The Influence Of Additives And Nano-particles On Surface Tension Of Lithium Bromide And Ammonia

Many countries have paid great attention to absorption refrigeration technologywith the emergence of the worldwide energy crisis. In China, with the pressure of theentire power system increasing, the electricity used by air-conditioning is alsolimited, and this provides an opportunity for the development of absorptionrefrigeration driven by heat. The absorber is the main component of determining theabsorption chiller performance, and strengthening the absorption effect of itsworking medium LiBr aqueous solution and ammonia has an important significanceto improve its thermal coefficient and its application in the air-conditioning industry.The characteristic of additives and nano-particles enhanced the absorption process ofLiBr aqueous solution and ammonia is studied by many scholars. In this paper, thesurface tension of LiBr aqueous solution and ammonia with additives andnano-particles was measured using Wilhelmy plate method.In this paper, the surface tension was measured with additives added alonefirstly, and the additives of1-Octanol, CTAC, CTAB and PAM were selected in theexperiment. Through the comparison,1-Octanol has the best effect of reducing thesurface tension of LiBr aqueous solution and ammonia, but because1-Octanol hastoxic and is easy to decompose in high temperature, so it is not suitable used inmulti-effect absorption refrigeration system. CTAC and CTAB also have better effectto reduce the surface tension of LiBr aqueous solution and ammonia, and they havethe characteristics of high temperature resistant and good stability. The effect ofPAM is poor. Then the nano-particles of Cu and TiO2were added separately intoLiBr aqueous solution. By comparison, the effect of Cu in reducing surface tensionis bad than that of TiO2, in addition, Cu nano-particles were strongly corrosion byLiBr aqueous solution, so TiO2was chosen in the latter experiments.In order to reduce the surface tension better, based on the two types experimentsabove, additive and nano-particle were added mixture into the working medium ofabsorption refrigeration. Then the surface tension of LiBr aqueous solution andammonia was measured. The results show that the additives play a main role ofreducing the surface tension, and because nano-particles not only can reduce thesurface tension of LiBr aqueous solution and ammonia but also can enhance the heattransfer, so the mixture addition of additives and nano-particles can both enhance theheat and mass transfer of working medium in absorption refrigeration. Because in the actual operation process of absorption refrigeration system, thetemperature of absorber has fluctuations, therefore, the experiment about theinfluence of temperature on surface tension of LiBr aqueous solution with additive iscarried out. The results show that the surface tension decreases with the temperatureincreasing which accords with the influence law of temperature on surface tension,that is, under normal circumstances, the surface tension of most substances decreaseswith the temperature increasing. But in this paper’s experimental temperature range,the experiment data shows the influence can be ignored when the temperaturefluctuations within±1℃.Finally, in order to reflect the effect of surface tension on mass transfer directly,the influence of surface tension reducing on mass transfer coefficient was analyzedfrom the theory perspective. The paper analyses the relationship between surfacetension and mass transfer coefficient from Marangoni convection perspective andcombined the empirical correlation of Marangoni convection and mass transfer in thevapor-liquid mass transfer process. Through the calculation results, it can be knownthat the mass transfer coefficient increases with the surface tension of LiBr aqueoussolution decreases, and obviously the absorption process of absorption refrigerationis enhanced.