A new micro-reformer system that consists of a micro-reformer (reactor), a micro-combustor and a micro-evaporator is studied experimentally and computationally. The micro-combustor as a heat source is a simply cylinder, which is easy to fabricate, but is two-staged (expanding downstream) to control ignition and stable burning. The micro-evaporator for vaporizing methanol-water mixtures is an annulus, which is effective to be heat-transferred from the first-stage micro-combustor. The micro-reformer for converting methanol-water mixture vapor to hydrogen is also an annulus, which is effective to be heat-transferred from the second-stage micro-combustor. The annulus-type micro-reformer system is designed to produce 1-10 W hydrogen using the steam reforming method. In order to satisfy the primary requirements for designing a stable and effective micro-reformer system, i.e., stable burning in the micro-combustor and maximum heat transfer through the wall, enhanced hydrogen production and minimized carbon monoxide concentration, catalyst is compactly installed in the micro-reformer and the micro-combustor geometry is varied. Results show that the aspect ratio and wall thickness of the micro-combustor substantially affect hydrogen production rates and the quality of reformed gas. For optimized design conditions, a premixed micro-flame is easily ignited in the expanded second-stage combustor, moves into the smaller first-stage combustor, and finally is stabilized therein. The measured and predicted temperature distributions across the micro-reformer system walls indicate that heat generated in the micro-combustor is well transferred into the micro-evaporator and the micro-reformer. Thus, the present micro-reformer configuration can be applied to practical micro-reformer systems for use with fuel cells. For a typical operating condition, the designed micro-reformer system produces 3.6 W (in LHV) hydrogen with an overall efficiency of 12%.

Keywords: Micro-reformer, Micro-combustor, Micro-evaporator, Micro-combustion