What factors affect the particle shape of the dried products in a lab spray dryer?

Hey there! As a supplier of Lab Spray Dryers, I've gotten a ton of questions about what affects the particle shape of dried products in these machines. So, I thought I'd sit down and share some insights on this topic.

First off, let's talk about what a lab spray dryer does. It's a nifty piece of equipment that turns liquid solutions or suspensions into dry powders by spraying them into a hot drying chamber. This process is super useful in various industries, like food, pharmaceuticals, and chemicals.

Now, onto the factors that can mess with the particle shape of the dried products.

1. Feed Properties

The stuff you're putting into the spray dryer, known as the feed, plays a huge role.

Viscosity

If the feed has a high viscosity, it can be a real pain. High - viscosity liquids don't atomize as well as low - viscosity ones. When you try to spray a thick liquid, the droplets tend to be larger and more irregular. These large droplets take longer to dry, and as a result, the particles can end up being misshapen. For instance, in the production of some high - protein plant extracts, the high viscosity of the feed can lead to non - spherical particles. You can check out our Plant Extract Spray Dryer Machine which is designed to handle different feed viscosities to some extent.

Solids Concentration

The amount of solids in the feed also matters. A high solids concentration can cause the droplets to have a higher internal resistance during drying. As the water evaporates, the solids start to come together, and if there are too many solids, they can clump up and form irregular particles. On the other hand, a very low solids concentration might result in particles that are too small and fragile. You need to find that sweet spot for the best particle shape.

Surface Tension

Surface tension affects how the liquid forms droplets during atomization. Liquids with high surface tension tend to form larger, more spherical droplets. But if the surface tension is too high, the droplets may not break up easily, leading to larger particles. You can adjust the surface tension of the feed by adding surfactants in some cases, but this has to be done carefully as it can also affect other properties of the final product.

2. Atomization Process

This is where the liquid gets turned into tiny droplets, and it's a crucial step for getting the right particle shape.

Nozzle Type

There are different types of nozzles used in spray dryers, like pressure nozzles, two - fluid nozzles, and centrifugal nozzles. Pressure nozzles work by forcing the liquid through a small orifice under high pressure. They can produce relatively fine and uniform droplets, but if the pressure is not set correctly, the droplets can be uneven. Two - fluid nozzles mix the liquid with a gas (usually air) to break it up into droplets. These can give good control over droplet size, but the gas - liquid ratio needs to be just right. Centrifugal nozzles, which are commonly used in high - speed centrifugal spray dryers, spin the liquid at high speed to create droplets. Our High Speed Centrifugal Spray Drying Machine for Powder uses this type of nozzle, and it's great for getting consistent particle shapes when set up properly.

Atomization Pressure and Speed

Whether you're using a pressure nozzle or a centrifugal nozzle, the pressure and speed are key. Higher atomization pressure or speed generally leads to smaller droplets. But if you go too high, you might create a lot of fine dust, which can be a problem. And if it's too low, the droplets will be large and the particles won't be the right shape. You have to find the optimal pressure or speed for your specific feed and the desired particle size and shape.

3. Drying Conditions

Once the droplets are formed, the drying process takes over, and this can also impact the particle shape.

Inlet Air Temperature

The temperature of the hot air entering the drying chamber is a big deal. A high inlet air temperature can cause the outer layer of the droplet to dry quickly, forming a crust. As the inner part of the droplet continues to evaporate, the pressure inside can build up and cause the particle to burst or form a hollow structure. On the other hand, a low inlet air temperature may result in incomplete drying, and the particles can stick together, creating irregular clumps.

Airflow Pattern

The way the hot air flows inside the drying chamber affects how the droplets dry. A well - designed airflow pattern ensures that the droplets are evenly exposed to the hot air. If the airflow is uneven, some droplets may dry faster than others, leading to a mix of particle shapes. For example, in a poorly designed dryer, some areas might have a high - velocity airflow that dries the droplets too quickly, while other areas have a low - velocity airflow that causes incomplete drying.

Residence Time

This is how long the droplets stay in the drying chamber. If the residence time is too short, the droplets won't dry completely, and you'll end up with wet or sticky particles. If it's too long, the particles may over - dry, become brittle, and change shape. You need to adjust the residence time based on the feed properties, atomization conditions, and the desired particle characteristics.

4. Additives and Solvents

Sometimes, you add things to the feed to improve the properties of the final product. But these additives can also affect the particle shape.

Antioxidants and Preservatives

Adding antioxidants or preservatives can change the physical and chemical properties of the feed. For example, some antioxidants may increase the viscosity of the feed, which as we've seen, can affect atomization and particle shape. You need to test how these additives interact with the feed and the drying process to make sure they don't mess up the particle shape too much.

Solvents

If you're using solvents in the feed, their evaporation rate can have an impact. Fast - evaporating solvents can cause the droplets to dry quickly on the outside, while slow - evaporating solvents may lead to longer drying times. This can result in different particle shapes, from solid and spherical to hollow or irregular.

Alright, so now you know about the main factors that can affect the particle shape of dried products in a lab spray dryer. But how can you make sure you get the best results?

Well, it all starts with choosing the right spray dryer for your needs. Our 5KG/H Laboratory Spray Dryer is a great option for small - scale experiments and production. It allows you to precisely control the atomization, drying conditions, and other parameters to optimize the particle shape.

If you're in the market for a lab spray dryer or have more questions about getting the perfect particle shape, don't hesitate to reach out. We're here to help you with all your spray - drying needs, whether it's for plant extracts, powders, or any other product. Contact us to start a discussion about your specific requirements and let's work together to get the best results for your business.

References

• Masters, K. (1991). Spray Drying Handbook. Longman Scientific & Technical.
• Mujumdar, A. S. (ed.). (2007). Handbook of Industrial Drying. CRC Press.