Measured Temperature Difference Research Articles

All-Electrical Thermal Monitoring of Terahertz Quantum Cascade Lasers

A key limitation, especially for the continuous-wave operation of terahertz quantum cascade lasers, is the large amount of heat dissipated in the active region. We demonstrate an all-electrical technique for monitoring the lattice temperature and characterizing the thermal properties of the active region, using the waveguide of the device as a temperature sensor. We report a measured temperature difference between the heat sink and top waveguide layer of up to 27 K during the continuous-wave operation of GaAs/Al 0.15 Ga 0.85 As-based devices, lasing at 2.4 THz. A thermal model of the devices is used to determine the thermal conductivity of the active region perpendicular to the semiconductor interfaces to be 7.3 W/(m·K).

Model for Increasing the Power Obtained from a Thermoelectric Generator Module

We have developed a model for finding the most efficient way of increasing the power obtained from a thermoelectric generator (TEG) module with a variety of operating conditions and limitations. The model is based on both thermoelectric principles and thermal resistance circuits, because a TEG converts heat into electricity consistent with these two theories. It is essential to take into account thermal contact resistance when estimating power generation. Thermal contact resistance causes overestimation of the measured temperature difference between the hot and cold sides of a TEG in calculation of the theoretical power generated, i.e. the theoretical power is larger than the experimental power. The ratio of the experimental open-loop voltage to the measured temperature difference, the effective Seebeck coefficient, can be used to estimate the thermal contact resistance in the model. The ratio of the effective Seebeck coefficient to the theoretical Seebeck coefficient, the Seebeck coefficient ratio, represents the contact conditions. From this ratio, a relationship between performance and different variables can be developed. The measured power generated by a TEG module (TMH400302055; Wise Life Technology, Taiwan) is consistent with the result obtained by use of the model; the relative deviation is 10%. Use of this model to evaluate the most efficient means of increasing the generated power reveals that the TEG module generates 0.14 W when the temperature difference is 25°C and the Seebeck coefficient ratio is 0.4. Several methods can be used triple the amount of power generated. For example, increasing the temperature difference to 43°C generates 0.41 W power; improving the Seebeck coefficient ratio to 0.65 increases the power to 0.39 W; simultaneously increasing the temperature difference to 34°C and improving the Seebeck coefficient ratio to 0.5 increases the power to 0.41 W. Choice of the appropriate method depends on the limitations of system, the cost, and the environment.

Ultra-sensitive chip-based photonic temperature sensor using ring resonator structures

Resistance thermometry provides a time-tested method for taking temperature measurements. However, fundamental limits to resistance-based approaches has produced considerable interest in developing photonic temperature sensors to leverage advances in frequency metrology and to achieve greater mechanical and environmental stability. Here we show that silicon-based optical ring resonator devices can resolve temperature differences of 1 mK using the traditional wavelength scanning methodology. An even lower noise floor of 80 μK for measuring temperature difference is achieved in the side-of-fringe, constant power mode measurement.

Method for Simultaneous fMRI/EEG Data Collection during a Focused Attention Suggestion for Differential Thermal Sensation

In the present work, we demonstrate a method for concurrent collection of EEG/fMRI data. In our setup, EEG data are collected using a high-density 256-channel sensor net. The EEG amplifier itself is contained in a field isolation containment system (FICS), and MRI clock signals are synchronized with EEG data collection for subsequent MR artifact characterization and removal. We demonstrate this method first for resting state data collection. Thereafter, we demonstrate a protocol for EEG/fMRI data recording, while subjects listen to a tape asking them to visualize that their left hand is immersed in a cold-water bath and referred to, here, as the cold glove paradigm. Thermal differentials between each hand are measured throughout EEG/fMRI data collection using an MR compatible temperature sensor that we developed for this purpose. We collect cold glove EEG/fMRI data along with simultaneous differential hand temperature measurements both before and after hypnotic induction. Between pre and post sessions, single modality EEG data are collected during the hypnotic induction and depth assessment process. Our representative results demonstrate that significant changes in the EEG power spectrum can be measured during hypnotic induction, and that hand temperature changes during the cold glove paradigm can be detected rapidly using our MR compatible differential thermometry device.

Method for Simultaneous fMRI/EEG Data Collection during a Focused Attention Suggestion for Differential Thermal Sensation

In the present work, we demonstrate a method for concurrent collection of EEG/fMRI data. In our setup, EEG data are collected using a high-density 256-channel sensor net. The EEG amplifier itself is contained in a field isolation containment system (FICS), and MRI clock signals are synchronized with EEG data collection for subsequent MR artifact characterization and removal. We demonstrate this method first for resting state data collection. Thereafter, we demonstrate a protocol for EEG/fMRI data recording, while subjects listen to a tape asking them to visualize that their left hand is immersed in a cold-water bath and referred to, here, as the cold glove paradigm. Thermal differentials between each hand are measured throughout EEG/fMRI data collection using an MR compatible temperature sensor that we developed for this purpose. We collect cold glove EEG/fMRI data along with simultaneous differential hand temperature measurements both before and after hypnotic induction. Between pre and post sessions, single modality EEG data are collected during the hypnotic induction and depth assessment process. Our representative results demonstrate that significant changes in the EEG power spectrum can be measured during hypnotic induction, and that hand temperature changes during the cold glove paradigm can be detected rapidly using our MR compatible differential thermometry device.

DETERMINATION OF MATERIAL CATALYCITY AT HIGH TEMPERATURES IN THE VAT-104 HYPERSONIC WIND TUNNEL

Nitrogen and airflows in a duct of the VAT-104 high-temperature wind tunnel are modeled by means of the numerical solution to the unsteady two-dimensional Navier−Stokes equations in wide ranges of the total pressure (1−40 kPa) and stagnation temperature (5500−8000 K). Parametric numerical studies of nonequilibrium heat transfer on the end face of a thermally insulated circular cylinder at different cylinder surface catalycity values are performed. For each flow regime, the dependence of the surface temperature on the heterogeneous recombination rate constant Kw is obtained and the derivative α = dTw /dKw is determined. The catalycity of the C−SiC thermoprotective material in nitrogen and air plasma flows at surface temperatures of Tw = 1500−1900 K is determined in the calculations and experiments based on the measured temperature differences of the reference and examined materials.

轻型空间相机支撑桁架的精确控温

As the changed temperature of truss structure in a long focus camera will effect the image quality of an optical system, this paper explores the thermal design of supporting truss of the camera. First, the absorbed heat flux and heating powers of a truss rod were analyzed based on the temperature limit requirement of the optical system and the orbital parameters of the satellite. According to the analysis of thermal balance equation, it points out that the temperature difference of the truss is mainly determined by the heating power and arrangement of the heaters. Then, through the theoretical analysis of a simplified mathematical model of the truss, the temperature difference equation of supporting truss was derived, and two thermal control methods including increasing heater areas or increasing the effective thermal conductivity of the truss were presented. A new kind of material named Pyrolytic Graphite Sheet (PGS) was proved to be a candidate that can well satisfy the design requirements of increasing thermal conductivity and lighting the weight of supporting truss. On the calculation, it shows that the temperature difference has decreased from 7.9C to 0.83C with the mass of each truss increasing only 12 g by using 0.076 mm thick PGS. Finally, through the thermal vacuum test and temperature difference measurement test, it demonstrates that the analysis and simulation is valid and the PGS can withstand vacuum and temperature changes under the test conditions. The method presented in this paper is practical and effective.

Estimating extreme temperature differences in steel box girder using long-term measurement data

The extreme temperature differences in flat steel box girder of a cable-stayed bridge were studied. Firstly, by using the long-term measurement data collected by the structural health monitoring system installed on the Runyang Cable-stayed Bridge, the daily variations as well as seasonal ones of measured temperature differences in the box girder cross-section area were summarized. The probability distribution models of temperature differences were further established and the extreme temperature differences were estimated with a return period of 100 years. Finally, the temperature difference models in cross-section area were proposed for bridge thermal design. The results show that horizontal temperature differences in top plate and vertical temperature differences between top plate and bottom plate are considerable. All the positive and negative temperature differences can be described by the weighted sum of two Weibull distributions. The maximum positive and negative horizontal temperature differences in top plate are 10.30 °C and −13.80 °C, respectively. And the maximum positive and negative vertical temperature differences between top plate and bottom plate are 17.30 °C and −3.70 °C, respectively. For bridge thermal design, there are two vertical temperature difference models between top plate and bottom plate, and six horizontal temperature difference models in top plate.

Self-powered wireless thermoelectric sensors

Sensors capable of measuring various performance parameters of an operational power generation unit could help improve system performance and overall efficiencies. For example, measurement of temperatures, temperature differences, or exhaust gas concentrations could provide both a quick quantitative and qualitative assessment of system health and allow for operation of power units with smaller safety margins and therefore higher efficiencies. For this study a technique is presented that can transmit data about an operational system wirelessly in real-time to an external location. For these experiments thermoelectric element leads were connected to a solenoid coil. When the thermoelectric was exposed to a temperature difference a current was generated in the thermoelectric and solenoid coil resulting in a magnetic field. A receiver was then used to measure the changes in magnetic field of the system. Two primary configurations were developed to test this wireless sensor configuration: dynamic and static. For dynamic measurements a pendulum and pneumatic air cylinder were used to simulate a moving component that may pass the external Hall sensor such as a fan or turbine blade. For dynamic measurements it was determined that for accurate results it is very important to maintain the distance constant between the Hall sensor and solenoid coil. For stationary measurements the temperature difference across the thermoelectric was related to output measurements from the Hall sensor. Overall, results show that data can be wirelessly transmitted to an external location using this method.

Infrared ocular thermography in dogs with and without keratoconjunctivitis sicca

Infrared thermography was used to measure temperature differences of the corneal surface between nasal and temporal limbus regions and central cornea of normal dogs and dogs with keratoconjunctivitis sicca (KCS), in order to establish temperature values in normal canine eyes and in patients with decreased Schirmer tear tests (STT) values. Dogs investigated were all either patients seen at the Veterinary Teaching Hospital of Federal University of Paraná or normal dogs that belonged to the same institution. STT were performed in all eyes. A total of 40 control eyes (STT ≥15mm/min) and 20 eyes with low STT values (STT ≤14mm/min) were examined. The mean STT value for eyes with normal STT values was 22.9±3.9mm/min (mean±standard deviation), and the mean STT value for eyes with low STT value was 7.2±4.8mm/min. The mean corneal temperature was significantly lower in eyes with low STT values than in control eyes (P<0.0001). The following significant correlations were found: (i) Schirmer and breakup time (BUT) (P=0.0001, r=0.5); (ii) STT values and corneal surface temperature (P=0.001, r=0.256); (iii) STT values and age (P=0.0001, r=-0.448); (iv) age and corneal surface temperature (P=0.0001, r=-0.281); and (v) BUT and corneal surface temperature (P=0.0001, r=0.36). Thermography is a method that can differentiate between eyes with normal and abnormal STT values. In the future, thermography might be incorporated as part of the ophthalmic examination and perhaps become a popular ancillary test for the diagnoses of ocular surface disorders.

Compact Split Disk Laser With SiC Wafer and &lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;${\rm Nd}{:}{\rm YVO}_{4}$&lt;/tex&gt;&lt;/formula&gt; Bonding via Liquid Capillarity

The design of split disk laser is proposed and demonstrated with SiC wafer and uncoated Nd:YVO4 disk bonding via liquid capillarity. Using the SiC wafer as an intracavity heat spreader, the thermal effects and thermal induced distortions are greatly relieved. Depending on the excellent thermal and optical properties of SiC, a high slope efficiency of 43.3% and 5.3 W CW output power is demonstrated at room temperature without active cooling. No delamination of split disks occurred under lasing conditions. The measured temperature difference agreed with the numerical simulations.

Determination of mechanisms and parameters which affect radon entry into a room

There are practically no direct techniques for measuring radon entry rate in the rooms. The suggested technique allows estimating such parameter under real conditions. The technique for radon diagnostic procedures including radon entry rate and air change rate assessment was proposed and tested in the field under various experimental conditions.The method consists of the continuous measurement of radon concentration, temperature and pressure difference between indoor and outdoor atmosphere. It was demonstrated that the study of dependence of radon entry rate on temperature difference ΔT between indoor and outdoor atmosphere allows to estimate the dominant radon entry mechanism – diffusion mechanism (absence of the dependence on ΔT) or convective (radon entry rate increase at ΔT increase). It was shown that simultaneous measurements of time series of radon concentration and pressure difference between building envelope and outdoor atmosphere allow assessing such room parameter as Effective Leakage Area.The approach applied in this paper to estimate the air change rate practically is not differing from tracer gas techniques when the constant gas entry rate is used. It was shown that radon could be used as kind of tracer gas to estimate the air change rate.Obtained measurement results for all buildings confirmed the seasonal variations of radon concentrations. A correlation of radon concentration and air change rate with outside temperature occurred in general.

Rayleigh-Bénard convection for viscoplastic fluids

The influence of rheological and interfacial properties of yield stress fluids is investigated on the onset of the Rayleigh-Bénard convection. Different Carbopol® (B.F. Goodrich) gels are used in a circular cell for Rayleigh-Bénard experimental setup. The influence of the boundary conditions is also investigated by controlling either slip or no-slip conditions. The onset of thermoconvection is shown by measuring temperature differences and also by using shadowgraph flow visualization. Experimental results show that convection occurs in the range of our experiments. Considering Carbopol gels as elasto-plastic materials with a yield stress τy, a generalized Rayleigh number is obtained: Rag = Y−1, with Y the yield number, which represents the balance between the yield stress of the gel and the buoyancy effects. The results show that the Rayleigh number is proportional to d, the height of the setup, and that the control parameter is the yield number at the onset of convection. Critical values of Y−1 have been determined for slip conditions \documentclass[12pt]{minimal}\begin{document}$1/Y_c^S\approx 40$\end{document}1/YcS≈40 as well as for no-slip conditions \documentclass[12pt]{minimal}\begin{document}$1/Y_c^{NS}\approx 80$\end{document}1/YcNS≈80. It highlights that the change in surface conditions affect significantly the critical conditions.

Error analysis of thermal response tests

The ground thermal conductivity and borehole thermal resistance are essential parameters for the design of a ground source heat pump system. As it is hardly possible to obtain sufficiently accurate values of these parameters from geological or soil-profile information, thermal response tests have been developed that provide measurements in situ. These tests have become part of the standard toolkit of the shallow geothermal energy systems engineer, but a systematic evaluation of the different sources of uncertainty (error) and their effect on the quality of the result is lacking. This paper explores the different error sources and shows how they contribute to the final overall error in estimated thermal properties. The results show that the theoretical errors are expected to be on the order of 5% for the soil thermal conductivity and 10–15% for the borehole resistance. The largest contributions to the error of the thermal conductivity are the measured temperature difference, fluid heat capacity and slope of the regression coefficient. The borehole resistance error is mainly influenced by the error of thermal conductivity.

MEASUREMENT AND PREDICTION OF VAPOR-SPACE CONDENSATION OF REFRIGERANTS ON TRAPEZOIDAL-FINNED AND TURBO-C GEOMETRIES

This paper reports vapor-space condensation heat transfer measurements for R123, R134a, and R245fa for the integral trapezoidal fin, and the Turbo-CII geometries on vertical plates. The data consisted of heat flux and wall temperature difference measurements. Condensation heat transfer measurements on a smooth plate agreed well with both measurements and predictions from the literature. Overall, the heat transfer performance of the three refrigerants on the trapezoidal fin was within approximately 8 kW/m of one another. Similarly, the condensation heat flux for R134a and R245fa on the Turbo-CII was within approximately 18 kW/m of each other, while the heat flux of R123 on the Turbo-CII was between 10 and 80 kW/m less than that of R245fa. An existing finned tube condensation model was modified to be expressed in terms of the gradient of the condensate curvature with respect to the length of the liquid–vapor interface. Curvature gradients for the two surfaces were developed that, when substituted into the modified model, predicted the present measured driving temperature differences for the trapezoidal fin and the Turbo-CII to within 0.4 and 1.2 K, respectively, for all measurements except for R123 on the Turbo-CII surface. With the aid of the curvature gradients, simple models were developed to predict the performance of the trapezoidal, low-finned tube, and the Turbo-C tube. The heat flux to the low-finned tube and the Turbo-C tube were predicted to within 10% and 15%, respectively, of the measured values from the literature for four different fluids.

A case of non validity of MRTD concept

MRTD is considered as the most important parameter of thermal imagers. It is a function of a minimum temperature difference between the bars of the standard 4-bar target and the background required to resolve the thermal image of the bars by an observer versus spatial frequency of the target. Both theoretical models and experimental tests presented in available literature show MRTD as a monotonically increasing bijective mathematical function. This paper presents results of measurements of MRTD that contradict this common opinion. These results show that in rare cases MRTD can be a non-bijective function. Imagers having such MRTD function can fulfill formal requirements on MRTD but will perform poorly at real life conditions. Full Text: PDF References STANAG 4349, Measurement of minimum resolvable thermal difference (MRTD) of thermal cameras, 1995. ASTM standard E 1213-2002, Standard Test Method for Minimum Resolvable Temperature Difference for Thermal Imaging Systems G.C. Holst, Testing and evaluation of infrared imaging systems (JCD Publishing Company 2008). G.C. Holst, The Infrared & Electro-Optical Systems Handbook, Vol.3: Electro-Optical System Design, Analysis and Testing, Ch. 4, 206-207 (SPIE 1993). K. Chrzanowski, Testing Thermal Imagers - Practical Guide (Military University of Technology, Warsaw, Poland 2010). Night Vision Thermal Imaging Systems Performance Model, User?s Manual & Reference Guide, U.S Army Night Vision and Electronic Sensors Directorate, AMSEL-RD-NV-MS-SPMD, 2001. R.G. Driggers, A. Van Hodgkin, R.H. Vollmerhausen, P. O'Shea, "Minimum resolvable temperature difference measurements on undersampled imagers", Proc. SPIE 5076, 179 (2003). CrossRef MERX Website DirectLink Phare Program no PL0103.03.01 PL0108.19.01-L002, Purchase and installation of portable thermo-vision cameras, Phare Program No. PL0103.03.02 purchase of 5 surveillance units for helicopters, 2004.

A large aperture blackbody bath for calibration of thermal imagers

Thermal imagers are becoming widely used instruments for noncontact absolute temperature measurements as opposed to previous practice when they were mostly used to measure temperature differences. To assure accurate and reliable absolute temperature measurements, a calibration procedure including evaluation of the thermal imager entire field of view (FOV) is needed. The challenge was to construct a large aperture blackbody, covering the complete FOV of the thermal imager and having better stability and non-uniformity than the thermal sensitivity of the imager. The blackbody calibration bath was designed on hypothesis analogous to the multi zone furnace, where the role of electrical heaters was superseded by electrically controlled valves. The experimental work showed that the designed system enables traceable calibration of thermal imagers in the temperature range from 10 to 70 °C with the expanded uncertainty of 0.2 °C, while further investigations are needed to cover ranges beyond that.

The first pilot demonstration: solar updraft tower power plant in Jordan

The high cost of importing heavy fuel oil from neighbouring countries of Jordan stimulated the need to consider renewable energy as an alternative to imported power. The paper describes a systematic experimental study on the pilot solar updraft tower power plant model system. Particular attention is given to measurements of air velocity, temperature, solar radiation and voltage difference. This is the first pilot solar updraft power plant that has been built in Jordan to evaluate such technology in Mutah Area. In this paper, all the experimental data were taken from a very small pilot project (compared with other prototypes that we constructed which were placed in the backyard of our faculty). For the experimental part, the solar updraft power plant was a pilot project with an updraft power plant height H=4(m), updraft power plant radius R c=0.29(m), plastic solar collector area A coll=36(m2), collector roof height=1(m), wind turbine that was a compensation of the suction fan with a diameter D fan=0.5(m), and a small generator (6 V) The experimental results in this paper show that the maximum height (H max) gradually increases with the solar irradiation (G). Also, in the same way, with the pressure difference (Δ p) increases with solar irradiation.

Erratum: Towards high-speed imaging of infrared photons with bio-inspired nanoarchitectures

Nature Photon. 6, 195–200 (2012); published online 12 February 2012; corrected after print 11 July 2012. In the version of this Article originally published, the measured temperature difference ΔT was at the detector plane, whereas the definition of noise-equivalent temperature difference (NETD) in equation (2) requires ΔT to be a thermal scene temperature difference.

Emissivity estimation for accurate quantitative thermography

In this paper an emissivity measurement method is proposed; it relies on individual calibration functions, and is based on the spectral response of a specific IR sensor. The reflected temperature is kept constant during the test, and its knowledge is not required. Results of measurements on materials commonly used as emissivity references in quantitative thermography are reported. Computer simulations of indoor and outdoor thermographic inspections show the differentiated influence of emissivity and surroundings temperature on the measurement accuracy. Finally experimental results of absolute and differential temperature measurements are discussed.