Zogzas although some (1994) consider one visible occurrence relies on the volume diminishing coefficient and wetness stuff (Table 3, Eq

Obvious thickness (?b) habits

Centered on Krokida and Philippopoulos (2005) , obvious density is a purpose of wetness blogs, type of strong, and you will air regularity ratio. A lot of the habits to possess anticipating visible occurrence utilized in the brand new books are empirical; important or theoretical patterns just have come proposed by the a limited amount of experts ( Rahman while some 1996 ). New visible thickness habits were invented predicated on moisture blogs (X), as opposed to because of the negative effects of drying temperature; not many thought shrinking, although it is actually tall regarding most times ( Moreira and others 2000 ; ).

18), where the volumetric shrinking coefficient (?) is a linear function of moisture content vrai site de rencontre pour célibataires de 30 ans. 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 although some (2000) keep that visible density can be obtained making use of the obvious occurrence of strong ( ) plus the bulk away from drinking water ( ) early in drying since the a reference to own first volume (Eq. 20, Table step three).

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)].

Because ?(X) and ?(X) certainly are the services off water stuff, he’s influenced by control criteria, the type of your product being dried, the latest drying out means, as well as the drying phase ( Khalloufi while some 2010 ).

Brand new collapse equation (Eq. 27) recommended because of the Khalloufi although some (2009) pledges your failure mode usually initiate in a single and you may closes into the zero.

In the event that material is during a good rubbery state, shrinking compensates nearly entirely having water losings, together with level of the material reduces linearly with water articles ( ). However, low-temperatures dehydration off foodstuffs suppresses this new moisture stuff regarding heart of point away from ever-being much more than that the exterior, minimizing inner be concerned, and therefore, cracking ( Bai and others 2002 ).

An incorrect formula out of ?(X) and you can ?(X) gives rise in order to an error on formula out of obvious density. This occurs often, as most of writers think that diminishing is actually linear ( Zogzas while some 1994 ; Moreira and others 2000 ; ), otherwise they can fit they to help you an extra-knowledge polynomial ( Khalloufi while others 2010 ).

Upcoming habits should try and depict the behavior of visible thickness which have higher precision, taking into account X plus the thermal reputation for the materials being dehydrated.


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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