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Improving sweeping gas membrane distillation applicability and specific thermal energy consumption

Ravisankar, Vishnu Arvind (2018) Improving sweeping gas membrane distillation applicability and specific thermal energy consumption. PhD thesis, Murdoch University.

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The compatibility of sweeping gas membrane distillation (SGMD) with simple solar thermal devices, and ambient air and pressure operation make it attractive for desalination in off-grid remote communities.

Since simplicity of operation is critical for small-scale, remote applications and unbuffered, solar thermal energy generation varies greatly through time, SGMD operation will also be highly variable. However, theoretical models that accurately predict performance of variable-input (feed temperature, solar thermal input) SGMD systems are lacking in the literature. This study develops a robust transient model to accurately estimate SGMD performance when directly coupled to a highly variable solar thermal energy source, verifies its simulation against experimental data, and highlights the differences between the proposed and the conventional predictive models. Depending on input signal characteristics, the transient model was 40% more accurate as opposed to the traditional models, for the particular cases considered.

Widespread acceptance of SGMD has been hampered by its high-energy consumption relative to conventional technologies like reverse osmosis (RO). Additionally, conventional literature asserts without validation, that it is not possible to reduce energy consumption in SGMD, thus leading to it being largely unstudied. To address the issue of high energy consumption, an innovative multistage SGMD system design with internal latent heat recovery was developed. The study showed up to 10% reduction in energy consumption in the new design in laboratory operation. To investigate if the new design was capable of lowering specific thermal energy consumption (STEC) further, an optimization of operational parameters was conducted, using energy consumption and permeate flux as constraints. Optimization of the prototype yielded only small advantages over a system without internal heat recovery capabilities. Externally recovering exit airstream energy into makeup brine shows additional reduction in energy consumption (up to 10%) in the proposed and conventional designs with comparable permeate flux. The analyses also indicated directions for future design enhancements, which may improve this result.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Engineering and Information Technology
United Nations SDGs: Goal 7: Affordable and Clean Energy
Supervisor(s): Ela, Wendell and Li, Linda
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