Wybrane zagadnienia cieplno-przepływowe urządzeń stosowanych w technice chłodniczej i cieplnej w ujęciu numerycznym i eksperymentalnym

W monografii przedstawiono wyniki wybranych prac badawczych eksperymentalnych i numerycznych urządzeń stosowanych w technice chłodniczej oraz w energetyce zawodowej. Przedstawione zostały wyniki badań lamelowej chłodnicy powietrza wykorzystywanej w chłodni owocowo-warzywnej pracującej w warunkach szronienia. Pokazano wpływ narastającego szronu na pogorszenie wymiany ciepła pomiędzy czynnikiem chłodzącym a powietrzem, co skutkowało zmianą temperatury oraz obniżeniem mocy chłodniczej wymiennika. Autor ocenił degradację termiczną wentylatorowej chłodnicy powietrza wywołanej szronieniem. Prezentowane wyniki mają wartość poznawczą i praktyczną. Przedstawione w monografii wyniki mają wartość poznawczą, aplikacyjną i wdrożeniową. Prace podjęte przez autora cechują się nowością, oryginalnością i wpisują się w kierunki najnowszych prac badawczych. Uzyskane wyniki mogą być wykorzystane jako materiał źródłowy do prac projektowych oraz stać się przyczynkiem do rozszerzenia prac związanych z opracowaniem i zastosowaniem prostych metod pozwalających na poprawę efektywności energetycznej urządzeń stosowanych w technice chłodniczej i cieplnej.

This monograph presents the results of research on selected thermal and flow phenomena which were carried out as part of scientific, research and implementation projects. Basics and motivation of necessity of the presented investigations as well as more detailed description of chapters content are presented in the Introduction section. Chapter 1 presents selected results of investigations of the air cooler operating in the vegetables cold storage chamber. Based on these results the assessment of the influence of frost on the air cooler surface on its efficiency was carried out. The changes in cooling capacity, air temperature and by-pass factor as well as thermal resistance caused by frosting process were investigated. The air-cooler investigated in Chapter 1 was applied in the analysis presented in Chapter 2 for the modeling of fin-and-coil heat exchanger with simplified methods. The experimental data were used as an input parameters. Also, they were used for validation of the numerical results. The simulations were performed for the simplified geometrical models, with application of the standard modeling approach (porous medium model) and the innovative approach using the so called dual model. The obtained results were also used to simulate the entire cold store and to carry out additional numerical analyzes that could not be carried out experimentally. The application of a porous medium model for modeling of the air flow is developed in Chapter 3. In this case, the model was applied for the perforated plate panels used in the electrofilters. The perforated panel contains of dozens of plates with various degrees of the opening. The use of a porous medium model allowed to simplify the geometry of the perforated plates to a uniform plane reducing both time and computational power required for simulation and saving the accuracy of the obtained results. The chapter presents the results of the numerical calculations carried out for the plates of various openings. Chapter 4 presents the results of theoretical analysis and experimental investigations on the improvement of Coefficient of Performance (COP) of the ejection refrigeration systems. An innovative way to effectively improve the COP was presented. The regenerative heat transfer between superheated vapour discharged by the ejector and the liquid feeding the vapour generator was used as a basic approach for the COP improvement. Therefore, the vapour phase superheating was used to preheat the liquid phase that feeds the vapour generator. As an effect, the obtained temperature increase of the liquid reduces the demand for the motive heating power. The results show that COP can be improved up to 13 % depending on the refrigerant used in the system. Chapter 5 contains the theoretical basis and the results of the experimental investigations of a mini-channel heat exchanger operating with propane. Such mini- channel heat exchanger can be applied in various refrigeration systems. Two cases of heat transfer modes in these heat exchangers were investigated, i.e.: evaporation and condensation heat transfer. The modified indirect method based on a combination of Wilson method and thermal resistances separation method was developed and applied to determine the average heat transfer coefficient at the refrigerant side. Based on the experimental data, the flow resistance in the investigated cases of the heat exchanger operation as evaporator and condenser was evaluated. The obtained results also allowed to develop a simple and physically based relationship for the assessment of the flow resistance for both the mini-channel condenser and evaporator.