Flow studies in non circular tubes with wall injection

An analysis of inviscid incompressible flow in a tube of sinusoidally perturbed circular cross section with wall injection has been made. The velocity and pressure fields have been obtained. Measurements of axial velocity profiles and pressure distribution have been made in a simulated star shaped tube with wall injection. The static pressure at the star recess is found to be more than that at the star point, this feature being in conformity with the analytical result. Flow visualisation by photography of injected smoke seems to show simple diffusion rather than strong vortices in the recess

Stabilisation of Red Phosphorus to Prevent Moisture Absorptionand Suppression of Phosphine Release

Red phosphorus (RP) is an essential ingredient to generate smoke for multi-spectralobscuration and is receiving wide attention throughout the world for military applications.However, oxidation of phosphorus occurs in moist air resulting in the formation of variousphosphorus acids and subsequently the evolution of the toxic gas, phosphine (PH3), even inthe sealed systems. Entrapped moisture leads to deterioration of the stores. The commercial-RPat ambient temperature and 95 per cent  RH conditions indicates 15 per cent  moisture absorptionand 13 per cent acidity development with the generation of more than 100 ppm of phosphinegas. Efforts were made to overcome this problem by suppressing acid formation. The technologyadopted was: (i) use of stabiliser, and (ii) doping stabiliser-coated particles with polymericsubstance. The aim to use metal oxide as stabiliser was to neutralise the phosphorus acids,which are catalysing the phosphine generation. MgO due to its basic nature seems to be fasterthan amphoteric Al2O3, in removing the acid from site of reaction, thus suppressing the phosphinerelease effectively. Though MgCO3 as stabiliser suppresses moisture absorption and aciditydevelopment, phosphine release is not controlled effectively. Study of RP coated with thesematerials independently and monitoring them at different RH conditions indicated superiorityof MgO in suppressing acidity and phosphine formation

Modelling of DMNB Content for Marked Plastic Explosives

2,3-dimethyl-2,3-dinitrobutane (DMNB) has been internationally accepted as an additive forthe purpose of marking, as it has desired vapour pressure for reliable detection. It is reportedto be compatible with known explosive formulations and has a good shelf life. Explosivecompositions with DMNB as marking agent can be detected in the temperature range –20 ºC to+ 50 ºC. This paper describes modelling for quantifying activation energy for depletion of  DMNBin the marked explosives, period for definite detection of the marked explosives and optimuminitial concentration needed for the detection of DMNB content in the marked  plastic explosives

Nanocrystalline Pentaerythritoltetranitrate using Sol-Gel Process

The secondary explosives developed with reduced particle size tend to be more insensitive for mechanical stimuli and may release energy with faster rate and gaining more importance nowadays. Therefore, aiming to reduce the particle size of one of the popular explosives, viz., pentaerythritoltetranitrate (PETN) to the nanometer range, a method for preparation of nanocrystalline PETN in the silica (SiO2) gel matrix using sol-gel process has been demonstrated. The PETN-SiO2 xerogels were prepared containing PETN content ranging from 50 per cent to 90 per cent (w/w) and the xerogels were characterised using different techniques. An exothermic peak at around 185 oC preceded by an endotherm in thermal analysis accompanied with weight loss in the temperature range from 150 oC to 200 oC   for the xerogel confirmed the presence of PETN in xerogel. Infrared spectra of xerogels showed peaks at around 1285 cm-1 and 1700 cm-1 assigned to O-NO2 and C-O bond representing PETN. Small angle x-ray scattering measurements on xerogels indicated that PETN entered in the pores of silica matrix. Transmission electron microscopy revealed that cystalline PETN    with particle size of around 15 nm dispersed in silica xerogel. The specific surface area for the PETN-SiO2 (90:10) xerogels was found to be 75 m2/g.Defence Science Journal, 2011, 61(6), pp.534-539, DOI:http://dx.doi.org/10.14429/dsj.61.59

Flow Studies in Non Circular Tubes with Wall Injection

An analysis of inviscid incompressible flow in a tube of sinusoidally perturbed circular cross section with wall injection has been made. The velocity and pressure fields have been obtained. Measurements of axial velocity profiles and pressure distribution have been made in a simulated star shaped tube with wall injection. The static pressure at the star recess is found to be more than that at the star point, this feature being in conformity with the analytical result. Flow visualisation by photography of injected smoke seems to show simple diffusion rather than strong vortices in the recess

Advances in High Energy Materials (Review Paper)

Research and development efforts for realizing higher performance levels of high energy materials (HEMs) are continued unabated all over the globe. Of late, it is becoming increasingly necessary to ensure that such materials are also eco-friendly. This has provided thrust to research in the area of force multiplying HEMs and compounds free from pollution causing components. Enhancement of the performance necessitates introduction of strained structure or increase in oxygen balance to achieve near stoichiometry. The search for environment friendly molecules is focused on chlorine free propellant compositions and lead free primary explosives. Energetic polymers offer added advantage of partitioning of energy and thus not necessitating the concentration of only solid components (HEMs and metal fuels) in the formulations, to achieve higher performance, thereby leading to improvement in energetics without adversely affecting the processability and mechanical properties. During recent times, research in the area of insensitive explosives has received impetus particularly with the signature of STANAG. This paper gives a review of the all-round advances in the areas of HEMs encompassing oxidizers, high-energy dense materials, insensitive high-energy materials, polymers and plasticizers. Selected formulations based on these materials are also included.Defence Science Journal, 2010, 60(2), pp.137-151, DOI:http://dx.doi.org/10.14429/dsj.60.32