Heat transfer in rotary kilns with interstitial gases

Shi, Deliang; Vargas, Watson L.; McCarthy, Joseph J.

doi:10.1016/j.ces.2008.06.006

Cited by 90 publications

(36 citation statements)

References 34 publications

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“…These systems have been investigated in detail by Smart et al [4], Shi et al [5], or Vargas et al [6]. Also, a hotly debated question is the heating of brittle rocks in fault gouges during earthquakes in the field of geophysics, for instance as discussed in Rice [7].…”

Section: Introductionmentioning

confidence: 99%

Heat transfer rates in sheared beds of inertial particles at high Biot numbers

et al. 2017

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We investigate heat conduction rates through the contact network of sheared granular materials that consist of particles with a density much larger than that of the ambient fluid. The tool ParScale, a finite difference solver for intra-particle transport processes, is coupled to the discrete element method solver LIGGGHTS to carry out the simulations. Heat transfer to the surrounding fluid is considered via a fixed heat transfer coefficient. We identify a combination of Biot and Peclet number as the key non-dimensional influence parameter to describe the non-dimensional heat flux through the particle bed and provide an analytical solution to calculate mean particle temperature profiles. Simulations over a wide range of particle volume fractions, Biot and Peclet numbers are then performed in order to develop a continuum model for the heat flux. We show that for Biot numbers below 10 −3 our results agree with a simple model based on a uniform particle temperature. However, for Biot numbers above a certain threshold, the conductive heat flux decreases substantially depending on the flow situation, and temperature gradients within the particle should be considered in order to correctly predict the heat transfer rate to the surrounding fluid.

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Section: Introductionmentioning

confidence: 99%

Heat transfer rates in sheared beds of inertial particles at high Biot numbers

et al. 2017

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“…In addition to this obvious advection, in turbulent flow of water vortices develop and induce heat transfer normal to the mass flux [6]. Granular flows exhibit similar turbulent-like patterns of velocity vortices [7], leading to temperature mixing normal to the mass flux [8], but the corresponding heat flux has not been studied. Unlike water, vortice-like motion in granular media results from force chain buckling, leading to high fluctuations in local strain and kinetic energies, and thereafter, as we show, to thermal convection that increases with vertical stresses.…”

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confidence: 99%

Thermal Transients and Convective Particle Motion in Dense Granular Materials

Rognon

Einav

2010

Phys. Rev. Lett.

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The mechanism of dry granular convection within dense granular flows is mostly neglected by current analytical heat equations describing such materials, for example, in geophysical analyses of shear gouge layers of earthquake and landslide rupture planes. In dry granular materials, the common assumption is that conduction by contact overtakes any other mode of heat transfer. Conversely, we discover that transient correlated motion of heated grains can result in a convective heat flux normal to the shear direction up to 3-4 orders magnitude larger than by contact conduction. Such a thermal efficiency, much higher than that of water, is appealing and might be common to other microscopically structured fluids such as granular pastes, emulsions, and living cells. DOI: 10.1103/PhysRevLett.105.218301 PACS numbers: 47.57.Gc, 47.55.pb, 65.20.Àw, 91.32.Jk The temperature evolution within sheared granular layers is balanced by heat production and transfer. Identifying the dominant modes of the heat transfer is therefore critical to temperature predictions. As typical with any classical fluid, the two most important modes of heat transfer during granular flow are those by conduction and convection. Heat conduction is now well understood to rely on the properties controlling the contact network: contact size, anisotropy, and heterogeneity [1][2][3][4]. Various studies examined the effect of convection on the heat transfer between the flowing granular materials and bounding walls [5]. In such cases where the wall interacts with the flow, the heat transfer is affected by the first layer of wall-contacting grains that may or may not recirculate. Moreover, the efficiency of the overall heat transfer depends on the thermal properties of the wall. Here, we examine the heat transfer that is purely intrinsic to the granular media, independent of wall properties. Intrinsic to the flow, the heat is carried by grains as they move. We term this process dry granular convection. Some heat is thus simply flowing along the mass flux. In addition to this obvious advection, in turbulent flow of water vortices develop and induce heat transfer normal to the mass flux [6]. Granular flows exhibit similar turbulent-like patterns of velocity vortices [7], leading to temperature mixing normal to the mass flux [8], but the corresponding heat flux has not been studied. Unlike water, vortice-like motion in granular media results from force chain buckling, leading to high fluctuations in local strain and kinetic energies, and thereafter, as we show, to thermal convection that increases with vertical stresses.In this Letter, we discover that dry granular convection does add a striking contribution to the overall heat transfer budget in dense granular flows. The study is based on a series of numerical experiments using thermal discrete element method [2]; the motion and the temperature evolution of the grains are simulated while they experience a plane shear flow and a temperature gradient in the direction transverse to the shear plane [ Fig. 1(a)]. ...

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“…The average diameter of flame d f depends strongly on the hydrodynamic feature of turbulent diffusion. By visual observation of the flame in a practical rotary kiln, in which a burner is operated under similar flow conditions to the one planned, we can estimate the approximate value of d f /d ti The average temperature T is calculated using the following equation: (2) 3 Radiant heat transfer from inner wall surface to rotating solids layer…”

Section: Mathematical Modeling Of Inside Heat Transfer On a Rotary Kimentioning

confidence: 99%

Energy recovery of a rotary kiln system in a calcium oxide plant

Aldeib¹,

El-Alem²,

Elgezawi³

2011

WIT Transactions on Ecology and the Environment

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The dominant source of calcium carbonate is limestone; the most common constituent of all rocks. It occurs in nature with clay, silica and other minerals, which may interfere in many applications. Synthetic calcium carbonate is produced on a large scale where a calcium chloride stream is treated with sodium or ammonium carbonate to produce a high grade of calcium carbonate. In turn, calcium carbonate is heated to 900-1000 degree centigrade in a horizontal lime kiln to produce calcium oxide (burned lime). Calcium oxide is used extensively in cement, iron and steel industries due to the low cost of the material and its accepted chemical properties. In this study, composition of raw meal, ultimate analysis of the fuel, dust contents in the exhaust gases, losses in ignation (COI) and exhaust gas composition in the preheated suspension are calculated. The heat losses from kiln exhaust are minimized. A secondary shell on the kiln surface is also investigated. In this work mathematical models for the calculations of inside heat transfer on the rotary are used, and the total energy utilized by burning fuel oil in the process of calcium oxide production is also calculated. The heat losses for kiln exhaust gas, hot air from the cooler stock losses and radiation losses from kiln surface are also minimized. A secondary shell on the kiln surface is studied in the present study, where 4% of total energy input is saved. This energy saving would result in a considerable reduction of fuel consumption in the kiln system. The overall efficiency would be improved by 5%.

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Heat transfer in rotary kilns with interstitial gases

Cited by 90 publications

References 34 publications

Heat transfer rates in sheared beds of inertial particles at high Biot numbers

Heat transfer rates in sheared beds of inertial particles at high Biot numbers

Thermal Transients and Convective Particle Motion in Dense Granular Materials

Energy recovery of a rotary kiln system in a calcium oxide plant

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