Because of technological advances into the temperatures controllers and you can operating manage techniques, it has become you’ll so you can consist of drying out air temperature handle steps (nonisothermal drying), where you can go after sinusoidal trend profiles (Shape 1a), square wave otherwise box form users (Figure 1b), increasing and you will p pages, saw-tooth wave users, and you can trapezoidal wave pages (Contour 1c), among others. Nonisothermal drying out makes they you can easily to track down issues of high quality as well as quicker drying out minutes than others received that have constant convective drying ( Chua and others 2002 ). No matter if some top quality features was indeed studied inside the material published to nonisothermal drying, architectural qualities have not been advertised, nor has equations already been advised to describe their choices ( Chua although some 2000 ; Chua while some 2002 ). Yet, no equations was basically proposed so you can connect changes in the latest structural qualities out of content met with adjustable outside standards.
This has been seen that there is no significant difference anywhere between the fresh new choices out-of genuine thickness according to the X away from the information presented during convective drying and you will shortly after becoming rehydrated to several wetness content material; although not, variations was seen between apparent density according to the X of the topic throughout lyophilization and you can then rehydration to several wetness articles ( 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.
Several efforts have been made to predict different tendencies of ? as incontri sobrio 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 ).
Real density (?p) designs
Some experts provides advised correlations received compliment of nonlinear regression to possess anticipating genuine occurrence and you will noticeable thickness due to the fact a purpose of wetness blogs. Yet not, the results not be extensive and are usually merely valid towards the procedure, geometry, and drying requirements included in men and women works (Dining table step 3).
They seen linear decisions out-of thickness for various suspensions regarding absolute ingredients, such as for instance healthy protein, fats, carbohydrates, material, and ash. These people opposed the designs having fresh occurrence thinking to have milk products, lime fruit juice, and you will bratwurst sausage, obtaining a max error of just one.45%, and you will finding a beneficial quadratic functionality to own liquid.