Zhang 2007, An Optimization of Intermittent Corn Drying in a Laboratory Scale Thin Layer Dryer (3)

This article was downloaded by: [Cinvestav del IPN] On: 09 April 2013, At: 08:55 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Drying Technology: An International Journal Publication details, including instructions for authors and subscription information: AN OPTIMIZATION OF INTERMITTENT CORN DRYING IN A LABORATORY SCALE THIN LAY
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  This article was downloaded by: [Cinvestav del IPN]On: 09 April 2013, At: 08:55Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK Drying Technology: An International Journal Publication details, including instructions for authors and subscription information: AN OPTIMIZATION OF INTERMITTENT CORN DRYING IN ALABORATORY SCALE THIN LAYER DRYER  Q. Zhang a  & J.B. Litchfield aa  Department of Agricultural Engineering, University of Illinois, Urbana, IL, 61801Version of record first published: 25 Apr 2007. To cite this article:  Q. Zhang & J.B. Litchfield (1991): AN OPTIMIZATION OF INTERMITTENT CORN DRYING IN A LABORATORYSCALE THIN LAYER DRYER, Drying Technology: An International Journal, 9:2, 383-395 To link to this article: PLEASE SCROLL DOWN FOR ARTICLEFull terms and conditions of use: article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form toanyone is expressly forbidden.The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses shouldbe independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly inconnection with or arising out of the use of this material.   RYING TECHNOLOGY, 9 2), 383-395 1991) AN OPTIMIZ TION OF INTERMITTENT CORN DRYING IN L BOR TORY SC LE THIN L YER DRYER Q. Zhang and J.B. Litchfield Department of Agricultural Engineering University of Illinois Urbana, IL 61801 Key Words and Phrases: Tempering; time lag; multi-stage drying; control strategy ABSTRACT An intermittent corn drying process of drying-tempering-drying in a laboratory scale thin layer dryer was optimized. A time lag function was developed to describe the influence of the tempering period on the drying rate in the post-tempering drying period. Three dryer control strategies 1) a drying-rate-first strategy, 2) an energy-efficiency-first strategy, and 3) an equal- importance ratelefficiency) strategy were investigated. Results showed that intermittent drying processes were optimal except when a high drying rate was desired. INTRODUCTION During the falling-rate drying regime, the drying rate falls with time because the internal migration rate of moisture is slower than the evaporation rate from the surface. By inserting a tempering, or holding, period during the 383 Copyright 1991 by Marcel Dekker nc    D  o  w  n   l  o  a   d  e   d   b  y   [   C   i  n  v  e  s   t  a  v   d  e   l   I   P   N   ]  a   t   0   8  :   5   5   0   9   A  p  r   i   l   2   0   1   3   84 ZH NG ND LITCHFIELD falling-rate regime, the net drying rate can be raised. A drying process which includes both active drying stages and tempering periods is an intermittent drying process. Intermittent drying also makes it convenient to apply different drying temperatures for each stage. Brook and Bakker-Arkema 1978) found that a high drying temperature might be safely applied in early stages of drying in a multi-stage dryer. The authors also noted the possibility of obtaining higher quality dried corn from an intermittent drying process than from a continuous drying process. The objectives of this study were to: 1) develop a time lag function to determine the influence of tempering on drying rate during post-tempering drying; and 2) optimize an intermittent drying process under three control strategies: drying rate first, energy efficiency first, and equal importance. METHO OLOGY This study included two steps. First, we developed a time lag function for describing the influence of tempering on the drying rate in the subsequent drying period. A laboratory thin layer dryer was used, and a series of intermittent drying tests with different tempering periods between two drying periods were conducted. Secondly, we conducted a system optimization to develop an optimal drying process for specific control strategies. Three control strategies, with objectives of, 1) drying rate first, 2) energy efficiency first, and 3) equal importance of both rate and efficiency), were studied. A laboratory thin layer dryer was developed with a load cell to determine product weight during drying. The temperature and the velocity of    D  o  w  n   l  o  a   d  e   d   b  y   [   C   i  n  v  e  s   t  a  v   d  e   l   I   P   N   ]  a   t   0   8  :   5   5   0   9   A  p  r   i   l   2   0   1   3  INTERMITTENT CORN DRYING 85 the drying air were measured by thermocouple and anemometer. The dry- and wet-bulb temperatures of ambient air were measured with a psychrometer. The initial and final moisture content of samples was determined by oven test (ASAE Standard S352.1, 1989). EVELOPMENT OF TIM L G FUNCTION Page's equation of thin layer drying (1949) was applied in this study. where: M. is kernel initial moisture content, M is kernel current moisture content, Me is kernel equilibrium moisture content, is the drying time, and k and n are constants. Misra and Brooker (1980) compiled data for shelled corn drying in thin layer dryers and derived two expressions for the constants k and n in Page's equation. where: T is drying temperature (2.2 C T 71.1 C), V, is drying-air velocity near the kernels (0.025 mls V 2.33 mls), RH s relative    D  o  w  n   l  o  a   d  e   d   b  y   [   C   i  n  v  e  s   t  a  v   d  e   l   I   P   N   ]  a   t   0   8  :   5   5   0   9   A  p  r   i   l   2   0   1   3
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