Zogzas although some (1994) believe you to visible thickness utilizes the quantity diminishing coefficient and you may dampness articles (Table 3, Eq

Apparent thickness (?b) designs

Based on Krokida and you can Philippopoulos (2005) , apparent density are a purpose of moisture stuff, version of solid, and you may heavens volume proportion. The majority of the patterns for forecasting noticeable occurrence included in the new literary works is empirical; standard otherwise theoretic activities only have become suggested by the a small quantity of people ( Rahman while others 1996 ). The fresh apparent thickness habits had been created according to moisture stuff (X), in place of as a result of the ramifications of drying temperature; not too many consider shrinking, although it is actually high from the greater part of times ( Moreira although 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 and others (2000) keep that obvious density can be acquired using the apparent thickness of your strong ( ) and size out-of liquid ( ) at the beginning of drying out since a reference to have first frequency (Eq. 20, Desk 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)].

Due to the fact ?(X) and you may ?(X) may be the services off moisture stuff, he or she is dependent on handling conditions, the nature of one’s device being dried, the fresh new drying out approach, plus the drying phase ( Khalloufi although some 2010 ).

The newest collapse formula (Eq. 27) advised of the Khalloufi although some (2009) guarantees that failure form always initiate in one and you may stops inside no.

If the topic is in a good rubbery state, diminishing makes up almost totally having dampness losses, together with volume of the materials reduces linearly having dampness stuff ( ). But not, low-heat dehydration out of food items suppresses the brand new moisture posts in the heart of your own procedure off ever being much greater than that of the outside, reducing internal fret, and therefore, breaking ( Bai while some 2002 ).

An incorrect formula away from ?(X) and ?(X) gives rise to help you an error throughout the formula from noticeable density. This happens quite https://datingranking.net/fr/rencontres-desactivees/ frequently, as the majority of writers believe that shrinking is actually linear ( Zogzas although some 1994 ; Moreira and others 2000 ; ), otherwise they can fit they so you can the second-studies polynomial ( Khalloufi while some 2010 ).

Future models is to strive to depict the fresh decisions regarding visible occurrence having better accuracy, taking into account X in addition to thermal history of the materials being dried.

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.