The Drying Process

What is the first thing that comes to your mind when you hear the word “drying”?

My first thought is always a hair dryer. And that even though my wife says: “You don’t need any dryer for the few hairs you have.” And she's right! Oh, my goodness, did I just say that? Another possible answer is the ever-popular drying rack.

And now we've got it!  An example for an air-drying process (drying rack) and one for a technical drying process (hair dryer). What is the difference between these two processes? A sharp separation is not always possible because the principle of air drying is also an integrated part of many methods of technical drying.

The facts about drying

All drying processes that use only the natural energy of the sun and the wind are air drying processes. And we speak of technical drying as soon as technical aids are used that consume additional energy for drying.

Our ancestors already used the air-drying process to obtain salt from seawater or to preserve food and feed. They dried fruits and grains in the sun or in drying chambers. Grass was dried to make hay for cows, sheep and other animals to get through the winter. Drying was essential for survival for many people in the past. And it still is today.

Thanks to the possibilities of technical drying, nowadays drying is more than just preserving food and feed. Drying is furthermore used for:

● Reducing the volume and weight from goods for having advantages in transport, storage, and packing.

● Product design to produce certain properties, qualities, and forms.

Coffee is an excellent example. It cannot be made by freshly harvested coffee beans. The drying process, the roasting, is essential for further processing, taste and storability. Or take milk as an example. After it has been processed in a spray dryer into milk powder, it has lost a lot of volume and weight. The milk powder has a much longer storage life, can be transported at low cost, and can even be added to other powders easily.

Experts estimate that about 10% of the electricity consumed in industry is used for drying processes. This shows how important drying is in industrial manufacturing and that it needs a lot of energy.

Before we look at the technical drying processes, we should clarify what drying is. Don’t worry, the answer is easy. A common definition is: “Drying is the withdrawal of liquids from a substance or an object.” No more and no less.

But drying on an industrial scale isn’t as simple as the definition may suggest. In some cases, it can be really challenging. That is why there are many different processes and a lot of specialised systems needed for drying. These systems are complex and have chips inside. They need electricity, a couple of motors, heating, cooling in some cases and

sensors. They are huge and located in factory buildings. They need care from an engineer, they sometimes drink oil and follow the word via logically programmed procedures. And wake up, I’m not talking about your partner…

Every child knows the difference between wet and dry. And every child knows that wet clothes should be dried. But how does the drying process work?

Humidity is removed by evaporation or vaporisation. Evaporation is the transition from the liquid to the gaseous state of aggregation below the boiling point. Vaporisation is the conversion of a substance from the liquid or solid state into the gaseous state at the boiling temperature. So please, don’t tell anyone that the humidity from your laundry actually is vaporising…

In every drying process, three processes take place:

Heat transport: Heat is transferred to the drying goods or to the surrounding atmosphere

Humidity transport: The liquids change their aggregate state to gaseous and emerge from the to be dried solid

Vapour transport: The vapor is carried away by the surrounding gases (air)

It has become common practice to classify thermal drying systems according to the type of heat transport. The three most important types of construction are: Convective drying, Contact drying and drying by radiation.

Thermal drying stresses the material to be dried. Whether hair, bricks, or potatoes. Choosing the most suitable process is therefore not always easy. Beside the material properties, the issues of safety, economy, and the impact on the environment also play an important role in the selection of the drying processes.

A Little Overview For You

About Thermal Drying Systems

At Triangular, we help you find the best partner for your drying tasks. No matter if you are a system owner, a material owner or maybe an industry expert. With our new and innovative services, we can connect you with the best fitting partner to achieve your goals – worldwide.