Temperature Gradient Measurements Research Articles

A dense water outflow from the Ross Sea, Antarctica: Mixing and the contribution of tides

We use hydrographic, current, and microstructure measurements, and tide-forced ocean models, to estimate benthic and interfacial mixing impacting the evolution of a bottom-trapped outflow of dense shelf water from the Drygalski Trough in the northwestern Ross Sea. During summer 2003 an energetic outflow was observed from the outer shelf (∼ 500 m isobath) to the ∼ 1600 m isobath on the continental slope. Outflow thickness was as great as ∼ 200 m, and mean speeds were ∼ 0.6 m s − 1 relative to background currents exceeding ∼ 1 m s − 1 that were primarily tidal in origin. No outflow was detected on the slope in winter 2004, although a thin layer of dense shelf water was present on the outer shelf. When the outflow was well-developed, the estimated benthic stress was of order one Pascal and the bulk Froude number over the upper slope exceeded one. Diapycnal scalar diffusivity ( K z ) values in the transition region at the top of the outflow, estimated from Thorpe-scale analysis of potential density and measurements of microscale temperature gradient from sensors attached to the CTD rosette, were of order 10 − 3 −10 − 2 m 2 s − 1 . For two cases where the upper outflow boundary was particularly sharply defined, entrainment rate w e was estimated from K z and bulk outflow parameters to be ∼ 10 − 3 m s − 1 (∼ 100 m day − 1 ). A tide-forced, three-dimensional primitive equation ocean model with Mellor-Yamada level 2.5 turbulence closure scheme for diapycnal mixing yields results consistent with a significant tidal role in mixing associated with benthic stress and shear within the stratified ocean interior.

Radial heat transfer in fixed-bed packing with small tube/particle diameter ratios

This paper presents an integrating approach to the description of radial heat transfer in catalyst packing with a flow without chemical reactions. The derived model combines the conventional αW model with the more recent λr(r) model. Particular attention is paid to small tube/particle diameter ratios. Experimental data including different tube diameters and particle shapes are used for adjustment. Spheres were used to represent a type of ordered single-size packing, and hollow cylinders to represent a type of chaotic random packing. A gradual quasi-steady experimental concept allows measurement of temperature gradients even at low flow velocities. Adjusted radial temperature profiles are compared with known approaches from literature, and correlation equations for heat transfer parameters are specified.

Modeling of Catalyst Activity Profiles in Fixed-Bed Reactors with a Moment Transformation Method

A model for pseudo-steady-state catalyst activity profiles in a fixed-bed reactor is presented. It is based on conservation of moments of the exact catalyst activity profile, as calculated from the catalyst deactivation rate. These moments are then transformed analytically into a polynomial approximation of the activity profile for each time step. Then temporal and spatial evolution of the catalyst activity can be followed, and correspondingly accurate predictions of reactor performance with partly deactivated catalyst can be carried out. The present model is especially suitable for situations where the observed reaction rate is not solely determined by kinetics of a catalytic reaction, but also by heat or mass transfer limitations, or if the pressure drop in the reactor affects reaction rates. A further important class is when multiple reactions are taking place with different mechanisms so that the dominant mechanism changes as catalyst is deactivated. It can also be used in catalyst lifespan design, since measured temperature gradients can be followed by the model and transformed into information regarding catalyst activity profile. Also optimization of reactor operation with partly deactivated catalyst can be improved.

Sapwood temperature gradients between lower stems and the crown do not influence estimates of stand-level stem CO2 efflux

Temperature plays a critical role in the regulation of respiration rates and is often used to scale measurements of respiration to the stand-level and calculate annual respiratory fluxes. Previous studies have indicated that failure to consider temperature gradients between sun-exposed stems and branches in the crown and shaded lower stems may result in errors when deriving stand-level estimates of stem CO(2) efflux. We measured vertical gradients in sapwood temperature in a mature lowland podocarp rain forest in New Zealand to: (1) estimate the effects of within-stem temperature variation on the vertical distribution of stem CO(2) efflux; and (2) use these findings to estimate stand-level stem CO(2) efflux for this forest. Large within-stem gradients in sapwood temperature (1.6 +/- 0.1 to 6.0 +/- 0.5 degrees C) were observed. However, these gradients did not significantly influence the stand-level estimate of stem CO(2) efflux in this forest (536 +/- 42 mol CO(2) ha(-1) day(-1)) or the vertical distribution of stem CO(2) efflux, because of the opposing effects of daytime warming and nighttime cooling on CO(2) efflux in the canopy, and the small fraction of the woody biomass in the crowns of forest trees. Our findings suggest that detailed measurements of within-stand temperature gradients are unlikely to greatly improve the accuracy of tree- or stand-level estimates of stem CO(2) efflux.

Precise measurements of radial temperature gradients in the laser-heated diamond anvil cell

A new spectroradiometry system specialized for measuring two-dimensional temperature gradients for samples at high pressure in the laser heated diamond anvil cell has been designed and constructed at UCLA. Emitted light intensity from sample hotspots is imaged by a videocamera for real time monitoring, an imaging spectroradiometer for temperature measurement, and a high-dynamic-range camera that examines a magnified image of the two-dimensional intensity distribution of the heated spot, yielding precise measurements of temperature gradients. With this new system, most systematic errors in temperature measurement due to chromatic aberration are bypassed. We use this system to compare several different geometries of temperature measurement found in the literature, including scanning a pinhole aperture, and narrow-slit and wide-slit entrance apertures placed before the imaging spectrometer. We find that the most accurate way of measuring a temperature is to use the spectrometer to measure an average hotspot temperature and to use information from the imaging charge coupled device to calculate the temperature distribution to the hotspot. We investigate the effects of possible wavelength- and temperature-dependent emissivity, and evaluate their errors. We apply this technique to measure the anisotropy in temperature distribution of highly oriented graphite at room temperature and also at high pressures. A comparison between model and experiment demonstrates that this system is capable of measuring thermal diffusivity in anisotropic single crystals and is also capable of measuring relative thermal diffusivity at high pressures and temperatures among different materials. This shows the possibility of using this system to provide information about thermal diffusivity of materials at high pressure and temperature.

Performance and Validation Tests on the NIST Hybrid Humidity Generator

A new humidity generator has been constructed at the National Institute of Standards and Technology. Once fully operational, the NIST hybrid humidity generator (HHG) will generate frost/dew points from −70°C to +85°C using calibration gas-flow rates up to 150 standard liters per minute and is expected to outperform the present humidity generator at NIST in terms of accuracy. The HHG combines the two-pressure and divided-flow humidity-generation techniques (hence, the name “hybrid”). The centerpiece of the HHG is a heat exchanger/saturator that is immersed in a temperature-controlled bath stable to within 1 mK. For dew/frost-point temperatures above −15°C, the two-pressure principle is employed. For frost points at or below −15°C, the water-vapor/air mixture is produced by mixing metered streams of moist air produced by the two-pressure method with purified, dry air. A series of performance and validation tests on the HHG in the two-pressure mode, including measurements of temperature gradients and pressure stability in the generator under various operating conditions, and comparison of the humidity generated by the HHG to that generated by the other NIST humidity-generation standards, are reported.

Processes Controlling the Thermal Regime of Saltmarsh Channel Beds

Spatially and temporally continuous temperature measurements were collected over 32 h using a fiber-optic distributed temperature sensing (DTS) system deployed along 330 m of two intertidal saltmarsh channel beds in northern California. Measured temperature gradients imparted ecosystem-scale structure to the saltmarsh tidal channel thermal regime, which was punctuated by potential warm and cold refugia. Anomalous bed temperatures of 2-4 degrees C occurred throughout the 1.3 tidal cycles at some locations. Discrete locations of consistently warm temperatures characterized sustained seepage of recently infiltrated tidal waters. Low-variance temperature anomalies were typically collocated with hidden microtopographic tributaries that facilitated mixing of warm surface waters and cold groundwater. Bed temperature gradients (approximately 2 degrees C/100 m, average) decreased from high temperatures similar to bay water at the channel mouths to low inland temperatures comparable to groundwater. The trends were maintained by cold groundwater discharge throughout the channels, which affected bed temperatures in proportion to channel reach exposure time; the opposing effect, conductive bed-warming by tidal waters, was proportional to flood duration. DTS is a promising tool for identifying spatial and temporal temperature patterns of hydroecological importance amidst complex natural systems.

Microwave Correlation Measurement Crossed-pair Antennas Techniques Diagnosis of Breast Cancer

Microwave correlation radiometry is a possible alternative technique to multi-frequency radiometry for obtaining a measurement of the subcutaneous temperature gradient in living tissue. In its simplest form this technique consists of combining the outputs of two antennas feeding a microwave correlation radiometer. Microwave correlation is based on the coherent detection of noise, here presented as the correlated signal from the two antennas. We propose here new processes, an add and square correlation radiometer and the non-resonant perturbation, which thoroughly investigated for different muscle phantom materials to define the optimum penetration depth of the electromagnetic field at fixed distance between the antennas. Keywords: Microwave correlation radiometer, non-resonant perturbation, Medical application Technologies Avancees Vol. 18 2006: pp. 12-17

Effects of river discharge on hyporheic exchange flows in salmon spawning areas of a large gravel‐bed river

AbstractThe flow magnitude and timing from hydroelectric dams in the Snake River Basin of the Pacific north‐western US is managed in part for the benefit of salmon. The objective of this research was to evaluate the effects of Hells Canyon Dam discharge operations on hydrologic exchange flows between the river and riverbed in Snake River fall Chinook salmon spawning areas. Interactions between river water and pore water within the upper 1 m of the riverbed were quantified through the use of self‐contained temperature and water level data loggers suspended inside of piezometers. The data were recorded at 20 min intervals over a period of 200 days when the mean daily discharge was 218–605 m3 s−1, with hourly stage changes as large as 1·9 m. Differences in head pressure between the river and riverbed were small, often within ± 2 cm. Measured temperature gradients in the riverbed indicated significant interactions between the surface and subsurface water. At the majority of sites, neither hydraulic nor temperature gradients were significantly affected by either short‐ or long‐term changes in discharge operations from Hells Canyon Dam. Only 2 of 14 study sites exhibited acute flux reversals between the river and riverbed resulting from short‐term, large magnitude changes in discharge. The findings suggest that local scale measurements may not be wholly explanatory of the hydrological exchange between the river and riverbed. The processes controlling surface water exchange at the study sites are likely to be bedform‐induced advective pumping, turbulence at the riverbed surface, and large‐scale hydraulic gradients along the longitudinal profile of the riverbed. By incorporating the knowledge of hydrological exchange processes into water management planning, regional agencies will be better prepared to manage the limited water resources among competing priorities that include salmon recovery, flood control, irrigation supply, hydropower production, and recreation. Copyright © 2007 John Wiley & Sons, Ltd.

Multi-solid multi-channel Mithrandir (M 3) code for thermal–hydraulic modelling of ITER Cable-in-Conduit Superconductors

We present a new multi-solid multi-channel (M 3) thermal–hydraulic model for the analysis of the International Thermonuclear Experimental Reactor (ITER) Cable-In-Conduit Conductors (CICC). The model discretizes the cross section of an ITER CICC into M current carrying cable elements (e.g., the six last-but-one cabling stages—the petals), coupled with N hydraulic channels (e.g., the six petals + the central channel) and K non-current carrying solid components (e.g., the jacket of the CICC), with M, N and K arbitrary integers. Along each of the M + K solid components a 1D transient heat conduction equation is solved, whereas along each of the N channels three Euler-like 1D equations, derived from the conservation laws for compressible He flow, are solved. The resulting quasi 3D model, in which 1D equations are coupled by heat and mass transfer between the different CICC components, is implemented in the M 3 code and validated against experimental results from the ITER Good Joint sample and the ITER Poloidal Field Conductor Insert Full Size Joint Sample. The new code is able to reproduce with good accuracy the measured temperature gradients on the CICC cross section, provided sufficiently accurate input data are available.

The ‘Cell-See-Us’ cellular thermometer

We report the design, construction, and characterisation of a five-component cellular fluorescence-based thermometer and its individual parts, built from the bottom up in Escherichia coli. The sensing mechanism is based on the temperature-sensitive regulatory activity of the mutated LacIts transcription factor. Such microscale temperature sensors have potential applications in the measurement of temperature gradients on 2D and 3D contours and in microelectromechanical system (MEMS) devices.

X-band RF structure thermal analysis and tests

The design of X-band multi-cell RF structures for particle accelerators requires an accurate estimation of the sensitivity to the mechanical deformations induced by the surface power loss on the metallic walls. The prediction of these effects is important for conceiving a tuning strategy that assures the correct structure operation when integrated into the accelerator complex. An experimental technique is proposed for preliminary testing of the mechanical deformations caused by a thermal load that can generate in the RF cavity a temperature gradient profile as close as possible to the real one induced by the electromagnetic power loss. Because we want to find a method that can be easily and cheaply implemented in the laboratory, a thermal radiator with uniform heating power density, placed on the axis of the RF cavity, has been chosen as heating source. A multi-physics finite-element code (ANSYS) has allowed comparing the measured temperature gradients with the computed ones. The good agreement validates the application of the code, which has been extended to the joint solution of the electromagnetic and thermal problem. Thus the sensitivity to deformations can be directly evaluated.

Temperature Measurement and Microstructure Control for Rene88DT Superalloy during Laser Rapid Forming

Laser rapid forming (LRF) is a new manufacturing technology, which has been developed on the basis of multi-layer laser cladding. In the LRF process, the microstructure has important effects on the mechanical properties of the partsbut the control of microstructure is a problem. In this study, the influences of crystallography orientations of substrate and profile of solid/liquid interface on microstructure were discussed. Further, with the combining of the columnar to equiaxed transition (CET) model during alloy solidification, the growth law of microstructure of Rene88DT alloy was established. It has been found that the temperature gradient was lowest and the solidification velocity was greatest at the solid/liquid interface of the tail of molten pool, and hence the CET occurs easily at this position. The temperature measurement system of molten pool was developed by using a two-color infrared thermometer in this study. With the measurement of temperature gradient of the tail of molten pool by using a two-color infrared thermometer, the process parameters of laser multi-layer cladding were optimized. Finally, directional solidification even single crystal was achieved in laser multi-layer cladding.

In situ measurement and simulation of temperature and stress gradients during sintering of large ceramic components

A special thermooptical measuring system was used to determine mechanical, thermal and sintering properties during firing simultaneously. Combining customary and novel in situ measuring methods, a complete dataset was obtained which includes elastic and viscous moduli, thermal conductivity and coefficients of heat transfer, specific heat, reaction and sintering data and gas permeability. Using finite element methods (FEM) the temperature fields in large components were simulated for various time temperature cycles. From the temperature field local reaction and shrinkage rates were calculated. The corresponding stresses were obtained using FEM again. The time temperature cycle was optimized taking into account both a sufficient safety margin to the respective strength of the sintering material and the economic requirement for a short firing cycle. The use of the methods was demonstrated considering as example a large high voltage porcelain insulator, which undergoes a number of phase transformations during firing.

Measurement of temperature gradients through local extinction using Raman scattering spectroscopy

Measurements of temperature in laminar flames with localised extinction points were made using line imaging of spectrally resolved laser Raman scattering through the extinction process. A fit to the nitrogen scattering spectrum was used to determine temperature with an accuracy of 30 K. Temperature gradients through the extinction process were measured as the flame strength prior to extinction and the rate of extinction was separately controlled. The results were compared to previously reported numerical simulations for this flame and were found to validate the modelling of the flame extinction process. The measured temperature gradient is affected by the radial rate at which strain is increased, as well as inner flame strength. Measurements of integrated flame emission were also made at the extinction point and indicate that reactions persist at temperatures well below the onedimensional extinction temperature, which is consistent with reaction rate profiles from the numerical simulations.

MIRO: Microwave Instrument for Rosetta Orbiter

The European Space Agency Rosetta Spacecraft, launched on March 2, 2004 toward Comet 67P/Churyumov-Gerasimenko, carries a relatively small and lightweight millimeter-submillimeter spectrometer instrument, the first of its kind launched into deep space. The instrument will be used to study the evolution of outgassing water and other molecules from the target comet as a function of heliocentric distance. During flybys of the asteroids (2867) Steins and (21) Lutetia in 2008 and 2010 respectively, the instrument will measure thermal emission and search for water vapor in the vicinity of these asteroids. The instrument, named MIRO (Microwave Instrument for the Rosetta Orbiter), consists of a 30-cm diameter, offset parabolic reflector telescope followed by two heterodyne receivers. Center-band operating frequencies of the receivers are near 190 GHz (1.6 mm) and 562 GHz (0.5 mm). Broadband continuum channels are implemented in both frequency bands for the measurement of near surface temperatures and temperature gradients in Comet 67P/Churyumov-Gerasimenko and the asteroids (2867) Steins and (21) Lutetia. A 4096 channel CTS (Chirp Transform Spectrometer) spectrometer having 180 MHz total bandwidth and 44 kHz resolution is, in addition to the continuum channel, connected to the submillimeter receiver. The submillimeter radiometer/spectrometer is fixed tuned to measure four volatile species – CO, CH3OH, NH3 and three, oxygen-related isotopologues of water, H2 16O, H2 17O and H2 18O. The basic quantities measured with the MIRO instrument are surface temperature, gas production rates and relative abundances, and velocity and excitation temperature of each species, along with their spatial and temporal variability. This paper provides a short discussion of the scientific objectives of the investigation, and a detailed discussion of the MIRO instrument system.

A comparative study of geothermal and meteorological records of climate change in Kamchatka

To reconstruct the recent climate history in Kamchatka, a series of repeated precise temperature logs were performed in a number of boreholes located in a broad east-west strip (between 52 and 54°N) in the central part of Kamchatka west of Petropavlovsk-Kamchatski. Within three years more than 30 temperature logs were performed in 10 holes (one up to six logs per hole) to the depth of up to 400 metres. Measured temperature gradients varied in a broad interval 0 to 60 mK/m and in some holes a sizeable variation in the subsurface temperatures due to advective heat transport by underground water was observed. Measured data were compared with older temperature profiles obtained in the early eighties by Sugrobov and Yanovsky (1993). Even when older data are of poorer precision (accuracy of about 0.1 K), they presented valuable information of the subsurface temperature conditions existing 20–25 years ago. Borehole observations and the inverted ground surface temperature histories (GSTHs) used for the paleoclimate reconstruction were complemented with a detailed survey of meteorological data. Namely, the long-term surface air temperature (SAT) and precipitation records from Petropavlovsk station (in operation since 1890) were used together with similar data from a number of local subsidiary meteo-stations operating in Central Kamchatka since 1950. Regardless of extreme complexity of the local meteorological/climate conditions, diversity of borehole sites and calibration of measuring devices used during the whole campaign, the results of the climate reconstruction supported a general warming of about 1 K characteristic for the 20th century, which followed an inexpressive cooler period typical for the most of the 19th century. In the last three to four decades the warming rate has been locally increasing up to 0.02 K/year. It was also shown that the snow cover played a dominant role in the penetration of the climate “signal” to depth and could considerably smooth down the subsurface response to the changes occurred on the surface.

Determination of strain distribution and temperature gradient profiles from phase measurements of embedded fibre Bragg gratings

In this paper, a powerful method for measuring non-uniform strain is reviewed and extended to the measurement of temperature gradients inside an epoxy part. The sensor is an embedded fibre Bragg grating and the method is based on the measurements of the grating phase obtained by combining optical low coherence interferometry and an inverse scattering algorithm. This method has a great potential and for the first time experimental results obtained for both strain distribution and temperature gradient are presented. By applying a tensile test, strain distribution measurements are first compared with finite element simulations to validate previous published results. Second, original temperature gradient measurements in a solid body are shown. The results are in good accordance with reference measurements achieved with thermocouples incorporated into the body.

On the difference between thermal cycling and thermal shock testing for board level reliability of soldered interconnections

In this work, the endurance behavior of a ball grid array package is determined at two different temperature cycle conditions: a thermal cycle test and a thermal shock test. The observed failure distributions and failure modes allow deriving a translation factor between the two test conditions. Finite element analyses are carried out to design a predictive simulation model for the fatigue lifetime. Using an isothermal approach, a discrepancy is found between the experimental and simulated results. Incorporating the experimentally measured temperature gradients into a semi-transient model leads to a better match with the observed lifetimes. In particular for the fast thermal shock loading this turns out to be necessary. The results prove that temperature gradients in BGA-packages play an important role in board level reliability testing.

Estimating mud expulsion rates from temperature measurements on Håkon Mosby Mud Volcano, SW Barents Sea

The Håkon Mosby Mud Volcano (HMMV), located on the Norwegian–Barents–Svalbard continental margin in 1250 m water depth, has been identified and described as a structure caused by upward transport of mud, pore water and gas [e.g. Eldholm, O., Sundvor, E., Vogt, P.R., Hjelstuen, B.O., Crane, K., Nilsen, A.K., Gladczenko, T.P., 1999. SW Barents Sea continental margin heat flow and Håkon Mosby Volcano. Geo-Marine Letters 19, 29–37]. During RV Polarstern expedition ARK XIX/3b in 2003, an integrated study took place to investigate the detailed morphology, biology, chemistry and geophysical aspects of HMMV [Klages, M., Thiede, J., Foucher, J.-P., 2004. The Expeditions ARK XIX 3a, 3b and 3c, Berichte zur Polarforschung, 488.]. In this paper, we describe a detailed survey involving more than 100 temperature gradient measurements in order to reveal the temperature structure of HMMV. Values of apparent heat flow up to 3000 mW/m 2 and absolute temperatures up to 25.8 °C have been detected. These enormously high heat flux values do not reflect deep-seated thermal gradients but are a result of surface mud flows. The occurrence and abundance of mud flows varies in different areas within the HMMV inner crater. A combination of very shallow, ROV-derived temperature measurements, a large number of intermediate depth temperature gradients and nine deep penetrating gravity corers allows us to reconstruct the history of activity of HMMV. Modeling of the observed temperature gradients indicates vigorous activity with very recent mud flows. Furthermore, the supply of energy and material from the HMMV is estimated to have an annual mass volume of ∼15,000 m 3. From the thermal corona of HMMV and the observed horizontal heat flux, it is possible to deduce that the long term temperature of the mud pond is stable at a temperature approximately similar to the recent maximum temperature of 25 °C.