Design of Heat Exchangers with Low-Boiling Working Fluids: Algorithm Development and Parameter Optimization

Heat exchangers are key components of advanced waste-heat recovery energy systems that operate on low-boiling working fluids. The efficiency and cost of power plants depend directly on their design characteristics. Increasing the heat-transfer surface area, on the one hand, reduces temperature differences and improves cycle efficiency, but on the other hand increases material consumption and equipment cost. For given fluid parameters and heat-exchanger duty, the required surface area is determined by the type of heat exchanger, the choice of device, the shape of the enhanced heating surface, and the methods of heat-transfer intensification. This paper provides a comprehensive analysis of the current state of heat exchangers for low-boiling working fluids and discusses their areas of application. A methodology has been developed for optimizing the main design characteristics of heat exchangers, including a search algorithm aimed at minimizing the total costs of equipment production and operation. Using this methodology, computational studies were carried out for advanced energy cycles with low-boiling working fluids (organic Rankine cycles, recompression supercritical CO2 (s-CO2) Brayton cycle). The relationships of weight, size, and cost parameters of heat exchangers for waste-heat recovery cycles using low-boiling fluids to exhaust-gas temperatures and external economic factors were obtained. Optimal channel geometric parameters and heat-exchanger design types were identified that ensure minimal material consumption and cost while delivering the required heat-transfer performance. Recommendations are formulated for selecting and designing heat exchangers for waste-heat recovery power plants using low-boiling working fluids, the implementation of which will improve their efficiency and reduce costs.