Regimes of heat transfer in finite-size particle suspensions

Yousefi, Ali; Ardekani, Mehdi Niazi; Picano, Francesco; Brandt, Luca

doi:10.1016/j.ijheatmasstransfer.2021.121514

Cited by 16 publications

(23 citation statements)

References 57 publications

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“…Beyond that point, a steep decrease is observed with the Nusselt number dropping to 7.8 for the highest particle volume fraction considered, Φ = 40 %. This observation is similar to what reported in Yousefi et al (2021) for finite-size particle suspensions in a channel flow. In that study, the maximum Nusselt number was encountered at a particle volume fraction of 10 %, for all the Reynolds numbers within the transitional or fully turbulent regimes.…”

Section: Heat Transfer Modulationsupporting

confidence: 91%

“…Relative to the particles, this resolution corresponds to 24, 32 and 48 grid points per particle diameter, for the different particle diameters listed in table 1. This resolution was proven to be appropriate in other turbulent direct numerical simulation studies (Ardekani et al 2018a;Yousefi, Ardekani & Brandt 2020;Yousefi et al 2021).…”

Section: Case Descriptionmentioning

confidence: 98%

“…The same study also considered turbulent conditions and reported that the particles have the opposite effect on the heat transfer rates, causing the laminarisation of the core region of the pipe even for relatively low particle volume fractions and thus a relative reduction of heat transfer. Yousefi et al (2021) studied turbulent channel flows, focusing on the characterisation of the different regimes of heat transfer encountered when varying the Reynolds number from laminar to turbulent conditions and particle volume fraction up to 35 %. Similarly to Ardekani et al (2018b), the maximum heat flux rates reported by Yousefi et al (2021) were found at low particle volume fractions, O(10 %); the heat transfer, however, decreases below the single-phase turbulent values for higher volume fractions due to particle migration and the laminarisation of the flow in the channel core, see also Brandt & Coletti (2022).…”

Section: Introductionmentioning

confidence: 99%

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Turbulent Rayleigh–Bénard convection in non-colloidal suspensions

et al. 2022

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This study presents direct numerical simulations of turbulent Rayleigh–Bénard convection in non-colloidal suspensions, with special focus on the heat transfer modifications in the flow. Adopting a Rayleigh number of $10^8$ and Prandtl number of 7, parametric investigations of the particle volume fraction $0\leq \varPhi \leq 40\,\%$ and particle diameter $1/20\leq d^*_p\leq 1/10$ with respect to the cavity height, are carried out. The particles are neutrally buoyant, rigid spheres with physical properties that match the fluid phase. Up to $\varPhi =25\,\%$ , the Nusselt number increases weakly but steadily, mainly due to the increased thermal agitation that overcomes the decreased kinetic energy of the flow. Beyond $\varPhi =30\,\%$ , the Nusselt number exhibits a substantial drop, down to approximately 1/3 of the single-phase value. This decrease is attributed to the dense particle layering in the near-wall region, confirmed by the time-averaged local volume fraction. The dense particle layer reduces the convection in the near-wall region and negates the formation of any coherent structures within one particle diameter from the wall. Significant differences between $\varPhi \leq 30\,\%$ and 40 % are observed in all statistical quantities, including heat transfer and turbulent kinetic energy budgets, and two-point correlations. Special attention is also given to the role of particle rotation, which is shown to contribute to maintaining high heat transfer rates in moderate volume fractions. Furthermore, decreasing the particle size promotes the particle layering next to the wall, inducing a similar heat transfer reduction as in the highest particle volume fraction case.

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Section: Heat Transfer Modulationsupporting

confidence: 91%

Section: Case Descriptionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Turbulent Rayleigh–Bénard convection in non-colloidal suspensions

et al. 2022

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“…An example where this might not hold true is when particle migration occurs. At low Reynolds numbers for semi-dilute suspensions, inertial migration has been reported (Ardekani et al 2018;Dash et al 2021;Yousefi et al 2021). We compare SNR patterns in Fig.…”

Section: Effect Of Bmentioning

confidence: 90%

Ultrasound imaging velocimetry in particle-laden flows: counteracting attenuation with correlation averaging

et al. 2022

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Ultrasound imaging velocimetry (UIV) refers to the technique wherein ultrasound images are analysed with 2D cross-correlation techniques developed originally in the framework of particle image velocimetry. Applying UIV to opaque, particle-laden multiphase flows have long been considered to be an attractive prospect. In this study, we demonstrate how fundamental differences in acoustical imaging, as compared to optical imaging, manifest themselves in the 2D cross-correlation analysis. A chief point of departure from conventional particle image velocimetry is the strong variation in the intensity profile of the acoustic wavefield, primarily caused by the attenuation of ultrasonic waves in particle-laden flows. Attenuation necessitates using a larger ensemble of correlation planes to obtain satisfactory time-averaged velocity profiles. For a given combination of imaging and flow conditions, attenuation sets upper limits on volume fraction, penetration depth, as well as temporal resolutions that may be accessed confidently. This behaviour is demonstrated in two experimental datasets and is also supported by a modified cross-correlation theory. The modification is brought about by incorporating a lumped model of ultrasonic backscattering in suspensions into existing spatial cross-correlation analysis. The two experimental datasets correspond to two distinct particle-laden pipe flows: (1) a neutrally buoyant non-Brownian suspension in a laboratory-scale flow facility, wherein particle sizes are comparable to the ultrasonic wavelength and (2) a non-Newtonian slurry in an industrial-scale flow facility, wherein particle sizes are much smaller than the ultrasonic wavelength. We illustrate how and to what extent correlation averaging can counteract the adversity caused by attenuation. The work herein offers a template for one to evaluate the performance of UIV in particle-laden flows. Graphical abstract

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“…Another recent work (Peng et al, 2019) demonstrated that the pseudo-turbulent heat flux that arises in filtering the heat equation, is an important factor describing thermal properties. Yousefi et al (2021) employed particle-resolved direct numerical simulation to probe the heat transfer in particle-laden channels at moderate volume fractions, demonstrating that the turbulent heat flux dominates large scale thermal behavior.…”

Section: Introductionmentioning

confidence: 99%

On the thermal entrance length of moderately dense gas-particle flows

Beetham¹,

Lattanzi²,

Capecelatro³

2021

Preprint

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The dissipative nature of heat transfer relaxes thermal flows to an equilibrium state that is devoid of temperature gradients. The distance to reach an equilibrium temperature -the thermal entrance length -is a consequence of diffusion and mixing by convection. The presence of particles can modify the thermal entrance length due to interphase heat transfer and turbulence modulation by momentum coupling. In this work, Eulerian-Lagrangian simulations are utilized to probe the effect of solids heterogeneity (e.g., clustering) on the thermal entrance length. For the moderately dense systems considered here, clustering leads to a factor of 2-3 increase in the thermal entrance length, as compared to an uncorrelated (perfectly mixed) distribution of particles. The observed increase is found to be primarily due to the covariance between volume fraction and temperature fluctuations, referred to as the fluid drift temperature. Using scaling arguments and Gene Expression Programming, closure is obtained for this term in a one-dimensional averaged two-fluid equation and is shown to be accurate under a wide range of flow conditions.

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Regimes of heat transfer in finite-size particle suspensions

Cited by 16 publications

References 57 publications

Turbulent Rayleigh–Bénard convection in non-colloidal suspensions

Turbulent Rayleigh–Bénard convection in non-colloidal suspensions

Ultrasound imaging velocimetry in particle-laden flows: counteracting attenuation with correlation averaging

On the thermal entrance length of moderately dense gas-particle flows

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