Egon Hassel

Laser diagnostics for studies of turbulent combustion

The demands on the quality of velocity, concentration and temperature data from turbulent combustion systems for comparison with numerical predictions are rising with the increasing performance of models for the numerical description of these effects. These demands lead to a high degree of maturity in laser-based methods for concentration, temperature and species information. Laser-based methods are able to give the required information without severely disturbing the observed effects and with the needed accuracy and temporal and spatial resolution. This article reviews the state of the art and recent developments of laser-Doppler velocimetry, Rayleigh spectroscopy, spontaneous Raman spectroscopy, coherent anti-Stokes Raman spectroscopy and laser-induced fluorescence. Emphasis is placed not only on aspects of these measurement techniques connected with spatially and temporally resolved quantitative measurements in turbulent combustion, but also on the interaction of the requirements of these methods on the object with the requirements of the characterized object itself and with demands from methods of numerical prediction on the generated data. New developments and requirements on the reviewed methods originating from new trends in combustion modelling are included.

Synthesis of homogeneous anisotropic divergence-free turbulent fields with prescribed second-order statistics by vortex dipoles

This Communication presents a mathematical procedure for generation of turbulent velocity fields with prescribed shell-summed energy spectra. The velocity field is represented as the sum of velocities induced by a set of randomly distributed vortex dipoles (vortons). Closed-form analytical solutions are found for the inner structure of the vortons from the condition that the shell-summed energy spectrum of the synthesizing field is equal to the prescribed one. The proposed procedure is applied to turbulent fields with the spectrum of the decaying turbulence and the typical velocity energy spectrum of homogeneous turbulence. The solution for decaying turbulence is the exact analytical solution of the Navier-Stokes equation for the turbulent field in the final stage of the decay.

(p, ρ, T) and (ps, ρs, Ts) properties and apparent molar volumes Vϕ of LiNO3 (aq) at T=298.15 to 398.15 K and at pressures up to p=60 MPa

Abstract ( p , ρ , T ) and ( p s , ρ s , T s ) properties and apparent molar volumes V ϕ of LiNO 3 (aq) at T =298.15 to 398.15 K at pressures up to p =60 MPa were reported, and apparent molar volumes at infinite dilution have been evaluated. An empirical correlation for partial molar volumes of lithium nitrate in water with pressure, temperature, and molality has been derived. The experiments were carried out at molalities m =(0.29600, 0.76338, 1.26123, 2.55955, 4.8347, and 7.80991) mol kg −1 of lithium nitrate.

Thermal properties of 1-butyl-3-methylimidazolium dicyanamide at high pressures and temperatures

Thermal properties of 1-butyl-3-methylimidazolium dicyanamide at high pressures and temperatures Thermophysical properties of 1-butyl-3-methylimidazolium dicyanamide [BMIM][DCA] {(p, ρ, T) data at T = (283.15 to 393.15) K, pressures up to p =100 MPa, and viscosity at T = (283.15 to 373.15) K and p = 0.101 MPa} are reported with an estimated experimental relative combined standard uncertainty of Δρ/ρ = ±(0.01 to 0.08) % in density and Δη/η = ±0.35 % in dynamic viscosity. The measurements were carried out with a recently constructed Anton-Paar DMA HPM vibration-tube densimeter and a fully automated SVM 3000 Anton-Paar rotational Stabinger viscometer. The vibration-tube densimeter was calibrated using double-distilled water, methanol, toluene and aqueous NaCl solutions. An empiric equation of state for fitting of the (p, ρ, T) data of [BMIM][DCA] has been developed as a function of pressure and temperature. This equation was used for the calculation of thermomechanical properties of the IL, such as isothermal compressibility, isobaric thermal expansibility, differences in isobaric and isochoric heat capacities, thermal pressure coefficient and internal pressure. Viscosity measurements were fitted to the polynomial equation.

Intermolecular potential energy surface and thermophysical properties of ethylene oxide

A six-dimensional potential energy hypersurface (PES) for two interacting rigid ethylene oxide (C2H4O) molecules was determined from high-level quantum-chemical ab initio calculations. The counterpoise-corrected supermolecular approach at the MP2 and CCSD(T) levels of theory was utilized to determine interaction energies for 10178 configurations of two molecules. An analytical site-site potential function with 19 sites per ethylene oxide molecule was fitted to the interaction energies and fine tuned to agree with data for the second acoustic virial coefficient from accurate speed of sound measurements. The PES was validated by computing the second virial coefficient, shear viscosity, and thermal conductivity. The values of these properties are substantiated by the best experimental data as they tend to fall within the uncertainty intervals and also obey the experimental temperature functions, except for viscosity, where experimental data are insufficient. Due to the lack of reliable data, especially for the transport properties, our calculated values are currently the most accurate estimates for these properties of ethylene oxide.

A Loschmidt cell combined with holographic interferometry for binary diffusion experiments in gas mixtures including first measurements on the argon–neon system

A new variant of the Loschmidt technique has been developed for measuring binary diffusion coefficients in gas mixtures in a temperature range from 10 to 80 °C and for pressures between 0.1 and 1 MPa. The two half cells of the thermostatted diffusion cell have a rectangular cross section and are fixed one upon the other. They can be connected and separated by means of a sliding plate provided with a pneumatically operated seal. The concentration in both half cells is determined simultaneously during the diffusion process using an optical system for holographic interferometry for each. The change in the refractive index results in an interference pattern which is recorded as a function of time. The concentrations of the diffusing components are derived by means of the Lorentz–Lorenz equation. The binary diffusion coefficients are calculated via the integrated ideal diffusion equation for the complete mole fraction range performing only a unique diffusion experiment. The performance of the apparatus is demonstrated on first measurements on the argon–neon system at 293.15 K. Separate refractive index measurements are carried out leading to values for the first refractivity virial coefficient of the pure gases with an estimated uncertainty of ±0.1%. This low uncertainty is required for the aimed uncertainty of ±0.5...1% for the diffusion measurements to determine the concentration and density dependences of the binary diffusion coefficient.

Fluid Mechanics and Heat Transfer in a Channel with Spherical and Oval Dimples

Vortex mechanism of heat transfer enhancement in a narrow channel with dimples has been investigated numerically using unsteady Reynolds averaged Navier Stokes equations (URANS SST and SAS) and Large Eddy Simulations (LES). The flow separation results in a formation of vortex structures which significantly enhance the heat transfer on dimpled surfaces conducted by a small increase of the pressure loss. The vortex structures and the flow are sufficiently unsteady. The vortex structure inside of the dimple changes steadily its orientation causing the long period oscillations with opposite-of-phase motion. The heat transfer enhancement is caused mostly by the amplification of convection. The effect of the wetted area increase is sufficiently smaller.

Numerical Modeling and Physical Simulation of Vortex Heat Transfer Enhancement Mechanisms Over Dimpled Reliefs

The paper presents a comprehensive analysis of conditions for numerical simulation and physical modeling of convective heat transfer in the vicinity of dimpled surface relief. Contradictory results, unreasonable assumptions, and non-justified conclusions are marked. Based on the analysis of physical experiments the correlation between the predictions and measured data is discussed. Detailed numerical study of turbulent air flow and heat transfer in the narrow channel with three types of dimples (spherical, conic and oval) was carried out. Various mathematical and discrete models, including, those based on solving Reynolds-averaged Navier-Stokes equations (RANS/URANS-SST), and also adaptive scale models (SAS-SST) are compared. The influence of flow parameters (Reynolds number) and geometric sizes (dimple diameter, depth, radius of rounding off of an edge, channel width and height) on local and integral characteristics of flow and heat transfer (total heat output and hydraulic losses) is determined. Special attention is given to reorganizing vortex structures and flow regime (with periodic fluctuations) with increasing relative dimple depth and Reynolds number. For the first time the influence of the scale factor of a constant cross-section channel is detailed. Thermal-hydraulic characteristics of various dimpled reliefs are compared, and the advantage of an oval dimple over a spherical one is shown.Copyright

A method to measure the density of seawater accurately to the level of 10−6

A substitution method to measure seawater density relative to pure water density using vibrating tube densimeters was realized and validated. Standard uncertainties of 1 g m−3 at atmospheric pressure, 10 g m−3 up to 10 MPa, and 20 g m−3 to 65 MPa in the temperature range of 5 °C to 35 °C and for salt contents up to 35 g kg−1 were achieved. The realization was validated by comparison measurements with a hydrostatic weighing apparatus for atmospheric pressure. For high pressures, literature values of seawater compressibility were compared with substitution measurements of the realized apparatus.

Effects of Wind Turbine Generated Power Fluctuations to Thermal Power Generation – Part I

Abstract Today, all over the world the number of installed wind turbines is increasing continuously. This causes more and more problems concerning the integration of the fluctuating wind power production into the existing electrical supply systems. To handle these problems the main aim for the future must be to guarantee the security of supply and the quality of electrical energy by taking the maximum advantage of the available wind potentials. Regarding these requirements, it is necessary to have modern fossil-fuelled power plants with high levels of efficiency and a very flexible and efficient operation especially at partial loads. These high dynamics of power plant operation will allow to integrate more power produced by fluctuating renewable energy sources like wind energy. In addition to these modern power plants the power plant operation management and the market for compensatory power to follow the wind power production has to be upgraded as well. With this in mind the maximum wind power integration with current and future power plant parameters is investigated in this study to identify the optimal required parameters that will help to increase the fraction of renewable fluctuating energy sources within the electrical grid.