How to Use a Liquid Mixer
Mixing is a fundamental process used in a wide variety of applications. Whether it’s dispersing agglomerates, keeping solid particles and colloids in suspension, or blending two liquids, mixing is necessary to achieve the desired results.
Traditional mixers process liquid by forming vortices at their blade or propeller tips. This localized mixing causes a strong shear and shear sensitivity in the mixture.
Viscosity
Flowing and mixing of less viscous liquids like water is easy, but achieving similar results with high-viscosity materials can be difficult. Using the right mixer to handle these products requires a thorough understanding of the dynamics of viscous fluids and the agitation forces that can affect them.
For example, a liquid’s temperature can affect its viscosity. The lower the temperature, the more viscous it is. Additionally, some additives can change a liquid’s viscosity. For instance, a surfactant can decrease or increase a liquid’s viscosity, depending on its properties and concentration.
Viscosity in a liquid also changes with time, as the material liquid mixer is subjected to shear. For example, a pseudoplastic product will decrease its viscosity over time when shear is applied, while a dilatant material will become thicker under shear.
High-viscosity materials are often shear sensitive, which creates challenges when attempting to mix them with an agitator. Shear-sensitive materials require a different type of agitation than non-shear-sensitive materials, which can lead to poor mixing.
In order to achieve good mixing results when working with high-viscosity products, it is recommended that you start with a low-viscosity liquid and then gradually introduce the higher-viscosity liquid. By doing so, you can take advantage of the agitation of the low-viscosity liquid to reduce the energy required to achieve the same level of blending in the higher-viscosity product.
Vortex
A vortex mixer is a simple laboratory tool that uses fast oscillating motion to create a turbulent flow within liquid samples. It is used in many different applications including resuspending cells, DNA extraction, and assay preparation. A vortex mixer is commonly found in many laboratories including biochemical, cell culture, and clinical settings.
The motor in a vortex mixer is attached to a rubber cup that rotates rapidly when the device is activated. The rapid rotation of the rubber cup creates a swirling motion, which is known as a vortex, in the liquid sample being mixed. The rubber cup can be placed on top of a sample container such as a test tube to begin the mixing process.
Most vortex mixers are equipped with a control panel that allows the user to select from multiple operating modes. There are also several speed options that can be controlled by the operator. This gives the lab technician flexibility to mix at low speeds for gentle agitation or at higher speeds for vigorous agitation.
Unlike a standard stirrer that can only mix one sample container at a time, the vortex mixer can combine fluids in sealed flasks and can be used to suspend cells as well as to prepare biochemical assays. This type of laboratory mixer is preferred for certain application areas such as resuspending cells or combining reagents in an experiment that requires high throughput.
Dispersion
Dispersing one liquid in another is a common operation in material processing. The goal of the process is to create a homogeneous mixture of different miscible liquids with various viscosities. This is usually achieved through stirring. In some cases the stirring action is so intense that it also creates fine emulsions, which are required for pharmaceutical processes.
The mixing process can be carried out in the same tank used for homogenization by means of agitators, for example rotor/stator or FCRS agitators with high shear blades that are particularly effective in breaking up hard agglomerations and dispersing fine droplets. A mixture is considered to be a true emulsion when the difference in the viscosities of the individual liquids can no longer be discerned after mixing.
A great deal of information exists on blending, solids suspension and gas dispersion, but little is known about the effect of shear on dispersed phase mixing rates in stirred tanks. This experimental work aims to measure these rates, and to investigate the variables that influence them.
The results show that agitator design and vessel size have an important impact on the mixing performance of dispersed phase systems. It is therefore essential to consider these variables in the design of a new mixer. For example, for low viscosity applications, a direct drive high speed mixer can be paired with a smaller impeller; as the viscosity increases a gear driven model becomes necessary to accommodate the additional shear needed.
Pumping
Mixing is important in many applications, especially when it involves a combination of liquids and solids. In these cases, a mixer can disperse agglomerates of solid particles and colloids in a liquid, keep a solution’s contents suspended in a tank or combine two different liquids into one. Mixers can also be used to heat or cool solutions, or as stirred tank reactors and bioreactors.
For instance, when a process requires high turnovers such as in agitating a 100-gallon tank of water-like chemical, it’s important to select a mixer that can handle the required agitation rate. To determine this, consult the mixing pump manufacturer and ask for the prop’s pumping rates at various rpms. For example, a 4-inch square pitch prop at 1,750 rpm pumps 250 gpm of fluid.
Other applications require a continuous flow of mixtures, such Packaging Machinery Supplier as evaporative distillation and air stripping. In these cases, a gas-liquid mixing pump can be used to avoid the need for a separate gas compressor and reaction tower.
A pumping action in a mixing system produces shear that can cause the solution to become unstable and potentially agglomerate, which is why you need a pump with low slip. Quattroflow pumps offer a unique operating style that allows them to pump shear-sensitive fluids without causing instability or compromising the integrity of the liquids they transport.
