Unsteady Film Flow Research Articles

Impacts of different shapes of nanoparticles on SiO 2 nanofluid flow and heat transfer in a liquid film over a stretching sheet

The present study manipulates the unsteady film flow and heat transfer of SiO 2 water nanofluid over a stretching sheet under convective boundary conditions. Governing partial differential equations (PDEs) are transformed into a set of nonlinear ordinary differential equations (ODEs) and then solved using BVP4C in MATLAB. The impact of multi-shape SiO 2 nanoparticles along with other pertinent parameters, such as Prandlt, Eckert and biot-number on flow and heat transfer characteristics is examined via graphical simulations. Moreover, the skin-friction coefficient and Nusselt number are also computed and tabulated, numerically. The study reveals that platelet shape of SiO 2 nanoparticles possess the high flow and heat transfer rate. In addition, temperature profile enhances by augmenting volume-fraction parameter and biot-number but the reverse trend is found for slip parameter.

Liquid film flow on a high speed rotary bell-cup atomizer

In a high-speed rotary bell-cup atomizer, which is mainly used in the automotive industry, atomization is achieved by disintegration of a thin liquid film at the bell-cup edge. To obtain the hydrodynamic behavior of the liquid film as it passes over the bell cup, the liquid-film formation was simulated using the volume of fluid method under various conditions of the rotational speed, flow rate, liquid viscosity, and surface tension coefficient, based on industrial painting conditions. The liquid supplied from the liquid supply nozzle to the bell-cup surface flowed radially upon rotation of the bell cup and formed a film, which reached steady-state. We clarified the flow field depended on the rotational speed, flow rate, and liquid viscosity, and was independent of the surface tension coefficient. Based on these results, an equation for the liquid film thickness was proposed. In addition, the unsteady behavior of film with flow fluctuation in liquid supply was also investigated; the fluctuations persisted at the edge of the bell-cup atomizer. The proposed equation can be applied to this case regardless of the normalized amplitude of the fluctuation up to 50%. Thus, in this condition, unsteady film flow may be described in the proposed equation, which assumes a steady flow.

Flow and heat transfer in a nano-liquid film over an unsteady stretching surface

The unsteady film flow and heat transfer of nanofluids caused by a linear stretching velocity over a horizonal elastic sheet is investigated. By means of similarity variables, the boundary layer equations describing the momentum and energy conservations are reduced to a set of ordinary differential equations with an unknown constant. The homotopy analysis method (HAM) is then applied to give exact solutions for this particular kind of equations. A linear relationship between the film thickness β and the unsteadiness parameter S is found. Besides, the effects of the unsteadiness parameters S, the solid volume fraction of the nanofluid ϕ and the Prandtl number Pr on the velocity and the temperature distributions are presented and discussed, respectively. It is found that the usage of nanoparticles in the base fluids can effectively improve on the heat transfer characteristics.

Conditions of ascending cocurrent flow in variable-diameter tubes

The working tube of diameter 25.6 mm had terminal portions of smaller diameters (16.8 and 21.4 mm). When a steady film flow is realized in the terminal portions, only unsteady conditions (flooding or unsteady film) are possible in the main middle portion. A diagram of flow modes (falldown, pickup, fluctuating flow, unsteady film flow, steady film flow, etc.) is constructed in phase (water–air) flow rate coordinates. Entrainment boundary, incomplete wetting, and types of wave modes are noted.

Millimeter wave rheometry: theory and experiment

A novel millimeter wave (MMW) rheometry is developed to determine the viscosity of fluids based on an unsteady film flow on an inclined plane. The method measures fringes due to MMW interference between the front and back surfaces of a fluid flowing across the field of view of a ceramic wave guide coupled to a MMW receiver operating at 137 GHz. With knowledge of the dielectric constant, the interference fringe spacing is used to calculate the thickness of the fluid layer. This thickness is then transformed into the viscosity by means of a simple hydrodynamic theory. Our results show that the MMW rheometry can practically distinguish between the 30, 100, and 200 Pa·s silicone oils. The geometry of the method allows for potential industrial applications such as measuring viscosity of the flowing slag down the walls of coal gasifiers. The MMW rheometry with simple modifications can be easily extended to measure important non-Newtonian fluid characteristics such as yield stress.

Unsteady film flow of power-law liquids on a rotating disk

A boundary-layer-type approximation of the equations of motion for the flow in a film or power-law liquid on a rotating disk is derived. For a given non-steady angular elocity an exact, similarity, solution to the obtained equations is presented. Flow velocity and the evolution of the initally non-uniform thickness of the film are studied for relatively small times after the start of rotation.