Product and Process Engineering - Delft University of Technology

Erik Sewalt

Erik Sewalt

Drying and colliding droplets in a spray dryer

Contact details

  • Erik Sewalt
  • Delft University of Technology
  • Dept. Chemical Engineering - PPE
  • Room E2.480
  • van der Maasweg 9, Delft, The Netherlands

Research interests and expertises

  • Spray drying
  • Single droplet drying
  • Transport phenomena
  • Optical coherence tomography


  • MSc, Food Technology (Sustainable Process Engineering), Wageningen University & Research, Netherlands, 2017
  • BSc, Food Technology, Wageningen University & Research, Netherlands, 2015


Research description

In spray drying a powder is made by atomizing a solute-containing liquid and rapidly drying the resulting droplets in a hot air stream. Advective transport by droplet shrinkage competes with the mobility of internal components and is typically faster, which causes accumulation of these components near the liquid-gas interface. This may result in the formation of a skin layer, which in turn affects the drying process. The development of the skin can cause a variety of dried particle structures to develop. A “hollow” morphology, is shown in the figure below.

For a more efficient process and better control over the product properties the industry is trying to make a macro-scale model of the spray drier, which can be used as a predictive tool. However, there are two key aspects that are inadequately understood. These are the influence of timescale on the drying process, specifically for droplets < 100 µm, and how to incorporate the result of droplet collisions into the model.

    Scanning Electron Microscopy image of solid particle from spray dried whole milk

My project focuses on the collisions of semi-dried droplets. For these collisions it is important to know the state of the droplets upon the collisions, hence a large portion of my research is dedicated to the drying process of a single droplet itself. Finally, I aim to develop relations between the initial drying & collision parameters and the result of the collisions (e.g .sticking, bouncing). These relations are meant to be implemented into the macro-scale spray drier model.

Student Projects

I currently have two student projects available related to my research:

  • Drying solute-containing droplets in a microfluidic dryer (Msc, experimental)
  • Revealing how droplets transform into particles with Optical Coherence Tomography (Msc, experimental)
  • If you are interested in the topic or in a Bsc/Msc project, please contact me at

. © Delft University of Technology - PPE group 2015