Closure of a macroscopic turbulence and non-equilibrium turbulent heat and mass transfer model for a porous media comprised of randomly packed spheres

Khan, Furqan Ahmad; Straatman, Anthony G.

doi:10.1016/j.ijheatmasstransfer.2016.05.106

Cited by 18 publications

(10 citation statements)

References 40 publications

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“…It is important that all directions be considered since proper specification of permeability/inertial coefficients and heat/gas exchange coefficients for a porous-continuum model of the same domain requires knowledge of anisotropy of all processes. The Reynolds number has been calculated based on the average fruit diameter and the extrinsic velocity [1,2], and ranges from 0.1 to 200 covering most of the laminar flow regime. The Reynolds numbers correspond to a range of extrinsic velocities of 10 −5 to 0.05.…”

Section: Resultsmentioning

confidence: 99%

“…In this manner, the simulations represent the near steady-state storage condition under which the produce can remain for a long period of time. In addition, the fixed-temperature condition enables use a log-mean-temperature-difference (LMTD) approach, similar to that used in [1,2], for calculating the convective heat transfer coefficient, which can then be applied in porous continuum simulations. It is noticed here that heat transfer is highest for vertical-direction (y) flow, owing once again to the fact that flow in this direction is forced to pass throughout the stacked produce, while in the x or z directions, much of the air can pass over the stack.…”

Section: Resultsmentioning

confidence: 99%

“…In cases of weak tortuosity and dispersion effects, both may be represented in terms of the point-form constants, i.e., εk f and εD i f , respectively [2,33,42]. It is noted that unlike the work of Elhalwagy and Straatman [33], the specific heats c p,i are based on absolute temperature herein and not referenced at 0 • C. As elaborated above, there is no need for closure coefficients for the respiration source terms and hence, closure is only needed for K, c E and h f s .…”

Section: The Porous Continuum Modelmentioning

confidence: 99%

“…For macroscopic calculations, the transport equations are volume-averaged and the influence of the detailed shape and packing arrangement are characterized by drag and exchange models, which require closure coefficients. The closure process can be either physically based, which depends on selection of a representative elementary volume (REV) of the porous media [1,2], or empirical in that it depends on experimental verification and sensitivity analysis of closure parameters [3,4].…”

Section: Introductionmentioning

confidence: 99%

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A Multi–Level Approach for Simulation of Storage and Respiration of Produce

2019

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A produce gas respiration model and fruit-stack geometric digital generation approach is used with commercial CFD software (ANSYS CFXTM) to conduct shape-level simulations of the fluid flow, heat and respiration processes that occur during the storage of produce, with the ultimate purpose of providing detailed information that can be used to develop closure coefficients for volume-averaged simulations. A digital generation procedure is used to develop an accurate representation of the shapes of the different produce. The produce shapes are then implemented into a discrete element modelling tool to generate a randomly-distributed stack of produce in a generic container, which is then utilized as a representative elementary volume (REV) for simulations of airflow and respiration. Simulations are first conducted on single pieces of produce and compared to a recently published experimental data for tomatoes and avocadoes to generate coefficients for the respiration model required for the shape-level simulations on the REV. The results of the shape-level simulation are then processed to produce coefficients that can be used for volume-averaged (porous-continuum-level) calculations, which are much more practical for simulations of large areas of storage comprised of hundreds or thousands of boxes of different commodities. The results show that the multi-level approach is a viable means for developing the simulation parameters required to study refrigeration, ripening and storage/transport of produce.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: The Porous Continuum Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Multi–Level Approach for Simulation of Storage and Respiration of Produce

2019

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“…However, using this approach requires that detailed information about the pore-level structure and flow field be determined and provided via physical models that characterize the porous region [35].…”

Section: Packed Beds Of Particlesmentioning

confidence: 99%

The development and numerical modelling of a Representative Elemental Volume for packed sand

Thabet

Straatman

2018

Chemical Engineering Science

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The motivation of this thesis is the development of simple microscopic-scale model (representative elemental volume; REV) that can be used to conduct flow and heat transfer simulations from which closure coefficients can be established for the volume-averaged transport equations for porous media (packed bed). The thesis provides a brief introduction to the computational technique adopted for the geometric generation of the REV (YADE), followed by a parametric study undertaken to reveal the minimum number of particles inside the REV that are required to mimic the appropriate physics. Additional analysis was conducted with the goal of determining the influence of deviation in particle diameter. A wide range of particle temperatures was considered for analyzing the convective heat transfer and hydrodynamic behavior such the influence of property variation on temperature could also be studied. The key research output is a detailed comparison of the results related to the hydrodynamics and heat transfer closures produced by an idealized, YADE-generated model against a three-dimensional, digitized model of packed sand. It is shown that the YADE model gives results that are in very good agreement with the digitized packed-sand model in the range of Reynolds numbers considered. The YADE model results were then compared with experimental findings and it was found that while the trends in convective heat transfer were well-predicted, there was a difference in the magnitude of the convective coefficients predicted and measured in previous experiments.

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