Numerical study of effect of oxygen fraction on local entropy generation in a methane-air burner

This study considers numerical simulation of the combustion of methane with air, including oxygen and nitrogen, in a burner and the numerical solution of local entropy generation rate due to high temperature and velocity gradients in the combustion chamber. The effects of equivalence ratio (Φ) and oxygen percentage (γ ) on combustion and entropy generation rates are investigated for different Φ (from 0.5 to 1.0) andγ values (from 10 to 30%). Combustion is simulated for the fuel mass flow rate resulting in the same heat transfer rate (Q)y to the combustion chamber in each case. Numerical calculation of combustion is performed individually for all cases with the use of the Fluent CFD code. Furthermore, a computer program has been developed to calculate the volumetric entropy generation rate and the other thermodynamic parameters numerically by using the results of the calculations performed with the FLUENT code. The predictions show that the increase of Φ (or the decrease of λ) significantly reduces the reaction rate levels. Average temperature in the combustion chamber increases by about 70 and 35% with increase ofγ (from 10 to 30%) and Φ (from 0.5 to 1.0) respectively. With increase ofγ from 10 to 30%, volumetric local entropy generation rate decreases by about 9 and 4% for Φ = 0.5 and 1.0 respectively, while total entropy generation rate decreases exponentially and the merit numbers increase. The ratio of the rates useful energy transfer to irreversibility therefore improves as the oxygen percentage increases     

Tool wear condition monitoring in drilling operations using hidden Markov models (HMMs)

Monitoring of tool wear condition for drilling is a very important economical consideration in automated manufacturing. Two techniques are proposed in this paper for the on-line identification of tool wear based on the measurement of cutting forces and power signals. These techniques use hidden Markov models (HMMs), commonly used in speech recognition. In the first method, bargraph monitoring of the HMM probabilities is used to track the progress of tool wear during the drilling operation. In the second method, sensor signals that correspond to various types of wear status, e.g., sharp, workable and dull, are classified using a multiple modeling method. Experimental results demonstrate the effectiveness of the proposed methods. Although this work focuses on on-line tool wear condition monitoring for drilling operations, the HMM monitoring techniques introduced in this paper can be applied to other cutting processes.     

Deformation of NiTiCu shape memory single crystals in compression

Single-crystal orientations of NiTi10Cu alloys were studied under incremental, cyclic compression conditions to establish the pseudoelastic and shape memory response of this class of alloys. This material exhibits a two-step transformation involving cubic to orthorhombic martensite (B2 → B19) followed by orthorhombic to monoclinic martensite (B19 → B19′). The transformation parameters (shear magnitudes and directions for habit and twin planes) were determined associated with the B2 → B19 transformation. The growth of monoclinic martensite correspondent variant pairs (CVPs) emanating from the orthorhombic structure was also analyzed. The transformation strain for the B2 → B19 case was orientation dependent and lower than the B19 → B19′ transformation in compression for all orientations except those near the [001] pole. The experimental results show that the critical transformation stress is orientation dependent and is in the range 30 to 58 MPa. Orientations that exhibit lower transformation stress (or high resolved shear stress factors, [100] and [012]) produce higher recoverable strains (as high as 4 pct), while other orientations ([011], [111], and [123]) with lower resolved shear stress factors result in recoverable strains less than 3 pct. At higher strains, inelastic deformation develops, limiting recoverability. The recoverable strains are lower than the theoretical values for two main reasons: the transformation is curtailed first by austenite slip and subsequently by martensite slip, and the orthorhombic structure does not fully transform to the monoclinic martensite.     

The use of polyaniline films on flexible tape for supercapacitor applications

A sticky surface of a tape was adhered to a graphite surface and then the tape was peeled off. The insulator tape was coated with thin graphite and became conductive in order to use flexible tape as a current collector. Aniline was electrodeposited onto a flexible tape substrate having graphite layer by electrochemical polymerization method from an aqueous (H₂SO₄ solution containing aniline monomers) and non-aqueous media (a deep eutectic solvent containing aniline). The prepared polymeric electrodes were characterized by Fourier transform infrared spectroscopy, Raman, thermogravimetric analysis and scanning electron microscopy techniques. The electrochemical properties of coated and uncoated electrodes were also examined by cyclic voltammetry and galvanostatic charge discharge techniques. The polyaniline (PANI) coated tape can be used as a flexible electrode in supercapacitor applications because PANI coated electrodes are highly electroactive in Na₂SO₄ electrolyte. After 3000 cycles, the capacitance retention of PANI film electrodeposited from Ethaline bath was 90%, while the areal capacitance of PANI film obtained from acidic medium reaches 50% after 500 cycles. As PANI electrode is stable in an ionic liquid for long cycling, Ethaline ionic liquid can be used as electrolyte for PANI based supercapacitor electrode. PANI coated graphite on tape, which is prepared in an easy and inexpensive way is a promising flexible material for high performance supercapacitors.     

Self-assembled fibrillar polyethylene crystals with tunable properties

Due to its simple linear chain structure, crystal morphology of linear low-density polyethylene (LLDPE) fibers can be controlled to fulfill the needs of diverse advanced applications. This study presents a simple two-step method to produce LLDPE fibers with self-assembled fibrillar crystals and highly oriented amorphous phase. Rather than conventional melt spinning, fibers were treated in a two-step eco-friendly bath without drawing after extruded fibers emerge from the spinneret. Treated fibers through the baths demonstrated lower crystallinity, but significantly higher degree of crystal orientation when compared to control fibers of traditional melt spinning. Morphological analysis revealed that a unique microstructure was formed after spinning through a two-step eco-friendly bath. As-spun fibers demonstrated spherulitic morphology which can be transformed into a fibrillar structure followed by post-drawing process. Cross sectional images of the treated LLDPE fibers produced at 400 m/min showed fibrillar PE crystals which can be more dominant upon post-drawing. After two-step bath treatment, produced fibers need low draw ratios to exhibit high performance. Our novel modification followed by hot drawing process can manipulate internal structure with performance of PE fibers to an outstanding level of 0.35 GPa strength and 3 GPa modulus at a production speed of 400 m/min.