Heat Transfer Enhancement in Industrial Heat Exchangers Using Graphene Oxide Nanofluids.

In this study, the heat transfer characteristics within the heat exchanger using water-based GO nanofluids were comprehensively assessed. An apparatus was constructed by scaling down an industrial heat exchanger. The nanofluid's thermal conductivity, specific heat capacity, viscosity, density, Prandtl number, and Nusselt number were examined at varying temperatures and GO nanoparticle concentrations. The results revealed that the thermal conductivity of the nanofluid increased with both temperature and nanoparticle concentration, reaching a peak value of 0.380 W m-1 K-1 at 85 °C and 0.1 wt %, leading to enhanced heat transfer rates through conduction and convection mechanisms. The specific heat capacity increased with temperature but decreased with higher GO nanoparticle contents with a maximum value of 3403.821 J kg-1 K-1 recorded at 40 °C and 0.01 wt %. The viscosity of the nanofluid increased with higher concentrations of GO nanoparticles, and the minimum value of 0.83 mPa s was observed at 85 °C and 0.01 wt %. The Prandtl number decreased with the temperature but increased with increasing GO nanoparticle concentration, suggesting a transition from convective to conductive heat transfer. A newly derived correlation equation for the Nusselt number, Nu = 0.0059(1 + 7.62ϕ0.6886)Pe 0.001 Re 0.9238 Pr 0.4, allows predicting heat transfer enhancement in nanofluids. The findings emphasize the potential of nanofluids for improving heat exchanger performance and offer valuable insights into optimizing nanofluid applications in thermal systems.

Arsenate removal from contaminated water using Fe2O3-clinoptilolite powder and granule.

Natural clinoptilolite (Clin) was modified with iron oxide using three different methods including precipitation, wet-impregnation and ion-exchange and then the modified adsorbent with highest As(V) removal efficiency was encapsulated into Alginate by a simple cross-linking method to obtain Fe-Clin granules. The surface morphology and chemical composition of the Fe-Clin sorbents were characterized by scanning electron microscope and X-ray diffraction analysis. The selected Fe-Clin powders and granules possessed enhanced affinity towards the highly toxic arsenic pollutant in a very short time. Batch adsorption experiments showed that the Fe-Clin adsorbent can be widely used within a wide range of pH (2-9). In addition, to reach a high removal percentage (over 90%) of As(V), the optimum dosage of powder and granule shaped adsorbents was obtained as 0.1 and 0.6 g L-1, respectively. Both adsorbents could successfully remove As(V) in a very short amount of time as 20 and 30 min in the case of powders and granules, respectively. The maximum adsorption capacity of Fe-Clin granules evaluated by using Langmuir adsorption isotherm was found to be 11.17 mg g-1. By testing the granules in a circulated fluidized column experiment, it was demonstrated that Fe-Clin granules could remove As(V) up to an acceptable level (93%) within 10 min. This study demonstrates that Fe-Clin granules, obtained by exploiting natural clinoptilolite, iron oxide and alginate, are efficient, sustainable and fairly cheap adsorbents for the removal of arsenate from the aquatic environment in a very short contact time.