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The Multiple Equiaxed Dendrite Interaction (MEDI) experiment was launched on the MASER-13 sounding rocket campaign to investigate polycrystalline equiaxed solidification in the transparent phase change material Neopentylgycol-30wt.%(d)Camphor. This material is of interest as an energy-storage material and as a transparent analogue system of solidification in hypoeutectic metal alloys with a Face Centred Cubic lattice. The liquid sample was cooled under a controlled rate of 0.75 K/min with sufficient time to allow semi-solid conditions to develop under microgravity conditions with the absence of gravity-driven convection. This manuscript provides details on the experimental apparatus and procedures. In addition, the experimental method has been augmented with a numerical model to assist with the characterisation of the essential thermal aspects of the experiment. The model followed a volume-averaging, continuum approach for mushy-zone development. A fast algorithm for computing non-isothermal crystallisation kinetics was applied to the case of binary alloy solidification. To build confidence, a formal numerical verification procedure was performed. The model converged sufficiently with second order accuracy as expected. Application of the model gave close agreement between experimental thermocouple readings and numerical simulation data with a Root Mean Square of 0.2 K for the error. A 2D thermal model is sufficient with a suitable heat loss coefficient at the sample-viewing window boundary. Thermal gradients within the sample and along the growth direction were uniform and approximately 0.3 K/mm. Lateral thermal gradients in the sample ranged from zero at the median plane to 0.3 K/mm at the boundary with the containing structure. However, temperature variation in the lateral direction was predicted to be less than 0.22 K. [ABSTRACT FROM AUTHOR]

A Nucleation Progenitor Function (NPF) approach that accounts for the interdependence between nucleation and growth during equiaxed solidification is proposed. An athermal nucleation density distribution, based on undercooling, is identified as a progenitor function. A Kolmogorov statistical approach is applied assuming continuous nucleation and growth conditions. The derived progeny functions describe the (supressed) distribution of actual nucleation events. The approach offers the significant advantage of generating progeny functions for volumetric (3D) data and projected image (2D) data. The main difference between 3D and 2D data in transparent alloy experiments is due to a stereological correction for over-projection. Progeny functions can be analysed to obtain statistical output information, e.g., nucleation counts, average nucleation undercooling and standard deviation. The statistical output data may be calculated in a formative (running) or a summative (final) mode. The NPF kinetics have been incorporated into a transient thermal model of equiaxed solidification. The model has been applied to characterise a microgravity solidification experiment with the transparent alloy system Neopentylgycol-30 wt%(d)Camphor. The model predicted thermal and observed nucleation and growth data with a good level of agreement. [ABSTRACT FROM AUTHOR]

Abstract: Direct steam generation (DSG) is one alternative to the current oil-based parabolic trough solar thermal power plants. Within the German research project ITES, the dynamic behavior of a DSG collector field and the interactions with the conventional power block are assessed in detail. A transient solar field model developed by DLR is used to simulate the steam temperature behavior. Artificial irradiance disturbances as well as real irradiance data are used as input to the system. The resulting main steam temperature gradients are then analyzed by Siemens considering the standards for steam turbines. This paper presents the transient simulation results of the steam temperature as well as the corresponding results of the steam turbine analysis. It is found that the occurring temperature gradients are challenging for a safe turbine operation, if a conservative control system is used. Therefore, the use of an additional thermal inertia to stabilize the steam temperature is suggested. Its impact is also analyzed and discussed in this paper. [Copyright &y& Elsevier]

Abstract: For the understanding of the formation of microstructures the initial transient, i.e. the very beginning of solidification, is of major relevance. At this stage a complex interaction between the velocity of the solidification front, the concentration pile-up and the temperature gradient takes place. In a Bridgman-Stockbarger furnace directional solidification experiments with binary AlCu 1.3wt.% were performed allowing solidification with a planar solid–liquid interface. The velocity and temperature profile were measured during the experiments, concentration profiles afterwards. In this paper we present experimental results. Parallel to the experimental work numerical simulations based on the model of Coriell et al. were performed and first results are compared to the experiments. [Copyright &y& Elsevier]