Volume 8, Issue 2 (February 2011)
Modeling and Simulation of the Heat and Mass Transfer Characteristics of Binary Mixtures for Boiling Flow Applications
In this paper, we discuss the development of a new mass transfer model to simulate the thermal and phase change characteristics encountered by binary mixtures during a flow boiling process. The constructed boiling mass transfer model, based on detailed empirical analysis of the heat transfer coefficients pertinent to binary systems and fully implemented within the commercial computational fluid dynamics code AVL FIRE®, is exercised within a multi-fluid framework along with an interfacial area transport modeling procedure to study the heat and mass transfer characteristics of boiling flows inside a rectangular duct. Turbulence in the fluidic system and those generated by the bubbly flow are treated using an advanced k-ζ-f model. The simulation results, comprising of flow variables such as volume fraction, fluidic velocities, temperature and the resultant heat flux generated on the heated wall section, clearly monitors the suppression in heat transfer coefficients with enhancement in flow convection. Competing mechanisms such as phase change process and turbulent convection are identified to influence the heat transfer characteristics. In particular, the varying influence of the mass transfer effects on the heat flux characteristics with alteration in wall temperature is well demonstrated. For example, under low convection velocities, phase change dominates the heat removal from the wall with distinct bubbly flow activity in the boiling regions, while a considerable reduction in bubble dynamics and the phase change contribution towards heat removal with an increase in convection velocities can be clearly extracted. Comparisons of the predicted heat transfer coefficients for varying wall superheat and varying fluidic velocity indicate a very good agreement with experimental data wherever available. A description of the flow field inclusive of interfacial area and number density distribution is provided. The current model can be easily extended to simulate multi-phase flow in complex systems such as a cooling water jacket for automotive applications.