A study is made of the natural convection of a fluid contained in a long horizontal enclosure of rectangular cross section with one vertical wall heated and the other cooled. Two‐dimensional motion is assumed. The governing vorticity and energy transport equations are solved by an implicit alternating direction finite‐difference method. Transient and steady state isothermals and streamlines are obtained for Grashof numbers up to 100,000 and for height‐to‐width ratios of 1, 2, and 3.

Rheometric data for short‐fiber‐filled thermoplastics are presented using a parallel‐plate viscometer. Polypropylene tensile bars contain short and long fibers with glass weight percentages of 0%, 5%, 10%, 20%, and 30%, polycarbonate tensile bars with glass percentages of 0%, 5%, and 10% long fibers, and nylon 6/6 tensile bars with 0%, 15%, 30%, and 45% short fibers. The short fibers were initially 3 mm in length and 12.7 microns in diameter. The long fibers were initially 6 mm in length and 10 microns in diameter. In the steady‐state experiments, the fibers increase the viscous stresses and the normal stresses in proportion to the concentration of fibers. At low shear rates, the viscosity is increased by the addition of the fibers, but at high shear rates the viscosity approaches that of the neat resin. In dynamic testing, the fibers increase the viscous and elastic components as measured by the complex viscosity and modulus. The fibers increase the viscous and elastic nature of the fiber‐filled composite at low frequencies and to a lesser extent at higher frequencies. The fibers increase the elastic component more than the viscous component at low frequencies and less at higher frequencies as demonstrated by tan δ.

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The steady and transient behavior of jets generated by circular and slit nozzles are analyzed by the Galerkin finite-element method with free-surface parametrization and Newton iteration. A novel constitutive equation is used to approximate Bingham liquids that is valid uniformly in yielded and unyielded domains and which approximates the ideal Bingham model and the Newtonian liquid in its two limiting behaviors. At steady state the influence of yield stress on the die swell is equivalent to that of surface tension; that is, suppression of jet diameter at low Reynolds numbers and necking at high Reynolds number. The predictions at high Reynolds numbers agree with the asymptotic behavior at infinite Reynolds number of the jet far downstream. In the transient analysis, surface tension destabilizes round jets and increases the size of satellite drops. Yield stress was found to retard jet breakup times in addition to producing smaller satellites. Shear thinning was found to result in shorter collapse times than those for Newtonian fluid; furthermore, the satellite drop size increased with increasing shear thinning. The nonlinear analysis predicts that, although round jet breakup may occur spontaneously by surface tension, an external factor, commonly air shear, must be applied to break a planar jet at Reynolds numbers below its transition to a turbulent jet.