Yutthana Tirawanichakul

Mathematical Model of Fixed-Bed Drying and Strategies for Crumb Rubber Producing STR20

The objectives of this research were to investigate empirical and diffusion models for thin-layer crumb rubber drying for producing STR20 rubber using hot air temperatures of 110–130°C and to study the effect of drying parameters such as inlet drying temperature, volumetric flow rate, and initial moisture content on the quality of dried rubber. Finally, a mathematical drying model for predicting the drying kinetics of crumb rubber was developed using inlet air flow rates of 300–600 m3/min-m3 of crumb rubber (equivalent to 1.8–5.0 m/s) with the crumb rubber thickness fixed at 0.25 m. The average initial moisture content of samples was in the ranges of 40 and 50% dry basis while the desired final moisture content was below 5% dry basis. The results showed that the drying equation of crumb rubber was highly related to the inlet air temperature, while the drying constant value was not proportional to the initial moisture content. Consequently, the experimental data were formulated using nine empirical models and the analytical solution of moisture ratio equation was developed by Ficks law of diffusion. The result showed that the simulated data best fitted the logarithmic model and was in reasonable agreement to the experimental data. The effective diffusion coefficient of crumb rubber was in the range of 1.0 × 10−9 to 2.15 × 10−5 m2/s corresponding to drying temperatures between 40 and 150°C, respectively. The effects of air recirculation, inlet drying temperature, initial moisture contents, air flow rate, and drying strategies on specific energy consumption and quality of samples were reported. The experiments were conducted using two different drying strategies as follows: one-stage and two-stage drying conditions. The results showed that initial moisture content and air flow rates significantly affected the specific energy consumption and quality of rubber, while the volumetric air flow rate acted as dominant effect to the specific energy consumption. The simulated results concluded that the percentage of recycled air between 90 and 95% provided the lowest specific energy consumption as compared to the others.

Drying kinetics study of parboiled rice by using artificial neural network model

The objective of this research was to predict hybrid hot air-infrared radiation drying kinetics of Leb Nok Pattani parboiled rice using a mathematical model and an artificial neural network model. Drying kinetics of parboiled rice was investigated considering different drying conditions. The drying experiments were performed at three levels of drying air temperatures of 60–100°C, two levels of infrared intensity of 5,118 and 7,678 W/m2, air velocity was fixed at 1±0.2 m/s. Nine different mathematical models available in the literature were fitted to the experimental data. Among the considered mathematical drying models, Two-term model was found to be more suitable for predicting drying of parboiled rice. In addition, a feed-forward Levenberg-Maqurdts propagation artificial neural network was employed to determine the relationship between the moisture ratio of the material to be dried and the input parameters of the drying time, air temperature and infrared intensity. A selected neural network structure was used for studying the influence of transfer function in hidden, output layer and the number of hidden neurons. The results between mathematical model and artificial neural network model were compared with the experimental data. In this research, it was obviously found that the prediction results of feed-forward Levenberg-Maqurdts propagation with four nodes in one hidden layer, logarithmic sigmoid (logsig) and hyperbolic tangent sigmoid (tansig) transfer function in hidden and output layer, respectively, are good agreement with experimental results than empirical model. Thus, it was concluded that the artificial neural network could be effective for modeling of the grain drying process. For quality of parboiled rice drying, the result reveals that was insignificantly different with different drying temperature and infrared intensity. Increases in drying temperature result in whiteness and specific energy consumption decrease.

Experimental study of the effects of different drying methods on the kinetics and quality of air dried sheet (ADS) rubber

Rubber (Hevea brasiliensis) is the most important commercial natural source in ASEAN countries. Mostly natural rubber (NR) industries were followed by old traditional method. However, understanding in the rubber drying process occurred. Then, this research aims to study effect drying conditions on kinetics and quality of air dried sheet (ADS) rubber. The five different drying strategies were carried on by green house drying (GH), green house and natural convention (GH-NC) drying, open sun and natural convention (OS-NC) drying, infrared radiation (IR) drying and hot air (HA) drying. Initial moisture content of fresh rubber sheet was varied between 30 and 50% dry-basis and dried samples had final moisture content of 0.5% dry-basis. From the experiments, it was found that falling drying rate stages and mathematical models of Approximation of diffusion model can predict the behavior of ADS rubber was good. ADS rubber was dried by GH-NC drying longer period than those of OS-NC drying, GH drying, HA drying and IR drying, respectively. Additionally, drying at a low drying temperature has a low specific energy consumption compared to those drying of high temperature. To determine qualities following the highest standard Thai rubber (STR5L) grade, the results showed that quality of samples was acceptable in market level.

Surface Modification of Asymmetric Polysulfone/Polyethylene Glycol Membranes by DC Ar-Glow Discharge Plasma

Polysulfone/polyethylene glycol (PSF/PEG) membranes were prepared by dry/wet phase inversion method. Effects of direct current glow discharge plasma using argon as working gas on morphological structures and gas separation properties of membranes were studied. Alteration of membrane characteristics were analyzed by various techniques like contact angle, scanning electron microscope, Fourier transform infrared spectroscopy, and dynamic mechanical thermal analysis. Gas separation properties were measured in terms of permeation and ideal O2/N2 selectivity. Results showed that hydrophilic and gas separation properties of PSF/PEG membranes increased by plasma surface modification. It was also shown that the dosage of PEG and plasma treatment affected the morphological structures and mechanical and gas separation properties. The macro voids and transmembrane structure disappeared with a little amount of PEG dosage. Pore size and mechanical strength tend to decrease with increasing PEG dosage up to 10 wt%. Glass transition temperature receded from 201.8 to 143.7°C for pure PSF and PSF/PEG with PEG dosage of 10 wt%. O2 and N2 gases permeation through the 10-minute plasma treated membranes tend to increase. However, the permeation strongly dispersed when treatment time was more extended.

Determination of Isosteric Heat and Entropy of Sorption of Air Dried Sheet Rubber Using Artificial Neural Network Approach

Equilibrium moisture contents (EMC) of air dried sheet (ADS) rubber were determined by commonly gravimetric-static method with saturated salt solution among surrounding temperatures of 40-70°C correlated to water activity (aw) ranges between 0.10 and 0.9. The experimental results was analyzed by 5 commonly EMC model. The results showed that equilibrium moisture content of ADS rubber decreased with increase of surrounding temperature at constant water activity and the simulated data using Chung-Pfost model has a good relation to experimental data with R2, RMSE and χ2 equal 0.9565, 0.0235 and 0.0006, respectively. However some physical property of ADS rubber sample affects to evaluate EMC modeling. Due to avoid this effect, thus the aim of this research work was to determine EMC value by using Artificial neural network (ANN) method and also evaluate the isosteric heat of sorption by following the Clausius-Clapeyron equation. The results showed that simulated results using ANN approach has relatively high accuracy compared to common EMC model. Finally determination of isosteric heat of sorption and entropy of sorption of ADS rubber were carried on. The results stated that the enthalpy and entropy of heat sorption was power function and polynomial function of moisture content respectively. These two parameters of ADS rubber can be used for prediction suitable storage condition and drying condition for ADS rubber drying in the near future work.

Empirical Model and Artificial Neural Network Model Approach for Air Dried Sheets (ADS) Rubber

The objective of this research was to predict drying behavior of hot air drying using an empirical model (EM) and an artificial neural network model (ANN). Rubber sheet with initial moisture content ranging of 23-40% dry-basis was dried by temperature ranging of 40-70°C and air flow rate of 0.7 m/s. The desired final moisture content was set at 0.15% dry-basis. The results showed that drying rate of rubber sheet dried with hot air convection was faster than conventional natural aeration. The EM and ANN were simulated to describe the drying behavior of products. Furthermore, prediction results between EM and ANN were compared with the experimental data. In this research, it was obviously found that ANN can describe the drying behavior effectively. Additionally, it was also found that predicted results of Multilayer feed forward Levenberg-Maqurdt’s Back-propagation ANN were good agreement with the experimental results compared to those results of EM. It is the optimum architecture for prediction the evolution of moisture transfer for hot air drying.

Physics applications: IV characteristics of CO 2 and O 2 dielectric barrier discharges

This research aims to evaluate the electrical characteristics of CO2 and O2 gas discharges by the coaxial-cylindrical dielectric barrier discharge (DBD) reactor. The DBD reactor was made of stainless steel with inner diameter of 17.5 mm and length of 100 mm while Teflon tube placing between both electrodes was acted as dielectric barrier. The spacing discharges gap between inner electrode and dielectric barrier was fixed at 1.5 mm width. The high voltage power source was used for applying to both electrodes during CO2 and O2 discharges by following at 11, 15, 19 and 23 kVp. The flow rate of each gas was fixed at 10 ml/min. A high density of discharge current peak occurred at 23 kVp for both gas species. Moreover, the discharge power and energy density by supplying with 23 kVp for CO2 was 0.71 W and 4.28 kJ/L of feed gas, respectively, while the discharge power and energy density at the same voltage for O2 was 0.73 W and 4.37 kJ/L of feed gas, respectively. The conclusion stated that the discharge power and energy density highly related to applied voltage and flow rate of gas, corresponding to the Lissajous figure.

Two-stage optimal fixed-bed drying for natural rubber producing STR20 block rubber

The objectives of this research were to study effect of drying parameters on two stage drying of natural rubber producing STR20 block rubber and to verify drying model program prediction of moisture transfer and specific energy consumption. The experiment was set-up at the 1st stage drying with upward inlet air temperature between 110 and 150°C (30–60 min) and the 2nd stage drying with downward inlet air temperature between 110 and 140°C (100–120 min). Specific air flow rate was varied between 0.07 and 0.25 kg dry air/s-kg dry rubber while natural rubber bed-depth was varied between 0.1 and 0.3 m. The average initial moisture content of the fresh natural crumb rubber was in ranges of 38.1–52.5% dry-basis. As the results of 19 experiments, the drying kinetics exhibited only one falling rate period while drying temperature and bed depth of natural rubber relatively affected drying kinetics of crumb rubber sample. The simulation drying system program including energy consumption analysis was developed using the basic principle of near thermal equilibrium drying model. Simulation was carried out to validate the drying model against experimental results. The results conclude that the predicted results were in good agreement with experimental results. In addition, the qualities of the dried crumb rubber producing block rubber satisfied all standard STR20 criteria. The optimal drying strategy of STR20 block rubber process is the 30 cm. bed depth natural rubber drying operated under the conditions of rapid 1st drying with 130°C and following the 2nd stage drying with 110°C for all drying period of 220 min.

Drying kinetics model and physical properties of herb Pandanus leaf

The objectives of this research were to study drying kinetic of Pandanus leaf for herbal tea by hot air (HA) convection, infrared (IR) radiation and combined HA and IR heat sources (HA+IR). The thin-layer drying kinetics equation of Pandanus leaf was mathematical simulated for all three drying strategies. Determination of physical quality and specific energy consumption (SEC) were carried on. The experiments were carried out under the conditions of infrared radiation power of 1,000 W and drying temperature ranges between 45 and 65°C. The hot air flow rate was fixed at 1.0–1.2 m/s. Initial moisture content of Pandanus leaf was range of 400 to 600% dry-basis and the final moisture content was between 8 and 12% dry-basis. The experimental results showed that the drying rate using combined HA+IR was faster than drying using HA and IR, respectively. The simulated data using empirical Logarithmic model for all heating methods had a good relation to the experimental data. According to the liquid diffusion following Ficks law, the effective diffusion coefficient was depended on drying temperature and drying method. Evaluation of SEC showed that SEC of IR drying was lower than drying with HA and combined HA+IR, respectively. The SEC with all three heat sources was in ranges of 8.33–17.70 MJ/kg.H2O evaporated. The SEC is decreased with increase of drying temperature. For product quality analysis, percentage of rehydration and the colorness value (CIE lab) of dried using HA, IR and combined HA+IR are significantly different (p≤0.05).

Drying kinetics of unsmoked rubber sheet by forced and natural convection

The objectives of this research were to investigate model for describing equilibrium moisture content of fresh rubber sheet and drying kinetics of Air Dried Sheet (ADS) rubber using hot air (HA) drying, green house (GH) drying and conventional open-air (OA) drying. The experimental results were mathematical simulated by non-linear regression analysis. Equilibrium moisture content (EMC) of natural rubber (NR) were evaluated using the gravimetric-static method among surrounding temperature of 40–60°C provided to relative humidity surrounding of 10–90%. The results showed that The Modified Halsey model was found to be the most suitable for describing the relationship among equilibrium moisture content, relative humidity and temperature. The appropriate thin-layer drying equation model for predicting the drying kinetic of rubber sheet. The experiments were carried out under the conditions of constant drying temperature 30–55°C, the initial moisture contents of sample rubber were operated in range of 15–40 % dry-basis. The final moisture content for each drying strategies was fixed at 1±0.05 % dry-basis. The effects of drying conditions on evolution of moisture content, drying rate and quality of rubber were determined. The experimental results showed that for both forced and natural convection the drying rate of rubber sheet was relatively related to drying temperature. The fresh rubber sheets were dried by OA drying took longer drying period than those of HA drying. Twelve thin layer drying equation models were used for evaluating experimental data and the results showed that the simulated data using Weibull Distribution model had a good relation to the experimental values of sample drying with HA, experiment results using Modified Henderson and Pabis model was the best fitting model for GH and conventional OA drying. According to the quality and energy analysis, the results showed that quality of the rubber sheet was acceptable in market level for all drying heat sources. However, ADS rubber drying with HA and OA were slightly better than GH drying.