Fujii Motoo

Experimental Studies on Thermal and Electrical Properties of Platinum Nanofilms

We experimentally studied the in-plane thermal and electrical properties of a suspended platinum nanofilm in thickness of 15 nm. The measured results show that the in-plane thermal conductivity, the electrical conductivity and the resistance-temperature coefficient of the studied nanofilm are much less than those of the bulk material, while the Lorenz number is greater than the bulk value. Comparing with the results reported previously for the platinum nanofilm in thickness of 28 nm, we further find that the in-plane thermal conductivity, the electrical conductivity and the resistance-temperature coefficient decrease with the decreasing thickness of the nanofilm, while the Lorenz number increases with the decreasing thickness of the nanofilm. These results indicate that strong size effects exist on the in-plane thermal and electrical properties of platinum nanofilms.

Influence of various surface roughness on the natural convection

Abstract Experimental results are presented with respect to the influence of various surface roughness on the natural convection of water and spindle oil along a vertical cylinder. Here are introduced the roughness of repeated-ribs of 0.5 mm height and 6.4, 12.8, 25.6 spacing-height ratio, that of dispersed-protrusions of 0.5 mm height, and that of dense-pyramids of 1.0 mm height. The local heat-transfer coefficients in the turbulent region, which are evaluated based on the base area of the cylinder, increase slightly in the case of water and decrease slightly in the case of oil. The magnitudes of the variations, however, are at most 10 per cent of the values in the case of the smooth surface. The upper limit of the laminar region is also not affected so much by the roughness. Some considerations on these results are presented in reference to the results of measurements made on temperature profiles in the boundary layer and rising velocities of vortex-pairs and turbulent lumps, beside those of observation done on the fluid motion in the boundary layer and those hitherto reported on the case of forced convection.

Natural convective heat transfer from a vertical isothermal surface to a non-Newtonian Sutterby fluid

This paper deals with the laminar natural convection of a non-Newtonian fluid along a vertical isothermal surface. The boundary-layer equations for a Sutterby fluid are solved numerically, and several characteristics of the non-similarity solution are represented graphically. An approximate expression of local Nusselt number Nux is proposed as Nux = 0·.50(Gr0xPr0)0·.25(1+m) , where m= 0−04 Pr00.23 A3·7 Pr0−0.34 Z00·63A0.66 Gr0x and Pr0 are Grashof number and Prandtl number based on zero viscosity respectively, and A and Z0 are non-Newtonian parameters. Local heat-transfer coefficients are obtained by experiments with aqueous solutions of polyethyleneoxide (PEO) and carboxymethylcellulose (CMC). The experimental results are in excellent agreement with the theoretical ones.

Natural convective heat-transfer from a vertical surface of uniform heat flux to a non-newtonian sutterby fluid

Abstract This paper deals with the laminar natural convection of a non-Newtonian fluid along a vertical surface with uniform heat flux. The boundary layer equations for a Sutterby fluid are solved numerically, and the typical results for the local Nusselt number Nux, are represented graphically. From the results an approximate expression of Nux, is proposed as Nu x = 0.62(Gr ∗ ox Pr o ) 0.2(1+m ∗ where m ∗ = 0.06Pr o −0.28 A 3.7 pr o -0.34 Z ∗ o 0.35A0.66 , Gr∗0x and Pr0 are Grashof and Prandtl numbers based on zero viscosity respectively, and A and Z ∗ 0 are non-Newtonian parameters. Local heat-transfer coefficients are obtained by experiments with aqueous solutions ofpolyethyleneoxide (PEO) and carboxymethylcellulose (CMC). The experimental results are in excellent agreement with the theoretical predictions.

Experimental study on the in-plane thermal conductivity of Au nanofilms

Abstract The in-plane thermal conductivity of Au nanofilms with thickness of 23 nm, which are fabricated by the electron beam-physical vapor deposition method and a suspension technology, is experimentally measured at 80–300 K by a one-dimensional steady-state electrical heating method. Strong size effects are found on the measured nanofilm thermal conductivity is much less than that of the bulk material. With the increasing temperature, the nanofilm thermal conductivity increases. This is opposite to the temperature dependence of the bulk property. The Lorenz number of Au nanofilms is about three times larger than the bulk value and decrease with the increasing temperature, which indicates the invalidity of the Wiedmann-Franz law for metallic nanaofilms. *Supported by National Natural Science Foundation of China (Grant No. 50606018)