This paper attempts to study numerically a differentially heated square cavity, which is formed by horizontal adiabatic walls and vertical isothermal walls. Two perfectly insulated baffles were attached to its horizontal walls at symmetric position. Heat transfer by natural convection of dry air was studied by solving mass, momentum and energy equations numerically. Streamlines and isotherms are produced and heat transfer is calculated. A parametric study is carried out using following parameters: Rayleigh number from 10⁴ to 10⁸, non-dimensional thin baffles length are 0.6, 0.7, and 0.8, non-dimensional baffle positions S_b from 0.2 to 0.8. It was observed that the two baffles trap some fluid in the cavity and affect the flow fields. The flow for cavities with S_b<0.5 at low Ra tends to circulate as a primary vortex strangled by the baffles while at high Ra it tends to separate into two different vortexes. For the cavities with S_b>0.5 it tends to separate into two different vortexes at low Ra while at high Ra tends to circulate as a primary vortex strangled by the baffles. It is found that Nusselt number is an increasing function of Ra, a decreasing one of baffle length, and strongly depends on S_b. Another interesting phenomenon of the typical cavity is that a particular case is the opposite of the other case as long as the sum of S_b is equal to 1. Thus, the typical cavity can allow the heat flow in one direction but significantly blocks it in the opposite direction. The typical cavity can be proposed as a heat version of a diode. The heat may be transferred up to 42% from one direction but blocked up to 98% in the opposite direction by using a particular cavity with L_b=0.7 and S_b=0.4 at Ra=10⁸.

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Synthesis of vertically aligned single-walled carbon nanotube (VA-SWNT) thin films by alcohol catalytic chemical vapor deposition has been clarified using an in situ optical absorbance measurement technique, which makes it possible to control the final film thickness. These VA-SWNT films can be detached from the substrates on which they are grown and reattached onto arbitrary solid surfaces by a simple hot water-assisted process. This will allow many new areas of SWNT applications to be investigated.

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Gas-liquid flows usually include multi-scale free surfaces, for example, fuel sprays used for automobile engines become liquid films at the outlet of fuel injectors, and then the liquid films break up into droplets. Fluid flow with free surfaces, like the liquid films, are mainly simulated using grid methods, where the front of the free surface is directly captured on regular, fixed grids that cover both liquid and gas domains. In these methods, however, free surfaces are sometimes lost due to numerical diffusion in case the scale of the free surfaces becomes smaller than the grid size. Particle methods can avoid the occurrence of such the unreal loss of free surfaces. The particle methods treat the free surfaces as groups of particles that move in a pattern based on a Lagrangian description. To simulate the multi-scale free surfaces, we have developed a hybrid particle/grid method where the free surfaces within a sub-grid region are simulated with particles located near the liquid interfaces. Velocities determined using the particle method are combined with those obtained from the grid method. However, the interaction between gas and liquid still depends on the grid size because the gas regions within the sub-grid regions were calculated by the grid method. Accordingly, the present method adopts a two-particle model as the particle method; that is, the free surfaces within the sub-grid region are simulated with two types of particles, one for the gas and the other for the liquid. The sub-grid regions are determined by using the volume fraction of liquid calculated using the grid method, and then the two-particle model is applied to the sub-grid regions. We will verify the new method by applying it to prediction of large deformation in free surfaces (the Rayleigh-Taylor instability) and to the fragmentation of a water column. The predicted deformed shape of the water column shows good agreement with measurements reported by Koshizuka et al.

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