Measurement of coatings' elastic properties by mechanical methods: Part 2. Application to thermal barrier coatings

Elastic properties of a thermal barrier ceramic coating composed of an NiCoCrAIY bond coat and a ZrO₂(Y₂O₃) top coat were measured by a four-point bending rig in the temperature range 20°C–900°C. Different types of specimens (i.e., with bond coat only or with bond coat and top coat, on one side or on both sides) were employed. Test procedures were based on the theory discussed in Part 1 to enhance accuracy and to estimate confidence intervals. In particular, the method employed at high temperature was calibrated at room temperature by comparing the results with those obtained by methods with low sensitivity to layer thicknesses. For the bond coat, Young's modulus was found to be temperature independent up to about 500°C; a decreasing trend was observed above this temperature. For the top coat, a slightly temperature range examined. A possible explanation is given on the basis of phase transformation and the microstructure of the two layers. At room temperature, Poisson's ratio for the bond coat was found to be near 0.3, whereas a near zero value was measured for the top coat.     

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     

Neue Bestimmung des kritischen Punktes von leichtem und schwerem Wasser

Zusammenfassung Im Rahmen der internationalen Wasserdampfforschung [1, 2, 3] wurden in den letzten Jahren genaue Messungen verschiedener Zustandsgrößen von leichtem und teilweise auch von schwerem Wasser vorgenommen. In diesem Zusammenhang war auch die Kenntnis genauerer Werte für die kritischen Zustandsgrößen von großem Interesse.In einer zylindrischen, waagerecht liegenden Druckkammer mit durchsichtigen Beobachtungsfenstern wurden beim langsamen Durchlaufen des kritischen Punktes mit sehr geringfügigen Temperaturänderungen von 0,01 bis 0,03 °C/h fortlaufend Temperaturen und Drücke gemessen. Gleichzeitig wurde die Phasentrennfläche zwischen Flüssigkeit und Dampf beobachtet, die beim Durchlaufen des kritischen Zustandes in einem sehr kleinen Temperatur- und Druckbereich verschwindet bzw. wiedererscheint.Es ergaben sich folgende Werte für die kritischen Temperaturen und Drücke von H₂O und D₂O: H₂O t_krit=(373,91±0,03) °C P_krit=(220,45±0,03) bar D₂O t_krit=(370,66±0,03) °C P_krit=(216,59±0,03) bar.Die Temperaturangaben beziehen sich auf die Internationale Praktische Temperaturskala von 1948.

---

New determination of the critical point of water and heavy water

The apparatus used for determining the critical data of water and heavy water consists in principle of a horizontal cylindrical pressure chamber of INCONEL X-750. Observation windows of synthetic saphire (Al₂O₃) are located at the ends.During the experiments the critical point was passed with very small rates of temperature change of about 0.01 to 0.03 °C/h. The disappearance and appearance of the meniscus could be observed continuously with a telescope enlarging 10 times, with simultaneous measurement of pressure and temperature.The following results were obtained for the critical temperature and critical pressure of H₂O and D₂O: H₂O t_crit=(373.91±0.03) °C P_crit=(220.45±0.03) bar D₂O t_crit=(370.66±0.03) °C P_crit=(216.59±0.03) bar.These temperatures are related to the International Practical Temperature Scale of 1948.

---

---

Über diese Arbeit wurde auf dem VDI-Thermodynamik-Kolloquium 1967 in Bad Neuenahr berichtet.     

Free convection effects on the oscillatory flow of water at 4° C. past an infinite vertical,porous plate with constant suction

An analysis of a two-dimensional flow of water at 4 °C past an infinite vertical, porous plate is presented under the following conditions — i) suction velocity normal to the plate is constant, ii) the free stream oscillates in time about a constant mean, iii) the plate temperature is constant, iv) the difference between the temperature of the plate and the free stream is moderately large causing free convection currents. — Approximate solutions to coupled non-linear equations are derived for the mean velocity, the mean temperature, the mean skin-friction, the mean rate of heat transfer, the transient velocity and the transient temperature, the amplitude and the phase of the skin-friction and the rate of heat transfer. The mean flow of water at 4 °C is compared with that of water at 20 °C in a quantitative manner for both G >0 (cooling of the plate) and G < 0 (heating of the plate). — It is observed that owing to a fall in the temperature of the water from 20 °C to 4 ° C, there is a fall in the mean skin-friction when the plate is being cooled by the free convection currents, and a rise in the mean skin-friction when the plate is being heated by the free convection currents. The amplitude of the skin-friction, for water at 4°C, remains the same for both G > <0 whereas greater cooling of the plate causes a rise in the amplitude of the rate of heat transfer ¦Q ¦ /E and greater heating of the plate causes a fall in ¦ Q ¦ /E.

---

Zusammenfassung Die zweidimensionale Stromung von Wasser bei 4 °C an einer unendlichen senkrechten Wand wird unter folgenden Bedingungen untersucht: 1) konstante Absauggeschwindigkeit normal zur Wand, 2) zeitliche Schwankungen der Freistromgeschwindigkeit um einen Mittelwert, 3) konstante Wandtemperatur, 4) mäßige Temperaturdifferenz zwischen Platte und Freistrom zur Erzeugung freier Konvektion. — Näherungslösungen der gekoppelten nichtlinearen Gleichungen sind abgeleitet für die mittlere Geschwindigkeit, die mittlere Temperatur, die mittlere Wandreibung, die mittlere Wärmeübertragung, die nichtstationäre Geschwindigkeit und Temperatur und die Amplitude und Phase der Wandreibung und der Warmeübertragung. Die Strömung von Wasser bei 4°C is quantitativ verglichen mit der bei 20°C für G > 0 (Kühlung der Platte) und G < 0 (Heizung der Platte). — Erniedrigung der Temperatur von 20°C auf 4°C ergibt geringere Wandreibung bei Kühlung und höhere Wandreibung bei Heizung der Platte. Für Wasser von 4°C bleibt die Amplitude der Wandreibung für G < 0 gleich; stärkere Kühlung ergibt einen Anstieg in der Amplitude der Warmeübertragung ¦Q¦/E, starkere Heizung einen Abfall in ¦q¦/E.

---

Nomenclature ¦B¦ amplitude of the skin-friction - C_p specific heat at constant pressure - E Eckert numer {U ₀ ² /c_p(T'_w–T')} - g_x acceleration due to gravity - G Grashoff number {vg_x(T'_w–T')/u₀v ₀ ² } - k thermal conductivity - M_r, M_i fluctuating parts of the velocity profile - P Prandtl number,c _p /k - p pressure - q' rate of heat transfer - ¦Q¦ amplitude of the rate of heat transfer - t' time - T' temperature of fluid - T'_w temperature of the plate - T' temperature of the fluid in the free-stream - T_r,T_i fluctuating parts of the temperature profile - u',v' velocity components in the X8,y' directions - U' free stream velocity - U₀ amplitude of free stream fluctuations - u₀ mean velocity - v₀ suction velocity - x', y' coordinate system - ' frequency of free stream oscillations - non-dimensional frequency,'/vsk0/2 - ' skin-friction - ₀ mean tempeature - ₁ amplitude of the temperature fluctuations - phase angle of the skin-friction - ₁ coefficient of volume expansion - ' density of fluid in the boundary layer - ' density of fluid in the free-stream - viscosity     

Two-phase frictional pressure drop multipliers for SUVA R-134a flowing in a rectangular duct

The adiabatic two-phase frictional multipliers for SUVA, R-134a flowing in a rectangular duct (with D_H = 4.8 mm) have been measured for three nominal system pressures (0.9 MPa, T_sat = 35.5 °C; 1.38 MPa, T_sat = 51.8 °C; and 2.41 MPa, T_sat = 75.9 °C) and three nominal mass fluxes (510, 1020 and 2040 kg/m²/s). The data is compared with several classical correlations to assess their predictive capabilities. The Lockhart–Martinelli model gives reasonable results at the lowest pressure and mass flux, near the operating range of most refrigeration systems, but gives increasingly poor comparisons as the pressure and mass flux are increased. The Chisholm B-coefficient model is found to best predict the data over the entire range of test conditions; however, there is significant disagreement at the highest pressure tested (with the model over predicting the data upwards of 100% for some cases). The data shows an increased tendency toward homogeneous flow as the pressure and flow rate are increased, and in fact the homogeneous model best predicts the bulk of the data at the highest pressure tested.     

Experimental investigation of heat conduction in polyester-Al2O3 and polyester-CuO nanocomposites

This paper presents an experimental analysis of the thermal conductivity of nanocomposite systems composed of unsaturated polyester resin (UPR) as matrices and two different metal-oxides nanoparticles as fillers: alumina (aluminum oxide) and tenorite (copper oxide). The nanoparticles used were alpha-Al₂O₃ (30-40 nm) and CuO (30-50 nm). Samples were fabricated using simple molding and homogenization using magnetic stirring. Thermal conductivities were measured using a device that complies with ASTM norms C518-04 and E1530-06. Measurements were taken at three different temperatures (0 °C, 25 °C and 50 °C), for different sets of samples, varying the nanoparticle fraction used in composite systems. Finally, the experimental data are compared with traditional models for predicting the thermal conductivity of composite materials, showing that the traditional models underestimate the measured values.     

Incipient behaviour of gelatin gels

The present work describes isothermal (25°C) gelation measurements for gelatin gels over a range of concentrations. Methods for the estimation of the gel time are discussed, and data compared with two recent models. The isothermal time growth of modulus is also investigated, and the superposition of such data discussed. For concentrations close to the critical gel concentration C ₀ there are significant deviations in the latter case. These may be related to the approach to the biphasic region of the phase diagram suggested by other workers.     

Measurement of the first normal-stress difference at high shear rates for a polyisobutylene/decalin solution “D2”

Reasonable agreement is found between values of the first normal-stress differenceN ₁ for samples of D2, a polyisobutylene/decalin solution, measured in steady shear flow using three different instruments: a Weissenberg Rheogoniometer (a cone-plate rotational rheometer), a Torsional Balance (plate-plate rotational) Rheometer, and a Stressmeter (a transverse-slot slit-die rheometer). Viscosity values are also in reasonable agreement. Ranges of variables common to at least two rheometers include values of shear stress up to 3,700 Pa and shear rate up to 20,700 s^–1 near 25 °C. The agreement supports the approximate validity of the semi-empirical HPBL equation used to calculateN ₁ from Stressmeter data over a range of shear rates up to 20,700 s^–1 near 25 °C. Time-temperature superposition behavior exhibited by Stressmeter data at temperatures in the range 21 °C to 111 °C suggest that the range of validity of the Stressmeter method for determiningN ₁ approximately may extend up to shear rates of 290,000 s^–1 at 111 °C.     

FEM application in phase change exchangers

Application of FEM in the analysis of condenser and vaporizer has been illustrated taking into account property variation with temperature. Accurate shell side pressure drop in a condenser has been determined by the present method taking into account the gradual reduction in vapour flow due to condensation from inlet to outlet. As the present method analyses the exchanger in small elements, analysis of an evaporator working under the conditions of partial vapour blanketing is also possible.

---

Anwendung der Finite Elemente Methode bei Wärmetauschern mit Phasenwechsel

Zusammenfassung Die Verwendung der Finite Elemente Methode zur Berechnung von Kondensator und Verdampfer unter Berücksichtigung von temperaturabhängigen Stoffwerten ist hier dargestellt worden. Mit dem dargestellten Verfahren ist der genaue Druckverlust im Rohrraum eines Kondensators bestimmt worden, wobei die schrittweise Verminderung der Dampfströmung aufgrund der Kondensation von Ein-zu Auslaß mit berücksichtigt wurde. Mit der gegenwärtigen Methode, die einen Wärmeaustausch mittels kleiner Elemente berechnet, ist ebenso eine Auslegung eines Verdampfers mit einer partiellen Dampfabdeckung möglich.

---

Nomenclature A heat transfer area in an elment upto any section, m² - A _c elemental heat transfer area, m² - B weightage - C UA/2 - D _e characteristic dimension, m - D _s shell diameter, cm - F _t temperature correction factor - f friction factor, m²/cm² - G mass velocity, kg/m² sec - G W/LN ^2/3 - g acceleration of gravity, m/sec² - h condensing coefficient, W/m²°C - h ₀ boiling coefficient, W/m²°C - k ₁ thermal conductivity of condensate atT _f , W/m°C - L length of tubes in the element, m - l distance of the fluid stream traverses in the element, m - LMTD log mean temperature difference, °C - N ₁,N ₂ shape functions - N _t number of tubes effective for condensation - P pressure drop, N/cm² - P _shell shell side vapour pressure drop, N/cm² - P _tube tube side stream pressure drop, N/cm² - q heat flux in the element, W/m² - S specific gravity of vapour - T _c tube side stream temperature, °C - T _c2 tube side stream exit temperature, °C - T _f (T _w +T _s )/2 - T _s saturation temperature, °C - T _w mean wall temperature in an element, °C - T ₁,T ₂ temperatures at nodes 1 and 2, °C - U overall heat transfer coefficient, W/m²°C - W ₁ tube side fluid thermal capacity rate, W/°C - W ₂ vapour mass flow rate, kg/hr - W mass of vapour condensed in any element, kg/sec - _f viscosity of condensate atT _f , N sec/m² - _f density of condensate atT _f , kg/m³     

On the propagation of elastic waves through composite media

Summary With the aid of an ultrasonic pulse technique, the propagation of elastic waves (longitudinal as well as transverse) through polyurethane rubbers filled with different amounts of sodium chloride particles was studied. The velocity of both longitudinal and transverse waves was found to increase with filler content. From the measured wave velocities, the effective modulus for longitudinal waves,L, bulk modulus,K, and shear modulus,G, were calculated according to the relations for a homogeneous isotropic material. All three moduli appear to be monotonously increasing functions of the filler content over the whole experimentally accessible temperature range (–70 °C to + 70 °C forL andK;}-70 °C to about –20 °C forG) and they, moreover, reflect the glassrubber transition of the binder.Poisson's ratio,, was found to decrease with increasing filler content and show a rise at the high temperature side of the experimentally accessible temperature range (about –20 °C) as a result of the approach of the glass-rubber transition.In addition to the velocities, the attenuation of both longitudinal and transverse waves was measured in the temperature ranges mentioned. It was found that in the hard region tan _L as well as tan _G are independent of the filler content within the accuracy of the measurements. In the rubbery region, however, tan _L, increases with increasing filler content.Finally, the experimental data are compared with a simple macroscopic theory on the elastic properties of composite media.     

Temperature distribution inside hot-water storage tanks of solar collectors

An analytical-experimental investigation into the temperature field inside the hot-water storage tank of a solar collector is carried out. A transient two-dimensional semi-infinite cylindrical length model with time and space boundary conditions dependency is selected. Conduction and convection heat transfer modes in the axial direction together with conduction in the radial direction are considered. Good agreement between theoretical and experimental predictions is verified. The radial direction temperature dependency disappears for axial lengths greater than one quarter of the tank depth for most practical operating conditions especially for low inflow velocities and low inlet to outlet temperature ratios. The axial conduction term in the governing equation can be dropped out for inflow velocities greater than a certain critical value without disturbing the theoretical consequences.Temperature profiles in the axial direction can be assumed to be linear especially for high inflow velocities as well as low temperature differences at inlet and outlet of the storage tank.

---

Temperaturverteilung in einem Heißwasser-Speichertank eines Sonnenkollektors

Zusammenfassung Eine analytisch-experimentelle Untersuchung des Temperaturfeldes in einem Heißwasser-Speichertank eines Sonnenkollektors wurde durchgeführt. Es wird ein zweidimensionales instationäres halbunendliches zylindrisches Modell mit zeitlichen und örtlichen Randbedingungen ausgewählt. Wärmeübertragung durch Leitung und Konvektion in axialer Richtung zusammen mit Leitung in radialer Richtung werden betrachtet. Gute Übereinstimmung zwischen theoretischen und experimentellen Ergebnissen werden festgestellt. Die Temperaturabhängigkeit in radialer Richtung verschwindet für axiale Längen größer als ein Viertel der Tanktiefe für die meisten praktischen Anwendungen, speziell für niedrige Einströmgeschwindigkeiten und für ein niedriges Ein- und Auslaß-Temperaturgefälle. Der Term, der die axiale Leitung beschreibt, kann für Einströmgeschwindigkeiten, die eine bestimmte kritische Größe überschreiten, in der Gleichung eliminiert werden, ohne die theoretischen Folgerungen zu stören. Die Temperaturprofile in axialer Richtung können speziell für hohe Einströmgeschwindigkeiten und kleine Temperaturunterschiede an Ein- und Auslaß des Lagertanks als linear angenommen werden.

---

Nomenclature a radius of the tank, m - A _c collector area, m² - C _p constant pressure heat capacity, kJ/(kg·°C) - F _R heat removal factor - F collector flow factor - h wall heat transfer coefficient, W/(m²·°C) - J _o zero-order Bessel function - J ₁ first-order Bessel function - K thermal conductivity, W/(m·°C) - L length of the tank - r radial direction - t dimensionless time - T dimensionless temperature - T _p,m mean plate temperature, °C - ¯T temperature, °C - T¯ ₁ maximum temperature, °C - T¯ ₂ minimum temperature at inlet, °C - T¯ _f,i inlet fluid temperature to the collector, °C - U _t top loss coefficient, W/(m² · °C) - ¯V _r radial velocity component, m/sec - ¯V _i initial temperature in the tank, °C - ¯V _z axial velocity component - V velocity component, m/sec - V dimensionless axial constant value of velocity - W _i heat generation, kW/m³ - Z dimensionless axial direction - thermal diffusivity, m²/sec - _n roots of first-order Bessel function - impulse function - absolute value of viscosity - Laplace transform of temperature density - density, kg/m³     

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     

Measurement of the probability of the transition P20 (00 °1–10 °0) in CO2 and impact broadening in collisions with CO2, N2, and He

We measured the dependence of the absorption, coefficient on the pressure for the vibrational-rotational transition P20 (00 °1–10 °0) in CO₂ using a CO₂ laser as a light source. We consider the question of the systematic error due to the contribution of impact broadening, when finding the probability from the experimental absorption. The refined value of the transition probability A _{10 °0.20} ^{00 °1.19} =0.169 sec^–1. We obtain the values of the impact half-widths for collisions of the type CO₂-CO₂, CO₂-N₂, CO₂-He, the values of which at J=300 °K are respectively 3.28, 2.74, and 2.27 MHz/torr.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 24–28, November–December, 1972.The authors thank A. K. Konyukhov for interest in the work and for valuable discussions.     

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.     

Analysis of transformation superplastic deformation in pure iron

Summary Transformation superplastic deformation in pure iron is analysed. The transformation phenomenology is first studied when the material is exposed to the constant-rate cyclic temperature histories between 20°C and 1100°C. Transformation diagrams (T-T-A, T-T-T, C-H-T and C-C-T diagrams) are shown to be constructed by means of the transformation kinetics employed. Change in the fraction of austenite, or of ferrite, during the cyclic process is calculated. The deformation in thin-walled tubular specimen is then estimated when it is exposed under a constant tensile or torsional stress to the temperature cyclings. Accumulation of the superplastic deformation due to A ₃ transformation is shown to be well simulated by the theory presented here.

---

Deformationsanalysis der Umwandlungsplastizität bei Eisen

Übersicht Die superplastische Deformation während der allotropen Umwandlung bei Eisen, A ₃ (Austenit Ferrit)-Umwandlung, wird analysiert. Die Umwandlungsphänomenologie wird theoretisch diskutiert, wenn das Material einer zyklischen Temperaturgeschichte zwischen 20°C und 1100°C ausgesetzt wird. Es wird gezeigt, daß man Umwandlungsdiagramme mit Hilfe der vorgeschlagenen Umwandlungskinetik gut konstruieren kann. Die Austenitbildung oder die Ferritbildung während des zyklischen Prozesses wird berechnet. Die Deformation von dünnwandigen, rohrförmigen Proben wird dann analysiert, wenn sie bei konstanter Zugspannung oder Torsionsspannung gleichzeitig durch ein zyklisches Temperaturfeld belastet werden. Die Ergebnisse zeigen, daß die akkumulierende Superplastizitätsdeformation von der Theorie gut beschrieben werden kann.

     

Heat transfer during dry spinning of fibers

Summary Heat transfer to fibers formed in dry spinning has been subjected to fundamental analysis. Solutions of the equation of energy have been derived and tested with experimental data. Results were deemed satisfactory in view of the accuracy of the experimental data. The present work is believed to yield a good representation of the heat transfer in the dry spinning process.Nomenclature h heat transfer coefficient, cal/cm² °C sec - k thermal conductivity, cal/cm °C sec - r radial distance, cm - t time, sec - Z axial distance, cm - A surface area, cm² - A _n or n-th root of - A ₀ energy required for solvent evaporation, cal/sec cm³ - C _p specific heat cal/gm °C - J ₀ Bessel function of first kind, order zero - J ₁ Bessel function of first kind, order one - J ₂ Bessel function of first kind, order two - N k/(R ² C _p V) - Q volumetric flow rate cm³/sec - R outside radius, cm - T point temperature, °C - T _S surface temperature °C - T ₀ initial fiber temperature °C - T ambient air temperature, °C - average fiber temperature, °C - ₁ average fiber temperature of preceding segment, °C - V average fiber velocity relative to air strean, cm/sec - V _r radial velocity component, cm/sec - V _z axial velocity components, cm/sec - V direction velocity component cm/sec - W weight of solvent evaporated in a given fiber segment, gms - _n a solution of the equation J ₀(X)=0 - heat of vaporization of solvent, cal/gm - dimension - r/R - density, gms/cc     

On the quenching of steel and zircaloy spheres in water-based nanofluids with alumina,silica and diamond nanoparticles

The quenching curves (temperature vs time) for small (∼1 cm) metallic spheres exposed to pure water and water-based nanofluids with alumina, silica and diamond nanoparticles at low concentrations (?0.1 vol%) were acquired experimentally. Both saturated (ΔT_sub = 0 °C) and highly subcooled (ΔT_sub = 70 °C) conditions were explored. The spheres were made of stainless steel and zircaloy, and were quenched from an initial temperature of ∼1000 °C. The results show that the quenching behavior in nanofluids is nearly identical to that in pure water. However, it was found that some nanoparticles accumulate on the sphere surface, which results in destabilization of the vapor film in subsequent tests with the same sphere, thus greatly accelerating the quenching process. The entire boiling curves were obtained from the quenching curves using the inverse heat transfer method, and revealed that alumina and silica nanoparticle deposition on the surface increases the critical heat flux and minimum heat flux temperature, while diamond nanoparticle deposition has a minimal effect on the boiling curve. The possible mechanisms by which the nanoparticles affect the quenching process were analyzed. It appears that surface roughness increase and wettability enhancement due to nanoparticle deposition may be responsible for the premature disruption of film boiling and the acceleration of quenching. The basic results were also confirmed by quench tests with rodlets.     

Hydrodynamically induced crystallization of polymers from solution

Summary This paper deals with a study on the melting behaviour of polyethylene crystals showing a fibrillar morphology. These crystals were prepared by hydrodynamically induced crystallization from xylene solutions. Use was made of several techniques, such as differential scanning calorimetry, polarizing microscopy and infrared dichroism. The experimental observations indicate that the melting process of the fibrous crystals can only partly be related to morphological structures. The infrared dichroism and persistent birefringence up to temperatures of 200 °C are due mainly to the molecular orientation in the melt. The shrinkage on melting was found to depend on the thickness of and fibre orientation in the sample, as well as on the molecular weight of the polyethylene. A maximum shrinkage value of 93% was measured on fibrillar crystals of Marlex (M _w =90 · 10³). Calorimetric studies on the fusion of fibrillar crystals of high molecular weight polyethylene (M _w =1.5 · 10⁶) revealed that extendedchain backbones melt at 150 °C and even at 180 °C. The melt of these crystal structures remains partly oriented, as could be inferred from the constant temperature position of the melting peak on repeated crystallizing and melting.The areas of the melting peaks at 150 °C and 180 °C were found to depend on the maximum temperature at which the samples were heated and, in addition, on the exposure time. From measurements of the area of the backbone crystallization peak as a function of time and heating temperature, an apparent activation energy of 100 kcal/mole was derived, which suggests that several chains are simultaneously involved in the relaxation of structural order of the backbone melt.The melting temperatures of the lamellar over-growth and backbones were found to increase with the crystallization temperature of the fibrillar crystals. The melting studies also suggest that extended-chain fibrillar crystals can be formed in xylene solutions at a low temperature (85 °C) if the stirrer speed is sufficiently high.

---

Zusammenfassung Dieser Bericht befaßt sich mit einem Studium des Schmelzverhaltens von Polyäthylen-Kristallen, welche eine faserige Morphologie aufweisen. Diese Kristalle werden durch eine hydrodynamisch induzierte Kristallisation aus Xylollösungen hergestellt. Es werden verschiedene Techniken angewandt, z. B. differential scanning calorimetry, Polarisationsmikroskopie und Ultrarot-Dichroismus.Die experimentellen Beobachtungen zeigen, daß es nur teilweise eine Beziehung zwischen dem Schmelzvorgang der faserigen Kristalle und morphologischen Strukturen gibt. Der Ultrarot-Dichroismus und die anhaltende Doppelbrechung bis zu Temperaturen von 200 °C sind hauptsächlich auf die Molekularorientierung in der Schmelze zurückzuführen.Die Kontraktion beim Schmelzvorgang wird, wie sich herausstellt, bedingt durch die Dicke der Probe und die Orientierung der Fasern in der Probe, sowie durch das Molekulargewicht des Polyäthylens. Eine maximale Kontraktion von 93% wird bei faserigen Kristallen von Marlex gemessen (M _w =90 · 10³). Kalorimetrische Untersuchungen des Schmelzvorgangs faseriger Kristalle von Polyäthylen mit hohem Molekulargewicht (M _w =1,5 · 10⁶) ergeben, daß extended-chain-Faserkerne bei 150 °C und sogar bei 180 °C schmelzen.Die Schmelze dieser Kristallstrukturen bleibt teilweise orientiert, wie aus der konstanten Temperaturlage des Schmelzpeaks nach wiederholtem Kristallisieren und Schmelzen abgeleitet werden kann.Es stellt sich heraus, daß die Oberfläche der Schmelzpeaks bei 150 und 180 °C bedingt wird durch die maximale Temperatur, bei der die Proben erhitzt werden, und darüber hinaus durch die Erhitzungszeit. Anhand der gemessenen Oberfläche der Kristallisationspeaks der Faserkerne als Funktion von Zeit und Erhitzungstemperatur wird eine scheinbare Aktivierungsenergie von 100 kcal/Mol festgestellt; dies deutet darauf hin, daß mehrere Ketten gleichzeitig an der Relaxation der strukturellen Ordnung der Faserkernschmelze beteiligt sind. Es ergibt sich, daß die Schmelztemperaturen der Lamellarüberwachsung und Faserkerne mit der Kristallisationstemperatur der faserigen Kristalle zunehmen. Die Schmelzuntersuchungen deuten auch darauf hin, daß extended-chain-Faserkerne bei niedriger Temperatur (85 °C) in Xylollösungen gebildet werden können, wenn nur die Rührgeschwindigkeit ausreichend hoch ist.

---

---

Paper presented at the Symposium at Leende of De Nederlandse Rheologische Vereniging on 21st and 22nd May 1970.     

Flow interference between a stationary cylinder and an elastically mounted cylinder arranged in proximity

The flow interference between two circular cylinders, one stationary and the other free to oscillate in the transverse direction, are studied numerically at Re=150. The incompressible Navier–Stokes equation in two space dimensions, an assumption that is expected to be valid at the considered Re, is solved by the characteristic-based-split (CBS) finite element method using the T4/C3 MINI triangular element. The center-to-center spacing between the two cylinders is fixed at 4D, where D is the cylinder diameter. The angle of incident flow, α, with respect to the line through the two cylinder centers, varies within the range from α=0° to 90°. For the elastically mounted cylinder, the reduced mass considered is M_r=2.0; the structural damping coefficient is assigned to be zero, which encourages high amplitude oscillations. For each α, the computations are conducted for a wide range of reduced velocities, U_r. The flow interference is examined by scrutinizing (i) the frequency characteristics of the vortex shedding and oscillation; (ii) the dynamic response of the oscillating cylinder, including the amplitude of displacement, the drag and lift force characteristics and the phase relationship between the lift and the displacement series; and (iii) the flow response in terms of the instantaneous vorticity field. It was found that the flow interference type is significantly affected by the angle of the incident flow. As the cylinder is oscillated outside of the region of the wake behind the stationary cylinder (α≥30°), it behaves similarly to its isolated counterpart. In contrast, if the cylinder is partially or entirely submerged within the upstream wake (α<30°), then both the flow and body responses are substantially modified due to the vigorous interaction between the upstream wake and the oscillating cylinder; the response therefore belongs to the wake-induced regime. The U_r range associated with the higher amplitude response is significantly shifted toward a higher U_r. The maximum vibration amplitude builds up to a significantly higher level, even increasing the U_r far beyond the resonance regime. In general, the wake flow associated with the wake-induced vibration (WIV) regime appears to be more unperiodic than does that corresponding to the vortex-induced oscillation regime. It is also revealed that both the vortex-cylinder and the shear layer-cylinder interaction mechanisms are responsible for the characteristics of the responses of oscillating cylinder. The larger momentum required for the higher oscillation amplitude is obtained from the duration of the energy transfer from the fluid to the cylinder, which is ascribed to the phase lag between the lift force and the cylinder displacement.     

Non-equilibrium contributions to the internal energy of PVAc melts

Summary Adiabatic deformation experiments have been used as a test for the non-equilibrium thermodynamic behavior of PVAc melts. At temperatures slightly aboveT _g (i.e. 50°C and 60°C), an appreciable dependance of internal energy upon deformation history is found. The non-equilibrium contributionU represents up to 50% of the total internal energy change and plays the role of an endothermic effect. In transient shear tests,U shows an overshoot with respect to deformation. During adiabatic stress relaxation a temperature relaxation is also observed. The nonequilibrium internal energy term becomes negligible at 80°C, both during deformation and stress relaxation. At that temperature, the entropic elasticity theory holds true.

---

Zusammenfassung Deformationsversuche unter adiabatischen Bedingungen wurden als Test für das thermodynamische Verhalten von PVAc-Schmelzen im Nicht-Gleichgewichts-Zustand durchgeführt. Bei Temperaturen wenig oberhalb der GlastemperaturT _g (d. h. 50°C und 60°C) wurde eine merkliche Abhängigkeit der Inneren Energie von der Deformationsvorgeschichte gefunden. Auf den NichtgleichgewichtsbeitragU entfällt bis zu 50% der Änderung der totalen Inneren Energie, und zwar kennzeichnet sie einen endothermen Effekt. Bei Anfahrversuchen zeigtU als Funktion der Scherung ein Überschießen. Während der adiabatischen Spannungsrelaxation wird ebenfalls eine Temperatur-Relaxation beobachtet. Der Nicht-Gleichgewichts-Term der Inneren Energie wird bei 80°C vernachlässigbar gering, sowohl während der Deformation als auch der Spannungsrelaxation. Bei dieser Temperatur ist somit die Theorie der reinen Entropie-Elastizität anwendbar.

---

---

With 6 figures