Experimental and Theoretical Studies of Different Parameters on the Thermal Conductivity of Nanofluids.

This work experimentally investigated the effects of different factors, including nanoparticle size and type, volume fraction, and base fluid, on the thermal conductivity enhancement of nanofluids. The experimental results indicate that the thermal conductivity enhancement of nanofluids is proportional to the thermal conductivity of the nanoparticles, with the enhancement being more pronounced for fluids with lower thermal conductivity. Meanwhile, the thermal conductivity of nanofluids decreases with increasing particle size and increases with increasing volume fraction. In addition, elongated particles are superior to spherical ones for thermal conductivity enhancement. This paper also proposes a thermal conductivity model by introducing the effect of nanoparticle size based on the previous classical thermal conductivity model via the method of dimensional analysis. This model analyzes the magnitude of influencing factors on the thermal conductivity of nanofluid and proposes suggestions for an improvement in thermal conductivity enhancement.

A novel antibiotic wastewater degradation technique combining cavitating jets impingement with multiple synergetic methods.

Antibiotics degradation remains a longstanding challenge in wastewater treatment. Towards this objective, we have developed a novel technique combining cavitating jets impingement with multiple synergetic methods, i.e., UV/Fenton, analogous Fenton, and photocatalytic oxidation in the present work. Three kinds of antibiotics namely amoxicillin, doxycycline and sulfadiazine sodium, are selected as model pollutants. Individual application of cavitating jets impingement is firstly conducted to evaluate the effects of jets impinging forms and nozzle inlet pressure. The effects of impingement on promoting antibiotics degradation and weakening the coalescing effects of cavitation bubbles are confirmed. Perpendicular double cavitating jets impingement is proved to be the most effective impinging form and brought a COD (chemical oxidation demand) reduction of 30.04% with the impinging effect index 1.22 at jet inlet pressure 10 MPa. Increasing the jet inlet pressure can improve the COD reduction and the effectiveness of impingement. Subsequently, UV/Fenton process is introduced to intensify the degradation process. The effects of important parameters are investigated by means of orthogonal experiments and the maximum COD reduction is up to 71.16% under the optimum conditions. Then, analogous Fenton process and photocatalytic oxidation are adopted for further enhancing the COD reduction. Different approaches used in the present work are assessed in view of multiple aspects. With COD reduction of 79.92%, the combination of cavitating jets impingement, UV/Fenton, analogous Fenton and photocatalytic oxidation is proved to be optimum method for antibiotic wastewater treatment.

A novel device for hazardous substances degradation based on double-cavitating-jets impingement: Parameters optimization and efficiency assessment.

Hydrodynamic cavitation is an effective advanced oxidation process. But sometimes it cannot obtain satisfactory treatment efficiency by using hydrodynamic cavitation individually, so it is necessary to introduce intensive methods. Based on double-cavitating-jets impingement, this paper presents a novel device that has advantages of strong heat and mass transfer and efficient chemical reactions. Based on the device, a series of experimental investigations on degradation of a basic dye, i.e. Rhodamine B were carried out. Significant Rhodamine B removal from aqueous solution was observed during 2h treatment and the degradation reaction conformed to pseudo-first-order kinetics. The synergetic effects between double-cavitating-jets impingement and Fenton chemistry on simultaneous degradation of Rhodamine B were confirmed. Both single-variable experiments and orthogonal experiments were carried out to study the effects of initial hydrogen peroxide, ferrous sulfate and Rhodamine B concentrations and the optimum conditions were found out. Effects of jet inlet pressure in the range of 6-12MPa and solution pH value in the range of 2-8 were also investigated. The cavitation yield was evaluated to assess the energy efficiency. The present treatment scheme showed advantages in terms of reducing the demand of hydrogen peroxide concentration and enhancing the treatment efficiency in large scale operation.