Thermocouple Network Research Articles

Data-Driven Fault Detection in a Thermocouple Network Using Neighboring Redundancy, XGBoost Classifier, and Up–Down Counter

Data-Driven Fault Detection in a Thermocouple Network Using Neighboring Redundancy, XGBoost Classifier, and Up–Down Counter

Inverse Estimation and Sensitivity Analysis of Mars 2020 Entry Aeroheating Environments

The Mars Entry, Descent, and Landing Instrumentation 2 (MEDLI2) sensor suite collected heating and pressure data during entry of the Mars 2020 Perseverance rover into Mars’s atmosphere. MEDLI2 included temperature, heat flux, and pressure sensors on the heat shield and backshell. This paper covers inverse estimation of surface heating based on the MEDLI2 instrumented sensor plugs, which are a network of thermocouples embedded in thermal protection system plugs across the aeroshell. Monte Carlo analysis was conducted to assess the sensitivity of calculated surface heat rate and temperature to uncertainties in thermocouple depth and material properties, and a variance decomposition method was employed to understand the relative contributions of each uncertainty parameter. Performing this analysis using results from the inverse analysis tool FIAT_Opt was found to require an extremely high computation time; thus, machine learning models were trained and evaluated as a surrogate for FIAT_Opt. This paper demonstrates that machine learning models can be efficient, accurate alternatives to state-of-the-art inverse analysis tools like FIAT_Opt, especially for computationally expensive processes. Ensuing sensitivity analysis showed that the main drivers for overall uncertainty in the reconstructed heat flux and heat load were heat capacity and thermal conductivity on the backshell, and they were thermal conductivity and thermocouple depth on the heat shield.

An experimental study of the cooling performance and airflow patterns in a model Natural Ventilation Augmented Cooling (NVAC) greenhouse

A Natural Ventilation Augmented Cooling (NVAC) greenhouse is a natural ventilation greenhouse that is improved by coupling natural ventilation with a non-conventional misting system. In the design, an added inside roof, called the NVAC roof, prevents unevaporated water droplets from reaching the crop foliage and guides the cooled air into the main area of the greenhouse. Previous work on the cooling performance of the NVAC greenhouse design investigated temperature and relative humidity within the greenhouse under field conditions. To investigate the cooling capabilities and the nature of the airflow in the NVAC greenhouse, a network of thermocouples and a three-dimensional sonic anemometer were used for the measurement of temperature, relative humidity and air velocities inside a 1:4 model single-span NVAC greenhouse. The cooling performance of the NVAC greenhouse design without plants varied from a temperature reduction of 1.9–12.6 °C and relative humidity increase of 1.4–31.2% RH depending on the ambient conditions. The NVAC greenhouse reduced vapour pressure deficit by 0.3–4.9 kPa. Although temperature distributions were more uniform under natural ventilation, the amount of cooling was significantly greater with the use of the NVAC design, compared to none. It was shown that the NVAC greenhouse can provide air movement in the greenhouse at velocities up to 0.38 m s−1 without the use of fans. The average turbulence intensity of the air inside the greenhouse was increased to 0.32 with the use of the NVAC design, compared to 0.19 under natural ventilation.

Wireless Concrete Strength Monitoring of Wind Turbine Foundations.

Wind turbine foundations are typically cast in place, leaving the concrete to mature under environmental conditions that vary in time and space. As a result, there is uncertainty around the concrete’s initial performance, and this can encourage both costly over-design and inaccurate prognoses of structural health. Here, we demonstrate the field application of a dense, wireless thermocouple network to monitor the strength development of an onshore, reinforced-concrete wind turbine foundation. Up-to-date methods in fly ash concrete strength and maturity modelling are used to estimate the distribution and evolution of foundation strength over 29 days of curing. Strength estimates are verified by core samples, extracted from the foundation base. In addition, an artificial neural network, trained using temperature data, is exploited to demonstrate that distributed concrete strengths can be estimated for foundations using only sparse thermocouple data. Our techniques provide a practical alternative to computational models, and could assist site operators in making more informed decisions about foundation design, construction, operation and maintenance.

Experimental study of a phase change thermal energy storage with copper foam

Thermal energy storage is an attractive option for effectiveness in many applications such as concentrated solar thermal power or district heating network, since it gives flexibility and reduces energy consumption and costs. The objectives of the present study are to assess copper foam interest as thermal conductivity enhancement technique for latent heat thermal energy storage and to compare copper foam with other heat transfer enhancement systems for shell-and-tubes heat exchangers. The best heat transfer fluid injection side is sought for charge and discharge. Besides, a method is proposed to estimate the characteristic time for melting/solidification and enable comparison between various tests conditions and heat exchanger geometries.In this paper, a copper foam is implemented in a shell-and-tube heat exchanger as phase change thermal energy storage unit and studied experimentally. Visualization enables the melting/solidification front to be seen, followed and recorded. Bottom and top injection for charge and discharge are compared, vertically and horizontally. It appears that vertical charge and discharge are faster than horizontal ones and that top charge and discharge are faster than bottom ones, thus assessing the significance of volume expansion and natural convection for heat transfer in the phase change material. Moreover, the tested copper foam enhanced geometry is compared with other heat exchangers such as finned copper tube, tube surrounded by carbon foam and a simple tube. It is shown that copper foam combines low-density with high heat transfer performance since it is as efficient as copper fins with half the copper mass, and far more efficient than other presented heat exchangers. Besides, a method for estimating solidification and melting time is proposed. Based on a thermocouple network, this method rests upon measured temperatures inside the phase change material.

In-Situ Temperature Sensing of SOFC during Anode Reduction and Cell Operations Using a Multi-Junction Thermocouple Network

Temperature driven performance degradations is one of the major problems that impedes the successful commercialisation of Solid Oxide Fuel Cell (SOFC) technology. To mitigate such degradations as well as to further enhance stack’s performance, it is very important to understand the temperature distribution of a SOFC stack while in operation. Researches for experimental measurement of the temperature distribution are very limited in literature. The available efforts are also confined for measuring temperature in both (air/ fuel) channels and they mostly do not measure the temperature from a SOFC electrodes, which is more desirable than gas temperature measurement for investigating cells’ behaviour and the correlation to the stack’s performance. Further, the most widely adapted method for stack temperature measurement is to insert commercial thermocouples inside a fuel cell stack, which introduce disturbance to the normal operation of a stack and impose significant limitations on the number of independent point within a stack where temperature can be measured. Therefore, the in-situ cell temperature monitoring is a topical research area where a technical challenge is necessary. The proposed thermocouple network architecture can independently measure the temperature at N2 number of points with only 2N number of thermo-elements/ external wires. Hence, it requires much less number of external wires than a set of thermocouples require for the same number of independent temperature measuring points. Reduction in the number of external wires requirement enables to measure the temperature with greater spatial resolution and lower disturbance to the normal operation of the cell/ stack. In addition to measuring the temperature, the propose thermocouple network can simultaneously collect the current from the electrodes while measuring temperature. The authors have experimentally validated and confirmed these abilities prior to applying the thermocouple network for in-situ temperature monitoring presented below. A thermocouple network was fabricated by weaving K-type thermocouple wires (ϕ 0.25mm), and then spot welding its intersections to form a mesh where each spot welded point acts as a temperature measuring point. The intersection of 3 Alumel (Ni: Al: Mn: Si – 95:2:2:1 by wt.) and 3 Chromel (Ni:Cr – 90:10 by wt.) wires formed 9 independent temperature measuring points with a pitch of about 10mm. Using this thermocouple network, authors measured the cathode temperature during an anode reduction process and then measured the same during normal cell operation of a commercial SOFC test cell (50mmx50mm, NextCell-5) while the air/fuel ratio varies. In addition, Open Circuit Voltage (OCV) was also measured during the operation. The thermocouple network was in direct contact with the cathode and hence, measured the cathode temperature. The gas temperature was also measured simultaneously using a commercial K-type thermocouple from 5 mm adjacent to the electrode to investigate how effectively the gas temperature can represent the electrode’s temperature of a cell. Hydrogen and Air flow rates were altered to investigate cell’s response in terms of OCV change and temperature change. The measurements showed that the thermocouple network on cathode was very sensitive to even a trivial temperature changes whilst the commercial thermocouple adjacent to the cell was almost non-responsive to most of subtle temperature changes that occurred on the cell. During the monitoring, dramatic temperature fluctuation and uneven temperature distribution were detected during the anode reduction process. A correlation between the OVC and the cell temperature was also investigated.

In-Situ Temperature Sensing of SOFC during Anode Reduction and Cell Operations Using a Multi-Junction Thermocouple Network

Understanding in-situ temperature distribution of a SOFC stack while in operation is very important for its performance and degradation studies. The available efforts in literature are incapable of measuring the temperature of electrodes. The proposed multi-junction thermocouple network, which requires only 2N thermo-elements for N2 measuring points, can measure temperature directly from electrodes. A multi-junction thermocouple network having 9 measuring points was fabricated using K-type thermocouple wires (ϕ 0.5mm) for an in-situ measurement of the temperature distribution on a cathode (50mmx50mm, NextCell-5). The measurements were performed during an anode reduction process and during a normal cell operation while the air/fuel ratio varies. The gas temperature was measured simultaneously using a commercial K-type thermocouple from 7 mm adjacent to the cathode. The monitored cathode temperature via the in-situ sensors was directly correlated with the cell’s OCV whilst the commercial thermocouple 7mm adjacent to the electrode showed a dull change to them.

Proper Orthogonal Decomposition-Based Modeling Framework for Improving Spatial Resolution of Measured Temperature Data

This paper presents a proper orthogonal decomposition (POD)-based reduced-order modeling framework to improve spatial resolution of measured temperature data in an air-cooled data center. This data-driven approach is applied on transient air temperature data, acquired at the exhaust of a server simulator rack. Temperature data is collected by a distributed thermocouple network at 1 Hz sampling frequency following a step impulse in the rack heat load. The input data are organized in a 2-D array, comprising transient temperature signals measured at various spatial locations. Because its computational time scales logarithmically with the input size, the proposed POD-based approach is potentially useful as an efficient tool for handling large transient data sets. With spatial location being the parameter for the input data matrix, the proposed approach is suitable for rapid synthesis of transient temperature data at new spatial locations. The comparison between POD-based local air temperature predictions and corresponding data indicates a maximum prediction uncertainty of 3.2%, and root mean square prediction uncertainty of 1.9%.

Starch Foam Expansion in a Closed Mold

Processes with thermal treatment of starch-based materials for biologically degradable packaging products are analyzed here. The paper describes experiments on thermal forming of potato starch-based water suspensions in a closed mold at elevated pressures and temperatures of walls heated up to 200 °C. The time course of temperatures and also the sample expansion were detected by a network of thermocouples and compared with the pressure recorded inside the mold. Evolution of temperature profiles enables the estimation of time courses of sample expansion. Experiments with marking particles show that the crust sticks to the heater walls and only the sample core expands. Temperatures and pressures are closely related during expansion and the free water evaporation stage. Experiments confirm that temperatures are more or less uniform in the longitudinal direction and that the time profiles of temperature and pressure are characterized by peaks corresponding to perforation and recovery of foamed structure.

The effects of fire on soil nitrogen associated with patches of the actinorhizal shrub Ceanothus cordulatus

Nitrogen is a limiting resource in many temperate forests and nitrogen-fixing plants are usually limited to the early stages of post-disturbance succession. In fire-dependent Sierra Nevada forests, however, Ceanothus cordulatus is relatively abundant even in old-growth forest conditions which are at least partly maintained by fire. We conducted a field experiment to determine if soil beneath Ceanothus patches represent ‘resource islands’ of available N which persist after fire. Nine plots containing discrete patches of Ceanothus, Arctostaphylos patula (manzanita; chosen as a non N-fixing reference species), and bare forest floor were subjected to either a low-intensity (n = 3) or high-intensity (n = 3) bum treatment, or remained unburned as controls (n = 3). Soil temperatures during the bum were monitored by a network of thermocouples placed at the surface of the mineral soil and at ca. 10 cm depths. Sod samples were collected from the organic horizon. 0–10 cm and 15–25 cm depths within each patch type immediately before burning and 2 days, and 6, and 11 months after. Soil moisture, total C and N, and ammonium and nitrate concentrations were determined in the laboratory. Before the burn, Ceanothus patches were significantly enriched in total and inorganic N in the organic horizon relative to the other patch types. A sharp increase in inorganic N was observed in all patch types and depths immediately following burning, but by 6 months after the burn, Ceanothus patches were significantly enriched relative to the surrounding patch types and remained so at months. Resprouting Ceanothus patches will continue to be an important source of a limiting nutrient in this fire-prone ecosystem.

Thermocouple Structure for Measurements of Surface Temperature

This Note describes a thermocouple network for measuring an average temperature of a convex surface. A version for a cylindrical surface is illustrated. The device combines advantages of a resistance thermometer and of a simple thermocouple. It is relatively easy to mount; it provides a distributed temperature measurement; and it is operated as an ordinary thermocouple.

A Differential Microcalorimeter for the Measurement of Ultrasonic Powers at the Milliwatt Levels

A microcalorimeter system has been developed to evaluate ultrasonic power outputs, especially of pulsed diagnostic transducers. The system is composed of two basically identical calorimeters, interwoven by an extensive network of thermocouples serving as an averaging temperature comparator. Borh calorimeters are mounted into a common housing with heavy aluminum walls so geometrically as to ensure a well-balanced thermal equilibrium. Either calorimeter may be used as an energy recipient, while the other serves as a temperature reference. Their filling consists of a silicon oil that matches the acoustical impedance of water. Each calorimeter contains a heating wire for calibration and a cooling system to achieve a fast temperature equilibrium following the measurement. The thermocouple battery is formed by 30 pairs of junctions, made of 20-μ-diam copper and constantan wire. It permits temperature evaluations at the millicentigrade level. The overall sensitivity of the system is approximately 0.08°C per calorie. Transducers to be measured are inserted into one of the calorimeters and are energized for about 30 sec and then pulled out to prevent the heat created in the transducer from reaching the area of measurement. Both pulsed or CW diagnostic transducers have been measured to ultrasonic power levels as small as 1 mW and with an accuracy of about ±4%.