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Research

• Topics

  Desalination, Energy and Environment, Water and Power Cogeneration, Second Law Analysis, Optimization, Economics.

• Purpose

  To develop a better understanding of the thermodynamics involved in producing potable water from seawater.

• Adviser

  John H. Lienhard V

• Doctoral Thesis: Irreversibilities and Nonidealities in Desalination Systems

  Energy requirements for desalination systems must be reduced to meet increasing global demand for fresh water. This thesis identifies thermodynamic limits for the energetic performance of desalination systems and establishes the importance of irreversibilities and solution composition to the actual performance obtained.

  Least work of separation for a desalination system is derived and generalized to apply to all chemical separation processes driven by some combination of work, heat, and chemical energy (fuel) input. At infinitesimal recovery, least work reduces to the minimum least work of separation: the true exergetic value of the product and a useful benchmark for evaluating energetic efficiency of separation processes. All separation processes are subject to these energy requirements; several cases relevant to established and emerging desalination technologies are considered.

  The effect of nonidealities in electrolyte solutions on least work is analyzed through comparing the ideal solution approximation, Debye-Hückel theory, Pitzer's ionic interaction model, and Pitzer-Kim's model for mixed electrolytes. Error introduced by using incorrect property models is quantified. Least work is a strong function of ionic composition; therefore, standard property databases should not be used for solutions of different or unknown composition.

  Second Law efficiency for chemical separation processes is defined using the minimum least work and characterizes energetic efficiency. A methodology is shown for evaluating Second Law efficiency based on primary energy inputs. Additionally, entropy generation mechanisms common in desalination processes are analyzed to illustrate the effect of irreversibility. Formulations for these mechanisms are applied to six desalination systems and primary sources of loss are identified.

  An economics-based Second Law efficiency is defined by analogy to the energetic parameter. Because real-world systems are constrained by economic factors, a performance parameter based on both energetics and economics is useful. By converting all thermodynamic quantities to economic quantities, the cost of irreversibilities can be compared to other economic factors including capital and operating expenses.

  By applying these methodologies and results, one can properly characterize the energetic performance and thermodynamic irreversibilities of chemical separation processes, make better decisions during technology selection and design of new systems, and critically evaluate claimed performance improvements of novel systems.

  PhD Thesis: DSpace@MIT, Direct download (PDF)

  PhD Defense: Direct download (PDF)

• Master's Thesis: Second Law Analysis and Optimization of Humidification-Dehumidification Desalination Cycles

  Humidification-Dehumidification (HD) desalination is a thermal distillation method that has the potential to be driven using solar heating. It is a promising technology that can potentially bring safe drinking water to people of the developing world. Surprisingly, few systematic efforts have been made to find the best HD cycles or to improve and optimize existing cycles.

  This thesis applies irreversibility analysis to characterize HD desalination cycles and to identify how to further improve cycles and components. It is shown that minimizing the specific entropy generation of the cycle maximizes the gained output ratio (GOR). It is also shown that each cycle has one limiting component that cannot be substantially improved and a second component that should be the target of efforts to minimize entropy generation. Finally, the failure of exergy analysis to yield conclusive results for on-design HD cycle analysis is discussed briefly.

  Following the Second Law analysis, an optimization effort is performed using nonlinear programming techniques in order to optimize HD desalination cycles for operating conditions that result in maximum GOR. Closed air, open water and open air, open water cycles with either air and water heating were considered in this analysis. Numerical optimization resulted in substantial improvement in GOR for all four cycle types considered. It was found that the GOR of the cycles decreases with increasing component terminal temperature difference (TTD) and that different cycles perform best at different temperature differences. Optimization also revealed that some counterintuitive design configurations can result in superior performance under the appropriate operating conditions.

  Other topics discussed include the behavior of exergy for pure substances and psychrometric mixtures as well as the effect of salinity on the performance of HD cycles.

  SM Thesis: DSpace@MIT, Direct download (PDF)

• Publications

  1. K. H. Mistry, J. H. Lienhard V, S. M. Zubair, Effect of entropy generation on the performance of humidification-dehumidification desalination cycles, International Journal of Thermal Sciences 49 (9) (2010) 1837--1847.
  2. G. P. Narayan, K. H. Mistry, M. H. Sharqawy, S. M. Zubair, J. H. Lienhard V, Energy effectiveness of simultaneous heat and mass exchange devices, Frontiers in Heat and Mass Transfer, 1 (2) (2010) 1--13.
     
     Available on DSpace@MIT
  3. K. H. Mistry, A. Mitsos, J. H. Lienhard V, Optimal operating conditions and configurations for humidification-dehumidification desalination cycles, International Journal of Thermal Sciences 50 (5) (2011) 779--789.
  4. K. H. Mistry, R. K. McGovern, G. P. Thiel, E. K. Summers, S. M. Zubair, J.H. Lienhard V, Entropy generation analysis of desalination technologies, Entropy 2011, 13(10) 1829--1864.
     
     Available on DSpace@MIT
  5. K. H. Mistry, M. A. Antar, J. H. Lienhard V, An improved model for multiple effect distillation, Desalination and Water Treatment 51 (4--6) (2013) 807--821.
     
     Available on DSpace@MIT
  6. K. H. Mistry, J. H. Lienhard V, Effect of composition and nonideal solution behavior on desalination calculations for mixed electrolyte solutions with comparison to seawater, Desalination 318 (2013) 34--47.
  7. K. H. Mistry, J. H. Lienhard V, Effect of nonideal solution behavior on desalination of a sodium chloride (NaCl) solution and comparison to seawater, Journal of Energy Resources Technology. 135(4), 042003 (Jun 24, 2013).
  8. K. H. Mistry, J. H. Lienhard V, Generalized least energy of separation for desalination processes, Entropy 2013, 15(6) 2046--2080.
  9. K. H. Mistry, J. H. Lienhard V, An Economics-Based Second Law Efficiency, Entropy 2013, 15(7) 2736--2765.
  10. D. M. Warsinger, K. H. Mistry, K. G. Nayar, H. W. Chung, J. H. Lienhard V, Generation of Desalination Powered by Variable Temperature Waste Heat, Entropy 2015, 17(11) 7530--7566.

• Conferences

  1. K. H. Mistry, G. P. Naryan, A. Mitsos, J. H. Lienhard V, Multi-pressure humidification-dehumidification desalination using thermal vapor compression and energy recovery, Proceedings of the 21st National & 10th ISHMT-ASME Heat and Mass Transfer Conference. ISHMT_USA_015. 1--9. December 27--30, 2011. IIT Madras, India.
     
     Available on DSpace@MIT
  2. K. H. Mistry, M. A. Antar, J. H. Lienhard V, An improved model for multiple effect distillation, European Desalination Society. April 23--26, 2012. Barcelona, Spain. DOI:10.1080/19443994.2012.703383
     
     Available from Taylor & Francis Group
  3. K. H. Mistry, J. H. Lienhard V, Effect of nonideal solution behavior on desalination of a sodium chloride (NaCl) solution and comparison to seawater, Proceedings of ASME 2012 International Mechanical Engineering Congress and Exposition. IMECE2012-88261. November 9--15, 2012. Houston, Texas, USA.
     
     Available on DSpace@MIT

• Patents

  1. G. P. Narayan, K. H. Mistry, J. H. Lienhard V, and S. M. Zubair. High-Efficiency Thermal-Energy-Driven Water Purification System. Assigned to MIT, Patent Pending. #USSN 13/028170, Feb 15, 2011.

• Relevant Links

  Lienhard Research Group
  Center for Clean Water and Clean Energy
  Rohsenow Kendal Heat Transfer Laboratory
  MIT Department of Mechanical Engineering
  Massachusetts Institute of Technology