Achim Wenka

Numerical investigation of interfacial mass transfer in two phase flows using the VOF method

ABSTRACT A mass transfer model is developed using the volume-of-fluid (VOF) method with a piecewise linear interface calculation (PLIC) scheme in ANSYS FLUENT for a free-rising bubble. The mass flow rate is defined via the interface by Ficks law and added into the species equation as a source term in the liquid phase using the user-defined functions (UDFs) in ANSYS FLUENT. The interfacial concentration field for the mass flow rate is discretized by two numerical methods. One of them is based on the calculation of the discretization length between the centroid of the liquid volume and the interface using the liquid void fraction and interface normal vectors at the interface cells, while in the second method the discretization length is approximated using only the liquid void fraction at the interface cells. The influence of mesh size, schemes, and different Schmidt numbers on the mass transfer mechanism is numerically investigated for a free-rising bubble. Comparison of the developed mass transfer model with the theoretical results shows reasonable and consistent results with a smaller time-step size and with cell size.

Comparison of Crossflow Micro Heat Exchangers With Different Microstructure Designs

Microstructure heat exchanger are well known for their superior heat transfer capabilities and the good temperature management for applications. Most microstructure heat exchangers presented so far consisted of a number of microchannels in a defined arrangement to provide the transfer of thermal power from one fluid to another, mostly in laminar flow regime. In this publication, several crossflow microstructure heat exchangers are presented. The devices design ranges from simple linear microchannels of different dimensions and shape, complex micro column arrangements up to three dimensional flow structures like crossed sinusoidally shaped microchannels, a kind of split-and-recombine structure. By comparing experimental results of the most interesting devices, microstructure devices with good performance can be chosen.Copyright