| 摘要: | 本論文應用氫與蜂巢式白金觸媒，分別結合熱再循環技術和衝擊流流場來產生熱源，並利用熱電材料(thermoelectric module, TE)和熱交換器(heat exchanger, HE)，設計實作三種新輕巧型可攜式潔淨電源產生器，可提供諸如戶外照明、手機等小型電子設備充電用。此觸媒熱電轉換技術，首重在設計與改良觸媒熱源產生器(catalytic heat generator, CHG)和HE，使置於其中之TE接觸表面能有均勻溫度分佈，並有約200ºC的溫差及約200 psi的壓力負載，這是達到最佳TE發電效率之必要條件。本研究有三種CHG之設計並配合兩種HE：(1)採用不銹鋼和銅兩種不同材料所製之流道截面積為5 cm × 1 cm的2.5圈瑞士捲(Swiss-roll, SR)CHG，搭配氣冷式鋁製散熱鰭片；(2)與設計(1)類似，使用銅材料所製之流道截面積為0.8 cm × 0.8 cm的1.5圈SRCHG，搭配水冷式銅製HE；(3)衝擊流CHG，即運用觸媒圓管噴流，直接衝擊置於一傳熱銅片上之TE，並搭配水冷式銅製HE。我們以多達15支K型熱電偶和氣體分析儀，定量量測三種不同CHG設計之溫度分佈和生成物成分，進而分析材料特性、SR圈數、燃氣雷諾數(Re)以及氫體積濃度([H2])等效應，對CHG性能之影響，以評估三種不同設計之電源產生器的輸出功率大小。另一研究重點，為建立SRCHG和衝擊流CHG的二維數值模型，以CFD-RC為基礎，結合CHEMKIN 4.1中13個步驟之氫與白金觸媒表面反應機制，來模擬分析設計(2)和設計(3)之化學反應流場，並考慮熱損失效應。 實驗量測和數值模擬結果，均顯示以氫為燃料之三種不同設計CHG，其生成物僅為水，完全沒有可量測之[CO]和[NOx]，確為潔淨電源產生器。我們發現，CHG材料之熱傳導係數，對TE接觸表面能否維持溫度均勻之分佈有重大影響，例如[H2] = 3%和Re = 380操作條件下，銅製設計(1)SRCHG，其輸出功率遠高於設計(1)不銹鋼製SRCHG約達4倍之多。增加SRCHG捲道圈數，雖然可提高熱再循環率，但無助於達到所需之最佳溫度差，且還會增加電源產生器的體積，故若以SRCHG為小型電源產生器之熱源，設計(2)遠比設計(1)優良。在[H2] = 1% ~ 4%和Re = 350 ~ 1300範圍內，SRCHG內部不同位置之溫度皆會隨著[H2]和Re增加而增加，故由控制[H2]和Re，可增加電源產生器之輸出功率密度。設計(3)的特色，不僅有最小的體積，且具備更寬廣的操作範圍([H2] = 1% ~ 10%，Re = 1000 ~ 6000)，可輕易產生高達500 mW/cm2的輸出功率密度，優於設計(2)最高的320 mW/cm2和設計(1)最高的240 mW/cm2。本研究實作出手掌大小以氫為燃料之零污染電源產生器，足以提供一般小型電子設備用，並成功建立相關之化學反應流場之數值模型，應具有重要的應用和學術價值。 This study uses hydrogen as a fuel in honeycomb Pt catalysts, combines with heat-recirculation technology or impinging jet flow to produce heat, and further integrates thermoelectric (TE) modules and the heat exchanger (HE) as a cooler, to propose three portable clean electric power generators for the use of small electronic devices such as outdoor lighting and cell phones. There are three different designs of catalytic heat generators (CHG) together with two different HEs in this study, each having a HZ-2 TE module between CHG and HE. Design (1) is a 2.5-turn Swiss-roll CHG (SRCHG), made of either stainless steel or copper, having a flow channel cross-section of 5 cm * 1 cm with an aluminum-fin HE. Design (2), similar to design (1) and copper-made only having 1.5-turn squared flow channel of 0.8 cm side length, is water-cooled by a copper HE. An impinging thermal jet was applied to design (3) for directly heating the copper plate adjacent to the TE module with the same HE used in design (2). The first objective is to design suitable CHG and HE, for which the temperature distribution on TE can be as uniform as possible having a temperature gradient of 200 ºC with a high compressive load of about 200 psi for achieving the best TE performance. As many as 15 thermocouples are used to measure the temperature distribution in these three CHGs and the product concentrations were also measured by the gas analyzer. Thus, these data can be used to analyze the effects of material properties, the number of turns of SRCHG, flow Reynolds number (Re = VfDin/n) and hydrogen volume concentration [H2] to the TE power performance, where Vf is the average velocity of reactants, Din is the width of flow channel or the jet diameter, and n is the kinematic viscosity of reactants. The second objective is to build two-dimensional CFD-RC based numerical models with submodels from CHEMKIN 4.1 including 13 hydrogen-Pt surface reactions and with the consideration of heat losses for simulation of chemically reacting flows occurred in designs (2) and (3). Both experimental and numerical results show that all three CHGs have zero [CO] and [NOx] emissions with only water as the product, so they are true clean electric power generators. For the design (1), we found that the copper-made SRCHG has up to four times higher TE power density output than the steel-made SRCHG due to higher thermal conductivity of coppor. Furthermore, it is found that increasing channel turns of SRCHG does not increase the power density output. For the design (2), values of temperature at various positions inside the SRCHG increase linearly with [H2] and/or Re, at least in the ranges of [H2] = 1% ~ 4% and/or Re = 350 ~ 1300. By adjusting [H2] and/or Re of the SRCHG (2), we can control TE power output, and the design (2) is much better than the design (1) in terms of smaller volume and higher power density output. Finally, the design (3) has the smallest volume, widest operation ranges ([H2] = 1% ~ 10% and Re = 1000 ~ 6000), and highest power density output (500 mW/cm2) among all three designs. Finally, the present palm-sized clean hydrogen-fueled electric power generators and their corresponding 2D numerical models successfully established here are of both practical and academic fundamental values. |
