Elham Doroodchi

Pilot plant trial of the reflux classifier

Abstract The Ludowici LMPE Reflux Classifier is a new device designed for classifying and separating particles on the basis of size or density. This work presents a series of experimental results obtained from the first pilot scale study of the reflux classifier (RC). The main focus of the investigation was to assess the particle gravity separation and throughput performance of the device. In this study, the classifier was used to separate coal and mineral matter less than 2 mm in size. The experimental results were then compared with the performance data on a teetered bed separator (TBS). It was concluded that the classifier could offer an excellent gravity separation at a remarkably high solids throughput of 47 t / m 2 h more than 3 times higher than for a TBS. The separation performance of the RC was also better, with significantly less variation in the D50 with particle size. A simple theoretical model providing an explanation of the separation performance is also presented.

Influence of Controlled Aggregation on Thermal Conductivity of Nanofluids

Nanoparticles aggregation is considered, by the heat transfer community, as one of the main factors responsible for the observed enhancement in the thermal conductivity of nanofluids. To gain a better insight into the veracity of this claim, we experimentally investigated the influence of nanoparticles aggregation induced by changing the pH value or imposing a magnetic field on the thermal conductivity of water-based nanofluids. The results showed that the enhancement in thermal conductivity of TiO2–water nanofluid, due to pH-induced aggregation of TiO2 nanoparticles, fell within the ±10% of the mixture theory, while applying an external magnetic force on Fe3O4–water nanofluid led to thermal conductivity enhancements of up to 167%. It is believed that the observed low enhancement in thermal conductivity of TiO2–water nanofluid is because, near the isoelectric point (IEP), the nanoparticles could settle out of the suspension in the form of large aggregates making the suspension rather unstable. The magnetic field however could provide a finer control over the aggregate size and growth direction without compromising the stability of the nanofluid, and hence significantly enhancing the thermal conductivity of the nanofluid.

The Role of Liquid Layering on the Enhancement of Thermal Conductivity in Nanofluids

Liquid layering is considered to be one of the key mechanisms responsible for the remarkably high thermal conductivities exhibited by nanofluids. A number of models have been presented in recent years to quantify the effect of liquid layering. However, many of these models are either based on unrealistic assumptions or have been incorrectly formulated. In this study we propose a new, yet simple, model that resolves the shortcomings of earlier models. The new model is based on the Maxwell theory and takes into account the effect of nanolayering. The model was compared with several sets of experimental data on Copper Oxide-in-ethylene glycol, Copper Oxide-in-water, Alumina-in-water, and Gold-in-toluene. The results indicate that the contribution of nanolayering to the enhancement of thermal conductivity in nanofluids is relatively modest and as such cannot be solely responsible for the observed enhancements.Copyright