Fast computation of multidimensional discrete Hartley transform

Efficient algorithms for the fast computation of 2D and 3D discrete Hartley transforms have been proposed. It is shown that the proposed algorithms offer a significant saving in computation over the existing methods for various array sizes.<>     

CFD study of forced convective heat transfer enhancement in a 90° bend duct of square cross section using nanofluid

In this paper, the forced convective heat transfer enhancement with nanofluids in a 90° pipe bend has been presented. Numerical investigation is carried out for the turbulent flow through the pipe employing finite volume method. The governing differential equations are discretized using hexahedral cells, and the resulting algebraic equations are solved using Commercial solver Fluent 6.3. In order to close the time averaged Navier–Stokes equations, the two-equation k–? turbulence model with a standard wall function have been used. The duct Reynolds number is varied in the range of 2,500–6,000. It is observed that the heat transfer is enhanced significantly by varying the volume fraction of the nanofluid. It is also found that the heat transfer is increased with Reynolds number. A strong secondary flow is observed due to the presence of the wall. Turbulent kinetic energy near outer wall is found to be higher than the inner wall of the bend. A comparative assessment for the heat transfer enhancement with different types of nanofluids is also presented. The computed results of area weighted average Nusselt numbers are validated with some of the existing literature.     

Erosion wear response of ramie-epoxy composites using artificial neural network integrated with Taguchi technique

This paper aims on evaluating the erosion wear behavior of epoxy composites reinforced with ramie fibers. The possibility of reinforcing ramie fiber to improvise the wear resistance of epoxy is investigated in this study. Composites are fabricated by reinforcing multiple layers of woven ramie fiber mats into epoxy resin using conventional wet lay-up technique and erosion wear trials are conducted using solid particle erosion test setup. Taguchi analysis is done to assess the relative significance of each of the factors influencing the erosion rate using L₁₆ orthogonal array. The analysis reveals that the impact velocity followed by impingement angle are the most significant control factors affecting the erosion wear rate of ramie-epoxy composites. Steady state erosion analysis is done to ascertain the effect of each of the significant factors while keeping other factors fixed. Further, an analytical and predictive model based on the principle of neural computation is used to predict the rate of erosion wear of the composites and the obtained results are compared with the experimental outcomes. The worn morphologies of the eroded surfaces of the composites are studied and analyzed to identify possible mechanisms causing wear.     

Morphology and crack toughness behaviour of nanostructured block copolymer/homopolymer blends

The crack initiation and propagation behaviour of styrene-butadiene (SB) star block copolymer/polystyrene blends (ST3/PS) forming PS-rich and polybutadiene (PB)-rich nanosized domains by self-assembling have been investigated using the essential-work-of-fracture (EWF) approach. Three morphological transitions have been observed, which are crucial to understand the crack toughness behaviour: (i) 0-30 wt.% PS homopolymer: A co-continuous domain structure of PS-rich and PB-rich domains has been observed. For PS homopolymer fraction (?_PS) < 10 wt.% PS homopolymer (i.e. only pure ST3) the rubbery PB-rich phase forms the major phase and for ?_PS > 10 wt.% the glassy PS-rich phase. (ii) At 40-60 wt.% PS homopolymer, a layer-like morphology is formed where the PS-rich layer thickness is ?50 nm, a critical dimension, which is crucial for understanding the ductile-to-semiductile transition. (iii) For 80 wt.% PS homopolymer, PS-rich phase starts to form the matrix combined with a transition from shear stress dominated (shear yielding) to normal stress dominated behaviour (PS-like crazes). The co-continuous morphology at 20 wt.% and 30 wt.% PS is capable of improving toughness of block copolymers, demonstrated by the observed maximum in the non-essential work of fracture and thus explaining a new way of toughening of polymers while retaining high transparency. The correspondence between the ductile-to-semiductile transition and the change in the shape of plastic zone from circular to elliptical as revealed from strain field analysis could be clearly reaffirmed by the observed transition from shear to normal force induced deformation in the fractured surface analysis of these blends. The conceptual correspondence of βw_p and w_e with T_J and δ_0.2 respectively reveal that resistance against crack propagation (βw_p and T_J) is morphology sensitive while the resistance against crack initiation (w_e and δ_0.2) is matrix sensitive.     

Combustion analysis of the diesel–biogas dual fuel direct injection diesel engine – the gas diesel engine

In this investigation, biogas (BG) was used as an alternative fuel in a single-cylinder, four-stroke, air-cooled, direct injection (DI) diesel engine that was operated on a dual fuel mode. Biogas was produced from a non-edible seed de-oiled cake-pongamia pinnata (Karanja), which was collected from the biodiesel industries. The BG was inducted along with the air in suction of the engine at four different flow rates varying from 0.3?kg/h to 1.2?kg/h in steps of 0.3?kg/h. The investigation results revealed that BG inducted at a flow rate of 0.9?kg/h gives better combustion characteristics of engine behaviour than those of other flows throughout the engine operation. The ignition delay (ID) and combustion duration of the engine run by dual fuel operation at a BG flow rate of 0.9?kg/h were found to be longer by about 2 °CA and 2.9 °CA, respectively, in comparison with diesel at full load. The cylinder peak pressure was found to be overall higher by about 11?bar than that of diesel at full load.     

Performance assessment of hybrid composite friction materials based on flyash–rock fibre combination

Friction composites based on several combinations of flyash and inorganic mineral rock fibres such as lapinus™ fibre were fabricated, characterised and tribo-evaluated. The tribo-performance in terms of their friction-fade and friction-recovery behaviour has been rigorously evaluated while synchronously taking into account of the in situ braking induced temperature rise in the disc at the braking interface on a Krauss friction testing machine following pulse velocity wave (PVW) 3212 norms as per the Economic Commission for Europe (ECE) regulations. The fade behaviour has been observed to be highly dependent on the combination of flyash–lapinus fibre e.g. fade remained maximum (45%) in the composite with the highest amount of lapinus fibre content and lowest amount of flyash whereas the frictional fluctuations in terms of μ_max − μ_min has been observed to be higher in case of low flyash–high lapinus fibre combination. The recovery response seemed unaffected by the disparity of ingredients and remained consistently stable within the range of 112 ± 2%. The analysis of friction and wear performance has revealed that flyash along with lapinus fibre provide thermo-mechanical stability and overall mechanical integrity to the system causing reduction in friction-fade whereas wear was found to be more recovery-controlled and less fade controlled. Worn surface morphology investigation using SEM has been carried out which has revealed that the interplay of flyash–lapinus combination and topographical attributes vis-a-vis dynamics of contact patches (formation–destruction) largely influence the friction and wear performance of such composites.     

Exergy analysis of a compression–absorption system for heating and cooling applications

An exergy analysis of a single‐stage compression–absorption system with R22‐E181 as the working fluid pair is carried out. Theoretical results obtained have been compared with those obtained from the experiment. Results show that the heat of mixing of the refrigerant vapour and solution at absorber and desorber contributes a significant amount to the internal entropy generation rates. A significant part of internal entropy generation rate is also due to non‐isentropic compression of refrigerant vapour at higher absorber pressure. The exergetic efficiency of the system increases with the increase in absorber pressure due to reduction in internal irreversibilities. Higher value of weak solution concentration along with the increase in solution concentration difference results in higher exergetic efficiency of the system. Thus, a compression–absorption system performs better when operated at higher absorber pressure, and an improved system performance can also be achieved with higher value of weak solution concentration with higher possible solution concentration difference. Copyright © 2008 John Wiley & Sons, Ltd.     

Merox and Related Metal Phthalocyanine Catalyzed Oxidation Processes

Alkyl and aromatic mercaptans are among important organic sulfur compounds distributed in petroleum products. The mercaptans cause foul odor and are corrosive toward metals. In addition, mercaptans may cause oxidative deterioration as well as inhibit the performance of various additives (TEL, antioxidants) in finished products. Therefore, it is necessary to remove them, either by extractive processes or by converting them into innocuous disulfides. Such processes are usually referred to as “sweetening.”     

Hybrid composite friction materials reinforced with combination of potassium titanate whiskers and aramid fibre: Assessment of fade and recovery performance

Composite friction materials based on synergistic ternary combination of potassium titanate whiskers, aramid fibre and graphite have been characterized for friction braking performance on Krauss friction tester. The dynamics of friction build-up and friction-decay as a function of number of braking instances and modes of braking cycles have been found to be more consistent in the composites with ≥7.5 wt% of aramid fibres whereas the absolute friction effectiveness remained higher in the composites with ≥25 wt% of potassium titanate whiskers. Wear surface morphology has revealed topographical variations and their underlying role in controlling the friction and wear performance.     

Thermo-mechanical correlations to erosion performance of short carbon fibre reinforced vinyl ester resin composites

Thermo-mechanical properties and erosion performance of short carbon fibre reinforced vinyl ester resin based isotropic polymer composites with four different fibre weight fractions have been investigated. The storage, loss and damping characteristics were analysed to assess the energy absorption/viscous recoverable energy dissipation and reinforcement efficiency of the composites as a function of fibre content in the temperature range of 0–140 °C. The composite with 30 wt.% of short carbon fibres has been observed to exhibit superior thermo-mechanical response with highest energy dissipation/damping ability accompanied with a constant storage modulus without any substantial decay till 60 °C. The erosion rates (Er) of these composites are evaluated at different impingement angles (30–90°), fibre loadings (20–50 wt.%), impact velocities (43–76 m/s), stand-off distances (55–85 mm) and erodent sizes (250–600 μm) following the erosion test schedule in an air jet type test rig. An optimal parameter combination is determined and subsequently validated for erosion rate minimization following Taguchi method and by conducting confirmation experiments. A correlation between the loss-modulus inverse and the erosion rate has been observed which conceptually establishes a possible mechanistic equivalence between erosion and dynamic mechanical loading modes. The morphologies of eroded surface are examined by the scanning electron microscopy to investigate the nature of wear-craters, material damage mode and other qualitative attributes responsible for promoting erosion.