Because of technical advances within the temperatures controllers and handling handle process, it is you can easily to incorporate drying out air temperature control methods (nonisothermal drying), making it possible to pursue sinusoidal trend users (Shape 1a), square-wave otherwise container means users (Shape 1b), broadening and p profiles, saw-tooth revolution pages, and you may trapezoidal wave users (Contour 1c), as well as others. Nonisothermal drying made they you can easily to find circumstances out-of large quality and even quicker drying out times than those obtained which have constant convective drying ( Chua although some 2002 ). Although certain quality functions was indeed learned in the content submitted to nonisothermal drying out, architectural services have not been said, neither has equations started advised to describe their behavior ( Chua while some 2000 ; Chua while some 2002 ). To date, zero equations had been suggested in order to associate changes in this new architectural qualities out-of materials confronted with adjustable exterior conditions.
It’s been noticed that there surely is no factor between new conclusion of correct density with respect to the X off the materials during convective drying out and just after are rehydrated to various water information; although not, distinctions had been seen between noticeable density according to the X of one’s thing during the lyophilization and you may subsequent rehydration to various moisture content ( Krokida and ).
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 jak zjistit, kdo vÃ¡s mÃ¡ rÃ¡d na blendr bez placenÃ 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 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 ).
Genuine thickness (?p) habits
Some authors has actually recommended correlations received due to nonlinear regression to own anticipating correct thickness and you can obvious occurrence because the a function of moisture stuff. But not, the outcomes maybe not getting prevalent and therefore are just valid into the material, geometry, and drying conditions used in those works (Desk step three).
They seen linear decisions off density for different suspensions of natural ingredients, like healthy protein, oils, carbohydrates, fabric, and you may ash. Such writers opposed the patterns which have experimental occurrence values to own dairy, tangerine fruit juice, and you can bratwurst sausage, getting an optimum error of 1.45%, and you may seeking good quadratic functionality to own h2o.