Numerical Study of Heat Transfer Mechanism in Turbulent Supercritical CO2 Channel Flow

李新亮,; Hashimoto, K.; Tominaga, Yoichi; Tanahashi, Mamoru; Miyauchi, Toshio

doi:10.1299/jtst.3.112

Cited by 17 publications

(12 citation statements)

References 11 publications

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“…We remark that the variable-property algorithm employed in this work is similar to those developed by Bae, Yoo & Choi (2005), Li et al (2008), Sewall & Tafti (2008) and Kang, Iaccarino & Ham (2009). In all of these cases the viscosity, density and thermal conductivity vary with temperature.…”

Section: Introductionmentioning

confidence: 81%

“…Kang et al (2009) considered conjugate heat transfer around a cylinder in a channel heated from below where the working fluid is water, yet its dependency upon temperature is implemented using tabulated data. Bae et al (2005) performed DNSs of turbulent CO 2 fluid at supercritical pressure in heated vertical tubes with low-Mach-number approximation and considering buoyancy effects, whereas Li et al (2008) analysed a similar problem (supercritical CO 2 turbulent flow) in a different geometry (channel flow) and with a fully compressible approach (albeit neglecting buoyancy effects).…”

Section: Introductionmentioning

confidence: 99%

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Modulation of turbulence in forced convection by temperature-dependent viscosity

2012

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In this work, we run a numerical experiment to study the behaviour of incompressible Newtonian fluids with anisotropic temperature-dependent viscosity in forced convection turbulence. We present a systematic analysis of variable-viscosity effects, isolated from gravity, with relevance for aerospace cooling/heating applications. We performed an extensive campaign based on pseudo-spectral direct numerical simulations of turbulent water channel flow in the Reynolds number parameter space. We considered constant temperature boundary conditions and different temperature gradients between the channel walls. Results indicate that average and turbulent fields undergo significant variations. Compared with isothermal flow with constant viscosity, we observe that turbulence is promoted in the cold side of the channel, characterized by viscosity locally higher than the mean: in the range of the examined Reynolds numbers and in absence of gravity, higher values of viscosity determine an increase of turbulent kinetic energy, whereas a decrease of turbulent kinetic energy is determined at the hot wall. Examining in detail the turbulent kinetic energy budget, we find that turbulence modifications are associated with changes in the rate at which energy is produced and dissipated near the walls: specifically, at the hot wall (respectively cold wall) production decreases (respectively increases) while dissipation increases (respectively decreases)

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Section: Introductionmentioning

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Modulation of turbulence in forced convection by temperature-dependent viscosity

2012

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“…The streamwise extent of the computational domain is deemed sufficient for the present study as several authors have observed that heated turbulent flows with supercritical working fluids are dominantly affected by nearwall flow phenomena. 25,27,28,40 To ensure that the coherent flow structures are self sustaining, the span of the computational domain must adhere to L z + > 220. 39 The domain span of L z + > 740 (L z = 3.2δ) for the present study is therefore quite conservative.…”

Section: B Computational Domainsmentioning

confidence: 99%

Effects of spatial gradients in thermophysical properties on the topology of turbulence in heated channel flow of supercritical fluids

Azih

Yaras

2018

Physics of Fluids

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The current literature suggests that large spatial gradients of thermophysical properties, which occur in the vicinity of the pseudo-critical thermodynamic state, may result in significant variations in forced-convection heat transfer rates. Specifically, these property gradients induce inertia- and buoyancy-driven phenomena that may enhance or deteriorate the turbulence-dominated heat convection process. Through direct numerical simulations, the present study investigates the role of coherent flow structures in channel geometries for non-buoyant and buoyant flows of supercritical water, with buoyant configurations involving wall-normal oriented gravitational acceleration and downstream-oriented gravitational acceleration. This sequence of simulations enables the evaluation of the relative contributions of inertial and buoyancy phenomena to heat transfer variations. In these simulations, the state of the working fluid is in the vicinity of the pseudo-critical point. The uniform wall heat flux and the channel mass flux are specified such that the heat to mass flux ratio is 3 kJ/kg, with an inflow Reynolds number of 12 000 based on the channel hydraulic diameter, the area-averaged inflow velocity, and fluid properties evaluated at the bulk temperature and pressure of the inflow plane. In the absence of buoyancy forces, notable reductions in the density and viscosity in close proximity of the heated wall are observed to promote generation of small-scale vortices, with resultant breakdown into smaller scales as they interact with preexisting larger near-wall vortices. This interaction results in a reduction in the overall thermal mixing at particular wall-normal regions of the channel. Under the influence of wall-normal gravitational acceleration, the wall-normal density gradients are noted to enhance ejection motions due to baroclinic vorticity generation on the lower wall, thus providing additional wall-normal thermal mixing. Along the upper wall, the same mechanism generates streamwise vorticity of the opposing sense of rotation in the close vicinity to the respective legs of the hairpin vortices causing a net reduction in thermal mixing. Finally, in the case of downstream-oriented gravitational acceleration, baroclinic vorticity generation as per spanwise density gradients causes additional wall-normal thermal mixing by promoting larger-scale ejection and sweep motions.

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“…The validity of using shorter domains and hence not resolving the largest scales is discussed in detail by Jimenez et al (1999Jimenez et al ( , 1991. (Azih et al, 2012;Bae et al, 2008;Li et al, 2007;Bae et al, 2005). To ensure that the coherent flow structures are self sustaining, the span of the computational domain must adhere to L z + >220 (Jimenez & Moin, 1991).…”

Section: Computational Domainsmentioning

confidence: 99%

“…This velocity profile is specified at the inflow boundary and is used to initialize the computational domain. In Equation A-1, the origin is located at the bottom surface as illustrated in Figure A- phenomena (Azih et al, 2012;Bae et al, 2008;Li et al, 2007). Therefore, the computational domain must be sufficiently long to accurately capture the transient flow structures developing in the near-wall region.…”

Section: A12 Computational Domains Boundary Conditions and Initialmentioning

confidence: 99%

Computation and Modelling of Convection Heat Transfer of Supercritical Fluids

Azih¹

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Current literature suggests that large spatial gradients of thermophysical properties, which occur in the vicinity of the pseudo-critical thermodynamic state, may result in significant variations in forced-convection heat transfer rates. Specifically, these property gradients induce inertia-and buoyancy-driven flow phenomena that may enhance or deteriorate the turbulence-dominated heat convection process. Understanding of these inertia/buoyancy-driven mechanisms has not been sufficiently established to date. Consequently, the full set of dynamic similarity parameters remains to be identified. Through direct numerical simulations of turbulent boundary layers and channel flows, the present study investigates the characteristics of the flow structures of turbulence in heated flows of supercritical water under buoyant and non-buoyant conditions. In the absence of buoyancy forces, notable reductions in the density and viscosity in close proximity of the heated wall are observed to promote an increase in the wall shear stress, with resultant loss of coherence of the new near-wall flow structures. This leads to the dominance of larger-scale structures in the wall-normal thermal mixing process that comes at the expense of the smaller-scale thermal mixing, and yields a net reduction in the overall thermal mixing. Under the influence of wall-normal gravitational acceleration, the wall-normal density gradients are noted to enhance ejection motions due to baroclinic vorticity generation on the lower wall of the channel, thus providing additional wall-normal thermal mixing.

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Numerical Study of Heat Transfer Mechanism in Turbulent Supercritical CO2 Channel Flow

Cited by 17 publications

References 11 publications

Modulation of turbulence in forced convection by temperature-dependent viscosity

Modulation of turbulence in forced convection by temperature-dependent viscosity

Effects of spatial gradients in thermophysical properties on the topology of turbulence in heated channel flow of supercritical fluids

Computation and Modelling of Convection Heat Transfer of Supercritical Fluids

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