PhD for project: "Enhancing the local water cycle via evaporation for a sustainable water supply"

Topic background 

In many arid regions, water resources are scarce due to the low rainfall. Water scarcity leads to lowered agricultural productivity and impairs the population’s health. This situation is expected to deteriorate due to climate change, growing population, and agricultural activities. Existing methods of increasing freshwater resources, such as water desalination do not solve the root cause of the problem i.e. a lack of sufficient precipitation. To change this situation, we propose a novel approach that aims to sustainably restore the local water cycle. Restoring the water cycle requires additional water evaporation to lower the condensation level in the atmospheric boundary layer, which in turn is expected to give enhanced water precipitation in the watershed making more water available. A restored water cycle can sustain itself as the evaporated water returns as precipitation within the watershed.

Research challenges 

Water availability is crucial for restoring a well-functioning local water cycle. In this work, we will investigate technologies to produce water vapour from brackish or seawater via direct evaporation, driven by abundant solar energy. The basic principle is that solar radiation is converted into heat to increase the water temperature. This increased temperature leads to increased vapour pressure, which in turn causes the water vapour transport to the atmosphere through a suitable membrane or from a wet surface. This membrane is the interface between the brackish or seawater and the atmosphere that prevents brine leakage into the environment. We will investigate the suitability of different processes, namely membrane evaporation vs. pervaporation. The performance of this process will strongly depend on the atmospheric conditions, like solar irradiance, turbulence in the lower boundary layer, temperature, wind speed, and humidity profiles. These conditions are strongly variable in time and space. Therefore, understanding and connecting the mass transport processes occurring inside and adjacent to the membrane surface with the surrounding atmosphere is essential.

Objectives and methodology 

The aim of the project is to understand the performance of direct evaporation technology under realistic atmospheric conditions. As most membrane systems are applied in relatively stable conditions, the interaction between measured evaporation performance and the surrounding atmosphere remains unknown. An experimental setup will be developed to assess the evaporation performance and study underlying mass and heat transfer processes. The experimental data obtained from the laboratory will be upscaled using evaporation process modeling and an atmospheric boundary layer model. Notably, the atmospheric boundary model is part of a separate PhD project that will investigate the overall performance and impacts of the studied membrane system on the localized water cycle in previously selected geographical regions. The outcome of this work is expected to steer the technology development and may lead to the identification of more suitable routes.