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Solid Dielectrics
Published in N. H. Malik, A. A. Al-Arainy, M. I. Qureshi, Electrical Insulation in Power Systems, 2018
N. H. Malik, A. A. Al-Arainy, M. I. Qureshi
Whereas LDPE and HDPE are being produced by reaction processes introduced several decades ago, a new family of reaction processes is presently being used to produce linear low-density polyethylene (LLDPE) and medium-density polyethylene (MDPE). As shown in Figure 6.2, LLDPE and HDPE (also MDPE, not shown) molecules are generally linear in structure. The linear resins exhibit short-chain, rather than long-chain, branching. This fundamental difference in molecular structure accounts for many of the major differences in mechanical and dielectric properties as compared to LDPE [5]. LLDPE has become the most prominently used plastic in underground power cable jacketing because of its excellent mechanical properties, installation temperature range, vapor transmission resistance and environmental stress cracking resistance (ESCR). The other two linear polyethylenes, HDPE and MDPE, also have excellent properties but are stiffer because of their higher densities.
Bulk and pipe wall chlorine degradation kinetics in three water distribution systems
Published in Urban Water Journal, 2021
John McGrath, Mahnoush Maleki, Christian Bouchard, Geneviève Pelletier, Manuel J. Rodriguez
Values of kb reported in the literature range from 3.3 to 740 10−3/h, for water temperatures from 6°C to 25°C, which is also the likely range for most of the studies for which the temperature was not reported. It is possible that other factors such as organic matter and inorganic indicators that affect chlorine demand, could also explain such a wide range, but water quality data is not often considered or reported in the mentioned studies. According to the literature, kb values are also larger for larger values of . For studies that did not report the values, it is possible that the range was wider then reported in Table 1 (0.33 to 2.5 mg/L). The average in-situ values of kw reported by Hallam et al. (2002) range from 50 (medium-density polyethylene) to 130 × 10−3 h−1 (cast-iron) with very large variations (one order of magnitude) for each type of pipe materials. These studies provide a general idea of the range of kb and kw but the conditions in which the studies took place are not explicitly given, making it hard for water managers to grasp the impact of pipe characteristics on chlorine degradation.
A review on the co-processing of biomass with other fuels sources
Published in International Journal of Green Energy, 2021
The thermal behavior of plastics medium density polyethylene, isotactic and atactic polypropylene with biomass sources beech wood, pinewood, cellulose, hydrolytic lignin, was considered in a rotating autoclave (Sharypov et al. 2002). The mechanism of the co-pyrolysis process was investigated and it was found that the biomass-derived radicals had a pronounced effect on the thermal decomposition of polyolefins (Sharypov et al. 2003). This took place by first the formation of radicals from biomass and then these radicals interacted with polyolefin molecular chains leading to the formation of tertiary polyolefinic radicals. High content of carbonyl and hydroxyl groups and low aromaticity in the heavy liquids was observed. Even high amounts of 2-alkenes in the co-pyrolysis liquid fraction indicated the presence of the chemical interaction between the thermally degraded products of the biopolymers of lignocellulosic biomass and of polyolefins-derived products. This plethora of reactions leads to the formation of stabilized products having low molecular weight. Catalytic pyrolysis of polyolefinic plastics/polymers with pinewood mixtures was studied in a hydrogen atmosphere with hematite and pyrrhotite materials as catalysts (Sharypov et al. 2006). These catalysts had a prominent effect and led to an increase in the yield of distillable liquid amounts by 14–21 wt. %.
Modelling chlorine wall decay in a full-scale water supply system
Published in Urban Water Journal, 2020
Laura Monteiro, Joana Carneiro, Dídia I.C. Covas
where C is the free chlorine concentration in water (mg/L), kw is the wall decay coefficient (m/day), kf is the mass transfer coefficient (m/day) and R is the pipe radius (m). The wall decay coefficient depends on temperature, as any kinetic constant, and has been correlated to pipe age and material. The mass transfer coefficient is often calculated as a function of the molecular diffusivity of the reactive species and of the Sherwood number (Rossman 2000). According to Equation (1), the rate of reaction of chlorine at the pipe wall is always inversely related to the pipe diameter and can be limited by the rate of mass transfer of chlorine to the wall. The FO model has been used to describe chlorine wall decay in pipes of low reactivity materials such as cement lined ductile iron (Digiano and Zhang 2005), PVC and medium-density polyethylene (Hallam et al. 2002) and asbestos cement (Minaee et al. 2019a).