Korobko V. Development of scientific and technical bases for utilization of low-potential heat of ship power plants by thermoacoustic technologies

Dissertation for the scientific degree of the Doctor of Technical Sciences, Specialty 05.05.03 - Engines and Power Plants (Technical sciences). - Admiral Makarov National University of Shipbuilding, Ministry of Education and Science of Ukraine, Mykolaiv, 2021. The dissertation solves an important scientific and technical problem - increasing the efficiency of secondary energy resources and reducing emissions of toxic components of exhaust gases by rational organization of energy conversion processes in thermoacoustic systems for utilization of low-potential heat of ship power plants. For today, the task of decarbonisation of marine power plants and reduction of greenhouse gas emissions is becoming a priority. On modern ships, the use of liquefied cryogenic fuels leads to a decrease in the temperature of heat emissions and causes the emergence of new cryogenic sources of heat emissions, which requires new technologies for their utilization. In the dissertation work the universal scheme of power plant with thermoacoustic energy saving system was developed. Such a thermoacoustic system is able to use external low-temperature thermal resources, including cryogenic. A multilevel mathematical model of such installation was synthesized. The mathematical model allowed to investigate the influence of various factors on the efficiency of a ship power plant with a thermoacoustic heat recovery circuit. A generalized mathematical model of a power plant with an energy-generating thermoacoustic system for the use of low-temperature waste heat resources capable of using energy sources with temperatures of 111 to 500 K, with a temperature potential of 55 K and producing mechanical work by means of pulsed bidirectional impulse is synthesized. The research results showed that the uneven temperature distribution on the surface of heat exchangers and the matrix of thermoacoustic motors reduces their efficiency. The feasibility of using heat exchangers with a phase transition was shown. It has been experimentally proven that the presence of a longitudinal temperature gradient in the matrix is only a sufficient condition for the occurrence of thermoacoustic oscillations, and an additional excitation is a necessary one. The possibility of utilization of low-temperature thermal resources by thermoacoustic technologies due to the use of two-component working media was experimentally shown. Physical experiments and CFD modeling have shown that during the operation of bidirectional turbines in the resonator of a thermoacoustic motor, the secondary circulating currents occurs. This leads to significant losses of acoustic energy. Reduction of these losses by profiling the stator blades of the turbine is possible. The result of scientific research are scientifically proven principles of creating thermoacoustic systems for utilization of low-potential heat emissions from marine power plants. They can provide additional mechanical work and electricity, which reduces fuel consumption and emissions of harmful substances. Various thermoacoustic installations suitable for use in marine energy, industry, renewable energy have been proposed. The effectiveness of these solutions is confirmed experimentally and by calculations, using models of thermoacoustic devices and their components. The scientific significance of the obtained results is in the new obtained knowledge about rational methods for increasing the efficiency of sequential processes of conversion of low-potential waste heat into acoustic energy and further into mechanical work by thermoacoustic methods. The practical value of research is developed recommendations thermoacoustic energy saving systems design for marine renewable energy, industry and climate systems. Keywords: ship power plants; thermal emissions; thermoacoustic technologies; energy saving; impulse bidirectional turbine.