A. James Clark School of Engineering

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Mapping of a Novel Zero-Liquid Discharge Desalination System Based on Humidification–Dehumidification onto the Field of Existing Desalination Technologies
(MDPI, 2022-08-30) Romo, Sebastian A.; Elhashimi, Mohammed; Abbasi, Bahman; Srebric, Jelena
It is well-established that increasing demands for fresh water are paving the way for desalination technologies. However, this correlates with an increase in brine production whose treatment and disposal can be complicated and expensive. This paper presents a thermodynamic model to bound the operation and development of a novel Humidification–Dehumidification-based system featuring Zero-Liquid Discharge and off-grid capabilities. The model employs conservation laws to find feasible state points to meet a baseline operation of 10 kg/h of product water separated from a hypersaline feed stream with 100 g/kg salt concentration. The system incurs in a 1039 kWh/m3 energy intensity that can be supplied completely by an electric source or in combination with heating steam. Follow-up sensitivity analysis highlights the robustness of the system in handling variations of 25% in product flowrate and 75% in feed salinity, practically without incurring any additional energy demands. The proposed system operating costs between 72 USD/m3 and 96 USD/m3 are comparable to those of existing brine disposal techniques. Furthermore, an operational map of existing desalination technologies suggests a niche characterized by high recovery rates and high feed salinities that are generally unfulfilled by conventional desalination methods. Overall, the proposed system shows potential for off-grid hypersaline brine treatment. This study sets the stage for future development of physics-based and data-driven predictive models as the proposed system iterates into a pilot plant deployment.
PRESSURE-BASED PREDICTION OF SPRAY COOLING HEAT TRANSFER
(2010) Abbasi, Bahman; Kim, Jungho; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
One of the main challenges of spray cooling technology is the prediction of local and average heat flux on the heater surface. It has been suggested that spray cooling heat transfer depends on the local spray mass flux. However, in this work it is hypothesized and demonstrated that local single-phase and boiling heat transfer can be predicted within ±25% of the measured values from the local normal pressure produced by the spray. In the single-phase study, hollow cone, full cone, and flat fan sprays operated at three standoff distances, five spray pressures, and two nozzle orientations were used to identify the relation between impingement pressure and heat transfer coefficient. PF-5060, PAO-2, and PSF-3 were used as test fluids, resulting in Prandtl number variation between 12-76. A 7×7 mm2 micro-heater array consisting of 96 platinum resistance heaters operated at constant temperature was used to measure the local heat flux. A separate test rig was used to make impingement pressure measurements for the same geometry and spray pressure. The heat flux data were then compared with the corresponding impingement pressure data to develop a pressure-based correlation for single-phase spray cooling heat transfer. Hollow cone and full cone PF-5060 sprays at three subcooling levels were used for the two-phase heat transfer study. The conventional wisdom is that the temperature at which critical heat flux (CHF) is observed changes with the droplet impact velocity, droplet number density, and droplet size. However, the present measurements indicate that although the magnitude of CHF is strongly dependent on the spray characteristics, the temperature at which CHF occurs lies within a very narrow band (about ±5°C) for smooth flat surfaces. This was also observed from local measurements at various radial distances using hollow cone and full cone spray nozzles where the local mass flux varies dramatically. This observation along with liquid properties and subcooling were used to develop a correlation to predict local CHF for PF-5060 sprays. The single-phase and CHF correlations were combined to predict local spray cooling curve within ±25% of the measured valued over the sprays impingement zones.