Due to technical advances during the heat controllers and handling handle process, it has become you can easily in order to include drying out air temperatures handle tips (nonisothermal drying), where you can follow sinusoidal wave pages (Shape 1a), square-wave otherwise package setting profiles (Contour 1b), increasing and you may p profiles, saw-enamel revolution users, and you can trapezoidal revolution profiles (Figure 1c), among others. Nonisothermal drying has made it it is possible to to locate activities of high high quality and also smaller drying out times as opposed to those gotten having ongoing convective drying out ( Chua while others 2002 ). Although some high quality services was in fact read in information submitted to nonisothermal drying, structural services have not been said, nor have equations already been advised to spell it out its conclusion ( Chua while others 2000 ; Chua while some 2002 ). At this point, no equations had been advised to help you associate changes in the fresh new architectural attributes from information confronted by changeable exterior requirements.

It’s been observed there is no factor anywhere between the fresh behavior of real thickness depending on the X from the information presented throughout convective drying and you will immediately following are rehydrated to different water articles; but not, differences was observed ranging from noticeable density depending on the X of procedure while in the lyophilization and you will then rehydration to various moisture material ( Krokida and you will ).

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 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.

Thickness Habits

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 ).

True density (?p) patterns

Certain article authors features proposed correlations received courtesy nonlinear regression getting forecasting genuine thickness and you may noticeable thickness since a purpose of moisture content. However, the outcome perhaps not become extensive and tend to be only valid to your thing, geometry, and you will drying criteria utilized in the individuals work (Table step three).

It seen linear behavior regarding density for different suspensions away from natural ingredients, such as for instance healthy protein, oils, carbohydrates, materials, and you will ash. Such writers opposed their models that have experimental thickness opinions to own whole milk, lime juice, and you may bratwurst sausage, getting an optimum error of 1.45%, and in search of a quadratic functionality getting liquids.