AUSTRALIA SINGAPORE
Dilatant Fluid (Shear-Thickening)
Description: Dilatant fluids become more viscous as shear rate increases. They flow easily when undisturbed but become thick and resistant when stirred rapidly or subjected to sudden force.
Examples: Cornstarch in water, some dense slurries.
Challenges: Sudden increases in flow or agitation can cause the fluid to thicken dramatically, stressing pumps and pipes. They can cause pressure surges, vibrations or flow instability in processing equipment.
Bingham Plastic
Description: Bingham plastics behave like a solid until a minimum force (yield stress) is applied. Once that threshold is overcome, they flow like a Newtonian fluid.
Examples: Toothpaste, mayonnaise, sludges.
Challenges: Systems must be designed to overcome the yield stress to initiate flow. Inadequate pressure can cause blockages or poor flow. In low-shear areas, these fluids may not move at all, leading to sedimentation or uneven distribution.
Yield-Pseudoplastic Fluid
Description: Yield-pseudoplastic fluids require an initial force to start flowing and then exhibit shear-thinning behaviour once in motion. They combine the characteristics of Bingham plastics and pseudoplastics.
Examples: Drilling muds, tomato paste, some cosmetic creams.
Challenges: Starting flow can be difficult without sufficient force. Once flowing, they need carefully controlled agitation to maintain consistency. If left idle, they can become very thick and may block equipment or settle unevenly.
Liquid-Based Systems
Liquid + Dispersed Solid = Colloid (Sol)
Description: Solid particles are uniformly dispersed within a liquid. The particles are small enough (1 nm to 1 µm) that they do not settle under gravity and often exhibit Brownian motion.
Examples: Paints, inks, milk (casein micelles), mud.
Challenges: Stability issues, particle aggregation, difficulty in separation, sensitivity to temperature and pH changes.
Liquid + Dispersed Solids (High Volume Fraction) = Suspension / Slurry
Description: High-concentration mixtures where solid particles are dispersed in a liquid, often exceeding 10% by volume. The particles are large enough to settle if not agitated.
Examples: Mineral slurries (iron ore, coal), cement paste, paper pulp suspensions, food processing slurries (chocolate, peanut butter).
Challenges: Settling, high viscosity, wear and erosion, handling difficulty.
Liquid + Gas = Bubbles, Foam
Description: Gas bubbles dispersed within a liquid. The gas phase can exist as discrete bubbles or as a continuous network forming foam.
Examples: Beer foam, shaving cream, whipped cream, aerated liquids.
Challenges: Instability, drainage, bubble coalescence, difficulty in maintaining uniform distribution.
Liquid + Immiscible Liquid = Emulsion
Description: Droplets of one immiscible liquid dispersed within another. Stability often requires emulsifiers to prevent separation.
Examples: Milk (fat droplets in water), mayonnaise, oil-water emulsions.
Challenges: Phase separation, instability without emulsifiers, viscosity variations, sensitivity to temperature and shear.
Gas-Based Systems
Gas + Dispersed Liquid = Droplets, Sprays
Description: Liquid droplets dispersed within a continuous gas phase. Commonly formed through atomisation or aerosolisation processes.
Examples: Aerosol sprays, mist, gas scrubbers, fuel sprays in combustion systems.
Challenges: Droplet coalescence, evaporation, uneven distribution, inefficient mass transfer.
Gas + Dispersed Solids = Granular
Description: Solid particles dispersed within a gas. The particles are typically large enough to be influenced by gravity but can be suspended temporarily if agitated or fluidised.
Examples: Dust in air, powdered materials in pneumatic conveying systems.
Challenges: Segregation, dust formation, difficulty in fluidisation, wear and abrasion.
Gas + Solid + Liquid = Wet Granulates
Description: A mixture where gas is present along with solids and liquid. Typically involves wetting or coating of solid particles by the liquid phase.
Examples: Wet sand, slurry in pneumatic systems, granulation processes in pharmaceuticals.
Challenges: Inconsistent coating, particle agglomeration, drying issues, difficulty in achieving uniform mixing.
Handling non-Newtonian fluids requires the right experience and expertise because their behaviour is complex, unpredictable and often counterintuitive. Unlike Newtonian fluids, their viscosity can change with shear rate, duration or both, leading to challenges such as clogging, flow instability, equipment overload or product inconsistency. Without a deep understanding of how these fluids respond under different operating conditions, even well-designed systems can fail. Experienced engineers can anticipate these behaviours, select appropriate equipment and design processes that maintain stable, efficient and safe operations, ultimately preventing costly downtime or quality issues.
Time-dependent Fluids
Thixotropic Fluid
Description: Thixotropic fluids become less viscous over time when subjected to constant shear. They start off thick, but gradually thin out the longer they are stirred or pumped. Once the shear stops, they slowly return to their original, thicker state.
Examples: Ketchup, some clays, gel-based paints, certain drilling fluids.
Challenges: These fluids can be difficult to start flowing, but once in motion, they may become too thin if shear is prolonged. They require careful timing in mixing, transferring or applying, as flow properties change with duration. Inconsistent behaviour during stop-start operations can also lead to quality or performance issues.
Rheopectic Fluid
Description: Rheopectic fluids become more viscous over time under constant shear. They begin with low resistance to flow, but the longer they are sheared, the thicker and more resistant they become. Once shear stops, they gradually return to their original, more fluid state.
Examples: Some printer inks, high-solid suspensions, certain lubricants.
Challenges: These fluids may initially flow well but become problematic over time in continuous operations. Pumps and mixers can strain as the fluid thickens unexpectedly. If not accounted for, this behaviour can lead to equipment overload or loss of flow. Start-stop cycles must be managed carefully to avoid sudden viscosity build-up.
Complex Fluid
Complex fluids are those that exhibit non-linear flow behaviours, unlike simple Newtonian fluids such as water or air. They require specialised analysis due to interactions between multiple phases, and may include multiphase fluids, non-Newtonian fluids, reactive fluids, and multispecies systems. Industries such as chemical processing, energy production, mining, and water treatment frequently encounter such fluids. These systems often involve challenging physics, significant economic implications, and safety concerns. When not properly understood, they can lead to inefficiencies, operational issues, or safety risks. As complex fluid specialists and complex flow consultants, we bring a deep understanding of both fluid behaviour and flow dynamics to help clients achieve reliable, efficient performance across a wide range of applications.
Time-Independent Fluids
Newtonian Fluid
Description: Newtonian fluids exhibit a consistent relationship between applied force and flow rate. Their viscosity remains constant regardless of how fast they are stirred, pumped or sheared.
Examples: Water, cooking oil.
Challenges: Although easy to handle, Newtonian fluids are relatively uncommon in complex industrial applications. Processes built around this behaviour may underperform if the actual fluid deviates from it. They provide no resistance to settling or phase separation, making them ineffective for suspending solids without continuous agitation.
Pseudoplastic Fluid (Shear-Thinning)
Description: Pseudoplastic fluids become less viscous as the shear rate increases. They are thick or resistant to flow when at rest, but flow more easily when stirred or pumped.
Examples: Blood, paint, yoghurt, polymer solutions.
Challenges: These fluids tend to settle or clog when idle, requiring agitation to maintain uniformity. Process equipment must be selected to handle large viscosity changes. Under low flow conditions, performance may degrade or solids may accumulate.