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Bartosz Zajaczkowski, PhD DSc, Assoc. Prof. from the Department of Thermal Sciences was awarded with the OPUS 22 grant in the competition of the National Science Center. The project entitled "Influence of the geometry of the tube bundle on pool boiling heat transfer in thermodynamic conditions close to the triple point" received PLN 922,200 of funding. 154 applications were submitted in the ST8 panel, 28 were funded. The success rate was 18%. The project will take 36 months to complete.
In recent decades, rapid societal and technological development increased energy demand and substantially depleted fossil fuel reserves, caused pollution and overall disruption of the global climate. To prevent depreciation of living standards, it is time to focus on safe, efficient and inexpensive renewable energy solutions. In modern societies, almost half of energy is used for cooling (especially for thermal comfort, production, distribution, and storage of food and medications) and the demand will certainly increase. Therefore, to reduce energy consumption it is very important to switch from electric to thermally driven refrigeration equipment. Moreover, equipment that relies on environment friendly refrigerants (especially water). Unfortunately, it appears that the performance of thermal equipment using common heat transfer fluids has reached its operational limit. Now it is more important than ever to turn the gaze from applied sciences (i.e., development of a new kind of heat exchangers and systems) back to the basic research including phase transitions (i.e., boiling) and thermal performance of natural working fluids.
This project focuses a little studied aspect of pool boiling phenomena of water - heat transfer during formation and departure of bubbles from a bundle of tubes at thermodynamic conditions near the triple point. In bundled configurations, bubbles growing and detaching from the lower tubes are expected to slide along the surface of the upper tubes, promoting both the activation of additional cavities and the evaporation of a superheated thin film captured at the bubbles’ base. On the other hand, large bubbles typical for low pressures may prohibit subcooled liquid from reaching the surface of neighbouring tubes and decrease heat transfer. Which effect dominates at low-pressure and why? These are the interesting scientific questions that we intend to answer in this project. Our experimental studies will fill the knowledge gap in low-pressure boiling on tubes, allow to determine boiling regimes for different working conditions, and provide new data to form valid heat transfer coefficient (HTC) correlations.
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