8. Results of case study

In this study, cases with porosity of 74, 66, and 49 are individually discretized as face-centered unstructured packing of hydrate in sediment. CO2H pellets with initial temperature of 253.15 K dissociate due to the variation of driving force, ex. 0.89 and 0.77 MPa, under thermal stimulation of ambient warm water, ex. 282.15 and 276.15 K. Comparative small driving forces selected here is due to the assumption of no surface's collapse. Computational conditions are listed in Table 2. Result of flux at the surface is the converge value as shown in Figure 3. In Figure 4(a)–(c) at time 0.16(s) show velocity vector of case 1 in three specific sections. In Figure 5, the distributions of concentration at 0.16 s are presented. Slight CO2 discharges at the surface. Relative temperature distributions are indicated in Figure 6. As time increases, the dissociation heat of CO2 hydrate results in water temperature drop significantly as shown in

Figure 3. Converge value of case 1.

Figure 4. Velocity vector in the vicinity of pellets (case 1: T = 282.15 K, Tini = 253.15 K, Re = 50, Sc = 755, Pr = 10, VTL = 5, and time = 0.16 s). (a) Front section, (b) Center section and (c) Back section.

Figure 5. Concentration profile in three specific sections of cubic unit (case 1: time = 0.16 s, unit: mole/m<sup>2</sup> s). (a) Front section, (b) Center section and (c) Back section.

Figure 7(a)–(c). Relative concentration distribution in center section is shown in Figure 8. The heat of water conducts to the solid-side pellet rapidly in few seconds, and slow mass transfer at

Figure 8. Concentration versus time in center section of cubic unit (case 1, time = 0.16 s, 0.27 s, and 0.54 s, unit: mole/m<sup>2</sup> s).

Figure 7. Temperature versus time in center section of cubic unit (case 1, time = 0.16 s, 0.27 s, and 0.54 s, unit: K). (a) Front

Direct Numerical Simulation of Hydrate Dissociation in Homogeneous Porous Media by Applying CFD Method…

the surface dominates the dissociation rate rather than fast heat transfer at the surface.

<sup>¼</sup> kD0exp � <sup>Δ</sup><sup>E</sup>

is the fugacity of the quadruple equilibrium. They obtained kD<sup>0</sup> and ΔE for CO2H as

<sup>s</sup>�1m�<sup>2</sup> is the rate constant, <sup>f</sup> <sup>g</sup>ð Þ Pa is the fugacity of gaseous CO2, and <sup>f</sup> eq

RT <sup>f</sup> eq � <sup>f</sup> <sup>g</sup>

(15)

http://dx.doi.org/10.5772/intechopen.74874

35

, respectively, at temperature and pressure

9. Discussion

where kD<sup>0</sup> mol Pa�<sup>1</sup>

<sup>1</sup>:<sup>83</sup> � 108 mol Pa�<sup>1</sup>

To follow the modeling illustrated in [14]:

(a) Front section, (b) Center section and (c) Back section.

section, (b) Center section and (c) Back section.

F<sup>3</sup> ¼ kD f eq � f <sup>g</sup>

s�1m�<sup>2</sup> and 102:88 kJ mol�<sup>1</sup>

Figure 6. Temperature profile in three specific sections of cubic unit (case 1, time = 0.16 s, unit: K). (a) Front section, (b) Center section and (c) Back section.

Direct Numerical Simulation of Hydrate Dissociation in Homogeneous Porous Media by Applying CFD Method… http://dx.doi.org/10.5772/intechopen.74874 35

Figure 7. Temperature versus time in center section of cubic unit (case 1, time = 0.16 s, 0.27 s, and 0.54 s, unit: K). (a) Front section, (b) Center section and (c) Back section.

Figure 8. Concentration versus time in center section of cubic unit (case 1, time = 0.16 s, 0.27 s, and 0.54 s, unit: mole/m<sup>2</sup> s). (a) Front section, (b) Center section and (c) Back section.

Figure 7(a)–(c). Relative concentration distribution in center section is shown in Figure 8. The heat of water conducts to the solid-side pellet rapidly in few seconds, and slow mass transfer at the surface dominates the dissociation rate rather than fast heat transfer at the surface.
