Student Interviews On Their Projects With Our Dredge Pump Slurry Test Circuit In Damen Nieuws

Damen dredge pump slurry test circuit on the outfitting quay in Nijkerk
Damen dredge pump slurry test circuit on the outfitting quay in Nijkerk

‘What sets men apart from boys is the size of their toys.’ And that wisdom applies to a lot of students that we’ve had at our company and have grown from boy to man working on our dredge pump slurry test circuit for their internship or graduation. As the test circuit has seen some intense activity these last months and yielded us with some very innovative concepts and possible new products, it was the right time to cover this interesting piece of equipment in the internal Damen Nieuws1 of January 2021 to share with all our colleagues. And that occasion in turn is an excellent opportunity to share with you the article and zoom into some of the details of the circuit.

General arrangement of the dredge pump slurry test circuit
General arrangement of the dredge pump slurry test circuit

Already more than ten years ago, we felt the need to have our own testing facility to experiment with the processes in our dredges or check the performance of new products2. After defining the specifications of the circuit, we had Hylke Visscher assisting us in designing the circuit for his internship. Subsequently he could actually supervise the manufacturing of the circuit for his graduation. Hylke worked in close cooperation with Arjan de Vries who in turn did his graduation on the building, outfitting and commissioning of the circuit. Both students from then are now esteemed and valuable colleagues as we have appreciated their performance on their projects.

After those ten years, we have a new generation of students working on the circuit. Arend van Roon recently graduated on his project with the circuit, as covered in my last post3. Currently Wim Kleermaker is preparing his experiments on the dredge pump. Upcoming is Williem Salim, not yet mentioned in the article, but now already starting his internship on the instrumentation of our laboratory. All project on the test circuit are supervised by Pieter van der Kooi as plant manager, Frank Bosman as student coordinator. Depending on the project, Ewout van Duursen, Suman Sapkota and me are supervising the student projects more on a subject level.

Various executions of a U-bend c-meter in the test circuit, for delivery and installed on a dredge
Various executions of a U-bend c-meter in the test circuit, for delivery and installed on a dredge

The odd thing you might notice in the loop of the test circuit is the U-bend directly after the dredge pump. Contrary to most first impressions, it is not to generate resistance, although it does so slightly. It is to measure how much sand has been transported. As the circuit is by nature closed, there is no way to check how much we’ve transported through the dredge pump. Sure, there is a density sensor4, but this will only indicate the so called volumetric density; how much material is there in the cross section. It will not differentiate between fast moving slurry and a slow sliding bed. In the extreme you could have a static bed, indicating a very high concentration. Multiplying this with a very high fluid speed, that is squeezed through the remaining aperture, you would expect an impressive production. Wrong! Not a single particle gets transported.

Enter: the U-bend. It measures the hydrostatic pressure differences over a certain hight in the upstream and downstream branches. This will cancel out the velocity differences but will yield the actual transported mass flow. So, that is how we can claim that we already dredged millions of cubic meters, all on the floor area of a 40 foot container flatbed.

Explanation of the U-bend measuring principle
Explanation of the U-bend measuring principle

References

  1. Testcircuit, Damen
  2. Innovation, Damen
  3. Graduation of Arend van Roon: Detecting Flow Regime And Optimising Transport Efficiency, Discover Dredging
  4. Production management, Damen

See also

Graduation of Arend van Roon: Detecting Flow Regime And Optimising Transport Efficiency

Arend van Roon defending his graduation thesis
Arend van Roon defending his graduation thesis

Our first happy event this year is the graduation of Arend van Roon. He recently graduated on a project in the slurry test circuit at our Research and Development department at Damen Dredging Equipment1. His research was an interesting investigation in the detection of flow regimes. It gives some insight in the processes involved in the transport of water-solids mixtures. Let me share some details from the background with you, as I think this might be helpful for your own operation also.

Overview of the Damen Dredging Equipment slurry pumping test circuit
Overview of the Damen Dredging Equipment slurry pumping test circuit

At first sight, it is hard to imagine, how something heavier than water, the grains, can be lifted when the fluid is moving. Sape Miedema has written the standard on mixture transport in his book ‘Slurry Transport’, explaining his approach with the ‘Delft Head Loss & Limit Deposit Velocity Framework2’. Without going into the academic details, I will try to help you grasp the gist of the phenomena.

DHLLDV book (Credit: Sape Miedema)
Slurry Transport text book cover (Credit: Sape Miedema)

First the grains have to be picked up. When they are lying on the bottom of the pipe, they are fully immersed, surrounded by the fluid on all sides. The free fluid on top and the pore water between the grains under and on the side of the grains. Now comes Bernoulli’s trick. When the fluid in the pipe starts moving, he says that the local dynamic pressure decreases, while the static fluid in the pores remains at the same pressure. The pressure difference between the pressure in the pores and in the moving fluid, pushes the grains out of the bed into the fluid.

Grain pickup and suspension process explained
Grain pickup and suspension process explained

Once the particles are in the fluid are in the fluid, they should stay suspended, or they fall back into the bed. The driving force here is the turbulence in the fluid. Usually dredging slurry mixtures are turbulent. This turbulence causes the fluid to flow in eddies. These are little vortices that generally move in the direction of the flow, but in a moving frame of reference tumble in all directions. Mmh, as they rotate in all directions, why don’t they cancel each other out? Now, imagine being a particle yourself, surfing on those eddies. When it is in a fluid, it tends to sink with a certain settling velocity. Independent of the local movement of the fluid. This means, that on the downward side of the eddy, the particle has a higher total velocity than on the upward side. As the eddy is sort of symmetric, the particle dwells longer in the upward draft than on the downward fall. In this infinitesimal time difference, the eddy transfers some extra kinetic energy from the fluid to the potential energy of the particle. As this loss of kinetic energy is compensated by an increase in pressure (remember Bernoulli) carrying grains in a fluid increases the pressure loss in the slurry transport.

Flow regimes and excess hydraulic gradient requirements in dredging slurry transport (Credit: Sape Miedema)
Flow regimes and excess hydraulic gradient requirements in dredging slurry transport (Credit: Sape Miedema)

This turbulence is in short the background of suspension in the slurry transport process. Depending on al the various governing parameters: densities, viscosity, diameters, velocities etc, the equilibrium of forces result in several different regimes in the slurry flow. Ranging from homogeneous, through stratified to ultimately a static bed. Each with their own particular pressure losses. And that is what we are interested in. On our dredges, we want to transport as much material to the least amount of energy3. We are constantly looking for improvements in our equipment and sensors to assist the operator in visualising and controlling the actual state of his process4. Thanks to Arend’s project and the promising results, we can set the next step in our product development.

Explanation on slurry flow conditions, critical speed and specific power consumption
Explanation on slurry flow conditions, critical speed and specific power consumption

References

  1. Innovation, Damen
  2. Slurry Transport: Fundamentals, A Historical Overview & The Delft Head Loss & Limit Deposit Velocity Framework 2nd Edition, TU Delft
  3. Innovations In The New MAD Series To Increase Uptime And Reduce Fuel Consumption, Discover Dredging
  4. Dredging Instrumentation, Damen

See also

2021: Muddling Along To A Healthy Year In Dredging

Calendar picture of a sunny dredging site
Calendar picture of a sunny dredging site

Dear readers, I sincerely wish you all the best for this new year. As things are looking positive on the vaccine front, we should keep testing negative this year. There are lots of items and events to look forward. Last year was not quite what we’ve hoped for and wished each other.

I do hope all of you are OK and are still together with your loved ones. I am fortunately in that respect. So, next to the Covid situation, there were a lot of other noteworthy items. Most of them have been featured here on Discover Dredging. My trip to Bangladesh, just before all the lockdown measures. The graduation of Carsten1 and Omar2 that were completely over Teams. Some attention to our Damen Dredging Experience3. And some other items. Did you enjoy the Donald Duck review?4

Opening scene of ‘Muddy Fine Business’ or ‘Success Test’ (Credit: Disney)
Opening scene of ‘Muddy Fine Business’ or ‘Success Test’ (Credit: Disney)

One sad event was, the last issue of Dredging and Port Construction5. We’ve had to say goodbye to our trusted DPC. Although by now, there has been a kind of digital revival on the CEDA Website6. They opened up a section for Industry News, edited by Namrata Nadkarni. It stands out from the other online media covering dredging as there has been some attention to smaller topics, that would normally not get covered. As I think it is a good initiative, I urge you to subscribe and also participate by sending them any noteworthy news items for publication. Not specifically the usual company press releases, but also the more thought provocative opinions and perspectives on the activities of our dredging community. Active participation could make this CEDA Industry News flourish this year.

Announcement of the CEDA Industry News section (Credit:CEDA)
Announcement of the CEDA Industry News section (Credit:CEDA)

Further personal activities within CEDA are the Dredging Management Commission7 and I am looking forward to the exciting new concept for the CEDA Dredging Days8. Will you participate? Also, I already took the course on ‘Dredging for Sustainable Infrastructure’9, but you should keep an eye out on the next instalment, coming soon10.

A continuation from last year on my Discover Dredging will be some more articles on our Damen Dredging Experience. There are still some exhibit left to review and teaser:… There are some new exhibits arriving! Hope to have that covered when the pandemic will fizzle out we can show you around through our museum. And I hope to continue on pump and dredge technology.

Overview of the Damen Dredging Experience
Overview of the Damen Dredging Experience

Currently, there are some students working on their graduation thesis. Their very interesting topics will be highlighted here as well. Some others will start soon. When you are looking for a fun place to have your internship our your graduation, you might consider a visit to our career page11 or contacting Frank Bosman for any opportunities. Although most positions are filled at the moment, later this year we would welcome fresh brains again.

As our offices will be closed for regular work, I will be working from home most of the time. Probably most of you will do likewise. To keep track of the passage of time over the days, you should have a calendar. As a special service to my audience, I was granted the use of a set of beautiful pictures to create a calendar. You can download the file here and with some DIY skills you should have some original wall decoration for this year.

Stay healthy and stay safe. Hope to see you later this year.

Selection of calendar pictures
Selection of calendar pictures

References

  1. Graduation Of Carsten Markus: Designing And Casting Of Impellers, Discover Dredging
  2. Graduation Omar Karam: Rock Cutting The Egyptian Way, Discover Dredging
  3. Selected articles on the Damen Dredging Experience, Discover Dredging
  4. Book Review: Donald Duck A Muddy Fine Business; Artistic Equipment Design; Discover Dredging
  5. The Last Dredging And Port Construction Magazine, The End Of An Era; Discover Dredging
  6. Debut of CEDA Industry News section and monthly newsletter, CEDA
  7. Selected articles on the CEDA Dredging Management Commission, Discover Dredging
  8. Call for Papers for CEDA Dredging Days 2021 issued, CEDA
  9. Book Review: Dredging For Sustainable Infrastructure, Discover Dredging
  10. 2nd Online Course Dredging for Sustainable Infrastructure planned for March 2021!, IADC
  11. Welcome to the best years of your life, Damen

See also