Difference Between Magnetic Digital Stirrers and Overhead Stirrers
It's not always easy to decide between overhead and magnetic digital stirrers. Both pieces of equipment would be a good choice for many tasks. One of its significant benefits is that magnetic stirrers are typically less expensive than overhead stirrers.
There are some factors to consider if you're choosing between buying one or the other for your lab:
Quantity of samples
Type of Vessel
Factors for Shear Stress
Viscosity of Samples
To help you in the best decision, we examine each issue in depth in this article.
Quantity of Samples
You must ensure that your equipment can handle processing high volumes. Laboratory overhead stirrers can bear maximum volumes ranging from 15 to 100 L. Overhead stirrers with a larger volume do exist. However, they are categorized as a process or industrial equipment.
Although most benchtop variants handle significantly lower maximum volumes between 250 mL and 5 L, these are still regarded as high-volume devices. Magnetic digital stirrers can handle similar amounts, which can process up to 25 L. There are even a few models which exist which are capable of handling 150 L of capacity.
Vessel Type
You should also consider the probability that the shape or size of your vessel prevents using an overhead stirrer, in which case a magnetic digital stirrer would be necessary. Although you are limited in terms of shape, there are foldable impellers that can fit into narrow-mouthed vessels. A magnetic stir bar can easily fit in containers with narrow necks because it lacks a shaft.
In closed vessels, magnetic stirrers can also provide mixing, which helps prevent contamination or carry out a process in a vacuum. An overhead stirrer can create a closed system, but this calls for particular stirrer bearings with vacuum pressure and stirrer speed restrictions.
Factors of Sheer Stress
Shear stress and whether your application requires high or low shear are other things to consider. Although your choice of stir bar can influence this somewhat, overhead mixers are generally preferable for high-shear applications. Impellers typically produce more shear stress than stir bars due to the nature of their design compared to stir bars. Additionally, there are impellers made mainly to create high shear. On the other hand, since metal impellers apply a lot of shear stress to a sample, you might want to bypass metal impellers. It will be more considerate to use a magnetic stirrer, and even dedicated cell culture stirrers may be ideal for the task.
Viscosity of Samples
When processing a high-viscosity sample with an overhead stirrer, there is a risk of straining the drive motor, which could lead to overheating and rapid wear. Some overhead stirrers have a torque sensor; if the torque rises too high, the power will be cut off, or the machine will completely shut off. Others have red warning lights that flash when they are loaded to capacity. Most contain a little internal fan that prevents the motor from overheating.
The magnetic coupling must be powerful enough to get through the viscous material's resistance with a magnetic digital stirrer. Additionally, the stir bar's vortex in viscous liquids will be relatively minor and could not be large enough to mix the sample thoroughly.
While stir bars come in various designs, unlike overhead stirring impellers, they typically do not have specialized geometries created to maximize churning in viscous materials.
Therefore, from the differences mentioned above, we hope that you are clear about which stirrer is required to fulfill your work.