A high-temperature calorimetric flow sensor employing ion conduction in zirconia

Abstract

This paper presents the use of the temperature-dependent ion conductivity of 8 mol % yttria-stabilized zirconia (YSZ8) in a miniature high-temperature calorimetric flow sensor. The sensor consists of 4 layers of high-temperature co-fired ceramic (HTCC) YSZ8 tape with a 400 μm wide, 100 μm deep, and 12 500 μm long internal flow channel. Across the center of the channel, four platinum conductors, each 80 μm wide with a spacing of 160 μm, were printed. The two center conductors were used as heaters, and the outer, up- and downstream conductors were used to probe the resistance through the zirconia substrate around the heaters. The thermal profile surrounding the two heaters could be made symmetrical by powering them independently, and hence, the temperature sensing elements could be balanced at zero flow. With nitrogen flowing through the channel, forced convection shifted the thermal profile downstream, and the resistance of the temperature sensing elements diverged. The sensor was characterized at nitrogen flows from 0 to 40 sccm, and resistances at zero-flow from 10 to 50 MΩ. A peak sensitivity of 3.1 MΩ/sccm was obtained. Moreover, the sensor response was found to be linear over the whole flow range, with R2 of around 0.999, and easy to tune with the individual temperature control of the heaters. The ability of the sensor to operate in high temperatures makes it promising for use in different harsh environments, e.g., for close integration with microthrusters.

Alumina-Doped Zirconia Submicro-Particles: Synthesis, Thermal Stability, and Microstructural Characterization

“…Micro- and nanoscale zirconia ceramics and zirconia-based composite materials have attracted significant scientific interest due to their very favorable properties, such as exceptional thermal stability, wear resistance, fracture toughness, high refractive index, chemical inertness, thermal insulation, and bio-compatibility [1,2]. These characteristics give rise to a number of potential applications, including corrosion protection [3], catalysis [4], chromatography [5], sensors [6,7], and solid oxide fuel cells [8,9], as well as bioceramics [10,11,12].…”

Effect of Joule heating and temperature‐dependent zeta potential on electroosmotic flow measurements in calorimetric flow sensors

“…During the past three decades, many theoretical and experimental studies investigated the typical performance of different configurations of calorimetric flow sensors starting with simple two‐dimensional models [3] and ending with more comprehensive studies that investigated different means to improve sensor performance. For example, the heater of the sensor was offset from the channel wall towards the channel centreline to enhance sensor sensitivity [4], zirconia's ion conductivity was used to increase sensor sensitivity [5], and heat exchanging fingers were integrated into the flow channel to enhance heat transfer within the sensor [6]. In other modifications, a fluorescent layer was integrated inside the microchannel of the sensor to optically read a highly variable flow rate [7].…”

High temperature gradient micro-sensor for wall shear stress and flow direction measurements

“…The movement implies a variation of an electrical parameter: capacitive sensors 5 or cantilever based sensors 6,7 are part of this category. For indirect flow measurement, various methods have been applied as, for example, micro-fences using a cantilever structure and piezoresistors, 8 optical resonance such as whispering gallery modes of dielectric microspheres shifting with radial deformations of the spheres due to the shear stress, 9 the deflection of micro-pillars, 10 and thermal-based sensors, [11][12][13][14][15][16][17][18][19][20] which are developed below. Among all these devices, thermal sensors are widely adopted when dealing with fluid dynamics, including laminar or turbulent flows, as they do not contain mechanical moving parts and are thus less prone to wear than the others.…”

“…14,15 These sensors are nonetheless often used for flow separation detection and wall shear stress measurement as they are robust and easy to mount flush to the wall. Hotwire sensors are mainly free from the substrate, which enables an optimal heating uniformity and high sensitivity, [16][17][18][19] but they are more fragile than hot-film sensors.…”