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Research Papers

Computer Simulation of Drying of Food Products With Superheated Steam in a Rotary Kiln

[+] Author and Article Information
Koustubh Sinhal, Bhaskar Dasgupta

 Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India

P. S. Ghoshdastidar1

 Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, Indiapsg@iitk.ac.in

1

Corresponding author.

J. Thermal Sci. Eng. Appl 4(1), 011009 (Mar 19, 2012) (13 pages) doi:10.1115/1.4005256 History: Received October 03, 2010; Revised October 06, 2011; Published March 09, 2012; Online March 19, 2012

The present work reports a computer simulation study of heat transfer in a rotary kiln used for drying and preheating food products such as fruits and vegetables with superheated steam at 1 bar. The heat transfer model includes radiation exchange among the superheated steam, refractory wall and the solid surface, conduction in the refractory wall, and the mass and energy balances of the steam and solids. The gas convection is also considered. Finite-difference techniques are used, and the steady state thermal conditions are assumed. The false transient approach is used to solve the wall conduction equation. The solution is initiated at the inlet of the kiln and proceeds to the exit. The output data consist of distributions of the refractory wall temperature, solid temperature, steam temperature, and the total kiln length. The inlet of the kiln is the outlet of the gas (superheated steam), since the gas flow is countercurrent to the solid. Thus, for a fixed solid and gas temperature at the kiln inlet, the program predicts the inlet temperature of the gas (i.e., at the kiln exit) in order to achieve the specified exit temperature of the gas. In the absence of experimental results for food drying in a rotary kiln, the present model has been satisfactorily validated against numerical results of Sass (1967, “Simulation of the Heat-Transfer Phenomena in a Rotary Kiln,” Ind. Eng. Chem. Process Des. Dev., 6 (4), pp. 532–535) and limited measured gas temperature as reported by Sass (1967, “Simulation of the Heat-Transfer Phenomena in a Rotary Kiln,” Ind. Eng. Chem. Process Des. Dev., 6 (4), pp. 532–535) for drying of wet iron ore in a rotary kiln. The results are presented for drying of apple and carrot pieces. A detailed parametric study indicates that the influence of controlling parameters such as percent water content (with respect to dry solids), solids flow rate, gas flow rate, kiln inclination angle, and the rotational speed of the kiln on the axial solids and gas temperature profiles and the total predicted kiln length is appreciable. The effects of inlet solid temperature and exit gas temperature on the predicted kiln length for carrot drying are also shown in this paper.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic cross-section of a rotary kiln showing heat transfer processes, the fill-angle and the coordinate system

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Figure 2

Section of the kiln showing wall and solid surface elements

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Figure 3

Energy transport in the solid and gas in an axial segment in the first and third sections of the kiln

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Figure 4

Energy transport in the solid and gas in an axial segment in the second section of the kiln

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Figure 5

Validation of the results (axial solid and gas temperature distributions) based on the present model for drying of wet iron ore in a rotary kiln

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Figure 6

Axial solid and gas temperature distributions versus percent kiln length for apple and carrot drying based on the input data in Table 1

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Figure 7

Axial solid and gas temperature distributions for various proportions of water in solid feed (for apple drying)

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Figure 8

Axial solid and gas temperature distributions for different mass flow rates of the (dry) solid (for apple drying)

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Figure 9

Axial solid and gas temperature distributions for different mass flow rates of the gas (for apple drying)

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Figure 10

Axial solid and gas temperature distributions for different angles of inclination (for apple drying)

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Figure 11

Axial solid and gas temperature distributions for different rotational speeds (for apple drying)

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Figure 12

Shape factor between infinite parallel surfaces

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Figure 13

Velocity vector diagram for a solid particle in the Kiln

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