Fouling in a low-density polyethylene (LDPE) tubular polymerization reactor is caused by the polyethylene/ethylene mixture forming two phases inside the reactor. Some of the polymer-rich phase is deposited on the reactor's inside wall, which considerably reduces heat-transfer rates. At a given reactor pressure, the reactor inside wall temperature is the critical parameter in determining when fouling occurs and this is controlled by the coolant stream temperatures. In this work, plant data and a heat-transfer model were used to determine the fouling thickness in a LDPE industrial reactor and the speed at which the foulant material is deposited.

Improving the fatigue resistance of DLC coatings under highly loaded repetitive contact is an important step to increasing their performance in demanding applications. The nano-impact test has been shown to be effective at highlighting differences in resistance to contact damage in thin hard carbon coatings deposited on hardened steel. A novel micro-scale rapid impact test capability capable of producing repetitive impacts at significantly higher strain rate and energy than in the nano-impact test has been developed recently enabling the study of coating fatigue with less sharp spherical indenters than in the nano-impact test.Results with the new micro-impact technique on two commercial hard carbon coatings (Graphit-iC and Dymon-iC from Teer Coatings) on tool steel are presented. The role of coating mechanical properties on the fatigue resistance and the load-sensitivity of the impact failure mechanism is discussed. The harder coating with higher sp 3 /sp 2 bonded C (Dymon-iC) was found to be significantly less durable under fatigue loading than the softer Graphit-iC. Reasons for the observed differences are discussed.

A high temperature micro-impact test has been developed to assess the fracture resistance of hard coatings under repetitive dynamic high strain rate loading at elevated temperatures. The test was used to study the temperature dependence of the resistance to micro-scale impact fatigue of TiAlSiN coatings on cemented carbide at 25-600 C. Nanoindentation and microscratch tests were also performed over the same temperature range. The results of the microimpact tests were dependent on the impact load, coating microstructure, coating and substrate mechanical properties, and their temperature dependence. At higher temperatures there was a change in failure mechanism from fracture-dominated to plasticity-dominated behaviour under the cyclic loading conditions. This was attributed to coating and substrate softening.

No abstract

Fouling in a low-density polyethylene (LDPE) tubular polymerization reactor is caused by the polyethylene/ethylene mixture forming two phases inside the reactor. Some of the polymer-rich phase is deposited on the reactor's inside wall, which considerably reduces heat-transfer rates. Phase equilibria calculations show a high degree of sensitivity of the single-phase/two-phase process fluid boundary to temperature. Almost all of the process stream is single phase and the fluid mixture is only two phase in the boundary layer close to the reactor wall where the temperature is low enough to cause phase separation. At a given reactor pressure, the reactor inside wall temperature is the critical parameter in determining when fouling occurs, and this is controlled by the coolant stream temperatures.