Design, numerical simulation and experimental testing of a modified probe for measuring temperatures and humidities in two-phase flow

This paper describes the design of a modified gas sampling probe for measur ing gas temperatures and humidities in a two-phase flow, based on the layou t of Kieviet et al., [EG. Kieviet, J. Van Raaij, P.J.A.M. Kerkhof, A device for measuring temperature and humidity in a spray drying chamber, Trans. I nst. Chem. Engrs, Part A, 75 (1997) 329-333]. This device separates small p articles from the gas how by means of the difference in inertia between the fluid and the particles. Two mechanisms of separation are employed success ively, namely a swirling motion and a sharp change in direction of the flow . A small fraction of the clean flow is then directed to a thermocouple and subsequently to a dew-point hygrometer. The commercial computational fluid dynamics (CFD) package CFX4.2 has been used to assess the performance of t he probe and to optimise the flow rates of the main and the clean air flow. Experimental testing confirms the prediction that this probe is able to me asure temperatures and humidities in two-phase flows accurately down to par ticle diameters of 5 mu m in droplet-laden flows. Due to deposition of wet solids on the swirl vanes, the separation performance for them decreases, s o that only wet particles of more than 16 mu m can be separated. (C) 2000 E lsevier Science S.A. All rights reserved.