Moisture Removal Rate Research Articles

Thin-Layer Modeling of Microwave, Microwave-Convective, and Microwave-Vacuum Drying of Pharmaceutical Powders

Common pharmaceutical excipients and active ingredients, wetted with specific solvents, were dried under selected microwave, microwave-convective, and microwave-vacuum conditions in an experimental drying system (2.45 GHz, 90 W). The generalized drying profile was independent of drying technique and material characteristics, with a constant rate stage and two falling rate periods being observed. Moisture removal rate was, however, dependent on the drying technique (pressure and presence/absence of external heating source), and powder and solvent properties (dielectric, physical and thermal). The experimental moisture loss data were fitted to selected semi-theoretical and empirical thin-layer drying equations. The correlations were compared according to two statistical tests, namely root mean square error and reduced chi-square. The microwave, microwave-convective, and microwave-vacuum drying behaviors were adequately represented by the Page, Logarithmic, Chavez-Mendez et al. and Midilli et al. equations, with the latter providing the best description of the experimental results.

Comparison of Vacuum Drying Characteristics of Radiata Pine Timber Using Different Heating Methods

Timber logs 14 × 14 × 240 cm long were dried in a vacuum kiln to compare vacuum drying characteristics using contact heating, radiofrequency heating, and the combination of both. Relationships between moisture content (MC) and time for vacuum conductive drying (VCD), RF/vacuum drying (RFVD), and hybrid vacuum drying (HVD) were close to linear. The hybrid vacuum drying offered the higher moisture removal rate than VCD and RFVD. Specific energy consumption curves as a function of MC comprised three sections; rapidly increasing, slightly decreasing, and moderately increasing. Average specific energy (kWh/kg of water removal) for VCD, RFVD, and HVD was 0.352, 0.520, and 0.461 kWh/kg, respectively. Transverse MC distribution represented the convex profile for VCD, the fluctuating profile for RFVD, and the flat profile for HVD. Transverse and longitudinal moisture gradient of HVD was much lower than those of VCD and RFVD. HVD has a very beneficial effect on preventing of surface checks. There were no end- and internal checks of dried timber in three vacuum drying methods.

Experimental investigation of the energy efficiency of gas commercial laundry dryers

In this paper the energy efficiency of commercial laundry dryers is investigated. Previous studies have found that a small energy saving can be found in household tumbler dryers, but there has been no investigation of larger commercial gas-fired tumbler dryers. Two relatively new gas-fired dryers have been tested in an in situ commercial setting in Auckland. One of the dryers incorporated an energy efficiency measure that allowed it to recirculate the exhaust air directly back into the drum. Both the dryers were found to be very energy intensive but to remove moisture at very high rates. The recirculation was found to decrease both the energy efficiency and the moisture removal rate of the dryer.

Effect of structured packing density on performance of air dehumidifier

Abstract An experimental study has been conducted to investigate the performance of a liquid desiccant air dehumidifier equipped with a structured packing made of wood for three different densities using triethylene glycol (TEG) as the liquid desiccant. The structured packing densities used were 77, 100 and 200 m2/m3. The performance of the dehumidifier was expressed in terms of the moisture removal rate and the dehumidifier effectiveness under different air and desiccant parameters, i.e. the air and TEG flow rates, air and TEG inlet temperatures, inlet air humidity and inlet TEG concentration. In general, the trend in the dehumidifier performance was similar to that reported by other investigators using random packing. The effect of packing density on moisture removal rate and dehumidifier effectiveness is assessed. The differences in the effectiveness of different packing densities are attributed to the wetting condition. Lower effectiveness of the column is shown with the packing density of 200 m2/m3 compared to the other two packing densities when the air flow rate, inlet concentration and desiccant flow rate are increased. However, higher effectiveness is shown when either the inlet temperature of the air or desiccant is increased.

Predictions of moisture removal rate and dehumidification effectiveness for structured liquid desiccant air dehumidifier

In hot and humid climates such as in the Sultanate of Oman, the humidity puts extra load on the electric vapor-compression air conditioning (VAC) systems. Liquid and solid desiccants can reduce the moisture content of humid air and thus reduce the latent load imposed on the VAC systems. In the present work, the performance of air dehumidifiers using triethylene glygol (TEG) as desiccant was investigated. Three differently structured packing densities were used (77, 100 and 200 m 2/m 3). The performance of the dehumidifier was evaluated and expressed in terms of the moisture removal rate ( m cond) and the dehumidifier effectiveness ( ε y). The experimental work was undertaken to study the effects of several influencing design factors on this performance. The design factors covered included the air and TEG flow rates, air and TEG inlet temperatures, inlet air humidity and the inlet TEG concentration. The desiccant flow rate investigated was much less than that covered in previous studies and the range of the inlet temperatures of air and desiccant was significantly wider. The objective this study was to use the multiple regression method and the principal component analysis to obtain statistical prediction models for the water condensation rate and the dehumidification effectiveness in terms of these design factors. The results of both techniques agree with each other affirmed that the desiccant flow rate, desiccant inlet concentration and air inlet temperature are the most significant variables in predicting m cond, whereas desiccant flow rate, air inlet temperature and packing density are the most significant variables in predicting ε y.

Effect of greenhouse on crop drying under natural and forced convection I: Evaluation of convective mass transfer coefficient

In this paper, a study of convective mass transfer coefficient and rate of moisture removal from cabbage and peas for open sun drying and inside greenhouse drying has been performed as a function of climatic parameters. The hourly data for the rate of moisture removal, crop temperature, relative humidity inside and outside the greenhouse and ambient air temperature for complete drying have been recorded. The experiments were conducted after the crop harvesting season from September to December 2001. These data were used for determination of the coefficient of convective mass transfer and then for development of the empirical relation of convective mass transfer coefficient with drying time under natural and forced modes. The empirical relations with convective mass transfer for open and greenhouse drying have been compared. The convective mass transfer coefficient was lower for drying inside the greenhouse with natural mode as compared to open sun drying. Its value was doubled under the forced mode inside the greenhouse drying compared to natural convection in the initial stage of drying.

Air dehumidification by triethylene glycol desiccant in a packed column

The performance of an air dehumidifier using triethylene glycol (TEG) as desiccant under hot and humid conditions was investigated. The performance of the dehumidifier was evaluated and expressed in terms of the moisture removal rate and the dehumidifier effectiveness. A packed bed column (dehumidifier) was employed, with low packing density (77 m 2/m 3), to provide direct contact between the air and the TEG. Two different structured packings were used, wood and aluminum. The experiments covered a wide range of parameter space that included the air and TEG flow rates, air and TEG inlet temperatures, inlet air humidity and inlet TEG concentration. The liquid flow rate investigated is much less than that covered in previous studies (<1 kg/m 2 s). The trend of the dehumidifier performance was similar to that reported in the literature using high density and random packing. The results were compared to the Chung and Luo correlation, which over predicted the effectiveness. The Martin and Goswami correlation failed to predict the effectiveness under the conditions of this study. In the present study, it was found that the moisture removal rate increased with increasing inlet TEG concentration, TEG flow rate and air flow rate. This was seen for both the wood and the aluminum packings. In addition, the moisture removal rate is increased with increasing the inlet air temperature for the aluminum packing only. The effectiveness of the column was increased by increasing the TEG flow rate and inlet TEG temperature for the two packings.

Specific energy and quality aspects of infrared (IR) dried parboiled rice

Qualities of infrared (IR) dried parboiled rice in terms of head rice yield, colour, percent-gelatinized kernel and specific energy consumption have been evaluated using five levels of radiation intensity (5514, 4520, 3510, 2520 and 1509 W/m 2) and four levels of grain bed depths (3 mm (single kernel thickness), 6, 12 and 25 mm) in a vibratory IR dryer. Response surface methodology was followed to predict the effect of above mentioned independent parameters on quality variables and specific energy. The major factor in reduction of head yield was observed because of a marked increase in moisture removal rate with the increase in radiation intensity. The drop in percent head yield was about 6–8% for all the grain bed depths, when the intensity increased from 1509 to 5514 W/m 2. Both grain bed depth and radiation intensity influenced the colour (Yellowness Index) of the milled rice at 1% level of significance. The Yellowness Index of the product was found to vary between 30.54 and 52.44. Radiation intensity and bed depth significantly changed the percent gelatinization of the kernels at the 1% level of significance. The percent of gelatinized kernels increased about 8% at maximum bed depth, and 4% at lower bed depths. The variation of specific energy consumption values was between 14.7 and 73.4 MJ/kg at 1% and 5% levels of significance with the increase in radiation intensity and bed depth, respectively.

Thermodynamic modeling of fluidized bed drying of moist particles

A thermodynamic analysis of the fluidized bed drying process of large particles is performed to optimize the input and output conditions. Energy and exergy models were used for the study. The effects of the hydrodynamic and thermodynamic conditions such as the inlet air temperature, the fluidization velocity and the initial moisture content on the energy efficiency and the exergy efficiency were analyzed. The analysis was carried out using two different materials, wheat and corn. It was observed that the thermodynamic efficiency of the fluidized bed dryer was the lowest at the end of the drying process in conjunction with the moisture removal rate. The inlet air temperature has a strong effect on thermodynamic efficiency for wheat, but for corn, where the diffusion coefficient depends on the temperature and the moisture content of particles, an increase in the drying air temperature did not result in an increase of the efficiency. Furthermore, the energy and exergy efficiencies showed higher values for particles with high initial moisture content while the effect of gas velocity varied depending on the particles. A good agreement was achieved between the model predictions and the available experimental results.

MODELING MOISTURE AND CHEMICAL CHANGES DURING BULK CURING OF FLUE–CURED TOBACCO

Mathematical models to predict moisture content, chlorophyll, starch, and reducing sugar concentrations weredeveloped as a function of curing variables like temperature, initial moisture content, airflow rate, time, and initial chemicalconcentrations. The moisture removal model was based on a twoterm (liquid and vapor) thinlayer drying equation, whilechlorophyll, starch, and respiration models were based on firstorder rate equations. Several product parameters requiredin secondary equations were determined through regression and comparison of root mean square errors. The models werefitted to the experimental data collected during the first year of the experiments (1997) to determine the product parametersby minimizing root mean square errors. The models were then verified using the experimental data obtained in the secondyear of the experiments. The models will help predict effects of curing variables on rate of moisture removal and chemicalconcentrations in the cured tobacco leaf. This information will contribute to the optimization of the curing process in termsof process efficiency and product quality.

Liquid diffusion model for drying a stack of rough rice

Drying of a stack of rough rice was experimentally and theoretically investigated. Stacks of rough rice having different heights were dried with forced convection of warm air. A theoretical model was developed for predicting the bulk drying kinetics of a stack of rough rice using the analytical solution of liquid diffusion equation based on Fick's law. Effective diffusion coefficients were obtained minimizing the sum of squared differences between the theoretical results and experimental data obtained for various drying conditions. Drying air temperature is the most effective factor on the total rate of moisture removal from the stack. The bulk drying rate of a stack of rough rice was considerably reduced as compared to that of a single layer as the height of the stack increased. Agreement between the theoretical and experimental result is very good. Copyright © 2003 John Wiley & Sons, Ltd.

Thermal aspects of open sun drying of various crops

Open sun drying (OSD) is the most common method of crop drying in developing countries. Despite several disadvantages, it is widely practiced because it is a simple way of drying. Crop temperature, temperature around the crop, solair temperature, and rate of moisture evaporation are the important parameters in OSD. The thermal behavior of OSD of green chillies, green pea, white gram (kabuli chana), onions, potatoes, and cauliflower was studied. The heat transfer analysis which is mainly dependent on the rate of moisture transfer has also been extended during drying process. A mathematical model has been developed to predict the crop temperature, rate of moisture removal, and solair temperature for a steady state condition. The rate of moisture transfer for potato slices and cauliflower was significantly higher than that in other crops. A fair agreement was observed between predicted and experimental results with coefficient of correlations ranging from 0.8936 to 0.7520, 0.9792–0.4172, and 0.9986–0.9942 for crop temperature, temperature above the crop surface, and rate of the moisture removal during drying, respectively except potato slices.

AE—Automation and Emerging Technologies: Prediction of Performance Indices and Optimal Parameters of Rough Rice Drying using Neural Networks

An artificial neural network was developed for rough rice drying to predict six performance indices: energy consumption, kernel cracking, final moisture content, moisture removal rate, drying intensity and water mass removal rate. Four drying parameters: rice layer thickness, hot airflow rate, hot-air temperature and drying time were the inputs of the neural network. After evaluating a large number of trials with various neural network architectures, the optimal model is a four-layered back-propagation neural network, with 8 and 5 neurons in the first and the second hidden layers, respectively. The effectiveness of the proposed model is demonstrated using experimental data. The mean relative error varied from 2·0 to 8·3% for six predictions with an average of 4·4%. Using a multiple-objective programming for optimisation of the drying parameters, the optimal values are rice layer thickness of 66 cm, hot airflow rate of 0·30 m s −1, hot-air temperature of 93°C and drying time of 23 min.

Thermal analysis of a fluidized bed drying process for crops. Part II: Experimental results and model verification

An experimental investigation was undertaken to provide key data for the drying of wheat, and to assess the validity of the mathematical model described in Part I, and test its accuracy. The results of numerical solutions are compared with experimental data for wheat grains. Wheat is one of the main agricultural products and has extensive application in drying systems and therefore the accuracy of results for this product is of primary concern. Furthermore, as the desorption isotherms of wheat material are well documented, it is possible to accurately simulate the drying processes. Wheat belongs to the hygroscopic materials group and has a very low-mass diffusivity. Usually, no constant rate period is observed in the course of drying of wheat in the moderate range of initial moisture content, and drying takes place in the falling rate mode. In this study, it was confirmed that immediately after the particles are exposed to the drying medium, the surface moisture of material transfers rapidly due to low external resistance to heat and mass transfer. However, later on the moisture removal rate decreases noticeably with time because of the high internal resistance to diffusion. In the experiments, temperature at different elevations, humidity of the exit air, bed pressure drop, fluidization velocity and moisture content of particles at different times are measured. Each experiment is repeated at three inlet air temperatures: 40, 49.5, and 60°C. Results of the model predictions show very good agreement with a large number of experimental data obtained in drying wheat. The agreement of model prediction and experimental data indicates that the model is fully predictable for drying of other materials in the fluidized bed with no restriction in the range of operational conditions such as the air temperature and the relative humidity. The model can be applied to the other type of processes such as spouted bed and fixed-bed drying with slight modification. It is found that the drying of grain materials is usually controlled by internal mass transfer parameters. The inlet air temperature has an important effect on the magnitude of drying rate while the gas velocity and bed hold-up do not show significant contribution to the drying rate. The initial moisture content of the bed materials can have an important effect on the drying rate depending on the physical properties of bed materials. Copyright © 2000 John Wiley & Sons, Ltd.

Thermal analysis of a fluidized bed drying process for crops. Part II: Experimental results and model verification

An experimental investigation was undertaken to provide key data for the drying of wheat, and to assess the validity of the mathematical model described in Part I, and test its accuracy. The results of numerical solutions are compared with experimental data for wheat grains. Wheat is one of the main agricultural products and has extensive application in drying systems and therefore the accuracy of results for this product is of primary concern. Furthermore, as the desorption isotherms of wheat material are well documented, it is possible to accurately simulate the drying processes. Wheat belongs to the hygroscopic materials group and has a very low-mass diffusivity. Usually, no constant rate period is observed in the course of drying of wheat in the moderate range of initial moisture content, and drying takes place in the falling rate mode. In this study, it was confirmed that immediately after the particles are exposed to the drying medium, the surface moisture of material transfers rapidly due to low external resistance to heat and mass transfer. However, later on the moisture removal rate decreases noticeably with time because of the high internal resistance to diffusion. In the experiments, temperature at different elevations, humidity of the exit air, bed pressure drop, fluidization velocity and moisture content of particles at different times are measured. Each experiment is repeated at three inlet air temperatures: 40, 49.5, and 60°C. Results of the model predictions show very good agreement with a large number of experimental data obtained in drying wheat. The agreement of model prediction and experimental data indicates that the model is fully predictable for drying of other materials in the fluidized bed with no restriction in the range of operational conditions such as the air temperature and the relative humidity. The model can be applied to the other type of processes such as spouted bed and fixed-bed drying with slight modification. It is found that the drying of grain materials is usually controlled by internal mass transfer parameters. The inlet air temperature has an important effect on the magnitude of drying rate while the gas velocity and bed hold-up do not show significant contribution to the drying rate. The initial moisture content of the bed materials can have an important effect on the drying rate depending on the physical properties of bed materials. Copyright © 2000 John Wiley & Sons, Ltd.

99/03506 Mechanism and application of coal dry beneficiation with air-dense medium fluidized bed: Wei, L. J. Cent. South Univ. Technol., 1998, 5, (2), 100–103

A thermodynamic analysis of the fluidized bed drying process of large particles is performed to optimize the input and output conditions. Energy and exergy models were used for the study. The effects of the hydrodynamic and thermodynamic conditions such as the inlet air temperature, the fluidization velocity and the initial moisture content on the energy efficiency and the exergy efficiency were analyzed. The analysis was carried out using two different materials, wheat and corn. It was observed that the thermodynamic efficiency of the fluidized bed dryer was the lowest at the end of the drying process in conjunction with the moisture removal rate. The inlet air temperature has a strong effect on thermodynamic efficiency for wheat, but for corn, where the diffusion coefficient depends on the temperature and the moisture content of particles, an increase in the drying air temperature did not result in an increase of the efficiency. Furthermore, the energy and exergy efficiencies showed higher values for particles with high initial moisture content while the effect of gas velocity varied depending on the particles. A good agreement was achieved between the model predictions and the available experimental results.

発酵熱を利用した焼酎粕処理技術の開発

Composting was applied to Syochu-distillery waste treatment. A bulking agent was mixed with Syochu-distillery waste in order to improve the efficiency of aeration of the mixture and to neutralize citric acid during the composting process. Before mixing with bulking agents (composted cattle manure) barley Shochu-distillery waste contains 88% moisture and had a BOD of 87000mg/kg. The temperature rapidly rose to 60 °C or more due to the generation of a large quantity of heat during the oxidation of the organic matter. After by 7 days of fermentation, the BOD and moisture content of the mixture was reduced from 23000mg/kg to 5680mg/kg and from 48.6% to 37.5% respectively. When supplementary bulking agents, such as coffee grounds, were added to Sweet-potato Shochu-distillery waste containing 95% of moisture and with a BOD of 39000mg/kg, it was possible to carry out semi-continuous treatment. Removal of 100kg moisture required the consumption of 32.1kg of organic matter by this treatment. An industrial-scale test showed that the rate of moisture removal was 18kg/day·m2

Feasibility Tests for a Two-Stage Batch Dryer for Curing Farmer Stock Peanuts1

Abstract A two-stage batch dryer for farmer stock peanut was developed by a commercial grain dryer manufacturer and tested at a commercial peanut buying point during the 1996 and 1997 harvests. A 7.3-m diameter grain bin provided the superstructure for two peanut curing chambers. Each chamber had an approximate capacity of 18,000 kg of in-shell peanuts. Comparisons between conventional peanut curing wagons and the bin dryer were conducted. Recorded data included temperature and relative humidity in both type dryers, drying time, moisture content throughout curing, farmers stock grades, milling quality, and seed germination. A total of 451,717 kg were cured in the two-stage dryer and 215,460 kg in conventional dryers. The initial moisture content of peanuts averaged 19% wet basis and dried at an average moisture removal rate of 0.45%/hr. The moisture removal rates for the two dryers were not significantly different. The final moisture content averaged 11%. Moisture content at the time of grading averaged 9%. Farmers stock grades and milling quality were not significantly different. The average quota support price, including LSK for peanuts cured in conventional dryers, was $630.47/1000 kg compared to $636.08/1000-kg peanuts cured in the two-stage dryer. Seed germination averaged 75.8 and 76.1% for conventional and bin-dried peanuts, respectively. The twostage batch dryer was comparable to the current wagon-drying system. A single batch in the two-stage dryer was equivalent to three peanut wagons.

Heat and Mass Transfer Characteristics of Barley During Fir Drying

Higher moisture removal rate and higher temperature of grain were observed with the increase in intensity level. Contrary to convective grain drying, an increase in air velocity caused a negative effect while relative humidity resulted in increase of drying rate. Initial moisture content of grain does have influence on the drying rate but less significant than radiation intensity and inlet air velocity. The drying data were fitted to the modified exponential model using NLIN regression technique. The coefficients obtained were then correlated against independent variables using stepwise multiple linear regression. The proposed model gave adequate prediction of the experimental data.

A Two-Dimensional Finite Element Model For Wheat Drying In A Novel Rotating Jet Spouted Bed

ABSTRACT Based on Liquid diffusion model a two-dimensional finite element simulator was developed for the drying of wheat. Simulations were carried out for the drying of a single wheat particle in a novel rotating jet spouted bed. The effects of the choice of the geometric model for the wheat kernel, the temperature and flow rate of the drying air on the moisture removal rate as well as kernel temperature were investigated. Numerical experiments showed that the accuracy of the model geometry chosen has great influence on the computed moisture removal rate partly because of the way the moisture published diffusivily correlations were obtained. Sample results are presented and discussed.