The proposed research is an investigation of the generation of shock waves by flash evaporation. Flash evaporation occurs when a liquid is suddenly exposed to a pressure lower than its saturation pressure. Then some of the sensible heat must be transferred into latent heat of vaporization and a fierce and sudden process of vapor bubble formation occurs within the liquid while the temperature of the fluid decreases significantly. There have already been applications for flash evaporation, including water desalination, the depositing of thin layers of material and in vapor sterilization. Still shock wave processes induced by flash evaporation have not been much documented, hindering the exploitation for new technical applications. Extending this scientific knowledgebase will help to overcome this barrier. Although these phenomena can damage industrial equipment; these shock waves have been hypothesized as useful in creating compression. It has been predicted that condensation can follow the pressure rise, leading to a new phase change compression principle also applicable for thermodynamic cycles. The newly invented condensing wave rotor is an example for a technical application. Such novel technology can yield higher energy efficiency for refrigeration cycles, particularly in combination with the natural and benign refrigerant water (R718). Additionally, this knowledge may be applied to other refrigerant cycles, but also to fuel pumps and to pressure recovery devices for liquefied gases and more. To increase understanding flash-induced shock behavior, basic experimental investigations will be conducted to verify and extend an analytical model. To verify and investigate the generation and behavior of flash-driven shock waves in water vapor under vacuum, particularly the relationship between flash evaporation conditions and shock wave strength will be investigated through a controlled experiment. For this, a single-chamber test rig will be constructed in which pressure and temperature changes will be recorded with transducers and an infrared camera. The experiment shall verify and extend an analytical model previously generated by the PI's team. The Intellectual Merit of the Proposed Activity The main objective of the experiment is the verification, recording and investigation of flash evaporation induced shock waves under vacuum in water vapor for which there appears to be no accessible scientific documentation yet. Therefore, the results will extend the fundamental knowledgebase and will help to improve and validate the mathematical models which have been used to describe the dynamics of this compressible phase-change flow. Additionally, this experiment shall confirm that flash induced shock waves can generate pressure rises applicable for the condensation of water vapor at higher pressures. The Broader Impacts The understanding of the fluid behavior of flash evaporation induced shock wave processes is important to prevent disastrous effects of flash evaporation and for the development of industrial applications. A first technical application can be in the novel condensing wave rotor that uses the basic principles of flash evaporation and shock waves to increase the efficiency of water refrigeration systems that use only water (no chemicals) as refrigerant. The novel concept of a condensing wave rotor may then replace and combine in one dynamic system three subsystems needed in conventional systems: the compressor, the intercooler, and the condenser. This will compact these systems considerable and reduce the resources used for such systems. Application of the principle for other refrigerants is also envisioned as well as for fuel pumps and for pressure recovery devices for liquefied gases. A female graduate student will work on this exploratory one year project, supported by undergraduate students. The information obtained will be presented in both undergraduate and graduate classes as the PI has a tradition in his classes like Refrigeration, Thermodynamics, Heat Transfer and Turbomachinery. Furthermore, the findings are planed to be published in the International Journal of Heat and Mass Transfer and the Annual Review of Fluid Mechanics, and will be presented at the ASME IMECE and ASHRAE Annual Meeting to inspire further applications. The test rig shall also be used for impressive demonstrations to high-school students at the SET day of the MSU Engineering College, where prospective students are invited to visit the laboratories.
