tailieunhanh - Báo cáo hóa học: " Numerical study of instability of nanofluids: the coagulation effect and sedimentation effect"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Numerical study of instability of nanofluids: the coagulation effect and sedimentation effect | Ni et al. Nanoscale Research Letters 2011 6 183 http content 6 1 183 o Nanoscale Research Letters a SpringerOpen Journal NANO REVIEW Open Access Numerical study of instability of nanofluids the coagulation effect and sedimentation effect Yu Ni JianRen Fan YaCai Hu Abstract This study is a numerical study on the coagulation as well as the sedimentation effect of nanofluids using the Brownian dynamics method. Three cases are simulated focusing on the effects of the sizes volume fraction and z potentials of nano-particles on the formation of coagulation and sedimentation of nanofluids. The rms fluctuation of the particle number concentration as well as the flatness factor of it is employed to study the formation and variation of the coagulation process. The results indicate a superposition of coagulation and sedimentation effect of small nano-particles. Moreover it is stable of nanofluids with the volume fraction of particles below the limit of resolution of the fluids. In addition the effect of z potentials is against the formation of coagulation and positive to the stability of nanofluids. Introduction The nanofluid is characterized by the fluid with nanometer-sized solid particles dispersed in solution 1 which can increase the heat transfer coefficient 2-6 enhance the critical heat flux in boiling heat transfer 7-9 reduce the wall friction force 10 improve the optical characteristics 11 etc. Nano-sized particles are utilized because of its better stability than the suspension of micro-sized particles. For a badly stable suspension sedimentation or coagulation agglomeration may occur. It compromises the above-mentioned advantages of the nano-suspension. As is well known 12 the occurrences of coagulation and sedimentation are the two main factors for the instability of nanofluid. The phenomenon of coagulation is characterized by the formation of particle clusters . particles are in contact with each other and the cohesion takes place. Then