Multiwall carbon nanotube (MWCNT) nanofluids have been shown to 12 enhance the crystallization process of water to ice. While the beneficial effects of 13MWCNTs on phase change processes are well documented, little work has been 14 conducted to investigate the behavior of MWCNTs during and after exposure to freezing 15conditions. In this work, the crystallization morphology of water droplets containing 16 surface-functionalized hydrophilic MWCNTs was evaluated at three temperature driving 17forces and two concentrations of nanofluid. At low supercoolings, the MWCNTs are 18 completely expelled from the crystal matrix due to slow solidification rates. At high 19supercoolings , the MWCNTs are embedded in the solid droplet within air volumes and 20 interdendritic regions as a result of rapid crystallization speeds. The results show that the 21 dispersion of MWCNTs within the solid ice matrix itself was not achieved at these levels 22 of supercooling. At all conditions, freezing of the colloidal system results in 23 destabilization of the MWCNTs and loss of dispersion. These effects are important 24 considerations for applications requiring successful freeze/thaw cycling of nanofluid 25 systems, as well as in the storage and transport of colloidal suspensions. 26 27 28 29 30 31 32 Abstract 64 Multiwall carbon nanotube (MWCNT) nanofluids have been shown to enhance the 65 crystallization process of water to ice. While the beneficial effects of MWCNTs on phase 66 change processes are well documented, little work has been conducted to investigate the 67 behavior of MWCNTs during and after exposure to freezing conditions. In this work, the 68 crystallization morphology of water droplets containing surface-functionalized 69 hydrophilic MWCNTs was evaluated at three temperature driving forces and two 70 concentrations of nanofluid. At low supercoolings, the MWCNTs are completely 71 expelled from the crystal matrix due to slow solidification rates. At high supercoolings, 72 the MWCNTs are embedded in the solid droplet within air volumes and interdendritic 73 regions as a result of rapid crystallization speeds. The results show that the dispersion of 74 MWCNTs within the solid ice matrix itself was not achieved at these levels of 75 supercooling. At all conditions, freezing of the colloidal system results in destabilization 76 of the MWCNTs and loss of dispersion. These effects are important considerations for 77 applications requiring successful freeze/thaw cycling of nanofluid systems, as well as in 78 the storage and transport of colloidal suspensions. 79 80

No abstract

Gas hydrate inhibition is a prime focus of industrial hydrocarbon research as pipeline blockages can be costly and dangerous. Historically, many chemical species have been studied for their effects on the hydrate formation process. One of the most investigated compounds in the kinetic hydrate inhibitor (KHI) category is polyvinylpyrrolidone (PVP). While the effects of PVP on hydrates are well-documented, the mechanism that defines its function is still not completely understood. To obtain further insight into its behavior, bulk liquid samples in a PVP-containing system were extracted at six specific times throughout a methane hydrate formation process. The effect of PVP loading concentration was also investigated. It was found that as time progressed, concentration of PVP in the liquid decreased, suggesting that PVP binds to the surface of growing hydrates. Furthermore, this decrease in concentration was more prevalent in situations where lower initial PVP loadings were used.

The three-phase hydrate–liquid–vapor (H–Lw–V) equilibrium conditions of the methane clathrate hydrate in aqueous solutions of d-(+)-glucose were experimentally determined. Equilibrium curves were generated via an isothermal pressure-search method for systems containing (10 to 30) wt % glucose at temperatures between (275.15 and 281.25) K and with pressures ranging from (3.4 to 8.0) MPa. Experimental results show that glucose-containing systems exhibit a considerable inhibiting effect on methane hydrate equilibrium conditions, as the phase equilibria conditions for these systems are shifted to higher pressures than those for pure water systems at a given temperature. It was also found that the degree of inhibition increases in relation to the concentration of the glucose additive and that the inhibition of 30 wt % solutions of glucose is superior to low concentrations of methanol and to equal concentrations of magnesium sulfate.

No abstract