Multiple instabilities of thermocapillary flow in a cylindrical pool with a rotating disk on the free surface.

The thermocapillary flow instabilities of silicon melt in a cylindrical pool with a rotating disk on the free surface (a simplified model of the Czochralski crystal growth) are numerically investigated by using the linear stability analysis. The complete neutral or critical stability curves are determined. Results show that the neutral stability curves form a closed region in the parameter plane, in which the steady axisymmetric flow is linearly stable. Two types of rotating wave (RW1 and RW2) instabilities and two types of hydrothermal wave (HTW1 and HTW2) instabilities are found. The energy analysis shows that all the instabilities are hydrodynamic (inertial) in nature. Specifically, RW1 and RW2 are caused by the azimuthal shear induced by the crystal rotation, while HTW1 and HTW2 are caused by the radial shear induced by the thermocapillary force.

Concrete Elastic Modulus Experimental Research Based on Theory of Capillary Tension.

The risk of cracking in the early stage is a critical indicator of the performance of concrete structures. Concrete cracked when the tensile stresses caused by deformation under restraint conditions exceeded its tensile strength. This research aims at an accurate prediction of shrinkage cracking of concrete under constraints. Based on the theory of capillary tension under the concrete shrinkage mechanism, the method to test and compute the elastic modulus of a micro-matrix around the capillary, Et, was derived. Shrinkage and porosity determination tests were conducted to obtain the shrinkage values and confining stresses of concrete at different strength grades, different ages and under different restraint conditions, accordingly. Meanwhile, the proposed method of this research was used to obtain Et. The restraint stress given by Et was compared with the experimental result under the corresponding time. The results suggested a positive correlation between the elastic modulus of a micro-matrix around the capillary, Et, precomputed by the theory, and the static elastic modulus, Ec, and that the ratio between the two gradually decreased with the passage of time, which ranged from 2.8 to 3.1.