An Experimental Study of A Small Heat—Recirculating Catalytic Burner and Its Applications

• Main Authors: Sheng-Je Wu, 吳昇哲
• Other Authors: Shenqyang Steven Shy
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/18937908390789602346

碩士 === 國立中央大學 === 機械工程研究所 === 91 === 英文摘要 This thesis includes two parts. The first part is to design a small energy-saving geyser using the concept of the Swiss-roll burner. We measure the outlet water temperature and analyze the thermal efficiency of geyser by changing the geometry of the burner as well as varying the arrangement of the water tube. The Swiss-roll burner employs the principle of heat recirculation to minimize heat losses, to increase burning efficiency, and thus to make excess enthalpy burning possible. The premixed fuels used in the experiments are propane and air mixtures. We use a long water tube wrapped along the upper product channel of the Swiss-roll burner, so that the water can be heated via the heat conduction from the high temperature product channel. The second part of the thesis is to fabricate a small excess enthalpy burner that can supply a stable heat source using catalytic combustion, which is attempted to generate electricity in the future. Concerning the study of the energy-saving geyser, we varied the water tube layer number (lay), the water volume flow rate (Qw), and the flow Reynolds number (Ref =VfD/ν) to evaluate the influence of these parameters on the water outlet temperature (Tw-out) and the corresponding thermal efficiency (η) of the geyser, where Vf is the fuel mixture’s mean velocity, D is the reactant channel’s width, andνis the reactant kinematic viscosity. It is found that Tw-out and η are decreased when Qw and/or Ref are increased. For examples, when the value of Ref increases from 503 to 754, η reduces from 80.1% to 37.2% for the conditions of lay = 1 and Qw = 2.0 liter/min. When lay increases from 1 to 2, η can increase up to 10% at Ref = 503 and Qw = 2.0 liter/min. For the catalytic burner, we varied the operating conditions to measure temperature distributions and the emissions. The results indicate that the catalytic outlet temperature Tc-out (just outside the honeycomb catalyst) is increasing when the number of rolls of the burner N is increasing. If we increase Ref and the length of catalyst Lc, Tc-out will decrease. We also found that the Pd catalytic burner can be operated at a critical equivalence ratio c = 0.06, which is much less than the common lean flammability limit of C3H8/air mixtures where = 0.57. The honeycomb catalytic burn is much better than that using Pt pellets. For emission measurements, the NOx emission is below 1 ppm because the catalytic experiment is operated at low combustion temperature (＜ 800℃). The concentrations of CO are less than 20 ppm at ＜ 0.4. If = 0.2, the concentrations of CO are no more than 1 ppm. For the test of durable ability of the catalytic burner, the results show that Tc-out is decreased by increasing the operating time at fixed = 0.5 and Ref = 377 conditions. Using the scanning electron microscope (SEM) to take the particle surface of catalytic substrate, we found that the scope of catalytic sinter is increased by increasing the operating time. The particle of catalytic substrate surface is obviously sintered by high temperature (T up to 1000℃) after 120min operations at = 0.2 ~ 0.4 conditions. On the surface of Pt catalytic, we found that the lump sinter is produced. Both Pt and Pd catalytic surface are forming great range of sinter when the operation time is up to 4 hours at = 0.2 ~ 0.4 for highest temperature up to 1000℃. Furthermore, we found that the chap phenomenon on the catalytic surface may be formed by the unbalanced cooling shrink after experiment. In the future, we shall build a small catalytic burner together with thermoelectrical materials to generate electricity.