The evolution of the crystallization front from a planar to a dendritic one as a function of the GL/(Rc0) parameter was investigated during the crystallization of Al-Cu alloys by the vertical Bridgman method. Six series of alloys with different initial composi- tions of Cu were solidified at different growth rates. A mathematical model for the heat transfer during vertical Bridgmen crystal growth was developed. The model was solved using the finite element method. The temperature gradient in the melt at the beginning of crystal growth was calculated using the obtained model. Discrete stages of the crystalliza- tion front were identified in the experiments, as the ratio GL/(Rc0) decreased.

In a project which deals with degassing of polymer solutions using pipe-bundle heat exchangers, noticeable discrepancies have been observed between experimental results for boiling highly viscous mixtures and predictions of available correlations. These differences revealed shortcomings in understanding and modeling of the process. An experimental project is presented, which focuses on fundamentals of heat and mass transfer in boiling highly viscous mixtures. Effects that have been predicted for boiling in such mixtures are discussed. In order to distinguish between the influence of viscosity and marginal vapor pressure of the highly viscous component, an extremely wide-boiling model system with low viscosity will be investigated. A standard apparatus for measuring heat transfer in an equilibrated pool is modified for measurements on such systems. The design of the modified apparatus is described. Additional modifications necessary to adapt a standard apparatus to wide-boiling highly-viscous mixtures are briefly discussed. Results are presented for mixtures of n-pentane and poly dimethyl siloxane (silicon oil) with a viscosity of 10 m Pa s boiling in a simple pod-boiling equipment at ambient pressure. Temperature distributions in the pool are reported and nucleation mechanisms are discussed. A new mechanism is observed for bubble formation above the test tube.

The need to reduce CO2 emissions from fossil-fuel based power production creates the need for new power plant solutions where the CO 2 is captured and stored or reused. Oxygen Transfer Membrane (OTM) is the key component of oxy-fuel combustion processes as pure oxygen is usually required to process reactions (e.g. Natural Gas Combined cycle NGCC, Pulverised Coal-fired power plants PC-plants, Integrated Gasification Combined Cycle IGCC). The transfer of oxygen across such OTM is limited by a number of processes, such as surface exchange and ambipolar diffusion through mixed-conducting gas separation layer. This paper shows a mathematical model of an oxygen transfer membrane incorporated into OTM reactor (OTM reactor consists of High Temperature Heat Exchanger and OTM), where transient behavior takes place. The modeling of the OTM reactor has been carried out to show the importance of optimizing OTM parameters (temperatures, oxygen partial pressures, oxygen flux) and reactor design that enables a high oxygen transfer for optimum performance of future power cycles with CO2 capture. All modeling work was carried out in the modeling language Modelica, which is an open standard for equation-based, object-oriented modeling of physical systems. The OTM reactor model has been built using the CombiPlant Library, a modeling library for combined cycle power plants which is under development. Copyright (Less)

Movement of the Adria microplate is one of the main elements for understanding crustal deformations in the central Mediterranean and central Europe. To study present-day tectonics in Adria and the nature of its boundary relative to those of the Africa and Eurasia plates, three GPS (Global Positioning System) campaigns involving 41 stations were carried out within CRODYN (the Croatian and Slovene Geodynamic Network). Movement of stations derived in the International Terrestrial Reference Frame 1996 (ITRF96) with respect to the permanent ITRF/IGS (International GPS Service) station GRAZ in Austria, located north of the network, and values of the principal strain rates determined on the basis of analytical surface deformation theory suggest that Adria is divided into three different deformation zones (northern, central, and southern). The domain of northeastern Italy moves 5 mm/yr in an east-northeast direction. The stations in southwestern Slovenia move 3-7 mm/yr in a north-northwest direction, whereas those in southern and northeastern Istria move 4-5 mm/yr in a more easterly direction. The greatest movement (8-10 mm/yr) occurs in central Adria between the Gargano zone and the central Dinarides ; there, the movement is northeastoriented. A fragmentation of Adria into subblocks linking the Gragano zone to the central Dinarides cannot be clearly demonstrated. The southeastern part of Adria, along the coastline of Albania, moves 5-7 mm/yr in an almost east-west direction, and eastern Albania moves 6 mm/yr in an east-southeast direction. The permanent ITRF/IGS stations POTS and WTZR in Germany, BOR1 in Poland, and PENC in Hungary demonstrate no significant movement. The movement of the stations discussed here differs very clearly from the known north-west motion of the Africa plate and suggests that Adria is an independent microplate.

In the present work, a numerical study has been performed to simulate the effect of free-stream turbulence, length scale and variations in rotational speed of the rotor on heat transfer and fluid flow for a transonic high-pressure turbine stage with tip clearance. The stator and rotor rows interact via a mixing plane, which allows the stage to be computed in a steady manner. The focus is on turbine aerodynamics and heat transfer behavior at the mid-span location, and at the rotor tip and casing region. The results of the fully 3D CFD simulations are compared with experimental results available for the so-called MT1 turbine stage. The predicted heat transfer and static pressure distributions show reasonable agreement with the experimental data. In general, the local Nusselt number increases, at the same turbulence length scale, as the turbulence intensity increases, and the location of the suction side boundary layer transition moves upstream towards the blade leading edge. Comparison of the different length scales at the same turbulence intensity shows that the stagnation heat transfer was significantly increased as the length scale increased. However, the length scale evidenced no significant effects on blade tip or rotor casing heat transfer. Also, the results presented in this paper show that the rotational speed in addition to the turbulence intensity and length scale has an important contribution to the turbine blade aerodynamics and heat transfer. Copyright (Less)

In this work, a numerical study has been performed to simulate the unsteady fluid flow and heat transfer in a transonic high-pressure turbine stage. The main objective of this study is to understand the unsteady flow field and heat transfer in a single transonic turbine stage using an unsteady structured Navier-Stokes solver. For the time accurate computation, a fully implicit time discretization, dual-time stepping, is performed. The results of the CFD simulations are compared with experimental heat transfer and aerodynamic results available for the so-called MT1 turbine stage. The predicted heat transfer and static pressure distributions show reasonable agreement with experimental data. In particular, the results show significant fluctuations in heat transfer and pressure at mid-span on the rotor blade, and that the rotor has a limited influence on the heat transfer to the NGV at mid span. Copyright (Less)