Conduction based calibration of handmade platinum thin film heat transfer gauges for transient measurements

Heat transfer measurement using thin film gauges (TFG) is the most prevalently used technique for determination of surface heat flux. They are best suited for short duration transient surface temperature measurements and typically used in the applications where convection is a dominant mode of heat transfer such as gas turbine engines, high speed flights etc. However, in few interdisciplinary research areas, there are practical issues and difficulties in exposing the gauges for convection based measurements. These present investigations are aimed at exploring the possibility of using thin film gauges for short duration conduction based transient measurements with pure conduction mode of heat transfer. A simple calibration set-up has been used to supply known heat flux of different magnitudes to the thin film gauges that are fabricated in-house with platinum as sensing element and pyrex as an insulating substrate. Experimentally recorded temperature signals from the gauges are compared with simulated temperature histories obtained through finite element analysis. Convoluted integral of one-dimensional heat conduction equation is used to predict the surface heat flux and compared with input heat loads. The presently developed calibration setup is seen to be very useful for conduction based measurements of thin film gauges.     

Synthesis of Biopolymer‐Derived Zirconium Carbide Powder by Facile One‐Pot Reaction

Zirconium carbide (ZrC) was synthesized by polycondensation and carbothermal reduction reactions from an organic–inorganic hybrid complex. A natural biopolymer Gum Karaya (GK) and zirconyl oxychloride octahydrate (ZOO) were used as the sources of carbon and zirconium, respectively. FTIR of as‐synthesized dried complexes revealed formation of Zr–O. Pyrolysis of the complexes at 1200°C/1 h under argon resulted in tetragonal and monoclinic zirconia which after heat treatment at 1400°C–1550°C transformed to zirconium carbide. Thermal analysis shows that the GK–ZOO complexes lost less mass than the pristine GK to 600°C. The intensity of exothermic decomposition decreases and shifted to higher temperature for the hybrid complexes indicating that zirconia induced thermal stability. A maximum ZrC yield of ~60 wt% is obtained for the intermediate GK–ZOO ratio of 1:2. Particles pyrolyzed for 1 h at 1550°C were coarser (5–10 μm) with flakes for lower GK–ZOO weight ratio, but were spheroidal with narrow size distribution (~1 μm) with increasing GK–ZOO weight ratio.     

Enhanced dispersion of carbon nanotubes in hyperbranched polyurethane and properties of nanocomposites

Hyperbranched polyurethane (HBPU) nanocomposites with multi-walled carbon nanotubes (MWNTs) were prepared by in?situ polymerization on the basis of poly(ε-caprolactone)diol as the soft segment, 4,4'-methylene bis(phenylisocyanate) as the hard segment, and castor oil as the multifunctional group for the hyperbranched structure. A dominant improvement in the dispersion of MWNTs in the HBPU matrix was found, and good solubility of HBPU-MWNT nanocomposites in organic solvents was shown. Due to the well-dispersed MWNTs, the nanocomposites resulted in achieving excellent shape memory properties as well as enhanced mechanical properties compared to pure HBPU.     

Vacuum-induced Bubble Formation in Liquid-tempered Chocolate

ABSTRACT: Bubble inclusion is one of the fastest growing operations practiced in the food industry. A variety of aerated foods is currently available in supermarkets, and newer products are emerging all the time. This paper aims to combine knowledge on chocolate aeration with studies performed on bubble formation and dispersion characteristics. More specifically, we have investigated bubble formation induced by applying vacuum. Experimental methods to determine gas hold-up (volume fraction of air), bubble section distributions along specific planes, and chocolate rheological properties are presented. This study concludes that decreasing pressures elevate gas hold-up values due to an increase in the number of bubble nuclei being formed and release of a greater volume of dissolved gases. Furthermore, bubbles are observed to be larger at lower pressures for a set amount of gas because the internal pressure needs to be in equilibrium with the surrounding pressures. Temperature-induced changes to the properties of the chocolate have less of an effect on bubble formation. On the other hand, when different fats and emulsifiers are added to a standard chocolate recipe, milk fat was found to increase, significantly, the gas hold-up values and the mean bubble-section diameters. It is hypothesized that this behavior is related to the way milk fats, which contain different fatty acids to cocoa butter, crystallize and influence the setting properties of the final product. It is highlighted that apparent viscosity values at low shear rate, as well as setting behavior, play an important role in terms of bubble formation and entrainment.     

Mesua ferrea L. seed oil based highly branched polyester/epoxy blends and their nanocomposites

Mesua ferrea L. seed oil based highly branched polyester and epoxy resins blends were prepared by mechanical mixing at different weight ratios. The best performing blend was used as the matrix for the preparation of nanocomposites with different dose levels of organophilic montmorillonite (OMMT) nanoclay. The prepared nanocomposites were characterized by X‐ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. Data resulting from the mechanical and thermal studies of the blends and nanocomposites indicated improvements in the tensile strength and thermal stability to appreciable extents for the nanocomposites with OMMT loading. The nanocomposites were characterized as well‐dispersed, partially exfoliated structures with good interfacial interactions. From the X‐ray diffraction analysis, the absence of d₀₀₁ reflections of the OMMT clay in the cured nanocomposites indicated the development of an exfoliated clay structure, which was confirmed by transmission electron microscopy. The homogeneous morphologies of the pure polyester/epoxy blend and clay hybrid systems were ascertained with scanning electron microscopy. The tensile strength of the 5 wt % clay‐filled blend nanocomposite system was increased by 2.4 times compared to that of the pure blend resin system. The results suggest that the prepared nanocomposites have the potential to be used as active thin films for different applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Frying of potato chips in a blend of canola oil and palm olein: changes in levels of individual fatty acids and tocols

The changes occurring in the levels of nutritionally relevant oil components were assessed during repeated frying of potato chips in a blend of palm olein and canola oil (1:1 w/w). The blend suffered minimal reductions in omega‐3 and omega‐6 polyunsaturated fatty acids. There was no significant difference between the fatty acid composition of the oil extracted from the product and that of the frying medium, in all three cases. The blend also contained a significant amount of tocols which add a nutritional value to the oil. The concentration of the tocols was satisfactorily retained over the period of oil usage, in contrast to the significant loses observed in the case of the individual oils. The blend also performed well when assessed by changes in total polar compounds, free fatty acids, p‐anisidine value. When fried in used oil, the product oil content increased progressively with oil usage time. This study shows that blended frying oils can combine good stability and nutritional quality.     

Mathematical aspects of Rietveld refinement and crystal structure studies on PbTiO3 ceramics

The core mathematics, goodness-of-fit parameters of Rietveld refinement technique is introduced for structural analysis of crystalline materials not available as single crystals. X-ray diffraction (XRD) patterns of PbTiO₃ compound prepared by following solid-state route, suggests it to be in single crystal form. All the observed peaks could be indexed to P4mm space group with tetragonal symmetry. XRD pattern is analysed by employing Rietveld method. The unit cell parameters are found to be a = b = 38987 (0.0008) Å and c = 4·1380 (0·0009) Å. The axial ratio c/a and unit cell volume are found to be 1·0614 and 62·896 (0.023) ų. Bond lengths and angles are calculated using the cell parameters. Using the Rietveld refinement parameters a stable PbTiO₃ structure is suggested.     

Structural study of Zr doped PbTiO3 materials by employing Rietveld method

Single phase materials of PbZr_1?xTi_xO₃ (x = 1.00, 0.65 and 0.35) were prepared by following the solid state route. All the materials were prepared in nanocrystalline form as well as microcrystalline form. Evolution of crystallization was studied by characterizing the samples annealed at different temperatures. XRD patterns were analyzed with the help of Fullprof program by employing Rietveld refinement technique. The patterns for x = 1.00 and 0.65 could be refined using P4mm space group in tetragonal symmetry. However, the samples for x = 0.35 could be refined using R3c space group in rhombohedral symmetry. It has been found that crystallite size increases with the annealing temperature for all the samples. The scanning electron microscope (SEM) and energy dispersive X-ray spectroscope (EDS) analysis reveals that the materials are uniform and their composition is as per the chemical formulae. All the samples exhibit ferroelectric to paraelectric transition.     

Study of dynamic viscoelastic behavior of polystyrene films on addition of oleic acid

We have investigated the dynamic mechanical behavior of films prepared from polystyrene solutions in chloroform containing oleic acid as an additive. The response of the films has been measured by means of a dynamic mechanical analyzer operated in tension mode over a temperature range of 30-150 °C, using sinusoidal motion with a maximum strain of 0.04% and a frequency of 2 Hz. The long term creep behavior has also been evaluated. Our results show that the oleic acid softens and disentangles the polystyrene chains backbone, resulting in a decrease in the dynamic mechanical properties of the polystyrene films.