## 2 Experiments
When the temperature of H\({}_{2}\)O and R134a binary system is 275 K, hydrate formation is driven at pressures larger than 79.6 kPa (the three-phase equilibrium pressure among water, vapor R134a, and hydrate). If the pressure is larger than 314.6 kPa (saturation pressure of R134a), the condensation of injected gas occurs simultaneously [53]. The duration of stabilization was determined taking two opposite influences into account: to allow for the significant dissolution of gas, and to prevent the hydrate formation. Since the flow loop pressure was larger than 79.6 kPa, R134a hydrate can form past the induction time. The stabilized flow loop pressure smaller than 314.6 kPa indicated that the void resulted from water withdrawal was filled with gaseous R134a. When the gas supply port was opened again, the flow loop was pressurized with R134a up to 400 kPa, to initiate the formation of hydrate. The gauging of injected gas was also started by marking the pressure and temperature of the gas storage tank as the initial state. The gas supply under near constant pressure condition was continued while the flow of hydrate slurry was qualitatively observed with the help of the sight glass. The gas supply was ceased when the amount of injected gas, which was calculated by the Peng-Robinson equation of state, reached the predetermined value. Figure 2 shows that the flow loop pressure (_Ps_) decreased afterwards approaching steady state, which indicated the completion of hydrate formation. The hydrate formation took about five min for the solid fraction of 15 vol.%, and about 25 min for the solid fraction of 30 vol.%. Finally, the pressure drops across the orifice were measured for the steady slurry flow of different flow rates. The pressure measurements for a specific combination of flow rate and solid fraction were made at least five times while the flow rates were increased and decreased, to check for the presence of any hysteresis effect, which was not found. After completing a series of pressure measurements for a given solid fraction, the entire flow loop was emptied and flushed with water, before repeating the experiment for the different hydrate fractions. 1. The uncertainty in the thus-obtained solid volume fraction is mainly attributed to four contributions:  
2. The amount of R134a that filled the void created by the water removal is neglected in the calculation of the required gas injection amount. For example, the void having 6.8% of total volume  
Figure 2: Transient changes in R134a storage tank pressure (\(P_{T}\)), temperature (\(T_{T}\)), flow loop pressure (\(P_{S}\)), and temperature (\(T_{S}\)) during the typical test run. is created in order to form the 30% hydrate volume fraction slurry. The void at the pressure and temperature of 275 K and 120 kPa (the stabilized pressure in Figure 2) contains the R134a amount equivalent to 0.03% of the required gas injection. 3. The amount of R134a dissolved into liquid water, which does not participate in hydrate formation, is neglected. The solubility of R134a at the pressure and temperature of 275 K and 140 kPa (the steady flow condition of Figure 2) is about 570 ppm, which is equivalent to 1.9% of the required gas injection amount to form the slurry of 10% hydrate volume fraction. 4. The largest contribution originates from the uncertain hydration number. The hydration number can increase 7% due to hydrate clathrate unoccupied with guest molecule. This contribution is equivalent to an uncertainty of 5.2% [Equation (1)]. The contribution caused by the error in measuring the mass of removed water is about 0.5%, the error in measuring the pressure is about 0.4%, etc. Therefore, it can be concluded that the uncertainty in the solid volume fraction is smaller than 9%. During the pressure drop measurements, the hydrate slurry within the flow loop was brought into near phase equilibrium, even though the pressure and temperature fluctuated within the limited extents.