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The achievement of materials hardness was difficult in heat treatment through quenching methods. At the same time, the quenching medium was not covered the entire surface of the work piece. In present topic was discussed about the development of water quenching method for chromel composite. For these experimental investigations, the different levels of control factors were considered such as water velocity, the rotational speed of the work piece, and Standoff Distance (SOD). The response such as hardness was evaluated according to the variation of control or input factors. The effects of quenching factors were reported through the Taguchi technique and variance analysis. The maximum hardness of 545BHN was achieved through the developed quenching apparatus. The water velocity (74.22%) was the influential factor on hardness. It was validated through variance analysis.

This paper makes an investigation on the synthesis of tantalum carbide (TaCx) based chromel composites and their tribological behaviour using pin on disc under various load conditions. The reinforced chromel alloy with TaCx was prepared at the rate of 0, 3 and 6 wt.% of TaC using stir casting route. The wear resistance of composites was found to improve with the increase in weight percentage of TaC. The wear properties of Chromel-TaCx composite were enhanced due to the presence of 6% TaC. The wear worn out surface of chromel composite was studied through microstructures. The optimal process factors and their effect on responses have been analyzed through Response Surface Methodology (RSM) and Analysis of Variance (ANOVA).

The chromel was one type of nickel-based metal matrix (MMC) and it was fabricated through stir casting technique. The titanium carbide (TiC) was used as a reinforcement material. The particles were analyzed through Atomic Force Microscopy (AFM) and Dynamic Light Scattering (DLS). Abrasive Water Jet Drilling (AWJD) was mechanical energy based non-traditional process that was applied to pierce the stir casted chromel MMC. During the drilling process, jet pressure, traverse speed, and standoff distance were pointed as the main input factors. The Material Subtraction Rate (MSR) and Surface Finish (SF) have been chosen as the response factors. The effect of factors and their correlation were validated through variance test and interface plots.

We developed thermocouple probes consisting of constantan and chromel segments with nanoscale sharpness. The ends of wires made of these alloys were polished utilizing a single step drop-off electrochemical procedure in a H3PO4 solution. The macroscopic shapes of the etched wires were designed to detect ultra-small heat inputs with high sensitivity after assembling a thermocouple. After electrochemical treatment, ultimately smooth, mirror-polished wire surfaces were observed. The etched wires were then assembled in a transmission electron microscope (TEM) to create a miniature thermocouple by using which we successfully detected a small temperature increase induced by focused TEM electron beam irradiation. Judging from high- resolution TEM imaging, a thermocouple with the tip-end of only ~5 nm in diameter was fabricated.

International audience; An experimental setup for 3 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 method. The tests were performed under vacuum and atmospheric pressure for chromel wire as a reference sample and under vacuum for two types of polyacrylonitrile-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.

Temperature is one of the most measured parameters within industry. Thermocouple is an extremely versatile device widely used in industry for critical high temperature, achieving extremely high accuracy with a thermocouple can be more difficult because of their inhomogeneity. Temperature drift in thermocouple is a common problem that affects the accuracy of a measurement system. Due to prolonged usage of thermocouple under different conditions causes changes in the properties of the thermocouple and in turn degrade the thermocouple which is followed by drift. Hence it is important to analyze the rate of degradation of the thermocouple material. In this work, material analysis using scanning electron microscopy by an energy dispersive X-ray (SEM-EDAX) has been performed on the thermocouple, due to change in temperature gradient at different insertion positions.

Measurement of transient heat flux values is a challenging task as it requires fast response sensors. The standard heat flux sensors cannot satisfy the requirement for transient measurement due to more response time. Therefore, a thermal probe has been prepared in-house for capturing transient response in high speed flows especially in aerodynamics studies. The probe has been fabricated from bare chromel and constantan thermoelements named as “coaxial surface junction thermocouple (CSJT).” Experiments are carried out for heat flux calibration with the help of a laser unit to access the capability of the probe in measuring heat flux values. The inferred experimental temperature signal is used to estimate the surface heat flux values analytically. Similarly, a numerical simulation has been performed to validate the results. The values are found to have a matching with the applied heat flux in terms of trend and magnitude in a timescale of 0.4 s.

Coaxial thermocouples have the advantages of fast response and good durability. They are widely used for heat transfer measurements in transient facilities, and researchers have also considered their use for long-duration heat transfer measurements. However, the model thickness, transverse heat transfer, and changes in the physical parameters of the materials with increasing temperature influence the accuracy of heat transfer measurements. A numerical analysis of coaxial thermocouples is conducted to determine the above influences on the measurement deviation. The minimum deviation is obtained if the thermal effusivity of chromel that changes with the surface temperature is used to derive the heat flux from the surface temperature. The deviation of the heat flux is less than 5.5% when the Fourier number is smaller than 0.255 and 10% when the Fourier number is smaller than 0.520. The results provide guidance for the design of test models and coaxial thermocouples in long-duration heat transfer measurements. The numerical calculation results are verified by a laser radiation heating experiment, and heat transfer measurements using coaxial thermocouples in an arc tunnel with a test time of several seconds are performed.

The magnitude of surface heat flux and its accurate estimation are very crucial owing to their applicability in impulsive thermal loads for high-speed flights. The correctness of such heat flux is associated with the implications from highly responsive thermal sensors in ground-based aerodynamic studies. In the present study, the performance effectiveness of an indigenous, in-house-made coaxial thermal probe (CTP) is validated against a standard silver thin film gauge (TFG) counterpart. The thermal probe has been fabricated in-house from two metal alloys; chromel (3.25 mm diameter and 10 mm length) and constantan (0.91 mm diameter and 15 mm length), by disposing one in the annulus of another coaxially, subsequently clubbed by a thin layer of epoxy in between them. Similarly, the thin film gauge is fabricated by putting silver paste (~1 µm thickness) on the pyrex substrate (3.25 mm diameter, 10 mm length). The fabrication process is followed by different calibration activities to determine the characteristics constants for sensors (sensitivity, thermal product value for CTP, and temperature coefficient of resistance for TFG). Both the probes are tested in a highly transient environment in a shock tube that generates high density, high pressure, and high enthalpy flows. The response time of the CTP and TFG are found to be 265 µs and 240 µs, respectively. The heat flux values estimated through temperature responses are having a nice match for CTP as well as TFG with a deviation in peak heat flux value within a range of ±2%. A similar trend and magnitude are also re-assured through numerical simulation within an uncertainty band of ±1.5%. The exhaustive study carried out in a shock tube has assured the performance and reliability of a CTP. Hence, it is recommended as an effective heat flux sensor for routine measurements in impulsive heat loadings.

Heat transfer in the contact zone of a rail and thermocouple chromel electrode was investigated. The diameter of the contact spot and angle of sharpening the electrode for reducing the measurement error with consideration of the initial temperature of the thermocouple electrode were found.

Sufficiently large amount of data is needed to prepare a training set for a neural network. However, there is no enough experimental data of thermocouple leg errors to prepare an adequate training set for the neural network. The method of preparation of a training set for the neural network is proposed in this paper. This method is based on hierarchical interpolation and extrapolation of the experimental data of thermocouple leg error using the method of conditional least squares. The neural network model of thermocouple leg error is presented on the example of the chromel leg of type K thermocouple.

The development of advanced nuclear fuels requires detailed understanding of their transmutation and micro-structural evolution. Alloy fuels have the advantage of high thermal conductivity and improved characteristics in fuel-cladding chemical reaction. However, information on thermodynamic and thermophysical properties is limited. The objective of this work was to develop an experimental system, integrated with thermal conductivity measurement capability to measure the thermodynamic properties of solid materials, from which an understanding of their phase change(s) can be determined. With the coupled system, both thermal conductivity and electromotive force (EMF) may be measured. In order to validate the system, the apparatus was employed to measure the EMF of several materials. As an initial calibration test, the EMF of Chromel was measured from 100 °C to 800 °C and compared with theoretical values. Subsequent EMF measurements were made for pure iron, iron-nickel alloy, and ANSI 1018 carbon steel rods. The measured phase transition temperatures were compared with the corresponding alloy equilibrium phase diagrams. The results indicate that the system is able to determine material phase change based on EMF measurement. In the future, this prototype system is to be adapted for hot-cell use on irradiated samples.

Understanding the cell temperature distribution of solid oxide fuel cell (SOFC) stacks during normal operation has multifaceted advantages in performance and degradation studies. Present efforts on measuring temperature from operating SOFCs measure only the gas channel temperature and do not reveal the cell level temperature distribution, which is more important for understanding a cell's performance and its temperature-related degradation. The authors propose a cell-integrated, multi-junction thermocouple array for in-situ cell surface temperature monitoring of an operational SOFC. The proposed thermocouple array requires far fewer numbers of thermoelements than that required by sets of thermocouples for the same number of temperature sensing points. Hence, the proposed array causes lower disturbance to cell performance than thermocouples. The thermoelement array was sputter deposited on the cathode of a commercial SOFC using alumel (Ni:Al:Mn:Si – 95:2:2:1 by wt.) and chromel (Ni:Cr – 90:10 by wt.). The thermocouple array was tested in a furnace over the entire operating temperature range of a typical SOFC. The individual sensing points of the array were shown to measure temperature independently from each other with equivalent accuracy to a thermocouple. Thus, the concept of multi-junction thermocouples is experimentally validated and its stability on a porous SOFC cathode is confirmed.

We developed a method to determine the absolute pressure effect on thermocouple electromotive force (EMF), based on a single wire method using Kawai-type multi-anvil apparatus. In this method, pressure conditions along the wires were evaluated based on in situ X-ray diffraction using synchrotron X-ray radiation. The pressure effect of the Seebeck coefficients of chromel and alumel was determined up to 7 GPa and 600°C by the analyses of single wire EMFs and pressure-temperature profiles along the wires. The temperature correction for the type K thermocouple was calculated to be from 0°C to –3°C in the studied conditions. Since the multi-anvil apparatus is capable of achieving much higher pressure and temperature, the method presented in this study promises to reveal absolute temperature correction for thermocouples over a wide range of pressure and temperature conditions.

This work presents steady-state and transient microscale temperature measurements by optical and multispectral method in the ultraviolet-visible wavelengths. Regarding the classic laws of radiative heat transfers, the photon counting is preferred to the energy measurement. The photonic emission is a random phenomenon and is here measured with statistical laws such as the Gaussian law. The spectral dependence of the optical apparatus transfer function is taken into account by a linear function and the temperature is estimated by inversion with a Levenberg–Marquardt algorithm. Measurements are performed with a small-dimension blackbody developed in the laboratory and with a Chromel wire. Both of them are capable of heating up above 1000 °C. The diameters of the observed surfaces are 10 µm and 5 µm, respectively. The theoretical criterion of wavelength selection and least-squares parameter estimation allow for a difference between the estimated and controlled temperatures lower than 4%.

A transition boiling on a high temperature solid beyond the Leidenfrost temperature is characterized by a strong unstable heat transfer. This unstable one brings a rapid temperature change beneath the surface in the solid and causes a repetition in time as well as a space of wet and dry on the surface. Therefore, the development of a fast temperature measurement technique is indispensable to understand this transition phenomenon. The developed temperature sensor has a junction of the end face of chromel fine wire of ϕ0.32 mm diameter, whose position is 3 μm away from the surface of nickel disk of 5 mm thickness and can follow a rapid temperature change within 100 kHz. The heat transfer can be calculated from the measured temperature by using an inverse problem analysis for one-dimensional unsteady heat conduction. Besides, the calculated heat flux is also confirmed to be sufficient to capture the characteristics of unsteady boiling heat transfer in the experiment that a sessile ethanol droplet impacts onto the hot surface.

International audience; The purpose of this paper is to investigate a steady-state method enabling the measurement of the thermal conductivity of an electric conducting wire. Instead of varying the pulsation of a periodic current as done in the 3ω method, the proposed method is based on steady-state measurements realized for different lengths of the same wire. The model developed takes into account an external heat transfer coefficient (conduction + radiation) often neglected in previous works. A sensitivity analysis shows the possibility of estimating simultaneously the wire thermal conductivity and the external heat transfer coefficient. The experimental results obtained with Chromel and Copper wires are in good agreement with references values (less than 5% deviation).

The objective of the current investigation is to find out temperature distribution regimes in a horizontal pipe when condensation process is happened. The research was conducted at Pusat Studi Ilmu Teknik Universitas Gadjah Mada. The experiment apparatus consists of an inner annulus pipe made from copper (din = 17.2 mm, do = 19 mm) with the length of 1.8 m. The outer annulus pipe is a galvanized iron pipe (din = 108.3 mm, do = 114.3 mm) with the length of 1.6 m. Thermocouples type K 36 TT OMEGA with chromel (+) and alumel (-) materials were used as temperature sensors, to detect the spread of temperature in radial or axial direction along the pipe. The measurement ranged from -50 to 260 oC, with an accuracy of 0.01 °C. A data logger of RX 40 serial (OMRON, 20 Channels) was used to read and record temperature data with the sampling rate of 5 Hz. In the experiment, the water (H2O)was heated using a boiler to generate steam which was then flowed and condensed inside the annulus pipe to form a steam-condensate two-phase flow in horizontal pipe. On the other hand, the water was used as a coolant in the outer of annulus pipe. The results indicated that the temperature distribution regimes are influenced by axial posisition.The farther distances from the inlet the lower the temperatures being recorded which indicate the increase of film condensate thickness. Such phenomena can affect slugging in the location.

K-type thermocouples are fabricated using a chromel wire and an alumel wire of 50 m by the non-contact discharge welding method. The welding is carried out at six different butt angles. The size of the hot junction tends to decrease with an increase in butt angle, when the butt angle is larger than 1.4 rad. The response rate is measured and it is almost proportional to the reciprocal of the size of the hot junction. It is shown that the size of the hot junction is an important factor for the response rate. Wire diameter is another important factor for temperature measurement of small objects. When temperature is measured at the same point by a thermocouple under the conditions that only the hot junction and its vicinity are heated, the output of electromotive force, i.e. indicated temperature, will depend on the wire diameter. As the metal wire is a good thermal conductor and the rate of heat transport is proportional to the area of the wire cross section, deviation from the true value increases with an i...

Novel multi-junction thermocouple architecture was developed and simulated to in-situ monitor the temperature distribution over a Solid Oxide Fuel Cell (SOFC). This thermocouple architecture requires only {N+1} number of wires for N number of independent temperature measuring points. Therefore, N+1 architecture can independently measure temperature at multiple points simultaneously with much less number of wires than a set of thermocouples require for the same number of independent temperature measurements. Requiring less number of external wires is a distinct advantage, particularly, in constrained environments such as those within SOFC stacks. A thermocouple array having 4 independent temperature measuring points with 5 thermo-elements was simulated in MATLAB. Alumel (Ni:Al:Mn:Si – 95:2:2:1 wt) and Chromel (Ni:Cr – 90:10 wt) were chosen as thermo-element materials because of their wide applicability in the industry as K-type thermocouples. The junctions were considered to be spot welded. Three sets of simulations were performed to investigate two aspects: validation of the multi-junction thermocouple concept and investigation of the effect of the heat affected zone created in spot welding to the temperature measurement. Simulation code generates random temperature values for each junction within a pre-defined range. Temperatures at the boundaries of heat affected zones were also generated randomly according to a pre-defined criterion. The change of Seebeck coefficients within the heat affected zone was set as a percentage change of their corresponding materials Seebeck coefficient. The temperature gradient induced emf values for each sensing point were calculated from Seebeck coefficients. The calculated emf was then mapped back to temperature using ASTM approved inverse conversion function. These mapped temperatures were then compared with the set temperatures for each junction and they were in very good agreement.

The occurrence of an error due to the thermoelectric inhomogeneity of thermocouple electrodes, acquired during prolonged use, is considered, and the properties of this error are formulated. A mathematical model of the error of chromel and alumel electrodes is constructed, the error in measuring the temperature is estimated, and the most dangerous mode of operation of the thermocouples is revealed.

International audience; This paper presents a dynamic characterization setup to calibrate transient surface temperature sensor in radiative conditions. The temperature sensor is a K type (Chromel/Alumel) wire microthermocouple which hot junction is obtained from a layer deposition by PVD process. Three different metallic layers are used (Tungsten, gold and chromium) with two thin film thicknesses (0.4 μm and 0.8 μm). The aim of this work is to develop a dynamic characterization with a radiation source from a laser focused onto the thermocouple's hot junction. The dynamic performance of the sensor is obtained by measuring its unit-impulse response function (Yag laser) and its periodic response under a chopped continuous laser beam (Argon laser). Experiments are realized at atmospheric pressure. The best results are obtained with deposited probes with gold junction of 0.4 μm thickness. The rise-time and decrease-time are equal to 10 μs and 80 μs respectively (Yag laser).

Base-metal thermocouples play a significant role in industrial measurements, and among the many varieties and formats, bare-wire Type K is often preferred. The reason for this preference is its low cost, durability and tolerance of high temperature. Unfortunately, Type K, like all base-metal thermocouples, is made based on a temperature-to-emf relationship and not on a specific metallurgical formulation. The original Hoskins Chromel/Alumel couple was simple in composition, and it had known thermal drift characteristics associated with reversible crystallographic changes and irreversible oxidation, and these two drift mechanisms led to large instabilities in use. To improve the stability of Type K, most modern manufacturers now adopt compositions with alterations that can depart significantly from those of the original formulation. These alterations are usually made to improve the stability and/or manufacturing processing of their wire. So, although the wire is made to meet the limits of error and tables, this is only true at the time of manufacture. As soon as the wire is exposed to temperatures above $$150~{^{\circ }}\hbox {C}$$ , the supplier-dependent alloys can exhibit a wide range of drift behaviors that depend on composition and even the batch of the wire. This study investigates the change in Seebeck coefficient as a function of temperature for Type K bare-wires from different suppliers by using a linear-gradient furnace and a high-resolution homogeneity scanner. Wires were exposed to temperatures over the range $${\sim }20~{^{\circ }}\hbox {C}$$ to $$950~{^{\circ }}\hbox {C}$$ for time periods between 24 h and 500 h. The results show that most wires have very different drift behaviors, which the end user could not realistically predict or correct.