Use Of Thermocouples Research Articles

Determination of t8/5 cooling times for underwater local dry welding of steel

Knowledge of thermal history is the basic condition for studying the structure - properties of welded joints. The determinant of thermal history is the thermal cycle, whose in-situ measurements are still a big challenge. Water as the welding environment complicates this issue even more. The article presents a method to determine an equation for calculating t8/5 cooling times for underwater gas metal arc welding of unalloyed steels using the local dry cavity method. The work uses the contact method of temperature measurements with the use of thermocouples to obtain the temperature changes of the points of welded joints covered by the thermal field. On this basis, the values of the t8/5 cooling times were determined. A regression analysis of the Response Surface Method was used to determine the equation, which resulted in a second-order model with interactions. Statistically significant factors were determined (thickness of welded elements and heat input value) and the model veracity was confirmed as the assumptions of normality and homogeneity of variance (homoscedasticity) of the residuals were met. The t8/5 cooling time values depend on the thickness of the welded elements and heat input value in a nonlinear way. In terms of the test conditions, the cooling times ranged from 3.0 to 7.7 s. The equation allowed for the calculation of t8/5 cooling times during underwater welding of unalloyed steels using the local dry cavity method based on the variability of the experimental conditions with satisfactory accuracy.

On the Use of Temperature Measurements as a Process Analytical Technology (PAT) for the Monitoring of a Pharmaceutical Freeze-Drying Process.

The measurement of product temperature is one of the methods that can be adopted, especially in the pharmaceutical industry, to monitor the freeze-drying process and to obtain the values of the process parameters required by mathematical models useful for in-line (or off-line) optimization. Either a contact or a contactless device and a simple algorithm based on a mathematical model of the process can be employed to obtain a PAT tool. This work deeply investigated the use of direct temperature measurement for process monitoring to determine not only the product temperature, but also the end of primary drying and the process parameters (heat and mass transfer coefficients), as well as evaluating the degree of uncertainty of the obtained results. Experiments were carried out with thin thermocouples in a lab-scale freeze-dryer using two different model products, sucrose and PVP solutions; they are representative of two types of commonly freeze-dried products, namely those whose structures are strongly nonuniform in the axial direction, showing a variable pore size with the cake depth and a crust (leading to a strongly nonlinear cake resistance), as well as those whose structures are uniform, with an open structure and, consequently, a cake resistance varying linearly with thickness. The results confirm that the model parameters in both cases can be estimated with an uncertainty that is in agreement with that obtained with other more invasive and expensive sensors. Finally, the strengths and weaknesses of the proposed approach coupled with the use of thermocouples was discussed, comparing with a case using a contactless device (infrared camera).

Thermocouple-based thermometry for laminar sooting flames: Implementation of a fast and simple methodology

This work reports the implementation and the validation of the extrapolation method for thermocouple temperature measurements corrected from the radiation losses in sooting flames. This simple method relies on the use of thermocouples having different size diameters and enables a fast and direct determination of the flame temperature by extrapolation to zero diameter. We propose here a detailed study of the possibilities and limitations offered by this method based on experimental measurements and comparison with well-established methods carried out in a laminar diffusion sooting flame. In details, a specific fast insertion setup using four different sized thermocouples has been implemented to record temperature values at different heights in the flame. From these data, we highlight that a linear calibration curve correlates the raw measured temperatures to the flame temperatures corrected of the radiation losses can be easily and rapidly obtained. The impact of soot deposition on the thermocouple on the temperature measurement is also discussed. To assess the reported thermocouple methodology, a direct comparison is made between the temperature profile determined along the vertical central axis of the flame by the extrapolation method with OH and NO LIF thermometry measurements as well as numerical simulation. Finally, we also report the comparison of experimental and simulated radial temperature profiles highlighting the adequate dynamic of the method for temperature profile determination in high temperature gradient conditions (500 K/mm). This work demonstrates that the extrapolation method is an efficient and fast method to determine accurate temperature profiles in flames, even in presence of soot particles up to a few hundred ppb, which can be useful for the development of fast and cheap sensors for either laboratory or larger-scale applications.

On the temperature evolution and related crystallinity of polypropylene parts processed via material extrusion

This research exposes a new methodology to follow the evolution of polymer crystallinity during material extrusion thanks to the use of thermocouples and fast scanning calorimetry (FSC). Micrometric thermocouples allowed recording the thermal history at different locations on a polypropylene (PP) part, which was then used to reproduce the thermal process conditions in FSC. This method allows to precisely study the evolution of PP crystallinity as function of time, which is an important feature to predict the printability of polymers, since crystallization is known to restrain fusion between beads. The results highlighted the dependence of the periodic thermal stress undergone by PP on several characteristics ( e.g. layer surface area, location in the part, filling strategy). Therefore, the crystallization behavior was found to be different depending on the location in the part. Crystallization was delayed at the center of the part compared to the edges because the nozzle sweep frequency was higher at the center, resulting in lower cooling kinetics. • The evolution of a polymer crystallinity was measured during a production run. • The crystallization kinetics of a polymer depend on the location in the part. • The crystallization kinetics could be controlled by adjusting the deposition pathway. • A partial crystal re-melt was observed during the deposition of successive layers.

Thermocouple response time estimation and temperature signal correction for an accurate heat flux calculation in inverse heat conduction problems

Many heat transfer processes do not allow temperature measurements with advanced instruments like IR cameras, and thus require the use of thermocouples – often inserted sheathed thermocouples – in order to measure the temperature in some key-regions. Nevertheless, thermocouples have an intrinsic response time that can dampen substantially temperature measurements and, when applicable, affect heat flux estimations by inverse methods. In this study, a thermocouple measurement correction method is proposed, especially for fast thermal transients like quenching, to avoid underestimation of the boundary heat fluxes due to delayed temperature responses. A simplified energy balance at the hot junction allowed modeling the temperature measurement by a thermocouple, in which heat losses and the response time were taken into account so they can be estimated using the least squares method on experimental data. A series of tests was performed to validate the present method with a heated jet impinging on a copper body instrumented with two thermocouples: one ungrounded and sheathed, then with high response time (”slow”); and another with exposed welded wires, hence with low response time (”fast”). After having estimated the slow thermocouple response time and heat loss parameters, the model allowed a good reconstruction of the fast thermocouple signal using the slow thermocouple measurements. Also, the heat flux estimation by the inverse method using the reconstructed signal resulted in practically the same results obtained using the fast thermocouple data. A parametric sensitivity analysis showed the heat loss parameters can be neglected for heat flux estimations, while simulations showed that temperature noises degrade the response time estimation but data filtering can mitigate this noise effect. Finally, the present method was applied to a large scale jet-cooling of a hot plate – near industrial conditions – and showed a substantially higher dissipated heat flux than the initially estimated. In fact, the results using reconstructed signals demonstrated that the heat flux dissipated by the jet has a higher dependence on the jet Reynolds number than the observed with the original thermocouple measurements, showing how important the temperature measurement correction is to evaluate fast thermal processes.

The Assessment of the Maximum Heat Production and Cooling Effectiveness of Three Different Drill Types (Conical vs. Cylindrical vs. Horizontal) during Implant Bed Preparation—An In Vitro Study

The aim of this experimental study was to verify thermal diffusion differences, by measuring the maximum temperature achieved with different drill shapes. Synthetic bone blocks of type I density made from solid rigid polyurethane (PUR) foam were used to perform the drilling procedures. The experiment was conducted at three different rotation speeds: 800, 3000 and 5000 rpm. Conical drills (with and without an internal cooling hole) were compared with horizontal drills and disc drills. The temperature during drilling for implant bed preparation was estimated with the use of thermocouples and an infrared (IR) camera. The temperature during drilling with disc cutters for lateral basal implants did not exceed 33 ∘C and the temperature decreased in proportion to higher drill speed. The results indicate that the tested design is safe and will not cause bone overheating.

Application of the subsecond calorimetry technique with both contact and radiance temperature measurements: case study on solid phase tungsten at very high temperatures

This work presents an application of the subsecond calorimetry technique at very high temperatures, which uses both contact and radiance temperature measurements. This technique is normally applied for thermophysical characterization of high temperature solid phase materials in the temperature range from ambient up to about 2600 K, which is the limit of the standard tungsten-rhenium thermocouple use. Simultaneously with contact temperature measurements, noncontact or radiance temperature detection may be performed in the approximate range from 1000 to 2600 K in order to acquire information on spectral normal emissivity of specimen under test. In this study, however, the specimen is heated above 2600 K and, then, the temperature is measured only by the noncontact mean. In the extended temperature range, the obtained values of the spectral normal emissivity are extrapolated for each experimental run, which makes possible a conversion from radiance to absolute specimen temperature. In order to test this application, a pure polycrystalline specimen of tungsten in the form of rod, 3 mm in diameter and 200 mm in length, has been used. The specimen has been heated in vacuum environment of about 10–4 mbar by short pulses of high DC current with a gradual increase of the total heating time from about 0.5–2.5 s. During the specimen heating and the beginning of the cooling period, four sets of experimental data have been recorded and reduced by using the corresponding data reduction procedure. Obtained results of specific heat and specific electrical resistivity from ambient to 3700 K, total hemispherical emissivity from 1000 to 3700 K and spectral normal emissivity from 1000 to 2600 K (extrapolated to 3700 K) are presented, discussed and compared with related literature data.

TEMPERATURE MEASUREMENT OF POLYMERS UNDER INTERMITTENT HEATING THROUGH USE OF THERMOCOUPLE AND ARDUINO® MICROCONTROLLER

The combination of relatively low production costs and a versatility makepolymers one of the most used classes of engineering materials. Thecomplexity of their chemical bounds, however, make the thermomechanicalprocessing of these materials a challenge since thermal flux frommanufacturing might significantly alter their properties. In this paper wasevaluated the use of thermocouple with Arduino® compatible hardware formeasurement and control of an intermittent heating system for processing ofNylon-6 and polycarbonate thermoplastics. A 2² factorial design was createdfor using K-type thermocouple for the two polymers at two different surfacefinishes obtained by sanding with mesh #80 and #600 abrasives. The resultsindicate that the Arduino interface has satisfactory processing capacity formonitoring heating cycles and temperature logging, making it possible toknow how temperature variated and at what level it stabilized for the heatingconditions presented. The difference in material specific heat capacity andthermal conductivity will affect the observed temperature profile. Roughnessmight present a considerable effect on the material heating since it is linkedto the heat exchange area of the process.

Laboratory stand for studying the interaction of rubbing bodies in a magnetic field

The paper presents the basic principles for the implementation of experimental studies of the tribological characteristics of friction pairs, taking into account the effect of a magnetic field on them. It has been established that modern experimental studies are carried out on laboratory units using powerful tools to analyze the data obtained, which makes it possible to study the structures of systems by changing the properties of materials under the influence of external factors and wear processes. Taking into account the influence and further research in tribo-conjugated metal bodies (for example, a wheel-rail) of such factors as magnetostriction, external magnetic field (constant, alternating, pulsed), current (direct, alternating, pulsed) passing through the contact, acting both separately, and in various combinations, the design of an experimental laboratory installation was proposed and implemented. The installation allows testing with two types of friction sliding and rolling with sliding. To measure the friction force (friction coefficient), a 6-wire bridge circuit is used, which is described in the article. The paper shows a diagram of a noise-immune strain-gauge circuit of the installation, which allows a significant level of interference during research. Due to the fact that the friction coefficient with a change in temperature can vary over a wide range, the proposed installation implements a method for automatic temperature compensation in the contact zone of tribological samples. The use of thermocouples is proposed as temperature sensors. The signals from the thermocouples of the installation are transmitted to a measuring device consisting of an analog-to-digital converter and a personal computer. The proposed laboratory setup allows for a wide range of tribological testing studies and monitoring of processes in the friction zone exposed to the magnetic field.

A critical review of the common thermocouple reference functions

The use of thermocouples in many present-day applications can often occur with little consideration as to the inherited historical burden of the reference functions the thermocouples must meet. For base-metal thermocouples, the reference functions are specified by equations relating temperature to electro-motive-force and not by alloy composition. Most of the common thermocouples contain at least one alloyed thermoelement, the bulk of which are now known to be inherently unstable above 200 °C. As manufacturing technologies change, along with the material feedstock from which thermocouples are made, modern thermocouples can frequently give measurements that deviate significantly from the ASTM and IEC standards. This study first reviews the development of the thermocouple alloys and historical conditions under which the reference functions were derived and contrasts this with modern thermocouple alloys and new testing methods. From this comparison, it is shown that users of modern base-metal thermocouples need to be extremely cautious when anticipating likely behaviour, with even short exposures to modest temperatures revealing a myriad of manufacturer-dependent instabilities. Minor variations in composition are shown to strongly influence reversible crystallographic ordering effects in addition to passivation behaviour at high temperatures, in some instances leading to catastrophic failure. It is also shown that the initial anneal state given by the manufacturer has a significant effect on the stability and hence, drift rate, with inadequate anneal leading to unnecessarily large drift rates at less than 200 °C. Lastly, this review looks at recent attempts to develop more-stable thermocouples, based on state-of-the-art techniques able to identify specific causes of instability in many of the historic thermocouple alloys and demonstrates how these new thermocouples might better serve the end user’s needs.

Identification of gradient temperature and heat flow area of geothermal Ijen Volcano Indonesia

A researcher carried out a study about gradient temperature and heat flow in the field of regional area of solfatara Ijen Banyuwangi Regency, East Java province, Indonesia. It is according to the temperature from the surface to about 100 cm deep, while making use of thermocouples with the accuracy of ± 0.5 % and ± 1 °C. Coordinate position measurements using a Garmin GPS device. This research aims to study the distribution of the temperature at any given depth, which is the gradient of temperature at a depth of 2000 m and the value of heat transfer through conduction. Temperature distribution of the depth contour, there are zones with high-temperature, and they increase along with the increase in depth. The gradient of temperature is 35 °C m−1 at a depth of 2000 meters generates 175.6 °C. The maximum heat flow value is always obtained in the presence of sulfur, while the average heat flow of solfatara on the field is 21.08 W m−2.

Finding Ablation Rates via Temperature Measurements from the Mars Science Laboratory

The determination of the ablation rate for thermal protection systems on atmospheric entry is a difficult task, but can have significant implications in terms of safety and heat shield design. Ablation sensors of various kinds can be used to measure ablation directly, but in the event of a failure of these sensors, the use of thermocouples imbedded in the heat shield for determining the ablation rate is somewhat more difficult. A numerical model was developed as part of this research to determine ablation rate as a function of temperature using measurements from the Mars Science Laboratory Entry, Descent, and Landing Instrumentation Mission, which took place in 2012. The numerical model accounts for ablation as well as temperature-dependent thermal conductivity and volumetric heat capacity. A temperature-dependent ablation rate is calculated simultaneously with the heat flux for each time step of data acquisition. Regularization is provided for the heat flux calculation through the use of cubic splines. A significant reduction in the residual values between the mathematical model and the measured temperatures was obtained when accounting for ablation and refined temperature-dependent thermal properties. In some cases, the standard deviation of the residuals was reduced by 70% or more, indicating a greatly improved conformance of the mathematical model to the measured temperatures when accounting for ablation.

104 Optimization of handheld Wand to Activate a Shape Memory Penile Prosthesis

We previously described a novel shape memory alloy penile prosthesis that could be activated using an external wand via magnetic induction, thus obviating the need for internal hydraulics, pumps and reservoirs found with inflatable penile prostheses. Optimally, this wand would be portable, battery-powered, quick and easy to use. Herein, we characterize the parameters required to optimize the external wand for touchless activation of this novel shape memory penile prosthesis. Using a commercially purchased external inductor (Miniductor II) with 1000Watt of maximum power, we measured the time of activation of the SMA prosthesis. We compared the time of activation of the existing design (fig 1b) vs an alternate design with circumferential cross section (fig 1c). Activation is reached when the Nitinol component of the prosthesis reaches the full activation temperature of 42C. The time of activation and temperatures were measured with the use of thermocouples on the spine of the prosthesis. Additional parameters examined included distance, angle and shape of the coils (ring or flat).

Experimental fire testing of an innovative three-layer chimney for residential buildings

Fires in residential buildings originating in flue ducts pose a significant problem in Europe, especially in countries where heating systems rely on devices fired with solid fuel. The high temperature of fumes emitted from heating devices is a main cause of fires. In the case of soot fires, the risk increases, as the temperature in the flue duct can exceed 1000 °C. Chimneys are often located close to flammable (wooden) construction materials, which further increase the risk of fire. This article presents statistical data confirming the significance of the problem. The subject of this study is fire safety of a three-layer chimney system. The diameter of the flue duct of the inspected chimney was 180 mm, while air space and insulation measured 30 mm. The main research involved the use of thermocouples and a thermal imaging camera. The analysed chimney is an innovative construction, as it is equipped with an additional insulating air layer. The purpose of the research is to assess the impact of this air layer on fire safety during the use of a three-layer thin-walled flue pipe. The air space discharges heat from the flue duct through a parallel flow of cold air. Analysis explored the impact of the chimney's thermal radiation on unprotected and easily flammable construction materials. Particular attention has been devoted to the impact the air layer has on reduction of the amount of thermal radiation. Final conclusions from the study can be used to increase fire safety of residential buildings. This may be achieved by reducing temperatures emitted from the chimney cladding.

Electrochemical characterization of the interaction between ammonium nitrate and reactive ground

Cyclic voltammetry is used to examine the interaction between aqueous solutions of NH4NO3 and FeS2, a major component of reactive ground. Voltammetric processes corresponding to the Fe(II)/Fe(III) redox couple and the reduction of nitrate are observed. This is significant as the existing reaction mechanism shows nitrate reacting in the electrolyte, but not being reduced on the surface of the FeS2. An irreversible oxidation occurs at ∼0 V versus SCE associated with the re-oxidation of species formed at lower potentials. This is not associated with a change in the potential of the electrolyte, indicating a surface reaction. With the use of thermocouples, an exothermic reaction above 0.4 V is observed. FeS2 is initially unreactive in NH4NO3 solutions. After FeS2 exposure to potentials above 0.6 V versus SCE, the material becomes active and catalytic in nature. Material reacted following the industry standard Australian Explosives Industry Safety Group (AEISG) test method shows similar catalytic behaviour in the presence of fresh NH4NO3. This is significant for the safety and testing of reactive ground, as even FeS2 that has completed reaction still has the potential to undergo further reaction if introduced to fresh NH4NO3.

Estimation of the Temperature in the Stirred Zone and Cooling Rate of Friction Stir Welding of EH46 Steel from TiN Precipitates

Measuring the peak temperature in the contact region of the tool/workpiece in friction stir welding (FSW) is difficult using conventional methods such as use of thermocouples or a thermal imaging camera, hence an alternative method is required to tackle this problem. The objective of the present work was to estimate more accurately, for the first time, the peak temperature and cooling rate of FSW from precipitation of TiN in friction stir-welded steel samples. Microstructures of nine friction stir-welded samples of high-strength shipbuilding steel of EH46 grade were examined closely by SEM-EDS to detect the TiN precipitates. Thermal heat treatments using an accurate electrical digital furnace were also carried out on 80 unwelded EH46 steel samples over a range of temperatures and cooling rates. Heat treatments were to create a basis to understand TiN precipitation behavior under various heating and cooling regimes for the studied alloy. Heat treatment showed that TiN particles can precipitate at a peak temperature exceeding 1000 °C and the size of TiN precipitate particles increases with decreasing cooling rate. In a temperature range between 1100 °C and 1200 °C, the TiN precipitates were accompanied by other elements such as Nb, S, Al, and V. Pure TiN particles were found after the peak temperature exceeded 1250 °C with limited precipitation after reaching a peak temperature of 1450 °C. The comparison between the friction stir welding samples and the heat treatments in terms of types and sizes of TiN precipitates suggests that the welding peak temperature should have been in the range of 1200 °C and 1350 °C with a cooling rate in the range of 20 to 30 K/s. The current work represents a step change in estimating the friction stir welding temperature and cooling rate which are difficult to determine using thermocouples and thermal imaging camera.

Method of reducing the inertia of a thermocouple cable CTMS based on a cable of variable cross-section to improve reliability in aviation and rocket and space technology

The method of reducing the inertia of the thermocouple cable ctms based on the use of a cable of variable cross-section is considered. The comparative analysis of time of establishment of thermal equilibrium of a thermocouple cable with variable cross-section and without it is given. The time before the establishment of thermal equilibrium is considered. From a technological point of view, the use of thermocouples based on chromel-alumel is justified. The parameters of inertia of a thermocouple cable of variable cross-section are given.

Time-dependent study of boiling heat transfer coefficient in a vertical minichannel

Purpose The purpose of this paper is to determine the time-dependent heat transfer coefficient during FC-72 flow boiling in a 1.7-mm-deep vertical and asymmetrically heated minichannel. Design/methodology/approach The temperature of the minichannel heated wall was recorded continuously with the use of thermocouples. The heat transfer coefficients for the subcooled and saturated boiling regions at the heated wall–fluid contact surface were calculated from the Robin boundary condition. Both the wall and fluid temperatures were obtained from the solution of the inverse nonstationary problems in two adjacent domains: the heated wall and flowing fluid. The FEM with Trefftz-type basis functions was applied to solve the inverse problem. Findings The obtained time-dependent heat transfer coefficient in subcooled boiling achieved rather low values, whereas in saturated boiling, the coefficient was the highest at the channel inlet. The boiling curves were plotted to illustrate the results. Practical implications The results of experiments are the best source of information for the design of minichannel cooling systems used for thermoregulation of components and heat exchangers. High-tech minichannel heat exchangers are applied in various industrial applications as microelectronics devices, gas turbines, internal combustion engines, nuclear reactors, X-ray sources and organic rankine cycle (ORC) modules. Originality/value In the study, the Trefftz functions for the nonstationary Fourier–Kirchhoff equation with the factor describing void fraction were determined and then used to construct the time-dependent basis functions in FEM.

Development of a rotary two-colour pyrometer for thermal measurements in face grinding operations

Grinding burn is one of the main problems in grinding and it is nowadays a matter of concern both for Academia and Industry. Research works along the last 50 years have shown that as much as 60-85% of the total consumed power is conducted to the workpiece in the form of heat. As a consequence, surface and subsurface temperature of the component rises, leading to phase transformations, loss of previous heat treatments, development of harmful tensile residual stresses, etc. Temperature measurement becomes thus a critical point to predict thermal problems and for optimization of process parameters. However, temperature measurement in grinding is a very difficult task: values over 800ºC, thermal gradients over 4000ºC/s, the presence of large amounts of cutting fluid and high pressure, and the difficulty to access the contact point have led researchers to study very different approaches. For instance, the use of thermocouples has been presented in numerous research works. However, thermal inertia of thermocouples and the problems related to efficient location limit their actual application field. Other instruments such as one colour pyrometers and infrared cameras have also been used in research, but effective calibration is very difficult. Also, the presence of cutting fluid has limited their use to dry grinding operations. The problem is even more evident in cylindrical grinding, where specific wireless instrumentation must be developed. In this work, with the aim of avoiding grinding burns in the face grinding operations in automotive-part manufacturing, a new efficient pyrometer together with the electronics has been developed.

Experimental research of heat transfer in supersonic separated compressible gas flow

The results of an experimental study of heat transfer for supersonic flow around plane surface in the wake of a rib are presented. The study was conducted on unsteady regime during the launching supersonic wind tunnel before reaching the equilibrium thermal state. The initial flow Mach number was 2.2, Reynolds number based on the length of the dynamic boundary layer from the nozzle throat was over 20 million at the nozzle exit section. The rib height was varied from 2 to 10 mm while boundary layer thickness for smooth model flow in the region of rib placement was about 6 mm. Recovery temperature and the coefficient of heat transfer enhancement for flow past the rib are presented in comparison with the regime of a smooth model flow. The research was carried out with the use of thermocouples with thermal compensation, total and static pressure probes, LabView automation programs.