بررسي جوشش استخري نانو سيال آب / Al2O3 روي صفحه تخت

چكيده انگليسي :

Pool Boiling Investigation of Al2O3 Water Nanofluid on Flat Plate Zahra Shahmoradi z shahmoradi@ce iut ac ir 26 4 2011 Department of Chemical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Nasrin Etesami netesami@cc iut ac ir Mohsen Nasr Esfahani mnasr@cc iut ac irAbstractIn the past two decades an increasing amount of research has been conducted in nanoscale science One importantcase of this field involves adding nanoparticles to a conventional base liquid named nanofluid The main thrust ofnanofluid research has been the development of better heat transfer fluids Recently researchers have consideredthe possibility of enhanced boiling heat transfer in nanofluids Results reported in literatures are in conflict due tothe dependence of experimental results upon many parameters such as the nanofluid type heater material andspecific test conditions surfactant use heater geometry saturation pressure and measurement equipments In orderto investigate on pool boiling in nanofluids based on water we need to prepare very high critical heat fluxes thussome limited experimental data on boiling nanofluids over the flat plate has been reported Also previous resultsshow that there are some conflicts The comparison of the limited existing results of the pool boiling on the flatplate shows that research work on boiling heat transfer characteristics is still not enough This paper is aimed atexperimental investigation on pool boiling of Al2O3 water nanofluids on flat plate in different concentrations ofnanoparticles Experiments are carried out to investigate the effects of the nanoparticles concentration on poolboiling features such as boiling curve the CHF and boiling heat transfer coefficient This study will also try topresent some plausible explanations in results by analyzing the heater surface Nucleate pool boiling of Al2O3 basedaqueous nanofluid on flat heater has been studied experimentally The maximum value of the surface d 36mm heat flux for all the boiling experiments was restricted to around 1 800 kW m Reduction in nucleate boiling heattransfer has been observed at four volume fraction of nanoparticles compare to pure water for 0 1 0 05 0 02 and0 002 vol 40 34 23 13 respectively Results showed that the rate of heat transfer falls with solidconcentration Also enhancement in critical heat flux CHF has been observed for 0 1 0 05 0 02 0 002 and 0 001 vol 47 40 30 22 17 respectively The CHF enhancement increases with volume fraction of nanofluids After each test of nanofluid pool boiling a white and thin layer on the heater surface observed Increasing thicknessof this layer for higher nanofluid concentration is clearer In addition the contact angle of the drop on basic surfacebefore boiling is bigger 45 than that on nanofluid boiled surface 20 In fact Enhancement wettability afternanofluid boiling due to reduction contact angle of drops on surface and creates conduction resistance betweensurface and fluid Deposition of nanoparticles during pool boiling on the heating surface generates an extra thermalresistance to the boiling surface and hence prevents the direct contact of liquid with the boiling surface Also AFMsamples prepared and changing in roughness after boiling nanofluids is observed Roughness reduction afternanofluid boiling for both polished and unpolished surface observed For polished surface roughness changed from5 nm to 376 nm and for unpolished surface changed from 77 nm to 197 nm This means that the sediment layercauses to fill up and reduction nucleation sites and increasing CHF Keywords pool boiling nano fluid flat pate CHF wettability heat transfer

شاهمرادي، زهرا

بررسي جوشش استخري نانو سيال آب / Al2O3 روي صفحه تخت

شار حرارتي بحراني , ضريب انتقال حرارت , توپولوژي سطح , ترشوندگي , زبري