Abstract
The combustion characteristics of methane/moist air in micro-tube reactors with different numbers and shapes of inner wall protuberances are investigated in this paper. The micro-reactor with one rectangular protuberance (six different sizes) was studied firstly, and it is shown that reactions near the protuberance are mainly controlled by diffusion, which has little effect on the outlet temperature and methane conversion rate. The formation of cavities and recirculation zones in the vicinity of protuberances leads to a significant increase of the Arrhenius reaction rate of CH4 and gas velocity. Next, among the six different simulated conditions (0–5 rectangular protuberances), the micro-tube reactor with five rectangular protuberances shows the highest methane conversion rate. Finally, the effect of protuberance shape on methane/moist air catalytic combustion is confirmed, and it is found that the protuberance shape has a greater influence on methane conversion rate than the number of protuberances. The methane conversion rate in the micro-tube decreases progressively in the following order: five triangular slight protuberances > five rectangular protuberances > five trapezoidal protuberances > smooth tube. In all tests of methane/moist air combustion conditions, the micro-tube with five triangular protuberances has the peak efficiency and is therefore recommended for high efficiency reactors.
Highlights
With micro-combustion gradually becoming a significant technology for energy production, the miniaturization of devices such as micro-thrusters, micro-engines, micro-robots, and micro-combustors, etc. in Micro-electromechanical Systems (MEMS) [1,2,3,4] has become an important subject
0–5 rectangular protuberances, the results indicate adding slight protuberancesnumber on the wall increases the area of the recirculation zones at lowthat velocity, and the protuberance has a increases areaon of the and the protuberance number has positive positive the effect the recirculation mixture gaszones flowatinlow thevelocity, micro-tube channel
A micro-tube reactor with multiple slight protuberances is investigated in this paper
Summary
With micro-combustion gradually becoming a significant technology for energy production, the miniaturization of devices such as micro-thrusters, micro-engines, micro-robots, and micro-combustors, etc. in Micro-electromechanical Systems (MEMS) [1,2,3,4] has become an important subject. In the micro-reactor, the surface-to-volume ratio (S/V) increases and the residence time of gas mixtures in the micro combustion chamber is reduced, which results in high thermal losses, high free radical losses, and even flameouts, etc. Most researchers believe that catalytic combustion [7,8] is an effective way in reducing the heat losses and enhancing the combustion stability under the fuel-lean conditions [9]. In the field of micro-scale catalytic combustion for energy production [13,14,15], most researchers focus on the use of natural gas, methane, as the main component [16,17,18], which is regarded as a clean, renewable and universal fuel [19,20,21].
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