Design and Fabrication of a Thick Film Heat Flux Sensor for Ultra-High Temperature Environment

Abstract

In this paper, a ceramic-based thick film heat flux sensor (TFHFS) to monitor the heat flux in high-temperature environments is described. The TFHFS consists of 130 pairs of Pt-Pt/Rh thermocouples distributed in a serpentine form on a ceramic substrate. An insulator was used to generate the temperature difference, which increases the thermoelectric potential (output voltage) and improves the sensitivity of the proposed TFHFS. There are two pairs of independent thermocouples for temperature monitoring. The screenprinting process is used as the fabrication process. The characterization results indicate that the Pt electrodes and the Pt/Rh electrodes were well connected after sintering at 1350 • C, and the thickness and width of the thermocouple electrodes were approximately 20 µm and 300 µm, respectively. The test results indicate that the proposed heat flux sensor has a maximum output voltage of approximately 1.44 mV, and the heat flux sensitivities for 3-57 kW/m 2 were well distributed in the range of 0.025-0.030 mV/(kW/m 2), thereby demonstrating that the fabricated sensor exhibits high sensitivities in the given heat flux range. Furthermore, the reusability investigation indicated that the prepared TFHFS achieves a stable output voltage and a low error level at 50-900 • C. Therefore, we assume that the proposed sensor can be used for monitoring the heat flux in harsh applications such as turbomachinery and aerospace industries. INDEX TERMS Ceramic sensor, heat flux sensor, high temperature monitoring, thermocouple.

Studies on the Platinum Thick Film Sensor Conformally Written by Laser Micro-Cladding: Formability, Microstructure, and Performance

“…Correspondingly, a rapid mass loss and a minor mass loss of about 13.7 and 0.6% occur at 110–200 and 300–700 °C, respectively, as shown in the TG curve. Therefore, it can be deduced that the Pt paste mainly experiences three procedures during the sintering process: (1) the rapid volatilization and combustion of the organic phases in Pt paste at about 110–300 °C; (2) the softening or melting of the glass phases (such as that contains Ba and Ca elements) and the recrystallization and growth of Pt grains at about 300–1165 °C, which can improve the sintering of Pt particles; , and (3) the melting of glass phases and the growth of Pt grains at a higher temperature, promoting the sintering and densification of Pt thick films.…”

“…However, vacuum chambers and masks are generally essential in the above PVD processes; thus, not only is the relevant equipment expensive, but also the films are harder to be deposited conformally, especially on large-scale or three-dimensional (3D) components. Besides, the deposition rate of PVD is relatively low, hence it is typically used to deposit films less than 5 μm. − Further, it is worth noting that deteriorations including selective oxidation, metallurgical changes, and dewetting are more likely to occur in such thin Pt films, especially at high temperatures (≥ 800 °C), resulting in poorer electrical performance, weaker sensing stability, and lower service temperature and lifetime than thicker Pt films (thickness larger than about 5 μm). − This is mainly attributed to the smaller grain size, lower film thickness, and larger boundary effects and surface energy therein.…”

“…As is well known, Pt thick films can be fabricated by traditional thick film technologies such as screen printing and spin-coating. , Zhang et al prepared a Pt–Pt10%Rh thick film heat flux sensor by the screen printing technique and subsequent sintering in a furnace at 1350 °C, which achieved stable linear output at 50–900 °C. However, these methods usually need a whole oven-sintering at high temperatures and are particularly difficult to achieve 3D conformal in situ preparation of Pt thick films.…”

High Temperature Heat Flux Sensor With ITO/In2O3 Thermopile for Extreme Environment Sensing

“…Among them, ITO-In2O3, as a transparent conductive oxide, has the advantages of high-temperature resistance, high output, and strong oxidation resistance in hightemperature environments, which can be used as a substitute for precious metal thermopiles 28 . The main materials for the thermal resistance layer are alumina 2,19 , silicon dioxide 19,20,[23][24][25]27,29 , YSZ 28 , etc. Li et al 2 fabricated an ITO-In2O3 thermoelectric stack thin film heat flux meter using magnetron sputtering method on a nickel alloy substrate, with a sensitivity of 61.93 uV/(kW/m 2 ) and a maximum operating temperature of 888 ℃.…”

Highly sensitive flexible heat flux sensor based on a microhole array for ultralow to high temperatures

“…Thin-film heat flux sensors have thermopiles in thin film form, which are currently popular for heat flux measurement due to their small size, easy installation, and large measurement range 19 , 20 . However, existing studies focus more on HFSs used at high temperatures 21 and less on devices that are flexible, bendable, and easy to attach and install. Li et al 22 , 23 studied HFSs for aeroengines with a sensitivity of 0.06193 μV/(W/m 2 ), which could measure 236.4 kW/m 2 at 888 °C through an anti-emission coating, ultimately achieving a sensitivity of 0.04856 μV/(W/m 2 ).…”