| 摘要: | 本論文以氫為燃料，結合熱再循環、觸媒反應、及熱電轉換技術，實作一潔淨可攜式熱電產生器。本系統包含三個核心組件：(1)瑞士捲熱源產生器(Swiss-roll Catalytic Heat Source, SRCHS)，(2)熱電模組(Thermoelectric Module, TEM)，(3)熱沉裝置(Heat Sink, HSI)，依序以三明治堆疊方式組成。SRCHS由類陶瓷板材(B85)所製成，厚度僅10 mm，而面積為50 mm × 50 mm，並以CNC銑床加工流道截面積為4 mm × 4 mm的1.5圈瑞士捲式流道，於流道不同處置放不同長度(5 mm ~ 10 mm)的蜂巢式白金觸媒。利用預混氫氣/空氣與白金觸媒表面化學反應所產生的熱釋放，加上B85板材極低之熱傳導係數及瑞士捲流道的熱再循環特性，以及高熱傳導係數的銅製上板，可產生均勻熱源供TEM熱端使用，並以水冷式HSI置於TEM冷端，提供一可控制之溫差範圍(50℃ ~ 250℃)，並找出優化之壓力負載條件，使TEM產電。有關實驗量測方面，針對觸媒長度與分段擺放位置與不同氫體積濃度([H2] = 8 ~ 12%)及以流道寬度定義之雷諾數(Re = Vf D/? = 500 ~ 2000；Vf為燃料流速，D為流道寬度而?為燃料運動黏滯係數)來探討流道內溫度分佈，利用10支K型熱電偶量測流道內部溫度，及3支K型貼片式熱電偶量測銅製上板表面溫度(即TEM熱端溫度)，找出適當的溫度控制範圍，優化本系統之輸出功率。在數值模擬方面，以CFD-RC軟體建立三維模式的計算模擬，結合13步驟白金觸媒與氫氣/空氣的化學表面反應機制，並考慮邊界熱損失來預測模擬SRCHS的化學反應流特性，模擬結果與實驗結果一致。本研究也模擬TEM的熱場與電場的轉換效應，考慮TEM的有效接觸面積與適當的Seebeck係數，來分析TEM之開迴路電壓(OCV)。由模擬與實驗比對的結果，我們找出此系統的較佳操作條件，在[H2] = 12%、Re = 1500、及兩段各長5 mm之分段觸媒位置，控制TEM在溫差為200℃及200 psi的壓力負載之下，本系統可輸出功率密度為520 mW/cm2。此一創新可攜式電源供應器，為一潔淨氫能利用技術，可供許多小型電子產品使用，例如照明燈具、筆記型電腦、或充電系統所使用。 This thesis applies hydrogen as a fuel and combines three clean energy-saving technologies, including heat-recirculating, catalytic reaction and thermoelectric conversion, to devise a clean portable thermoelectric generator (TEG). This TEG system consists of three key parts: (1) A Swiss-roll catalytic heat source (SRCHS), (2) a thermoelectric module (TEM) and (3) a heat sink (HSI), in which the TEM is sandwiched between the SRCHS and the HSI. The SRCHS made of B85 material with properties similar to that of the ceramic material is manufactured by a CNC machine to have a 1.5-turn Swiss-roll channel with a cross-sectional area of 4 mm × 4 mm. The cross-sectional area of SRCHS is 50 mm × 50 mm with a height of 10 mm, in which various lengths (5 ~ 10 mm) of honeycomb platinum catalysts located inside the SRCHS`s channel are need to generate heat from the surface reaction between premixed H2/air mixtures and Pt catalyst. Because of very low heat conductivity of B85 material together with the Swiss-roll heat recirculation, the SRCHS features as a uniform heat source for the TEM provided that a copper plate with very high heat conductivity is used. In addition, we apply a water cooling HSI, so that the wanted temperature range (50 ~ 250℃) across the TEM can be stably controlled. For temperature measurements, ten K-type thermocouples positioned at different locations along the SRCHS flow channel as well as three K-type thermocouple films positioned on the upper copper plate surface are applied to measure temperature distributions of the SRCHS. Various hydrogen concentrations in volume percentage ([H2] = 8 ~ 12%) are used with a wide range of the flow Reynolds number (Re = VfD/?) varying from 500 to 2000, where Vf is the mean velocity of reactants, D = 4 mm is the width of the flow channel, and ? is the kinematic viscosity of H2/air mixtures. This study also measures emissions of [H2], [O2], and [NOx] using the gas analyzer. For numerical simulations, a 3D reacting model is established using CFD-RC packages combined with a 13-steps platinum surface reaction mechanism with the consideration of heat losses to predict chemical reacting flows in the SRCHS. Moreover, efforts are made to simulate heat and electric fields of the Seebeck effect for the TEM by using the effective contact area and the proper Seebeck coefficient of the TEM. Thus, the relation between the open circuit voltage and the temperature gradient can be simulated and obtained. Numerical results are found to be in reasonably good agreement with experimental data. Finally, when using two segments of catalysts each having 5 mm long placed inside the channel of the SRCHS with the water cooling HSI, the TEG system has the highest power density up to 520 mW/cm2, where [H2] = 12%, Re = 1500, and ΔT ? 200℃ between the cold and hot sides of TEM with a mechanical load of 200 psi. This novel portable TEG system is a pollution-free power generator which is useful for many small electric devices. |
