Augmentation of boiling heat transfer from horizontal cylinder to liquid by movable particles

This paper presents a series of experimental results on a passive augmentation technique of boiling heat transfer by supplying solid particles in liquid. A cylindrical heater 0.88 mm in diameter is placed in saturated water, in which a lot of mobile particles exist, and the nucleate and film boiling heat transfer characteristics are measured. Particle materials used were alumina, glass, and porous alumina, and the diameter ranged from 0.3 mm to 2.5 mm. Particles are fluidized by the occurrence of boiling without any additive power, and the heat transfer is augmented. The maximum augmentation ratio obtained in this experiment reaches about ten times the heat transfer coefficient obtained in liquid alone. The augmentation ratio is mainly affected by the particle material, diameter, and the height of the particle bed set at no boiling condition. The augmentation mechanism is discussed on the basis of the experimental results. © 2001 Scripta Technica, Heat Trans Asian Res, 31(1): 28–41, 2002     

Supercritical fluid extraction of fungal oil using CO2, N2O,CHF3 and SF6

The extraction of oil from fungi (Mortierella ramanniana var.angulispora) was studied using carbon dioxide (CO₂), nitrous oxide (N₂O), trifluoromethane (CHF₃) and sulfur hexafluoride (SF₆) under supercritical conditions. The oil solubility was highest in SC-N₂O followed by SC-CO₂, while both SC-CHF₃ and SC-SF₆ showed poorer solvent power. The recorded oil solubilities at 333 K and 24.5 MPa were 2.3 wt% in N₂O, 0.48 wt% in CO₂, 0.0099 wt% in CHF₃ and 0.0012 wt% in SF₆. The oil solubilities in SC-N₂O and SC-CO₂ were measured over the pressure range 15.7–29.4 MPa and at temperatures ranging from 313–353 K. N₂O always showed greater solvent power than did CO₂ at the same temperature and pressure. The solvent power of a supercritical fluid increases with density at a given temperature, and increases with temperature at constant density. The change in neutral lipid composition of the extracted oil with the extraction ratio was measured. Free fatty acids or diglycerides were extracted more easily than triglycerides or sterol esters. The change in fatty acid composition was also measured. The proportion of γ-linolenic acid in the extract remained constant throughout the extraction.     

Hydrothermal epitaxy of KTaO3 thin films under supercritical water conditions

Potassium tantalate powders were hydrothermally synthesized at 400 °C using Ta₂O₅ and KOH as starting materials with various KOH concentrations (0.1–1.0 M) and heating durations (2–48 h). A defect pyrochlore phase of KTa₂O₅(OH)·nH₂O, was obtained at low KOH concentration and short reaction time. The perovskite phase of KTaO₃ predominated as the heating duration and the KOH concentration increased. Pure KTaO₃ was obtained in 0.5–1.0 M KOH aqueous solutions and reaction times of 8–48 h. Heteroepitaxitial KTaO₃ thin films were achieved on the (100) SrTiO₃ substrate in 0.5 M KOH solution under supercritical water conditions. Based on the XRD, SEM-EDX and EBSP (Electron BackScatter Pattern) results, epitaxial KTaO₃ crystals were grown on the (100) oriented single-crystal SrTiO₃ substrate. Synthesis of perovskite KTaO₃ crystals in supercritical water employed significantly low KOH concentrations (<0.5 M), which was far less than the very high concentrations (>7 M) required for conventional hydrothermal method.     

New bleeding model of additives in a polypropylene film under atmospheric pressure II

Many additives are commercially used to add more favorable qualities to films. The bleeding process by which the additive in a film comes to the surface is considered. A new bleeding model of additives in a polypropylene film under atmospheric pressure was investigated. Solubility and diffusion are found to be important for explaining this bleeding process. It was found that the experimental results were explained more precisely by assuming a two‐step transport process between the crystalline regions and the amorphous ones. The solubilities and diffusion coefficients of UV‐stabilizers such as 2‐(2H‐benzotriazol‐2‐yl)‐4‐(1,1,3,3‐tetramethylbutyl)phenol and 2‐(2H‐benzotriazol‐2‐yl)‐4‐methylphenol were determined at 40°C. The difference between the saturation solubilities and the diffusion coefficients of UV‐stabilizers was discussed by comparing with the results of molecular dynamics (MD) simulation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Sludge depositions in a long tube-high flow MSF test plant

During the operation of a multistage flash (MSF) evaporation plant, a rather rapid decrease was observed in the economy ratio of the plant when the dissolved oxygen (DO) content of the circulating brine was at a high level. This phenomenon was brought about by the reduction of heat transfer coefficients of condenser tubes due to sludge formation on the inside tube surface by the co-precipitation of ferric hydrous oxide with silica, alumina, and organic materials. The chemical analysis of the sludge and circulating brine showed a close relationship to DO values in the brine, the concentration of iron in the sludge, and the decreasing value of the heat transfer coefficient. The lowering of DO was found very effective for avoiding the sludge trouble.     

Concentration of heavy water in seawater distillation process

Distributions of deuterium in two multi-stage flash plants and a multi-effect plant were calculated by use of a numerical model. The calculated values were in good agreement with the observed ones. The maximum error was less than 1%. Product water of high deuterium concentration can be obtained from the distillation chamber at the highest temperature with a high concentration factor. The deuterium concentration in the product water was around 155 ppm.     

Kinetics of the catalytic decomposition of hydrogen iodide in the thermochemical hydrogen production

The decomposition rates of hydrogen iodide over platinum supported γ-alumina were measured in the range from 480 to 700 K by the use of a flow method. It was found that Pt/γ-alumina catalyst was effective for the decomposition of hydrogen iodide. According to the Langmuir-Hinshelwood model, an overall rate equation was obtained on the basis of the mechanism where the rate-determining step was a surface reaction. Experimental data were well correlated with the rate equation.