Zogzas while others (1994) believe you to noticeable thickness depends on the amount shrinking coefficient and you can wetness blogs (Table 3, Eq

Zogzas while others (1994) believe you to noticeable thickness depends on the amount shrinking coefficient and you can wetness blogs (Table 3, Eq

Obvious density (?b) designs

Based on Krokida and you will Philippopoulos (2005) , apparent occurrence is a function of water articles, variety of strong, and you may heavens volume proportion. All of the patterns to own forecasting apparent density found in this new books are empirical; simple or theoretical designs have only started proposed of the a finite level of writers ( Rahman while others 1996 ). The latest visible occurrence activities was designed based on dampness blogs (X), without due to the results of drying out temperatures; not many believe diminishing, though it are significant about majority of cases ( Moreira while others 2000 ; ).

18), where the volumetric shrinking coefficient (?) is a linear function of moisture content. Boukouvalas and others (2006) mention that the parameters ( , ?) included in Eq. 18 of Table 3 depend on the drying method and processing conditions; as such, they propose Eq. 19, which considers ? to be a function of , ?w, and X.

Moreira while others (2000) hold you to noticeable density exists making use of the obvious occurrence of your own good ( ) and size out-of liquid ( ) at the beginning of drying out just like the a reference to own initial volume (Eq. 20, Dining table 3).

In Eq. 18 and 19, X= 0 is taken as a reference; in Eq. 20, the reference is X0= moisture content at the onset of drying.

The most recent theoretical model (Eq. 21) was put forth by Khalloufi and others (2010) . They consider ?b to be a function of the initial porosity of the material (?), X, ?w, ?s, ?(X), and collapse [?(X)].

While the ?(X) and you may ?(X) would be the attributes of dampness posts, he could be determined by handling conditions, the nature of your own tool becoming dehydrated, the new drying strategy, in addition to drying out phase ( Khalloufi while some 2010 ).

This new failure picture (Eq. 27) proposed by the Khalloufi and others (2009) pledges that collapse form usually begins in one and you will ends from inside the zero.

When the matter is actually a good rubbery state, diminishing compensates nearly totally for dampness losings, as well as the number of the information presented reduces linearly that have dampness posts ( ). However, low-heat dehydration from food products prevents the brand new dampness posts regarding the cardio of issue out of ever being much greater than regarding the outside, minimizing inner be concerned, and therefore, breaking ( Bai although some 2002 ).

An incorrect computation out of ?(X) and ?(X) offers rise to an error throughout the formula from visible thickness. This happens quite frequently, as the majority of authors believe that diminishing is actually linear ( Zogzas while some 1994 ; Moreira and others 2000 ; ), otherwise they fit they in order to a moment-studies polynomial ( Khalloufi although some 2010 ).

Upcoming designs is make an effort to depict brand new choices out of apparent density having better precision, looking at X and the thermal reputation of the materials are dried.


The tendencies of density with respect to moisture content and drying temperature have been discussed within the framework of currently available theories of second-order phase changes, structural changes, and changes in chemical composition occurring in the mass and heat transference processes. The majority of the empirical and theoretical equations representing true density do not fit the concave-down tendencies of certain materials. Equations for calculating apparent density based on shrinking and collapse are not reliable, as errors arise from failing to consider minimal variations in volume at the end of the drying process. It is recommended that variations in ?s and ?w as a function of the internal temperature of the material, according to the drying conditions (X, T), be included to yield a better fit to the tendencies of density with respect to X.

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