Direct numerical simulations of heat transfer to a turbulent annular upward flow at supercritical pressure

Research output: Contribution to conferenceAbstractScientific

Abstract

Heated or cooled fluids at supercritical pressure show large variations in thermophysical properties, such as the density, dynamic viscosity and molecular Prandtl number, which strongly influence turbulence characteristics. To investigate this, direct numerical simulations were performed of a turbulent flow at supercritical pressure (CO2 at 8 MPa) in an annulus with a hot inner wall and a cold outer wall. The pseudo-critical temperature lies close to the inner wall, which results in strong thermophysical property variations in that region. We aim to obtain a better theoretical understanding of how the variable thermophysical properties attenuate both the flow field, as well as the heat transfer.
Turbulence in the near wall cycle can be thought of as a cycle of events or coherent structures; near wall streaks (coherent low speed fluid regions) become unstable, which results in the formation of quasi streamwise vortices that in turn may create streaks. The disruption of a component of this cycle may lead to laminarization of the flow. First, we will present how the generation of streaks is affected by variable density effects (such as local thermal expansion and buoyancy) as well as variable viscosity effects. We will also present a similar analysis for the generation of streamwise vorticity.
Secondly, we will focus on the effect of the (highly) variable molecular Prandtl number. The turbulent heat flux can be interpreted as the result of different turbulent events. The effectiveness of these turbulent events with respect to heat transfer is modulated due variations in the density, as well as the Prandtl number.
We believe that the presented insights may be of use in developing better heat transfer prediction models for heated fluids at supercritical pressure.
Original languageEnglish
Pages25-25
Publication statusPublished - 2016
EventThe 3rd International Meeting of Specialists on Transfer and Fluid Mechanics at Supercritical Pressure - Sheffield, United Kingdom
Duration: 25 Aug 201626 Aug 2016
http://hfscp2016.group.shef.ac.uk/

Conference

ConferenceThe 3rd International Meeting of Specialists on Transfer and Fluid Mechanics at Supercritical Pressure
Abbreviated titleHFSCP2016
CountryUnited Kingdom
CitySheffield
Period25/08/1626/08/16
Internet address

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