A Conceptual Design of a Polymer-Derived Ceramic Hot-Wire Anemometer for Gas Turbine Environment

Abstract

This paper attempts to prove the feasibility of high temperature hot-wire anemometer for gas turbine environment. No such sensor exists at present. Based on the latest improvement in a new type of Polymer-Derived Ceramic (PDC) material, the authors present a conceptual design of a hot-wire anemometer (HWA) based on PDC material, and show that such a sensor is indeed feasible. This HWA is microfabricated by using three types of PDC materials such as SiAlCN, SiCN (lightly doped) and SiCN (heavily doped) for sensing element (hot-wire), support prongs and connecting leads respectively. The PDC-SiAlCN is selected as a sensing element, because of its high temperature coefficient of resistance (4000 ppm/°C) and resistivity. Direct measurements and characterization of the relevant material properties are presented, to show that the proposed design can lead to a viable constant temperature anemometer. In our current design, the hot wire is 200μm in length and 20 μm × 20 μm side. Analysis of the sensor performance is used to predict sensor response behavior, and the systematic analysis of this new device, especially the steady state characteristics, frequency response and directional dependence are discussed. This novel hot wire anemometer is found to perform quite satisfactorily as compared to a conventional HWA in which the hot wire is made of Pt/W/Pt-Ir. Sensor output is predicted to be in the range of 10 to 50 V (without additional signal conditioning) for velocities in the range of 10 to 100 m/s. The sensitivity of the sensor is found to be better than a conventional sensor: 0.157 V/(m/s) (for sensor length of 0.2 mm) vs 0.014 V/(m/s) respectively at 50 m/s. However, L/d ratio may need to be limited to about 10 so that output voltage is not excessive, thus requiring careful consideration of support conduction during calibration. This type of PDC-HWA can be used in harsh environment due to its high temperature resistance, tensile strength and resistance to oxidation. This paper also discusses micro-stereolithography as a novel microfabrication technique to manufacture the proposed PDC-HWA.