Uniform Temperature Region Research Articles

Self-sustained movement of condensate drop on uniform temperature surface during Marangoni dropwise condensation

During the condensation of some binary vapor mixtures so-called ‘positive system’, in which the more volatile component has the higher surface tension (e.g., water–ethanol), Marangoni dropwise condensation occurs owing to the temperature-induced local concentration and surface tension instability. It was found that the spontaneous movement of condensate drops occurred from the low- to high-temperature side of the heat transfer surface due to the concentration and surface tension difference around the drops, which are induced by the bulk temperature gradient. In this study, it was newly discovered that the spontaneous movement of condensate drops could be ‘self-sustained’ even without the presence of a bulk temperature gradient on the heat transfer surface. By applying the neighboring temperature gradient region and uniform temperature region on the condensing surface, two different modes of drop behaviors were observed during the experiments: (1) For the condensate drops with notable initial velocities in the temperature gradient region, the spontaneous movement was sustained in the uniform temperature region; (2) for the condensate drops initially formed in the uniform temperature region, the spontaneous movement did not occur owing to the lack of initial velocity. The reason for self-sustained movement of condensate drops can thus be inferred to be the presence of a self-formed temperature gradient around the moving condensate drops.

Proposal of novel structure for wide wavelength tuning in distributed Bragg reflector laser diode with single grating mirror

We report a novel structure that is capable of wide wavelength tuning in the distributed Bragg reflector laser diode (DBR-LD) with a single grating mirror. This device's DBR section has two tuning elements, plasma, and heater tunings, which are implemented simultaneously on the top of a single waveguide by using an in-between dielectric layer. For the proposed structure, a three-dimensional thermal simulation was conducted. The results showed that the temperature profile within the waveguide is highly affected by the position of heater metal and thermal conductivity of the p-cladding layer. As a result, it is important to use a uniform temperature region in the DBR section for a wide tuning range and stable single-mode operation. For a 550-μm long DBR-LD with a 250-μm long DBR section, a tuning range of 26 nm (i.e., 7 nm for plasma tuning and 19 nm for heater tuning); an SMSR of more than 45 dB; and a peak power variation of less than ± 2.5 dB were obtained. From the comparisons of two DBR-LDs with only one tuning element, we confirmed that using the dielectric layer is a very effective way of achieving a wide tuning under the independent tuning operation.

Detonation onset in a thermally stratified constant volume reactor

Understanding detonation development from a flame kernel initiated by a pre-ignition event is important for modern internal combustion (IC) engines operating at boosted conditions. To provide fundamental insights into the effects of bulk gas temperature stratification on the characteristics of detonation development, one-dimensional high fidelity simulations were conducted for a constant volume reactor filled with a thermally stratified reactive stoichiometric hydrogen/air mixture. A linear temperature variation in the upstream end-gas was introduced to represent the thermal stratification of the bulk mixture, and the evolution from the initial deflagration flame front to detonation development was examined. The results showed that the bulk-gas temperature gradient has a significant effect on the run-up time and intensity of the developing detonation. Detailed analyses further revealed that the mechanism of detonation development is qualitatively different for the positive and negative temperature gradient cases. In the former, the detonation development is initiated by the end-gas autoignition at the wall, while the latter exhibits detonation development following the process of the self-acceleration of the flame similar to the deflagration-to-detonation transition. This behavior is attributed to the longer residence time in the end-gas allowing the reinforcement by the interaction of incident and reflected pressure waves during the flame propagation, and results in the peak pressure even higher than the case with the same level of positive temperature gradient. Furthermore, yet another detonation development pattern was observed for the negative temperature gradient condition in the presence of a uniform temperature region just ahead of the flame. In this case, autoignition was found to start in the middle of the bulk end-gas, and subsequently leads to the transition to detonation. The results demonstrate the importance of the bulk gas conditions in predicting the detonation development, which corroborate the existing theoretical framework.

Determining thermal stratification in rooms with high supply momentum

Computational Fluid Dynamics simulations of a typical occupied office were performed to study the effects of ventilation parameters (supply momentum and heat gain intensity) and inlet geometry (height and area of the supply) on the temperature profile of the air in the space. A knowledge of this profile is critical to ensure that the occupants are comfortable according to commonly used standards. Different room configurations were characterized in terms of their Archimedes number, which compares the effects of buoyancy and supply momentum, and dimensionless geometric variables. A high Archimedes space was found to be divided into a warm region of uniform temperature above the occupants and a zone where the temperature increases approximately linearly with height. In a low Archimedes space the air is mixed by the supply jet in the lower part of the room, especially near the outlet, resulting in this area having uniform temperature. However, the supply jet was found to be less efficient at mixing the air near the ceiling, resulting in higher temperatures in this zone than with higher Archimedes numbers. For a given Archimedes number, as the supply area increased, the air temperature was found to decrease in the lower part of the room but to increase near the ceiling. A high inlet increased the vertical mixing in the room. Correlations were proposed to establish the temperature profile within 5% of the temperature rise of the room. The inputs of the correlations are readily available in multi-zone software, facilitating their integration in this kind of software. The proposed correlations will allow the user of the multi-zone software to evaluate comfort conditions more accurately, while maintaining the high speed, simplicity and design flexibility of the multi-zone models.

Characteristics of heat transfer and flow of Al2O3/water nanofluid in a spiral-coil tube for turbulent pulsating flow

In the past two decades, enhancement of heat transfer characteristics of original fluid using nanofluids has been proposed by a large number of researchers. In this paper, an experimental study was carried out to investigate effect of pulsation on heat transfer of fluid flow inside a spiral-coil tube. In order to perform the experiments, a hot water reservoir tank was prepared and the spiral-coil was immersed horizontally inside the tank. Average temperature of the hot water bath was kept constant at 60 °C to establish a quiescent region of uniform temperature. The experiments were conducted in turbulent flow regime using distilled water and Al2O3/water nanofluid at 0.5, 1, and 1.5 % particle volume concentration. Results showed that overall heat transfer coefficient of the base fluid flow increases by using nanofluid or pulsation into the base fluid flow up to 14 %. Heat transfer results also indicated that combination of the nanofluid and the pulsation into the fluid flow can increase significantly the overall heat transfer coefficient up to 23 %.

Conduction heating of boron alloyed steel in application for hot stamping

In traditional hot stamping process, heating of the sheet by radiation heating occupies most of cycle time, which limits the application of hot stamping in automotive industry. Thus a faster heating method has great significance on the hot stamping. The conduction heating overcomes shortage of the radiation heating because of higher heating rate and greater energy efficiency. It attracts increasing attention in the application of heating blanks in hot stamping. In the present study, a movable conduction heating device on die was designed in terms of the Joule’s Law. Heating experiments of boron alloyed steel were performed using the developed device. Heating rate and uniform temperature region were investigated in the non-heat preservation condition (NHPC) and the heat preservation condition (HPC). The results revealed that in the HPC, the heating rate was improved by 13.1 °C/s. In addition, the length of the uniform temperature region was lengthened by 15 mm. It was demonstrated that the HPC was preferred. Furthermore, it was indicated that the mechanical properties of the blanks in uniform temperature region of the conduction heating were also superior to that of the radiation heating.

Experimental Study on Conduction Heating of Ultra-High Strength Boron Steel

Conduction heating overcomes the shortage of the furnace, due to rapid heating and high energy efficiency. The heating experiment of ultra-high strength boron steel (LG1500HS) of a rectangular blank was implemented on the conduction heating system. The variations of the average temperature rising rate, uniform temperature region and energy efficiency were investigated under the non-heating-retaining condition. The results show that the average temperature rising rate, uniform temperature region and energy efficiency are 44.5°C/s, 225 mm and 71.6%, respectively.

Experimental investigation of thermal loading of a horizontal thin plate using infrared camera

This study reports the results of experimental investigations of the characteristics of thermal loading of a thin plate by discrete radiative heat sources. The carbon–steel thin plate is horizontally located above the heat sources. Temperature distribution of the plate is measured using an infrared camera. The effects of various parameters, such as the Rayleigh number, from 107 to 1011, the aspect ratio, from 0.05 to 0.2, the distance ratio, from 0.05 to 0.2, the number of heaters, from 1 to 24, the thickness ratio, from 0.003 to 0.005, and the thermal radiative emissivity, from 0.567 to 0.889 on the maximum temperature and the length of uniform temperature region on a thin plate are explored. The results indicate that the most effective parameters on the order of impact on the maximum temperature is Rayleigh number, the number of heat sources, the distance ratio, the aspect ratio, the surface emissivity, and the plate thickness ratio. Finally, the results demonstrated that there is an optimal distance ratio to maximize the region of uniform temperature on the plate.

Numerical Simulation of Intermediate Frequency Induced Heating Steel Plate with Finite Element Method

The FEM simulation is used to study the intermediate frequency induced heating process. The temperature distributions and temperature differences are obtained by two kind frequencies of 500 and 1000Hz. It is found that, in this simulation condition, the length of uniform temperature region is about three times of the coil height. It is obvious that, no matter which frequency, the heating rate is very high. With the process of 1000Hz, in less than 20 seconds, the heating temperature can reach a reasonable temperature, and with a process of 500Hz, the temperature can reach a reasonable temperature in more than 40 seconds. It is recommended that the frequency between 500 to 1000Hz could be available for a practical use.

Perturbed Rankine vortices in surface quasi-geostrophic dynamics

An analytical dispersion relation is derived for linear perturbations to a Rankine vortex governed by surface quasi-geostrophic dynamics. Such a Rankine vortex is a circular region of uniform anomalous surface temperature evolving under quasi-geostrophic dynamics with uniform interior potential vorticity. The dispersion relation is analysed in detail and compared to the more familiar dispersion relation for a perturbed Rankine vortex governed by the Euler equations. The results are successfully verified against numerical simulations of the full equations. The dispersion relation is relevant to problems including wave propagation on surface temperature fronts and the stability of vortices in quasi-geostrophic turbulence.

Experimental Validation of Analytical Solutions for Vertical Flat Plate of Finite Thickness Under Natural-Convection Cooling

The analytical solution for a vertical heated plate subjected to conjugate heat transfer due to natural convection at the surface and conduction below is presented. The heated surface is split into two regions; the uniform heat flux region toward upstream and remaining fraction as the uniform wall temperature region. The fractional areas under the two regions are considered variable. Adopting thermally thin wall regime approximation, the possible solutions were investigated and found to satisfactorily deal with longitudinal conduction and temperature variation in the transverse direction. A test setup was developed and the experiments were conducted to obtain relevant data for comparison with the analytical solutions. The ranges for Rayleigh number and heat conduction parameter (α) during various test conditions were 2×108–6×108, and 0.001–1, respectively. The limiting solutions for stipulated conditions are analyzed and compared with experimental data. Reasonable agreement is observed between the experimental and analytical results.

Molecular filtered Rayleigh scattering applied to combustion

Molecular filtered Rayleigh scattering (FRS), employing an iodinevapour filter and an injection-seeded Nd:YAG laser, was utilized to measureinstantaneous and average temperature fields in combustion environments. WithFRS thermometry, the vapour within the cell strongly absorbs backgroundscattering from surfaces and particles, while much of the Doppler-broadenedRayleigh scattering is not absorbed by the iodine transition; the gastemperature can then be deduced from the measured transmission of themolecular Rayleigh scattering. For demonstration purposes and to evaluate theaccuracy of the technique, we employed a near-adiabatic hydrogen-air flame.The accuracy of the FRS measurements was investigated by comparing FRS-derivedtemperatures with those (1) calculated assuming adiabatic equilibriumconditions and (2) recorded with the CARS (coherent anti-Stokes Ramanspectroscopy) technique. For the hydrogen-air flames, the FRS method gavetemperatures within 2% of the expected value. The FRS thermometry instrumentwas then applied to a stagnation-flow, premixed methane-air flame; imagesrecorded here demonstrate the utility of the FRS method for temperatureimaging, particularly near surfaces. In this flow field, we compared the FRStemperatures with those from a one-dimensional model and investigated theradial extent of the uniform temperature region, to assess the assumption ofone-dimensionality. In addition, we demonstrated the feasibility ofsimultaneous measurements of the temperature and velocity fields, the latterderived from the particle image velocimetry technique.

A thermoelectric scanning facility for the study of elemental thermocouples

A scanning facility for studying the thermoelectric behaviour of the metals used in elemental thermocouples (Au, Pt and Pd) is described. The facility effectively measured changes in Seebeck coefficient along a 560 mm length of each of three wires, relative to a fourth, by moving them through a 50 mm long, EMF-producing zone into a uniform-temperature region at 250 °C. The uniform region was stable to within 0.7 mK and EMF measurements were made to 10 nV (equivalent to about 1 mK). Accordingly, the facility is able to detect changes of ~10 ppm in Seebeck coefficient. The precautions necessary to work at this accuracy are detailed and preliminary data on the changes that occur at temperatures up to 1000 °C are reported. For example, the measured Seebeck coefficient of Pd decreased at temperatures in the range 550 to 850 °C, a change opposite in sign to that previously reported.

A new combined deep-body-temperature/NIRs probe for noninvasive metabolic measurements on human skeletal muscle.

Temperature modulates tissue metabolism through thermodynamic phenomena, e.g. changes in enzymatic activities, pH variations, etc. In humans, temperature changes may be induced by stressful environmental conditions (e.g. immersion in cold water, etc.) or, artificially, during therapeutic procedures (extracorporeal circulation, cancer treatment using hyperthermia, etc.). Moreover, temperature distribution is not uniform in the body. In a forearm immersed in cold water at 20°C, it is possible to observe radial gradient values reaching 2°C/cm (Ducharme et al., 1991). Thus, the measurement of total tissue metabolism often results from the contribution of several subsets of tissue exposed to different temperatures, making the interpretation of the data sometimes difficult. In this context, the aim of the present study was to develop a non-in-vasive probe allowing one to simultaneously: 1) establish in a human skeletal muscle a region of uniform temperature; 2) measure the temperature; 3) measure the oxidative metabolism in the corresponding region.KeywordsHuman Skeletal MuscleNear Infrared SpectroscopyTissue Water ContentDeep Body TemperatureMuscular TemperatureThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Propagation of plastic waves in a long rod with consideration given to temperature rise

The strain and temperature distributions along a long rod subjected to a longitudinal impact at a high strain level are investigated using Malvern's linear strain-rate dependent theory with consideration being given to the temperature rise caused by the plastic work. The results show that a steeply decreasing part of strain appears near the impacted end and the region is followed by an uniform-strain (strain-plateau) one along the rod, and that the formation and growth of the uniform-strain region depends on the strain-hardening sensitivity of the rod. The computed profile of the temperature distribution is similar to that of the strain distribution. However, the growth of a uniform-temperature region (temperature plateau) is much slower that that of the strain plateau.

ChemInform Abstract: REEXAMINATION OF SOME ASPECTS OF THERMAL OXIDATION OF SILICON

AbstractEs wird über den Wasserdampfdruck und den Einfluß von Na‐Verunreinigungen auf die Oxidationsgeschwindigkeit von Si bei 1000 und 1230°C berichtet.

Reexamination of Some Aspects of Thermal Oxidation of Silicon

This paper reports a study of the water vapor pressure and low level sodium impurity dependence of the oxidation rate of silicon at 1000° and 1230° C. The oxidation studies were carried out in an rf heated cold wall oxidizer which is also described. The important aspect of the oxidizer is that the sample is placed between two closely spaced silicon blocks to give a very uniform temperature region and therefore uniform oxide properties. It is shown that the oxidation rate coefficient (in the parabolic range) increases monotonically with water vapor pressure. However, the rate also shows some dependence on the other gas phase constituents. At constant partial pressure the parabolic rate constant increases, going from mixture to pure (vacuum) or mixture. For sodium concentrations in the range 0.4–10 ppm (atomic) in the water vapor atmosphere no changes in oxidation rate were observed at 1000° or at 1230° C.

Thermal Neutron Flux in a Cell with Temperature Discontinuities

In calculations of thermal neutron flux, the interpretation of lattice measurements, in which the part of the lattice being studied is held at elevated temperature, is complicated by uncertainties as to the width of the transition region caused by the temperature discontinuity. As an altemative to a straightforward multigroup approach to the solution of the problem, a method wae developed which employs the formalism of few-group theory while retaining the qualitative features of neutron distribution in space and energy. The basic procedure is to approximate the actual neutron distribution by a superposition of overlapping thermal groups, one in eqtilibrium with each region of uniform temperature in the system. Neutrons in the nonequilibrium groups will then make transitions into the local equilibrium group at a rate that can be easily calculated. (M.C.G.)