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This paper describes the heat and mass transfer in a square microchannel that is heated from one side. This microchannel represents a reaction channel in a microreactor that is used to study the kinetics of the catalytic partial oxidation of methane. The microchannel is contained in a silicon wafer and is covered by a thin silicon sheet. At the top side of this sheet, heating elements are present which mimic the heat that is produced as a result of the exothermic chemical reaction. Correlations for Nusselt and Sherwood numbers as a function of the Graetz number are derived for laminar and plug flow conditions. These correlations describe the heat and mass transport at the covering top sheet of the microchannel as well as at its side and bottom walls. By means of computational fluid dynamic simulations, the laminar flow is studied. To determine an approximate laminar flow Nusselt correlation, the heat transport was solved analytically for plug flow conditions to describe the influence of changes in the thermal boundaries of the system. The laminar flow case is experimentally validated by measuring the actual temperature distribution in a 500 lm square, 3 cm long, microchannel that is covered by a 1 lm and by a 1.9 lm thick silicon sheet with heating elements and temperature sensors on top. The Nusselt and Sherwood correlations can be used to readily quantify the heat and mass transport to support kinetic studies of catalytic reactions in this type of microreactor.

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By using microreactors fabricated with silicon microtechnology, heterogeneous catalyzed gas-phase reactions can be studied which are difficult to control because of their exothermic nature, are explosive or use toxichazardous gases. In this type of microreactors, catalytic materials like rhodium or platinum are deposited on a thin membrane in deep trenches. Conventional techniques, like lift-off lithography, cannot be used in deep trenches and deposition through flat shadow masks does not yield well-defined regions of catalyst. For well-controlled deposition of a catalytic thin film on a membrane located in a deep trench, a technique is developed using sputter deposition with a 3-dimensionally shaped 'self-aligning' shadow mask. INTRODUCTIONDue to the small dimensions of the gas flow channels in silicon-technology based microreactors (high-surface-tovolume ratios) and integration of functional elements like heaters and sensors, it becomes possible to control hightemperature catalytic partial oxidation reactions and study