Aggregation and settling in aqueous polydisperse alumina nanoparticle suspensions

Nanoparticle suspensions (also called nanofluids) are often polydisperse and tend to settle with time. Settling kinetics in these systems are known to be complex and hence challenging to understand. In this work, polydisperse spherical alumina (Al2O3) nanoparticles in the size range of ~10-100nm were dispersed in water and examined for aggregation and settling behaviour near its isoelectric point (IEP). A series of settling experiments were conducted and the results were analysed by photography and by Small Angle X-ray Scattering (SAXS). The settling curve obtained from standard bed height measurement experiments indicated two different types of behaviour, both of which were also seen in the SAXS data. But the SAXS data were remarkably able to pick out the rapid settling regime as a result of the high temporal resolution (10s) used. By monitoring the SAXS intensity, it was further possible to record the particle aggregation process for the first time. Optical microscopy images were produced on drying and dried droplets extracted from the suspension at various times. Dried deposits showed the rapid decrease in the number of very large particles with time which qualitatively validates the SAXS prediction, and therefore its suitability as a tool to study unstable polydisperse colloids. Keywords: Nanoparticles, nanofluids, polydisperse, aggregation, settling, alumina, microscopy, SAX

Boiling of refrigerants on enhanced surfaces and boiling of nanofluids

NR 2014080

Bolgoda chat, crossing the borders in his own way: An interview with Emeritus Professor P A De Silva

IPT gained university status in 1972. However, in 1966 we had received a status equivalent to a university, under the name “Ceylon College of Technology”. I remember one interesting incident from that time. The first vice chancellor was Dr. Upali Kuruppu. I was responsible for selecting Junior Technical Officers (JTO), and these were highly capable students who had missed engineering by a narrow margin. There were around 80 deserving candidates, and we were only admitting 40. Late Prof. Patuwathawithana and I (we were both young and junior staff members at that time), approached the administration to request an increase in the intake. Indeed, we had space to accommodate. There was a fear that, if we produced more, there will be no demand. The University of Ceylon was thus unwilling to increase the intake beyond 25 students. Finally, we managed to increase the JTO intake from 40 to 60. The JTO students were very capable. Prof. Patuwathawithana and I started to teach IMechE part II subjects to them. While I taught Heat Engines and Materials, he used to teach Thermo-machines etc. Some of them went on to become chartered engineers, and that too paved the way for the Ceylon College of Technology

ENHANCED NATURAL CONVECTIVE HEAT TRANSFER OF CNT-ETHYLENE GLYCOL-WATER SUSPENSIONS

ABSTRACT: This paper presents an experimental study on the rheology and steady state natural convective heat transfer of suspensions of Carbon nanotubes (CNT) in the WaterEthylene Glycol (WEG) base liquid, heated in a cylindrical cavity. Two series of experiment were performed in two orientations of the central axis of the cavity; vertical, and, horizontal. In vertical axis experiments, the heat was supplied from the bottom. The cylindrical cavity was made out of Aluminium, 10mm in height and 240mm in diameter. The heat input was 215W/m 2 . The CNTs used had an aspect ratio of~150. There were six suspensions investigated in either series of tests; CNT 0.1wt%, and EG 0, 10, 25, 50, 75 & 100wt%. It was found that the vertical axis orientation deteriorates heat transfer in all cases. However for horizontal orientation, there is a spectacular enhancement of up to 83% depending upon the EG concentration. The results also show that WEG-CNT suspension demonstrates non-Newtonian behaviour, which augments with increasing EG concentration

The Ocean thermal energy conversion strategies and analysis of current challenges

This paper presents different roots of Ocean Thermal Energy Conversion (OTEC) strategies and challenges faced in terms of efficiency and economy of OTEC plants. The conversion strategies primarily focus on open cycle, closed cycle and hybrid plants. The efficiency studies mainly skew towards the effect of plant distance and thermal gradient towards plant efficiency. The economic analysis is based upon the effect of per unit cost for OTEC plant together with other important considerations such as Plant Factor (PF) and offshore distance, which determine the cost of power generation. Some illustrative examples are also provided using the derived equations under efficiency and economic studies

Stability of nanofluids in quiescent and shear flow fields

<p>Abstract</p> <p>An experimental study was conducted to investigate the structural stability of ethylene glycol-based titanium dioxide nanoparticle suspensions (nanofluids) prepared by two-step method. The effects of particle concentration, fluid temperature, shear rate and shear duration were examined. Particle size and thermal conductivity measurements in quiescent state indicated the existence of aggregates and that they were stable in temperatures up to 60&#176;C. Shear stability tests suggested that the structure of nanoparticle aggregates was stable in a shear interval of 500-3000 s^-1measured over a temperature range of 20-60&#176;C. These findings show directions to resolve controversies surrounding the underlying mechanisms of thermal conduction and convective heat transfer of nanofluids.</p