| Summary: | 博士 === 國立臺灣大學 === 應用力學研究所 === 103 === This dissertation includes two parts: the effect of the stack geometry design parameters, the spatial angle on the thermoacoutstic system and its onset value were studied in the first part; the feature of the double-acting and single-acting synthetic jet waere investigated in the second part.
In the first part, most of the previous works only focus on the effect of the stack’s cross-section and the resonator’s tube length without the discussion of the stack’s position and its length. Besides, although the effect of the different gas and the spatial angle on the temperature difference, pressure after onset has been studied, there is no discussion about the critical onset of thermoacoustic. In this dissertation, the relation between the dimensionless stack length (ls*), the dimensionless stack position (Xs*) and the spatial angle (θ) on the temperature difference (ΔT), temperature gradient (▽T), pressure (PA) and efficiency (η) in thermoacoustic system were investigated. Meanwhile, the relation between the minimum onset power (PWmin) of the thermoacoustic engine and the ls*,θwere also studied. In the part of the thermoacoustic heat pump, the effect of ls*, Xs*, opening ratio, thermal conductivity on ΔT, ▽T were studied.
In this dissertation, the effect of the ls* and Xs* in the standing-wave thermoacoustic engine on ls*, Xs*, ΔT, ▽T, PA, η were investigated systematically. The contour map of thermoacoustic engine efficiency on ls*-Xs* were build. The maximum efficiency is located at Xs* = 0.25、ls* = 0.086. In the study of the effect of ls*,θ on the critical onset of the thermoacoustic engine, the minimum onset power input PWmin was to compensate the heat loss of thermal conduction and thermal convection. Before the onset, short stack has larger temperature gradient, so it is easy to startup. The heat loss ratio of the conduction and convection is 2:3. While long stack has smaller temperature gradient, it is hard to startup. The heat loss ratio of the conduction and convection is reduced to under 1:4. After onset, the short stack has less working area between the air and the stack, so the sound pressure increase slowly along with the power input. While the long stack has larger working area in between. In the study of resonator’s spatial angle, the easiest startup system setup is open end up with the hot side up and cold side down ( θ = 90°) on the stack because the thermal buoyance can help the air break through the resistance. The glass stack with low thermal conductivity was build and tested. It can lower the minimum onset power 13% because of less heat loss of thermal conduction. The data curve can be merged based on the relation between thermal acoustic power PWacoustic and the unit length sound pressure. It shows that the similarity between different setup. In the study of thermoacoustic heat pump, the ls*-Xs* temperature difference contour map of the glass stack and the ceramic stack was build and found the maximum. The low thermal conductivity capillary glass tube stack can have 1.7 times higher temperature gradient than the ceramic stack in short stack. The high opening ratio glass tube stack can increase the temperature difference 13% in longer stack.
In the second part, the study of the double-acting synthetic jet (DAHSJ) and the single-acting synthetic jet (SASJ), the water was used as the working fluid. By the method of fluorescent dye visualization technique, the fluid exchange between the cavities and the formation of the vortex were clearly displayed. Comparing with the SASJ by PIV method, the DAHSJ has the feature of non-zero-net-mass-flux, so the fresh cold fluid can be supplied to cooling down the jet temperature, then the cooling ability can be improved. Besides, DAHSJ has 2 times more stronger vortex and half times less jet width than SASJ, so it can enhance the fluids mixing between the jet and the heating devices to improve the cooling. Finally, DAHSJ was modified and simplified the vertical wall of the central jet by numerical simulation (C.-F. Lin, 2007) to improve the volumetric efficiency and comparing with experiment. The results show that the blockage vortex forms at the side channel while the fluid pumps out from the central jet, which can prevent and reduced the central jet fluid sucking back into the side channle. By this way, it can enhance the net flow (more than 6 times) and the volumetric efficiency (more than 3 times). After removing 12 fluid diodes around the DAHSJ device, the volumetric efficiency can be enhanced more.
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