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.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2010

Author dc:creator

• Mistry, Karan H. (Karan Hemant)

Advisor dc:contributor.advisor

• John H. Lienhard, V.

• Mechanical Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/61911

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/61911