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Effect of gamma irradiation on the critical heat flux of nano-coated surfaces
A. Rahimian,H. Kazeminejd,H. Khalaf,A. Akhavan,M. Mirvakili 한국원자력학회 2020 Nuclear Engineering and Technology Vol.52 No.10
An anodic electrophoretic deposition (EPD) technique is used to create a uniform TiO2 thin film coating on boiling thin steel plates (1.1 mm by 90 mm). All of the effective parameters except time of the EPD method are kept constant. To investigate the effect of gamma irradiation on the critical heat flux (CHF), the test specimens were irradiated in a gamma cell to different doses ranging from 100 to 300 kGy, and then SEM and BET analysis were performed. For each coated specimen, the contact angle and capillary length were measured. The specimens were then tested in a boiling pool for CHF and boiling heat transfer coefficient. It was observed that irradiation significantly decreases the maximum pore diameter while it increases the porosity, pore surface area and pore volume. These surface modifications due to gamma irradiation increased the CHF of the nano-coated surfaces compared to that of the unirradiated surfaces. The heat transfer coefficient (HTC) of the nano-coated surfaces irradiated at 300 kGy increased from 83 to 160 kW/(m2 K) at 885 kW/m2 wall heat flux by 100%. The CHF of the irradiated (300 kGy) and unirradiated surfaces are 2035 kW/m2 and 1583 kW/m2, respectively, an increase of nearly 31%.
Lattice Boltzmann simulation of condensation over different cross sections and tube banks
M. Abbasi Hatani,H. Amirshaghaghi,M. H. Rahimian,A. Begmohammadi 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.10
In this paper a two-phase Lattice Boltzmann model, capable of handling large density jumps, is used to simulate the vapor filmwise condensation and dew drop sprinkling, outside different horizontal geometries. These geometries include circle, rectangle, square, and a bank of circular and rectangular tubes. In order to calculate the temperature field a passive scalar approach is combined with the Lattice Boltzmann framework and the flow field is assumed to be affected by temperature under the hypothesis of Boussinesq. Additionally, the effect of phase-change on velocity field is taken into account by adding a suitable source term to the pressure-momentum distribution equation. To simplify the model, it is assumed that the vapor remains at the saturation temperature and the amount of heat transferred through the interface is the only driving force for condensation. To demonstrate the validity of the model, the results are compared with a variety of analytical, numerical and experimental data. The validated model then is employed to study the influence of different parameters such as vapor temperature, Stefan number and Archimedes number on vapor condensation outside multiple cross sections. Finally, the condensate inundation and mean heat transfer coefficients are analyzed in horizontal tube banks.
PERFORMANCE OF TWO DIFFERENT HIGH-ACCURACY UPWIND SCHEMES IN INVISCID COMPRESSIBLE FLOW FIELDS
Hosseini R,Rahimian M.H,Mirzaee M Korea Society of Computational Fluids Engineering 2005 한국전산유체공학회지 Vol.10 No.1
Performance of first, second and third order accurate methods for calculation of in viscid fluxes in fluid flow governing equations are investigated here. For the purpose, an upwind method based on Roe's scheme is used to solve 2-dimensional Euler equations. To increase the accuracy of the method two different schemes are applied. The first one is a second and third order upwind-based algorithm with the MUSCL extrapolation Van Leer (1979), based on primitive variables. The other one is an upwind-based algorithm with the Chakravarthy extrapolation to the fluxes of mass, momentum and energy. The results show that the thickness of shock layer in the third order accuracy is less than its value in second order. Moreover, applying limiter eliminates the oscillations near the shock while increases the thickness of shock layer especially in MUSCL method using Van Albada limiter.
PERFORMANCE OF TWO DIFFERENT HIGH-ACCURACY UPWIND SCHEMES IN INVISCID COMPRESSIBLE FLOW FIELDS
R. Hosseini,M.H. Rahimian,M. Mirzaei 한국전산유체공학회 2005 한국전산유체공학회지 Vol.10 No.1
Performance of first, second and third order accurate methods for calculation of inviscid fluxes in fluid flow governing equations are investigated here. For the purpose, an upwind method based on Roe’s scheme is used to solve 2-dimensional Euler equations. To increase the accuracy of the method two different schemes are applied. The first one is a second and third order upwind-based algorithm with the MUSCL extrapolation Van Leer (1979), based on primitive variables. The other one is an upwind-based algorithm with the Chakravarthy extrapolation to the fluxes of mass, momentum and energy. The results show that the thickness of shock layer in the third order accuracy is less than its value in second order. Moreover, applying limiter eliminates the oscillations near the shock while increases the thickness of shock layer especially in MUSCL method using Van Albada limiter.