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Zogzas while others (1994) thought one to obvious thickness hinges on the volume shrinking coefficient and you can moisture blogs (Table 3, Eq

Escrito por em 23 de Setembro, 2022

Zogzas while others (1994) thought one to obvious thickness hinges on the volume shrinking coefficient and you can moisture blogs (Table 3, Eq

Obvious density (?b) designs

Predicated on Krokida and you may Philippopoulos (2005) , noticeable density try a purpose of wetness articles, brand of strong, and you will heavens frequency proportion. Most of the patterns to have anticipating noticeable thickness found in brand new books was empirical; fundamental or theoretical habits just have already been suggested of the a restricted number of article writers ( Rahman while some 1996 ). This new noticeable density models have been invented considering wetness content (X), without because of the outcomes of drying temperatures; very few envision diminishing, although it are high on the greater part of circumstances ( 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 while others (2000) hold one noticeable occurrence can be obtained making use of the noticeable density of the good ( ) while the size out of liquids ( ) early in drying while the a resource to possess first frequency (Eq. 20, Dining table step 3).

In Eq. 18 and 19, X= 0 is taken as a reference; in Eq. 20, the reference is X0= moisture gratis incontri online video 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 the ?(X) and you will ?(X) will be the features regarding dampness articles, he is determined by handling requirements, the nature of one’s unit getting dried, the new drying method, and drying out stage ( Khalloufi and others 2010 ).

The failure formula (Eq. 27) advised of the Khalloufi while others (2009) guarantees the collapse means constantly begins in one and you will stops when you look at the no.

In the event the question is actually a great rubbery county, diminishing makes up almost completely to possess wetness losings, in addition to volume of the material minimizes linearly with moisture articles ( ). Although not, low-temperature dehydration of foodstuff inhibits the newest wetness stuff on heart of your situation away from ever being much greater than compared to the exterior, reducing internal stress, and consequently, breaking ( Bai while others 2002 ).

An incorrect formula regarding ?(X) and you will ?(X) will provide rise so you’re able to a blunder in the computation of obvious occurrence. This occurs often, as the majority of people believe that shrinking try linear ( Zogzas although some 1994 ; Moreira although some 2000 ; ), or they fit they so you can the second-education polynomial ( Khalloufi and others 2010 ).

Upcoming models is make an effort to represent the new decisions of visible density that have higher accuracy, considering X in addition to thermal reputation of the information presented becoming dehydrated.

Conclusions

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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