Process parameters diameter

The cleaning studies on pipeline have so far concentrated on a diameter of 47.7 mm, to understand if the rules which have been established so far can be scaled to other diameters, cleaning studies have taken place on the ZEAL Pilot Plant on diameters of 23.9 mm ID (1 inch), 47.7 mm ID (2 inch), 73.2mm ID (3 inch) and 101.6 mm ID (4 inch). The flow volume available on the ZEAL Pilot Plant was between 0.002 m3 s-1 - 0.005 m3 s-1. Due to the different diameters, direct comparison across all diameters at the same flow velocities is not possible. The 23.9 mm system can achieve velocities of 4 m s-1, 8 m s-1 and greater on the ZEAL Pilot Plant, this is significantly different than for the other diameters. The 23.9 mm filled pipeline was placed in the Coupon Rig set-up and monitored by the Kentrak turbidity meter; this allowed a velocity of 0.5 m s-1 to be studied. All of these results are plotted in Figure 5.23.

Figure 5.23: Coupon Rig (0.5 m s-1) and ZEAL Pilot Plant: System: 23.9 mm diameter, 1 m, cleaning conditions: 20°C and 40°C, velocities based on a clean tube. Plot showing the effect of velocity on cleaning time for 23.9 mm diameter fully filled pipe.

The behaviour across the velocity range is divided into the 20°C data and the 40°C, as shown by the two lines in Figure 5.23.

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40°C data: time = 2155 exp -0.7 (ν), R2 = 0.998 (5.8)

The cleaning behaviour fits an exponential decay of cleaning time with velocity in the 23.9 mm diameter data for 20°C and 40°C.

General understanding of the cleaning time trends for different diameter pipes is sought as a function of different cleaning conditions. Different flow rates and temperatures have been explored for different diameters and presented graphically in Figure 5.24.

i)

ii)

Figure 5.24: ZEAL Pilot Plant: System: Length = 1 m, various diameters; 23.9 mm, 47.7 mm, 73.2 mm, 101.6 mm. Cleaning condition: various velocities based on a clean tube velocity. Velocity vs. Cleaning time for different diameter pipes of 1 m length, using water to clean at i) 20°C, ii) 40°C.

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Similar empty tube velocities can be compared in Figure 5.24 at 20°C for 47.7 mm and 73.2 mm diameters at ~ 1 m s-1 and these were seen to take similar times ~ 1000 s. However other data for 73.2 mm diameter at 1.1 m s-1 took around 2500 s. This spread of data for the 73.2 mm diameter below 1 m s-1, makes meaningful direct comparison difficult. This spread of data may result from the equipment which was used for this work. The ZEAL pilot plant is based on a 47.7 mm ID system, and conversions to the appropriate diameters were achieved by reducers and expanders. Reducers and expanders disturb the flow and in the case of expanders there is a likelihood that the flow will remain centralised in the centre of the pipe at the same diameter as the inlet to the expansion and a dead zone will be created in the initially expanded diameter pipe. In an effort to minimise this effect, an initial „start-up‟ length of the appropriate pipe diameter was in place prior to the filled test section and was 10 diameters of length.

To explore if the cleaning of the fully filled toothpaste pipes is still dominated by fluid dynamics at different diameters (as shown to be the case for different length pipes in Section 5.8), Reynolds is plotted against cleaning time for all diameter data in Figure 5.25.

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Figure 5.25: ZEAL Pilot Plant: System: Variety of diameters, 1 m, Cleaning conditions: 20°C and 40°C , Reynolds based on the physical parameters of the cleaning water, and the velocity is based on a clean tube. Reynolds number vs. cleaning time for different diameters.

In Figure 5.25, a general decrease in cleaning time is seen at increasing Reynolds number although the correlation is fairly weak. There is a spread of data for the diameters of 73.2 mm and 101.6 mm. This may be due to a greater variation in the way that the cleaning occurs, with the water picking up the toothpaste in different ways than that of the 47.7 mm diameter systems. This was not obvious from opening up the pipe.

The Reynolds number does not fully describe the system, as was the case in Section 5.9 for the length data. Reynolds is plotted against the nominal shear rate term defined in Section 5.9, in Figure 5.26.

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Figure 5.26: ZEAL Pilot Plant: System: various diameters at 1 m length. Nominal Shear (v.t.D-1) vs. Reynolds number for cleaning water at 20°C, 40°C and across diameters. The Reynolds number is based on the physical parameters of the cleaning water and the velocity on the clean tube.

The nominal shear measure versus Reynolds number shows this data is widely spread and gives little insight into predictive cleaning time. The 47.7 mm, 73.2 mm and 101.6 mm data are all clustered together, but the 23.9 mm diameter data is clearly separated from the rest of the data. The 47.7 mm diameter data produces a good straight line running through the cluster of data from diameters of 47.7 mm, 73.2 mm and 101.6 mm. This was the diameter that was used through the rest of the ZEAL Pilot Plant and did not need any reducers or expanders. The study of these larger diameters is more difficult due to the need for much greater resources and at a practical level due to the need to place cumbersome and heavy toothpaste filled pipes into the Pilot Plant and secure the pipe-work in place. This limited this study.