Due to technological advances inside the temperature controllers and you may operating handle techniques, it’s become you’ll so you’re able to put drying air heat manage actions (nonisothermal drying), making it possible to pursue sinusoidal revolution users (Contour 1a), square-wave otherwise package form users (Profile 1b), growing and you can p pages, saw-tooth trend users, and trapezoidal trend users (Profile 1c), yet others. Nonisothermal drying out makes it you’ll be able to to track down factors of highest high quality and also faster drying out times than others received with constant convective drying out ( Chua while others 2002 ). No matter if various high quality services had been analyzed when you look at the content submitted to nonisothermal drying, architectural functions haven’t been advertised, nor have equations been recommended to explain their conclusion ( Chua while others 2000 ; Chua although some 2002 ). Up until now, zero equations was indeed advised to help you relate changes in brand new structural functions from materials exposed to variable external criteria.
This has been noticed there is no factor between the fresh decisions out-of real density according to X away from the materials throughout the convective drying out and shortly after getting rehydrated to various moisture material; yet not, variations had been seen ranging from apparent thickness with respect to the X of one’s thing during lyophilization and you will then rehydration to various moisture information ( Krokida and you can ).
Three possible tendencies of ?p as a function of X have been found (Figure 2), both linear and nonlinear (concave-down and concave-up). p and X, which considers reduction in volume to be equal to the volume of the water eliminated from the material ( Madamba and others 1994 ). In tendency of Figure https://datingranking.net/fr/rencontres-video/ 2b, it can be observed how ?p increases slowly up to a critical point, followed by an exponential decay. This change has been explained by water loss in the material during drying ( Lozano and others 1983 ; Zogzas and others 1994 ). In tendency in Figure 2c, it is assumed that the increase in ?p to a critical point is due to the fact that the reduction in volume is greater than the reduction in mass; after this critical point, the pores in the material are considered to be closed, and measured volume is greater than true volume ( Lozano and others 1983 ). In the above-described tendencies, it is merely assumed that volume and solid dry mass are constant. However, when materials are heated, they may expand or contract; in such cases, volume is not constant.
Density Models
Several efforts have been made to predict different tendencies of ? as a function of X. Generally in these models, the foodstuff is considered to be a binary compound (water–solid). Table 3 shows models for true and apparent density proposed for foodstuffs. The models for predicting ?b and ?p are based on the development of pores during the lyophilization process, as the formation of pores is considered to be a function of ideal conditions, since there is no reduction in the volume of the solid as a result of water sublimation ( Karathanos and others 1996 ).
Correct occurrence (?p) patterns
Various authors possess advised correlations received using nonlinear regression to own predicting genuine thickness and visible thickness as the a function of moisture stuff. Although not, the outcomes perhaps not be prevalent and are usually only good toward situation, geometry, and you will drying out requirements used in those works (Desk step 3).
They observed linear decisions out of occurrence a variety of suspensions out of absolute substances, like proteins, fats, carbohydrates, materials, and ash. These writers opposed its patterns with experimental occurrence philosophy for milk products, orange liquid, and you will bratwurst sausage, acquiring an optimum mistake of 1.45%, and you can in search of a quadratic functionality to possess drinking water.