Experimental Study On Heat Transfer Of Al₂O₃-CuO/H₂O Nanofluids

As a new type of enhanced heat transfer working medium,nanofluids are of great significance for the development of efficient and compact heat exchange equipment.In this paper,the characteristics of pool boiling and forced convection heat transfer in water-based nanofluids are studied.Al₂O₃/H₂O nanofluids,CuO/H₂O Nanofluids and Al₂O₃-CuO/H₂O hybrid nanofluids with different volume fractions were prepared by two-step method.The stability of the three nanofluids met the experimental requirements.The thermophysical parameters of nanofluids are studied,and the calculation models suitable for solving the thermophysical properties of three different nanofluids in this paper are established.Using the experimental platform of boiling heat transfer in the nanofluid pool,the experiments of pure water and the three different particles of water-based nanofluids were carried out.The boiling heat transfer coefficients and heat transfer enhancement rates of pure water and several nanofluids at different volume fractions were calculated.The results show that the number of boiling heat transfer systems of nanofluids has a certain increase compared with pure water in the experimental concentration range（0.001%-0.1%）.Among them,the boiling of Al₂O₃-CuO/H₂O hybrid nanofluids The heat transfer coefficient of nanofluids is higher than that of single particles.The highest enhancement rates of boiling heat transfer coefficients of Al₂O₃,CuO and Al₂O₃-CuO/H₂O hybrid nanofluids are 178.2%,213.2% and 253.2%,respectively.The change of boiling heat transfer coefficient in nanofluid pool is the result of the increase of thermal conductivity,agglomeration of particles and surface deposition.The flow and heat transfer experiment platform of nanofluid in the tube was built and the experiment was carried out.By changing the flow rate,volume fraction and the type of nanoparticle in the tube,the convection heat transfer coefficient and Nu number of nanofluid were calculated,and the effect of Re,volume fraction of nanoparticle and other factors on the forced convection heat transfer effect in the tube was studied.The addition of nanoparticles enhances the flow and heat transfer of the working fluid in the tube,the micro movement of nanoparticles destroys the bottom layer of the flow laminar flow and strengthens the energy transfer process of the working fluid.A exergy analytical model was established for the laminar heat transfer of nanofluid under the condition of constant heat flow.Under the same Re condition,the addition of nanoparticles increases the friction entropy production and reduces the heat transfer entropy production,while the magnitude of friction entropy production is only 10^-6,which is negligible compared with the heat transfer entropy production.Therefore,in general,the loss of nanofluids is lower than that of pure water;for nanofluids,the loss of hybrid nanofluids is lower than that of single nanofluids at the same volume fraction.