Perapong Tekasakul

The spinning rotor gauge: Measurements of viscosity, velocity slip coefficients, and tangential momentum accommodation coefficients

A set of experimental measurements with a spinning rotor gauge (SRG) with 3.85, 4.00, and 4.50 mm nominal diameter steel spheres in He, Ar, and Kr is reported. The experiments covered the continuum and the slip regimes for all three gases. Theoretical results from a companion paper on the SRG, together with a calibration based on known viscosity for helium, are used to extract values of the viscosity, the velocity slip coefficient, and the tangential momentum accommodation coefficient for each of the gases. The measured viscosities are in good agreement with existing literature values.

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.

Emissions of particulate matter and associated polycyclic aromatic hydrocarbons from agricultural diesel engine fueled with degummed, deacidified mixed crude palm oil blends.

Mixed crude palm oil (MCPO), the mixture of palm fiber oil and palm kernel oil, has become of great interest as a renewable energy source. It can be easily extracted from whole dried palm fruits. In the present work, the degummed, deacidified MCPO was blended in petroleum diesel at portions of 30% and 40% by volume and then tested in agricultural diesel engines for long-term usage. The particulates from the exhaust of the engines were collected every 500 hr using a four-stage cascade air sampler. The 50% cut-off aerodynamic diameters for the first three stages were 10, 2.5 and 1 microm, while the last stage collected all particles smaller than 1 microm. Sixteen particle bounded polycyclic aromatic hydrocarbons (PAHs) were analyzed using a high performance liquid chromatography. The results indicated that the size distribution of particulate matter was in the accumulation mode and the pattern of total PAHs associated with fine-particles (< 1 microm) showed a dominance of larger molecular weight PAHs (4-6 aromatic rings), especially pyrene. The mass median diameter, PM and total PAH concentrations decreased when increasing the palm oil content, but increased when the running hours of the engine were increased. In addition, Commercial petroleum diesel (PB0) gave the highest value of carcinogenic potency equivalent (BaP(eq)) for all particle size ranges. As the palm oil was increased, the BaP(eq) decreased gradually. Therefore the degummed-deacidified MCPO blends are recommended for diesel substitute.

Rotatory oscillations of arbitrary axi-symmetric bodies in an axi-symmetric viscous flow: Numerical solutions

The problem of the rotatory oscillation of an axi-symmetric body in an axi-symmetric, viscous, incompressible flow at low Reynolds number has been studied. In contrast to the steady rotation of a body, which involves solving the Laplace equation, the study of an oscillating body requires solution of the Helmholtz equation which results from the simplification of the unsteady Stokes equations. In the present work, we have numerically evaluated the local stresses and torques on a selection of free, oscillating, axi-symmetric bodies in the continuum regime in an axi-symmetric viscous incompressible flow. The Helmholtz equation was solved by a Green’s function technique. The accuracy of the technique is tested against known solutions for a sphere, a prolate spheroid, a thin disk, and an infinitely long cylinder. Good agreements have been obtained. Finite cylinders have been studied and the edge correction factors for the circular disk geometry, that are basic to oscillating disk viscometers, have been calculated. It has been found that the calculated edge correction factors, based on the ratios of the real parts of the actual torques (calculated from this work) to the ideal torques, agree to within 1% to 10% with the reported values obtained by Clark et al. [Physica A 89, 539 (1977)] using the theory of Kestin and Wang [J. Appl. Mech. 24, 197 (1957)]. However, since the ratios of the real parts and the ratios of the imaginary parts of the torques do not coincide, the edge correction factors depend upon which ratio is used.

Computation of electric fields and particle motion in electrodynamic balances

Abstract A numerical method based on the Greens function (the potential theory) approach is adapted for computation of the electric fields in electrodynamic balances. The accuracy of the method is checked against analytical solutions for the case of a single torus and excellent agreement is found. Explicit numerical results for a typical double-ring balance are obtained. The method is an improvement over the existing “charge simulation technique” which, although often adequate, is not rigorously founded. Additionally, the equations of particle motion are solved using the numerically precise electric fields (rather than the linearized fields). Overall, the rigor of potential theory is combined with the computational /display power of Mathematica® to provide accurate descriptions of the electric fields and the particle motion. Use of Mathematica® also leads to the simple computation of particle stability diagrams.

Flow and Heat Transfer Characteristics of in-Line Impinging Jets With Cross-Flow At Short Jet-To-Plate Distance

The aim of this research is to numerically and experimentally study the flow and heat transfer characteristics of in-line impinging jets in cross-flow. The jets from a row of round orifices are perpendicularly impinged on the inner surface of a rectangular wind tunnel at a short distance between the orifice plate and impinged surface (H) of 2D, where D is a diameter of the orifice. The jet velocity was fixed corresponding to Re = 13,400 for all experiments, and the cross-flow velocity was varied at three different velocity ratios (velocity ratio, jet velocity/cross-flow velocity) of 3, 5, and 7. The heat transfer characteristic was visualized using a thermochromic liquid crystal sheet, and the Nusselt number distribution was evaluated by an image processing technique. The flow pattern on the impinged surface was also visualized by an oil film technique. The numerical simulation was used to explore a flow interaction between the impinging jets and cross-flow. The results indicated that Nusselt number peak increased by the increasing cross-flow velocity for short jet-to-plate distance. For the range determined, the maximum local Nusselt number peak was obtained at VR = 3 as the consequence of high velocity and high turbulence kinetic energy of jet impingement.

Urinary 1-Hydroxypyrene Levels in Workers Exposed to Polycyclic Aromatic Hydrocarbon from Rubber Wood Burning

Background Urinary 1-hydroxypyrene (1-OHP) was selected as a biomarker of polycyclic aromatic hydrocarbons (PAHs) to explore the accumulation level in the bodies of workers at rubber smoke sheet factories in southern Thailand. Methods Spot urine samples were taken from four groups of workers from June 2006 to November 2007. The nonexposure or control groups included habitual cigarette smokers and nonsmokers. The other two groups were workers exposed to particle-bound PAHs from rubber wood smoke and they were nonsmokers. All spot urine samples were analyzed for 1-OHP and creatinine levels. Results The mean ± standard deviation urinary 1-OHP in the control group of habitual smokers and the nonsmokers was 0.24 ± 0.16 μmol/mol creatinine and not-detected to 0.14 μmol/mol creatinine, respectively. In the workers, the 1-OHP levels on workdays had no significant difference from the 1-OHP levels on the days off. The yearly average 1-OHP level was 0.76 ± 0.41 μmol/mol creatinine whereas the average 1-OHP level during 10 consecutive workdays was 1.06 ± 0.29 μmol/mol creatinine (p > 0.05). Conclusion The urinary 1-OHP levels of workers exposed to PAHs were high. The accumulation of 1-OHP in the body was not clear although the workers had long working hours with few days off during their working experience. Therefore, a regular day off schedule and rotation shift work during high productive RSS should be set for RSS workers.

Evaporation from non-spherical particles:the equivalent-volume and inscribed sphere approximations for nearly spherical particles

Although numerical results for evaporation rates from arbitrarily shaped particles have been recently reported in the literature, it remains of interest to explore construction and accuracy of approximate analytical expressions that are simple and of general use. We have analyzed the popular equivalent-volume approximation and also the inscribed sphere approximations in this context, using a technique due to Zhang and Stone (J. Fluid Mech. 367 (1998) 329) who had studied rotatory oscillations of nearly spherical bodies. Comparison of the approximate results with accurate numerical results shows that both these approximations are quite useful. The equivalent-volume sphere approximation is particularly attractive as the error is of the order e2, where e is a measure of departure from the spherical shape.

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.

Performance of a Combined Cyclone-Filter Aerosol Collector

The collection efficiency of fine aerosol particles of a cyclone collector was improved by combining the cyclone with filters. The effects of particle size and inlet velocity on the penetration and pressure drop were studied. Results show that the penetration of the cyclone combined with a 4-mm and a 8-mm fibrous filter for particle sizes between 0.3 to 1.0 μm was lower than that of the cyclone up to about 20%. The penetration of the cyclone combined with 0.94 and 1.83 g stainless steel filter was found to be lower than that of the cyclone up to about 41%. Moreover, the pressure drop of the cyclone combined with a 4-mm and a 8-mm fibrous filter width was 39.9 and 48.9%, respectively, lower. For a cyclone combined with 0.94 and 1.83 g stainless steel, the pressure drop was 30.6 and 25.7%, respectively, lower. The improvement of the collection performance, a higher collection efficiency, and a lower pressure drop, is attributed to a change of the collection mechanism from centrifugal force to partial filtration at lower tangential velocity.