Оцінка ефективності процесів теплопередачі в утилізаційних котлах суднових енергетичних установок для забезпечення їх компактності

Heat recovery of low-speed diesel engines exhaust gases of marine power plants in waste heat recovery boilers is considered an effective way to increase its economic efficiency. Increasing the engine’s thermal efficiency and reducing the temperature of its exhaust gases has complicated the implementation of this method. Despite the increased requirements for the sulfur content of marine fuels and the corresponding possibility of lowering the temperature of gases behind the boiler, the problem of increasing their compactness still remains. The traditional method for this is to intensify heat transfer processes using finned surfaces. Spiral-ribbon, washer, H-shaped, split, with bent edges finning is used on round, flat-oval, and elliptical sections supporting pipes. This method has many advantages but a significant disadvantage of increased aerodynamic drag of the surface. The use of dimpled systems on the ribs is proposed to reduce the aerodynamic drag of the ribs and increase the overall thermal-hydraulic efficiency of the surface. The variants of such systems on circular-cross-section supporting pipes with spiral-ribbon finning and elliptical-cross-section flat fins on supporting pipes are considered. Since the application of dimpled systems has virtually no effect on the compactness of the surfaces, additional analysis of the thermal-hydraulic efficiency of heat transfer processes in waste-heat marine boilers is required, considering the spatial arrangement of the surfaces. Modern methods for assessing the intensification of heat transfer processes are mainly intended for individual channels and do not allow a full assessment of the effectiveness of the process in tube bundles. A comparative analysis of heat transfer and overall heat transfer processes for the specified finned surfaces is performed based on the proposed modified Reynolds analogy factor. The difference in the efficiency of heat transfer and overall heat transfer reached 21% with different spatial arrangement of bundles, which must be considered when substantiating the types of finned heat exchange surfaces.