Thermocouple

Résumé

Un thermocouple, ou couple thermoélectrique (CTE), est, en physique, un couple de matériaux dont l'effet Seebeck, découvert en 1821 par le physicien allemand Thomas Johann Seebeck, est utilisé pour la mesure de la température. Ils sont bon marché et permettent la mesure dans une grande gamme de températures. La principale limite est la précision obtenue. Il est relativement difficile d'obtenir des mesures avec une incertitude inférieure à . Principes de la mesure thumb|Schéma de principe de l'effet Seebeck L'effet Seebeck Lorsque deux métaux sont utilisés pour former une boucle ouverte (pas de courant circulant dans les fils) (voir schéma ci-contre), un potentiel électrique peut être généré entre les deux bornes non reliées de la boucle s'il existe un gradient de température dans la boucle. Le potentiel électrique généré peut être calculé à partir de l'équation suivante : dV = S_{ab}(T).dT :S_{ab} est nommé coefficient Seebeck (les ind

Source officielle

https://fr.wikipedia.org/wiki/Thermocouple

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Control Scenarios for an SOFC System

Joel Albrektsson

This report is intended to summarize the work of a semester project conducted on a gPROMS model (developed in LENI) of an existing stand-alone 1kW solid oxide fuel cell (SOFC) system. Different means of controlling the cathode gas temperature with single-input-single-output PID controllers were investigated. Particular attention was directed to the issue of erroneous thermocouple readings due to radiation and how this error can be minimized. It was shown that the discrepancy between thermocouple reading and real temperature depends strongly on the method used to control the temperature. In some cases, the incorrect thermocouple reading can be fatal for the system even in regular operation. With this basic type of PID controller, lambda control was shown to be the scenario with the smallest discrepancy. However, it is still non-negligible and a more advanced control approach should be investigated before an implementation on the physical system.

2011

Chargement

Multi-configuration evaluation of a megajoule-scale high-temperature latent thermal test-bed

Maurizio Barbato, Selmar Rudolf Binder, Sophia Haussener, Nithin Mallya, Alberto Ortona, Clemens Gregor Suter

Thermal energy storage via latent heat provides an energy dense solution and, during discharge, a hot stream at a well-defined temperature. Utilizing metal phase change materials (PCMs) and high-temperature operation might enable fast (dis)charging and application in previously unexplored areas (e.g. high-temperature processing industry). But detailed characterization and design guidelines of high-temperature metal latent heat storage systems with tailored characteristics are missing. Here, we introduce a combined experimental-numerical characterization and design tool for high-temperature heat storage units. We apply it to a megajoule-scale test-bed operated with steel encapsulated Al68.5Cu26.5Si5 (weight%) (melting temperature 791 K) as the PCM and air as heat transfer fluid (HTF) for charging and discharging. Thermocouples positioned at multiple locations throughout the storage unit are used to characterize the performance and heterogeneity. For the inaugural experimental campaign, three encapsulated tubes with a total of 1.83 kg PCM were vertically arranged in one of the modular stacks and several multi-hour charging/discharging cycles were performed with the HTF heated up to 30 - 70 K above and below the PCM melting point at a flow rate of 1500 lmin(-1). Specifically designed open-cell cellular Si-SiC lattices were wrapped around the PCM tubes to enhance the heat transfer. The experimental results showed a near-isothermal (+/- 10 K) exit temperature discharge maintained for 0.39 2.67 h. Temperature variations throughout the test-bed indicated that test-bed design is important to ensure homogeneous usage of the PCM and controlled phase change. A quasi-1D lumped parameter multi-mode heat transfer model was developed to quantify the thermal stratification within the PCM, heat losses, and phase change characteristics in the thermal storage, and provided explanation and quantification for the experimentally observed heterogeneities. The model was used to extrapolate the heat storage characteristics to larger scales: a 16.84 MJ and 50.51 MJ latent heat storage with the modular stacks filled with 25.7 kg (42 encapsulated tubes) and 77 kg (126 encapsulated tubes) of the PCM, respectively. The coupled experimental- numerical approach allowed for model validation, explanation of experimental variation, and to provide general design guidelines for practically relevant latent high-temperature (metal) thermal energy storage.

PERGAMON-ELSEVIER SCIENCE LTD2022

Chargement

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An efficient control system is paramount for the operability of Fuel Cell systems since, in ideal cases, it allows the regulation of power output, temperatures and economic performance under a dynamic working environment where they need to operate. Although several control strategies, scenarios and methodologies have been broadly investigated, it is usually taken for granted that the measurements from the system, necessary for the control feedback, are correct. Nonetheless, when simple thermocouples are used to measure gas temperatures there is a significant danger of systematic errors due to radiation effects between the surroundings and the thermocouple. The discrepancy between a real gas temperature and the one measured depends mainly on the temperature difference between the gas and the solids around as well as the gas velocity, radiation factors etc. The phenomenon has been described in our past publications. In this work we simulate an SOFC system and apply control scenarios in order to investigate potential problems arising from such systematic errors. The results show that important dysfunctions may occur and caution should be applied in design of both control and of the systems themselves.

2011

Chargement

Multi-configuration evaluation of a megajoule-scale high-temperature latent thermal test-bed

Maurizio Barbato, Selmar Rudolf Binder, Sophia Haussener, Nithin Mallya, Alberto Ortona, Clemens Gregor Suter

PERGAMON-ELSEVIER SCIENCE LTD2022