Moving freight in water-borne capsules – surely a blast from the past that could not play a part in modern logistics infrastructure? But researchers at Huddersfield University, using advanced CFD modelling techniques, believe it has a future.
The basic technology isn’t new. Provisional patent protection was granted to ‘R. Crawford’ in 1860 for a ‘hydraulic despatch apparatus for written communications, letters [and] parcels’ to be transferred between different parts of a building. However, pneumatic pipelines were adopted for these applications in the 1920s and are still in use today, transporting communications and money in shops and offices to moving thousands of tons of rock per day from mine faces to processing centres.
However, the full potential of hydraulic capsule pipelines (HCP) is yet to be realised, and that is the goal of Dr Taimoor Asim, research fellow in flow diagnostics at Huddersfield University’s School of Computing and Engineering.
“The main advantages of the system are that, compared to more traditional transportation methods, such as lorries for example, there are no traffic issues, no emissions and the possibility of an accident is marginal,” explained Dr Asim. “Also, the bulk of investment or cost is up-front for building and installing the pipeline and manufacturing the capsules.”
CFD model of rectangular capsules in the HCP pipeline
The design for the pipeline is relatively simple, essentially it consists of a terminal at each end for loading and unloading the capsule connected by a pipe, with a pump used to provide the force to propel the capsule forwards.
The original methodology for working out the optimum dimensions for a pipeline was developed in the 1980s when CFD wasn’t available. Simplified models were made using the Colebrook-White equation to predict the pressure drop in a pipeline.
“This hundred-year-old equation is not the best way to do that,” said Dr Asim. “I have replaced that part with CFD to get actual predictions about the pressure drop in the pipeline rather than a rough estimation of the flow behaviour, what happens if each capsule in a train of capsules produces a wake and what effect will that have on the capsules downstream?”
At lower speeds the capsule slides along the floor of the pipe, however once the speed of flow is high enough lift is generated and the capsule becomes waterborne. The best point to inject the capsules into the pipeline is where the flow has become stabilised. Dr Asim’s team used ANSYS Fluent to simulate the behaviour of spherical, cylindrical and rectangular capsules of varying lengths and densities, as well as different pipe dimensions.
“To move water through a 1m section of horizontal pipeline with a 4” diameter at 1m/s would take a force of 92Pa,” Dr Asim expounded. “This increases to 124Pa to move a single, spherical capsule that has the same density as the water and a diameter half that of the pipeline.”
He went on to say that the force would need to increase to 226Pa to move a capsule that was denser than the water in the pipeline, this almost doubles to 414Pa for a cylindrical capsule with a length the same as it’s diameter and as more capsules are added in a train the force required will get exponentially bigger. His team has also tested vertical pipelines which require a force of 9900Pa to move the water at 1m/s, with only an increase of 30Pa to carry a single, spherical, equi-density capsule. They are also running tests through inclined and declined pipelines, although these results have yet to be published.
Spherical capsules were found to require the lowest pressure, followed by cylindrical, and then rectangular. The team is currently attempting to blend the CFD data to come up with the optimum shape to make the capsules.
For now, the Huddersfield scientists are testing their capsules in a pipeline that is 10cm in diameter and just over 4m long. But, with the ultimate aim to replace road and rail transport, the scale up in width and length is obviously considerable. So, how far away is the technology from commercial realisation?
“As far as the practical aspects are concerned, it will take a few years of research - both lab-based and real-world - to be carried out before we come up with something that can be used on a bigger scale,” stated Dr Asim. “Our 2” pipeline can be scaled up to 4” quite easily, but going more than that is going to be a bit difficult for us here at Huddersfield.”
A bigger facility would be needed to carry out larger tests, especially into how to stop the capsules exactly where they need to be unloaded without stopping the flow in the whole system. Also, it is unlikely to be a straight swap in terms of volume from traditional freight to HCP: rather than being transferred straight into the HCP, a cargo container would have to be emptied, with the cargo divided equally between capsules so each was the same weight before being loaded into the HCP.
Dr Asim says that this particular application is ‘something for the future’ but smaller scale applications could be implemented quite quickly. He and his team are talking to colleagues in universities and companies in the USA, Canada and the Middle-East. Use cases being put forward are for the transportation of compressed coal logs over long distances, from mines to treatment centres, and the transportation of goods in the food and beverage industries.
For now, the Huddersfield scientists are concentrating on designing cylindrical capsules with conical noses to make them more hydrodynamic and integrating the new electronic sensors into their pipeline.
Dr Asim said: “Once the new transducers are in place we will test the new capsule designs immediately. Realistically, we think we’ll start to get some meaningful results by the end of March 2017.”
Clearly, a national infrastructure where goods are transported by HCP is many years away, but things are moving slowly, and in the right direction.