Numerical and experimental studies of available energy losses in laminar and turbulent flows.

摘要

A new experimental technique is developed for measuring the instantaneous entropy production using a non-intrusive laser based approach. The experimental procedure combines the method of Planar Laser Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV) for measured velocity and temperature fields in different applications. Unlike pointwise methods which yield a measured velocity at a single point in space, the method of PIV is used to derive velocity gradients over the entire problem domain. When combined with local temperatures and thermal irreversibilities, these velocity results can be used to determine the energy availability loss due to exergy destruction. The local entropy production data provides useful information regarding the spatial distribution of mechanical energy loss, which can be used to systematically optimize thermofluid systems. The measured data also provides validation for previous predictive models. Local entropy production rates due to fluid friction are determined from an experimental study of laminar and turbulent flow in a channel, as well as natural convection in an enclosure.; An entropy-based conversion algorithm in the measurement procedure is developed and compared with numerical predictions of free convection in a square cavity. The numerical predictions are obtained from a Control-Volume Based Finite Element Method (CVFEM) for the conservation equations and the Second Law. Analytical and direct numerical solutions are employed for a qualitative assessment of the experimental procedure in the channel flow problem. The predicted and measured results show close agreement. For the free convection problem, a measurement uncertainty analysis suggests that the algorithm post-processes velocity (accurate within +/-0.5%) to successfully give entropy production data, which is accurate within +/-9.34%. Extensions of the loss mapping technique to turbulent flow engendered a new model for a turbulence correlation in the entropy transport equation of viscous, incompressible flow. Additional terms were introduced into the entropy production relation in the conversion algorithm, due to the dissipation of turbulent kinetic energy. Previous methods of measuring dissipation rate are outlined in the context of the PIV technique.