ABSTRACT
A test was performed to determine the efficacy of a novel multi-channel thermocouple temperature sensor employing "N+1" array architecture for the in-situ detection of icing in cold climates. T-type thermoelements were used to fabricate a sensor with six independent temperature sensing points, capable of two-dimensional temperature mapping. The sensor was intended to detect the high latent heat of fusion of water (334 J/g) which is released to the environment during ice formation. The sensor was embedded on a plywood board and an aluminium plate, respectively by an epoxy resin. Three different ice accretion cases were considered. Ice accretion for all cases was achieved on the surface of the resin layer. In order to analyse the temperature variation for all three cases, the first 20 s response for each case was averaged between three cases. A temperature increase of (1.0 ± 0.1) °C and (0.9 ± 0.1) °C was detected by the sensors 20 s after the onset of icing, attributed to the latent heat of fusion of water. The results indicate that the sensor design is well-suited to cold temperature applications and that detection of the latent heat of fusion could provide a rapid and robust means of icing detection.
ABSTRACT
Thermal management of SOFCs (solid oxide fuel cell) is important for helping to minimise high temperature-related performance losses and maximising cell/stack lifetime. Thin film sensor technology is proposed as an excellent candidate to measure the cell temperature during operation due to its negligible mass, minimal disturbance to normal operation and higher temporal and spatial resolutions. However, the effective application of such sensors in SOFC systems is a challenging endeavour and predicated on incorporating the external wire attachments to complete the electrical circuit. This is because of the high sensitivity of SOFC materials to any interference to operation, limited available space and harsh operating conditions. In this paper, a new concept of packaging external wire attachments to the thin film sensor is described to enable the integration of the sensor in the SOFC system. Temperature measurements have been monitored under OCV and operating condition with the thin film sensor directly from SOFC cathode surface via proposed spring-based wire connection, from room temperature to SOFC operating temperature. The impact of the parameters including contact resistance (Rc) between sensor pads and attached wire on monitored temperature has also been analysed with the contribution of conductive paste. High temporal and spatial resolutions have been obtained with the implemented sensor.
ABSTRACT
Management of solid oxide fuel cell (SOFC) thermal gradients is vital to limit thermal expansion mismatch and thermal stress. However, owing to harsh operation conditions of SOFCs and limited available space in stack configuration, the number of techniques available to obtain temperature distribution from the cell surface is limited. The authors previously developed and studied a thermocouple array pattern to detect surface temperature distribution on an SOFC in open circuit conditions. In this study, the performance in terms of mechanical durability and oxidation state of the thin film thermoelements of the thermocouple array on the porous SOFC cathode is investigated. A thin-film multi-junction thermocouple array was sputter deposited using a magnetron sputter coater. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) characterisation techniques were carried out to understand characteristics of the thin film before and after temperature (20 °C-800 °C) measurement. Temperature readings from the sensor agreed well with the closely placed commercial thermocouple during heating segments. However, a sensor failure occurred at around 350 °C during the cooling segment. The SEM and XPS tests revealed cracks on the thin film thermoelements and oxidation to the film thickness direction.
