Fluid dynamic simulation of a measurement chamber for electronic noses

A fluid dynamic study of a sensor chamber used in a hit-commercial electronic nose is presented. In order to optimise the sensor signals in terms of stability, repeatability as well as amplitude and response time, the influence of many factors of the sampling device has to be kept under control. Concerning the characteristics of flow, the existence of a time-window where each sensor is exposed to a constant odour concentration has to be assured. This condition can be achieved by the proper dimensioning of the chamber volume and by other modifications to the inlet and outlet. The numerical analysis was performed by a CFD code which solves the Navier-Stokes equations for a dilatable fluid in 3D enclosures, discretised with finite volume elements. Two configurations were simulated: a basic case, referring to the conditions existing in the commercial device, and an optimised case. In each case, a static solution was calculated for the flow field and then the dynamic evolution of odour concentration was simulated by solving the transient transport equation of a tracer injected as a square pulse flow. Far from optimum conditions were found for the basic case; the improvement achieved through simple modifications in the geometry of the chamber for the optimised case was discussed.