This study provides an overview of new trends in the development of cooling systems for electric motors. It includes a summary of academic research and patents for cooling systems implemented by leading motor manufacturers at TRL9. New trends in the cooling management of air and liquid cooling systems are discussed and analyzed with a focus on temperature distribution and its influence on the power-to-dimension ratio of electric motors. The prevailing cooling method for synchronous and asynchronous motors is air cooling using external fins, air circulation ducts, air gaps, and fan impellers to enhance efficiency and reliability. Internal cooling with rotor and stator ducts, along with optimized air duct geometry, shows potential to increase the power-to-dimension ratio and reduce motor size. Liquid cooling systems offer a power-to-dimension ratio of up to 25 kW/kg, achieved through redesigned cooling ducts, stator heat exchangers, and cooling tubes. However, liquid cooling systems are complex, requiring maintenance and high ingress protection ratings. They are advantageous for providing high power-to-dimension ratios in vehicles and aircraft. Discussions on using different refrigerants to improve efficient motor cooling are underway, with ozone-friendly natural refrigerants like CO₂ considered to be promising alternatives to low-pressure refrigerants with high global warming potential.

Complex gas turbine schemes with air intercooling are usually used to bring the compression process of working fluid in compressor closer to isothermal one. A promising way to realize it is to use an aerothermopressor. The aerothermopressor is a two-phase jet apparatus, in which the highly dispersed liquid (water) is injected into the superheated gas (air) stream accelerated to the speed closed to the sound speed value (Mach number from 0.8 to 0.9). The air pressure at the aerothermopressor outlet (after diffuser) is higher than at the inlet due to instantaneous evaporation of highly dispersed liquid practically without friction losses in mixing chamber and with an increase in pressure of the mixed homogenous flow. The liquid evaporation is conducted by removing the heat from the air flow. In the course of the experimental research, the operation of the aerothermopressor for gas turbine intercooling air was simulated and its characteristics (hydraulic resistance coefficients, pressure increase, and air temperature) were determined. Within contact cooling of air in the aerothermopressor, the values of the total pressure increase in the aerothermopressor were from 1.02 to 1.04 (2–4%). Thus, the aerothermopressor use to provide contact evaporative cooling of cyclic air between the compressor stages will ensure not only compensation for pressure losses but also provides an increase in total air pressure with simultaneous cooling. Injection of liquid in a larger amount than is necessary for evaporation ensures a decrease in pressure losses in the flow path of the aerothermopressor by 15–20%. When the amount of water flow is more than 10–15%, the pressure loss becomes equal to the loss for the “dry” aerothermopressor, and with a further increase in the amount of injected liquid, they are exceeded. The values of errors in the relative increase of air pressure in the aerothermopressor measurements not exceeded 4%. The results obtained can be used in the practice of designing intercooling systems for gas turbines.

Contact cooling using thermopressor technologies is a promising direction for the development of energy-efficient technologies. This technology is based on the implementation of the thermo-gas-dynamic compression effect in special contact heat exchangers that consists of increasing the pressure while decreasing the temperature during the evaporation of a finely dispersed liquid injected into a gas flow moving at a speed close to sound. Upon application of the thermopressor for charge air cooling of the engine, the following result was obtained: an increase in the air pressure after the turbocharger by 340 to 480 kPa. The thermopressor can be used as a boost stage after the turbocharger, resulting in the reduction of a basic turbocharger compression work and the increase of engine power output accordingly. Reducing the work allows for the same air flow rate on the internal combustion engine to reduce the compressor power by 10 to 12%. This increases the temperature of the exhaust gases at the inlet of the exhaust boiler by 10 to 15 °C and boiler steam capacity, resulting in an increase in the power output of the utilization turbine generator with a corresponding reduction in the fuel consumption of the diesel generator of the ship power plant by 2 to 3%.

One of the promising trends to increase the fuel and energy efficiency of gas turbines is contact cooling of cyclic air by using a twophase jet apparatus – an aerothermopressor. The rational parameters of work processes of the aerothermopressor were studied. The experimental setup was designed to simulate the aerothermopressor operation in the cooling air cycle of the gas turbine and to determine pressure losses in the aerothermopressor flow part. Based on the obtained experimental data, an empirical equation was proposed to determine the hydraulic resistance coefficient of the aerothermopressor flow part, depending on the initial pressure and the amount of water injected. The deviation of the calculated hydraulic resistance coefficient from the experimental ones is ± 25 %. The obtained results can be used in the practice of designing the aerothermopressor for gas turbine cyclic air cooling.

One of the promising ways to increase fuel and modern gas turbine energy efficiency is using cyclic air intercooling between the stages of high- and low-pressure compressors. For intercooling, it is possible to use cooling in the surface heat exchanger and the contact method when water is injected into the compressor air path. In the presented research on the cooling contact method, it is proposed to use a thermopressor that implements the thermo-gas-dynamic compression process, i.e., increasing the airflow pressure by evaporation of the injected liquid in the flow, which moves at near-sonic speed. The thermopressor is a multifunctional contact heat exchanger when using this air-cooling method. This provides efficient high-dispersion liquid spraying after isotherming in the high-pressure compressor, increasing the pressure and decreasing the air temperature in front of the high-pressure compressor, reducing the work on compression. Drops of water injected into the air stream in the thermopressor can significantly affect its characteristics. An increase in the amount of water increases the aerodynamic resistance of the droplets in the stream. Hence, the pressure in the flow parts of the thermopressor can significantly decrease. Therefore, the study aims to experimentally determine the optimal amount of water for water injection in the thermopressor while ensuring a positive increase in the total pressure in the thermopressor under conditions of incomplete evaporation. The experimental results of the low-consumption thermopressor (air consumption up to 0.52 kg/s) characteristics with incomplete liquid evaporation in the flowing part are presented. The research found that the relative water amount to ensure incomplete evaporation in the thermopressor flow part is from 4 to 10% (0.0175–0.0487 kg/s), without significant pressure loss due to the resistance of the dispersed flow. The relative increase in airflow pressure is from 1.01 to 1.03 (5–10 kPa). Based on experimental data, empirical equations were obtained for calculating the relative pressure increase in the thermopressor with evaporation chamber diameters of up to 50 mm (relative flow path length is from 3 to 10 and Mach number is from 0.3 to 0.8).