Local Temperature Measurements Research Articles

The effects of natural and mixed convection on heat transfer across adjacent micro-channels, in extreme pressure and temperature conditions

This abstract summarizes a mainly experimental investigation of heat transfer across an insulation pack specimen used to protect the upper surface of the Hot Box Dome of an advanced gas cooled nuclear reactor from the hot gas above it, under actual operating conditions. The pack consists of multiple stainless steel layers forming narrow channels, less than 1mm wide between them. The facility developed, can operate at pressures of 40bar, temperature differences across the insulation pack of up to 500°C, with and without flow through the pack channels and at horizontal and inclined orientations. Measurements led to the calculation of the effective thermal conductivity and also the mapping of the temperature variation across the pack for a range of flow rates, and also for angles to the horizontal of up to 30°. The effective conductivity data show how, under these extreme pressure and temperature conditions, the rate at which thermal energy is transferred to the lower, cold side, of this multi-channel pack, depends on the Rayleigh and Reynolds numbers at different angles of inclination. The corresponding local temperature measurements advance understanding of the local thermal characteristics and suggest the presence of strong flow structures. The most striking finding is the strong influence of buoyancy for all flow rates investigated, even for the horizontal cases. Tests at inclined orientations suggest the presence of flow reversal. Complementary conjugate heat transfer numerical analysis, using a simplified two-dimensional representation of the pack, has also been carried out. For the inclined case the computed flow features are consistent with those suggested by the local temperature data.

Local temperature of an interacting quantum system far from equilibrium

A theory of local temperature measurement of an interacting quantum electron system far from equilibrium via a floating thermoelectric probe is developed. It is shown that the local temperature so defined is consistent with the zeroth, first, second, and third laws of thermodynamics, provided the probe-system coupling is weak and broad band. For non-broad-band probes, the local temperature obeys the Clausius form of the second law and the third law exactly, but there are corrections to the zeroth and first laws that are higher-order in the Sommerfeld expansion. The corrections to the zeroth and first laws are related, and can be interpreted in terms of the error of a nonideal temperature measurement. These results also hold for systems at negative absolute temperature.

Si-nanocrystal-based nanofluids for nanothermometry

The measurement of local temperature in nanoscale volumes is becoming a technological frontier. Photoluminescent nanoparticles and nanocolloids are the natural choice for nanoscale temperature probes. However, the influence of a surrounding liquid on the cryogenic behavior of oxidized Si-nanocrystals (Si-NCs) has never been investigated. In this work, the photoluminescence (PL) of oxidized Si-NCs/alcohol based nanocolloids is measured as a function of the temperature and the molecule length of monohydric alcohols above their melting–freezing point. The results unveil a progressive blue shift on the emission peak which is dependent on the temperature as well as the dielectric properties of the surrounding liquid. Such an effect is analyzed in terms of thermal changes of the Si-NCs bandgap, quantum confinement and the polarization effects of the embedding medium; revealing an important role of the dielectric constant of the surrounding liquid. These results are relevant because they offer a general insight to the fundamental behavior of photoluminescent nanocolloids under a cooling process and moreover, enabling PL tuning based on the dielectric properties of the surrounding liquid. Hence, the variables required to engineer PL of nanofluids are properly identified for use as temperature sensors at the nanoscale.

Segregated Ice Growth in a Suspension of Colloidal Particles.

We study the freezing of a dispersion of colloidal silica particles in water, focusing on the formation of segregated ice in the form of ice lenses. Local temperature measurements in combination with video microscopy give insight into the rich variety of factors that control ice lens formation. We observe the initiation of the lenses, their growth morphology, and their final thickness and spacing over a range of conditions, in particular the effect of the particle packing and the cooling rate. We find that increasing the particle density drastically reduces the thickness of lenses but has little effect on the lens spacing. Therefore, the fraction of segregated ice formed reduces. The effect of the cooling rate, which is the product of the temperature gradient and the pulling speed across the temperature gradient, depends on which parameter is varied. A larger temperature gradient causes ice lenses to be initiated more frequently, while a lower pulling speed allows for more time for ice lenses to grow: both increase the fraction of segregated ice. Surprisingly, we find that the growth rate of a lens does not depend on its undercooling. Finally, we have indications of pore ice in front of the warmest ice lens, which has important consequences for the interpretation of the measured trends. Our findings are relevant for ice segregation occurring in a wide range of situations, ranging from model lab experiments and theories to geological and industrial processes, like frost heave and frozen food production.

Calibration of dynamic tool–workpiece interface temperature measurement during friction stir welding

The objective of this work is to accurately measure the transient temperatures at the tool–workpiece interface during friction stir welding (FSW) using thermocouples that are embedded in the tool. Temperature sensors embedded in the friction stir (FS) tool provide a non-consumable localized temperature measurement capability that is crucial for process research, development, and control. A modification of the ASTM E-1461 standard for measuring thermal diffusivity with pulses of heat flux is proposed for calibrating the transient response of temperature sensors located near the surface of the FS tool. These tests enable the calculation of each sensor’s time constant, which are used in one-dimensional analytical models of the dynamic response to calculate the true interface temperature. Time constants between 21 and 43ms are measured for 0.25-mm-diameter, sheathed thermocouples located at the FS tool surface.

Partial Nucleate Pool Boiling at Low Heat Flux: Preliminary Ground Test for SOBER-SJ10

Focusing on partial nucleate pool boiling at low heat flux, SOBER-SJ10, one of 27 experiments of the program SJ-10, has been proposed to study local convection and heat transfer around an isolated growing vapor bubble during nucleate pool boiling on a well characterized flat surface in microgravity. An integrated micro heater has been developed. By using a local pulse overheating method in the experimental mode of single bubble boiling, a bubble nucleus can be excited with accurate spatial and temporal positioning on the top-side of a quartz glass substrate with a thickness of 2 mm and an effective heating area of 4.5 mm in diameter, and then grows under an approximate constant heat input provided by the main heater on the back-side of the substrate. Ten thin film micro-RTDs are used for local temperature measurements on the heating surface underneath the growing bubble. Normal pool boiling experiments can also be carried out with step-by-step increase of heating voltage. A series of ground test of the flight module of SOBER-SJ10 have been conducted. Good agreement of the measured data of single phase natural convection with the common-used empirical correlation warrants reasonable confidence in the data. It is found that the values of the incipience superheat of pool boiling at different subcooling are consistent with each others, verifying that the influence of subcooling on boiling incipience can be neglected. Pool boiling curves are also obtained, which shows great influence of subcooling on heat transfer of partial nucleate pool boiling, particularly in lower heat flux.

Light-Emitting Diodes as Supplemental Lighting in Viticulture Field Research

A light-emitting diode (LED) system was evaluated as a tool for field research to investigate light effects on grapevines. Preliminary laboratory trials were conducted to develop response curves for photosynthetically active radiation (PAR) and temperature as a function of distance from the LED light source. LED panels were subsequently deployed in a three-year field study of three light-exposure treatments on developing fruit clusters of Vitis vinifera cv. Cabernet Sauvignon: 1) clusters exposed to direct sunlight, 2) clusters shaded by the canopy, and 3) canopy-shaded clusters exposed to supplemental LED light. Laboratory trials and vineyard field studies demonstrated that LED panels could provide supplemental light to grapevines over a broad range of PAR, up to and exceeding the photosynthetic light saturation point for exterior leaves, by adjusting the distance of the LED panel to the target. Although bench trials indicated significant convective heat close to the LED panel, field studies detected few temperature differences among cluster treatments. Varying results were primarily attributed to temperature measurement locations related to experimental objectives; bench trials measured target surface temperature, but field studies monitored whole cluster temperature. LED panels were effectively deployed to provide supplemental light to shaded grape clusters without significantly altering cluster temperature.

Experimental characterization of pulverized coal MILD flameless combustion from detailed measurements in a pilot-scale facility

This paper presents a series of measurements on pulverized coal MILD flameless combustion in a pilot-scale facility for nitrogen oxides (NOx) emissions reduction. Local measurements of gaseous species concentrations, gas temperature and velocity associated to reaction zone imaging by OH* chemiluminescence highlight specific features of this MILD flameless combustion regime. The flameless burner used during the investigation could abate significantly NOx emission levels.Specific aerodynamics of the flow in the furnace induced by the burner geometry are discussed. High momentum turbulent air jets favor a large recirculation of hot flue gas in the combustion chamber. Such a recirculation induces a large diluted combustion regime from the entrainment in the air jets of devolatilized species from the pulverized coal jet and of recirculating hot inert combustion products. The main reaction zone is lifted from the burner exit as it starts in the mixing layers of separated pulverized coal and air jets. As is typical of a flameless combustion regime, such a large dilution of reactants induces low local heat release and temperature increase in the reaction zone. Nitrogen oxides are generated from the fuel NO route at quite a limited rate due to the low temperature environment.The effect of the carrier gas of the pulverized coal jet is also analyzed. The change from carbon dioxide to air as carrier gas generates a first reaction zone attached to the burner exit. This reduces the dilution and increases the heat release in the main lifted reaction zone, leading to higher NOx emissions.

Polarization mode coupling and related effects in fiber Bragg grating inscribed in polarization maintaining fiber.

Polarization mode coupling (PMC) and related effects from writing fiber Bragg gratings in polarization maintaining fiber (FBGs-in-PMF) are observed experimentally for the first time by optical fiber coherence domain polarimetry (OCDP) using a broadband light source. PMC is another useful aspect of FBG-in-PMF besides Bragg wavelength and its possible potential is evaluated and discussed. A localized and long range temperature measurement based on the PMC and Bragg wavelength is given as an example.

Plasmon dissipation in gapped graphene open systems at finite temperature

Numerical and closed-form analytic expressions for plasmon dispersion relations and rates of dissipation are first obtained at finite-temperatures for free-standing gapped graphene. These closed-system results are generalized to an open system with Coulomb coupling of graphene electrons to an external electron reservoir. New plasmon modes, as well as new plasmon dissipation channels, are found in this open system, including significant modifications arising from the combined effect of thermal excitation of electrons and an energy bandgap in gapped graphene. Moreover, the characteristics of the new plasmon mode and the additional plasmon dissipation may be fully controlled by adjusting the separation between the graphene layer from the surface of a thick conductor. Numerical results for the thermal shift of plasmon frequency in a doped gapped graphene layer, along with its sensitivity to the local environment, are demonstrated and analyzed. Such phenomenon associated with the frequency shift of plasmons may be applied to direct optical measurement of local electron temperature in transistors and nanoplasmonic structures.

Miniaturized implantable sensors for in vivo localized temperature measurements in mice during cold exposure.

We report on in vivo temperature measurements performed in mice at two specific sites of interest in the animal body over a period of several hours. In particular, the aim of this work was to monitor mouse metabolism during cold exposure, and to record possible temperature differences between the body temperature measured in the abdomen and the temperature of the brown adipose tissue (BAT) situated in the interscapular area. This approach is of biological interest as it may help unravelling the question whether biochemical activation of BAT is associated with local increase in metabolic heat production. For that purpose, miniaturized thermistor sensors have been accurately calibrated and implanted in the BAT and in the abdominal tissue of mice. After 1week of recovery from surgery, mice were exposed to cold (6°C) for a maximum duration of 6h and the temperature was acquired continuously from the two sensors. Control measurements with a conventional rectal probe confirmed good performance of both sensors. Moreover, two different mouse phenotypes could be identified, distinguishable in terms of their metabolic resistance to cold exposure. This difference was analyzed from the thermal point of view by computational simulations. Our simple physical model of the mouse body allowed to reproduce the global evolution of hypothermia and also to explain qualitatively the temperature difference between abdomen and BAT locations. While with our approach, we have demonstrated the importance and feasibility of localized temperature measurements on mice, further optimization of this technique may help better identify local metabolism variations.

Preliminary design of electrostatic sensors for MITICA beam line components.

Megavolt ITER Injector and Concept Advancement, the full-scale prototype of ITER neutral beam injector, is under construction in Italy. The device will generate deuterium negative ions, then accelerated and neutralized. The emerging beam, after removal of residual ions, will be dumped onto a calorimeter. The presence of plasma and its parameters will be monitored in the components of the beam-line, by means of specific electrostatic probes. Double probes, with the possibility to be configured as Langmuir probes and provide local ion density and electron temperature measurements, will be employed in the neutralizer and in the residual ion dump. Biased electrodes collecting secondary emission electrons will be installed in the calorimeter with the aim to provide a horizontal profile of the beam.

Fiber-optic control and thermometry of single-cell thermosensation logic.

Thermal activation of transient receptor potential (TRP) cation channels is one of the most striking examples of temperature-controlled processes in cell biology. As the evidence indicating the fundamental role of such processes in thermosensation builds at a fast pace, adequately accurate tools that would allow heat receptor logic behind thermosensation to be examined on a single-cell level are in great demand. Here, we demonstrate a specifically designed fiber-optic probe that enables thermal activation with simultaneous online thermometry of individual cells expressing genetically encoded TRP channels. This probe integrates a fiber-optic tract for the delivery of laser light with a two-wire microwave transmission line. A diamond microcrystal fixed on the fiber tip is heated by laser radiation transmitted through the fiber, providing a local heating of a cell culture, enabling a well-controlled TRP-assisted thermal activation of cells. Online local temperature measurements are performed by using the temperature-dependent frequency shift of optically detected magnetic resonance, induced by coupling the microwave field, delivered by the microwave transmission line, to nitrogen—vacancy centers in the diamond microcrystal. Activation of TRP channels is verified by using genetically encoded fluorescence indicators, visualizing an increase in the calcium flow through activated TRP channels.

Local Heat Generation in a Single Stack Lithium Ion Battery Cell

The local heat generation in a single stack lithium ion battery cell was investigated as a function of the C-rate and state of charge (SoC). For that purpose, a custom build electrochemical cell design developed for local in-operando temperature measurements is used. The local temperature evolution in both electrodes and the separator is compared with local heat generation rates calculated from galvanostatic intermittent titration technique (GITT) measurements. The impact of reversible and irreversible heats is evaluated as a function of the C-rate and the SoC. The results reveal substantial differences in the local heat generation rates of the individual components of the battery cell related to their kinetic and thermodynamic properties. Significant SoC dependencies of the local reversible and irreversible heat generation are reflected by both the local temperature measurements and the heat generation rates calculated from GITT. A distinct asymmetry between charging and discharging is revealed which results from the intrinsic asymmetry of the reversible heat as well as differences in the kinetic limitations of the lithiation and delithiation of active materials. This study indicates, that the heat generation rates of the individual cell components should be considered accurately in order to build up basics for targeted material-, design- and thermal management optimization to handle thermal issues in large battery packs.

Temperature Calibration for In Situ Environmental Transmission Electron Microscopy Experiments.

In situ environmental transmission electron microscopy (ETEM) experiments require specimen heating holders to study material behavior in gaseous environments at elevated temperatures. In order to extract meaningful kinetic parameters, such as activation energies, it is essential to have a direct and accurate measurement of local sample temperature. This is particularly important if the sample temperature might fluctuate, for example when room temperature gases are introduced to the sample area. Using selected-area diffraction (SAD) in an ETEM, the lattice parameter of Ag nanoparticles was measured as a function of the temperature and pressure of hydrogen gas to provide a calibration of the local sample temperature. SAD permits measurement of temperature to an accuracy of ±30°C using Ag lattice expansion. Gas introduction can cause sample cooling of several hundred degrees celsius for gas pressures achievable in the ETEM.

15. Measurement of esophageal temperature at two separate sites during pulmonary vein ablation

Pulmonary vein ablation (PVA) has been used to treat persistent supraventricular arrhythmias, in which a cardiologist first isolates and then thermally ablates the source of the arrhythmia1. Since the esophagus is in close proximity to the left atrium, heat induced injury to the esophagus may occur2. Although the incidence is low, the mortality rate is high. Luminal esophageal temperature (ET) monitoring is one of the most effective measures to minimize the risk of injury3. In this retrospective study, we elected to analyze temperature changes during PVA at two different temperature monitoring sites in the esophagus. The anesthetic technique was standardized and utilized general anesthesia, endotracheal intubation and an arterial line. ET monitors were placed at two mid-atrial locations, ET1 and ET2 separated by 1–1.5 inches in the esophagus, as determined by cardiologist using fluoroscopy. Temperatures at both ET1 and ET2 locations were recorded simultaneously when radio-frequency ablation was performed at different left atrial sites. The peak ET was recorded at each location. In particular, the increase over baseline ET and the difference between ET1 and ET2, were noted. Twenty five patients were studied. Ablation sites in the left atrium included the anterior, posterior, inferior regions and the pulmonary veins. The most significant increases in temperature were seen during ablation of the posterior left atrium ranging from 0.1 to 4.0 degrees. However, in 20 out of 25 patients, measurements of ET1 ≠ ET2. The absolute value of difference of temperature between ET1 and ET2 ranged from 0.4 to 3.8, with a mean of 1.3 and a standard deviation of 1.1. These findings suggest that measurement of temperature at two separate esophageal locations is more sensitive that one location in detecting temperature increases during PVA. The ablating electrode during PVA moves from different areas within the left atrium, and therefore, a wide area of temperature measurement is needed for more accurate monitoring. Furthermore, the most significant increases in temperature occurred when ablation performed in the posterior left atrium, adjacent to the esophagus. The implications of these observations suggest that one location of temperature measurement may not be accurate enough in detecting a “true” esophageal temperature. Further studies are needed to verify these findings in a prospective study and to ascertain whether this has any patient safety ramifications for preventing esophageal injury.

Wind turbine radiated acoustic signals—Propagation in a temporally and spatial variable marine meteorological boundary layer

The temporal and spatial properties of an acoustic field radiated from a wind turbine operating in a marine meteorological boundary layer and a spatial temporal variable impedance boundary will be quantified using paraxial equation based numerical simulations. A sound speed field will be constructed using wind field measurements made with a 915 MHZ radar wind speed sensor and local temperature and humidity measurements obtained from a meteorological tower. Temporally variable impedance boundary conditions for a tidal marine marsh will be included in the simulations.

Pteropod time series from the North Western Mediterranean (1967-2003): impacts of pH and climate variability

Environmental changes resulting from anthropogenic CO2 emissions occur at global and local levels and have potentially harmful effects, particularly for calcifying taxa in the marine environment. A time series of pteropod abundance covering the period 1967−2003 was isolated from the Point B (northwestern Ligurian Sea) zooplankton time series. Inter- and intra-annual changes in the abundance of 3 families (Limacinidae, Cavoliniidae and Creseidae) were com- pared with the copepod time series to identify any differential effects driven by ocean acidification and temperature. pH values were hind-cast from total alkalinity estimated from local temperature and salinity measurements, and atmospheric CO2 taken from the Mauna Loa time series. Although surface waters were supersaturated with respect to aragonite throughout the study period, it is estimated that pH declined by 0.05 units. All pteropod groups displayed a trend of increasing abundance, suggesting that any deleterious effect of declining pHT in the range of 0.05 units has not caused sufficient reductions in fitness as to decrease local abundances between 1967−2003. Pteropod populations are influenced by inter-annual changes in summer tempera- tures. Spectral analysis identified a ~14 yr periodic oscillation in sea surface temperature. Simi- larly timed oscillations in abundance are present for all pteropod families but not for copepods, indicating a possible influence of the North Atlantic quasi-decadal mode on pteropod populations. While laboratory studies have shown pteropods to be sensitive to changes in pH, this analysis sug- gests that local and regional scale drivers have had a greater effect on pteropod populations in the northwestern Mediterranean Sea in recent decades. It should be noted that pH changes in labo- ratory studies exceed 0.05 pH units and that the saturation state with respect to aragonite (Ωar) is usually much lower than that of the Mediterranean.

Convective heat transfer of Cu–water nanofluid in a cylindrical microchannel heat sink

One major hurdle in efficient design of electronic devices as they get smaller is to remove the generated heat. In this study, the thermal performance of a cylindrical microchannel heat sink was experimentally investigated for potential cooling of electronic devices. The heat sink comprised of 86 rectangular microchannels with hydraulic diameter of 560μm assembled into a cylindrical geometry. A number of thermocouples were embedded along the microchannel to provide local temperature measurements. The Cu–water nanofluid with different concentrations was used as coolant for heat fluxes of 35 and 50kW/m2. The Nusselt numbers of nanofluids with 0.05, 0.1 and 0.3wt% concentration were enhanced approximately 17%, 19% and 23% compared to that of pure water for similar Reynolds numbers. Further increase of Re in laminar flow regime (Re<900) led to lower Nusselt numbers for the nanofluid. Moreover, the increase of pressure drop versus Re was evaluated. While an appreciable enhancement was obtained for the heat transfer coefficient of 0.3wt% compared to that of pure water, the corresponding pressure drop was nonetheless less than 0.15bar.

Evaluation of radiofrequency safety by high temperature resolution MR thermometry using a paramagnetic lanthanide complex.

The current practice of calculating the specific absorption rate (SAR) relies on local temperature measurements made using temperature probes. For an accurate SAR measurement, a temperature imaging method that provides high temperature sensitivity is desirable, because acceptable levels of SAR produce small temperature changes. MR thermometry using paramagnetic lanthanide complexes can be used to obtain absolute temperature measurements with sub-degree temperature and sub-millimeter spatial resolution. The aim of this study was to develop and evaluate a high temperature resolution MR technique to determine SAR. MR thermometry using a paramagnetic lanthanide complex thulium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis (methylene phosphonate) (TmDOTP(5-)), which has an almost 10(2) times stronger chemical shift temperature dependence than water, was used to develop a novel method for SAR measurement. Three-dimensional temperature and SAR images were calculated using MR images acquired with a conventional gradient recalled echo sequence and SAR-intensive T1ρ sequence. Effects of the presence of conducting wire and increasing T1ρ spin-lock pulse duration were also examined. SAR distribution could be visualized clearly and surges associated with conducting wires and increasing pulse duration were identified clearly in the computed high spatial resolution SAR images. A novel method with high temperature sensitivity is proposed as a tool to evaluate radiofrequency safety in MRI.