No abstract

To better understand the local wind systems in the Himalayas, wind and related atmospheric parameters were observed in the Rongbuk Valley on the northern slope of Mt. Everest, during the HEST2006 campaign, from May 29 to June 29, 2006. Data analysis and a simple numerical simulation show that the dominating down‐valley flow in this valley is mainly formed by the thermally driven winds, “valley wind”, “mountain wind” and “glacier wind”. The vertical air motion is composed of a descending flow from the morning to midnight and an ascending flow for the rest of the day, with important modification from the vertical component of the above down‐valley flow and a compensation flow of the “slope wind”. The analysis also shows that the local wind system is well confined in the Rongbuk Valley due to topographic shielding effects.

This work introduces a novel approach by use of high-energy collision-induced dissociation for fragmenting asphaltenes into their constituent stable aromatic cores as a means for determining the relative proportions of island-to-archipelago structures. This approach is particularly useful for comparing asphaltenes from various crude oils. Ion generation from asphaltenes was performed by use of atmospheric pressure photoionization, which has been demonstrated to provide hydrogen-to-carbon ratios consistent with bulk measurements by combustion analysis with less than 10% relative error. The fragmentation behavior of asphaltenes was first evaluated with model compounds consisting of island and archipelago structures by use of low- and high-energy collision-induced dissociation (CID and HCD). Unlike CID, HCD enables dissociation of model compounds to their stable aromatic cores. This allows facile classification as either island or archipelago on the basis of the discrepancy in the double-bond equivalents between the precursors and stable aromatic cores. Model compound studies also showed that when HCD is utilized for the simultaneous dissociation of multiple precursor ions, efficient fragmentation of all precursors only occurs when ions within a narrow mass window are presented for analysis. The HCD approach was then applied to characterize narrow mass segments of crude oil asphaltenes, including those derived from hydrotreated resids. Observed island-to-archipelago proportions were consistent with the chemical transformations that occur during the hydrotreating process. Importantly, the method also demonstrates that the proportion of island-to-archipelago structures in asphaltenes decreases with increase molecular weight.

Hydrate formation and wax deposition pose great flow assurance challenges to subsea oil pipes, especially when the two phenomena co-occur. Wax crystals can have a significant impact on hydrate nucleation and growth kinetics, but this phenomenon has not been studied in great detail. Here, the effect of wax crystals on hydrate nucleation was investigated using both molecular dynamics simulation methods and experiments conducted using a custom-designed high-pressure autoclave equipped with an on-line viscometer. Both the simulation and the experimental results demonstrated that the presence of wax crystals inhibits hydrate nucleation. The simulations showed that water droplets tend to approach and adsorb on wax crystals prior to nucleation, thus inhibiting the formation of hydrate cages. The experiments demonstrated that water cut and stirring rate play a significant role in determining the hydrate nucleation rate. In addition, adding more wax increased the viscosity of the emulsion, which limits mass transfer of gas to the oil−water interface.