Study On The Heat Transfer Characteristics Of Lithium Bromide Solution Added Nano-Particles

With the growing contradiction between increasing in energy consumption and shortage of resources and increasingly serious environmental pollution, the desire of searching for industrial property with low energy consumption and low pollution is more intense. As a substance with specific properties, nano-particles have become a hot topic for investigators, and being gradually used in various industries. They are uniformly dispersed in a liquid to form a stable heat exchange medium. It is an important measure to improve the heat transfer capability of equipment.In this paper, nano-fluids are prepared by two-step process with two kinds of nano-particles and lithium bromide solution (LiBr). Homemade thermal analyzer and ubbelohde viscometer are applied to measure thermal conductivity and viscosity of nano-fluids. Gravity sedimentation method is used to observe the stability of the nano-fluids. The experimental results show that the nano-particle concentration and dosage of dispersant are important influence factors for thermal conductivity and viscosity of nano-fluids. With the increase of mass fraction of nano-particles, thermal conductivity and viscosity of nano-fluids first increase and then maintain stable, even on a downward trend. The effect of addition of Gum Arabic (GA) is obvious and is bigger than that of nano-particles. The thermal conductivity of nano-fluids increase by about twenty-two percent with the addition of CNT(1.0%) and GA(0.4%).An experimental study of falling film heat transfer outside horizontal tubes with LiBr-CNT nano-fluids is carried out in order to show how the heat transfer coefficient is affected by different parameters, such as, flow density, temperature of water, tube pitch and CNT concentration. The results showed that all these factors would affect the average heat transfer coefficient outside the tube. The average heat transfer coefficient increases firstly and then decreases with the increase of spray density and tube spacing. The best effect can be obtained when the distance between tubes is about one hundred and twenty percent of diameter. The average heat transfer coefficient increases firstly and then maintain stable. It increases by thirty-one percent with the addition of CNT (0.8%). Adding CNT nano-particles in lithium bromide solution can significantly improve the heat transfer performance of the liquid.A two-dimensional model of falling film flow is carried on to study the flow characteristics of lithium bromide solution outside the tube. By studying the influence of spray density and tube spacing to falling film flow, we find that spray density and tube spacing reveal different impacts on the liquid film distribution and thickness. Only using the appropriate tube spacing and spray density can make this exchanging heat system reach an optimal performance.