Measured Temperature Difference Research Articles

Applicability Limits of the Holm–Kohlrausch Approximation to Determine Heating of High-Current Symmetrical Electric Contacts

On the basis of numerical simulation of heating of symmetric contacts with flowing current, conclusions were drawn about the accuracy of determining the temperature by the Holm–Kohlrausch method for various methods of cooling the contacts, including with intensive air and liquid cooling. The possibility to apply this method at pulse heating of the contacts has been considered. The dependence of accuracy of determination of the temperature of contact pads on the choice of points of measurement of the surface temperature and potential difference has been revealed.

Investigation of Thermal Properties of Epoxy Composites Filled with Alluminium Nitride (AlN)

Investigation of thermal properties of epoxy composites embedded with Aluminum Nitride (AlN) micro-fillers is estimated in the present thesis with help of the experimental and ANSYS results. Thermal conductivity of AlN powder filled epoxy composite is calculated by measuring temperature difference at two surfaces by using instruments thermal heater and thermal laser gun. The samples of composites prepared with AIN for three different sizes of AIN powder particles [AIN particles size 1)70µm 2)80µm 3)90µm]. For each size three samples are prepared with different concentration of AIN powder [AIN concentration by wt. 1)10 gm 2)20 gm 3)30 gm].The numerical results obtained by using the ANSYS software. The effective thermal conductivity values obtained from experimentally validate with ANSYS results. It is observed that The conductivity values measured experimentally are compared with the ANSYS results. These Epoxy composites with AlN and glass fiber have been fabricated and thermal conductivities of the samples are calculated by using experimentally obtained temperature values. Observations can be made that with At highest testing temp. 80oC for size 70µm of AIN particles we get thermal conductivity of epoxy composites for sample 20weight %(30gm AIN powder out of total weight of sample) has increased by 30 times than epoxy. Epoxy composites with 80µm size of AIN particles the sample with 20 % of AIN gives thermal conductivity at heater temp.80oC has increased by about 32 times than epoxy. For 90 µm size AIN particles samples at heater temp.80oC we found better thermal conductivity for sample with 20% AIN particles out of the nine samples the thermal conductivity of epoxy has increased by 34 times as compare to epoxy. A conclusion to draw from the measured values we got better thermal conductivity of epoxy composites with 20% of AIN with size of 90µm.Increase of thermal conductivity of epoxy composites with increase of size and percentage of AIN powder.

Study of microwave heating of reference liquids in a coaxial waveguide reactor using the experimental, semi-analytical and numerical means

In this work, a new application of coaxial waveguides for microwave heating of individual liquid substances and reaction mixtures is considered. The studied reactor is a small hollow coaxial waveguide in which liquids (methanol or ethanol) are exposed to microwaves generated by a miniature semiconductor source of 2.45-GHz frequency. The temperature of a liquid in the coaxial chamber is measured using an IR temperature sensor, thermocouple and optic fiber probes through non-radiating (in microwave range) openings in the thick copper reactor's wall, with the satisfactory accord between their readings at the medium-level power (10 W). The dynamics of microwave heating is studied using the semi-analytical and numerical simulations, which prove to be in good agreement with the experimental data. Two semi-analytical models of microwave heating in the coaxial waveguide as particular cases of the general electromagnetic-thermal problem are developed. One of them is the lumped system model in which uniformity of the temperature field is assumed. It gives good agreement with the measurements and is physically justified at late heating times. Another one is a simplified non-uniform heating model which is based on consideration of a convective turbulent boundary layer in a short horizontal coaxial waveguide. This model furnishes a quantitative explanation of the measured temperature difference at opposite ends of this waveguide over the entire heating period. The results of this study are interesting for development of miniature reactors for on-demand chemistry and pharmacy.

Temperature Difference Measurement between Nanogap Fabricated by Cleavage of Single Crystal Silicon Using Raman Microscopy

Temperature Difference Measurement between Nanogap Fabricated by Cleavage of Single Crystal Silicon Using Raman Microscopy

Magnetocaloric Effect in an Antidot: The Effect of the Aharonov-Bohm Flux and Antidot Radius.

In this work, we report the magnetocaloric effect (MCE) for an electron interacting with an antidot, under the effect of an Aharonov-Bohm flux (AB-flux) subjected to a parabolic confinement potential. We use the Bogachek and Landman model, which additionally allows the study of quantum dots with Fock-Darwin energy levels for vanishing antidot radius and AB-flux. We find that AB-flux strongly controls the oscillatory behaviour of the MCE, thus acting as a control parameter for the cooling or heating of the magnetocaloric effect. We propose a way to detect AB-flux by measuring temperature differences.

Thermoelectric Characterization of the Kondo Resonance in Nanowire Quantum Dots.

We experimentally verify hitherto untested theoretical predictions about the thermoelectric properties of Kondo correlated quantum dots (QDs). The specific conditions required for this study are obtained by using QDs epitaxially grown in nanowires, combined with a recently developed method for controlling and measuring temperature differences at the nanoscale. This makes it possible to obtain data of very high quality both below and above the Kondo temperature, and allows a quantitative comparison with theoretical predictions. Specifically, we verify that Kondo correlations can induce a polarity change of the thermoelectric current, which can be reversed either by increasing the temperature or by applying a magnetic field.

A novel method to quantify atmospheric stability

SummaryAtmospheric stability significantly influences the characteristics of a wind resource and strongly affects wind turbine power production and structural loads. Stability is governed by the thermal structure of the atmospheric boundary layer (ABL). Unstable ABLs are convective and increase turbulence, but reduce vertical wind shear, while stable ABLs reduce turbulence and increase wind shear. In neutral ABLs mechanical effects of terrain and roughness dominate.The Monin-Obukhov length (MOL) and Richardson numbers are the recommended methods to quantify atmospheric stability. These methods require advanced and expensive measurements of temperature differences or 3D-sonic covariances, not installed on standard wind power masts.This study presents a novel methodology to quantify stability based only on standard wind measurements. At high wind speeds turbulence and wind shear converge to the neutral ABL response in a given direction while the relative deviations of shear and turbulence at lower wind speeds strongly correlate with stability. When normalized by the neutral shear and turbulence, these deviations directly quantify stability. Here we present a novel method to estimate MOL directly from the ratio of normalized shear and turbulence.The proposed method to quantify stability from standard wind measurements, provides an important input to advanced wind flow modelling of stability effects to improve the accuracy of predicted power production and structural loads.

Optical differential temperature measurement with beat frequency phase fluorometry.

We present, to the best of our knowledge, a new method for differential temperature measurement based on thermal sensitivity of the fluorescence lifetime of thermographic phosphors. Pairs of thermographic phosphors are excited with intensity-modulated light at frequencies ω and ω+Δω. The phase shift Δθ of the summary fluorescence intensity beat signal envelope is measured. A prototype of a fluorometric differential temperature sensor is developed, and feasibility of the method is experimentally demonstrated with a Sm2+:SrFCl crystal and the D15->F70 transition for high thermal sensitivity. The observed linear dependence between envelope phase shift Δθ and temperature difference ΔT agrees with the theoretical prediction. Sensitivity of S=-0.97°/°C was achieved. This method could also be applied to differential measurements of any parameter affecting fluorescence lifetime.

Experimental investigation of an adjustable standing wave thermoacoustic engine

This work is primarily concerned with the experimental investigation of the performance of a standing wave thermoacoustic engine (TAE). The TAE technology converts thermal power into acoustic power which may be used to generate electricity or, to drive thermoacoustic cooling devices. Although there is a number of existing researches that suggest the link between the geometrical configuration of the device and its performance, there are no existing work that point out how to incorporate this aspect in the designing. Therefore, this study proposes the use of an adjustable TAE in order to alter the performance of the device while in operation. This new TAE model has an adjustable resonator length, which consisted of a 103 mm (4-in.) honeycomb ceramic stack sample, buffer volume and a cooling shell-tube heat exchanger was developed. Six different stacks were used to evaluate the performance of the TAE. Three different stack lengths (50, 100, and 150 mm), positioned at three different locations, were investigated. These locations were measured from the hot ends of the stack to the pressure antinode. In addition, the influence of the mean pressure and the working gas was investigated. Measurement of temperature difference across the stack and sound pressure levels at the steady state were used to determine the efficiency of the device. Through the adjustment of the resonator length, this study point out the benefit of choosing the best frequency so that TAE can work optimally and produce higher acoustic power.

Convective dropwise condensation out of humid air inside a horizontal channel – Experimental investigation of the condensate heat transfer resistance

A new facility feasible for the investigation of dropwise condensation at a vertical polymer surface (9 × 6 mm, L × H) is described in detail. The droplets are liquefied out of humid air, which flows through a rectangular channel (12 × 32 mm, W × H) and passes the sub-cooled surface of a sensor. The latter one is flush mounted into one of the vertical channel walls beyond a hydrodynamic entry length of 550 mm determining perpendicular heat fluxes by measuring temperature differences. Furthermore the droplet covered surface is observed through the opposite channel wall by an infrared camera. The variable experimental parameters include temperature, water content and flow velocity of the humid air, as well as the surface temperature of the sensor.The scope of the experimental study is to investigate the mean heat transfer resistance of the condensate droplets which form on the substrate surface. The procedure is based on the determination of heat fluxes and the evaluation of the temperature differences between the substrate surface and the liquid/gas interface by means of thermography, both of them carried out synchronously. The experimental droplet heat transfer coefficient, hd, is evaluated as an average value and it considers both heat conduction through the droplets and the augmentation of heat transfer due to inner convection. The parameter variation covers Reynolds numbers between 7900 and 21400, relative humidities between 56% and 95% and air temperatures between 30 °C and 46 °C for a broad range of cooling temperatures. The latter one influences the droplet surface temperature and together with the water content of the bulk, it determines the driving force for mass transfer. hd was found to increase with the Reynolds number and the driving force for mass transfer. However, increasing the latter one beyond a certain value causes massive accumulation of noncondensable gases at the liquid/gas interface inhibiting the vapour mass flux and leading to invariant droplet heat transfer coefficients. The experimental data is correlated providing the basis for the experimental investigation of the heat transfer at the liquid/gas interface which will be done in future.

Experimental investigation of an adjustable thermoacoustically-driven thermoacoustic refrigerator

An experimental investigation is conducted on a new adjustable thermoacoustically-driven thermoacoustic refrigerator (TADTAR). This refrigerator comprises of a thermoacoustic engine which drives a thermoacoustic refrigerator. This study aims to demonstrate the possibility to alter the TADTAR performance through the adjustment of specific design parameters. An adjustable resonator, which consisted of stacks, spacing couplings and shell-tube heat exchangers was designed and built. Six different honeycomb ceramic stacks were investigated. For each system, three different stack configurations were studied. Measurements of temperature difference across the refrigerator stack and sound pressure levels at steady states were used to determine the performance of the device. Through the adjustment of the length and the insertion of the heat exchanger, the performance of the device with a longer resonator was relatively higher. This study shows that an adjustable resonator successfully alters the frequency output of the thermoacoustic engine to match the frequency required by the thermoacoustic refrigerator and achieve resonance. In addition, this study demonstrates the possibility to change the geometrical configuration of the device and ultimately alter the performance of the TADTAR. Through the adjustment of the length of the resonator, this study shows that a single device could have different operating points. This creates new possibilities to introduce control system able to adjust the geometry of thermoacoustic system while in operation.

Comparison between the liquidus temperature and triple-point temperature of tin realized by heat pulse-based melting

In this work, the consistency of the heat pulse-based melting technique, which was used to determine the liquidus temperature of tin, was examined by comparing the liquidus temperatures of tin at 101 325 Pa and at the vapour pressure of tin (i.e. the triple-point temperature), both of which were realized by heat pulse-based melting. Periodic square wave-type temperature steps with an amplitude of 0.7 °C were generated in the isothermal region of the pressure-controlled loop heat pipe, and the tin sample, having a segregated impurity distribution established by the prior outward slow freezing, was melted by application of the temperature step-based heat pulses. The triple-point temperature was found to be lower than the liquidus temperature of tin at 101 325 Pa by 3.23 mK with an expanded measurement uncertainty of 0.24 mK (i.e. a coverage factor of k = 2), while the ideal temperature difference calculated from the ITS-90 given pressure coefficient (i.e. 3.3 × 10−8 K Pa−1) is about 3.34 mK. The difference between the measured temperature difference and ideal temperature difference was attributed to the incomplete removal of the gases in the tin triple-point cell. Overall, these results further corroborated the notion that the heat pulse-based melting technique was shown to yield results consistent with the prescription of the ITS-90, and to be a reliable method in terms of the realization of the fixed-point temperatures.

Water pipeline failure detection using distributed relative pressure and temperature measurements and anomaly detection algorithms

ABSTRACTThis paper presents the validation of a novel leak detection method for water distribution pipelines, although it could be applied to any buried pressurized fluid flow pipe. The detection method is based on a relative pressure sensor attached non-invasively to the outside of the pipe combined with temperature difference measurements between the pipe wall and the soil. Moreover, this paper proposes an anomaly detection algorithm, originally developed for monitoring website traffic data, which differentiates a ‘leak’ event from ‘normal’ pressure change events. It is compared to two more commonly used methods based on a fixed threshold and a moving average. The validation of the new system in a field trial over a 6-month period showed that all the known leaks were identified with 98.45% accuracy, with the anomaly detection algorithm performing best, making this system a real contender for leak detection in pipes.

Experimental investigation of air distribution and ventilation efficiency in an ice rink arena

ABSTRACTThis study presents extensive experimental measurements in a modern Finnish ice rink arena including temperature, relative humidity, carbon dioxide, air speed, air flow and pressure difference measurements in addition to smoke tests. Furthermore, the air exchange rate (ACH), air-exchange efficiency, and mixing factor were calculated. The main aim was to determine ventilation effectiveness, vertical stratification of the air and how commonly re-circulation can be used in a modern ice rink arena representing common practice. Results show that re-circulation of return air was virtually continuous and in normal operating conditions the outdoor air fraction of the supply air was only 3.7% corresponding to ACH of 0.03 1/h. The ceiling distributed mixing ventilation was not able to mix the whole volume sufficiently, leading to two imperfectly mixed zones with an average air-exchange efficiency of 39% in the lower zone, corresponding to a mixing factor of 1.7.

Transient Thermal Response of a Guarded-Hot-Plate Apparatus for Operation Over an Extended Temperature Range.

A mathematical model is presented for a new-generation guarded-hot-plate apparatus to measure the thermal conductivity of insulation materials. This apparatus will be used to provide standard reference materials for greater ranges of temperature and pressure than have been previously available. The apparatus requires precise control of 16 interacting heated components to achieve the steady temperature and one-dimensional heat-transfer conditions specified in standardized test methods. Achieving these criteria requires deriving gain settings for the 16 proportional-integral-derivative (PID) controllers, comprising potentially 48 parameters. Traditional tuning procedures based on trial-and-error operation of the actual apparatus impose unacceptably lengthy test times and expense. A primary objective of the present investigation is to describe and confirm the incremental control algorithm for this application and determine satisfactory gain settings using a mathematical model that simulates in seconds test runs that would require days to complete using the apparatus. The first of two steps to achieve precise temperature control is to create and validate a model that accounts for heating rates in the various components and interactions with their surroundings. The next step is to simulate dynamic performance and control with the model and determine settings for the PID controllers. A key criterion in deriving the model is to account for effects that significantly impact thermal conductivity measurements while maintaining a tractable model that meets the simulation time constraint. The mathematical model presented here demonstrates how an intricate apparatus can be represented by many interconnected aggregated-capacity masses to depict overall thermal response for control simulations. The major assemblies are the hot plate with four subcomponents, two cold plates with three subcomponents each, and two edge guards with three subcomponents each. Using symmetry about the hot plate, the number of components in the simulation model is reduced to 12 or 15, depending on the mode of operation for the apparatus. Configurations of the main components with embedded heating elements were carefully designed earlier using detailed finite-element analyses to give essentially isothermal surfaces and one-dimensional heat flow through test specimens. It is not tractable, or perhaps justified, to extend these prior analyses to simulate the controlled transient responses of the apparatus. The earlier design criterion does, however, support the aggregated-capacity simplification implemented in the present thermal model. The governing equations follow from dynamic energy balances on components with controlled heating elements and additional intermediate ("floating") components. Thermal bridges comprise conduction paths, with and without surface convection and radiation, between components and fixed-temperature "heat sinks." An implicit finite-difference numerical method was used to solve the resulting system of first-order differential equations. The mathematical model was initially validated using measurement data from test runs where a step change in heating rate was applied to single elements in turn, and component temperatures were recorded up to a nearly steady condition. Thermocouples and standard platinum resistance thermometers were used to measure temperatures, and thermopiles were used to measure temperature differences. Next, extensive simulations were conducted with the mathematical model to estimate suitable gain settings for the various controllers. The criteria were tight temperature control after reaching set points and acceptable times to achieve quasi-steady-state operation. Comparisons between measurements and predicted temperatures for heated components are presented. The results show that the model incorporating the above simplifying approximations is satisfactory for components comprising the hot-plate and cold-plate assemblies. For the edge guards, however, the conventional aggregated-capacity criteria are not as fully satisfied because of their configuration. Temperature variations in the edge guards, fortunately, have a lesser effect on the accuracy of the thermal conductivity measurements. Therefore, the thermal response model is deemed satisfactory for simulating PID feedback to investigate "closed-loop" control of the apparatus, thus meeting the primary objective.

Measurement of temperature difference between cleavage plane nanogap using microscopic Raman spectroscopy

Measurement of temperature difference between cleavage plane nanogap using microscopic Raman spectroscopy

Experimental studies of temperature channel efficiency for solar energy systems

The methods to improve the thermal test equipment and determine the efficiency of solar collectors are proposed. To improve the performance specifications of such equipment, it is proposed to use highly sensitive semiconductor sensors. Based on experimental studies, planar transistors are chosen and sensors that can be used in temperature channels of devices for solar system studies are designed. Series connection of several transistor diodes enables an increase in sensitivity while reducing technological variations and simplifying secondary devices. The experimental studies have shown that the maximum temperature characteristics variation of the nine studied sensors does not exceed ±0.06 °С throughout the measuring range of 0 °С to +80 °С. The structure of a digital temperature difference meter with the studied sensors is designed. The temperature difference meter circuit is based on two current-to-voltage converters, in the feedback of which temperature sensors are enabled. By using a single reference voltage source, the same currents will flow through the sensors. The output signals of both converters are equal to voltage drops on the sensors and are fed to the differential inputs of the ADC, which provides a source code proportional to the measured temperature difference. The meter calibration at any temperature in the measuring range while ensuring the temperature uniformity of both sensors is proposed. After calibration, the estimated error value of the temperature difference meter does not exceed ±0.1 °С throughout the measuring range. The calibration method of precision digital thermometers with the designed sensors in two temperature points is proposed. At 0 °С, the thermometer additive error is determined, which is later used as a correction to all measuring results. The multiplier factor value is expedient to determine near the maximum measured temperature as the ratio of the nominal and the resulting values of the code that matches the calibration temperature. A method for adjusting a nonlinear error component in the whole measuring range is developed. It is based on determining the parameters of sensors approximating dependencies using experimental data. The logarithmic approximation temperature dependence of semiconductor sensors, whose value is equal to zero at both calibration temperature values is proposed. It is shown that this approximation dependence can be easily implemented in the modern microcontrollers base. After calibration, the acceptable error limit of digital thermometers in the measuring range from 0 °С to 100 °С does not exceed ±0.1 °С.

A Study of the Heat Capacity of Textile Materials

An experimental plant for use in the study of the process of determining the heat capacity of textile materials is considered. The calorimetric experiment consists in finding the unknown quantity of heat absorbed by the calorimeter in the case of a measured temperature difference in the course of heat absorption.

Experimental Investigation of Ceramic Substrates in Standing Wave Thermoacoustic Refrigerator

This work experimentally investigates the performance of ceramic substrates used as stacks in standing wave thermoacoustic coolers. Thermoacoustic technology is proposed in this study as an alternative sustainable solution to current issues with vapour compression refrigerators because of its environmentally friendlier attributes. However, the main hindrance to the expansion of this technology is its current lack of efficiency. Hence, an experimental investigation was conducted in this study. The influence of the geometrical configuration of the stack, described as the heart of the device, is investigated. The device was equipped with different selected low-cost porous materials (ceramic substrates) for performance testing and studies. Porosity, length and position of the ceramic substrates are variables that are considered in order to investigate the performance of the cooler. Eight cordierite honeycomb ceramic substrates with square cross sections and of four different lengths (26mm, 48mm, 70mm and 100mm) were considered. Five different stack positions, measured from the hot ends of the stack to the pressure antinode in increments of 100mm, were investigated. Measurement of temperature difference at steady state was used to determine the performance of a particular configuration. Guidance on the design of this sustainable solution for refrigeration and selection of the best geometrical configuration of ceramic substrates are provided. In addition, clarity on the relation between the geometrical configurations and the frequencies of the sound wave is highlighted.

Comparison of temperature difference measurement technologies used in vehicular heat exchangers

In the vehicle industry, thermal balance experiments have been extensively conducted on engines to determine energy distribution from fuel to engine power. The temperature differences between the hot and cold sides of the vehicular heat exchanger are the key parameters used to calculate the heat quantity. However, in certain gas–liquid heat exchangers, the temperature difference of the liquid side is significantly smaller than that of the gas side. Measurement errors can be increased if an inappropriate measurement method is adopted. To minimize the measurement errors, a new temperature difference measurement method based on compound thermocouple (CTC) is introduced in this study. This method is calibrated using a thermostatic oil tank. An empirical formula is used to evaluate cases in which the basic temperature ranges from 20°C to 120°C, and a temperature difference of less than 20°C is gained. The proposed method has been implemented in a practical thermal balance experiment using a vehicle radiator, and the results are compared with that of pairing calibrated resistance temperature detectors (RTDs). The results show that the CTC-based method can reduce the averaged thermal balance error in vehicular cooling systems to less than 4%.