Papers by Author: Wei Dong Wu

Abstract: The objective of this paper is to analyze the enhancement mechanism of ammonia bubble absorption performance by nanofluid. In this paper, the process of ammonia bubble absorption is divided into three different steps: the bubble growing, the gas absorption in liquid phase and the interface phase transfer. According to the analysis, nanofluid can enhance the diffusion coefficient or the absorption performance in each step, and enhance the whole absorption performance resultly; the gas mass transfer during the bubble growing is enhanced by nanofluid for the surface tension decrease; the main cause for the enhancement of the gas absorption in liquid phase is considered as the transport effect of nanoparticles carrying ammonia gas molecule and the vortex transfer effect arising from Brownian motion of nanoparticles; the main cause for the enhancement of the transfer at phase interface is considered as the Marangoni convection and the vortex transfer effect due to nanoparticles.

Abstract: The main objectives of this work are to experimentally examine the enhancing mass transfer performance of FeO nanofluid on the bubble absorption and to find the optimal method to design highly effective compact absorber for NH₃/H₂O absorption refrigerator. Based on the microcosmic analysis of the factors affecting the stable performance of nanofluid, FeO nanofluid was prepared by using the ultrasonic dispersion method. The ammonia bubble absorption experiments with FeO nanofluid were carried out and the data of absorption height were acquired. The results showed that FeO nanofluid had an enhancing effect on mass transfer performance, and the absorption height was 2mm higher than that of the water based solution in 2 minutes of the experiment conditions. The curves of the solution temperature in absorption were also given. According to the data of the absorption height and the solution temperature, it is pointed out that there are two factors which might have negative influences on the mass transfer enhancing process.

Abstract: Several water-based nanofluids were prepared under the action of surfactant by using ultrasonic dispersion method. The absorbency and viscosity of the nanofluids prepared under different conditions were measured and analyzed. The results showed that, when the mass fractions of nanoparticles were 0.2%, the most appropriate surfactants for Al₂O₃, FeO, γ-Fe₂O₃ water-based nanofluids were SDBS (Sodium Dodecyl Benzene Sulfonate), ACT (ammonium citrate), CTAB (Cetyltrimethyl Ammonium Bromide), respectively and the optimum mass fractions of the surfactants corresponding to the three nanofluids were 0.2%, 0.1%, 0.2%, respectively, to obtain the best dispersion stability. The optimum ultrasonic condition was 60 min of ultrasonic time under 300 W of ultrasonic power or 90 min of ultrasonic time under 200 W of ultrasonic power, in which the water-based nanofluids had the largest absorbency, the smallest viscosity and the strongest stability. In addition, the greater the size of the nanoparticles the easilier the reunion, and the poorer the dispersion stability was. When the pH value was about 4, the absorbency of Al2O3 nanofluid was larger and the dispersion stability was better. The inherent mechanism of keeping stability of nanofluids was discussed.

Abstract: Bubbling absorption experiments of ammonia water(NH3/H2O) solution added with FeO nano-particles were carried out in some conditions. The results showed that the absorption effect of the ammonia-water solution with the nano-particles was improved. The several key factors affecting the absorption process, such as preparing of nanofluid, absorption pressure, solution temperature and the flow rate of cooling water, were also analyzed, repectively, and finally it was pointed out that there exist certain possible coupling relations between these influencing factors.

Abstract: The object of this paper is to study the effects of nanofluid on NH₃/H₂O bubble absorption performance under adiabatic and non-adiabatic conditions. Mono nano Ag with the concentration of 0.02wt% was used as the enhancement medium, and the absorption performance experiments under the heat insulation and water cooling for absorption test section were respectively conducted and contrastively analyzed. The results showed that the absorption rate with mono nano Ag in bubble absorption process is higher than that without any nanoparticles; in adiabatic case, when the initial temperature of NH₃/H₂O solution is gradually increased within 6～18°C, the absorption rate decreases correspondingly, and so does the effective absorption ratio; in non-adiabatic case, with the cooling water temperature rising within 10～25°C, the absorption rate decreases but the effective absorption ratio increases. Therefore, it is concluded that the heat transfer enhancement of nanofluid can promote the NH₃/H₂O bubble absorption performance to a certain degree, and the enhancement of the absorption is not completely dependent on heat transfer.