Entropy production calculation for turbulent shear flows and their implementation in cfd codes

Computational fluid dynamics (CFD) solutions of turbulent convective heat transfer problems based on the mass, momentum and energy conservation principle provide all information to calculate the entropy production rate in such a transfer process. It can be determined in the post processing phase of a CFD calculation. Two methods are discussed in detail which can provide the information about the entropy production with different degrees of accuracy.

Direct and indirect methods of calculating entropy generation rates in turbulent convective heat transfer problems

Multi-objective shape optimization of a heat exchanger using parallel genetic algorithms

Entropy production analysis of hysteresis characteristic of a pump-turbine model

Thermal performance and entropy generation analysis of a high concentration ratio parabolic trough solar collector with Cu-Therminol®VP-1 nanofluid

Local entropy production in turbulent shear flows: a high-Reynolds number model with wall functions

Performance evaluation of heat transfer devices can be based on the overall entropy production in these devices. In our study we therefore provide equations for the systematic and detailed determination of local entropy production due to dissipation of mechanical energy and due to heat conduction, both in turbulent flows. After turbulence modeling has been incorporated for the fluctuating parts the overall entropy production can be determined by integration with respect to the whole flow domain. Since, however, entropy production rates show very steep gradients close to the wall, numerical solutions are far more effective with wall functions for the entropy production terms. These wall functions are mandatory when high Reynolds number turbulence models are used. For turbulent flow in a pipe with an inserted twisted tape as heat transfer promoter it is shown that based on the overall entropy production rate a clear statement from a thermodynamic point of view is possible. For a certain range of twist strength there is a decrease in overall entropy production compared to the case without insert. Also, the optimum twist strength can be determined. This information is unavailable when only pressure drop and heat transfer data are given.

Local entropy production in turbulent shear flows: A tool for evaluating heat transfer performance

We report numerical simulation of pure continuum-based laminar gas micro-flow convection with steep density gradients, which cause, for the case of heated air, flattening and rate of flattening of axial velocity profile. This flattening is similar to the characteristics in constant-properties slip flow, and high rate of flattening can cause hydrodynamic undevelopment of flow—the reverse process of hydrodynamic development. By continuity, radially outward velocities and radial convection are induced, which degrades convection performance. The low densities near the wall reduce the axial mass flux near the wall, which also degrades convection performance. In heated-gas micro-flows, these negative effects dominate to dictate the net convection characteristics, which differ considerably from the known characteristics of conventional continuum models. The identification of such microscale effects also has implications in possibly extending the limits of applicability of continuum models to higher Knudsen numbers.

Fabian Kock

Papers

Local entropy production in turbulent shear flows: a high-Reynolds number model with wall functions

Entropy production calculation for turbulent shear flows and their implementation in cfd codes

Direct and indirect methods of calculating entropy generation rates in turbulent convective heat transfer problems

Local entropy production in turbulent shear flows: A tool for evaluating heat transfer performance

Laminar gas micro-flow convection characteristics due to steep density gradients