Impact of environmental moisture on C(3)A polymorphs in the absence and presence of CaSO4 center dot 0.5 H2O

The phenomenon of water vapour sorption by anhydrous C3A polymorphs both in the absence and in the presence of CaSO4·0·5 H2O was studied utilising dynamic and static sorption methods. It was found that orthorhombic C3A starts to sorb water at 55% relative humidity (RH) and cubic C3A at 80% RH. Also, C3Ao sorbs a higher amount of water which is predominantly physically bound, whereas C3Ac preferentially interacts with water by chemical reaction. In the presence of calcium sulfate hemihydrate, ettringite was observed as the predominant pre-hydration product for both C3A modifications: that is, ion transport had occurred between C3A and sulfate. Environmental scanning electron microscopic imaging revealed that in a moist atmosphere, a liquid water film condenses on the surface of the phases as a consequence of capillary condensation between the particles. C3A and sulfate can then dissolve and react with each other. Seemingly, pre-hydration is mainly facilitated through capillary condensation and less through surface interaction with gaseous water molecules

Performance evaluation on an air-cooled heat exchanger for alumina nanofluid under laminar flow

This study analyzes the characteristics of alumina (Al2O3)/water nanofluid to determine the feasibility of its application in an air-cooled heat exchanger for heat dissipation for PEMFC or electronic chip cooling. The experimental sample was Al2O3/water nanofluid produced by the direct synthesis method at three different concentrations (0.5, 1.0, and 1.5 wt.%). The experiments in this study measured the thermal conductivity and viscosity of nanofluid with weight fractions and sample temperatures (20-60°C), and then used the nanofluid in an actual air-cooled heat exchanger to assess its heat exchange capacity and pressure drop under laminar flow. Experimental results show that the nanofluid has a higher heat exchange capacity than water, and a higher concentration of nanoparticles provides an even better ratio of the heat exchange. The maximum enhanced ratio of heat exchange and pressure drop for all the experimental parameters in this study was about 39% and 5.6%, respectively. In addition to nanoparticle concentration, the temperature and mass flow rates of the working fluid can affect the enhanced ratio of heat exchange and pressure drop of nanofluid. The cross-section aspect ratio of tube in the heat exchanger is another important factor to be taken into consideration

Preparation and characterization of carbon nanofluid by a plasma arc nanoparticles synthesis system

Heat dissipation from electrical appliances is a significant issue with contemporary electrical devices. One factor in the improvement of heat dissipation is the heat transfer performance of the working fluid. In this study, we used plasma arc technology to produce a nanofluid of carbon nanoparticles dispersed in distilled water. In a one-step synthesis, carbon was simultaneously heated and vaporized in the chamber, the carbon vapor and particles were then carried to a collector, where cooling furnished the desired carbon/water nanofluid. The particle size and shape were determined using the light-scattering size analyzer, SEM, and TEM. Crystal morphology was examined by XRD. Finally, the characterization include thermal conductivity, viscosity, density and electric conductivity were evaluated by suitable instruments under different temperatures. The thermal conductivity of carbon/water nanofluid increased by about 25% at 50°C compared to distilled water. The experimental results demonstrated excellent thermal conductivity and feasibility for manufacturing of carbon/water nanofluids