| 摘要: | 本論文以氫為燃料，整合三項潔淨節能技術，即熱再循環、觸媒反應與熱 電轉換技術，實作一可攜式零CO2 排放之熱電產生器(thermoelectric generator, TEG)，其核心組件有三：(1)瑞士捲觸媒熱源產生器(Swiss-roll catalytic heat source, SRCHS)，(2)熱電模組(thermoelectric modules, TEM)和(3) 熱沉裝置(heat sink, HSi)，依序以三明治堆疊方式而組成。本研究有三組同 樣尺寸但不同材料之SRCHS，其面積為50×50 mm2 而厚度僅為10 mm，分 別採用銅、不鏽鋼S304 和陶瓷材料B85 所製成，其熱傳導係數分別為k = 385、26 和0.38 Wm-2K-1，三組SRCHS 內均含有以CNC 車床加工之1.5 圈 瑞士捲流道(截面積4×4 mm2)，流道內置入蜂巢式白金觸媒塊長5 mm，當 預混氫/空氣燃料經流道入口通過白金觸媒，在常溫時即可產生化學反應並 釋放熱。因瑞士捲流道具有熱再循環特性，故可提供均勻的熱源給TEM， 再以多種不同熱交換設計概念之HSi，來穩定控制以碲化鉍(Bismuth Telluride, Bi2Te3, 最高操作溫度400oC) 為材料之TEM 熱冷兩端的溫差，同 時並探討不同壓力負載對TEG 系統功率密度之影響。在實驗量測方面，針 對不同氫體積濃度([H2] = 6% ~ 13%)及不同雷諾數 (Re = VfD/v = 500 ~ 3,000；Vf 為燃料流速，D 為流道寬度而v 為燃料運動黏滯係數)，以10 支K 型熱電偶沿著瑞士捲流道及在觸媒塊前後，定量量測反應後溫度隨時間之 變化，並使用3 組熱電偶貼片量測SRCHS 和TEM 間之表面溫度，以找出 適當溫度控制之範圍，使系統功率可達最高；同時，也採用氣體分析儀， 量測[H2]、[O2]和[NOx]等排放物之濃度。在數值分析方面，我們首度建立 了三維模式，以CFD-RC 軟體結合13 個白金觸媒表面反應機制，並考慮 SRCHS 邊界之熱損失，合理地預測SRCHS 之化學反應流特性，模擬結果 與實驗量測結果相符合。經由一系列完整測試與分析，我們找到以B85 為 材料之SRCHS 有最大之熱再循環效應，在[H2] = 12%、Re = 2,000 和系統壓 力負載為200 psi 條件下，控制TEM 熱冷端溫差在200oC，可獲得高達540 mWcm-2 之系統功率密度。此一創新可攜式熱電產生器，完全沒有二氧化碳 和氮氧化物之排放，為一潔淨能源新技術，可提供許多電子產品，例如照 明燈具、手機、隨身聽、手提電腦等等，其使用或充電所需之電源。未來 若能結合高溫型之TEM，可研發高功率之熱電產生器，來驅動新世代無污 染之熱電汽車。 This thesis uses hydrogen as a fuel and combines three clean energy-saving technologies, including heat-recirculating, catalytic reaction, and thermoelectric conversion techniques, to innovate and devise a portable thermoelectric generator (TEG) with zero CO2, CO and NOx emissions. The TEG has three key components: (1) the Swiss-roll catalytic heat source (SRCHS), (2) the thermoelectric module (TEM), (3) and heat sink (HSi), which are sequentially sandwiched. Three SRCHSs of the same size (50 × 50 × 10 mm) but using different materials including copper (Cu), stainless steel (S304), and ceramic (B85) with corresponding thermal conductivities 385, 26, and 0.38 Wm-2K-1 are manufactured by the CNC machine. All three SRCHSs have 1.5-turn Swiss-roll reactant and product channels having 4×4 mm2 cross-sectional areas. A 5-mm long platinum honeycomb catalyst is placed on the entrance reactant channel to produce heat via surface reaction when H2/air premixtures are flowing through the Pt honeycomb catalyst even at room temperature. Because SRCHS has heat-recirculating characteristics, it can provide uniform heat source to TEM together with different heat exchange designs of HSi and thus the wanted temperature gradient across the TEM can be stably controlled. The TEM material is Bismuth Telluride (Bi2Te3) and its maximum operation temperature is 400oC. In addition, the effect of different loading pressure to the power density output of the TEG system is measured and discussed. For experimental measurements, we use 10 K-type thermocouples along the SRCHS channel and in front of the Pt honeycomb catalyst and behind to measure temperature distributions as a function of time in the SRCHS. Three cement-on thermocouples are used to measure surface temperatures on the top area of the SRCHS. The hydrogen concentration in volume percentage varying from [H2] = 6% to [H2] = 13% is applied with a wide range of the flow Reynolds number (Re = VfDv-1) varying from 500 to 3000, where Vf is the reactant velocity, D is the width of the channel, and v is the kinematics viscosity of the reactant. Moreover, emission of [H2], [O2], [NOx] and more are measured by the gas analyzer. For numerical Simulations, a 3D model is established using CFD-RC package combined with 13 platinum surface reaction mechanisms with the consideration of heat losses to predict chemical reacting flows in the SRCHS. Numerical predications are in consistent with experimental measurements. It is found that the B85 SRCHS with very small thermal conductivity has the maximum heat recirculation among three SRCHSs, using [H2] = 12% and Re = 2,000 in the SRCHS, applying the water-cooling HSi, and adding a pressure load of 200 psi to the TEG system, the temperature difference across the TEM can be controlled at 200 oC, yielding the best power performance with a power density as high as 540 mW/cm2. This novel portable TEG is free of CO2 and NOx, which is a new clean energy technology and can used for many small electrical devices. |
