Thermodynamic balancing of a fixed-size two-stage humidification dehumidification desalination system

Chehayeb, Karim Malek; Narayan, G. Prakash; Zubair, Syed M.; Lienhard, John H.

doi:10.1016/j.desal.2015.04.021

Cited by 67 publications

(28 citation statements)

References 34 publications

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“…More recently, humidification dehumidification desalination (HDH) [5,6,7,8] has been developed as simple, low capital-cost thermal technology for treating ultra-saline produced waters [9,10].…”

Section: Context: Desalination Up To High Salinitymentioning

confidence: 99%

Energy efficiency of membrane distillation up to high salinity: Evaluating critical system size and optimal membrane thickness

et al. 2018

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This study presents a comprehensive analytical framework to design efficient single-stage membrane distillation (MD) systems for the desalination of feed streams up to high salinity. MD performance is quantified in terms of energy efficiency (represented as a gained output ratio, or GOR) and vapor flux, both of which together affect the specific cost of pure water production. Irrespective of the feed salinity, permeate or conductive gap MD (P/CGMD) performs better than direct contact MD (DCMD) when the heat transfer resistance of the gap (in P/CGMD) is lower than that of the external heat exchanger in DCMD. Air gap MD's (AGMD) better performance relative to the other configurations at high salinity and large system area can be explained in terms of its thicker 'effective membrane', which includes the air-gap region. CGMD and DCMD employing a thick membrane are also resilient to high salinity, similar to AGMD, while not being susceptible to the gap flooding that can harm AGMD's performance. A method is described to simultaneously determine the cost-optimal membrane thickness and system size as a function of the ratio of specific costs of heat energy and module area. At low salinity and small system size, GOR rises and flux declines with an increase in membrane area. For salty feed solutions, there exists a critical system size beyond which GOR also begins to decline. Since both GOR and flux are lower, no economic rationale favors operation above this critical size, irrespective of the costs of thermal energy and system area. A closed-form analytical expression for this critical system area is derived as a function of the feed salinity and two dimensionless ratios of heat transfer resistances within the MD module.Keywords: membrane distillation, high salinity, energy efficiency, system size, optimal membrane thickness * Corresponding author: lienhard@mit.

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Section: Context: Desalination Up To High Salinitymentioning

confidence: 99%

Energy efficiency of membrane distillation up to high salinity: Evaluating critical system size and optimal membrane thickness

et al. 2018

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“…Recent work by Magnanelli et al [21] showed that even when forces cannot be fully separated, the numerically optimal operating point is very close to that predicted by equipartitioning entropy production. Equipartitioning to increase the efficiency of desalination processes has been the subject of several studies [22][23][24], as will be discussed below.…”

Section: Equipartitioning Of Entropy Generationmentioning

confidence: 99%

Entropy Generation Minimization for Energy-Efficient Desalination

Lienhard

2018

Volume 6B: Energy

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Desalination systems can be conceptualized as power cycles, in which the useful work output is the work of separation of fresh water from saline water. In this framing, thermodynamic analysis provides powerful tools for raising energy efficiency. This paper discusses the use of entropy generation minimization for a spectrum of desalination systems, including those based on reverse osmosis, humidification-dehumidification, membrane distillation, electrodialysis, and forward osmosis. The energy efficiency of desalination is shown to be maximized when entropy generation is minimized. Equipartition of entropy generation is considered and applied to these systems. The mechanisms of entropy generation in these systems are characterized, including the identification of major causes of irreversibility. Methods to limit discarded exergy are also identified. Prospects and technology development needs for further improvement are mentioned briefly.

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“…• C was comparable to MSF, MSVMD and ORC-MVC [33], and HDH systems with extractions can demonstrate much higher thermodynamic efficiency [51]. In considering applications for these technologies operating on seawater, a dominant consideration is the system size, since some technologies are more scalable than others.…”

Section: Technology Comparisonmentioning

confidence: 99%

Entropy Generation of Desalination Powered by Variable Temperature Waste Heat

Warsinger

Mistry

Nayar

et al. 2015

Entropy

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Powering desalination by waste heat is often proposed to mitigate energy consumption and environmental impact; however, thorough technology comparisons are lacking in the literature. This work numerically models the efficiency of six representative desalination technologies powered by waste heat at 50, 70, 90, and 120• C, where applicable. Entropy generation and Second Law efficiency analysis are applied for the systems and their components. The technologies considered are thermal desalination by multistage flash (MSF), multiple effect distillation (MED), multistage vacuum membrane distillation (MSVMD), humidification-dehumidification (HDH), and organic Rankine cycles (ORCs) paired with mechanical technologies of reverse osmosis (RO) and mechanical vapor compression (MVC). The most efficient technology was RO, followed by MED. Performances among MSF, MSVMD, and MVC were similar but the relative performance varied with waste heat temperature or system size. Entropy generation in thermal technologies increases at lower waste heat temperatures largely in the feed or brine portions of the various heat exchangers used. This occurs largely because lower temperatures reduce recovery, increasing the relative flow rates of feed and brine. However, HDH (without extractions) had the reverse trend, only being competitive at lower temperatures. For the mechanical technologies, the energy efficiency only varies with temperature because of the significant losses from the ORC.Entropy 2015, 17 7531

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Thermodynamic balancing of a fixed-size two-stage humidification dehumidification desalination system

Cited by 67 publications

References 34 publications

Energy efficiency of membrane distillation up to high salinity: Evaluating critical system size and optimal membrane thickness

Energy efficiency of membrane distillation up to high salinity: Evaluating critical system size and optimal membrane thickness

Entropy Generation Minimization for Energy-Efficient Desalination

Entropy Generation of Desalination Powered by Variable Temperature Waste Heat

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