Measurement and Modeling of Void Fraction in High Pressure Condensing Flows through Microchannels

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Void fraction measurements are obtained using high speed video for the condensation of R404A in tubes of diameter 0.508, 1.00, and 3.00 mm. Experiments were conducted on refrigerant R404A throughout the entire condensation quality range (0.05 < x < 0.95) at varying mass fluxes (200 ≤ G ≤ 800 kg m-2 s-1) and saturation temperatures from 30 to 60°C (0.38 ≤ pr ≤ 0.77). These high pressures are representative of actual operation of air-conditioning and refrigeration equipment. The influence of saturation temperature on void fraction is most pronounced in the quality range 0.25 < x < 0.75. In addition, it was found that the influence of mass flux on void fraction was negligible for all saturation temperatures and tube diameters investigated. A new drift flux void fraction model is developed to predict void fraction for condensing flows in microchannels and compared with the R404A data and R134a void fraction data from Winkler et al. (2012a). Overall the model is able to predict 92.3% of the R404A data and 81.6% of all refrigerant data within 25%

Multi-scale space-variant FRep cellular structures

Existing mesh and voxel based modeling methods encounter difficulties when dealing with objects containing cellular structures on several scale levels and varying their parameters in space. We describe an alternative approach based on using real functions evaluated procedurally at any given point. This allows for modeling fully parameterized, nested and multi-scale cellular structures with dynamic variations in geometric and cellular properties. The geometry of a base unit cell is defined using Function Representation (FRep) based primitives and operations. The unit cell is then replicated in space using periodic space mappings such as sawtooth and triangle waves. While being replicated, the unit cell can vary its geometry and topology due to the use of dynamic parameterization. We illustrate this approach by several examples of microstructure generation within a given volume or along a given surface. We also outline some methods for direct rendering and fabrication not involving auxiliary mesh and voxel representations

Shape: A 3D Modeling Tool for Astrophysics

We present a flexible interactive 3D morpho-kinematical modeling application for astrophysics. Compared to other systems, our application reduces the restrictions on the physical assumptions, data type and amount that is required for a reconstruction of an object's morphology. It is one of the first publicly available tools to apply interactive graphics to astrophysical modeling. The tool allows astrophysicists to provide a-priori knowledge about the object by interactively defining 3D structural elements. By direct comparison of model prediction with observational data, model parameters can then be automatically optimized to fit the observation. The tool has already been successfully used in a number of astrophysical research projects.Comment: 13 pages, 11 figures, accepted for publication in the "IEEE Transactions on Visualization and Computer Graphics