| 1. |
- Ljung, Anna-Lena, et al.
(författare)
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Convective drying of an individual iron ore pellet : Analysis with CFD
- 2011
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310 .- 1879-2189. ; 54:17-18, s. 3882-3890
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this paper is to model convective drying of an individual iron ore pellet placed in a free stream of air with the aim to clarify the different stages of drying. A numerical model taking into account capillary flow of liquid moisture and internal vapor flow is developed and implemented in a commercial available software for Computational Fluid Dynamics where also the flow around the pellet is simulated, yielding heat- and mass transfer coefficients as a function of position. A real pellet is optically scanned for its geometry and simulations of the drying are compared to experiments with very good agreement. The result clearly shows four stages of drying; (i) evaporation of liquid moisture at the pellet surface, (ii) surface evaporation coexisting with internal drying as the surface is locally dry, (iii) internal evaporation with completely dry surface and (iv) internal evaporation at boiling temperatures. A moisture front moving towards the core of the pellet will start to develop at the second drying stage and the results show that the front will have a non-symmetrical form arising from the surrounding fluid flow.
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| 2. |
- Ljung, Anna-Lena, et al.
(författare)
-
Influence of air humidity on drying of individual iron ore pellets
- 2011
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Ingår i: Drying Technology. - : Informa UK Limited. - 0737-3937 .- 1532-2300. ; 29:9, s. 1101-1111
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Tidskriftsartikel (refereegranskat)abstract
- The influence of air humidity on drying is investigated at four inlet air dew points; T dp = 273, 292, 313, and 333 K. A numerical model taking into account capillary transport of liquid and internal evaporation is applied to a spherical geometry representative for an individual iron ore pellet. Drying simulations are carried out with commercial computational fluid dynamic (CFD) software and the boundary conditions are calculated from the surrounding fluid flow. The results indicate that the effect of air humidity arises from the start of the first drying period, that is, the surface evaporation period, whereas the difference is reduced at the end of the period due to a prolonged stage of constant rate drying attained at high saturations. At low saturations, there is no constant drying stage because the surface becomes locally dry before the pellet temperature has stabilized at the wet bulb temperature. The magnitudes of the drying rates and moisture contents are rather similar at the time when internal drying becomes dominating (i.e., when the total surface evaporation rate is zero) for the respective dew points, yet the drying time is increased at high saturations. It was also found that the moisture gradients at the surface and inside the pellet increased with drying rate.
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| 3. |
- Tano, Kent T., et al.
(författare)
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Feature Extraction of a Strain-Gauge Signal Using Wavelets for Monitoring of a Tumbling Mill
- 2004
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Ingår i: Elsevier IFAC Publications / IFAC Proceedings series. - 1474-6670. ; 37:15, s. 35-39
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Tidskriftsartikel (refereegranskat)abstract
- Techniques that measure the force acting on a lifter bar, when it hits the charge inside a tumbling mill, have got an increased interest because of its direct physical relation to the behavior of the grinding charge. The possibility to combine it with discrete element modeling (DEM), which gives an opportunity to visualize the charge motion, opens new possibilities to understand the complex phenomena that takes place inside a grinding mill. In this work, a method for the measurement of the apparent filling level in a pilot ball mill, the Metso Continuous Charge Measurement system (CCM) has been used. The technique uses a strain gauge sensor, mounted on a flat steel spring, which is fitted into a recess underneath a lifter bar. Deflection of the lifter bar during every mill revolution will then give rise to a characteristic signal pattern depending on different operating conditions.In this work, which should be treated as an introduction, we show how the discrete wavelet transform can be used in multivariate calibration. It will be shown that by using the fast wavelet transform on individual signals as a pre-processing method in regression modeling on CCM measurements, good compression is achieved with almost no loss of information. The predictive ability and diagnostics of the data compressed regression model is almost the same as for the uncompressed.
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