| dc.description.abstract | 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. | en_US |