Dehydrated vegetables & fruits

Zogzas while others (1994) consider one noticeable occurrence hinges on the quantity shrinking coefficient and you will wetness articles (Desk 3, Eq

Zogzas while others (1994) consider one noticeable occurrence hinges on the quantity shrinking coefficient and you will wetness articles (Desk 3, Eq

Apparent density (?b) models

Based on Krokida and you will Philippopoulos (2005) , apparent thickness was a purpose of water content, sorts of strong, and you will sky regularity proportion. A lot of habits getting anticipating visible occurrence utilized in new literary works is empirical; fundamental or theoretical activities just have already been advised by a finite level of authors ( Rahman although some 1996 ). The obvious occurrence models was in fact created centered on wetness articles (X), versus considering the results of drying out heat; not too many think diminishing, though it is actually significant on most 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 while some (2000) hold that noticeable density is present with the visible thickness of your strong ( ) and mass of water ( ) early in drying since a guide to possess initially volume (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)].

Since ?(X) and you may ?(X) are definitely the qualities out of water stuff, he’s dependent on processing criteria, the nature of one’s device being dried, the latest drying out strategy, and drying out phase ( Khalloufi and others 2010 ).

The newest failure equation (Eq. 27) recommended by the Khalloufi although some (2009) pledges that collapse setting always starts in one and you can finishes from inside the zero.

In the event the situation is within a beneficial rubbery condition, shrinking makes up almost entirely to possess water losses, as well as the number of the material reduces linearly with dampness stuff ( ). not, low-temperatures dehydration off food products inhibits the fresh new dampness content from the heart of the issue out of ever-being much greater than that of the outside, minimizing interior be concerned, and therefore, cracking ( Bai and others 2002 ).

An erroneous formula away from ?(X) and you can ?(X) will provide go up so you’re able to a mistake regarding computation out of visible thickness. This happens quite frequently, as most of article authors believe that shrinking was linear ( Zogzas and others 1994 ; Moreira while others 2000 ; ), otherwise they can fit it in order to a moment-education polynomial ( Khalloufi while some 2010 ).

Coming patterns would be to try and show the brand new choices out of obvious occurrence that have greater precision, taking into consideration X while the thermal reputation for the information presented getting 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.

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