Fan Shuanshi

Gas hydrate fast nucleation from melting ice and quiescent growth along vertical heat transfer tube

During the observation of HCFC141b gas hydrate growth processes outside a vertical heat transfer tube, two exciting phenomena were found: fast nucleation of gas hydrate from melting ice, and the spontaneous permeation of water into the guest phases along the surface of heat transfer tube to form gas hydrate continuously. These two phenomena were explained with Zhou & Sloan’s hypothesis and the theory of surface free energy respectively, and a novel method of gas hydrate formation was presented—gas hydrate fast nucleation from melting ice and quiescent growth along heat transfer tube. There is no mechanic stirring in this method, the formed gas hydrates are compact, the ratio of unreacted interstitial water is little, which overcome the drawback of high energy cost and high ratio of unreacted interstitial water among the formed gas hydrates in the system with mechanic stirring. This finding will benefit the gas hydrate application technologies such as natural gas storage technology or cool storage technology with gas hydrate.

Molecular Dynamics Simulation of CH4 Hydrate Decomposition in the Presence of Poly(2-ethyl-2-oxazoline)

Molecular dynamics simulations were carried out to study the decomposition of CH4 hydrate in the presence of poly(2-ethyl-2-oxazoline) (PEtO) at different concentrations, including 1.25% , 2.50%, and 6.06% (w, mass fraction). The simulation system was composed of a CH4 hydrate crystal and PEtO, which contained a 2×2×2 supercell of CH4 hydrate crystal and PEtO polymer. System configurations showed that hydrogen bonding networks between water molecules making up the main framework of the hydrate cages were distorted in the presence of the PEtO polymer. Final configurations in all of the systems were completely collapsed. Radial distribution functions of the oxygen atoms, mean square displacements, and diffusion coefficients of water molecules were applied to compare the effect of different PEtO concentrations on the CH4 hydrate. Within a certain concentration range, higher concentrations led to a better inhibition effect. It was confirmed that PEtO is a type of prospective low dosage inhibitor with biodegradability. The decomposition mechanism involves the absorption of the PEtO polymer onto the surface of the hydrate crystal, with its active functional group (N―C=O) forming hydrogen bonds with water molecules in the hydrate and decomposing the hydrate surface. PEtO continued to decompose the surface layer of hydrate, resulting ultimately in the collapse of the hydrate cages.

Calculation of NARM’s equilibrium with Peng-Robinson equation of state

The liquid molar volumes of nonazeotropic refrigerant mixtures (NARM), calculated with Peng Robinson (PR) equation, were compared with vapor -liquid equilibrium experimental data in this paper. Provided with co-reaction coefficient kij, the discrepancies of liquid molar volume data for R22+R114 and R22+R142b using PR equation are 7.7% and 8.1%, respectively. When HBT (Hankinson-Brobst-Thomson) equation was joined with PR equation, the deviations are reduced to less than 1.5% for both R22+R114 and R22+R142b.

Influence of 5A-Type Zeolite Powder on Tetrahydrofuran Hydrate Formation and Dissociation Process

Visual observations of tetrahydrofuran (THF) hydrate formation and dissociation processes with 5A-type zeolite powder were made at normal atmospheric conditions and below zero temperature by microscope. Results indicate that 5A-type zeolite powder can promote THF hydrate growth. At the same time, in the presence of 5A-type zeolite, agglomerated crystals and vein-like crystals of THF hydrate were also formed. SA-type zeolite powder increases the crystallization temperature and decreases the dissociation temperature. The particle size distribution of 5A-type zeolite powder influences THF hydrate formation and its dissociation characteristics significantly.