Yindong Song

Ventilation and dust removal systems in industrial buildings handle particulate-laden exhaust flows. Centrifugal fans are the primary gas-moving equipment in these systems, and straight plate blades are widely used in them. These blades resist particulate deposition and erosive wear. Their aerodynamics are governed by the inlet clearance between the stationary inlet nozzle and the rotating impeller. Design and simulation routinely idealize it as clearance-free. A 12-blade fan of this type was studied numerically. Four clearance conditions were quantified over the full flow range. This idealization overestimated the design point total pressure efficiency by 1%. Overlapped clearance dominated the aerodynamic performance. A clearance of 20 mm approached the original model. A clearance of 30 mm, in contrast, reduced the efficiency to 50% at high flow. The axial clearance itself lowered the total pressure efficiency. Its size, however, barely mattered. The three axial clearance models remained within 77–78% at the design flow rate. A circumferentially non-uniform clearance lowered the design point efficiency to 79% and the high-flow efficiency to 32%. Eddy viscosity accumulation and passage blockage show that leakage-induced backflow sets these limits. These results provide a basis for controlling inlet clearance tolerances during the design and assembly of the straight plate blade fans.

Liquefied natural gas (LNG)-powered ships possess available utilizable energy resources, including LNG vaporization cold energy and main engine flue gas waste heat. To improve the ship energy utilization efficiency, this paper takes a 215,000-ton Very Large Crude Carrier (VLCC) as the research object, and couples the organic Rankine cycle (ORC) and transcritical carbon dioxide (TCO₂) Rankine cycle to achieve the combined recovery of ship cold energy and waste heat. To systematically investigate the thermal performance of the integrated system, a simulation model is established by using Aspen HYSYS to acquire basic thermal parameters. Advanced exergy analysis is adopted as the core research method for the first time to evaluate the thermal performance of the system, and the obtained results are compared with those of the conventional exergy analysis. Conventional exergy analysis reveals that Heat Exchanger 1 is the core component restricting the performance optimization of the whole system. Further results from advanced exergy analysis show that the proportions of avoidable exergy destruction and endogenous exergy destruction of the overall system are 40.46% and 58.72%, respectively. Key optimization links are further identified based on the advanced exergy analysis results, and the genetic algorithm (GA) is applied for targeted system optimization. After optimization, the system output power reaches 1772.06 kW and the exergy efficiency is 48.32%, which are increased by 5.56% and 15.54% correspondingly. Economic evaluation indicates the annual net profit reaches 3.8336 million CNY, with a static payback period of 5.49 years.

Hydrophobic graphene nanosheets were successfully modified with TiO2 to create a pure and stable nanoparticle. The resulting material exhibited improved heat transfer efficiency when used as nanofluid in pool boiling. We prepared graphene nanofluid, TiO2 nanofluid, and graphene-TiO2 hybrid nanofluid with varying concentrations to investigate their heat transfer characteristics. The heat transfer coefficient of graphene-TiO2 hybrid nanofluid is higher than that of water at the same heat flow density, especially in the low heat flow density region( below q = 4 ? 105 W/m2). Additionally, by employing a high speed camera, we observed that the hybrid nanofluid displayed shorter bubble generation periods and smaller bubble separation diameters. These findings highlight the exceptional heat transfer performance of the covalently modified and hybridized nanofluid. Overall, our comprehensive testing program confirms the enhanced heat transfer capabilities of this modified nanofluid, positioning it as a promising choice for various heat transfer applications.