10. Conclusions

ranging from 274.15 to 281.15 K and from 1.4 to 3.3 MPa. However, new modified value of ΔE,

Reynolds number based on the size of a particle, about 16 μm, is calculated as 50. Clarke et al. [28] determined the dissociation rate of CO2H by measuring the nucleated methane gas in V-L state [14]. The comparison of three models is listed in Table 4. The results of dissociation flux are summarized in Figure 9. Higher water temperature induces higher dissociation flux at the surface of hydrate. Data correlated by [14] show much lower level than both Nihous' model and new model. The numerical results in this work marked as new model in Figure 9 show consistent result compared with Nihous' model. The dissociation flux in various flow rates in cases 5, 7, and 8 are listed in Figure 10. Here, it is noted that porosity is not considered in both Clarke's and Nihous' models, and these two models are only function of temperature and fugacity as presented in Eq. (15). The trend of flux becomes saturated in the figure due to the surface dissociation flux that becomes slow due to the fast mass transfer in bulk flow at

Item Modeling Intrinsic rate of dissociation Ref.

New Model Eq. (1) Kbl = exp(11,729/T + 26,398) [21]

. The order of

mole/Pa s m; ΔE = 102.89 kJ/mole [14]

mole/Pa s m; ΔE = 96.49 kJ/mole [16]

if considered the real case in the ocean quoted from [16], is 96:49 kJ mol<sup>1</sup>

36 Heat and Mass Transfer - Advances in Modelling and Experimental Study for Industrial Applications

Reynolds number over 100.

Table 4. The comparison of three models.

Clarke's Model Eq. (15) KD0 = 1.83 \* 108

Nihous' Model Eq. (15) KD0 = 1.83 \* 108

Figure 9. Results of simulation compared to existing two models.

The objective of this work is to establish a new pore-scale model for estimating the dissociation rate of CO2H in laboratory-scale sediment samples. It is assumed that CO2H formed homogeneously in spherical pellets. In the bulk flow, concentration and temperature of liquid CO2 in water flow was analyzed by computational fluid dynamics (CFD) method without considering gas nucleation under high-pressure state. In this work, finite volume method (FVM) was applied in a face-centered regular packing in unstructured mesh. At the surface of hydrate, a dissociation model has been employed. Surface mass and heat transfer between hydrate and water are both visualized. The initial temperature 253.15 K of CO2H pellets dissociated due to ambient warm water flow of 276.15 and 282.15 K and fugacity variation, ex. 2.01 and 1.23 MPa. Three tentative cases with porosity 74, 66, and 49% are individually simulated in this study. In the calculation, periodic conditions are imposed at each surface of packing. Additionally, the flux at CO2H's surfaces is compared to Clarke and Bishnoi [13] and Nihous and Masutani [15] 's correlations at Reynolds number of 50. Numerical results of this work show good agreement with Nihous' model. Kinetic modeling by using 3D unstructured mesh of regular cubic unit and CFD scheme seems to be a simple tool to estimate the dissociation rate of CO2H in laboratory-scale experiments, and could be easily extended to determine complex phenomena coupled with momentum, mass, and heat transfer in the sediment samples.
