Strumienicowe układy chłodnicze. Modelowanie i badania eksperymentalne

Materiał przedstawiony w niniejszej monografii stanowi podsumowanie wybranych prac badawczych autora realizowanych na przestrzeni ostatnich lat i wpisujących się w ogólną kategorię związaną z modelowaniem i badaniami eksperymentalnymi strumienic gazowych i strumienicowych układów chłodniczych.

The monograph presents the results of the author’s research concerning the modeling and experimental studies of supersonic gas ejectors and ejector refri- geration systems powered by low grade heat, which is treated as waste heat in the majority of technologies used nowadays. The first part of the work shows a multivariant analysis of issues related to the possibility of using environment-friendly and prospective working media in ejector refrigeration systems, such as natural media and new HFO media with a low GWP. Then, an original approach is presented as regards the modeling of a gas ejec- tors using a lumped model. The author proposed a model combining the key fe- atures of balance models described in source literature, including the model by Huang (1999), only applicable to the design area, which was extended by non-de- sign work by Chen et al., (2013), and the model by Kumar et al. (2014). The propo- sed approach involves the main aspect connected to physical processes occurring in the supersonic gas ejectors: the shock wave generated in the device, resulting in a considerable part of the pressure rise, which is modeled by the solution of Ray- leigh and Fanno equations, taking into account the friction forces. The presented model also takes into consideration non-isentropic processes and the properties of real gases, unlike other models used nowadays, in which the thermodynamic properties of the refrigerant are modeled as the ideal gas. In addition, separate adiabatic processes exponent ratios: were used for the propelling nozzle and for the remaining part of the ejectors. The proposed model can be applied both in the determination of the ejectors geometric parameters for the set working condi- tions a the determination of the work characteristics for the set geometry. The next part of the work presents the findings of numerical analysis of the influence of changing two key geometric parameters on the work of the super- sonic gas ejectors: the position of the propelling nozzle with relation to the mi- xing chamber, and the length of the mixing chamber. These issues have a crucial impact on the efficiency of the gas ejector’s work; yet, they are not taken into consideration in zero-dimensional models. The monograph also presents the findings of analyses of regulation capacity with the use of a regulatory needle. The analyses were performed using isobutane, which has never been described in literature before. It should be stressed that due to substantial differences be- tween the thermodynamic and thermokinetic properties of hydrocarbons and synthetic working media, the results of analyses cannot be transferred directly. Therefore, the analyses significantly contributed to filling the gap in knowled- ge on issues of key importance for supersonic gas ejectors, connected with the effects of geometry modification, including regulation with the use of the re- gulatory needle. The influence of the applied turbulence model on the results concerning the parameters of non-design work of ejector was also analyzed. The result of analysis performed in this study area allowed to propose an ori- ginal approach regarding the validation of turbulence models with reference to supersonic gas ejectors. The remaining part of the work presents the results of original experimental studies on supersonic gas ejectors. In the first stage, the experiments involved isobutane as the working fluid. The parameters of the experiments were chosen so as to correspond to using the driving force from solar air conditioning or wa- ste low grade heat. The numerical calculations concerning a gas ejectors wor- king with isobutane were validated with fully satisfactory results. It is worth adding that so far, the results of numerical modeling with the use of CFD were mostly validated in literature with the use of steam and air. The next section presents the results of studies involving an industrial-scale prototype ejector refrigeration system with a prospective and ecological refri- gerant R1234zeE. Based on the available literature, at the moment of carrying out the study, it was the world’s first prototype of a ejector refrigeration system using an ecological refrigerant on this sale. The research confirmed that a ejec- tor refrigeration system can work with the source temperature even lower than 50oC, which has never been reported in literature for cooling systems powered by heat. Based on multivariant analysis of the system’s work, the results of nu- merical analysis and the results obtained for the developed model 0D were va- lidated with the use of the results of experimental studies of phenomena occur- ring in the cooling system and in the ejector. The results were fully satisfactory, indicating that the adopted methodology of gas ejector modeling is justified. The author analyzed the influence of working parameters on the physical phenome- na occurring in the ejector, as well as the work of the whole ejector refrigeration system. In addition, a design instrument was built based on the CFD model and supported with the 0D model that can be used to design similar systems.