Evaporation heat transfer and pressure drop characteristics of R-290 (propane), R-600 (butane), and a mixture of R-290/R-600 in the three-lines serpentine small-tube bank

This paper reports an experimental investigation of heat-transfer and pressure-drop behavior of R-290, R-600, and R-290/R-600 in the three-lines serpentine small-diameter (2.46 mm) tube bank. Heat transfer coefficients and pressure drop characteristics are measured for a range of heat flux (5–21 kW/m²), mass flux (250–500 kg/m² s), equilibrium mass quality (0–0.86), and the fixed mixture composition ((R-290/R-600 (55 wt.%/45 wt.%)). The results show that the flow boiling heat transfer coefficients for R-290, R-600, and R-290/R-600 are 1.66–1.96-fold, 1.28–1.38-fold and 1.57–1.88-fold greater as compared with those for R-134a under equal heat and mass fluxes. Also, the two-phase flow frictional pressure drop for R-600, R-290/R-600 and R-290 are 1.41–1.60-fold, 1.32–1.50-fold and 1.22–1.40-fold smaller as compared with that for R-134a. A new heat transfer correlation was presented by using a superposition model to predict the experimental data for both pure refrigerants and refrigerant mixtures. Experimental results were compared with several correlations which predict the evaporative heat transfer, which are in good agreement with experimental data.     

Separation of oligonucleotides by reversed-phase high performance liquid chromatography

The use of Reversed-Phase High Performance Liquid Chromatography (RP-HPLC) was investigated for the separation of oligonucleotides. By the gradient elution with the mobile phase of methanol, 0.1 M KH₂PO₄ and 0.02 M MaCl₂, the mixtures could be separated in a 250 mm × 4.6 mm I.D. column. The number of theoretical plates and resolution were compared belween this technique and Micellar Electrokinetic Capillary Chromatography (MECC). The charged nucleic acid constituents in the RP-HPLC were relatively better separated than in the MECC.     

Structure sensitivity of the catalytic oxidative coupling of methane on lanthanum oxide

The oxidative coupling of methane (OCM) has been found to be structure sensitive on La₂O₃ catalysts exhibiting different crystallite morphologies. Thin plates obtained by thermal decomposition of lanthanum nitrate at 650 °C are more selective on OCM reaction performed at 750 °C than the particles obtained by decomposition of the nitrate at 800 °C. It is assumed that the oxycarbonate observed is formed from the methane deep oxidation on the catalyst surface. This compound appears to act as an intermediate in the production of CO₂ and is thus important hi the resulting selectivity.     

A study on membrane distillation by a solar thermal‐driven system

Membrane distillation (MD) is a membrane separation process that has long been investigated in small scale laboratory studies and has the potential to become a viable tool for water desalination. MD is a separation process that combines simultaneous mass and heat transfer through a hydrophobic microporous membrane. A solar collector is used in direct contact membrane distillation (DCMD) to heat seawater as a temperature driving force in heat transfer to establish seawater desalting systems. The effect of the temperature difference makes the brine vaporize in the hot fluid side and condense in the cold fluid side. The optimal operating parameters on the pure water production rate will also be examined in this study. The purposes of this study are to develop the theoretical heat and mass transfer formulations, simulate heat transfer rate of solar collector with internal fins in membrane distillation, and investigate the mass‐transfer efficiency improvement in membrane distillation with the brine flow rate, solar collector efficiency, and temperature difference between both sides of membrane as parameters. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(7): 417–428, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20172     

Characteristics of gas-liquid chromatography

The effects of sample size, liquid loading, particle size, column length, and column temperature on retention volumes were studied and separation factor, column efficiency, partition coefficient, and heat of solution were also obtained by gas-liquid chromatography. The feed materials were chosen by similar boiling points as diethylether, dimethoxymethane and dichloromethane. The relations between retention volume and above mentioned various variables were obtained. Separation factor was more affected by column temperature than other variables, and decreased with the temperature. HETP increased almost linearly with sample size. From the exponential relationship between partition coefficient and column temperature heat of solution of each material was calculated.     

The effect of the gas void distribution on the ohmic resistance during water electrolytes

Due to the presence of gas bubbles on the electrode surface and in the interelectrode gap during water electrolysis, the ohmic resistance in the cell increases. The main aim of this investigation is to obtain insight into the effect of the gas void distribution on the ohmic resistance in the electrolysis cell. The gas void distribution perpendicular to the electrode surface has been determined at various current densities, solution flow velocities and heights in the cell, taking high speed motion pictures. From these measurements it follows that two bubble layers can be distinguished. The current density distribution and the ohmic resistance in the electrolysis cell have been determined using a segmented nickel electrode. The current density decreases at increasing height in the cell. The effect is more pronounced at low solution flow velocities and high current densities. A new model to calculate the ohmic resistance in the cell is proposed.Nomenclature A _l electrolyte area (m²) - c constant (–) - d _wm distance between the working electrode and the diaphragm resp. the tip of the Luggin capillary (m) - E voltage of an operating cell (V) - f gas void fraction (–) - F Faraday constant (C/mol) - f ₀ gas void fraction at the electrode surface (–) - f _b gas void fraction in the bulk electrolyte (–) - h height from the bottom of the working electrode (m) - h _r reference height (= 1 cm) (m) - H total height of the electrode (m) - i current density (A m^–2) - i _av average current density (A m^–2) - i _r reference current density (= 1 kA m^–2) (A m^–2) - R resistance () - R specific resistance (_m) - R unit surface resistance (m²) - R ₁ resistance of the first bubble layer () - R ₂ resistance of the second bubble layer () - R _cell ohmic resistance in the cell () - R _b bubble radius (m) - s _l degree of screening by bubbles in the electrolyte (–) - _l liquid flow velocity (m s^–1) - _{1, r} reference liquid flow velocity (= l m s^–1) (m s^–1) - V _M molar gas volume (m³ mol^–1) - w width of the electrode (m) - x distance from the electrode surface (m) - thickness of the bubble layer adjacent to the electrode (m) - number of bubbles generated per unit surface area and unit time (m^–2 s^–1) Paper presented at the International Meeting on Electrolytic Bubbles organised by the Electrochemical Technology Group of the Society of Chemical Industry, and held at Imperial College, London, 13–14 September 1984.     

Structure development in melt‐spinning syndiotactic polystyrene and comparison to atactic polystyrene

Syndiotactic polystyrene (s‐PS) and atactic polystyrene (a‐PS) were melt‐spun into filaments. The s‐PS filaments exhibited increasing amounts of crystallinity and orientation with increasing drawdown ratio and spinline stress. The a‐PS filaments were amorphous but exhibited birefringence. The birefringence and Hermans orientation factors for a‐PS were proportional to this spinline stress. In ice water and at low drawdown ratios, the s‐PS is glassy or mesomorphic. At higher drawdown ratios and spinline stresses, it crystallized. The crystalline form was the zigzag TTTT hexagonal α‐form. The birefringence and orientation factors of the s‐PS filaments were higher than those of the a‐PS filaments and the difference of the birefringence increased with increasing spinline stress. Mechanical testing results showed that the Young's modulus and tensile strength generally increased with increasing spinline drawdown ratio for both a‐PS and s‐PS filaments. The elongation to break was enhanced for both materials by increased chain orientation. Polym. Eng. Sci. 44:2141–2147, 2004. © 2004 Society of Plastics Engineers.     

Thickness and composition dependence of the glass transition temperature in thin random copolymer films

Glass transition temperatures (T_g) of thin poly(styrene-co-methyl methacrylate) and poly(2-vinyl pyridine-co-styrene) films coated on a native oxide surface of Si wafer (100) were measured by ellipsometry. The thickness dependence of T_g can be properly fitted by previously suggested equation developed for homopolymers, based upon a continuous multi-layer model, although one component in thin random copolymer films demonstrates a slightly favorable interaction between a substrate and thin film, and another demonstrates a strongly favorable interaction. Surface and interface have a strong influence on T_g of thin film coated on substrate: the surface has the effect of reducing T_g, whereas the interface increases the T_g according to the degree of interaction between a substrate and thin film. This degree of interaction can be quantified as an interaction parameter (k), and is dependent on the composition of random copolymers. For the estimation of k values of thin random copolymer films, we proposed a parallel type additive function (1/k_ran=w₁/k₁+w₂/k₂) where w is a weight fraction of component.     

Increased Histone Acetylation and Decreased Expression of Specific Histone Deacetylases in Ultraviolet-Irradiated and Intrinsically Aged Human Skin In Vivo

Histone deacetylases (HDACs) are conserved enzymes that remove acetyl groups from lysine side chains in histones and other proteins and play a crucial role in epigenetic regulation. Previously, we showed that histone acetylation is implicated in ultraviolet (UV)-induced inflammation and matrix impairment. To elucidate the histone acetylation status and specific HDACs involved in skin aging, we examined the changes in histone acetylation, global HDAC activity, and the expression of HDACs and sirtuins (SIRTs) in intrinsically aged and photoaged human skin as well as in UV-irradiated human skin in vivo. Following acute UV irradiation, the acetylated histone H3 (AcH3) level was increased, but HDAC activity and the expression levels of HDAC4, HDAC11, and SIRT4 were significantly decreased. In intrinsically aged skin, AcH3 levels were increased, but HDAC activity and the expression levels of HDAC4, HDAC5, HDAC10, HDAC11, SIRT6, and SIRT7 were significantly decreased. However, histone acetylation and HDAC expression in photoaged skin were not significantly different from those in intrinsically aged skin. Collectively, HDAC4 and HDAC11 were decreased in both UV-irradiated and intrinsically aged skin, suggesting that they may play a universal role in increased histone acetylation associated with skin aging.     

Microkinetic model for the pyrolysis of methyl esters: From model compound to industrial biodiesel

A tool for the generation of decomposition schemes of large molecules has been developed. These decomposition schemes contain radicals which can be eliminated from the model equations if both the μ‐hypothesis and the pseudosteady‐state approximation are valid. The reaction rate coefficients and thermodynamic parameters have been calculated by incorporating a comprehensive group additive framework. A microkinetic model for the pyrolysis of methyl esters with a carbon number of up to 19 has been generated using this tool. It is validated by comparing calculated and experimental yields of the pyrolysis of methyl decanoate and novel rapeseed methyl ester pyrolysis data in the temperature range from 800 to 1100 K and methyl ester partial pressure range from 1 × 10^?3 to 1 × 10^?2 MPa. This modeling frame work allows to not only assess the use of methyl ester mixtures as potential feedstock for olefin production but also their effect as blend‐in or trace impurity. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4309–4322, 2015