| Energy is the driving force for economic and social development.In recent years,with the rapid development of China’s economy,people’s living standards have gradually improved,resulting in increasing energy consumption.Electric heaters using traditional fluids such as water and heat-conducting oil as working fluids have the disadvantages of slow heating,high energy consumption,low heating efficiency,and poor economy.Nanofluid is a new type of uniform and stable heat transfer medium made of solid particles with a nanometer diameter,base liquid（medium）and surfactant.It is widely used in energy,automotive,medical,chemical,microelectronics and other fields.Many scholars at home and abroad have long been engaged in nanofluid enhanced heat transfer research.In this paper,nanofluids with different nanoparticles and base fluids were prepared by two-step method,and the stability of the nanofluids was improved by physical and chemical methods.The physical methods are mainly mechanical stirring and ultrasonic,and the chemical method is mainly adding surfactant to the solution.The thermal conductivity and viscosity of Fe3O4-water nanofluid were measured,the effects of nanofluid concentration（mass fraction）and temperature on thermal conductivity and viscosity were analyzed.A small closed experimental system is constructed using thermal insulation materials.Different nanofluids are charged into electric heater to conduct heating experiments,and the heating efficiency of electric heater under different heat exchange working media was studied.The bar magnet was packaged in electric heater,and the heating efficiency of the electric heater under magnetic fluid was studied.Results show that when the concentration of the nanofluid are the same,the heating efficiency of the electric heater is the highest when Cu-water nanofluid is the working medium,followed by Mg O-water nanofluid and Al2O3-water nanofluid,and Si O2-water nanofluid as the working medium,the heating efficiency of electric heaters was lowest.When nanofluid was used as working fluids,the heating efficiency of electric heaters is greater than that of the base fluid.When a nanofluid configured with Cu,Mg O,Cu O,and Si O2 nanoparticles are used as a heat exchanger working medium,the heating efficiency of the electric heater monotonously increases with the increase of nanofluid concentration.When the nanofluid configured with Fe3O4 and Al2O3 nanoparticles is used as the heat exchanger working medium,the heating efficiency of the electric heater shows a non-monotonic increasing trend with the increase of the nanofluid concentration,and the optimal concentration of the nanofluid was 1.0%.In this paper,the model of electric heater is simplified.The simplified model of electric heater is simulated by using ANSYS FLUENT 18.0 software,and the mechanism of heat transfer enhanced by nanofluid was studied.Many scholars have done lots of research on the heat transfer enhancement of nanofluid,but less research on the application of nanofluid in electric heaters.Living appliances represented by electric heating structures such as electric heaters have greatly affected every family contribution and participation in energy saving and emission reduction.This study can provide guidance for the design and development of high heat flux heat sinks and high-efficiency heat exchangers. |
