Three-Dimensional Numerical Modeling of Heat and Moisture Transfer in Natural Rubber Sheet Drying Process

The effects of heat and moisture transfer on rubber sheet drying were investigated by 3-D modeling using computational fluid dynamics (CFD). Complexities arose due to the inclusion of moisture transport. Local convective heat transfer coefficients for the sheets were predicted and then used to determine the mass transfer coefficients using the Chilton–Colburn analogy. Deviations between experimental and simulated temperatures were observed to range from 4.0 to 7.7°C. Temperature and moisture content of the rubber sheets were accurately predicted, and agreement between the experimental and simulated results was acceptable. This is useful for the design of an efficient rubber sheet drying chamber.     

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 Fick's 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.     

Asymmetric polysulfone gas separation membranes treated by low pressure DC glow discharge plasmas

Asymmetric polysulfone (PSF) gas separation membranes were prepared at different conditions such as non‐solvent concentration, evaporation time (ET) and coagulation bath temperature (CBT). In addition, effects of low‐pressure DC glow discharge plasma on the characteristics of PSF membranes were investigated. PSF membranes both before and after plasma treatment were characterized by several techniques, including contact angle measurement, scanning electron microscope (SEM), dynamic mechanical thermal analysis (DMTA), and atomic force microscopy (AFM). Furthermore, the performance of membranes was evaluated in terms of permeability of CO₂, CH₄, O_2, and N₂ gases. The ideal selectivity of CO₂/CH₄ and O₂/N₂ and surface free energy was calculated. Results showed that the EtOH concentration, ET and CBT affect the morphology of PSF membranes. For membranes prepared from a casting solution consisting of PSF 26.0, NMP 28.0, THF 28.0, and EtOH 18.0 wt % and ET for 3 min, the maximum selectivity of untreated membrane is about 69.76 and 12.59 for CO₂/CH₄ and O₂/N₂, respectively. After plasma treatment, the ideal selectivity is receded; however, the CO₂/CH₄ is still higher than 40.41 at pressure of 5 bars. Finally, preparation conditions and DC glow discharge plasmas have significant effects on the characteristics of the PSF membranes and result in an increase of the gas permeation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42116.     

Modified direct torque control method for induction motor drives based on amplitude and angle control of stator flux

This paper proposes design and implementation of a direct torque controlled induction motor drive system. The method is based on control of separation between amplitude and angle of reference stator flux for determining reference stator voltage vector in generating PWM output voltage for induction motors. The objective is to reduce electromagnetic torque ripple and stator flux droop which result in a decrease in current distortion in steady-state condition. In addition, the proposed technique provides simplicity of a control system. The direct torque control is based on the relationship between instantaneous slip angular frequency and rotor angular frequency in adjustment of the reference stator flux angle. The amplitude of the reference stator flux is always kept constant at rated value. The system has been implemented to verify its capability such as torque and stator flux responses, stator phase current distortion both during dynamic and steady state with load variation, and low speed operation.     

Measures for controlling safety of crushed ice and tube ice in developing country

Contamination of pathogens in crushed and tube ice is a public health concern in many developing countries, calling for the development of practical preventive measures to reduce microbial and chemical contamination. By applying principles of hazard analysis and critical control points (HACCP), data on production and distribution processes in 11 ice-making plants in different provinces of Thailand were obtained. Results showed that producers of both ice forms lacked knowledge on water treatment and disinfection that could cause microbial contamination. Other sources of microbial contamination were from condensate in tube ice production and from dirty sacks used in ice transportation. A chemical hazard also was found in crushed ice due to chromium contamination in an anti-rusting agent.     

Magnetic actuation of hair cells

The bullfrog sacculus contains mechanically sensitive hair cells whose stereociliary bundles oscillate spontaneously when decoupled from the overlying membrane. Steady-state offsets on the resting position of a hair bundle can suppress or modulate this native motility. To probe the dynamics of spontaneous oscillation in the proximity of the critical point, we describe here a method for mechanical actuation that avoids loading the bundles or contributing to the viscous drag. Magnetite beads were attached to the tips of the stereocilia, and a magnetic probe was used to impose deflections. This technique allowed us to observe the transition from multi-mode to single-mode state in freely oscillating bundles, as well as the crossover from the oscillatory to the quiescent state.     

Influence of configuration on the performance of external loop airlift contactors

Various types of external loop airlift contactors (ELALCs) were examined for their hydrodynamic and mass transfer behavior. The investigation covered a variety of design parameters including the length of connection tubes (L_c), height of riser and downcomer (L_h), and the airlift configurations while maintaining the ratio between downcomer and riser cross sectional area constant at 0.269. The results demonstrated that the behavior of the external loop airlift could be modified by adjusting the design and operating variables. In general, a faster liquid velocity led to a presence of lower gas holdup and gas–liquid mass transfer rate. Increasing L_c and L_h seemed to increase liquid velocity while decreasing the overall gas holdup and the overall volumetric mass transfer coefficient. Empirical correlations for the estimation of the system behavior were finally formulated.     

Experiments on In-Store Paddy Drying Under Tropical Climate: Simulation and Product Quality

The main objective of this work is to study the rice whiteness and paddy qualities of rice in terms of hardness, stickiness, cohesiveness, and germination of rice. The prediction results of moisture content and whiteness are compared with the experimental results using a near-equilibrium drying model, which is modified by including whiteness kinetics of rice kernel. The long grain rice (Suphanburi 1 high amylose indica variety), which consists of 27% amylose was used for all experiments. The experiments were carried out at the average ambient temperature range of 28.6-30.8°C, average relative humidity of 65.2-80.6% with a fixed bed depth of 1.0 m. Specific air flow rates of 0.65 and 0.93 m³/min-m³ of paddy were forced continuously through the paddy bulk at initial moisture contents of 18.5% and 20.1% wet basis, respectively. The desired final moisture content of paddy is about 13.3 ± 0.6% wet basis. The results show that drying rate and the whiteness predictions are in good agreement with those from the experiments. The in-store drying using ambient air condition did not produce notable effect on the rice whiteness, head rice yield, and the percentage of paddy germination. However, the hardness, stickiness, and cohesiveness of rice were changed.