Because of technical improves within the heat controllers and processing manage process, it is possible so you can integrate drying out air heat handle strategies (nonisothermal drying), where you could realize sinusoidal wave users (Shape 1a), square-wave otherwise box mode pages (Profile 1b), expanding and you can p pages, saw-tooth revolution pages, and trapezoidal revolution profiles (Profile 1c), and others. Nonisothermal drying out made they you can to find affairs out-of high high quality and even faster drying minutes compared to those acquired which have constant convective drying ( Chua while others 2002 ). Regardless if individuals high quality attributes was basically learned during the materials submitted to nonisothermal drying, structural characteristics haven’t been reported, nor provides equations become advised to spell it out the behavior ( Chua while others 2000 ; Chua while others 2002 ). Yet, no equations was proposed in order to connect alterations in the newest architectural features out of content confronted with changeable external criteria.
It has been seen that there’s no factor between new decisions away from correct thickness depending on the X regarding the material throughout convective drying and you will shortly after are rehydrated to various wetness material; however, variations was basically observed anywhere between noticeable thickness depending on the X of material throughout the lyophilization and you may then rehydration to different dampness contents ( 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 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 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 sites de rencontre hÃ©tÃ©rosexuels vih 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 thickness (?p) habits
Various article writers have proposed correlations gotten by way of nonlinear regression to own forecasting real thickness and obvious occurrence given that a purpose of water posts. But not, the outcomes not be common consequently they are just legitimate into question, geometry, and you may drying out criteria included in those people functions (Table step 3).
They seen linear choices from thickness for several suspensions away from natural substances, such as for instance protein, fats, carbohydrates, material, and you will ash. These types of authors compared its models having fresh density thinking to own dairy, tangerine juices, and you will bratwurst sausage, acquiring an optimum mistake of just one.45%, and you may finding an excellent quadratic possibilities to have liquids.