## 2 Experiments  
The formation and circulation of aqueous tetraflouroethane (R134a) hydrate slurry were made to occur within a flow loop having an inner diameter of 21.5 mm. Figure 1 shows a schematic of the experimental apparatus. The flow loop consisted of a rectangular service flow loop section, and extended test flow loop section. The service flow loop section was about 4000 mm long, and rigged with flow driving pump, bubble removal chamber, water supply/drain port, volumetric flow meter, R134a gas supply port, sight glass assembly, and tabs to measure the service loop pressure (\(P_{S}\)) and temperatures (\(T_{S1}\) and \(T_{S2}\)). The flow is driven by the swash plate pump manufactured by Parker (Model F12-090-MF-IV-D), which had a displacement volume of 90 cm\({}^{3}\) per revolution. The rotation speed of the pump driving motor was controlled by a Rexroth (EFC 3600) inverter. The bubble removal chamber was a commercially available 1 L size sight glass assembly. The top of the bubble removal chamber was closed by a blank plate with a vent valve, and the bottom was welded to the T-type pipe fitting. A pneumatic control valve was installed between the gas supply port and the R134a storage tank to control the flow loop pressure close to the desired value engaged with a pressure transducer for (\(P_{S}\)). The volumetric flow rate was measured using an electromagnetic flowmeter (KTM-800), whose measuring range is a maximum 10 m/s with an uncertainty of \(\pm 0.5\%\) for the flow velocity larger than 0.3 m/s. The correlation coefficient between the pump rotation speed and volume flow rate was 99.99% for the experimental conditions of the present study. The flow velocity can be estimated from the pump rotation speed with the same uncertainty as the flow meter after calibration. Flow visualization was enabled using sight glass assemblies installed upstream and downstream of the pump. The test flow loop section was connected to the first downstream corner from the pump of the service flow loop and was about 8200 mm long. The orifice test segment was located 1.5 m downstream from the 180-degree bend of the test flow loop. For the non-Newtonian flow it is important to know required pipe length for the fluid to become fully developed as given by [PERSON] and [PERSON] et al. [51]. In this study the calculated entry length of straight pipe was smaller than 0.97 m for the test conditions employed in the discussion. The orifice test segment was a glass tube having a concentric square-edged orifice in the middle. The thickness of the orifice plate was 6 mm, and the bore diameter of the orifice was either (10 or 15) mm. SENSUS differential pressure transducers having an uncertainty of 0.025% up to 200 kPa were employed to measure the differences in pressure at 50 mm upstream (\(P_{O1}\)) and 100 mm downstream (\(P_{O2}\)) from the upstream face of the orifice. The pressure at 1000 mm downstream of the orifice (\(P_{O3}\)), as well as the representative pressures of the service flow loop (\(P_{S}\)) and test flow loop (\(P_{T}\)), were measured with SENSUS pressure transducers having an uncertainty of 0.4%, and maximum range of 1000 kPa. The service flow loop was immersed in an acrylic water bath. The test flow loop was immersed in a stainless steel water bath, which had a chilling water supply tube, and a chilling water overflow drain tube. The temperatures of the water baths were maintained close to 275 K by circulating  
Figure 1: Schematic of the flow loop: (1) swash plate pump, (2) water supply/drain port, (3) bubble removal chamber, (4) orifice test segment, (5) gas supply port, (6) volumetric flow meter, (7) sight glass, (8) acrylic water bath for service flow loop section, and (9) SUS water bath for test flow loop section. the chilled water from constant temperature baths, both with the flow rate of 28 LPM. The R134a storage tank was also immersed in the water bath, whose temperature was maintained close to 295 K, to avoid condensation.