Investigation On The Heat Transfer Enhancement Characteristics Of Water-Based Nanofluids In Microchannels

Phase change materials have potential application value in the fields of thermal energy storage and temperature regulation due to their advantages of large heat storage density and constant temperature of thermal energy storage process.However,it also has the disadvantage of low thermal conductivity.In addition,as the development of microelectronic devices,batteries and other devices are becoming smaller,the requirements for heat exchange systems and unit thermal storage components tend to be more efficient,compact,and lower energy consumption.The use of phase change materials for thermal management can perform thermal buffering of microelectronic devices so that avoid thermal runaway.In this paper,in order to deal with the problem of low thermal conductivity of phase change materials in thermal management processes such as electronic devices,the TiO₂-H₂O nanofluids of high thermal conductivity are combined with the microchannel to enhance the thermal conductivity of the phase change material paraffin and heat transfer effect.So that the heat transfer enhancement characteristics of water-based nanofluids in microchannels can be can reveal.The main research contents and conclusions are as follows:?1?Two kinds of TiO₂-H₂O nanofluids of anatase A and rutile R were prepared by"two-step method"with mass fraction of?=0.5 wt%,0.7%wt%,and 1.0%wt%,respectively.And its stability of them were analyzed.The zeta potential values of the two TiO₂-H₂O nanofluids measured by Zeta potential method are less than-30 mV,which means both of them are in a relatively stable state.It was found by sedimentation observation that,in the preparation process,the A TiO₂-H₂O nanofluid was more uniformly dispersed than R before the addition of SDBS.After adding SDBS,A and R TiO₂-H₂O nanofluids performed similarly.After the static processing,it was found that the sedimentation phenomenon of A TiO₂-H₂O nanofluid appeared on the 5th day,and appeared on the 7th day of R TiO₂-H₂O nanofluid.It can be seen that R TiO₂-H₂O nanofluid is better than A.By comparing the A and R TiO₂-H₂O nanofluids by particle size analysis,it is found that the average particle size of the R TiO₂-H₂O nanofluid is smaller than that of A,which means that the size of particle agglomerates in the R are smaller and the nanoparticles are more evenly dispersed.Therefore,its stability is better than the A.?2?For the thermal properties of A and R TiO₂-H₂O nanofluids,the thermal conductivity and viscosity of them were tested and compared.In terms of thermal conductivity,when the temperature is between 20°C and 50°C,the maximum increase in thermal conductivity of A TiO₂-H₂O nanofluid compared with deionized water at?=0.5 wt%,0.7 wt%and 1.0 wt%is 1.65².24%,1.86².52%and 1.99².88%respectively;while R increases 1.68².37%,1.92².91%and 2.55³.27%respectively.It can be seen that the thermal conductivity of R increases more.In terms of viscosity,since the base liquid used in the preparation process is deionized water and the added surfactant SDBS has a small amount,the viscosity of A and R TiO₂-H₂O nanofluids is small.When the temperature is in the range of 20⁴0°C,?=0.5 wt%,0.7 wt%and1.0 wt%of the A nanofluids increae the viscosity by 0.0280⁰.0 mPa·s,which is2.76⁷.45%;while it is 0.0050⁰.0343 mPa·s of Rnanofluids,which is 0.50⁴.87%.It can be seen that the viscosity of R TiO₂-H₂O nanofluids is smaller than that of A,which means R is more suitable for using in the microchannel.?3?In order to reveal the relevant characteristics of TiO₂-H₂O nanofluids combined withmicrochanneltoenhancethethermalenergystorage/release?melting/solidification?processes of paraffin,a nanofluid-bonded microchannel for enhancing paraffin phase change experimental bench was established.Through the storage and release experiments of different working fluids?base liquid deionized water and R?=0.5 wt%,0.7 wt%and 1.0 wt%TiO₂-H₂O nanofluids?through the microchannel for enhancing the storage/release process.It can be seen that during the melting process,the time for the complete melting of paraffin is reduced by 32.90%,and the corresponding Nu number is increased by 19⁴1%.During the solidification process,the time for complete solidification of paraffin is reduced by 22.57%,and the corresponding Nu number is increased by 6¹4%.After?=0.5 wt%,0.7 wt%and 1.0wt%of TiO₂-H₂O nanofluids were added to the microchannel,the pressure drop across the microchannel increased,but within 8%.During the melting process,the pressure drop across the microchannel increased by 2.44%,5.06%,and 7.76%,respectively;during the solidification process,the pressure drop across the microchannel increased by 3.80%,5.45%,and 7.53%,respectively.