수치해석을 이용한 선박 유기랭킨사이클 시스템의 이상유동형 열교환기 설계에 관한 연구

Abstract

A meticulous design approach is required for Waste Heat Recovery Units (WHRU) and condensers utilized in Organic Rankine Cycle (ORC) power systems, unlike conventional heat exchangers. This is due to the incorporation of phase change phenomena and the utilization of a refrigerant as a working fluid instead of water. The main goal of this research is to develop ship-based ORC systems that utilize WHRU and condensers. From the initial design stage, computational fluid dynamics (CFD) methodology was utilized to calculate heat transfer rates and analyze operational characteristics. Investigation of research cases on conventional heat exchangers using CFD techniques revealed that the majority of existing studies focus on enhancing efficiency in manufactured devices and analyzing local heat and flow, rather than on the fundamental design process. This research fills a gap by providing comprehensive performance analysis of two-phase flow heat exchangers, documenting their manufacturing process, and analyzing the system modeling of the ORC power generation system that incorporates the newly created heat exchangers. This work has significant implications for the future development and implementation of ORC systems in marine applications. When applying the ORC system to ships, it is crucial to take into account various factors. Primarily, this study focuses on discussing the characteristics of the heat source. The objective of this study is to develop a heat exchanger, which is fundamentally influenced by the heat source. The heat exchanger must be designed to leverage waste heat from the ship's main engine exhaust, taking pressure drop into account, without negatively impacting engine operation. The heat exchanger must be designed to effectively utilize waste heat from the ship's main engine exhaust, considering pressure drop, without causing any detrimental effects on engine operation. The demonstration showcased the design and fabrication process of the WHRU device, which incorporated CFD techniques. The simulation and experimental results were compared to confirm similar heat transfer performance during the design stage. A specific analysis was conducted on the temperature, pressure, and dryness distribution of the heat exchanger. Notably, the prediction of the phase change point, which is a crucial factor for the stable operation of the two-phase flow heat exchanger, was conducted for each refrigerant, and the corresponding operational performance was analyzed. The process of developing the condenser in the Organic Rankine Cycle (ORC) is illustrated. The CFD simulation results of the condenser showed a heat transfer performance similar to the experimental results, with an error margin of within 10%. The condenser, a brazed plate heat exchanger, was designed to independently calculate the heat transfer performance of an internally-shaped fin on each individual heat transfer plate. This allows for the prediction of the performance of a fully assembled condenser with a 25-layer stack. The ORC system was modeled using the Aspen Plus program, incorporating the CFD calculation conditions of the ship's ORC two-phase heat exchanger. It has been verified to be error-free. Moreover, the operating characteristics of each part were analyzed during system operation, with a specific focus on refrigerant properties. This analysis involved the application of four different types of refrigerants. As a result, similar heat transfer performance was confirmed through both CFD and Aspen modeling calculations.