Efficient mixing to enhance heat and mass transfer as needed for the application
of interest is of paramount importance in any chemical/biochemical reactor. An Oscillatory Flow (OF) is being utilized in chemical reactors to ensure the efficient mixing and to increase the heat and mass transfer in the process. The OF reactors have a combination of flow oscillation and baffled tube configuration. The technology, which has not yet been extended to mini-fluidic devices, is being explored as a novel approach for enhanced mixing at reduced scales. The principal constraints when designing a mixer are the flow rate and the fluid properties of the streams to be mixed and the desired level of mixing. In the first paper, “A Preliminary Investigation on Implementation of Oscillatory Flow (OF) in Mini-Channels”, the author, Kirubanandan Shanmugam, explores the fundamental working principles of operation and extension of conventional correlations applied to mini-fluidic scales. The paper presents the theoretical calculations of energy dissipation versus mixing and the results are compared to existing mini-fluidic mixers. The author has investigated the feasibility of OF technology in mini-channels and suggested that the OF in mini-channel showed increase of Nusselt numbers at equivalent energy dissipation relative to a smooth pipe at reduced dimensions. The author has noted that the oscillation and the pulsation create eddies in flow path at conventional scales that enhance convection currents and heat transfer. An interesting point to note is that the energy dissipation required (i.e., pumping requirements) to achieve an equivalent increase in Nu becomes higher as the intensity of oscillations increases.

Large spherical pressure vessels are extensively used for storage purpose in the petrochemical industry. They are also termed as energy vessels due to energy that is stored in the form of pressure inside. In the areas of large openings like hatch opening, due to the sudden change in the sectional area of deck plate, stress concentration is likely to occur at the corners. The insert plates allow the corner plates to withstand higher levels of stress that arise because of stress concentrations and eliminate the risk of failure. The second paper, “Modeling and Structural Analysis of Boot Nozzle and Insert Plate of a Pressure Vessel”, by Venkata Ravi Ram Pinninti, Ramakrishna Bhamidipati and TVK Bhanu Prakash, is a case study involving the design of a section of large refinery expansion project in India. In the study, the authors have carried out structural analysis using Ansys 14.0 to estimate the stresses at the junctions of boot nozzle-insert plate and shell-insert plate. The first load case is with the application of internal pressure corresponding to the design pressure, and the second one is with an external pressure of l.05 Kg/cm2. The meshing carried out in the 3D Finite Element Analysis (FEA) is validated by zero-error report generated by the system. The study suggested that the designs of insert plate and boot nozzle are safe for both the load cases analyzed.

Most of the gears used in power transmission system are spur gears and asymmetric gear drives are preferred over symmetric gears as they have more power transmission capacity, lower noise and vibration level. To improve load carrying capacity of a gear tooth, several ways have been suggested. Asymmetric involute spur gear is a nonstandard gear, with its teeth having different pressure angles at their drive side and coast side. Due to the geometry, it is very crucial in obtaining key properties, such as high load carrying capacity and low weight. In the third paper, “Experimental and Finite Element Analysis of Bending Strength of Asymmetric Involute Spur Gears” the authors, Narayan S Dharashivkar, Vilas B Sondur and Krishnakumar D Joshi, have carried out a comparative analysis between theoretical method, FE method and experimental method (3D photoelasticity) to determine bending strength of asymmetric involute spur gear. The authors conclude that as pressure angle increases, the bending stresses reduce. The study suggested that while maintaining maximum bending stress, it is possible to achieve a substantial weight reduction using asymmetric gear instead of symmetric one. The analysis yielded a fairly good agreement between theoretical, experimental and FE results.

Cylindrical components have many applications in aircraft design. Components made of Al 7075 T6 alloy material find wide applications in different areas because of its excellent metallurgical properties. The alloy is a more useful material with the characterization of material for fracture toughness, particularly with its characteristic fracture toughness. When the structural components are subjected to cyclic stresses, it results in premature failure by fatigue crack growth. In the next paper, “Experimental, Analytical and Numerical Analysis to Calculate Stress Intensity Factor on Circumferential Notched Round Bar”, the authors, Chetan Kaduba Mahajan and Ganesh D Korwar, have analyzed the influence of the geometry of the notch fracture parameters of a notched round bar subjected to tensile loading. The study suggests that by increasing diameter alloy along with notch diameter of the specimen made of Al 7075 T6, the values of fracture toughness also increase. Based on the FE and experimental analysis, the authors have indicated that the presence of notch in tensile test specimen causes failure in brittle mode although the material is ductile.

The composite armors—consisting of layers of different materials—are lighter than their all-metal equivalent, and at the same time occupy a larger volume for the same resistance of penetration. The effectiveness of the armor plating depends on the properties such as hardness, toughness, penetration resistance and its absorbing capabilities. In the last paper, “Some Considerations for the Design of Composite Armor”, the author, Rahul Basu, has reviewed the categories of armor and the techniques in vogue for armor protection.

S V Srirama Rao
Consulting Editor