טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentBerdugo Nir
SubjectStable Operation of a Two-Phase (Wet) Thermoacoustic Engine
DepartmentDepartment of Energy
Supervisors Dr. Dan Liberzon
Professor Yehuda Agnon
Full Thesis textFull thesis text - English Version


Abstract

Many low grade sources of excessive heat are being emitted to the environment; some are in the form of humid air (e.g. power plants, electrical appliances, car exhausts, etc.). The presented work was motivated by the desire to harvest such sources of excessive heat with a thermoacoustic engine by converting it into useful work.

The traditional dry thermoacoustic engines (DTE) that convert heat flow over stack into monotone acoustic wave being amplified by the housing resonator have recently gained an increased interest, which provided a possible option for harvesting sources of excessive heat. Being easy to build and operating without moving parts, the DTE offers high efficiency and a long life cycle, albeit requiring high temperature differences of Δ T=150-30 0 o C for operation, which is not available with the low grade excessive heat sources. A better alternative is the development of a wet thermoacoustic engines (WTE) as they incorporate water evaporation/condensation cycles and are able to operate across much lower temperature differences according to predictions available in literature ( ΔT=53-8 0 o C ,[Raspet2002, Ueda2013]).

Here, we report on a novel WTE that operates at ambient pressure across temperature differences as low as several degrees Celsius and capable of high acoustic energy outputs and working with resonator that forces an acoustic standing wave. A set of experiments was performed to isolate critical parameters that determine engine performance and emphasize achieving stable operation. We preformed experiments set on an “open system” (quarter wave resonator) and a set on a “close system” (half wave resonator). Each set included: different geometry, optimization of stack position and scouting for a suitable heating power for the engine configuration. It was found that the “open system” was highly influenced by environmental conditions and the experimental results were not repeatable. The “close system” gave repeatable results and the results are presented in the thesis. When the engine is in operation mode the acoustic pressure gain and the attenuation are steady while significant useful work is being generated at the output. It was found that control over two critical parameters (the partial vapor pressure/temperature gradient over the acoustic stack and the total water vapor flow rate through the resonator) is essential to achieve this task.