Numerical Investigation Of Forced Convection Heat Transfer Nanofluids In Curved Tubes

Due to the limited storage of non-renewable energy and the increasing demand for energy,the research and development of some new efficient heat transfer fluids has always been the main focus of scholars.Since the concept of nanofluid was proposed,researchers have carried out a lot of experimental research and numerical simulation analysis on the heat transfer condition of nanofluids.Through a lot of researchs,it is found that nanofluids is a kind of heat transfer medium with high heat transfer performance,and it will have a considerable application prospect in the field of heat transfer.In recent years,with the increasing demand for small size,light weight and compact structure of all kinds of heat transfer equipment,the research on the mechanism of nanofluids heat transfer enhancement has been received widespread attention by researchers at home and abroad.In the present study,the forced convection heat transfer of Al₂O₃-water nanofluids in two-dimensional and three-dimensional bends and helical tubes have been studied numerically under steady conditions.The main contents of this present research are as follows:?1?The forced convection heat transfer of Al₂O₃-water nanofluids in a two-dimensional bend tube with constant heat flow boundary condition is studied numerically.The effects of volume fraction of nanoparticles,nanoparticle size and Reynolds number Re on forced convection heat transfer of Al₂O₃-water nanofluids in bend tube are analyzed.The results show that the forced convection in the bend tube can be enhanced by adding nanoparticles in water,and the heat transfer properties of the nanofluids can also be enhanced by increasing the volume fraction of nanoparticles.When the volume fraction of nanoparticles is fixed,with the reducing the size of nanoparticles,the increase of heat transfer between nanofluids and water is increasingly larger.When Re is small,the heat transfer of nanofluids in the bend tube is dominated by thermal diffusion.With the increase of Re,the forced convection heat transfer of nanofluids in the bend tube can be greatly improved with the increase of the intensity of convection heat transfer.?2?The forced convection heat transfer of Al₂O₃-water nanofluids with constant heat flow boundary condition is studied numerically.In the present research,the forced convection heat transfer of spherical and rod-shaped Al₂O₃-water nanofluids in three-dimensional bends is studied respectively.Meanwhile,the effects of the different dynamic viscosity calculation models on forced convection heat transfer of Al₂O₃-water nanofluids in three-dimensional bend tubes are studied.It is found that compared with water,spherical and rod-shaped Al₂O₃-water nanofluids can improve the forced convection heat transfer in three-dimensional bends.Without considering the effect of the shape of nanoparticles on the dynamic viscosity of nanofluids,the rod-shaped Al₂O₃-water nanofluids with the same volume fraction of Al₂O₃ nanoparticles have a better ability to enhance forced convection heat transfer in three-dimensional bend tubes.However,considering the effect of nanoparticles shape on viscosity,the rod-shaped Al₂O₃-water nanofluids has a larger dynamic viscosity,the flow of the nanofluids in the bend tube has greater drag,so the effect of improving heat transfer is not obvious.?3?The forced convection heat transfer of Al₂O₃-water nanofluids in a three-dimensional helical tube is studied numerically under the condition that the temperature of the wall surface is constant.The effects of volume fraction of nanoparticles,shape of nanoparticles and nanoparticles size on forced convection heat transfer of Al₂O₃-water nanofluid in helical tube were analyzed.It is found that the increase of the volume fraction of nanoparticles can enhance the heat transfer in the helical tubes under the condition of the shape of the nanoparticles and the size of the nanoparticles have fixed values.Under the condition that the nanoparticles shape and nanoparticles volume fraction are fixed,reducing the nanoparticles size is helpful to the forced convection heat transfer of the nanofluids in helical tubes.When the volume fraction and nanoparticles size of the nanoparticles are certain,compared with spherical Al₂O₃-water nanofluids,the effect of rod-shape nanoparticles with low sphericity on strengthening forced convection heat transfer of Al₂O₃-water nanoparticles in helical tubes is more remarkable.