In the present research, the synthesis of highly stable multiwalled carbon nanotubes in aqueous media is developed using a one-pot, covalent and green functionalization technique to improve the heat transfer and hydrodynamic behavior of a horizontal stainless-steel tube subjected to a uniform heat flow at its outer surface. Instead of using corrosive inorganic acids, the free radical grafting of gallic acids is used in this procedure. In this work, GA-functionalized multiwalled carbon nanotubes water-based colloidal suspensions (nanofluids) were prepared at three different weight concentrations. Various characterization techniques comprising Fourier transform infrared spectroscopy, Raman spectroscopy, High resolution transmission Electron Microscopy, and zeta-potential measurements were performed and confirmed the success of MWCNT functionalization. The thermophysical properties were evaluated experimentally and validated using empirical correlations available in the literature. To prove the colloidal suspension stability, ultraviolet-visible spectroscopy was used, and the results showed that nanofluid was stable for almost 60 days. When the GAMWCNT concentration was increased, there was a significant improvement in the thermal conductivity. Moreover, the nanofluids' dynamic viscosity experienced a slight increment up to 7.30% when the GAMWCNTs were loaded relative to distilled water. Following the confirmation of the experimental setup's analytical correlations, tests for the colloidal GAMWCNT suspension flowing through a heated horizontal tube were carried out in a fully developed turbulent state. A significant enhancement in the convective heat transfer coefficient was obtained, with only minor growth in the relative pumping power by 33.05 and 1.19%, respectively. More importantly, the reported positive performance index indicator for all the Reynolds numbers of ranges shows the possibility of using the synthesized GAMWCNT aqueous suspensions as an alternative working fluid in heat transfer systems.

In this study, electrocoagulation was evaluated for landfill leachate as a complex wastewater. Effects of all significant parameters including inter-electrode gap, current density, electrode material, time, pH, electrode numbers, salinity, and concentration were investigated. This study reports the changing patterns for chemical xxygen demand (COD) removal, temperature, voltage, and pH during EC for both Fe and Al electrodes under different conditions. According to the results, the best COD removals were achieved at shortest inter-electrode distance (0.5 cm), highest current density (1000 A m⁻²), highest number of electrodes (6 plates), longest time (60 min), and within acidic pH. Furthermore, for different NaCl concentrations (0–16 g l⁻¹), both falling and rising patterns were observed. This study also provides separate results for the effect of operational parameters on pH, voltage, temperature, and energy consumption during EC. With higher inter-electrode distances, voltage and temperature rose to larger values, whereas pH fell. Besides, increases in initial pH caused rises in all voltage, temperature and pH parameters during EC. Experiments also displayed that higher values of voltage, temperature, and pH occurred at larger current densities. Additionally, with time, pH increased to more basic measures, and voltage similarly increased. Results also reported that although addition of NaCl into medium could drop the voltage and temperature, it formed both falling and rising patterns for pH at different NaCl concentrations. Plus, according to the results, voltage, temperature, and pH all experienced rising patterns in accordance with the increase in the number of electrodes. Finally, a comparative study of energy consumption was performed to analyse the operation parametric effect.

The dewatering of algal culture requires coagulation of the algal cells. However, the coagulation in a continuous operation is slowed down through the excretion of Soluble Algal Products (SAPs). Electrocoagulation (EC), already utilized as a coagulation technique, has been investigated for its effects on SAPs characterizations. A mixed culture of Chlorella vulgaris, Scenedesmus Obliquus, Botryococcus braunii, Botryococcus sudeticus, and Afrocarpus falcatus was prepared and SAPs characteristics, including Specific Ultra Violet Absorbance (SUVA), Zeta potential, Molecular Weight (MW) fractionation, Dissolved Organic Carbon (DOC), protein and carbohydrate content, Excitation-Emission Matrix, and hydrophobicity using XAD resins, were measured and evaluated before and after electrocoagulation using mild steel and aluminum electrodes at 5 and 10 min. The results showed several improvements after EC. According to results, EC can render SAPs hydrophobicity up to 95 %, and the fluorescence peak results showed the complete removal of humic-like. Moreover, the SAPs were removed up to 21, 60, and 47 % for protein, carbohydrate and DOC, respectively. Results collectively showed that electrocoagulation might be able to mitigate the negative effects of growth on flocculation.