With much of the world facing some form of freshwater stress and climate change exacerbating most of those stressors, desalination is appearing increasingly necessary to ensure a robust freshwater supply for humanity’s future. However, desalination to date has proven costly, difficult and energy-intensive. Now, researchers from Iowa State University, Penn State University, the University of Texas at Austin, DuPont Water Solutions and Dow Chemical are using supercomputing to study more efficient means of desalinating saltwater.
One area to learn from, it turns out, is biological membranes, which have proven remarkably efficient in filtering undesired compounds (including salt) from water – but those membranes have been challenging to scale up. The researchers conducted a series of simulations of water flow through four different polymer membranes to identify which factors might make such membranes more (or less) effective.
This was no trivial task: “The simulations themselves posed computational challenges, as the diffusivity within an inhomogeneous membrane can differ by six orders of magnitude,” explained Biswajit Khara, a doctoral student in mechanical engineering at Iowa State, in an interview with Mike Krapfl, also of Iowa State.
To run these intensive simulations, the researchers turned to the Texas Advanced Computing Center (TACC). At TACC, they used the Stampede2 supercomputer: a Dell EMC system powered by Intel Xeon Phi CPUs that delivers 10.7 Linpack petaflops and placed 25th on the most recent Top500 list.
The secret sauce of desalination, it turns out: exacting uniformity of the mesh, accurate to the nanometer scale. “The simulations were able to tease out that membranes that are more uniform – that have no ‘hot spots’ – have uniform flow and better performance,” said Baskar Ganapathysubramanian, a professor of mechanical engineering at Iowa State who worked on the high-performance computing aspects of the research. “The secret ingredient is less inhomogeneity.”
The discovery made the cover of the January 2021 issue of Science, in part due to a striking visualization of the water passing through the membrane. In the visualization, created by TACC’s Greg Foss and the Iowa State researchers, the high-pressure, high-salinity water (red) passes through the membrane (gold, with the water in white) and emerges as lower-salinity water (blue).
“We’re showing how water concentration changes across the membrane.” Ganapathysubramanian said. “This is beautiful. It has not been done before because such detailed 3D measurements were unavailable, and also because such simulations are non-trivial to perform.”
“These simulations provided a lot of information for figuring out the key to making desalination membranes much more effective,” said Ganapathysubramanian. The next step: figuring out how to make those ultra-dense, ultra-uniform membranes to improve desalination processes.
To read TACC’s Mike Krapfl’s article on this research, click here.