M. M. Sarafraz - Faculty of Chemical, Petroleum and Gas Engineering, Semnan University, Semnan, Iran
F. Hormozi - Faculty of Chemical, Petroleum and Gas Engineering, Semnan University, Semnan, Iran
S. M. Peyghambarzadeh - Department of Chemical Engineering, College of Chemical Engineering, Mahshahr branch, Islamic Azad University, Mahshahr, Iran
N. Vaeli - Department of Chemical Engineering, College of Chemical Engineering, Mahshahr branch, Islamic Azad University, Mahshahr, Iran

In this work, flow boiling heat transfer coefficients of deionized water and copper oxide water-based nanofluids at different operating conditions have been experimentally measured and compared. The liquid flowed in an annular space. According to the experiments, two distinguished heat transfer regions with two different mechanisms can be seen namely forced convective and nucleate boiling regions. Results demonstrated that with increasing the applied heat flux, flow boiling heat transfer coefficient increases for both of test fluids at both heat transfer regions. In addition to, by increasing the flow rate of fluid, the heat transfer coefficient dramatically increases at both regions. Influence of inlet temperature of fluid to the annulus as a complicated parameter has been investigated and briefly discussed. Results showed that inlet temperature of fluid displaces the boundary between forced convection and nucleate boiling areas such that with increasing the inlet temperature, nucleation mechanism become dominant mechanism at lower heat fluxes. Furthermore, higher heat transfer coefficient can be obtained due to interactions of bubbles and local agitations. Also, Chen type model was modified in terms of thermo-physical properties and examined to experimental data. Results showed that experimental data are in a good agreement with those of obtained by the correlation with deviation up to ۳۰%.

Flow Boiling, Pure distillated water, Heat transfer, Forced convection, Annulus