DRYING CHARACTERISTICS OF THE HAZELNUT

Abstract

Equilibrium moisture content isotherms for Spanish hazelnut (Corylus avellana L.) at different temperatures (30°C-80°C) were determined using static gravimetric method. Thin layer drying experiments were done with forced air circulation and were conducted with different operating conditions to determine the drying characteristics of hazelnuts. The effect of air temperature (30°C-70°C), air velocity (0.5 m/s - 2 m/s) and drying bed loading density (50 kg/m² - 150 kg/m²) on drying of unshelled and shelled hazelnuts was studied. Six mathematical models were used to fit the experimental equilibrium moisture content data, from which the G.A.B. model was found to give the best fit. Diffusion coefficients were determined by fitting experimental thin-layer drying curves to the Fick's diffusion model. Variation of the effective diffusion coefficient with temperature was of the Arrhenius type. The Page equation was found to describe adequately the thin layer drying of hazelnut. Page equation drying parameters k and n were correlated with air temperature and relative humidity.     

Drying Kinetics and Color Retention of Dehydrated Rosehips

Abstract

Freshly harvested rosehips (Rosa canina L.) were dehydrated in a parallel flow type air dryer at six air temperatures (30, 40, 50, 60, and 70°C) at air velocities of 0.5, 1.0, and 1.5 m/s. Drying air temperature and velocity significantly influenced drying time and energy requirement. Minimum and maximum energy requirement for drying of rosehips were determined as 6.69 kWh/kg for 70°C at 0.5 m/s, and 42.46 kWh/kg for 50°C, 1.5 m/s. In order to reduce drying energy consumption, it is recommended that the drying air velocity must not be more than 0.5 m/s and drying air temperature should be 70°C. In addition, the influence of drying air temperature and air velocity on the color of dried rosehip has been studied. Hunter L, a, b values were used to evaluate changes in the total color difference (ΔE) on dried rosehips. 70°C drying air temperature and 1 m/s air velocity were found to yield better quality product.     

DEVELOPMENT OF THE CHARACTERISTIC DRYING CURVE FOR CASSAVA CHIPS IN MONOLAYER

Drying kinetic curves and modelling for cassava chips were determined using a pilot-size air dryer. Operating conditions involved temperatures ranging from 35 to 90 ° C, air flow velocities from 0.5 to 2.0 m/ s, and air moisture content from 0.005 to 0.060 kg water/ kg dry air. Sorption isotherms at temperatures of 23, 45 and 60 ° C were obtained. Results for the drying experiments can be used to calculate the optimal drying conditions for dehydration of cassava roots in multilayers     

EXPERIMENTAL ANALYSIS OF THE DRYING KINETICS OF A FOOD PRODUCT

ABSTRACT

A laboratory system allowing for the characterization of the thin-layer drying kinetics of olive bagasse at relatively high temperatures was designed and constructed. The system, which permits a wide range of operating velocities and temperatures, up to 700°C, allowed the weight loss of the sample to be monitored continuously. Constant drying conditions were maintained using an on-line computer. The drying conditions investigated in this study included combustion products of atmospheric air and propane with dry-bulb temperatures ranging from 125°C to 250°C, relative humidity lower than 1% and gas velocities ranging from 0.5 to 2.0 m/s.     

DRYING '80 VOLUME 1: DEVELOPMENTS IN DRYING

ABSTRACT

The purpose of this research was to investigate strategies for papaya glacé drying in tunnel. To evaluate the optimum conditions of drying, corresponding mathematical models were also considered. The criteria set for this study included low drying time, low specific energy consumption and acceptable qualities of papaya glace. The results obtained from the model of batch tunnel drying were in good agreement with the experimental ones. From the mathematical models, it was found that the optimum conditions of the first stage of drying of papaya glace (3.1×7.8×1.4 cm) were drying temperature of 70°C, specific air flow rate of 12 kg/h-kg dry papaya glace (velocity of 1.25 m/s) and air recycle ratio of 70%. In the second stage of drying papaya glace (0.98×0.98×0.98 cm), it was found that the optimum drying conditions were: drying air temperature of 55°C, specific air flow rate of 10 kg/h-kg dry papaya glace (velocity of 0.6 m/s) and air recycle ratio of 80%. Ambient air temperature and relative humidity were 30°C and 70% respectively.     

INFLUENCE OF PROCESS CONDITIONS ON THE DRYING RATE OF CASSAVA CHIPS IN A SOLAR SIMULATOR

ABSTRACT

Experiments were carried out in a solar simulator to study the influence of air temperature (25-40°C), air relative humidity (40-80%), air velocity (0.95-2.2 m/s), radiation intensity (0-916 W/m²), and loading density (10-30 kg/m²) on the drying rate of a bed of cassava chips (2×2×2 cm). Well-known thin-layer drying equations were fitted to the experimental data, and the empirical constants were used in a statistical analysis of the influence of process conditions on the drying rate. The air temperature, air velocity, radiation intensity, and loading density influenced the drying rate significantly (p=0.05). The effects of the air temperature and the radiation intensity were attributed to the temperature-dependent diffusion of moisture within the chips, while the effect of the air velocity was ascribed to the resistance to mass transfer at the air-chip interface. Equations were presented to express the empirical constants as functions of the process variables.     

Drying Kinetics and Sorption Isotherms of the Nejayote

Abstract

The nixtamalization is an alkaline cooking process in corn tortillas industry that uses large quantities of water (5:1 corn weight) and producing a byproduct called nejayote. In this work, drying kinetic of insoluble fraction from nejayote was obtained using a hot air cabinet dryer at 60, 75, and 90°C. The air rate and water content were 1.5 m/s and 0.028 kg of water/kg of dry air, respectively. Sorption isotherms were measured by the COST method with sulfuric acid solutions at 30, 45 and 60°C. Results showed a difference in drying kinetics/drying time between drying temperatures of 60 and 75°C, and practically no difference between 75 and 90°C. This was probably due to the development of a superficial crust on the product. The shape of sorption curves was as expected; no temperature effect was identified but it is a common behavior for products with high sugar content. Finally the sorption isotherm was predicted based on primary chemical compounds (carbohydrates, proteins, crude fiber, and calcium hydroxide).     

OPTIMIZATION OF CONVECTIVE DRYING PROCESS BASED ON ECONOMIC INDICATORS

ABSTRACT

Drying of lightly salted sardine (Sardinella aurita) was accomplished using three air temperatures (35°C, 40°C, 50°C) and three air velocities (0.5 m/s, 1.5 m/s, 2 m/s); the effects of drying conditions on drying kinetics were studied. As for all biological products, air temperature is the main factor influencing the drying kinetics. However, over a given temperature which seems to correspond to protein modification (50°C), and at a high air flow rate (2 m/s and 2.5 m/s) a crust formation on the surface of the fish, due to the combined effect of heat and salt was observed. This phenomenon inhibited the drying rate. From the drying curves, two falling rate periods were observed. The dimensionless drying rate versus a dimensionless moisture content data were regressed by the Marquardt Levenberg non-linear optimization method to obtain an empirical equation describing the salted sardine characteristic drying curve.     

Drying and Heat Transfer Characteristics for a Novel Fluidized Bed Dryer

Abstract

The use of a fluidized bed dryer with a lateral air flow and mechanical agitation to the drying of sludge from a wastewater treatment plant was investigated. Experimental curves of moisture content vs. drying time, as well as heat transfer coefficients and the size characteristics of the products, were determined at temperatures between 80°C and 110°C, a stirring rate of 55 rpm and air velocity of 0.9 m/s for 3 kg sludge batches with initial moisture contents of 0.55 and 0.65 (d.b.). Experimental drying kinetics were compared with values derived from three models based on Fick's second law, namely: the constant diffusivity model, the simplified variable diffusivity model, and the modified quasi-stationary model.     

DRYING OF SUGAR BEET PULP USING A LABORATORY AIR DRIER

ABSTRACT

Drying curves for sugar beet pulp were obtained in a laboratory-scale air drier. Dehydration conditions were: temperatures in the range of 35 to 90 ^°C, air flow velocities of 0.5 to 2.0 m/s, and air moisture content of 0.005 to 0.06 kg water/kg air. Using data from thin layer experiments, a mathematical model was derived to describe the dehydration behaviour under the described conditions. The model was able to predict data obtained from deep bed experiments. Results from this work could be used to develop a design methodology for dryers that operate at relatively low temperatures (<90^°C).     

Mechanisms of Drying of Skin-Forming Materials. II.Droplets of Heat Sensitive Materials

ABSTRACT

Drying studies were carried out on single droplets of gelatin solution, typifying a skin forming, heat-sensitive material. Each droplet was suspended from a novel rotating glass nozzle which enabled direct measurement of its weight and temperature during drying. Observations using this appartatus successfully detected the decrease in core temperature and increase in drying rate resulting from granule dissolution at 30 °C.

The study covered air temperatures in the range 19 °C–175 °C. Scanning Electron Microscopy was used to examine the dried crusts. The resistance of the skin to vapour diffusion was significantly increased with an increase in the air temperature. At air temperature > 60 °C the dried particle lost the structure and properties of the original powder. The optimum drying conditions to avoid this were predicted for this type of skin forming-material.     

Mathematical Modeling of Withering Characteristics of Tea Leaves

The withering characteristics of tea leaves were examined for different temperatures. Tea leaves were withered at a temperature range of 20–45°C with a constant air velocity of 1.1 m/s. The experimental results illustrated the absence of constant-rate drying period and withering took place only in the falling-rate period. During the falling-rate period, at constant drying air flow rate, the drying rate increased and drying time decreased with the increase in drying air temperature. Drying models of Henderson and Pabis and Page were evaluated based on mean bias error (E_MB), root mean square error (E_RMS), correlation coefficient (R²), and the chi square (χ²). The Henderson and Pabis model was found to be a better model for describing the withering characteristics of tea leaves for each of the temperatures of 20, 25, 30, and 35°C. The values obtained from Page model were found to be more reasonable for temperatures of 40 and 45°C than the other model. Both the models closely fitted the withering data within a certain range of temperature. The Henderson and Pabis model gave better prediction and satisfactorily described the withering characteristics of tea leaves at temperatures lower than 40°C whereas the Page model fitted well at temperatures greater than 40°C.     

Energy requirements and production cost of the spray drying process of cheese whey

The influence of spray drying conditions on the energy required, production cost, and physicochemical characteristics of cheese whey was researched. The factors investigated were the inlet air temperature (180–220°C), outlet air temperature (80–100°C), and silica and maltodextrin (DE-10) as additives at 2 and 5% (w/w), respectively. Analysis of variance revealed that the inlet and outlet air temperatures, and the addition of additives had significant effects (p?T_inlet of 180°C, T_outlet of 80°C, and the addition of 5% additive material. Under these conditions, 0.2165?kg/h of dried product was obtained, with a moisture content of 2.08% and water activity of 0.125, and the product cost was $17.06?kg with an energy consumption of 2.0490?kW?·?h/kg of dry product.     

Influence of Temperature and Air Velocity on Drying Time and Quality Parameters of Pistachio (Pistacia vera L.)

Abstract

Drying is one of the important steps in pistachio processing. In this step kernel moisture content is decreased from 50 to less than 5% (d.b.) which will result in suitable condition for storage. Study of effective parameters in pistachio drying is important since these parameters influence drying time and kernel quality. In this research, a mono layer of pistachios was dried at three different temperatures (60, 75, and 90°C), and three levels of drying air velocity (1.5, 2, and 2.5 m/s). Changes of drying time, protein, fat and peroxide value were investigated for two common Iranian pistachio varieties Kalehghouchi and Fandoghi. Sensory tests were also used to check flavor of pistachios dried at the three temperature levels (60, 75, and 90°C). Statistical analysis of the data indicated that increasing the temperature to 90°C reduced drying time down by about 37% and caused a change in pistachio flavour. Taste tests indicated a consumer preference for pistachios dried at 75°C. If the air velocity is increased from 1.5 to 2.5 m/s, drying time reduces about 10 percent. Changes in temperature and air velocity have no significant effects on protein and fat content of pistachios, but if temperature reaches 90°C, peroxide value will increase to 0.55 meq/kg, which is still within the permissible limit for processed pistachios.     

Effect of Fluidized Bed Drying Temperature on Various Quality Attributes of Paddy

Abstract

As reported by many researchers, it was found that fluidized bed paddy drying using high drying air temperatures of over 100°C affected the head rice yield and whiteness of dried rice. However, only a few studies on fluidized bed paddy drying with drying air temperatures below 100°C were so far reported. The main objective of this work was therefore to study the effect of fluidized bed drying air temperature on various quality parameters of Suphanburi 1 and Pathumthani 1 Indica rice. Paddy was dried from the initial moisture contents of 25.0, 28.8, and 32.5% dry basis to 22.5 ± 1.2% dry basis using inlet drying air temperatures between 40 and 150°C at 10°C/step. After fluidized bed drying, paddy was tempered and followed by ambient air aeration until its final moisture content was reduced to 16.3 ± 0.5% dry basis. The results showed that the head rice yield of Suphanburi 1 was significantly related to the inlet drying temperature and initial moisture content whilst there was no significant relationship between the head rice yield, drying temperature and initial moisture content for Pathumthani 1. The whiteness of the two rice varieties was slightly decreased with increase in drying air temperature and initial moisture content. It was also found that the hardness of both cooked rice varieties exhibited insignificant difference (p < 0.05) comparing to rewetted rice, which was gently dried by ambient air aeration in thin layer. The thermal analysis by DSC also showed that partial gelatinization occurred during drying at higher temperatures. Using inlet drying air temperatures in the range of 40–150°C therefore did not affected the quality of cooked rice and paddy. The milling quality of paddy was also well maintained.     

Comparison of Drying Rate Curves of Porous Solids in Superheated Steam to Those in Air

ABSTRACT

Drying of porous solids was experimentally investigated in superheated steam as well as in air. Drying rate curves, including critical moisture contents, in steam at subatmospheric pressure, were compared to those for air at atmospheric pressure; moreover, they were compared to those for steam at atmospheric pressure as well. The former comparison was carried out under conditions of sample temperatures of 41.8–42.5°C (which were nearly equal to saturation temperatures of 42.1–42.2°C at pressures of 8.23–8.30 kPa) for the constant rate period in steam and the corresponding sample temperatures of 42.0–45.0°C (which were close to the wet-bulb temperatures) for the constant rate period in air. There were distinct differences between normalized drying rate curves, including critical moisture contents in steam and in air at the above similar sample temperatures for materials of baked clay, firebrick, and cemented glass balloons over the minimum value of 8.3 × 10^?3 µm and up to the maximum value of 1.2 × 10² µm in cumulative pore-size distributions: longer constant rate periods and lower critical moisture contents in steam than in air, and higher drying rates in steam than in air for the falling rate period. Moreover, the latter comparison of the drying rates in steam at subatmospheric pressure to those in steam at atmospheric pressure revealed that the differences in normalized drying rates between subatmospheric pressure and atmospheric pressure were small for both materials under mild external conditions. These findings were common to the baked clay, firebrick, and cemented glass balloons over a wide range of pore-size distributions studied in the present work, as well as sintered coarse glass beads as previously reported.     

Physicochemical and nutraceutical properties of barley grass powder microencapsulated by spray drying

ABSTRACT

Barley grass (Triticum aestivum L.) is popular, commonly known as a nutritional supplement in China. To obtain the highest chlorophyll and flavonoid content as well as other physicochemical characteristics, spray drying from barley grass juice was carried out for two different maltodextrin concentrations (10 and 20%, dried basis) and four different inlet air temperatures (140, 150, 160, and 170°C). After drying, color, water activity, odor, taste, density, particle size, glass transition temperature, and chlorophyll and flavonoid contents of the dried product were measured. Highest contents of flavonoid (5.66?mg/kg) and chlorophyll (7.29?mg/kg) were obtained under 150°C inlet air temperature, 10% maltodextrin concentration, at a feed flow rate of 1.8?L/h for the drying. Corresponding particle size was 19.58–13.33?µm. The glass transition temperature (T_g) increased with the increasing of maltodextrin concentration; and two max T_g of powder obtained from 10 and 20% maltodextrin concentration were 74.4 and 77.4°C, respectively. Retention of taste and flavor were highest with 20% maltodextrin. High inlet air temperature was contributed to the large discrepancy of odor and taste substances. The best color (lightness L*?=?64.44 and greenness b*?=??11.53) was obtained at 150°C inlet air temperature and 10% maltodextrin concentration. Both maltodextrin concentrations resulted in poor flowability of the dried product (C_I?≤?32.51).     

Heat pump drying of grape pomace: Performance and product quality analysis

Abstract

Grape is one of the most popular fruits and various types of grape have been cultivated by more than 100 countries around the World. The wine and juice industry produces large quantities of by-product, called grape pomace (GP) as an industrial waste and it consists of skins, seeds, and stems. Various processes such as separation, pressing, drying, and milling are applied to benefit from its health effects. In this study, the seeded black GP Kalecik karas? (Vitis vinifera) was dried in an assisted closed cycle heat pump dryer (HPD) designed for high-moisture products to investigate the drying behaviors of GP. The effects of drying air temperature on bioactive properties and the drying characteristics of GP, and performance of system have discussed. Experiments were carried out at two different temperatures (45 and 50°C) and air velocity of 1.0 m/s. It was seen that increasing temperature decreased the drying time, coefficient of performance of whole system (COP_ws), and specific energy consumption (SEC). The average values of COP_ws for temperatures 45°C and 50°C were calculated as 3.28 and 3.10, respectively. The drying efficiencies (DE) at drying air temperature of 45°C and 50°C ranged from 2 to 12% and from 2 to 15%, respectively. Additionally, result of analysis has indicated that using a HPD at lower temperatures increases performance of system despite of higher energy input. Bioactive properties of dried samples at drying air temperature of 45°C are better than 50°C. The results show that drying the GP at low temperature is more suitable for product quality. For this reason, heat pump may be preferred. It shows that this drying system with higher capacities in the future can be recommended as an alternative technique in terms of energy usage, drying time, and performance of system.     

DRYING RATE AND TEMPERATURE PROFILE FOR SUPERHEATED STEAM VACUUM DRYING AND MOIST AIR DRYING OF SOFTWOOD LUMBER

Abstract

Two charges of green radiata pine sapwood lumber were dried, either using superheated steam under vacuum (90°C, 0.2 bar abs.) or conventionally using hot moist air (90/60°C). Due to low density of the drying medium under vacuum, the circulation velocity used was 10 m/s for superheated steam drying and 5.0 m/s for moist air drying, and in both cases, the flow was unidirectional. In drying, stack drying rate and wood temperatures were measured to examine the differences between the superheated steam drying and drying using hot moist air.

The experimental results have shown that the stack edge board in superheated steam drying dried faster than in the hot moist air drying. Once again due to the low density of the steam under vacuum, a prolonged maximum temperature drop across load (TDAL) was observed in the superheated steam drying, however, the whole stack dried slower and the final moisture content distribution was more variable than for conventional hot moist air drying. Wood temperatures in superheated steam drying were lower.     

Thin-Layer Drying of Flax Fiber: I. Analysis of Modeling Using Fick's Second Law of Diffusion

Thin-layer drying of moist flax fiber was performed at four temperatures of 30, 50, 70, and 100°C with a constant absolute humidity of 0.0065 kg water per kg dry air. The coefficients of diffusion of the fiber at different drying conditions were estimated by modeling the drying process using the one- to five-term solutions of the second Fick's law of diffusion. The models underestimated the drying process during the initial stages of drying and overestimated this process during the final stages. The estimated coefficient of diffusions ranged from 5.11 × 10^?9 to 1.92 × 10^?8 m²/s and linearly increased with the drying air temperature.