بررسي پديده جوشش در نانو سيالات به روش عددي

چكيده انگليسي :

Numerical Investigation of Boiling Phenomenon of Nanofluids Mir Omid Hasheminia Mo hasheminia@ec iut ac ir March 14 2011 Department of Chemical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Masoud Haghshenas Fard haghshenas@cc iut ac ir Supervisor Seyed Hasan Hashemabadi hashemabadi@iust ac ir Abstract Common fluids with particles of the order of nanometer in size are termed as nanofluids which have created considerable interest in recent years for their improved heat transfer capabilities With very small volume fraction of such particles the thermal conductivity and convective heat transfer capability of these suspensions are significantly enhanced without the problems encountered in common slurries such as clogging erosion sedimentation and increasing in pressure drop This naturally brings out the question whether such fluids can be used for two phase applications or in the other words phase change in such suspensions will be assistant or detrimental to the process of heat transfer This research reviews the boiling of nanofluids by CFD method In the recent years a lot of experiments carried out about nanofluids heat transfer coefficient as two phase flow in which the results about enhancement and deterioration of heat transfer coefficient and critical heat flux were inconsistent In this research at first the simulation has been done for water in a tube with internal diameter of 7 7mm inlet velocity of 1m s inlet temperature of 200 C and inlet pressure of 45atm The constant heat flux was applied to fluid and the simulation results were compared with the experimental data The critical heat flux was obtained for water and it was about 440kw m2 Then the simulation with three nanofluids Al2O3 H2O SiO2 H2O ZrO2 H2O at various volume fractions 0 1 0 01 and 0 1 has been done According to the previous researches the critical heat flux is a point at which the volume fraction of vapor in the outlet is about 80 The critical heat flux is calculated for the three nanofluids and the increasing ratio of critical heat flux was compared in different volume fractions The results showed that critical heat flux of Zirconium oxide 0 001 increased up to 31 and the minimum enhancement belongs to aluminum oxide 0 1 that its critical heat flux was increased only 11 The results showed that for Al2O3 H2O and SiO2 H2O as the nanoparticle volume fraction increased the critical heat flux is decreased while the heat transfer coefficient is enhanced In the ZrO2 H2O nanofluid the maximum enhancement in critical heat flux was occurred in 0 01 volume fraction of nanoparticles which has the minimum heat transfer coefficient According to experimental results despite of expectation addition of the nanoparticles causes decreasing the boiling heat transfer coefficient This reduction is related to the changing of the surface characteristic causing by depositing the nanoparticles The experimental results for changing the surface contact angle of nanofluids during boiling is used in this project The predicted critical heat fluxes were in good agreement with the experimental results Key Words boiling nanofluids critical heat flux nucleation site density

هاشمي نيا، ميراميد

بررسي پديده جوشش در نانو سيالات به روش عددي

شار حرارتي بحراني , تعداد نقاط هسته زايي