The Role of Convection and Size Effects in Sensor Microhotplate Heat Exchange

The analysis of the influence of microhotplate size on the convective heat exchange of gas sen-sors is presented. It is demonstrated that there is a minimum size leading to the formation of convection heat exchange flow. Below this minimum, only the thermal conductivity of ambient air and IR radiation should be considered as channels for heat dissipation by microhotplate. This limit expression contains only fundamental constants of air, d~4· ν·Dg 3 , where ν is the kinematic viscosity of air, D is the diffusion coefficient, and g is the acceleration of free fall, d~0.5 cm.