Numerical Simulation And Experimental Research Of Falling Flim Generation With Ammonia Water Nanofluids

For the traditional ammonia absorption refrigeration unit, which is driven by low grade thermal energy, has the low coefficient of performance, large heavy equipment and other shortcomings, its widely application has been restricted. This paper is based on the latest nanofluids technology in the field of engineering thermal physics, namely, adding nanoparticles in ammonia to form the dispersed homogeneous solution in a suitable manner and proportion. This technology is applied to the falling film process of the NH3-H2O absorption refrigeration system, studing whether there is a strengthening effect on falling film generation with nanofluids. This article mainly focuses on the preparation and properties of ammonia-water nanofluids, numerical simulation and experimental research of falling film generation with ammonia-water nanofluids, and mechanism analysis of nanoparticles enhancing ammonia falling film generation. The specific contents and conclusions are as follows:1). Study on preparation and properties of ammonia-water nanofluids. A kind of method to optimize the preparation of AW nanofluids is introduced in this paper. Based on the stability study of AW nanofluids in ambient temperature conditions, the author researches the influence of heat treatment on the nanofluid. The results showed that:In the test range of nanoparticle species, nanofluids containing surfactant has weakened effect on solution dispersion stability, while for the separate good nanofluids have a strengthening effect. Meanwhile, the stability and surface tension properties of the anion and cation surfactant compound with AW nanofluids is explored in this article, the results showed that the anion and cation surfactant, under the appropriate distribution proportion, can effectively improve the dispersion stability and lower solution surface tension of AW nanofluids.2). Numerical simulation of falling film generation with ammonia-water nanofluids. An equation suitable for calculating the AW nanofluids properties is presented, and a more practical and convenient mathematical model to solve the heat and mass transfer in AW nanofluids falling film generation is established in this paper. By solving a discrete mathematical model, the influence of nanoparticle concentration and ammonia concentration to nanofluids physical parameters were obtained. Meanwhile, the process parameters can not be directly measured in test, such as the velocity field, temperature field and concentration field, film thickness, interfacial mass and heat flow rate distribution, can be simulated. Simulation results show that:The heat and mass transfer of gas-liquid interface are mainly decided by the diffusion term.3). Experimental Research of falling film generation with ammonia-water nanofluids. By the falling film generating system test, the influence of the type and concentration of nanoparticles, the inlet flow and concentration of ammonia-water, pressure of generator to the heat and mass transfer performance have been researched. Experimental results show that:In the test range of nanoparticle species, all five nanofluids have a certain effect of strengthening generation, which ZnFe2O4-AW nanofluids get the best generating effect, its effective generation ratio is 1.44, then carbon black(CB), TiN, SiC and γ-Al2O3 followed by decreasing; In the test range of nanoparticle concentration, as the nanoparticle concentration increases, the generating effect of CB-AW nanofluids presents a trend of first increasing and then decreasing, reaches the optimum value when the nanoparticle concentration is 0.3%, its effective generation ratio is 1.85;In the test scope of the initial ammonia concentration, with the increase of the initial ammonia concentration, the generation rate of ammonia water and CB-AW nanofluids both have the rising trend, but the effective generation ratio decreases with it; In the test scope of the solution inlet flow, with the increase of solution inlet flow, the generating effect of ammonia water and CB-AW nanofluids both have a trend of first increasing and then decreasing, the generation rate reaches the optimum value when the solution inlet flow is 12.7g/(m.s), but the effective generation ratio reaches the optimum value when the solution inlet flow is 9.6g/(m.s), its effective generation ratio is 1.38; In the test scope of the pressure of generator, as the generator pressure increases, the generation rate of ammonia water and CB-AW nanofluids both have a downward trend, but the effective generation ratio increases with it.4). Mechanism analysis of nanoparticles enhancing ammonia falling film generation. Combined with the simulation and experimental results of ammonia water nanofluids falling film generation, and previous studies on nanoparticles enhanced heat and mass transfer, based on the micro motion of the particles and solution properties of nanofluids, the mechanism of nanoparticles enhancing falling film generation are discussion and analysed.