As the global population grows and temperatures rise, the demand for freshwater increases. The 2012 Intelligence Community Assessment on Global Water Security warned about the lack of adequate drinking water becoming a destabilizing factor by 2040 in countries with insufficient technical ability to solve their water problems. Water scarcity in underdeveloped countries drives their populations to consume unsafe water, increasing the danger of water-borne diseases. Many countries have been turning saline waters, such as the sea waters or brackish waters, into drinking water using desalination techniques. Most developed countries employ Reverse Osmosis (RO), which is highly efficient. However, using RO on a large scale is not feasible for many countries that cannot afford the costs associated with it. People in remote regions without adequate infrastructure resort to less advanced, low-cost, small-scale technologies such as solar stills that use evaporation and condensation to remove impurities from saline water. While solar stills are affordable and do not require electricity to operate, they have considerably low water production outputs, especially compared to other technologies such as RO, thus making them inadequate to support a small community’s demands for drinking water. That is why NMSU’s Assistant Professor of Mechanical Engineering Sarada Kuravi is addressing this issue by developing innovative thermal science-based approaches that have the potential to improve solar stills’ output by 15x.
Tell us about yourself, how long you have been at NMSU, your research areas, the courses do you teach.
After I finished my PhD in 2009, I joined my postdoctoral adviser’s group, where I was exposed to challenges of developing cost-competitive renewable and alternative energy technologies. I joined NMSU in Fall 2014 as an Assistant Professor of Renewable Energy and Thermal Sciences. I think the research in this field is truly multidisciplinary, and the challenging part of it is that any newly-developed renewable energy technology must be more or at least as affordable as the conventional power technologies.
For conducting this research, I started the Renewable Energy and Thermal Systems Laboratory (REThermS Lab) at NMSU. My students work on a variety of projects with a focus on the fundamental thermal science and applied aspects as well as the economics of renewable and clean energy systems, water desalination, alternative energy systems such as hydrogen, building energy, energy consumption in fluid transport, and waste heat recovery with solar thermal energy, thermal energy storage, and thermodynamics as the central subjects.
I usually teach thermal science courses such as Thermodynamics and Heat Transfer. For the past three years, I have also been offering a dual senior-level elective/graduate course in the department titled, ‘ME 481: Alternative and Renewable Energy’, wherein I discuss the current state of the art in solar, geothermal, wind, hydro, biomass, and nuclear power technologies from the perspectives of thermal science and engineering, implementation, and economics.
Tell us about this project. How does it combine your expertise in renewable thermal energy research with water desalination?
Solar stills have many advantages when used for pure water production in rural or remote areas. They are cheap and easy to implement and can be used to produce purified water in a modular fashion. However, the critical issue is the low water production rate. In this project, I am using my prior experience working on concentrating solar power (CSP) projects and addressing this issue by significantly increasing the solar energy input to the still (the solar still) and enhancing the heat transfer process rates at various steps of the distillation process.
My collaborators and I have been working on this approach for almost two years now. College of Engineering Mini Grant Program first funded the idea, which enabled us to obtain the preliminary results. The project was later supported by NM-WRRI, which helped us identify a pathway for its successful implementation and to demonstrate the initial feasibility of using CSP for a still. I wrote a proposal to the Bureau of Reclamation which was successful. The award will help us combine all our prior knowledge and pursue a comprehensive demonstration of the idea by including the heat transfer enhancements along with CSP, solar heat recovery and storage, large-scale testing, and economics.
Can you tell us about your innovative approach?
When diffused sunlight is incident upon a still, water changes phase to vapor by evaporation, and this is what happens in state-of-the-art solar stills, but evaporation is a very slow process. Typically, thermal distillation approaches require a tremendous amount of thermal energy (usually obtained by burning fuels). In our project, we will use a new method to concentrate the solar energy as in a CSP system and focus it onto the saline water in the still. Solar energy is abundant and free. This CSP-based approach will increase the saline water temperature to induce boiling. None of the solar still techniques until now were able to achieve boiling at atmospheric pressures due to the energy-intensive nature of the distillation process. The boiling of the saline water will result in a rapid vapor generation rate. A simple explanation of boiling versus evaporation is the boiling of water in a pan to rapidly produce vapor versus leaving the water in a cup in a room to let it evaporate over time. The vapor condensation rate must match the increased vapor generation rate and is also a focus of this project. A passive heat storage system will be developed for enabling night-time operation.
My collaborators are Drs. Pei Xu and Huiyao Wang from Civil Engineering and Drs. Young Ho Park and Krishna Kota from Mechanical and Aerospace Engineering. They work on aspects such as water quality analysis, boiling and condensation heat transfer enhancements, solar thermal storage, and still design and performance testing. The still enhancement techniques that we are pursuing are highly scalable, cost-effective, and together can make this concept competitive, especially in arid and semi-arid regions and in rural or remote areas.
What other projects are you working on?
I am working on a high-efficient regenerator system for refrigeration applications in space, new materials for roof panel systems, thermal energy storage for buildings, novel receivers for supercritical carbon dioxide power cycle-based concentrating solar power plants, and studying the science of particulate suspensions. The umbrella research theme for all my projects is the same: to increase the thermal and the thermodynamic performance in an application in a cost-effective manner for/with renewable and/or alternative energy systems.
These are all excellent projects with enormous positive social impact. Thank you for advancing engineering research and education at NMSU.
Dr. Sarada Kuravi can be reached at firstname.lastname@example.org.