This study presents experimental results for the heat transfer coefficient during pool boiling of DI water and Al 2 O 3-water based nanofluid at saturation conditions. Based on these data, an analysis of the heat transfer enhancement due to the nanofluids was performed. The experiments were performed for Al 2 O 3-water based nanofluid with different volume concentrations (0.0007 vol.% and 0.007 vol.%, corresponding to low and high nanofluid concentration, respectively). A copper surface, with different roughness values (R a = 0.05 lm, corresponding to a smooth surface, and R a = 0.23 lm, corresponding to a rough surface), was used as test section. The nanoparticle average size was 10 nm and the applied heat flux ranged from 100 to 800 kW/m 2. For nanofluid pool boiling, it was observed an increase in the heat transfer coefficient up to 75 %, and 15% for the smooth and rough surfaces, respectively, in comparison to that of DI water. According to results, the surface roughness is strongly affected by nanofluid concentration due to the nanoparticle deposition on the heating surface. The results indicate that the use of nanofluids is effective on pool boiling heat transfer, for moderate heat flux and low volumetric concentration.

The authors investigate the influence of secondary flows in the thrust acting on the axis of a liquid oxygen radial pump with operating conditions like those of a Vinci upper-stage rocket engine. For a high circumferential Reynolds number, pressure and velocity distributions are obtained by varying geometrical parameters known to influencing the flow in the cavities between the impeller and the housing. The results obtained with the numerical method are compared with those calculated with formulae relying on the rotation factor. The Finite-Volume Method is applied to three-dimensional impeller-housing models. The results indicate the axial thrust estimated using the formulae returns overestimated values as compared with those computed with the numerical method, such fact suggesting that corrections might be needed when one considers applying the design guidelines to radial pumps driving liquid oxygen.

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