A method for determining the thermodynamic (true) temperature of opaque materials by the registered spectrum of thermal radiation under the conditions when we do not know emissivity of a free-radiating body is presented. A special function, which is a product of relative emissivity of tungsten by the radiation wavelength, was used as the input data. The accuracy of results is analyzed. It is shown that when using relative emissivity, the proposed algorithm can be used both within the range of applicability of the Wien approximation and the Planck formula.;A method for determining the thermodynamic (true) temperature of opaque materials by the registered spectrum of thermal radiation under the conditions when we do not know emissivity of a free-radiating body is presented. A special function, which is a product of relative emissivity of tungsten by the radiation wavelength, was used as the input data. The accuracy of results is analyzed. It is shown that when using relative emissivity, the proposed algorithm can be used both within the range of applicability of the Wien approximation and the Planck formula.;A method for determining the thermodynamic (true) temperature of opaque materials by the registered spectrum of thermal radiation under the conditions when we do not know emissivity of a free-radiating body is presented. A special function, which is a product of relative emissivity of tungsten by the radiation wavelength, was used as the input data. The accuracy of results is analyzed. It is shown that when using relative emissivity, the proposed algorithm can be used both within the range of applicability of the Wien approximation and the Planck formula.

EXPERIMENTS IN FLUIDS
ISSN：0723-4864 volume：59 Issue：1 page：1-19
Burns, Ross A
;
Cadell, Seth R
;
Woods, Brian G
;
Bardet, Philippe M
;
André, Matthieu A

A molecular tagging velocity (MTV) technique is developed to non-intrusively measure velocity in an integral effect test (IET) facility simulating a high-temperature helium-cooled nuclear reactor in accident scenarios. In these scenarios, the velocities are expected to be low, on the order of 1 m/s or less, which forces special requirements on the MTV tracer selection. Nitrous oxide $$({\rm N}_2{\rm O})$$ ( N 2 O ) is identified as a suitable seed gas to generate NO tracers capable of probing the flow over a large range of pressure, temperature, and flow velocity. The performance of $${\rm N}_2{\rm O}$$ N 2 O -MTV is assessed in the laboratory at temperature and pressure ranging from 295 to 781 K and 1 to 3 atm. MTV signal improves with a temperature increase, but decreases with a pressure increase. Velocity precision down to 0.004 m/s is achieved with a probe time of 40 ms at ambient pressure and temperature. Measurement precision is limited by tracer diffusion, and absorption of the tag laser beam by the seed gas. Processing by cross-correlation of single-shot images with high signal-to-noise ratio reference images improves the precision by about 10% compared to traditional single-shot image correlations. The instrument is then deployed to the IET facility. Challenges associated with heat, vibrations, safety, beam delivery, and imaging are addressed in order to successfully operate this sensitive instrument in-situ. Data are presented for an isothermal depressurized conduction cooldown. Velocity profiles from MTV reveal a complex flow transient driven by buoyancy, diffusion, and instability taking place over short $$(<1\, {\rm s})$$ ( < 1 s ) and long ( $$>30$$ > 30 min) time scales at sub-meter per second speed. The precision of the in-situ results is estimated at 0.027, 0.0095, and 0.006 m/s for a probe time of 5, 15, and 35 ms, respectively.

A tailor-made convective heat transfer test facility is constructed to study the single-phase convective heat transfer of deionized water and 30 vol% and 60 vol% aqua–ethylene glycol in a stainless steel tube of 4 mm in inner diameter and 1 m in length. The heat flux is varied between 1 and 4 kW·m?2 and for mass flux ranging from 160 to 475 kg·m?2 s?1. The experiments were predominantly conducted only for laminar flow regime. Finally, the heat transfer coefficient is recorded and compared with the conventional theories. It is observed that the presence of ethylene glycol in water decreases the heat transfer coefficient by more than 50%, due to the decreased Reynolds number and thermal conductivity of the mixture.;A tailor-made convective heat transfer test facility is constructed to study the single-phase convective heat transfer of deionized water and 30 vol% and 60 vol% aqua–ethylene glycol in a stainless steel tube of 4 mm in inner diameter and 1 m in length. The heat flux is varied between 1 and 4 kW·m?2 and for mass flux ranging from 160 to 475 kg·m?2 s?1. The experiments were predominantly conducted only for laminar flow regime. Finally, the heat transfer coefficient is recorded and compared with the conventional theories. It is observed that the presence of ethylene glycol in water decreases the heat transfer coefficient by more than 50%, due to the decreased Reynolds number and thermal conductivity of the mixture.;A tailor-made convective heat transfer test facility is constructed to study the single-phase convective heat transfer of deionized water and 30 vol% and 60 vol% aqua–ethylene glycol in a stainless steel tube of 4 mm in inner diameter and 1 m in length. The heat flux is varied between 1 and 4 kW·m?2 and for mass flux ranging from 160 to 475 kg·m?2 s?1. The experiments were predominantly conducted only for laminar flow regime. Finally, the heat transfer coefficient is recorded and compared with the conventional theories. It is observed that the presence of ethylene glycol in water decreases the heat transfer coefficient by more than 50%, due to the decreased Reynolds number and thermal conductivity of the mixture.

This article reports the magnetohydrodynamic (MHD) three-dimensional flow of viscoelastic fluid over a stretching surface with heat transfer. Mathematical analysis is formulated using convective boundary conditions. Computations of dimensionless velocity and temperature fields are presented. The tabulated values show excellent agreement between present and previous limiting analysis. Graphical results show the impact of embedded parameters entering into the problem.;This article reports the magnetohydrodynamic (MHD) three-dimensional flow of viscoelastic fluid over a stretching surface with heat transfer. Mathematical analysis is formulated using convective boundary conditions. Computations of dimensionless velocity and temperature fields are presented. The tabulated values show excellent agreement between present and previous limiting analysis. Graphical results show the impact of embedded parameters entering into the problem.;This article reports the magnetohydrodynamic (MHD) three-dimensional flow of viscoelastic fluid over a stretching surface with heat transfer. Mathematical analysis is formulated using convective boundary conditions. Computations of dimensionless velocity and temperature fields are presented. The tabulated values show excellent agreement between present and previous limiting analysis. Graphical results show the impact of embedded parameters entering into the problem.

The enthalpy of liquid cesium in the temperature range from 431 to 976 K was measured by a drop method on an isothermal calorimeter. The approximation equation of enthalpy was obtained and the isobaric heat capacity was determined. The estimated errors in the enthalpy and heat capacity data are 0.5% and 1.5%, respectively. The obtained results are compared with the literature data. The position of the minimum heat capacity of liquid cesium was clarified (733 K). Tables of recommended values of caloric properties in the investigated temperature range were developed.;The enthalpy of liquid cesium in the temperature range from 431 to 976 K was measured by a drop method on an isothermal calorimeter. The approximation equation of enthalpy was obtained and the isobaric heat capacity was determined. The estimated errors in the enthalpy and heat capacity data are 0.5% and 1.5%, respectively. The obtained results are compared with the literature data. The position of the minimum heat capacity of liquid cesium was clarified (733 K). Tables of recommended values of caloric properties in the investigated temperature range were developed.;The enthalpy of liquid cesium in the temperature range from 431 to 976 K was measured by a drop method on an isothermal calorimeter. The approximation equation of enthalpy was obtained and the isobaric heat capacity was determined. The estimated errors in the enthalpy and heat capacity data are 0.5% and 1.5%, respectively. The obtained results are compared with the literature data. The position of the minimum heat capacity of liquid cesium was clarified (733 K). Tables of recommended values of caloric properties in the investigated temperature range were developed.

Experimental data on the flow structure and mass transfer near the boundaries of the region existence of the laminar and turbulent boundary layers with combustion are considered. These data include the results of in-vestigation on reacting flow stability at mixed convection, mass transfer during ethanol evaporation “on the floor” and “on the ceiling”, when the flame surface curves to form the large-scale cellular structures. It is shown with the help of the PIV equipment that when Rayleigh–Taylor instability manifests, the mushroom-like structures are formed, where the motion from the flame front to the wall and back alternates. The cellular flame exists in a narrow range of velocities from 0.55 to 0.65 m/s, and mass transfer is three times higher than its level in the standard laminar boundary layer.;Experimental data on the flow structure and mass transfer near the boundaries of the region existence of the laminar and turbulent boundary layers with combustion are considered. These data include the results of in-vestigation on reacting flow stability at mixed convection, mass transfer during ethanol evaporation “on the floor” and “on the ceiling”, when the flame surface curves to form the large-scale cellular structures. It is shown with the help of the PIV equipment that when Rayleigh–Taylor instability manifests, the mushroom-like structures are formed, where the motion from the flame front to the wall and back alternates. The cellular flame exists in a narrow range of velocities from 0.55 to 0.65 m/s, and mass transfer is three times higher than its level in the standard laminar boundary layer.;Experimental data on the flow structure and mass transfer near the boundaries of the region existence of the laminar and turbulent boundary layers with combustion are considered. These data include the results of in-vestigation on reacting flow stability at mixed convection, mass transfer during ethanol evaporation “on the floor” and “on the ceiling”, when the flame surface curves to form the large-scale cellular structures. It is shown with the help of the PIV equipment that when Rayleigh–Taylor instability manifests, the mushroom-like structures are formed, where the motion from the flame front to the wall and back alternates. The cellular flame exists in a narrow range of velocities from 0.55 to 0.65 m/s, and mass transfer is three times higher than its level in the standard laminar boundary layer.

Flow characteristics of a liquid film flowing over a smooth surface and structured surface with the Reynolds number range from 10 to 1121 are studied. The mixture of R21 and R114 refrigerants is used as the test liquid. The 3D transient simulations are taken to capture the liquid film’s dynamic characteristics and spatial distribution. Effects of the inlet dimension, inlet flow rates, surface tension, and surface structuring on the wettability, average velocity, and film thickness are studied systematically. The obtained results show that surface tension is essential for an accurate simulation, while inlet width has no effect on the liquid film parameters in the steady-state flow regime. For low flow rates, wetting area and film thickness both are small, and a suggested range of Reynolds number is chosen to simulate further heat transfer in order to balance the film thickness and dry spots generation. It is shown that a ripple surface structure hinders the liquid film movement, reflected in a lower velocity and a larger film thickness compared to the smooth surface. Lateral movement of a liquid film can also be observed at the structured surface.;Flow characteristics of a liquid film flowing over a smooth surface and structured surface with the Reynolds number range from 10 to 1121 are studied. The mixture of R21 and R114 refrigerants is used as the test liquid. The 3D transient simulations are taken to capture the liquid film’s dynamic characteristics and spatial distribution. Effects of the inlet dimension, inlet flow rates, surface tension, and surface structuring on the wettability, average velocity, and film thickness are studied systematically. The obtained results show that surface tension is essential for an accurate simulation, while inlet width has no effect on the liquid film parameters in the steady-state flow regime. For low flow rates, wetting area and film thickness both are small, and a suggested range of Reynolds number is chosen to simulate further heat transfer in order to balance the film thickness and dry spots generation. It is shown that a ripple surface structure hinders the liquid film movement, reflected in a lower velocity and a larger film thickness compared to the smooth surface. Lateral movement of a liquid film can also be observed at the structured surface.;Flow characteristics of a liquid film flowing over a smooth surface and structured surface with the Reynolds number range from 10 to 1121 are studied. The mixture of R21 and R114 refrigerants is used as the test liquid. The 3D transient simulations are taken to capture the liquid film’s dynamic characteristics and spatial distribution. Effects of the inlet dimension, inlet flow rates, surface tension, and surface structuring on the wettability, average velocity, and film thickness are studied systematically. The obtained results show that surface tension is essential for an accurate simulation, while inlet width has no effect on the liquid film parameters in the steady-state flow regime. For low flow rates, wetting area and film thickness both are small, and a suggested range of Reynolds number is chosen to simulate further heat transfer in order to balance the film thickness and dry spots generation. It is shown that a ripple surface structure hinders the liquid film movement, reflected in a lower velocity and a larger film thickness compared to the smooth surface. Lateral movement of a liquid film can also be observed at the structured surface.

The problem of simulation of heat and mass transfer in the gas phase of film devices in the regime of weak and strong phase interaction has been solved. The Deissler three-layer model of turbulent boundary layer was used. Expressions have been derived for calculating the average Nusselt and Sherwood numbers. Examples of calculations for various conditions of phase interaction and comparison with experimental data are shown.;The problem of simulation of heat and mass transfer in the gas phase of film devices in the regime of weak and strong phase interaction has been solved. The Deissler three-layer model of turbulent boundary layer was used. Expressions have been derived for calculating the average Nusselt and Sherwood numbers. Examples of calculations for various conditions of phase interaction and comparison with experimental data are shown.;The problem of simulation of heat and mass transfer in the gas phase of film devices in the regime of weak and strong phase interaction has been solved. The Deissler three-layer model of turbulent boundary layer was used. Expressions have been derived for calculating the average Nusselt and Sherwood numbers. Examples of calculations for various conditions of phase interaction and comparison with experimental data are shown.

The buffet flow field around supercritical airfoils is dominated by self-sustained shock wave oscillations on the suction side of the wing. Theories assume that this unsteadiness is driven by an acoustic feedback loop of disturbances in the flow field downstream of the shock wave whose upstream propagating part is generated by acoustic waves. Therefore, in this study, first variations in the sound pressure level of the airfoil’s trailing-edge noise during a buffet cycle, which force the shock wave to move upstream and downstream, are detected, and then, the sensitivity of the shock wave oscillation during buffet to external acoustic forcing is analyzed. Time-resolved standard and tomographic particle-image velocimetry (PIV) measurements are applied to investigate the transonic buffet flow field over a supercritical DRA 2303 airfoil. The freestream Mach number is $$M_{\infty } = 0.73$$ M ∞ = 0.73 , the angle of attack is $$\alpha = {3.5}^{\circ }$$ α = 3.5 ° , and the chord-based Reynolds number is $$Re_c = 1.9\times 10^6$$ R e c = 1.9 × 10 6 . The perturbed Lamb vector field, which describes the major acoustic source term of trailing-edge noise, is determined from the tomographic PIV data. Subsequently, the buffet flow field is disturbed by an artificially generated acoustic field, the acoustic intensity of which is comparable to the Lamb vector that is determined from the PIV data. The results confirm the hypothesis that buffet is driven by an acoustic feedback loop and show the shock wave oscillation to directly respond to external acoustic forcing. That is, the amplitude modulation frequency of the artificial acoustic perturbation determines the shock oscillation.;The buffet flow field around supercritical airfoils is dominated by self-sustained shock wave oscillations on the suction side of the wing. Theories assume that this unsteadiness is driven by an acoustic feedback loop of disturbances in the flow field downstream of the shock wave whose upstream propagating part is generated by acoustic waves. Therefore, in this study, first variations in the sound pressure level of the airfoil’s trailing-edge noise during a buffet cycle, which force the shock wave to move upstream and downstream, are detected, and then, the sensitivity of the shock wave oscillation during buffet to external acoustic forcing is analyzed. Time-resolved standard and tomographic particle-image velocimetry (PIV) measurements are applied to investigate the transonic buffet flow field over a supercritical DRA 2303 airfoil. The freestream Mach number is M∞=0.73, the angle of attack is α=3.5°, and the chord-based Reynolds number is Rec=1.9×106. The perturbed Lamb vector field, which describes the major acoustic source term of trailing-edge noise, is determined from the tomographic PIV data. Subsequently, the buffet flow field is disturbed by an artificially generated acoustic field, the acoustic intensity of which is comparable to the Lamb vector that is determined from the PIV data. The results confirm the hypothesis that buffet is driven by an acoustic feedback loop and show the shock wave oscillation to directly respond to external acoustic forcing. That is, the amplitude modulation frequency of the artificial acoustic perturbation determines the shock oscillation.