Amplitude Of Temperature Oscillations Research Articles

Expanding the applications of holographic interferometry to the quantitative visualization of oscillatory thermofluid processes using temperature as tracer

In this paper we discuss a novel application of holographic interferometry in the simultaneous quantitative visualization of high-speed, oscillatory flow and temperature fields in complex flow geometries. We consider cases of (i) self-sustained oscillatory flows with main flow imposed in grooved and communicating channels as well as (ii) oscillating thermofluid processes with zero mean velocity in a thermoacoustic refrigerator model. Examples showing unsteady temperature distributions obtained by real-time holographic interferometry combined with high-speed cinematography illustrate the possibilities of the approach introduced in the paper. Our study shows that temperature distributions accurately mirror flow structures in certain types of complex, unsteady flows, thus allowing, apart from the measurement of temperature profiles and heat transfer, also the measurement of oscillatory amplitudes, frequencies, wavelengths as well as the speed of propagation of traveling waves by applying digital image processing techniques. In the grooved and communicating channels it is possible to visualize the structure of the Tollmien–Schlichting waves through isotherms by using the infinite fringe field alignment of holographic interferometry. In the thermoacoustic refrigerator model, small amplitude temperature oscillations generated by the acoustic standing wave are visualized and measured. Image processing as well as data reduction procedures used in the analysis of these flow fields are discussed in the paper. Experimental data obtained by applying the techniques introduced in the paper show good agreement with theory and results of numerical simulations. Our study suggests that using temperature as tracer offers numerous advantages in the study of certain types of complex, unsteady flows.

Measurement of thermal properties of thin dielectric films and anisotropic solids by ac hot-strip method

The present work deals with the foundations of the theory of the method of measuring the thermal properties of anisotropic solids and thin dielectric films deposited onto them. The experimental setup is briefly described. The authors demonstrate the possibility of measuring a set of thermal properties of solids by means of recording the amplitude and phase of temperature oscillations of a strip, which has a width comparable with the attenuation length of a temperature wave in the sample. The paper offers the results of measurements of the heat capacity, thermal conductivity, thermal diffusivity and thermal activity of leucosapphire. The thermal conductivity of an SrTiO3 film about 2 μm thick sputtered onto a single crystal of leucosapphire was determined by measuring the temperature oscillation amplitude at various frequencies.

Steady-periodic hyperbolic heat conduction in a finite slab

Amplitude and phase lag of temperature oscillations in a slab subjected to a harmonic heat flux are presented, by solving the hyperbolic heat conduction equation. Examples show how to obtain the temperature oscillations in any desired location for specified parameters. The results can be obtained for any other values of the parameters since this paper is a Mathematica notebook [1]. The plots demonstrate the resonance phenomena and that increasing the relaxation time decreases the damping of temperature amplitude.

Experimental studies of the thermal properties of thin films by a probe technique with periodic heating

The thermal properties of SrTiO3 thin films are investigated experimentally by recording the amplitude and phase of the temperature oscillations of a flat probe with the heat flux perpendicular to the plane of the film. Results are given from measurements of the specific heat and thermal conductivity of a leucosapphire substrate and the thermal conductivity of a SrTiO3 film of thickness 2 µm.

Numerical studies on the nonequilibrium inductively coupled plasma with metal vapor ionization

Nonequilibrium inductively coupled plasma (ICP) where cesium metal atoms contained in argon gas as a seed material are dominantly ionized is investigated with two-dimensional (2-D) numerical calculations which are based on a fully time-dependent (FTD) model and sinusoidal approximation (SA) model. Calculation results with the FTD model indicate that the amplitude of electron temperature oscillation over one radio frequency cycle is below about 120 K for the mean value of about 5600 K, and that of the electron number density is negligible due to its long relaxation time. Results with the SA model coincide with that with the FTD model, and it is valid to predict the plasma properties with the SA model. Under the suitable operating conditions, the region where electron number density is kept constant is formed and extended in the ICP, since the electron temperature ranging from 4000 to 6000 K is realized, and cesium atoms are fully ionized while the ionization of argon atoms is not significant. Since no current is induced at the center axis of ICP, the density profile around the axis is almost determined by the diffusion of electrons from the region of full seed ionization.

Mathematical modelling of the stability characteristics of a natural circulation loop

The natural circulation phenomenon in a rectangular loop has been mathematically simulated and its stability characteristics have been investigated. The conservation equations of mass, momentum and energy in the transient form were solved numerically using the finite difference method. The stable, unstable and neutrally stable points were identified by examining the amplitude of flow and temperature oscillations with time for a given set of operating conditions. The stability behaviour of the loop has also been investigated using the linear stability theory. The results show that the stability maps obtained by the two methods are in close agreement.

Influence of temperature on crystallization of lactose in ice‐cream

SummarySandiness in ice‐cream due to lactose crystallization can still be a problem in many circumstances. Lactose crystallization occurs in ice‐cream as the unfrozen phase becomes supersaturated. However, the effects of storage temperature and temperature fluctuations on lactose crystallization have not been very well quantified. In this work, an accelerated storage apparatus was used to determine the effects of thermal fluctuations (from ±0.01°C to ±2.0°C), at several mean storage temperatures (from −5.0 to −20.0°C), on the onset of lactose nucleation and subsequent crystal growth in a standard vanilla ice‐cream. the induction time for nucleation initially decreased as temperature was lowered (for temperature oscillations of ±1.0°C), until a minimum induction time of 3 h was found between −10.0 and −12.0°C. Further decreases in storage temperature caused the induction time to increase. the induction time for nucleation increased as the extent of temperature fluctuations increased, from 0.01 to 2.0°C, while initial lactose crystal growth rate showed the opposite trend. the initial growth rate increased as temperature decreased between −5.0 and −10.0°C, but then decreased for temperatures below −10.0°C. At −20.0°C lactose crystals grew very slowly. At −10.0°C the rate of growth decreased with increasing amplitude of temperature oscillations.

An investigation on the “Onset” of oscillatory Marangoni flow

It is known that thermocapillary convection in differentially and uniformly heated liquid bridges shows a transition (Marangoni instability) from an axisymmetric to an oscillatory regime. The “Onset” experiment, performed during the D2 Spacelab mission on the Advanced Fluid Physics Module (AFPM), was aimed to investigate this transition at various bridge geometries; in particular the goal was to determine the critical temperature difference applied to the end disks supporting the liquid bridges, and to study the structure of the flow at the onset of the Marangoni instability. The paper reports the main results, obtained analyzing the experimental data (temperatures and velocities). The evaluation of the transition (onset) condition obtained from temperature data was achieved with the aid of signal processing techniques. The onset determinations have been also validated by analysis of flow field velocities. The results concerning frequency and amplitude of temperature oscillations in the neighbourhood of the onset of Marangoni instability are reported. We provide an evaluation of the heat fluxes through the plates. A comparison between numerical and experimental results related to the two-dimensional flow field is made, a satisfactory agreement is reached.

Thermal resonance in the heat conduction problem with a heat source moving along a closed circuit

We found the conditions of resonant increase in the amplitude of temperature oscillations of the points of a thin heat-conducting rod in the shape of a closed ring with a variable-power heat source moving on its surface.

AHARONOV-BOHM OSCILLATIONS IN A SPIN-CHARGE-SEPARATED SYSTEM

The Little-Parks-like experiment for the superconducting phase of a spin-charge-separated system is analyzed. It is shown that the distinctive feature of spin-charge separation is the specific abrupt dependence of amplitude of critical temperature oscillations on the hole concentration.

Association of sleep-wake habits in older people with changes in output of circadian pacemaker

Many elderly people complain of disturbed sleep patterns but there is no evidence that the need to sleep decreases with age; it seems rather that the timing and consolidation of sleep change. We tried to find out whether there is a concurrent change in the output of the circadian pacemaker with age. The phase and amplitude of the pacemaker's output were assessed by continuous measurement of the core body temperature during 40 h of sustained wakefulness under constant behavioural and environmental conditions. 27 young men (18-31 years) were compared with 21 older people (65-85 years; 11 men, 10 women); all were healthy and without sleep complaints. The mean amplitude of the endogenous circadian temperature oscillation (ECA) was 40% greater in young men than in the older group. Older men had a lower mean temperature ECA than older women. The minimum of the endogenous phase of the circadian temperature oscillation (ECP) occurred 1 h 52 min earlier in the older than in the young group. Customary bedtimes and waketimes were also earlier in the older group, as was their daily alertness peak. There was a close correlation between habitual waketime and temperature ECP in young men, which may lose precision with age, especially among women. These findings provide evidence for systematic age-related changes in the output of the human circadian pacemaker. We suggest that these changes may underlie the common complaints of sleep disturbance among elderly people. These changes could reflect the observed age-related deterioration of the hypothalmic nuclei that drive mammalian circadian rhythms.

Hydrodynamics and oscillation of temperature in single crystal growth from high-temperature solutions with use of ACRT

The work presents the results of investigation of liquid phase hydrodynamics and temperature oscillations in a flux at accelerated rotation of a cylindrical crucible with a feeder. The dependences of shape and value of temperature oscillations in flux on the parameters of crucible rotation and temperature gradient were studied. The empirical dependence of temperature oscillation amplitude in a flux of the PbO-CaO/Bi 2O 3-Fe 2O 3/V 2O 5 system at the bottom of a crucible on the rotation parameters were obtained as well as the values of maximal temperature differential in the melt height.

Numerical and experimental analysis of unsteady laminar forced convection in channels

Unsteady heat transfer for fully developed laminar air flow with a parabolic velocity profile through a parallel plate channel, subjected to sinusoidally varying inlet temperature is considered. Numerical as well as experimental results are reported. A second order accurate explicit finite difference scheme is used in the numerical solution to the energy equation. A general boundary condition of fifth kind which accounts for both external convection and wall thermal capacitance effects is introduced. Experiments are performed on an apparatus specially designed for the investigation of unsteady forced convection heat transfer, resulting from a sinusoidal variation of the inlet temperature in rectangular channels. The variations in the amplitude of periodic temperature oscillations along the centerline of the rectangular channel, obtained from the numerical model and experiments are compared on both a quantitative and qualitative basis.

A study of thermal peak splitting in capillary GC

AbstractFluctuating thermal gradients are recognized as a distinct source of peak splitting in capillary column gas chromatography. In this study, the influence of analyte signal level, temperature oscillation amplitude, and oscillation frequency on splitting are quantitatively examined. Stable gradients are also considered. A simple, effective method is proposed for virtually eliminating thermal peak splitting in isothermal capillary GC analysis.

An air flow sensor based on interface thermal wave propagation

An air flow sensor that uses a flow-induced change of temperature oscillation phase at an air-solid interface is described and analyzed. The sensor is fabricated on silicon coated with polyimide. The source and detector of temperature oscillations are integrated on the same substrate but spatially separated. A narrow strip of metal film driven by ac is the source. A PbTe thin-film thermocouple is the detector. Device operation in still air is analyzed and compared with experiment. The temperature oscillation amplitude and phase on an interface with an oscillating strip heat source is derived for interface thermal resistance and for a layered substrate. Interference between thermal oscillations propagating from source to detector through the solid and through the air is predicted and observed with a 53-μm-thick polymide layer. In contrast, with a 16-μm-thick polyimide layer, interference that varies with frequency is not seen, also in agreement with theory. Experimental demonstration of flow response is also reported. Qualitative agreement with the predictions of a time-of-flight model of flow response is found.

The effect of temperature oscillations at the growth interface on crystal perfection

Dislocation-free silicon crystals are grown with the Czochralski technique under various growth conditions, including changed heater positions, pulling rates, and crystal and crucible rotation rates. The correlation between the microdefect density in crystals and temperature oscillations near the growth interface is investigated. It is found that the microdefect density decreases with higher heater position, increased pullong rate and decreased crystal rotation rate. Theseresults are in accord with the behavior of the temperature oscillation amplitude. Thus, the density of microdefects decreases as the oscillation amplitude is reduced. The relation between microdefect density and temperature oscillation amplitude is well explaines by the crystal remelt model. The microdefect density in a crystal varies for annealing at more than 1000δC immediately after growth. Thus, the reduction of microdefect density by annealing depends on the defect distribution in the as-grown crystals.

Measurements of thermal structure and thermal contrasts in the atmosphere of Venus and related dynamical observations: Results From the four Pioneer Venus Probes

Thermal structure of the atmosphere of Venus, and differences in structure with latitude (up to 60°) and clock hour (from midnight to 8 A.M.) have been measured in situ from an altitude of 126 km to the surface by instruments on the four Pioneer Venus entry probes. Several indications from the preliminary analyses are confirmed by the current analysis: Thermal contrasts below 45 km are a few K, with the mid‐latitudes warmer than both equatorial and the high latitudes. Sizeable temperature and pressure differences with latitude develop in the clouds (25 K and 20 mbar at the 200 mbar level). At 30° latitude, diurnal differences were small throughout the lower atmosphere from midnight to 7 A.M. A major stable layer 25 km deep exists just below the clouds. Waves of global extent were observed within this layer. A locally stable layer is indicated in the deep atmosphere, between 10 and 20 km, at latitudes up to 30°. In the middle cloud and immediately below the deep stable layer, the atmosphere is approximately neutrally stable, and there is evidence for convective overturning below the stable layer. Just above the clouds, the lapse rate becomes stable, and a ‘stratosphere’ begins which extends upwards to 110 km, becoming isothermal above 85 km. The stratospheric temperature profiles were essentially the same in three widely separated soundings. Upward of 110 km, there is evidence of large amplitude temperature oscillations with altitude, believed to signify the presence of large amplitude waves, perhaps thermal tides. By comparing data of several experiments, it is found that the large diurnal variations in the upper atmosphere begin at an altitude ∼115 km. Agreement of structure data from other Pioneer Venus experiments with the present results is generally excellent. Our measurements of the winds derived from Doppler data agree well with DLBI results and indicate a retrograde zonal velocity of 113 m/s at 63 km altitude and 30° latitude. The zonal winds predicted at cloud levels from pressure differences between 60° latitude and the mid‐latitude probes by assumption of cyclostrophic balance are in first order agreement with the observed winds. At latitudes below ∼30°, however, cyclostrophic balance of the zonal winds is not the dominant process. At altitudes from 60 to 105 km, the measured pressure differences and the assumption of cyclostrophic balance indicate zonal wind velocities peaking at 155 m/s at 68 km, remaining above 120 m/s up to 95 km, then decreasing rapidly.

NO x formation in premixed turbulent flames

NOx formation has been studied in lean, premixed, turbulent flames stabilized by perforated plates. The burner pressure was atmospheric, but other parameters were representative of gas turbine operating conditions. Prevaporized Jet A fuel was injected into preheated unvitiated air and thoroughly mixed prior to combustion. Mixture inlet temperature was 750°K and total residence times were approximately 4 msec. NOx, CO, CO2 and hydrocarbon levels were measured along the jet and recirculation zone axes. Results show a very rapid increase in NOx in the reaction zone which cannot be accounted for by O-atom radical overshoot. Post-flame zone NOx formation rates agree with the predictions of equilibrium theory. The relative contribution of “prompt NOx” to the final NOx levels increases with decreasing equivalence ratio. The rate of NOx formation in the reaction zone is found to be higher than in laminar flames. Turbulent transport processes are believed to be the dominant effect. NOx formation via nitrous oxide intermediate does not appear to be important under the present experimental conditions. Large amplitude temperature oscillations observed in turbulent premixed flames were found not to affect NOx formation rates.

ChemInform Abstract: SIMPLIFIED MATHEMATICAL MODEL SIMULATING HEAT TRANSFER IN GLASS‐FORMING MOLDS

AbstractDie Wärmeübertragung in für Glas benötigten Formen hängt von den Glaseigenschaften, den Wärmeübertragungskoeffizienten an den Grenzflächen Glas/ Form und Form/ Luft den Charakteristiken des Materials, aus dem die Form besteht, sowie von der Glas/Form‐Kontaktzeit ab.

Simplified Mathematical Model Simulating Heat Transfer in Glass‐Forming Molds

Heat transfer in glass‐forming operations depends on many factors, e.g. the properties of the glass, heat‐transfer coefficients at the glass/mold and mold/air interfaces, the characteristics of the mold material, and the glass/mold contact time. Using a computer model developed for one‐dimensional heat flow, the influences of these factors were calculated. The heat‐transfer parameters, which were analyzed individually, include e.g. the glass surface temperature, the peak inner mold surface temperature, the quantity of heat transferred from glass to mold during a steady‐state cycle, and the amplitude of mold surface temperature oscillation at steady state. Comments are given on the significance of the results.