Mid Sweden University

Aggregation of ice on electrical cables and apparatus can cause severe equipment malfunction and is thus considered as a serious problem, especially in arctic climate zones. In particular, cable damage caused by ice accumulation on railway catenary wires is in wintertime a common origin for delayed trains in the northern parts of Europe. This study examines how resistive heating can be used for preventing formation of ice on metallic, non-insulated electrical cables. The heat equation and the Navier Stokes equations were solved simultaneously with FEM in 3D in order to predict the cable temperature as function of external temperature, applied voltage, wind speed, wind direction, and heating time. An analytical expression for the heat transfer coefficient was derived from the FEM simulations and it was concluded that the influence of wind direction can typically be neglected. Experimental validation measurements were performed on Kanthal cables in a climate chamber, giving temperature increase results in good agreement with the simulation predictions. The resistive heating efficiency, i.e. the ratio between applied electrical energy and resulting thermal energy, was found to be approximately 68% in this particular study.

A Monte-Carlo simulation method for assessing the tie chain and trapped entanglement concentration in linear polyethylene was extended to enable the simulation of explicitly branched polyethylene. A subroutine was added to the model making possible the incorporation of different branch lengths and distributions. In addition, the microstructure of branched polyethylene was considered to be made of lamellar stacks of different thicknesses, acknowledging the segregation phenomenon during crystallization. Also, based on complete exclusion of bulky branches from the crystal lattice, a 'pull-out' mechanism was developed for the relaxation of branched parts of polyethylene chains in the vicinity of the crystal layer. Simulations of two series of real polyethylene samples showed the effect of short-chain branching on the concentrations of tie chains and trapped entanglements. Introducing a few branches to an unbranched polyethylene increased the concentration of inter-lamellar connections significantly. This effect decayed if the number of branches was further increased. The tracking of the position of all the carbon atoms during the crystallization process was implemented in the model, making the average square end-to-end distance < r(2) > of polyethylene chains calculable. Simulation of chains with the same molar mass but with different branch contents showed a reduction in the average end-to-end distance with increased branching. The use of real molar mass distribution data was also added to the model features.