Azimuthal instability in an impinging jet: adiabatic wall temperature distribution

The present work has been aimed at gaining some new insights into instability phenomena arising when an air jet impinges on a flat plate under certain conditions. At a critical Mach number, depending on the impingement distance, the jet loses its circumferential appearance with the formation of evenly equidistant azimuthal structures, whose number and location depend on the nozzle geometry and on the flow conditions. The instability is investigated in terms of pressure and adiabatic wall temperature; the latter is measured by means of an infrared scanning radiometer. Entrainment effects are found to play a key role in the priming and evolution of the instability

Chemical and irradiation crosslinking of polyethylene. Technological performance over costs

The present article is concerned with the production of cross-linked low-density polyethylene. The aim is to gain information about costs/benefits of two cross-linking methods, which are the chemical through silane grafting and the electron-beam irradiation. These two methods were used at the Megarad firm (Italy) for cross-linking of low-density polyethylene, which was mainly used for electric cable insulation. The two cross-linking processes were examined by evaluating the performance of the end product and the production costs. The performance of the final product was assessed through experimental tests, which consisted in the evaluation of some peculiar properties of the material such as gel fraction, thermal modifications under heat fluxes, modulus of elasticity at 150°C, elongation parameters. Costs were analyzed by considering both direct and indirect costs. It seems that, notwithstanding the elevated costs of installation, the electron-beam irradiation method is preferable because it allows for a product of superior characteristics with the lowest production costs