Quang Nhat Tran,Nhi Ngoc Thi Vo,Thao Thi Pham,Hai Son Truong-Lam
Freshwater scarcity is a critical issue in Vietnam, particularly in the Mekong Delta, a densely populated region with an agriculture-based economy. This scarcity is largely driven by saltwater intrusion during the dry season, severely affecting both agriculture and the local economy. In response, advanced desalination technologies have been proposed. In this study, we investigated the use of cyclopentane (CP), a liquid guest molecule, and 1,1,1,2-tetrafluoroethane (R134a), a gaseous guest molecule, as hydrate formers to desalinate saline water from the Mekong Delta. This study aimed to evaluate and compare the freshwater recovery efficiencies of these hydrate formers and assess the potential of hydrate technology for practical application in the region. We performed thermodynamic and kinetic investigations on sodium chloride solutions (1.0–3.5 wt%), representing the salinity levels of seawater in the Mekong Delta, to establish a laboratory-scale desalination system. The results showed a consistent thermodynamic trend: the higher concentration of samples leads to the longer time of hydrate formation to achieve the conversion of water into hydrates exceeding 60 %. Additionally, the CP and R134a hydrate structures were characterized using Raman spectroscopy, which revealed significant changes in the water peak and C–H band signal during the hydrate formation process. After a single-stage hydrate treatment using CP and R134a, the removal efficiencies for ions and total dissolved solids in saline water samples from the Mekong Delta exceeded 75 % and 70 %, respectively. These findings serve as a reference for developing a larger-scale hydrate-based desalination technology to address the challenges of saltwater intrusion in the Mekong Delta region.
The feasibility of combining novel halogenated hydrocarbon-based working pairs with low-pressure compression-assisted absorption refrigeration system (LCARS) was proved for the first time from the experimental perspective. An experimental prototype of the absorption-compression hybrid refrigeration system with a 1 kW cooling capacity was designed and tested to explore actual performances of selected R134a-DMETEG and performance improvements from compression in LCARS. At an evaporation temperature of approximately 5 °C, as the hot water inlet temperature and the solution flow rate change from 75 to 95 °C and 1.2–2.7 L/min, respectively, the coefficient of performance (COP) in the single-stage absorption refrigeration system (SSARS) varies from 0.211 to 0.412. At an increased evaporation temperature of approximately 10 °C, as the hot water inlet temperature and flow rate increase from 70 to 80 °C and 1.18–2.89 L/min, respectively, the COP in the SSARS varies from 0.238 to 0.552, while the COP in LCARS is improved and varies from 0.470 to 0.617. The LCARS increases the COP by a maximum of 91.04 % and can utilize a lower-grade heat source more efficiently due to its higher optimal COP at reduced hot water inlet temperatures. This study provided one feasible technical approach of combined use of R134a-DMETEG and LCARS to make up for the application limitations of traditional working pairs, contributing to application promotions of absorption systems, especially for the occasions with high requirement on safety and lightweight.
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