Compatibility enhancement of silica and natural rubber compound using UVA-induced silane-grafted saponified skim natural rubber

Silane coupling agents are potential reagents widely used to improve the compatibility between silica and less polar rubber, especially natural rubber (NR). Nevertheless, high temperature is generally required to generate the interaction between the components during the mixing process. Accordingly, an alternative method by grafting the silane coupling agent onto the rubber molecules would be a desirable approach to develop a compatibilizer for the silica-filled NR compound. In this work, skim NR was used as a starting material due to its linear structure. The optimal conditions of the grafting reaction were found to be 1 phr of an alkoxy silane and 5 phr of benzoyl peroxide under 8 min of UVA irradiation time. These conditions were applied for producing the rubber material used in the mixing process of STR 5L and silica. The cure characteristics, silica dispersion and mechanical properties of the rubber compounds were improved, suggesting that the modified rubber was an efficient material for increasing the compatibility between silica and NR.     

Thermo-fluid characterization of flue gas flows through a packed bed

Enhancement of thermal performance in an incinerator and flue gas treatment with a randomly packed bed of uniform spheres was investigated in a custom-made experimental facility and reported in the present paper. Pressure drop, temperature evolution and heat transfer characteristics were evaluated for a range of superficial velocities, Reynolds numbers and bed geometries. Results revealed that increases in both superficial velocity and bed thickness caused a rise in pressure drop across the packed bed in similar fashion to the Ergun equation but with different coefficients at low Reynolds number between 60–300. The two constants were empirically determined to be 68.5 and 4.95. It was also found that the packed bed affects axial temperature distribution from the incinerator chamber to stack. For the same heating rate, higher temperature was achieved in the chamber with the packed bed, and peak temperature was reached at a rate of 7–10% faster than that without the packed bed during the startup period. The downstream side of the thicker bed appeared to have lower temperature than the thinner bed for the same axial position, demonstrating less flue loss during the transient state. The incinerator chamber proved to have higher temperature rising rate and reached higher maximum temperature with the presence of the packed bed.     

Thermal characteristics of louvered fins with a low-reynolds number flow

A heat recovery system is crucial for the effective use of energy where heat rejection from production processes is unavoidable and must be reused. The response of the louvered fins to the low-Reynolds number hot gas is yet to be reported in the literature for the application of a heat exchanger on low-speed hot plume arising from heat sources in production processes. This study focuses on the effects of the louvered fin heat exchanger’s design parameters, which include the louver pitch and louver angle, on the convective heat transfer, which defines the thermal interaction between the hot, buoyant, naturally-induced air and the louvered fins. The resulting Colburn factors (j) are compared with those derived under forced convection with a similar range of low Reynolds number (233 to 1024). All experiments are done on a 15:1 scaled-up model. The fin aspect ratios between the fin spacing and louver pitch are set at 0.75, 1, and 1.5, while the louver angles are set at 18°, 23°, 30°, 35°, and 40°. The Colburn factor strongly depends on the louver angle, especially at the lower range of the Reynolds number. The decreasing aspect ratio induces more hot buoyant air into the louver-formed channels, increasing the heat transfer rate. When the fin angle increases towards 30°, a larger Colburn factor is produced. However, the heat transfer characteristic drops as the angle goes beyond 30°. The highest j for the low speed flow is attained when the louver angle is 30° and the fin aspect ratio is 1.     

Identification and quantification of performance losses for PEM fuel cells as determined by selective chemisorption and ESA measurements

Membrane electrode assemblies (MEAs) were fabricated using a high frequency spraying technique. Electrocatalyst powders were directly sprayed onto an electrolyte membrane by ultrasonic spraying. The weight ratios of Nafion to Pt/C were studied, and the ratio about 50–62% yields the maximum current density at the ohmic and gas diffusion region of the polarization curve. Cross sections of the MEA were analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM); images from SEM indicate that the supported catalysts are arranged in a layered manner and that pores in the catalyst coated layer (CCL) are formed. TEM images show the ionomer layer exists between the reaction zone and the electrolyte membrane. The concentration of Pt surface sites in the MEA was measured by selective H₂ chemisorption methods at dry conditions and by cyclic voltammetry (CV) for the electrochemical reaction. The chemisorption measurements indicate that ∼52% of the active Pt surface are lost due to ionomer coverage and CV shows an additional 28% of the Pt surface are lost due to blockage by condensed water and the isolation of Pt sites from ionomer and electrical conduction. In total 80% of the Pt surface sites present on the 20 wt% Pt/C starting material are lost during preparation and at operating conditions. Thus, both mechanisms of activity loss are separately identified and quantified.     

Performance analysis of solar ethanol distillation

Continuous solar ethanol distillation systems having flat-plate and evacuated heat pipe solar collectors are constructed to study their performances and economic viability. The mathematical model of each main component is carried out and the system simulation is developed. The simulated outputs express a reasonable agreement with the experimental results within 14% accuracy. From the simulation, start up with 10% alcohol concentration, the production cost of 80% alcohol concentration from the distillation system of which the yield at 12,500 l/year is evaluated. With the economic analysis, the results show that the use of solar distillation systems appear to be economical compared to the conventional distillation system using fuel oil as heat source. The minimum production cost of the system is 0.39 US$/l.     

Use of oscillating heat pipe technique as extended surface in wire-on-tube heat exchanger for heat transfer enhancement

This paper presents the performance of a wire-on-tube heat exchanger of which the wire is an oscillating heat pipe. The experiments for this heat exchanger were performed in a wind tunnel by exchanging heat between hot water flowing inside the heat exchanger tubes and air stream flowing across the external surface. R123, methanol and acetone were selected as working fluids of the oscillating heat pipe. The inlet water temperature was varied from 45 to 85 °C while the inlet air temperature was kept constant at 25 °C.     

Thermal analysis of slurry ice production system using direct contact heat transfer of carbon dioxide and water mixture

This research studies the heat transfer characteristic during ice formation of a direct contact heat transfer between carbon dioxide and water mixture. This research is divided into two parts. For the first part, the low temperature carbon dioxide, between − 15 and − 60 °C, is injected into water initially at 28 °C and exchanges heat directly. The flow rate of carbon dioxide is varied between 0.003 and 0.017 kg/s while the volume of water is between 1 and 3 L. From the experiment, it is found that the effectiveness of the direct contact heat transfer between the carbon dioxide and the water is closed to 100%. Moreover, the lumped model is found to be used for predicting the temperature of water and the mass of ice formation quite well.     

Pre‐Vulcanization of Large and Small Natural Rubber Latex Particles: Film‐Forming Behavior and Mechanical Properties

The pre‐vulcanized large rubber particle (LRP) and small rubber particle (SRP) latices are independently prepared to investigate their film‐forming process and mechanical properties after being cast into films. The surface morphologies and roughness of both LRP and SRP films are found to be dependent on crosslink densities. The networks inside each rubber particle (RP) restrict particle deformation resulting in residual contour of RP within the film surface. For highly crosslinked RP, the collapse of the top surface of the RPs in the LRP films appears to create many “crater‐like” structures within the film surfaces, while they present only protruding particles within the SRP and blend films. This seems to indicate that LRPs are easier to coalesce and form film than SRPs. Additionally, dynamic and mechanical properties and strain‐induced crystallization (SIC) behaviors of the latex films, are effectively enhanced after pre‐vulcanization. The pre‐vulcanized LRP films perform better tensile properties and SIC than the SRP can.