Reducing water consumption in cleaning systems: are vortex rings the answer?

High water use in cleaning systems is a growing concern for many manufacturers. Whether mixed with chemicals for washing, heated for sanitation, converted to steam for sterilisation, or used to rinse residues, water plays a vital role. So what can be done to minimise cleaning systems’ water consumption without compromising their performance? Various industries, from pharmaceutical and home/personal care to food, beverage, and dairy, are facing this challenge. We set out to explore the options from a science and engineering perspective.

Vortex rings: harnessing fluid mechanics for clean-in-place (CIP) systems

Our initial analysis of CIP systems used in manufacturing identified the rinse phase following wash cycles as an opportunity to innovate. We then moved onto ideation and concept development, landing on vortex rings as having high potential for certain applications.

Vortex rings are a naturally-occurring phenomenon seen in fluids (liquid or gas). Perhaps the most striking example is dolphins blowing vortex rings of air into water, which they chase, push, swim through, and play with. Self-propelling and long-lived, vortex rings can travel several metres in some circumstances¹. This, combined with high internal rotational velocity, presents vortex rings as a relatively simple way of generating and propagating agitation through a medium. A vortex ring is a torus (‘doughnut’) fluid structure which travels forward by rotating within itself. Think of a water snake toy, which slips through your hands as you try to hold it.

Figure 1

As the exterior of the film moves in one direction, the centre is pulled through the opposite way, creating a rotation from outside to inside. Vortex rings have the same mode of action; a torus cross-section reveals a velocity field with a smaller magnitude towards the centre and greater magnitude at the edges. Conversely, the classic slow flow of liquid through a pipe (described as ‘laminar flow’) is faster in the centre and slower towards the walls. This is the opposite of what is required to thoroughly and quickly mix cleaning product residue into the bulk flow and out of the system. Flow is also strongly aligned with the axial direction of the pipe, leaving radial edge-to-centre movement of molecules largely down to diffusion.

To combat the above challenge, average flow speeds must be high enough to induce turbulence to improve mixing. The overall impact is that CIP systems need to use a lot of water to rinse pipework. On the other hand, the velocity structure of vortex rings appears ideal for rinsing pipework during CIP operations. A vortex ring travelling down a pipe would induce mixing entraining fluid from the near-wall region into the central part of the tube. This could allow for equivalent rinsing action at lower overall speeds, ultimately reducing total water consumption.

Modular cleaning systems

A current technology trend in manufacturing centres on the development and integration of process modules. Employing modules for different steps in a manufacturing process can facilitate quicker installation and commissioning. Modules can also be interchangeable, bringing greater manufacturing flexibility. Combined with enhanced automation and robotics, they also offer potential for a more compact factory layout, meaning higher capacity with lower physical footprint.

Modularisation of cleaning systems will also present opportunities to embrace new technologies as they emerge. For example ‘vortex generators’ in modular form could be integrated with existing systems to significantly reduce the volume of water required for rinsing.

Commercial use of vortex rings

Figure 2

Existing literature and intellectual property confirm that vortex rings can be used for mixing liquids^2,3. However, our research indicates sparse commercial use of these fascinating phenomena. While recent academic research characterises the form and motion of vortex rings, very little work has been done on their behaviour in pipes, and even less in pipes which contain a background flow. Cleaning applications do exist or have at least been proposed. These include gaseous vortex rings for cleaning porous filters^4,5 and an air-based ‘vortex gun’ to lift particulate matter from hard-to-reach spaces in car interiors⁶. Yet there is little knowledge or application of vortex rings.

Sagentia Innovation aimed to fill this knowledge gap by modelling vortex ring behaviour in a pipe on a scale used in the food and beverage industry. Existing literature^7,8 was used to inform the build of a COMSOL model (see Figure 2). This enabled us to probe important factors such as pipe diameter, background flow rate, energy input to the vortex ring (controlling its initial vorticity), and the major and minor radii of the torus. The radius of the torus relative to that of the pipe is a significant metric. Too small, and it won’t impact pipe walls at all; too large, and it will interact too much, dying off quickly.

Figure 3: Animation of simulation of working vortex ring

Our COMSOL model determined two key factors regarding use of vortex rings in 1-4′ diameter pipes with low energy input:

A vortex ring can survive in such a pipe, moving tens of centimetres by self-propagation in a static background, i.e. with no flow.
Slow background flows enhance the travel distance of the vortex ring, and do not cause it to decay significantly faster; its lifetime remains approximately the same as in no flow.

These findings suggest that a simple vortex generation device (usually a piston which moves a short distance in a very short time, propelling a segment of fluid forward and providing it with rotation⁹) could be effective. Inserted into a pipe, it could generate a series of vortices which travel downstream, mixing in cleaning fluid residue as they go. Furthermore, this could potentially be done at much lower flow rates than currently used in CIP rinses.

We are now exploring vortex rings’ behaviour within faster-flowing turbulent media to understand if they can survive. In fact, they may be able to move much further – remember the dolphins, whose vortex rings travel metres in constantly moving seawater. Vortex rings could represent a rich new seam of innovation and product development for CIP systems.

How Sagentia Innovation can help

Here at Sagentia Innovation, we apply deep science and engineering-led approaches to support effective, cost-efficient manufacturing innovation. Find out more about how we support food and beverage processing clients here.

REFERENCES:

‘Decay of vortex rings in a rotating fluid’, 2009, Physics of Fluids
‘Stirring properties of vortex rings’, 1991, Physics of Fluids A: Fluid Dynamics
US052813A, ‘Tube type vortex ring mixers’, 1990
US3685257A, ‘Cleaning of filters using vortex rings’, 1970
‘Washing with vortices’, 2023, Physics
Elite Vortex Professional Surface Cleaning Gun – Elite Car Care
‘The decay of confined vortex rings’, 2012, Experiments in Fluids
‘Understanding evolution of vortex rings in viscous fluids’, 2017, Journal of Fluid Mechanics
US8556674B2, ‘Self-priming underwater device for generating or shooting a vortex ring’

Reducing water consumption in cleaning systems: are vortex rings the answer?

Vortex rings: harnessing fluid mechanics for clean-in-place (CIP) systems

Modular cleaning systems

Commercial use of vortex rings

How Sagentia Innovation can help

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