Kazuyoshi Nakabe

Numerical study for enhancement of laminar flow mixing using multiple confined jets in a micro-can combustor

Abstract To meet demands arising as a result of present trends towards miniaturization, an innovative design for promoting mixing enhancement in a miniature can combustor is investigated using an unstructured finite-volume technique. A multi-holed baffle plate is employed to create a ring of oxidizer jets surrounding a single fuel jet in parallel with the axis of the cylindrical chamber. The baffle plate is found to produce a dramatic improvement to the mixing performance when compared with simpler co-axial jet cases. Relatively small changes in geometry are found to have a major influence on mixing for laminar isothermal flow.

PERFORMANCE OF A THREE-DIMENSIONAL, PRESSURE-BASED, UNSTRUCTURED FINITE-VOLUME METHOD FOR LOW-REYNOLDS-NUMBER INCOMPRESSIBLE FLOW AND WALL HEAT TRANSFER RATE PREDICTION

Unstructured finite-volume methods, which are rapidly increasing in popularity, provide a powerful alternative for the seamless handling of fluid dynamics in complex geometry. A vertex-centered, three-dimensional, unstructured finite-volume formulation is presented and applied to a number of standard and nonstandard test cases involving incompressible flow and heat transfer at low Reynolds number. The entire numerical formulation, including the diffusion terms, is derived using a fixed, Cartesian coordinate frame of reference and an edge-based data structure, making the present approach straightforward to follow and implement. The method is found to perform very well for all cases considered.

The Effect of Upstream Flow Conditions to Laminar Mixing in a Miniature Combustion Chamber

A three-dimensional unstructured finite-volume method is used to investigate laminar flow characteristics of a miniature chamber with a possible application to micro gas turbine combustor design. The chamber is cylindrical in shape and 20mm in diameter with the fuel stream entering via a single jet in the center of one end of the can. Oxidizer jets are generated by a circular baffle plate having six holes surrounding the fuel jet. Attention is given to the effect of the inlet conditions on the flow structure and mixing pattern inside the chamber. Computations are carried out with the calculation domain inlet being positioned at two different locations; (1) at the immediate entrance to the combustion chamber (2) one combustor diameter upstream of the baffle plate. Numerous inlet conditions are considered including ‘top-hat’, fully-developed, swirling, an annular backward facing step and some asymmetrically skewed profiles. The baffle plate is shown to have a significant smoothing effect on the inlet conditions for a Reynolds number of 100.Copyright

G143 Development of Fluid Temperature Measurements in Microchannels Using Fluorescence Polarization Method

A method of non-contact fluid temperature measurement in microscopic scale which is based on the fluorescence polarization is presented in this study. FITC conjugated casein was mixed in the working fluid as measuring target and the polarization of the fluorescence emitted from the microchannel was measured. The relationship between the fluid temperature and polarization degree was evaluated. In the result, a linear relation between the polarization degree and fluid temperature could be obtained. This agreed with the theoretical characteristics that the polarization degree quenches linearly due to the Brownian motion of the fluid. These results showed the feasibility of the temperature measurement in microchannels.

Experimental study on a compact methanol-fueled reformer with heat regeneration using ceramic honeycomb (third report: observation of reaction structure and its effect on reforming characteristics)

A ceramic honeycomb is applied to a 1-kW class compact tubular-type fuel reformer based on non-catalytic partial oxidation (POX) of methanol. Liquid methanol was used due to its easy handling characteristics. It is confirmed that POX in a super-rich condition can be sustained within the reactor. In most conditions, the reaction was stabilized near the outlet surface of the ceramic honeycomb where the maximum temperature is observed. The maximum temperature reaches approximately the adiabatic flame temperature, therefore, the ceramic honeycomb works as an adiabatic layer and a reaction stabilizer which can sustain the reaction at a certain location. The location of the reaction varies with regard to the thermal load conditions. Stable and high conversion rate was obtained when the reaction is stabilized on the outlet surface of the ceramic honeycomb. This robust feature of reaction stabilization is a significant characteristic of the ceramic honeycomb. The reaction characteristic and its effect on the reforming performance are investigated in this study using detailed measurements of temperature distributions and gas components.

Experimental Study on a Compact Methanol-Fueled Reformer With Heat Regeneration Using Ceramic Honeycomb (2

A compact tubular-type fuel reformer was fabricated and operated under fuel-rich combustion conditions of methanol, focusing on the partial oxidation reaction (POR). Ceramic honeycomb strainer blocks were inserted in the reactor. In the authors’ previous study, Case-1 of only one honeycomb block insertion showed that the reaction region formed in the downstream of the block. This block worked as a reaction stabilizer. The other condition, Case-2, was operated with the secondary honeycomb block inserted in the downstream of the reaction region in addition to the first block. This geometrical structure sandwiched the reaction region between the two blocks, and the thermal energy possessed by the exhaust gas could be regenerated to the reaction region by radiation exchange between these two blocks, which resulted in enhancing the preheating of the premixed gas. By this effect, the methanol-conversion and hydrogen-production in Case-2 were enhanced by about 10% compared to Case-1. In the present study, the reaction characteristics of the fuel reformer were investigated in detail, by detecting the location of the reaction region. Detailed temperature profiles in the streamwise direction were measured with traversable thermocouples, and positive ion current distributions corresponding to the reaction region were measured with a Langmuir probe. It was confirmed by the both measurements that there exists a reaction region right after the first honeycomb block which accompanies with sharp temperature gradients. The estimated thickness of the reaction region, however, was as wide as several millimeters to a centimeter, which is believed to be a ‘mild reaction’ stabilized by the first honeycomb block. In Case-2, the high-temperature region became broader compared to Case-1, which indicates that the enhancement of preheating of premixed gas was achieved by the heat regenerated from the secondary honeycomb block.Copyright