Thermocouple Instrumentation Research Articles

Thermal Impulse Response in Porous Media for Transpiration-Cooling Systems

A solution of the coupled differential equations for fluid and solid phases in a one-dimensional porous medium in thermal nonequilibrium is presented using the concept of analyzing the impulse response. The impulse response is shown to be sensitive to the volumetric heat transfer coefficient and the coolant mass flux. Experimental data obtained from surface heating of transpiration-cooled porous zirconium di-boride () samples are compared to a newly developed theoretical model. The surface and backside temperatures of the solid are measured using thermographic imaging and thermocouple instrumentation. The noninteger system identification approach is used to experimentally obtain the thermal impulse response, which is then compared to the model prediction. Good agreement is found between the simulated and experimental data with average deviations below 10%. The developed model provides the basis for inverse heat transfer measurements and further analysis of transpiration-cooled materials.

Development of an Ultrasonic Thermometry System

The purpose of this study was to develop and apply a custom computational algorithm to estimate internal temperature distribution of heated materials by ultrasound. The experimental setup was carry-out using an ultrasonic pulser- receiver system to drive a longitudinal ultrasonic transducer of 5.0 MHz. A general-purpose oscilloscope was used as data acquisition system and ultrasonic signals waveform viewer. Measurements were performed during the heating and cooling regime of a structural aluminum block with the time-base of the oscilloscope set to 2.5 ns. A thermocouple temperature measurement system was used to verify and validate the temperature distribution found for ultrasonic thermometry method. The developed computational algorithm was responsible to communicate with oscilloscope device and evaluate the temperature of the block in real-time. The comparison of the temperature measurements derived from the ultrasonic thermometry with thermocouple temperature system showed an excellent accuracy raging from 97% to 99% for heating regime and cooling, respectivally. The presented methodology showed to be relevant to estimate internal temperature of the heated metal. Accurate data measurements were provided by oscilloscope, compared to those found using thermocouple instrumentation.

Comparison of three methods to quantify the fire spread rate in laboratory experiments

Different methods can be used to measure the time and distance of travel of a fire and thus its speed. The selection of a particular method will depend on the experimental objectives, design, scale, location (in the laboratory or field), required accuracy and resources available. In this study, measurements from ocular observation (directly by eye), visible spectrum video imagery and thermocouple instrumentation were used to compare their performance in quantifying the time of arrival and rate of spread of a fire burning across a eucalypt forest litter fuel bed in a combustion wind tunnel. All methods gave similar results, but there were some significant differences depending on the dryness of the fuel and speed of the wind.

Experimental and numerical analyses on the effect of increasing inflow temperatures on the flow mixing behavior in a T-junction

Thermal degradation of piping induced by high cycle thermal fatigue (HCTF) is of significant importance as operating Nuclear Power Plants (NPP) become older and lifetime extension activities are initiated. In particular, HCTF incidents related to turbulent thermal mixing of fluids in a T-junction piping system are not well understood and could not be adequately monitored using common thermocouple instrumentation. To investigate this phenomenon, an experimental T-junction test facility was commissioned at the University of Stuttgart, known as the Fluid Structure Interaction (FSI) test facility. The paper presents the experimental investigation and the corresponding numerical validation using the large eddy simulation (LES) method to study T-junction flow mixing. Three experimental test cases are investigated with temperature differences (∆T) of 51.5K (Case 1), 76K (Case 2) and 97K (Case 3) between the mixing fluids. A constant mass flow rate ratio (main/branch) of 4:1 is maintained in all the investigated cases. Flow mixing is observed to be incomplete in all the cases, resulting in a thermally stratified flow with an oscillating stratification layer downstream of the T-junction. Mean temperature and root mean square (RMS) temperature fluctuations predicted by LES in the mixing region are found to be in good agreement with measurement data, with the exception of few positions. Amplitudes of temperature fluctuations are observed to be higher near the stratification layer, ranging from 6.3–9.9% of ∆T. Power spectral density (PSD) analyses of temperature fluctuations indicate no dominant frequency (spectral peak) under prevailing flow conditions, an important factor in thermal fatigue analysis, and the energy of these fluctuations are mainly contained in the frequency range of 0.1–2Hz for all the investigated cases. LES is performed using the CFD software ANSYS CFX 14.0.

An alternative method to record rising temperatures during dental implant site preparation: a preliminary study using bovine bone.

Overheating is constantly mentioned as a risk factor for bone necrosis that could compromise the dental implant primary stability. Uncontrolled thermal injury can result in a fibrous tissue, interpositioned at the implant-bone interface, compromising the long-term prognosis. The methods used to record temperature rise include either direct recording by thermocouple instruments or indirect estimating by infrared thermography. This preliminary study was carried out using bovine bone and a different method of temperatures rising estimation is presented. Two different types of drills were tested using fluoroptic thermometer and the effectiveness of this alternative temperature recording method was evaluated.

Multidimensional Assessment of Modeling Error in Typical High-Speed Wind-Tunnel Heat-Transfer Data-Reduction Schemes

R IGOROUS validation of computational tools places stringent demands on the accuracy of measured experimental data. This is increasingly the case in fluid dynamics, in which computational approaches havematured to the point at which certain propertiesmay be predicted to the same level of accuracy that can be measured. In such a situation, a discrepancy between computation and experiment cannot simply be assumed to lie exclusively in either the computational or experimental result. Rather, a thorough evaluation of both the computational and experimental techniques is required. Such is the case for perfect-gas wind-tunnel measurements of surface heat transfer for a simple body in an attached laminar flow. A standard technique for measuring the heat-transfer rate to a surface is via thermocouple instrumentation. The thermocouples may be subjected to an unknown heat flux for some period of time, and temperature histories may be obtained. This surface temperature history can then be used as a boundary condition in a transient thermal analysis from which the heat-transfer rate may be inferred. This technique is often employed in wind-tunnel tests that seek to quantify the aerothermodynamic environment for a given geometry. In such applications, the thermocouple instrumentation is typically too sparse to determine a true multidimensional surface temperature distribution, which could then be used in a three-dimensional thermal analysis. Consequently, the thermocouple temperature histories are often used in conjunction with a one-dimensional heat-transfer analysis, which only considers conduction normal to the surface. For geometries with regions of tight curvature and/or substantial lateral gradients in heat-flux distribution, the validity of the onedimensional assumption comes into question. This Note investigates the modeling error induced by the combined factors of lateral heat-flux distribution and multidimensional curvature for a specific geometry that was recently tested in the Arnold Engineering Development Center’s Hypervelocity Wind Tunnel no. 9. A purely analytical approach is used that combines steady computational fluid dynamics simulation, transient threedimensional thermal analysis, and the standard transient onedimensional thermal analysis technique to quantify the modeling error introduced through the data-reduction process for each gauge. The remainder of the Note is organized as follows: Section II provides an overview of the experimental test series that provides the motivation for this work, Sec. III describes the analytical approach used to predict the external convective heat-transfer and the transient thermal analysis, Sec. IV presents results for the specific case of a scaled Orion Crew Module model at wind-tunnel conditions, and some general conclusions are discussed in Sec. V.

Heat transfer during transient compression: Measurements and simulations

Experiments have been performed to assess the utility of unsteady one-dimensional heat conduction modelling for the calculation of heat losses during a free piston compression process. Heat transfer measurements have been obtained within a gun tunnel barrel using surface junction thermocouple instrumentation. The gun tunnel was operated with a relatively heavy piston such that the shock waves induced by the piston motion were weak. Peak heat transfer values are estimated reasonably well by the unsteady one-dimensional model. However, overall quantitative agreement between the measurements and calculations has not been achieved at this stage, principally because the development of turbulent heat transport was not properly modelled.

PC-Based Data Acquisition Interface and Expansion System

A hardware interface and expansion system for PC-based data acquisition and control systems was developed for use within the Kansas State University Agricultural Engineering Department. The system, consisting of an interface box and analog input satellite boards, was designed to allow easy connection of sensors and to expand the original analog input capacity. The interface boxs star topology analog bus and the satellite boards optional thermocouple temperature compensation circuitry and instrumentation amplifier support are discussed. A variety of applications using the technology are presented.

The thermomechanical properties of gutta-percha. Part IV. A thermal profile of the warm gutta-percha packing procedure

A thermal profile of the warm gutta-percha technique was produced by the thermocouple instrumentation of natural teeth and the subsequent monitoring of intraradicular temperature changes during the packing procedure. Although variations in thermal patterns resulted from individual differences in timing and instrumentation, certain clinically accepted patterns of activity produced consistent, representative temperature ranges to which the gutta-percha was subjected. The maximum regional temperature determined for bulk gutta-percha in the body of the canal was 80° C., while the over-all peak temperature recorded in the apical region was 45° C. Thermal penetration of the gutta-percha was expectedly limited, with significant thermal effects rarely exhibited more than 4 to 6 mm. into the material.

The Measurement of Gas Temperature Using the Gas Jet Generator

Work done so far indicates the feasibility of using a gas jet generator as a temperature-frequency converter for the measurement of air or gas temperature up to 2000°R. In its optimum configuration for stability and level of output, the gas jet generator is not quite of constant wavelength characteristic. This does not matter, provided that any particular configuration is calibrated by using an airstream of known stagnation temperature and these results are used to predict the performance with other specified gases or gas mixtures. In comparison with thermocouple instruments such as the sonic suction pyrometer the gas jet generator is superior from the transient response and mechanical strength aspects, but inferior for steady state measurements, particularly at the higher temperatures. This is because its sensitivity decreases with increase in temperature owing to the square root relationship between the velocity of sound and absolute temperature.

Thermocouple Corrections from Irreversibility Theory

The correction for finite impedance of thermocouple instrumentation is derived rigorously from irreversible thermodynamics. Also, the indistinguishability of Peltier and Thomson “emf's” is elucidated.

Multirange, audiofrequency thermocouple instruments of high accuracy

Multirange, audiofrequency thermocouple instruments of high accuracy

Thermal converters as AC-DC transfer standards for current and voltage measurements at audio frequencies

Thermal converters and associated equipment that are used as ac-dc transfer standards at the National Bureau of Standards for the precise measurement of current and voltage at power and audio frequencies are described. The standards and the equipment are primarily used to standardize a-c ammeters and voltmeters submitted to the Bureau for certification. The ac-dc transfer may be made with these thermal converters at currents from 1 milliampere to 50 amperes, voltages of 0.2 to 750 volts, with an accuracy of 0.01 percent at frequencies from 25 to 20,000 cycles per second. The special tests to insure the required accuracy of the transfer standards are described, and the results are presented. A number of factors that limit the transfer accuracy of ther­ mal converters have been discovered, and the results of special tests and theoretical work to evaluate these factors are discussed. The solutions, by an approximation method, Of certain pertinent nonlinear differential equations governing the heating of a conductor by an electric current are given. The increasing use of electric energy for aircraft, induction furnaces, and induction heating, and the greater accuracy required in measurements in electronics, have led to increasing demands for the accurate standardization of ammeters and volt­ meters at frequencies extending upward from power frequencies through the entire audio-frequency range. To meet these demands, special instruments have been developed at the National Bureau of Standards for the measurement of current and voltage over rather wide ranges. They make use of thermal converters l (often called thermoelements) like those incorporated in ordinary thermocouple instruments, but differ in the manner of reading and use. They may be used either directly to measure the ac-dc differences of ammeters and voltmeters, or with a suitable potentiometer and accessories to measure alternating currents and voltages. They were designed and are used pri­ marily for testing electric instruments, at currents from 1 ma to 50 amp and voltages from 0.2 to 750 v, with an accuracy of 0.01 percent at frequencies from 25 to 20,000 c/s.

Some sources of error in microwave milliwattmeters

An approximate analysis is made of the factors that influence the intrinsic accuracy of a heated filament used as a transfer device for measuring power at microwavelengths in terms of a low-frequency calibration. It is shown that instruments incorporating such filaments are usually subject to errors of significant magnitude if the filaments are longer than about one-tenth of a wavelength, and that the errors are usually smaller in resistance milliwattmeters than in thermocouple instruments used in similar conditions.Experiments are described which show that serious errors, due to the inefficiency of the transformer used to match the power source to the filament of the instrument, can occur in addition to those described in the analysis. It is concluded that filament instruments cannot, in the present state of development, be relied on as standard transfer instruments for measuring microwave power in terms of a low-frequency calibration.

Standing-wave indicator for 3–22 Mc/s

The usual methods of measuring standing waves on feeder lines involve the use of:(1) Thermocouple instruments, which have poor overload characteristics and high mortality, and whose square-law scales seriously limit the range of standing-wave ratio measurement.(2) Rectifier and microammeter, the latter an expensive and delicate instrument.In the new instrument the radio-frequency current induced in the shielded loop coupled to the feeder lines, is rectified by a midget diode. An adjustable portion of the d.c. voltage across its load resistor is applied through 100 ft of cable to a d.c. amplifier, which operates a milliammeter (0–10 mA) of robust and tropical type, or an external meter.The instrument is self-contained and comprises loop and diode unit—stowed in lid of case for transit—adjustable for all usual transmission- line spacings, and a metal case containing the d.c. amplifier, meter and battery power supplies.Thus this instrument avoids the defects of (1) and (2) above, as overloads will not cause damage, and the sensitivity control permits adjustment over a wide range of test powers.

Temperature compensation of indicating and recording instruments

One cause of errors in indicating and recording instruments is their use at a temperature other than that at which they were calibrated. Most of the physical properties of materials on which the performance of an instrument depends, vary to a greater or less degree with temperature. It is therefore necessary when designing an instrument to reduce to a minimum any errors caused by changes in temperature, and if possible to make them negligibly small. This is done either by adopting a design such that the temperature errors themselves are very small, or by introducing other changes with temperature which will compensate them. An account is given in the paper of the more common methods employed, each method being briefly discussed to indicate the best arrangement for each type of instrument. The instruments considered are ammeters, voltmeters, millivoltmeters, wattmeters, and rectifier-operated and thermocouple instruments.

Temperature compensation in indicating and recording instruments

One cause of errors in indicating and recording instruments is their use at a temperature other than that at which they were calibrated. Most of the physical properties of materials on which the performance of an instrument depends, vary to a greater or less degree with temperature. It is therefore necessary when designing an instrument to reduce to a minimum any errors caused by changes in temperature, and if possible to make them negligibly small. This is done either by adopting a design such that the temperature errors themselves are very small, or by introducing other changes with temperature which will compensate them. An account is given in the paper of the more common methods employed, each method being briefly discussed to indicate the best arrangement for each type of instrument. The instruments considered are ammeters, voltmeters, millivoltmeters, wattmeters, and rectifier-operated and thermocouple instruments.