Effect of an Anomalous Temperature Dependence of the Water Density on Circular Jet Propagation

It is shown experimentally that an originally circular jet with a temperature greater than 4°C transforms into a thin sheet when propagating in water at a temperature of about 0°C and sinks rather than ascends. At large times, a peculiar fine structure of the hydrophysical fields is detected. This is due to the difference between the molecular diffusivities of heat and dissolved salts, as well as the breakdown of large-scale to small-scale vortices.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, 2005, pp. 39–47.Original Russian Text Copyright © 2005 by Bukreev.     

Dependence of the stagnation temperature of a jet of gas containing solid particles on the concentration of particles and their velocity

This article gives the results of experiments on the measurement of the stagnation temperature of a two-phase jet, issuing from a nozzle. The experiments were made using a mixture of air and aluminum oxide (particle diameter 50) with a ratio of the mass flow rate of the solid phase to the mass flow rate of the gas equal to 0.3–2.5, and at initial temperatures of the mixture of 150–450°C. It follows from the results of the experiments that the stagnation temperature of a two-phase flow considerably exceeds the temperature of the mixture at the inlet of the nozzle.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 175–176, July–August, 1970.     

A comprehensive experimental study of the rheological behaviour of HDPE.

Extensional properties of four high density polyethylenes with different molecular weights and molecular weight distributions are presented. The samples have already been well characterized in shear and non-isothermal extensional flow. The data were collected at 180 °C for elongational rates between 3 · 10^–1 and 10^–4s^–1. Some qualitative and quantitative generalizations of the results are given.     

Effect of specimen temperature on the breaking point for splitting-off in AMG-6 aluminum alloy

The investigation of the temperature dependence of the strength of constructional materials under intense shock loads, including breaking loads, is of considerable practical interest. There are certain technical difficulties involved in loading the materials and making the required measurements in such experiments. Hence, the number of papers devoted to this problem is extremely limited. In [1, 2] data is given on the elastic-plastic properties of a number of metals at normal and high temperatures, obtained by investigating the parameters of elastic waves excited by an explosion. In [3, 4] investigations were carried out of the temperature dependence of the breaking point for splitting-off in steel and copper. In the present paper we investigate the effect of the specimen temperature on the breaking point for splitting off in widely used AMG-6 aluminum alloy in the temperature range from 0°C to 550°C, i.e., practically up to the temperature at which the alloy begins to melt.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 133–137, May–June, 1979.     

Experiments on the effect of low temperature on some plastic properties of metals

Summary The yield value, breaking strength, elongation and hardness of a number of pure polycrystalline metals were measured at room temperature and at –183°C. The yield value is always higher at –183°C than at 20°, the difference being relatively small (<75%) for the cubic facecentered and a number of hexagonal metals (e.g. Mg). This difference is large for the body-centered metals and for Zn, Cd and Sn. The former metals have a larger elongation at lower temperature, the latter, however, become more or less brittle at low temperature. The breaking strength and the hardness increase generally with decreasing temperature.This research was carried out during the war in the physics laboratory of the N.V. Philips, Eindhoven. The author resides now in Delft.     

Development of temperature-compensated resistance strain gages for use to 800°C

This paper describes the development and evaluation of temperature-compensated resistance strain gages for use to 800°C. These gages included single-element gages and double-element half-bridge gages. The filament of single-element gages was fabricated from specially developed Fe–Cr–Al–V–Ti–Y alloy wire. When bonded to high-temperature Ni-based alloy GH39 after stabilization at 800°C for one hour, the apparent strain from room temperature to 800°C was less than 2000 m/m. Double-element gages were fabricated from Pt–W–Re–Ni–Cr–Y alloy wire (active grid) and Pt–Ir alloy wire (compensating grid). When bonded to different high-temperature alloy specimens and stabilized, and when ballast resistance in series with the compensating grid adjusted suitably, the gages' apparent strains from room temperature to 800°C were less than 2400 m/m.Effects of preoxidization of Fe–Cr–Al wire on the characteristics of the single-element gages are described.     

An experimental study of the evaporation characteristics of emulsified liquid droplets

This paper presents the results of an experimental investigation, into the effect of water in diesel and kerosene emulsions, on the evaporation time of a single droplet, on hot surfaces (stainless-steel and aluminum). Experiments are performed at atmospheric pressure, and initial water volume concentrations of 10, 20, 30, and 40%. The wall temperatures ranging from 100–460 °C, to cover the entire spectrum of heat transfer characteristics from evaporation to film boiling. Results show that, qualitatively, the shapes of emulsion evaporation curves are very similar to that of pure liquids. Quantitavely, there are significant differences. The total evaporation time, for the emulsion droplets is lower than that for diesel and kerosene fuels, and decreased as water initial concentration increases, up to surface temperatures less than the critical temperature. The value of the critical surface temperature (maximum heat transfer rate), decreases as initial concentration of water increases. In the film-boiling region, the evaporation time for the emulsion droplets is higher than for diesel and kerosene droplets, at identical conditions.List of Symbols h_fg latent heat of vaporization, KJ/kg - m mass of the droplet, gm - T_b boiling temperature, °C - T_c critical temperature, °C - T_L Leidenfrost temperature, °C - T_s initial surface temperature of the hot surface, °C     

A cryostat for use with a thermal conductivity hot wire system

Summary A cryostat for use with a thermal conductivity hot wire system is described in which temperatures between –70°C and –130°C can be maintained constant to within (0.01°C). Control of temperature is made by adjusting the vacuum between a five component mixture and liquid oxygen. Extra control is made by adjusting the current through a heating coil immersed in the cryostat mixture. The temperature indicator is a platinum wire surrounding the tubes.     

Can die swell be predicted?

Summary A calculational scheme has been developed to predict die swell values which are defined as the value after completion of the elastic recovery. The constants of the equations have been evaluated at 190 °C from the known results of several polyethylene samples. With the similar type but different sample of polyethylene, it is shown that the prediction is with ±3.4% for the shear rates of 90 to 600 sec^–1, for the dies ofL/D 2–20 and at temperature of 200 °C.With 3 figures and 4 tables     

The peculiar rheo-optical behavior of bisphenol A-polycarbonate and polymethylmethacrylate

The rheological and stress-optical behavior of the melts of several grades ob bisphenol-A-polycarbonate (PC) and polymethylmethacrylate (PMMA) is investigated. Pertinent flow birefringence measurements are carried out in a remodelled cone-plate apparatus [1]. The shear stress in the polymer melt is calculated from the dynamic moduli, which are determined separately. It is shown that the linear stress optical rule is obeyed. In this way, the stress-optical coefficient C of the melt can be determined. The low-Mw polycarbonates all behave as Maxwellian fluids. The main stress direction does not deviate significantly from 45°. In the temperature range from 160° to 260°C the stress-optical coefficients of the different grades lie between 3 and 4×10^–9 Pa^–1 and show a weak temperature dependence. The stress-optical coefficient of PMMA is about a factor of 100 lower and shows a peculiar temperature-dependence, changing its sign at 144°C. The results are discussed in terms of the anisotropy of the polarizability of the polymer chain.     

Heat Transport in Unsaturated Zone Thermal Energy Storage – Analysis with Two-Phase and Single-Phase Models

We analyze a field experiment where ambient air is injected into the soil during the summer and extracted again during the winter. A multiphase model accounting for the conductive transport as well as the convective transport with the moving liquid and gas phases is used along with a more simplified single-phase model where the convective transport is due to the gas alone. The latter model also accounts for subzero wintertime temperatures. The multiphase model captures well both the seasonal variations and the actual test sequence, the main calibration being in the adjustment of medium permeabilities based on the observed pressure responses. The effect of the injection pump on the temperature and humidity of the injection air needs to be known accurately. Taking into account the humidity of the injection air explicitly instead of using humidity-corrected enthalpy values also has an effect. The effect of various humidity and specific enthalpy assumptions is of the order of 1–1.5°C, while ignoring the wintertime subzero temperatures has an effect of 1–2°C. These differences are of the same order of magnitude as the heterogeneity-introduced differences in field data. Using the simplified single-phase model typically appears to cause a difference of 1–2°C, but can yield an even higher deviation of the order of 3–4°C.     

Drilling fluid shear stress overshoot behavior

Shear stress overshoot behavior was studied in four drilling fluid systems and ten bentonite dispersions. These overshoot properties, also described by the American Petroleum Institute as gel strengths, were measured after gelation times of 10 s to 24 h at temperatures of 20–80 °C. Two different rheometers were used to measure overshoot behavior. Gel strength development with time followed a first-order model. Gel development rates at 20 °C varied from 0.005 to 0.01 min^–1 for drilling fluid systems and from 0.0004 to 0.02 min^–1 for bentonite dispersions. Increasing the gelation temperature for each drilling fluid system caused an increase in the gelling rate constant. Comparison of gel strengths in bentonite dispersions were made using a Fann 35 A viscometer and a Weissenberg Rheogoniometer. Higher gel strength values observed using the Rheogoniometer were believed to be due to differences in instrument spring stiffness and fixture inertia.     

Hot-wire calibration over a large temperature range

The hot-wire calibration method as proposed by Cimbala and Park (1990) has been showen to be accurate within a temperature range of 20–45°C. This is a significant extension of the range used by Cimbala and Park (27.5– 34.5°C). The accuracy of the calibration is not affected by the ambient temperature. The calibration curve obtained seems to hold over a long period of time, thus reducing the need for frequent calibrations. Due to contamination the accuracy eventually decreases and the probe has to be re-calibrated.     

Kerr constant of water

Measurements are conducted of the Kerr constant of ultrapure water with resistivity 10⁷ · cm. Values of the Kerr constant of (3.26 ± 0.10) · 10^-7 and (2.29 ± 0.07) · 10^-7 esu were obtained at a temperature of 30 °C for wavelengths of 441.6 nm and 632.8 nm.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 157–160, January–February, 1976.The authors wish to express their appreciation to D. D. Ryutov for useful discussion.     

Viscoelasticity of a surfactant and its drag-reducing ability

There is considerable interest in the use of viscoelastic cationic surfactant-counterion mixtures in district heating and cooling systems to reduce pressure losses. A recent field test in a secondary system near Prague showed a 30+% reduction in pumping energy requirements.We have studied a number of commercial surfactants and we report here results of rheological, drag reduction and turbulence measurements on Arquad 18–50 (octadecyl trimethyl ammonium chloride (AR 18)) with an excess of sodium salicylate (NA). The concentration studied was 1.6 mM AR 18 and 4.0 mM NA which is about one third the concentration for excellent drag reduction in this surfactant's effective temperature range 30–90°C.Viscosity, , vs. shear rate,D, first normal stress difference,N ₁, vs. shear rate, drag reduction (as pressure drop,i=P/1) vs. average velocity,U _ave, in a 39.4 mm tube for AR 18, and turbulence intensity data for three drag reducing surfactants are reported.Of particular interest are the generally low turbulence intensities in all three directions which correspond to reduced heat, mass and momentum transfer rates compared to water, and the existence of large normal stress differences at 20°C for AR 18, a temperature at which no drag reduction occurs with this surfactant, indicating that normal stress effects do not correlate directly with drag reduction.The effect of time of pumping on increasing drag reduction demonstrates that this factor overwhelms the expected increase in drag reduction as temperature is raised from 18–19°C to 40.5°C.     

High-temperature pressure-shear plate impact experiments using pure tungsten carbide impactors

The pressure-shear plate impact experiment has been modified to test materials at high temperatures (up to 700°C). Together with the high strain rates characteristic of this experiment (10⁶ s^–1), the high-temperature capability allows the shearing resistance of materials to be measured under conditions unattainable with other testing equipment. The compressive and shear responses of pure tungsten carbide at different temperatures are presented, as well as the results of one test on OFHC copper at a temperature of 691°C and a shear strain rate of 1.4×10⁶ s^–1.     

A torsional creep instrument and a torsional pendulum,both with accurate temperature control

Summary This paper describes a torsional pendulum and a torsional creep instrument. With the pendulum shear moduli between 10⁶ and 10¹⁰ N/m² can be measured at frequencies from 0.1 to 20 Hz. The creep instrument is suitable for measurement of shear compliances lower than 10^–7 m²/N in the time range from 1 to 10⁵ seconds. In both instruments, specimens are kept at the right temperature by blowing heated nitrogen gas through a surrounding thermostatic chamber. The signal of a platinum resistance thermometer, provided in each chamber, automatically controls the heating of the gas. Temperatures from –180 to +300 °C can be maintained with an absolute accuracy of ±1 °C and a long term stability of ±0.05 °C. It is shown that one cannot directly compare one and the same shear property, calculated from the shear modulus as measured with the pendulum as well as from the shear compliance as measured with the creep instrument. This is due to differences in the temperature of one thermostatic chamber over against the other. Finally, the paper presents a method to reduce these differences to ±0.1 °C, although the absolute accuracy of temperature control remains ±1 °C.

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Zusammenfassung Die Arbeit beschreibt ein Torsionspendel und eine Torsions-Kriechapparatur. Mit dem Pendel können Schermoduli zwischen 10⁶ und 10¹⁰ N/m² bei Frequenzen zwischen 0,1 und 20 °C gemessen werden. Die Kriechapparatur ist geeignet für die Messung von Scherkomplianzen kleiner als 10^–7 m²/N in Zeiten zwischen 1 bis 10⁵ sec. In beiden Geräten werden die Proben durch das Einblasen von erhitztem Stickstoff durch eine umgebende thermostatische Kammer bei der richtigen Temperatur gehalten. Die Anzeige eines Platin-Widerstandsthermometers, das in jeder Kammer angebracht ist, kontrolliert automatisch die Erwärmung des Gases. Es können Temperaturen zwischen –180 und +300 °C mit einer absoluten Genauigkeit von ±1 °C und einer Langzeitstabilität von ±0,05 °C eingestellt werden. Es wird gezeigt, daß ein direkter Vergleich der gleichen Schereigenschaft, die zum einen aus dem mit dem Pendel gemessenen Schermodul und zum anderen aus der mit der Kriechapparatur ermittelten Kriechkomplianz errechnet wird, nicht möglich ist. Das beruht auf Temperaturdifferenzen zwischen den thermostatisierten Kammern.Abschließend stellt die Arbeit eine Methode vor, um diese Differenzen auf ±0,1 °C zu senken. Die absolute Genauigkeit der Temperaturkontrolle bleibt bei ±1 °C.

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Paper presented at the Conference on Experimental Rheology, University of Bradford, April 17–19, 1968.     

Elevated temperature testing with the torsional split hopkinson bar

The torsional split-Hopkinson-bar technique is modified for high-strain-rate testing at elevated temperatures by heating the specimen rapidly and keeping the rest of the apparatus at room temperature. Tests have been conducted with specimens made of several materials (Haynes-188, 1020 steel, and 1151 steel) at temperatures ranging from 650°C to 1060°C and strain rates on the order of 1000 s^–1.     

Hydrodynamics and boiling phenomena of water droplets impinging on hot solid

The collision of single water droplets with a hot Inconel 625 alloy surface was investigated by a two-directional flash photography technique using two digital still cameras and three flash units. The experiments were conducted under the following conditions: the pre-impact diameters of the droplets ranged from 0.53 to 0.60 mm, the impact velocities ranged from 1.7 m/s to 4.1 m/s, and the solid surface temperatures ranged from 170 °C to 500 °C. When a droplet impacted onto the solid at a temperature of 170 °C, weak boiling was observed at the liquid/solid interface. At temperatures of 200 or 300 °C, numerous vapor bubbles were formed. Numerous secondary droplets then jetted upward from the deforming droplet due to the blowout of the vapor bubbles into the atmosphere. No secondary droplets were observed for a surface temperature of 500 °C at the low-impact Weber numbers (∼30) associated with the impact inertia of the droplets. Experiments using 2.5-mm-diameter droplets were also conducted. The dimensionless collision behaviors of large and small droplets were compared under the same Weber number conditions. At temperatures of less than or equal to 300 °C, the blowout of vapor bubbles occurred at early stages for a large droplet. At a surface temperature of 500 °C, the two dimensionless deformation behaviors of the droplets were very similar to each other.     

A new transient method for analysis of solidification in the continuous casting of metals

Solidification processes involve complex heat and mass transfer phenomena, the modelling of which requires state-of-the art numerical techniques. An efficient and accurate transient numerical method is proposed for the analysis of phase change problems. This method combines both the enthalpy and the enhanced specific heat approaches in incorporating the effects of latent heat released due to phase change. The sensitivity and accuracy of the proposed method to both temporal and spatial discretization is shown together with closed-form solutions and the results from the enhanced specific heat approach. In order to explore the proposed method fully, a non-linear heat release, as is the case for binary alloys, is also examined. The number of operations required for the new transient approach is less than or equal to the enhanced heat capacity method depending on the averaging method adopted. To demonstrate the potential of this new finite-element technique, measurements obtained on operating machines for the casting of zinc, aluminum and steel are compared with the model predictions. The death/birth technique, together with the proper heat-transfer coefficients, were employed in order to model the casting process with minimal error due to the modelling itself.Nomenclature [A] conductance matrix - [B] matrix containing the derivative of the element shape functions - c, C _p specific heat (J kg^–1°C^–1) - effective specific heat (J kg^–1°C^–1) - f(T) local liquid fraction - f thermal load vector - H enthalpy (J kg^–1) - [H] capacitance matrix - h, h _r,h _c heat transfer coefficient (W m^–2°C^–1) - K thermal conductivity (W m^–1°C^–1) - L latent heat of solidification (J kg^–1) - l overall length (m) - N _i shape functions - Q rate of heat generation per unit volume (J m^–3) - q heat flux (W m^–2) - R residual temperature (°C) - T temperature (°C) - T _s solidus temperature (°C) - T _l liquidus temperature (°C) - T _pouring pouring temperature (°C) - T _top temperature at the top of the mould (°C) - T _w temperature of the water spray (°C) - approximated temperature (°C) - T surrounding temperature (°C) - cooling rate (°C/s) - t time (seconds) - x _i,x, y, z spatial variables (m) - t time step (s) - x element size (m) - diffusivity (m²s^–1) - density (kg m^–3) - time marching parameter - _n direction cosines of the unit outward normal to the boundary