Water Desalination Using Solar Thermal Collectors Enhanced by Nanofluids

Exploring the use of nanofluids in pump-free systems for solar thermal applications

By using nanofluids as a working fluid in pump-free designs, thermal energy systems can become more efficient and have reduced maintenance costs, ultimately extending the system's lifespan. In this paper, our goal is to investigate unsteady phenomena in the irradiation process and highlight their significance. To accomplish this, we conducted a series of experiments using a square loop of glass pipes filled with carbon black nanofluids and irradiated with a halogen lamp to simulate solar irradiation. The resulting convective motion of the nanofluids allowed us to observe the performance of different concentrations of carbon black, with 0.005-0.01 wt.% proving to be the most effective. Additionally, we identified unsteady processes that occur at the beginning of the process or when the irradiation changes. Finally, we employed computational fluid dynamics simulations to gain further insight into these phenomena.

Nanoparticle-Enhanced PVDF Flat-Sheet Membranes for Seawater Desalination in Direct Contact Membrane Distillation

In this study, hydrophobic functionalized carbon nanotubes (fCNTs) and silica nanoparticles (fSiO₂NPs) were incorporated into polyvinylidene fluoride (PVDF) flat-sheet membranes to improve their performance in membrane distillation (MD). The performance of the as-synthesized membranes was evaluated against commercial reference polytetrafluoroethylene (PTFE) flat-sheet membranes. The water contact angle (WCA) and liquid entry pressure (LEP) of the PVDF membrane were compromised after incorporation of hydrophilic pore forming polyvinylpyrrolidone (PVP). These parameters were key in ensuring high salt rejections in MD processes. Upon incorporation of fCNTS and fSiO₂NPs, WCA and LEP improved to 103.61° and 590 kPa, respectively. Moreover, the NP additives enhanced membrane surface roughness. Thus, an increase in membrane roughness improved WCA and resistance to membrane wetting. High salt rejection (>99%) and stable fluxes (39.77 kg m^-2 h^-1) were recorded throughout a 3 h process evaluation where 3.5 wt% NaCl solution was used as feed. These findings were recorded at feed temperature of 60 ℃. Evidently, this study substantiated the necessity of high feed temperatures towards high rates of water recovery.

Electro dialysis reversal (EDR) performance for reject brine treatment of reverse osmosis desalination system

In this study, the performance of bench-scale EDR was evaluated using the samples taken from the 1st and the 2nd stage RO from the Brackish Water Reverse Osmosis (BWRO) plant in Eshtehard, Iran. The measurements indicated that original TDS of the aquifer brackish water was equal to 3,229–3,664 mg/L, whereas TDS of the 1^st stage RO brine was between 5,500 and 7,700 mg/L, that TDS of the 2^nd stage RO brine was in the range of 9,500–10,600 mg/L. A batch bench-scale EDR system of 12 l/h was used with a direct electric current at three different scenarios. In the first, the brine was fed at 20°C (as a reference regulated point). In the second, temperature (14, 20, 26.5°C), and in the third, voltage were changed (6, 12, 18, 24 V) to investigate their influences on performance of the EDR process, while the other operational parameters (feed flow rate, recovery ratio, quality of feed brine)were kept constant. Based on the data analysis using the ANOVA and DUNCAN tests for the second and third scenarios, it was observed that the optimum TDS removal efficiency of the EDR process can be at temperature of 26.5°C and voltage of 18 V. On the other hand, the successful performance of the bench-scale EDR in reducing the 29,000 mg/L TDS and the 45,000 μmhos/cm EC of the 2^nd stage brine to 1,716 mg/L (TDS) and 2,640 μmhos/cm (EC) (at 26.5°C and 24V) could be considered as the main achievement of this research. Overall, the hybrid process RO-EDR-RO can be considered as the best technical, environmental and economical scenario for the development of Eshtehard Desalination Plant phase 2 at full scale.