Pressure In Drying Chamber Research Articles

Low-pressure conductive thin film drying of açaí pulp

Açaí has a high content of anthocyanins and unsaturated fatty acids, and drying parameters can affect the stability of these compounds. This study used a conductive thin-film dryer at a laboratory scale to mimic the (vacuum) drum drying of açaí pulp. The effect of drying chamber pressure on the drying kinetics and powdered product characteristics was investigated. Hot air drying and freeze-drying experiments were performed as references. A pilot-scale conductive dryer, namely a vacuum drum dryer, was used as well to dry açaí pulp. Conductive drying at low pressures led to lower boiling temperatures and shorter drying times but also more vigorous bubble formation. The anthocyanin content and antioxidant activity of contact-dried samples at low pressures were comparable to those of freeze-dried and significantly higher than those of hot air-dried. However, conductive drying caused greater lipid oxidation compared to freeze-drying and hot air drying. Oil loss was observed during vacuum drum drying except for the lowest pressure and the shortest drying time. Therefore, the results suggest that chamber pressure during conductive thin film drying should be carefully selected to obtain high-quality açaí powder.

Characteristic of Unhulled Rice Drying on Swirling Fluidized Bed Dryer

The most important thing of drying is removing moisture from materials towards the equilibrium moisture with normal ambient air. One of the drying ways is to use Swirling Fluidized Bed Dryer (SFBD) for drying materials in the form of granules or seeds. The experiment of Swirling Fluidized Bed to dry out unhulled rice was carried out. This research aims to find the characteristics of unhulled rice after the drying process and performance of SFBD. Swirling fluidized bed dryer with 15° angles of blade inclination, 650 mm of plenum chamber depths, and 30 blades were used to dry out unhulled rice 1 kg, 2 kg and 3 kg. In this study, 16.2 m/s hot air velocity and 55 °C were used to dryer out unhulled rice as long as 45 minutes. Initial moisture content of unhulled rice are 24.1% for 1 kg, 23.6% for 2 kg and 23.7% for 3 kg and final moisture content were 11.68%, 13.13% and 12.13% respectively. The evaporated mass of water was 123.2 gr, 217.5 gr, and 356.1 gr. The plenum pressure on the capacity unhulled rice of 1, 2, and 3 kg are 59.6 mmH2O and 16.7 mmH2O, 78.5 mmH2O, respectively. The drying chamber pressure on the capacity unhulled rice of 1, 2, and 3 kg are 35.1 mmH2O, 79.9 mmH2O, and 37.5 mmH2O, respectively.

Numerical and experimental analysis of heat and mass transfer in the drying process of the solar drying system

Design in a solar food drying system is crucial for food drying performance. In order to make effective use of the sun, the use of air-heated solar collectors is gradually increasing in drying systems. Dryer room temperature and pressure distribution modelling is a very important factor for system design and product selection. In this study, the drying air speed, drying temperature, and product moisture content values of a solar drying system were numerically modelled in a time dependent manner. In numerical analysis, temperature and drying air velocity were defined as variable under initial and boundary conditions. Polynomial equations based on time obtained from drying room inlet temperature and drying air velocity data were used. The R2 values of these equations were calculated as 0.96 and 0.91, respectively. COMSOL multiphysics program was used for temperature values, drying air velocity, product moisture content values and drying chamber pressure values modelling. Depending on the position of the sun and the time, the drying chamber inlet temperature values and air velocity values have been change. During the drying process of the product, moisture content values, heat and mass transfer values, drying efficiency values, diffusion coefficient and activation energy values were examined. Experimental data and computed fluid dynamics analysis (CFD) data were compared. Using the CFD numerical analysis program, the drying room temperature, moisture content and air velocity values were modelled with mean absolute percent error (MAPE) of 5.34%, 3.74% and 6.30%, respectively.

Design and performance evaluation of a pilot-scale pulsed vacuum infrared drying (PVID) system for drying of berries

The objective of current work was to develop a new pilot-scale pulsed vacuum infrared drying (PVID) system for the drying of berries. The system design and drying performance evaluation for grape and goji berries are reported here. The PVID system consisted of three major sections, including infrared heating section, vacuum section, and a controlling section. Electrical infrared (IR) emitter was made with carbon fiber sheet at the thickness of 2–4 mm, which emitted IR wavelength of 1–30 μm. The control system was used to achieve paused pressure by switching the drying chamber pressure between atmospheric pressure (101 kPa) and vacuum (3–10 kPa) successively and maintaining the pressure for different time periods. Grapes and goji berries were dried in a single layer at three different temperatures (55, 65, and 75 °C) with an atmospheric duration ranging from 1 to 12 min and vacuum duration from 10 min to constant vacuum. The drying characteristic and quality of PVID dried berries were investigated and compared with that of hot air (HA) dried berries. Results showed that the IR heating temperature, atmospheric duration, and vacuum duration had significant effects (p < .05) on the drying time. The optimum drying conditions for grapes and goji berries were IR heating at 65 °C, vacuum duration of 15 min, and atmospheric duration of 4 and 2 min, respectively. The corresponding drying time is nearly 720 min for grapes, and 450 min for goji berries. The PVID dried grapes and goji berries had more attractive color than that of HA dried ones. These findings demonstrated that PVID should be a promising method to produce high-quality dried berries. This study laid a good foundation for scaling up the technology in the future.

Parameter Optimization of Vacuum Freeze-Drying Processing on Tan Lamb

In this paper, the effects of drying chamber pressure, heating plate temperature and material thickness on the drying time of Tan lamb in vacuum freeze-drying process were studied using quadratic regression orthogonal design. The results showed that the drying time was significantly affected by drying chamber pressure, heating plate temperature and material thickness as well as the interaction of heating plate temperature and material thickness. The optimized parameters were drying chamber pressure 27.9 Pa, heating plate temperature 47.9°C and material thickness 4.3 mm. On these parameters, the drying time was 4.3 h.

Development of a Compact Vacuum Freeze Drying for Jelly Fish (Schypomedusae)

A new design of a vacuum freeze drying with internal cooling and heater from condenser’s heat loss was built and tested. The dryer was used to dry jelly fish (scyphomedusae) to study the effect of drying parameter such as temperature within the drying chamber on mass losses (evaporation) during freezing stage and moisture ratio at the end of drying process and also the drying rate of vacuum drying process. The cold trap temperature rise in when activated the heating from condenser’s heat loss. The midili thin layer mathematical drying model was used to estimate and predict the moisture ratio curve base on different drying chamber temperature. The result of this experiment show that mass loss during freezing stage decreased with a decrease in drying chamber temperature with constant pressure. Drying time reduced with an increase in drying temperature. Drying chamber temperature decreasing has a result pressure saturation of material lower than drying chamber pressure have an effect mass transfer should not occurs.

Vacuum drying characteristics of eggplants

The vacuum drying characteristics of eggplant were investigated. Drying experiments were carried out at vacuum chamber pressures of 2.5, 5 and 10 kPa, and drying temperature ranging from 30 to 50 °C. The effects of drying pressure and temperature on the drying rate and drying shrinkage of the eggplant samples were evaluated. The suitable model for describing the vacuum drying process was chosen by fitting four commonly used drying models and a suggested polynomial model to the experimental data; the effective moisture diffusivity and activation energy were calculated using an infinite series solution of Fick’s diffusion equation. The results showed that increasing drying temperature accelerated the vacuum drying process, while drying chamber pressure did not show significant effect on the drying process within the temperature range investigated. Drying shrinkage of the samples was observed to be independent of drying temperature, but increased notably with an increase in drying chamber pressure. A linear relationship between drying shrinkage ratio and dry basis moisture content was observed. The goodness of fit tests indicated that the proposed polynomial model gave the best fit to experimental results among the five tested drying models. The temperature dependence of the effective moisture diffusivity for the vacuum drying of the eggplant samples was satisfactorily described by an Arrhenius-type relationship.

Optimal Control of the Secondary Drying Stage of Freeze Drying of Solutions in Vials Using Variational Calculus

: The problem of operating freeze drying of pharmaceutical products in vials loaded on trays of freeze dryer to obtain a desired final bound water content in minimum time is formulated as an optimal control problem. Two different types of freeze dryer designs were considered. In the type I freeze dryer design, upper and lower plate temperatures were controlled together, while in the type II freeze dryer design, upper and lower plate temperatures were controlled independently. The heat input to the material being dried and the drying chamber pressure were considered as control variables. Only the scorch temperature was considered as a constraint on the system state variables during the secondary drying stage, because all the free water content (frozen water) is removed from the solid matrix during the primary drying stage of freeze drying. Necessary conditions of optimality for the secondary drying stage of freeze drying process in vials were derived and presented by using rigorous multidimensional unsteady-state mathematical models. The theoretical approach presented in this work was applied in the freeze drying of skim milk. Significant reductions in drying times of the secondary drying stage of the freeze drying process in vials were observed and more uniform bound water and temperature distributions in the material being dried were obtained compared to the conventional operational policies.

Optimal Control of the Primary Drying Stage of Freeze Drying of Solutions in Vials Using Variational Calculus

The problem of operating freeze drying of pharmaceutical products in vials placed in trays of a freeze dryer to remove free water (in frozen state) at a minimum time was formulated as an optimal control problem. Two different types of freeze dryer designs were considered. In type I freeze dryer design, upper and lower plate temperatures were controlled together, while in type II freeze dryer design, upper and lower plate temperatures were controlled independently. The heat input to the material being dried and the drying chamber pressure were considered as control variables. Constraints were placed on the system state variables by the melting and scorch temperatures during primary drying stage. Necessary conditions of optimality for the primary drying stage of freeze drying process in vials are derived and presented. Furthermore, an approach for constructing the optimal control policies that would minimize the drying time for the primary drying stage was given. In order to analyze optimal control policy for the primary drying stage of the freeze-drying process in vials, a rigorous multi-dimensional unsteady state mathematical model was used. The theoretical approach presented in this work was applied in the freeze drying of skim milk. Significant reductions in the drying times of primary drying stage of freeze drying process in vials were obtained, as compared to the drying times obtained from conventional operational policies.

OPTIMAL CONTROL OF THE PRIMARY AND SECONDARY DRYING STAGES OF BULK SOLUTION FREEZE DRYING IN TRAYS

The problem of operating a tray freeze dryer to obtain a desired final bound water content in minimum time is formulated as an optimal control problem with the use of the rigorous unsteady state mathematical model of Sadikoglu and Liapis [9] that has been found to describe satisfactorily the experimental dynamic behavior of the primary and secondary drying stages of bulk solution freeze drying of pharmaceuticals in trays. The heat input to the material being dried and the drying chamber pressure are considered to be control variables. Constraints are placed on the system state variables by the melting and scorch temperatures during primary drying, and by the scorch temperature during secondary drying. Necessary conditions of optimality for both the primary and secondary drying stages are derived and presented, and an approach for constructing the optimal control policies that would minimize the drying times for both the primary and secondary drying stages, is presented. The theoretical approach presented in this work was applied in the freeze drying of skim milk, and significant reductions in the drying times of primary and secondary drying were obtained, when compared with the drying times obtained using the operational policies reported in the literature, by using the optimal control policies constructed from the theory presented in this work. Furthermore, it is shown that the optimal control policy leads to the desired in practice result of having at the end of secondary drying temperature and bound water concentration profiles (in the dried layer) whose gradients are very small. It is also shown that by using the optimal control policy and an excipient capable of increasing the melting temperature without affecting product quality, one can significantly reduce the drying time of the primary drying stage.