Altukhova O. Mathematical modeling, improvement, and optimization of plate heat exchangers

Thesis for submission of a Candidate’s degree in technical sciences under specialty 05.14.06 – «Technical Thermal Physics and Industrial Heat-Power Engineering». National Technical University "KhPI", Kharkiv city, the Specialized Scientific Councils – D 08.084.05 of a “National Metallurgical Academy of Ukraine”, Dnipro city, 2021. The thesis is devoted to the solution of an important scientific and practical task: optimization of plate heat exchangers and improvement of methods of their calculation and optimization. The thesis proposes a new approach for automatic interval calculation of a plate heat exchanger as a complex of heat exchange surfaces using a fractal approach. This approach makes it possible to achieve an increase in the accuracy of the thermal calculation up to 10%, especially for HEXs with a small number of plates. The approach is fully automatic and can be used in plate heat exchanger optimization programs. A program for the optimization of plate heat exchangers has been created for various calculation problems, types of plate heat exchangers, with the possibility to use models of different accuracy. An integrated computational optimization experiment has been done for turbine lube oil coolers with 10-250 kg/s oil flow rate, heat exchangers of a heating system with 100-2000 kW transferred heat, regenerators of a supercritical CO2 cycle with 1-15 MW power, air heaters for an anti-icing system of 1-20 MW gas turbine. Optimal design and operating parameters for this equipment are recommended. It was found that plate heat exchangers are more efficient than shell-and-tube heat exchangers in terms of economic criteria for all ranges of the above-mentioned installations. The fluids velocities (water and oil) in the channels of plate heat exchangers relevant to the current level of prices for metal and energy have been determined; these velocities are significantly lower than it was believed until now and are 0.2 m/s for water and 0.35 m/s for lubrication oil. It has been established how the optimal velocities will change with an increase in prices for metal or electrical energy. An equation is recommended to determine the optimal water velocity depending on metal and energy prices, and can also be used to calculate the optimal velocity when using expensive metals. The independent variables are ranked in terms of their influence on the optimization results and recommendations are given on the order and step of using them, which leads to reduce the dimension of the optimization problem. Recommendations have been developed on the need to use refined calculation methods. Keywords: plate heat exchangers, optimization, modeling, refined interval heat calculation, lubrication oil coolers, heating, supercritical CO2 cycle, gas turbine, optimal fluid velocity.