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Zogzas while some (1994) believe you to definitely visible thickness depends on the quantity diminishing coefficient and you can water blogs (Table step three, Eq

Zogzas while some (1994) believe you to definitely visible thickness depends on the quantity diminishing coefficient and you can water blogs (Table step three, Eq

Obvious thickness (?b) designs

Centered on Krokida and you will Philippopoulos (2005) , apparent thickness is a function of moisture articles, version of good, and you can air volume proportion. A lot of the activities having forecasting apparent density included in the latest literature was empirical; basic otherwise theoretic designs have only started advised by a finite level of authors ( Rahman and others 1996 ). The latest apparent occurrence designs were invented according to moisture posts (X), without as a result of the results of drying out heat; few believe shrinking, although it is actually high on the almost all times ( Moreira while some 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 although some (2000) hold that visible occurrence can be acquired utilising the obvious thickness of one’s good ( ) in addition to bulk regarding liquids ( ) at the beginning of drying because the a guide to possess very first regularity (Eq. 20, Desk 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)].

Since the ?(X) and you may ?(X) are the services out-of moisture stuff, he or she is influenced by control standards, the kind of your equipment becoming dehydrated, the drying strategy, and drying stage ( Khalloufi although some 2010 ).

New failure formula (Eq. 27) suggested of the Khalloufi while others (2009) pledges that collapse function usually initiate in a single and you can concludes for the zero.

When the point is in a great rubbery state, diminishing makes up almost totally to have dampness losses, in addition to quantity of the material decrease linearly having dampness blogs ( ). Yet not, low-temperature dehydration out-of foodstuffs suppresses the wetness stuff regarding center of one’s question from ever-being much higher than that the exterior, minimizing inner stress, and therefore, cracking ( Bai while some 2002 ).

An incorrect computation away from ?(X) and you will ?(X) gives go up so you can a mistake regarding formula out of noticeable thickness. This happens quite frequently, http://www.datingranking.net/it/incontri-interrazziali/ as most of article writers believe that shrinking try linear ( Zogzas while some 1994 ; Moreira although some 2000 ; ), or they fit they so you can the next-training polynomial ( Khalloufi although some 2010 ).

Upcoming habits is strive to depict new choices of apparent thickness which have higher accuracy, taking into consideration X plus the thermal reputation of the material becoming dried.

Findings

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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