A hotplate stirrer is an essential piece of equipment used in laboratories to speed up reactions, and each variety has its own qualities which make it more suitable for certain applications. Whatever your specific needs, it’s important to select the correct piece of equipment for the job.
Firstly, it’s crucial that hotplates and hotplate stirrers are differentiated. Whilst a hotplate is a piece of laboratory equipment suitable for heating solutions above 100oC (212oF), a hotplate stirrer can also keep liquids circulated whilst they are being heated, offering additional benefits and a level of automation to your lab. In this article, we will look at the key variables to consider when selecting the right hotplate stirrer to suit your requirements.
Accuracy
If your work requires a hotplate with precise temperature control and stirring consistency, then a standard analog heating and stirring unit may not be the right piece of equipment. However, when absolute accuracy is not required, these simpler units can be a reliable and economical alternative.
If stirring control and heat stability is essential for your application, then a digital hotplate stirrer may be the most viable solution, offering temperature accuracy ±8°C and stirring control greater than ±20 rpm. Equipment that can offer digital feedback will provide the greatest degree of accuracy and stability. Although the price point is much higher, the precise controls for temperature and stirring speed help to accurately monitor the temperature of the hotplate and the solution.
Temperature range
The temperature range achievable by your hotplate, as well as the uniformity of temperature across its surface, is determined by two major factors – top plate composition and the type of temperature control.
Top plates can be manufactured from three main materials: ceramics, porcelain and aluminum. Ceramic top plates for example, are able to heat up very quickly and have excellent chemical resistance. However, this type of hotplate is also susceptible to thermal shock and should not be used to heat sand baths or metal vessels. A porcelain hot plate, on the other hand, will offer improved temperature uniformity and better sample visibility.
Depending on the size and operating temperature, an aluminum top plate can offer superior heat uniformity of ±10°C.This can be an ideal heating solution for applications involving multiple vessels, but aluminum plates are more difficult to clean and are generally resistant to physical forces.
Volume
Hotplate stirrers are available in multiple sizes and configurations, so it's important that you select the correct unit for your application. Although this type of equipment is compact and portable in nature, the size of the magnetic bar is limited and usually needs to be varied depending on the nature of the solution.
Magnetic coupling strength
When operating in ‘normal’ conditions, the majority of stirrers will perform adequately when running at speeds between 100 rpm and 1000 rpm. However, when magnetic coupling strength is considered, the ability of the drive-magnet and stir bar combination should be the top priority depending on your solution's viscosity.
Overhead stirrers
Used for larger volumes and more viscous solutions, overhead stirrers are generally more robust than their magnetic counterparts. This type of stirrer is made up of rods, paddles, and stands and can be used for a variety of applications. The wide range of uses comes from the different stirring motions they can create, including:
- Paddle - gentle mixing for menial turbulence.
- Centrifugal - used in round vessels with narrow necks to create an axial flow.
- Turbine - used for drawing the material to be mixed from above.
- Dissolver - used for drawing the material from the top to bottom to create an axial flow.
- Propeller - used for drawing the material from the top to bottom to create an axial flow.
- Anchor - ideal for high viscosity liquids to create a tangential flow.
The verdict
Hotplate stirrers hold plenty of advantages but, depending on the viscosity and volume of your solution, they might not all be suited to your needs. In order to get the best match for your application, it's important to keep the above variables front-of-mind.
Overall, hotplate stirrers reduce effort, do not produce noise, and are more efficient compared to mechanical stirrers. As this type of equipment also doesn’t make use of moveable mechanical components, they usually have less wear and tear, making them a cost-effective solution in the long term.
Laboratory equipment by Delta Scientific
Delta Scientific supplies a wide range of laboratory equipment from world renowned brands for scientific research. Among our core product portfolio is a range of heating and drying equipment which forefront simplicity and ease-of-use in lab-based settings. Find out more about our full range of hotplate stirrers here, or get in touch with our team of experts.