Carmeliet

Solar drying of soft cellular materials: a multiscale approach

Type. SNSF project

Funding. This PhD project is funded by the Swiss National Science Foundation (SNSF).

Duration. 3 years (2015-2018)

Collaborations. This project is a collaboration between the Chair of Building Physics (Dr. Defraeye, Prof. Carmeliet) at ETH Zurich and MeBioS (Prof. Nicolai) of KU Leuven.

Contact. Thijs Defraeye (principal investigator, defraeye@arch.ethz.ch).

Staff. Kevin Prawiranto (PhD student).

Project background. Solar drying has become a very attractive way of reducing the process energy required for drying of foods, wastewater sludge or wood. This convective drying process is particularly difficult to control due to fluctuations in incident radiation from the day-night cycle and in the presence of clouds. Additional complexity comes from the use of auxiliary heating or airflow and thermal energy storage systems to dampen these fluctuations, and the associated rehydration of the material. During dehydration, the material also undergoes large changes in properties and microstructure versus moisture content.

The primary objective of this project is to get insights in the underlying physics of solar drying of soft cellular materials, such as fruits, by approaching this convective drying process from a multiscale perspective, from cellular scale to dryer scale. To this end, we relate the heat and mass transport and deformation processes within the fruit and the exchange at the air-fruit interface to the environmental and operational conditions, and to the changes in tissue microstructure. We aim to unveil how fruits dry with respect to their location and loading density in the dryer and what the efficiency is of selected technologies to dampen fluctuations in solar radiation.

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