Investigation on the transformation of time domain spectroscopy data to frequency domain data for impregnated pressboard to reduce measurement time

The accuracy of different transformation methods for time domain dielectric response data to frequency domain and their limits are studied. First an approximated analytic function is considered, second an extended Debye model for the dielectric behavior of impregnated pressboard. The last method is a numerical integral form and Fast Fourier Transform. Hamon approximation relates time domain data at t to frequency domain data at f=0.1/t and gives the results by sole measurement of polarization current. Dielectric diagnosis of high voltage apparatus can be done by using Hamon approximation in minimum duration. All transformation methods show similar results and they are analyzed in order to demonstrate the limits of the methods.     

Study on morphological,rheological, and mechanical properties of PP/SEBS‐MA/SGF hybrid composites

Hybrid composite samples composed of polypropylene as matrix, 20% short glass fibers (SGF) as reinforcement and varying amount of maleic anhydride (MA) grafted SEBS as compatibilizer and impact modifier were prepared by melt mixing in a modular twin screw extruder. The SEM examination performed on cryogenically fractured surfaces of hybrid samples showed a three‐phase type morphology in which SGF and rubber phase finely distributed in the PP matrix. SEM results also revealed that in the hybrid samples containing SEBS‐MA, the surface of the SGF are coated with a thin layer of SEBS‐MA, indicating a strong adhesion between SGF and matrix materials. The results of rheological studies showed nearly equal viscosity for compatible and incompatible hybrid samples. Tensile yield strength enhanced with increasing rubber content up to 10% above which it decreased and highest impact strength enhancement was obtained for sample containing 20% rubber. The impact strength of composites was found to be increased with increasing the SGF content. In final, it was shown that a good balance between stiffness and toughness could be achieved by adjusting the SGF and rubber content in this ternary system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2704–2710, 2007     

Polypropylene/clay nanocomposite: kinetic and thermodynamic of dyeing with various disperse dyes

The preparation of polypropylene/clay nanocomposite fibers is interesting from the point of dyeability. This paper investigated the kinetics and the thermodynamic parameters of polypropylene/nanoclay dyeing with three disperse dyes as common dyestuffs for non-polar polymer (C.I. Disperse Blue 60, C.I. Disperse Red 324, and C.I. Disperse Yellow 211). The physicochemical parameters of dyeing are calculated in terms of sorption isotherm, standard affinity, enthalpy and entropy changes, and diffusion coefficient as well as activation energy of the diffusion. The sorption of disperse dye on polypropylene/nanoclay composite shows the linear isotherm. The value of dyeing rate constant and diffusion coefficient of dye molecules increases with the dyeing temperature. The standard affinity of Disperse Red 324 to polypropylene/nanoclay fiber is higher than the two other dyes due its higher partially polarity.     

The impact of UV/H2O2 advanced oxidation on molecular size distribution of chromophoric natural organic matter

The impact of hydroxyl radical (*OH) on the molecular weight distribution of natural organic matter (NOM) was investigated. *OH was generated via the photolysis of hydrogen peroxide (H2O2) by ultraviolet (UV) radiation of 254 nm, also known as UV/ H2O2 advanced oxidation (AO). Additionally, the impact of combined membrane and UV/H2O2 treatment on the molecular weight distribution of NOM was studied. High performance size exclusion chromatography (HPSEC) was used to determine the apparent molecular weight (AMW) distribution of chromophoric NOM (CNOM). Prior to AO, 33% of the CNOM in the water had AMW greater than 1400 Da. Meanwhile, lower AMW CNOM made up smaller amounts of the CNOM, with CNOM of AMW less than 450 Da making up 5% of the total. Under the AO conditions typically applied in drinking water treatment applications, NOM was not mineralized but was partially oxidized resulting in significant reduction in aromaticity. *OH preferentially reacted with higher AMW CNOM and the fragmentation of high AMW CNOM led to the formation of smaller AMW CNOM. Ultrafiltration removed all CNOM greater than 1400 Da AMW and a large portion of other high AMW fractions. In the absence of high AMW CNOM, *OH reacted more readily with all AMW fractions leading to a reduction in concentration of most AMW fractions. Whereas *OH reacted nonspecifically with all AMW fractions, the reaction rate between *OH and CNOM was observed to be dependent on molecular size.     

Thermooxidative reactions of polypropylene wax in the molten state

Thermooxidation of polypropylene wax was investigated in the molten state under an air‐flowing atmosphere. Calorimetric measurements were performed to investigate the effect of the inclusion of 1‐dodecanol as an efficient primary alcohol and to reveal the typical outlines of thermooxidation, that is, the induction time and oxidation rate. The same parameters were obtained and compared on the basis of the Fourier transform infrared (FTIR) peaks of major oxidation products, such as ketones and hydroxyl groups. The results showed that 1‐dodecanol caused a change in the shape of the calorimetric thermogram and also yielded oxidized products with more clarity in color. With the Arrhenius equation, the apparent activation energy was calculated on the basis of the induction time and oxidation rate for carbonyl and hydroxyl groups individually. The obtained apparent activation energy was in agreement with the proposed mechanism based on bimolecular hydroperoxide decomposition involving dodecanol. With FTIR spectroscopy, no changes in the chain helical conformation or double‐bond concentration were observed during oxidation up to 500 min. An acid value of up to 6 mg of KOH per gram was obtained at this time. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The significance of the buffer zone of boundary layer on convective heat transfer to a vertical turbulent flow of a supercritical fluid

A two-dimensional model is developed to simultaneously solve the momentum and energy equations in order to predict convective heat transfer to an upward turbulent flow of supercritical carbon dioxide in a round tube. It is very important to choose a proper turbulence model. An appropriate turbulence model, based on the previous studies, has been selected. The main focus of the present study is on significance of the buffer zone in the boundary layer. The results of this study indicate that in enhanced regime of heat transfer, the peak of heat transfer coefficient occurs when the pseudo-critical temperature, or the situation of maximum heat capacity, lies within the buffer layer. In deteriorated regime of heat transfer, the extent of the laminar sub-layer appears to be changed so that the buffer zone is experienced at a farther distance from the wall. This causes a delay in the turbulent diffusion near the wall and leading to a jump in the wall temperatures.     

Digitized Heat Transfer: A New Paradigm for Thermal Management of Compact Micro Systems

This paper presents theoretical and numerical results describing digitized heat transfer (DHT), a newly developing active thermal management technique for high-power density electronics and integrated micro systems. In describing DHT, we numerically investigate the mass, momentum, and energy equations governing the flow within a translating microdroplet. Our analysis shows the existence of a pair of recirculation zones inside the droplet. This internal circulation within discrete fluid slugs results in significantly increased overall heat transfer coefficients when compared to continuous Graetz-type flows. The internal circulation drives the cold fluid in the middle of the droplet to the vicinity of the walls and creates a higher local temperature difference between the wall and the fluid in contact with the wall, resulting in higher heat transfer rates. Nusselt numbers characterizing DHT flow are also shown to exhibit periodic fluctuations with a period equal to the characteristic time scale for droplet circulation. The overall effect of discretizing a flow on heat transfer capability is described and characterized in terms of a nondimensional circulation number defined by the ratio of characteristic thermal diffusion and fluid circulation time scales. DHT coolants, including liquid metals and alloys, are proposed, and their physical properties are shown to enable handling of significantly higher heat transfer rates than classical air- or water-cooled methods. The actuation method for DHT coolant transport is also outlined, and shown to provide the capability for active, on-demand suppression of transient hot spots. This overall analysis defines the key parameters for optimization of the DHT method and forms the basis of ongoing experimental work.