摘要：本計劃欲分三年執行，總目的為設計、製造及分析一小型熱聲學冷凍機。“小型”指冷凍機之特徵長度為公分尺度(第一年)到公釐(第二年)，但將使用MEMS製程製造關鍵零件在各年中(如圖8中之冷凍機)。第一年將進行系統設計、使用矽製造 stack 關鍵零件、安裝在熱聲冷凍機平台中、及測試。第二年將專注於熱聲 driver 之設計、製造及測試。第三年將進行熱聲冷凍機系統整合、製造及測試。
第一年目標在熱聲機中關鍵零件: stack。計劃中將使用矽製造數件MEMS stack片，並將stack片疊整齊，stack片與stack片間使用低熱傳導材料隔離。MEMS stack片之物理動機在於降低聲波軸向之熱傳導(以空氣為主，熱傳導係數約0.025W/m-K)並增加聲波徑向之熱傳導(以矽為主，熱傳導係數約150W/m-K)。Stack 片疊將安裝在一活塞為 driver (最大300Hz.)之共振器中。矽 stack 量測結果將與陶瓷 stack 比較。數值計算及設計將使用熱聲學程式 DeltaE。
第二年將專注於熱聲 driver 之設計、surface micro-machining製造及
Abstract: This three-year proposal aims at design, fabrication and experimental study of small cooling devices. The term ‘small cooling devices’ implies cooling systems whose overall length-scale ranges from centimeter (first year focus) to millimeter (second year focus), but with MEMS fabricated components throughout the course of the three-year project (as an example, see Fig. 8). The first year will focus on the stack, perhaps the key component in a thermoacoustic device, and its performance. The second year will focus on the driver (micro-speaker) and its performance. The focus of the third year would be to integrate results from the first two years.
The first year focus is on the design and testing of a new small-scale thermoacoustics refrigerator stack using micro-machined technique. The unique approach is to use several MEMS fabricated silicon wafers with equally spaced gap as the stack. The motivation is based on the physic of suppressing conduction heat transfer (due to the air gap) in the direction of acoustic oscillation while encouraging heat transfer in the normal direction, since thermal conductivity of silicon (150W/m-K) is much higher than that of air (0.025W/m-K). The stack assembly will be mounted adjacent to an oscillating piston (max 300 Hz) as an acoustic source. Results will be compared with a ceramic stack as baseline as well as computation by a linear acoustic code DeltaE.
The second year effort is on MEMS-based thermoacoustic driver. The driving mechanism will be micro-speaker (in place of the piston in the first year) to produce the acoustic wave. Thermoacoustic cooling device needs an independent driver (no motor nor piston) to generate the acoustic wave, and micro-speaker is ideal for this purpose. However, the micro-speakers will have to be fabricated in an array to increase the total acoustic power output.
The third year will focus on integrating the effort made by the first two years, which will entail fabrication and testing of a new thermoacoustic cooling device. Depending on the outcome of results then, the final year will tailor its effort on studying a small, unique cooling device. Most likely, the device will consist of a small or micro driver (oscillating source) and a stack housed within a resonator.