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An estimation scheme for clathrate-hydrate production rate with consideration about clathrate-hydrate film growing along a water/hydrate-forming fluid interface

考虑笼形水合物膜沿水/水合物形成流体界面生长的笼形水合物生产率的估计方案

基本信息

批准号：
15560172
负责人：
MOCHIZUKI Takaaki
金额：
$ 1.98万
依托单位：
Tokyo Gakugei University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2005
项目状态：
已结题

项目摘要

Lateral growth of a clathrate-hydrate film along a planar interface between liquid water and an immiscible hydrate-forming fluid (or guest fluid), such as HFC-32 or HFC-134a, was studied experimentally and numerically. It was found that the instantaneous rate of lateral film growth along the water/guest-fluid interface (i.e., the linear speed of the film-front) decreased asymptotically for several seconds after its nucleation. The asymptotic growth rate of HFC-32 hydrate film was about 5 mm/s at pressure, P = 617 kPa and a system subcooling, ΔT = 10.9 K, while that of HFC-134a hydrate film was about 0.4 mm/s at P = 246 kPa and ΔT = 6.0 K. In addition, two analytic models for the heat-transfer-controlled lateral growth of a clathrate-hydrate film along a planar interface between liquid water and a guest fluid were presented. The two models are different from each other only regarding the assumption of the film-front geometry. Either model assumes the film to be uniform and constant in thickness, ignoring possible changes in the thickness on a time scale relevant to its lateral growth. Another fundamental assumption employed in the model is that the film's hydrate-forming front is maintained at the hydrate/guest/water three-phase equilibrium temperature, thereby forming a two-dimensional temperature distribution in the surrounding three-phase space. Based on these assumptions, the transient, two-dimensional conductive heat transfer from the film front into the three phases is formulated and numerically solved to give the instantaneous lateral growth rate of clathrate-hydrate, while the film thickness is arbitrarily assumed as a fitting parameter. By comparing the predicted rate of film growth with the corresponding experimental data obtained with HFC-32 as the guest fluid, we estimated the film thickness to be about 1 μm at P = 617 kPa and ΔT = 10.9 K.

对水合物笼形物薄膜沿着液态水与HFC-32或HFC-134 a等不混溶水合物形成流体（或客体流体）之间的平面界面的横向生长进行了实验和数值研究。发现横向膜生长的瞬时速率沿着水/客流体界面（即，膜前沿的线速度）在其成核后几秒钟内渐近地降低。HFC-32水合物膜在压力P = 617 kPa和系统过冷度ΔT = 10.9 K时的渐近生长速率约为5 mm/s; HFC-134 a水合物膜在压力P = 246 kPa和ΔT = 6.0 K时的渐近生长速率约为0.4 mm/s。此外，提出了两个解析模型的传热控制的笼形水合物薄膜沿着之间的液态水和客体流体的平面界面的横向生长。这两个模型是不同的，彼此只是关于假设的膜前的几何形状。这两种模型都假定薄膜的厚度是均匀和恒定的，忽略了与横向生长相关的时间尺度上厚度的可能变化。在模型中采用的另一个基本假设是，膜的水合物形成前保持在水合物/客体/水三相平衡温度，从而在周围的三相空间中形成二维温度分布。基于这些假设，瞬态，二维传导传热从膜前到三相制定和数值求解，得到瞬时横向增长率的笼形水合物，而膜厚度被任意假定为一个拟合参数。通过与以HFC-32为客体流体的实验结果的比较，我们估算出在P = 617 kPa，ΔT = 10.9 K时膜厚约为1 μm。