Thermal analysis and simulation of the microchannel flow in miniature thermal conductivity detectors

The microchannel flow in miniature TCDs (thermal conductivity detectors) was investigated analytically and numerically. Effects of channel size, inlet and boundary conditions, as well as changes in gas properties on the heat transfer rate were examined in detail. Without preheating the gas stream the distance for a miniature TCD to reach the conduction-dominant region was found to be approximately four times the thermal entry length for pipe flows of constant properties and uniform boundary conditions. If the gas temperature at the channel inlet is in the neighborhood of the mean gas temperature in the conduction-dominant region, the entrance region is much shorter. Another important finding of the present study is that the change in heat transfer rate in the entrance region is proportional to the square roots of the changes in gas density, specific heat, and thermal conductivity, but depends primarily on the thermal conductivity change in the conduction-dominant region. (C) 2000 Elsevier Science S.A. All rights reserved.