Transient Temperature Measurements Research Articles

Measurements of transient high temperatures during the deformation of polymers

Measurements of transient high temperatures during the deformation of polymers

Measurements of transient high temperatures during the deformation of polymers

A novel and simple technique for the measurement of the magnitude and spatial distribution of transient high temperatures is described. The technique is applied to the measurement of the temperatures produced during the deformation under impact of a range of polymers. It is found that very high temperatures (up to 700‡ C) can be obtained in materials which undergo catastrophic failure, and that the temperatures obtained are related to the material's thermal and mechanical properties.

Temperature Measurement of Microscopic Areas Within a Simulated Head/Tape Interface Using Infrared Radiometric Technique

This study concerns the infrared measurement of steady-state and transient temperatures of microscopic areas within the contact region formed by a magnetic tape passing over a simulated recording head. This research demonstrates that the tape surface temperature can be measured within specific limits of response time and sensitivity. Due to its high tranmissivity in the relevant infrared band, sapphire was chosen as the material to be used in the fabrication of a simulated recording head. A Barnes RM2A infrared microscope was the principle radiometer used, while a best effort was made in scanning with an AGA Thermovision 750. The friction force versus load characteristics of the head-magnetic tape interface were also observed. The high speed measurements were divided into two regimes; non-contact hydrodynamic film region, and tape-head contact regime. The temperature measurements displayed a strong correlation with the measured friction force versus load curve. Almost no temperature rise was found in the noncontact hydrodynamic film region while a temperature rise of a few degrees Celsius was found when there was tape-head contact. The results with the AGA Thermovision 750 were consistent with the measurements obtained with the Barnes RM2A.

Obtaining local SAR and blood perfusion data from temperature measurements: steady state and transient techniques compared

A series of analyses and experiments was performed to determine the extent that SAR and blood perfusion information can be extracted from steady state temperature values and from transient temperature measurements following a step change in applied power. Multiple local temperature measurements were made in canine thighs heated by 2450 MHZ microwaves to evaluate two parameters: the local absorbed power in the tissue, and the local “effective blood perfusion.” The theoretical bases for these calculations are presented in order to identify their underlying assumptions and to obtain a unified basis for comparison of the various calculation methods used by previous investigators. From energy balance considerations it can be shown that the local absorbed power can be obtained from either the rate of increase of temperature immediately following a step increase in power, or from the rate of decrease in temperature immediately following a step decrease in power. These theoretical observations are verified experimentally by comparing the SAR results at fixed positions in canine thighs as calculated from both increasing and decreasing power steps. For decreasing power steps, the resulting decreasing temperature curves can also be used to calculate an effective blood perfusion rate if thermal conduction is included. Alternatively, this same effective blood perfusion rate can be calculated from steady state data. (These two approaches have been used by previous investigators to determine “blood perfusion” values. We have added the modifier “effective” to specifically denote the presence of thermal conduction effects in such perfusion calculations.) From our experimental results and theoretical calculations it appears that differences between the predictions of the two calculation methods arise from changing thermal conduction values during the cooling period of the thermal clearance method. The steady state calculation approach is easier to apply than the washout method, but it requires the additional knowledge of the local SAR value. It is important to realize that effective blood perfusion values calculated using thermal techniques are subject to large errors under conditions where thermal conduction is important, unless this conduction is explicitly included in the calculation. Such effective blood perfusion values should not be quantitatively compared to values calculated from non-thermal techniques that are not affected by thermal conduction. Unless such conduction effects are known to be negligible, effective perfusion values are only qualitative indicators of the presence of changes in blood perfusion.

Experimental studies of soot particle thermophoresis in nonisothermal combustion gases using thermocouple response techniques

Using transient size and temperature measurements obtained on a small thermocouple (TC) bead suddenly immersed in the soot-laden combustion products downstream of a water-cooled premixed flat-flame burner, we demonstrate that soot deposition rates are dominated by particle thermophoresis, i.e., soot particle drift down the temperature gradient prevailing in the gas thermal boundary layer (BL) surrounding the TC target. Observed soot deposition mass fluxes are estimated to be up to three orders of magnitude greater than those that would be expected on the basis of only Brownian (concentration) diffusion at the prevailing Reynolds numbers. It is shown that, for thermophoretically dominated soot particle transport, a suitable plot constructed from the transient TC-bead output should yield a straight line whose slope is proportional to the local soot volume fraction in the combustion gases. The latter dependence has been tested at several flame stoichiometries and heights above the burner surface, using the independent experimental technique of line-of-sight laser light (0.63 μm) extinction. Our results suggest that under these conditions small thermocouples can be used not only to estimate local gas temperatures, but also local soot volume fractions, without requiring restrictive assumptions about the prevailing particle size distribution, particle optical properties, or flame gas uniformity/symmetry. We conclude that (a) the dependence of the soot deposition rate on temperature “contrast” is in excellent accord with recently proposed thermophoretic BL-theories, and (b) the behavior of submicron soot particles in nonisothermal combustion products is strongly influenced by thermophoresis, with important implications for understanding rates of soot nucleation, growth, coagulation, burnout, and deposition.

Effect of channel restrictions on the axial heat transport in subcooled superfluid helium

The present study investigates the influence of partial restrictions on the axial heat transport and critical heat flux limits in subcooled superfluid helium (helium II) channels. Different size orifices are used to simulate partial plugging of superconducting magnets cooling channels by frozen oxygen, nitrogen, hydrogen, neon or moisture during the cool down process. Thin stainless steel sharp edged orifices of sizes 0.5, 1, 2 and 5 mm id are mounted between stainless steel flanges attached to 9 mm diameter (helium II) channel. The helium II channel is heated at one end with a copper block heater while the other end heat sinks to an atmospheric superfluid helium heat exchange. Temperature drop across the restriction is measured by two calibrated carbon resistors. Measurements are carried out at both temperatures ranging from 1.8 to 2.2 K. As the orifice/channel area ratio decreases, data show a considerable decrease in the axial heat transported by internal convection process resulting in lower critical heat flux at the phase transition from helium II to helium I by the destruction of superfluidity and inititation of boiling. A linear correlation between critical channel heat flux and orificeI channel area ratio gives a good fit to the experimental data. For heat fluxes higher than the critical heat flux, transient temperature measurements for a step heat input are correlated with the time required to reach the phase transition.

Estimation of formation temperature and thermal property from dissipation of heat generated by drilling

Dissipation of heat generated in the process of drilling depends upon the physical properties and condition of the rock and drilling mud, drilling rate and duration, mud circulation rate, casing, and depth of penetration. By treating the initial condition as an instantaneous temperature drop near the bottom of a drill hole, an analytical solution is obtained to show drilling‐induced heat dissipation. Two graphical methods are presented and illustrated with examples to determine, from transient temperature measurements, the equilibrium formation temperature as well as insitu thermal conductivity ratio and diffusivity of rock and drilling mud. One method requires the measurement of initial mud temperature [Formula: see text], while the other method requires knowing the thermal diffusivity of drilling mud [Formula: see text]. Either [Formula: see text] or [Formula: see text] can also be estimated with the trial‐and‐error procedure. A finite‐element analysis is further developed to handle thermal disturbance for the case where the temperature drop is not necessarily instantaneous; hence the solution is applicable at any depth in a drill hole.

Bismuth magnetoresistive thermometry for transient temperature measurements in liquid helium

We have developed a thermometric technique adapted from our work on the galvanomagnetic effects in bismuth at liquid helium temperatures. We find that a single crystal of bismuth can be used effectively as a thermometer for transient temperature measurements at these low temperatures. The thermometric property which is exploited is the strongly temperature-dependent magnetoresistance exhibited by these crystals at liquid helium temperatures. The bismuth thermometer is characterized by a fast thermal response, good sensitivity, low Kapitza resistance, and ease of electrical resistance adjustment, and it is particularly well suited to the situation in which the thermometer is itself used as a heater. In earlier work we successfully used these properties to study transient heat transfer from bismuth into liquid helium I and to measure the homogeneous nucleation temperature of liquid helium I.

Identifying heat- and mass-transfer constants from measurements under transient conditions

Explicit formulas are derived for determining heat- and mass-transfer constants from measurements of transient temperatures (concentrations) in processes which can be described by a general linear parabolic equation.

Pyrotechnic reaction of lead monoxide and silicon: measurement of reaction temperature

The measurement of transient high temperatures, from the fast pyrotechnic reaction of lead monoxide and silicon, using an automatic recording pyrometer and optical focussing system is described. The measured temperatures are compared with calculated reaction temperatures with which agreement is good. Practical difficulties are discussed with regard to thermocouple and pyrometer temperature measurements in pyrotechnic systems. Infra-red pyrometers have advantages over thermocouple systems e.g. response time and ability to make non-contact measurements. This work indicates that they can be put to practical use in the field of pyrotechnics.

A study of nucleate boiling near the peak heat flux through measurement of transient surface temperature

Measurements of transient surface temperature during nucleate boiling of water at high heat fluxes support the view of many investigators that a liquid film, herein called the macrolayer, exists beneath an agglomeration of vapor bubbles and is paramount in transferring heat. The macrolayer repeatedly dries out and reforms. Upon reforming, the surface temperature drops repeatedly for brief periods. This is apparently caused by microlayer evaporation beneath bubbles growing in the macrolayer. Sometimes, a brief quench precedes ebullition. Evaporation from the macrolayer just before it evaporates completely cools the surface effectively and evidence of nucleation then is absent.

Minimization of temperature distortion in thermocouple cavities

Introduction A DIRECT measurement of transient surface temperature and heat flux is often difficult. For example, a surface involves two modes of heat transfer, say radiative and convective heat transfer. In this case, if the measuring probe has a different radiative property from that of the surface, erroneous measurements will result. Therefore, indirect estimation by inverting the temperature history inside the heat conducting solid as measured by a thermocouple is often used for prediction of the surface temperature and heat flux. Beck, Herring and Parker, Frank, Imber and Khan, Stolz, and Chen and Thomsen have developed inversion solutions for this purpose. Since all of these solutions assumed that the cavity drilled into the solid does not distort the true temperature distribution, it is, therefore, important that the temperature measurement by an interior probe be accurate and involve little distortion or error. From studies made by Chen and Li and Beck, it was found that with a proper combination of the thermocouple cavity diameter, cavity depth, and the thermocouple material, the magnitude of the distortion of the temperature field with respect to space or time can be minimized. In this Note we study the optimum combination of geometrical parameters and material properties to eliminate the temperature distortion.

Experimental Investigation of Fuel-Coolant Interaction

n experimental investigation of thermal interaction of molten metals with cold liquids was made using measurements of transient temperature, pressure, and reactive force; postexperiment microscopic, metallographic, and chemical investigations completed the results. Thermal explosion, film boiling, and inverse Leidenfrost phenomena were considered. The origin of “jets” of small particles from the main particle was found to be a triggering mechanism of thermal explosion. Thermal explosion can be a phenomenon of coupled fragmentation and vapor explosion. Fast solidification was recognized as the main process that influenced fragmentation of the hot metal.

Thermal property estimation utilizing the Laplace transform with application to asphaltic pavement

This paper offers a new method for measurement of thermal properties of solids which are subject to arbitrary heating conditions. The method utilizes the Laplace transform and can be used for many geometries, but the primary case discussed here is that of a semi-infinite, homogeneous body. The calculations are relatively simple to perform with modern hand-held calculators, and the method can be utilized for determining thermal diffusivity when only temperatures are measured and for determining both thermal conductivity and volumetric specific heat if, in addition, the surface heat flux is known. The method is applied to the measurement of thermal properties of asphaltic pavement using temperature measurements from actual service conditions. Unlike other methods, exact solutions based on steady periodic heating conditions are not required. Transient temperature measurements in asphalt pavement are analyzed for two outdoor locations in Michigan, and calculated thermal property values of asphaltic pavement are compared with those found by using nonlinear estimation.

A mechanism supported by extensive experimental evidence to explain high heat fluxes observed during nucleate boiling

AbstractThis paper attempts to elucidate the mechanism responsible for high heat transfer rates occurring in nucleate boiling when liquid films exist on the heating surface. High‐speed cinematography and simultaneous transient surface temperature measurements provide a basis for describing the mechanism. In a liquid film, bubbles grow and detach rapidly. The film is quickly renewed. A liquid microlayer exists beneath a bubble its entire life. Conditions are very favorable for rapid evaporation from the microlayer so that heat transfer is rapid. A number of independent observations by other investigators working on diverse problems are cited in support of the mechanism.

Direct infrared measurements of filament transient temperature during switching in vanadium oxide film devices

Static and dynamic filament temperature profiles are shown in VO 2 film devices. The thermal switching is the consequence of the semiconductor to metal transition at 68°C arising from the fact that a conductive filament develops across the VO 2 device after switching. By use of an ir microscope, we have experimentally demonstrated large temperature spikes (some hundred degrees C) at the onset of switching in the growing filament. This maximum transient temperature (which may be destructive) is reached a few tens of microseconds after the generation of the filament. The external circuit parameters have a strong influence on this behavior. We have related this maximum filament temperature to the magnitude of the voltage drop during breakdown.

Combined conduction‐radiation energy transfer in stagnant water

The transient heating by radiation of a stagnant layer of water is studied both analytically and experimentally. Solar radiation (insolation) was simulated by tungsten filament lamps in parabolic reflectors of known spectral characteristics. The volumetric rate of internal absorption of radiation was predicted by considering spectral absorption, scattering, and multiple forward scattering by the water according to the model of Viskanta and Toor (1972). The transient temperature distribution was predicted by solving the one‐dimensional energy equation analytically in closed form after first linearizing the boundary condition at the air‐water interface. The analytical model was verified on the basis of laboratory experimental data obtained from transient temperature measurements made in pure water contained in a glass wall test cell using a Mach‐Zehnder interferometer. Comparison of experimental data with the predicted temperature distributions showed good agreement, thus verifying the radiation and total energy models. It was determined that the surface boundary condition and internal radiant heating rate of water must be correctly specified in order to model thermal stratification of stagnant water by radiation properly.

Pulse measurements of transient thermal response and temperature of avalanching p – n junction

A method is presented for measuring the junction temperature and the transient thermal response of oscillator-mounted avalanche diodes; the method requires an exact knowledge of the temperature dependence of the diode breakdown voltage. The junction temperature can be measured with unchanged accuracy within the measured temperature range of the breakdown voltage. The transient response as close as a few microseconds after the initiation of the junction-temperature step can be measured.

Transient Free Convection in a Revolving Tube

An experimental study has been made of transient free convection in a tube which revolves about an axis parallel to the tube axis. Three fluids have been studied for one tube diameter and one radius of rotation for centrifugal accelerations in the range 0 to 100g. The measurement of transient temperature and heat transfer coefficient shows that significant changes result from rotational buoyancy effects. A correlation of all the data to within ±20 percent has been effected by the use of a quasi-steady relation between a modified heat transfer coefficient and a rotational Rayleigh number as Nusseltnumber=0.107(Rayleighnumber)0.35

Determination of heat-transfer rates from transient surface temperature measurements

Determination of heat-transfer rates from transient surface temperature measurements