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Nicolas Boyard - One of the best experts on this subject based on the ideXlab platform.
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Accurate measurement of the longitudinal thermal conductivity and Volumetric Heat Capacity of single carbon fibers with the 3ω method
Journal of Thermal Analysis and Calorimetry, 2019Co-Authors: Ketaki Mishra, Bertrand Garnier, Steven Le Corre, Nicolas BoyardAbstract:An experimental setup for 3 ω method with a constant current source and two differential amplifiers was built to measure the thermal conductivity and the Volumetric Heat Capacity of single polyacrylonitrile (PAN)-based carbon fiber. In complement to a well-known analytical thermal model, a numerical one was developed that can check the validity of the analytical one and can also take into account the effect of convective Heat loss on the measurements. A detailed sensitivity analysis of the unknown parameters was presented that would finally help in the better design of the setup for 3 ω method. The tests were performed under vacuum and atmospheric pressure for chromel wire as a reference sample and under vacuum for two types of PAN-based carbon fiber. Detailed measurements were performed displaying the influence of convective loss and the thermal contact resistance between fiber and copper electrodes on the estimation of thermal properties of carbon fiber.
Ketaki Mishra - One of the best experts on this subject based on the ideXlab platform.
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Accurate measurement of the longitudinal thermal conductivity and Volumetric Heat Capacity of single carbon fibers with the 3ω method
Journal of Thermal Analysis and Calorimetry, 2019Co-Authors: Ketaki Mishra, Bertrand Garnier, Steven Le Corre, Nicolas BoyardAbstract:An experimental setup for 3 ω method with a constant current source and two differential amplifiers was built to measure the thermal conductivity and the Volumetric Heat Capacity of single polyacrylonitrile (PAN)-based carbon fiber. In complement to a well-known analytical thermal model, a numerical one was developed that can check the validity of the analytical one and can also take into account the effect of convective Heat loss on the measurements. A detailed sensitivity analysis of the unknown parameters was presented that would finally help in the better design of the setup for 3 ω method. The tests were performed under vacuum and atmospheric pressure for chromel wire as a reference sample and under vacuum for two types of PAN-based carbon fiber. Detailed measurements were performed displaying the influence of convective loss and the thermal contact resistance between fiber and copper electrodes on the estimation of thermal properties of carbon fiber.
Benitez Buelga Javier - One of the best experts on this subject based on the ideXlab platform.
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Heated fiber optic distributed temperature sensing for measuring soil Volumetric Heat Capacity and water content: A dual probe Heat-pulse approach
'Soil Science Society of America', 2014Co-Authors: Benitez Buelga Javier, Sayde C., Rodríguez Sinobas Leonor, Selker J.Abstract:The first feasibility study of using dual-probe Heated fiber optics with distributed temperature sensing to measure soil Volumetric Heat Capacity and soil water content is presented. Although results using different combinations of cables demonstrate feasibility, further work is needed to gain accuracy, including a model to account for the finite dimension and the thermal influence of the probes. Implementation of the dual-probe Heat-pulse (DPHP) approach for measurement of Volumetric Heat Capacity (C) and water content (θ) with distributed temperature sensing Heated fiber optic (FO) systems presents an unprecedented opportunity for environmental monitoring (e.g., simultaneous measurement at thousands of points). We applied uniform Heat pulses along a FO cable and monitored the thermal response at adjacent cables. We tested the DPHP method in the laboratory using multiple FO cables at a range of spacings. The amplitude and phase shift in the Heat signal with distance was found to be a function of the soil Volumetric Heat Capacity. Estimations of C at a range of moisture contents (θ = 0.09– 0.34 m3 m−3) suggest the feasibility of measurement via responsiveness to the changes in θ, although we observed error with decreasing soil water contents (up to 26% at θ = 0.09 m3 m−3). Optimization will require further models to account for the finite radius and thermal influence of the FO cables. Although the results indicate that the method shows great promise, further study is needed to quantify the effects of soil type, cable spacing, and jacket configurations on accuracy
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Implementation of the Heated Pulsed Theory using actively Heated fiber optics: measurements of soil Volumetric water content and soil Volumetric Heat Capacity
E.T.S.I. Agrónomos (UPM), 2014Co-Authors: Benitez Buelga JavierAbstract:Existe una creciente necesidad de hacer el mejor uso del agua para regadío. Una alternativa eficiente consiste en la monitorización del contenido volumétrico de agua (θ), utilizando sensores de humedad. A pesar de existir una gran diversidad de sensores y tecnologías disponibles, actualmente ninguna de ellas permite obtener medidas distribuidas en perfiles verticales de un metro y en escalas laterales de 0.1-1,000 m. En este sentido, es necesario buscar tecnologías alternativas que sirvan de puente entre las medidas puntuales y las escalas intermedias. Esta tesis doctoral se basa en el uso de Fibra Óptica (FO) con sistema de medida de temperatura distribuida (DTS), una tecnología alternativa de reciente creación que ha levantado gran expectación en las últimas dos décadas. Específicamente utilizamos el método de fibra calentada, en inglés Actively Heated Fiber Optic (AHFO), en la cual los cables de Fibra Óptica se utilizan como sondas de calor mediante la aplicación de corriente eléctrica a través de la camisa de acero inoxidable, o de un conductor eléctrico simétricamente posicionado, envuelto, alrededor del haz de fibra óptica. El uso de fibra calentada se basa en la utilización de la teoría de los pulsos de calor, en inglés Heated Pulsed Theory (HPP), por la cual el conductor se aproxima a una fuente de calor lineal e infinitesimal que introduce calor en el suelo. Mediante el análisis del tiempo de ocurrencia y magnitud de la respuesta térmica ante un pulso de calor, es posible estimar algunas propiedades específicas del suelo, tales como el contenido de humedad, calor específico (C) y conductividad térmica. Estos parámetros pueden ser estimados utilizando un sensor de temperatura adyacente a la sonda de calor [método simple, en inglés single Heated pulsed probes (SHPP)], ó a una distancia radial r [método doble, en inglés dual Heated pulsed probes (DHPP)]. Esta tesis doctoral pretende probar la idoneidad de los sistemas de fibra óptica calentada para la aplicación de la teoría clásica de sondas calentadas. Para ello, se desarrollarán dos sistemas FO-DTS. El primero se sitúa en un campo agrícola de La Nava de Arévalo (Ávila, España), en el cual se aplica la teoría SHPP para estimar θ. El segundo sistema se desarrolla en laboratorio y emplea la teoría DHPP para medir tanto θ como C. La teoría SHPP puede ser implementada con fibra óptica calentada para obtener medidas distribuidas de θ, mediante la utilización de sistemas FO-DTS y el uso de curvas de calibración específicas para cada suelo. Sin embargo, la mayoría de aplicaciones AHFO se han desarrollado exclusivamente en laboratorio utilizando medios porosos homogéneos. En esta tesis se utiliza el programa Hydrus 2D/3D para definir tales curvas de calibración. El modelo propuesto es validado en un segmento de cable enterrado en una instalación de fibra óptica y es capaz de predecir la respuesta térmica del suelo en puntos concretos de la instalación una vez que las propiedades físicas y térmicas de éste son definidas. La exactitud de la metodología para predecir θ frente a medidas puntuales tomadas con sensores de humedad comerciales fue de 0.001 a 0.022 m3 m-3 La implementación de la teoría DHPP con AHFO para medir C y θ suponen una oportunidad sin precedentes para aplicaciones medioambientales. En esta tesis se emplean diferentes combinaciones de cables y fuentes emisoras de calor, que se colocan en paralelo y utilizan un rango variado de espaciamientos, todo ello en el laboratorio. La amplitud de la señal y el tiempo de llegada se han observado como funciones del calor específico del suelo. Medidas de C, utilizando esta metodología y ante un rango variado de contenidos de humedad, sugirieron la idoneidad del método, aunque también se observaron importantes errores en contenidos bajos de humedad de hasta un 22%. La mejora del método requerirá otros modelos más precisos que tengan en cuenta el diámetro del cable, así como la posible influencia térmica del mismo. ABSTRACT There is an increasing need to make the most efficient use of water for irrigation. A good approach to make irrigation as efficient as possible is to monitor soil water content (θ) using soil moisture sensors. Although, there is a broad range of different sensors and technologies, currently, none of them can practically and accurately provide vertical and lateral moisture profiles spanning 0-1 m depth and 0.1-1,000 m lateral scales. In this regard, further research to fulfill the intermediate scale and to bridge single-point measurement with the broaden scales is still needed. This dissertation is based on the use of Fiber Optics with Distributed Temperature Sensing (FO-DTS), a novel approach which has been receiving growing interest in the last two decades. Specifically, we employ the so called Actively Heated Fiber Optic (AHFO) method, in which FO cables are employed as Heat probe conductors by applying electricity to the stainless steel armoring jacket or an added conductor symmetrically positioned (wrapped) about the FO cable. AHFO is based on the classic Heated Pulsed Theory (HPP) which usually employs a Heat probe conductor that approximates to an infinite line Heat source which injects Heat into the soil. Observation of the timing and magnitude of the thermal response to the energy input provide enough information to derive certain specific soil thermal characteristics such as the soil Heat Capacity, soil thermal conductivity or soil water content. These parameters can be estimated by capturing the soil thermal response (using a thermal sensor) adjacent to the Heat source (the Heating and the thermal sources are mounted together in the so called single Heated pulsed probe (SHPP)), or separated at a certain distance, r (dual Heated pulsed method (DHPP) This dissertation aims to test the feasibility of Heated fiber optics to implement the HPP theory. Specifically, we focus on measuring soil water content (θ) and soil Heat Capacity (C) by employing two types of FO-DTS systems. The first one is located in an agricultural field in La Nava de Arévalo (Ávila, Spain) and employ the SHPP theory to estimate θ. The second one is developed in the laboratory using the procedures described in the DHPP theory, and focuses on estimating both C and θ. The SHPP theory can be implemented with actively Heated fiber optics (AHFO) to obtain distributed measurements of soil water content (θ) by using reported soil thermal responses in Distributed Temperature Sensing (DTS) and with a soil-specific calibration relationship. However, most reported AHFO applications have been calibrated under laboratory homogeneous soil conditions, while inexpensive efficient calibration procedures useful in heterogeneous soils are lacking. In this PhD thesis, we employ the Hydrus 2D/3D code to define these soil-specific calibration curves. The model is then validated at a selected FO transect of the DTS installation. The model was able to predict the soil thermal response at specific locations of the fiber optic cable once the surrounding soil hydraulic and thermal properties were known. Results using electromagnetic moisture sensors at the same specific locations demonstrate the feasibility of the model to detect θ within an accuracy of 0.001 to 0.022 m3 m-3. Implementation of the Dual Heated Pulsed Probe (DPHP) theory for measurement of Volumetric Heat Capacity (C) and water content (θ) with Distributed Temperature Sensing (DTS) Heated fiber optic (FO) systems presents an unprecedented opportunity for environmental monitoring. We test the method using different combinations of FO cables and Heat sources at a range of spacings in a laboratory setting. The amplitude and phase-shift in the Heat signal with distance was found to be a function of the soil Volumetric Heat Capacity (referred, here, to as Cs). Estimations of Cs at a range of θ suggest feasibility via responsiveness to the changes in θ (we observed a linear relationship in all FO combinations), though observed bias with decreasing soil water contents (up to 22%) was also reported. Optimization will require further models to account for the finite radius and thermal influence of the FO cables, employed here as “needle probes”. Also, consideration of the range of soil conditions and cable spacing and jacket configurations, suggested here to be valuable subjects of further study and development
Changxing Zhang - One of the best experts on this subject based on the ideXlab platform.
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effect of vertical ground temperature distribution on parameter estimation of in situ thermal response test with unstable Heat rate
Renewable Energy, 2019Co-Authors: Changxing Zhang, Wei Song, Yufeng Liu, Xiangqiang Kong, Qing WangAbstract:This paper proposed a parameter estimation method for identifying ground thermal conductivity and Volumetric Heat Capacity using the Nelder-Mead Simplex search algorithm (NMSA) in in-situ thermal response test (TRT) with unstable Heat rate, the duct storage system (DST) model for borehole Heat exchanger (BHE) was applied to do with variable Heat rate and the vertical ground temperature distribution in initial soil temperature. The parameter estimation was carried out using the in-situ TRT data in Qingdao, and the effect of vertical ground temperature distribution on estimated results was compared and analyzed. The relative error of estimated ground thermal conductivity using the regression temperature fitted by the test temperatures from the 5th m depth to the 120th m depth decreased by about 9.1% than that corresponding to the integral mean temperature calculated by test temperatures from the 5th m depth to the 120th m depth. However, the estimated Volumetric Heat Capacity is hardly sensitive to initial soil temperature, and the relative errors are not higher than 2% no matter how to do with initial soil temperature.
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parameter estimation of in situ thermal response test with unstable Heat rate
Energy, 2015Co-Authors: Changxing Zhang, Wei Song, Shicai Sun, Donggen PengAbstract:This paper proposed the history-independent algorithm based on CSM (cylindrical source model) in the TRT (thermal response test) with unstable Heat rate. It achieved a faster computing speed and more accurate results than the usual superposition algorithms in processing variable Heat rate problem. In order to alleviate ill-posed problem and improve the reliability of parameter estimation, a Matlab program was compiled to perform inversion calculation to obtain the ground thermal properties based on the SAA (simulated annealing algorithm) with preset lower and upper bounds for estimated parameters. The estimated ground thermal conductivity and Volumetric Heat Capacity from in-situ TRT with unstable Heat rate (case A) showed closest agreement with those (case B) evaluated by the LSM estimation method, and calculated water temperatures corresponding to estimated results agreed well with the measured water temperature. Based on SAA coupled with the history-independent mathematical algorithm in in-situ TRT with unstable Heat rate, TRT can be performed continuously, independent of power fluctuation with both time and cost saved.
Qing Wang - One of the best experts on this subject based on the ideXlab platform.
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effect of vertical ground temperature distribution on parameter estimation of in situ thermal response test with unstable Heat rate
Renewable Energy, 2019Co-Authors: Changxing Zhang, Wei Song, Yufeng Liu, Xiangqiang Kong, Qing WangAbstract:This paper proposed a parameter estimation method for identifying ground thermal conductivity and Volumetric Heat Capacity using the Nelder-Mead Simplex search algorithm (NMSA) in in-situ thermal response test (TRT) with unstable Heat rate, the duct storage system (DST) model for borehole Heat exchanger (BHE) was applied to do with variable Heat rate and the vertical ground temperature distribution in initial soil temperature. The parameter estimation was carried out using the in-situ TRT data in Qingdao, and the effect of vertical ground temperature distribution on estimated results was compared and analyzed. The relative error of estimated ground thermal conductivity using the regression temperature fitted by the test temperatures from the 5th m depth to the 120th m depth decreased by about 9.1% than that corresponding to the integral mean temperature calculated by test temperatures from the 5th m depth to the 120th m depth. However, the estimated Volumetric Heat Capacity is hardly sensitive to initial soil temperature, and the relative errors are not higher than 2% no matter how to do with initial soil temperature.
