO₂/HZSM-5 catalysts were developed to promote in situ desulfurization and viscosity reduction of heavy oil. The physical and chemical properties of catalysts were characterized by XPS, XRD, TEM, NH₃-TPD, etc. The effects of temperature, catalyst type and addition amount on viscosity and composition of heavy oil were evaluated. The results showed that the presence of MoO₃–ZrO₂/HZSM-5 nanoparticles during aquathermolysis could improve the oil quality by reducing the heavy fractions. It reduced viscosity by 82.56% after the reaction at 280 ℃ and catalyst addition of 1 wt%. The contents of resins and asphaltic in the oil samples were 5.69% lower than that in the crude oil. Sulfur content decreased from 1.45% to 1.03%. The concentration of H₂S produced by the reaction was 2225 ppm. The contents of sulfur-containing functional groups sulfoxide and sulfone sulfur in the oil samples decreased by 19.92% after the catalytic reaction. The content of stable thiophene sulfur increased by 5.71%. This study provided a basis for understanding the mechanism of heavy oil desulfurization and viscosity reduction.