Characteristic Investigation Of Low Onset Temperature Differential Thermoacoustic Engines

Thermoacoustic technology is of a promising new technology using thermoacoustic effect to deal with the conversion between thermal energy and acoustic energy(a sort of mechanical energy), and there is a great application prospect in the utilization of low grade energy, and especially, in the new energy and low temperature industrial waste heat. The onset temperature of thermoacoustic heat engines is directly related to the grade of energy the system can use, therefore, the research of the low onset temperature thermoacoustic heat engine is of great significance in the utilizating various low grade energies. In this thesis numerical simulation investigations are carried out on low temperature difference thermoacoustic engines in order to explore the characteristic of the low onset temperature and high performance of thermoacoustic engine systems, the main contents are as follows.1) Using DeltaEC software, a low onset temperature difference of standing thermoacoustic engine is designed considering both the system efficiency and the heating temperature of high temperature heat exchanger. Meanwhile, the onset characteristic of standing wave thermacoustic heat engine is numerically analyzed using the two-port network model and onset criteria. The effects of structural parameters for the stack and resonance tube on the steady and onset state characteristics of the thermoacoustic engine are investigated closely. The studied results demonstrates that at different charging pressure there exists an optimal stack gap to achieve the lowest onset temperature, but the ratio of the optimal stack gap to thermal penetration depth remains unchanged, and is of 2.25 or so for the standing wave thermoacoustic engine in consideration..2) Based on the thermoacoustic network theory and transfer matrix method, the onset condition equation is derived for a multistage looped-tube thermoacoustic engine. This onset condition equations an implicit function in terms of the structure configuration of system, operating working condition, and thermal-physical properties of working substance, which can provide an engineering practical network method for the design, optimization and performance analysis of thermoacoustic engines. The onset characteristics and its influencing factors are analyzed numerically using this network method for a looped tube thermoacoustic engine. The studied demonstrates that at different charging pressure there exists an optimal hydraulic radius of regenerator screen mesh to achieve the lowest onset temperature, and the more stage the engine has, the lower the onset temperature and oscillation frequency is. At the same time, the steady-state characteristics of this looped type thermoacoustic engine are also investigated numerically. Using DeltaEC software, the output acoustic power and efficiency of the engine are calculated as well. The studied results indicates that at constant heating power, using mixture working substance will lower the temperature difference across the regenerator, and produce a larger acoustic power.3) The onset characteristics and its influencing factors are closely investigated using the derived onset condition equation for a multistage looped-tube thermoacoustically driven refrigerator. Meanwhile, the steady characteristic of the system, and the effects of refrigeration temperature and heating temperature of heat engine on the system performances is also analyzed. The studied demonstrates that this small thermoacoustic engine driven refrigeration system has lower onset temperature difference;There exists the maximum value of relative Carnot performance coefficient for the refrigerator unit, relative to the refrigeration temperature. Moreover, the higher heating temperature of heat engine is, the larger maximum value is, and the lower corresponding refrigeration temperature is.