The numerical simulation approach of heat carrier mixing regimes in the T-junction shows that the RANS approach is beneficial for a qualitative flow analysis to obtain relatively agreed averaged velocity and temperature. Moreover, traditionally, the RANS approach only predicts the averaged temperature distribution. This mathematical model did not consider the temperature fluctuation variations important for the thermal fatigue task. It should also be emphasized that unlike the LES approach, the steady RANS approach cannot express a local flow structure in intense mixing zones. Nevertheless, apparently the adopted RANS approach should be used for assessing the quality of computational meshes, boundary conditions with the purpose to take LES for further numerical simulation.

The present article uses the methods of numerical simulation and experimental visualization of flows to study convective heat transfer of single round tube with vortex generators shaped as spherical dimples placed on its external surface. Numerical simulation used ANSYS Fluent. The obtained data showed that the presence of vortex generators changes the flow structure and makes flow turbulent near these generators, which can decrease the wake length behind the tube and thus reduce hydraulic losses. It shows that in some cases, the thermal/hydraulic performance of smooth tubes is higher than that of dimpled ones. The analysis of the structure of flow around single dimpled tubes shows that vortex structures begin forming in dimples in a different way depending on their arrangement on the tube surface. With dimples made near the forward stagnation point of the tube (the angular coordinate is 0−30°, starting from the forward stagnation point) vortex structures are not formed. The interaction of incoming flow is similar to the case when the impact jet interacts with the wall. This deteriorates heat transfer near the dimples. Arranging dimples at an angular coordinate 40−90° gives rise to the formation of vortex structures in dimples and in the wake behind them, thus allowing the local heat transfer coefficient to be increased. In addition, we can say that the location of dimples changes the secondary vortex structure in the dimple and, hence, heat transfer. In the tube rear, the dimples made at an angular coordinate of more than 90° do not play the role of vortex generators, but they only develop a heat transfer surface. Thus, there is no unique answer how to enhance heat transfer by dimples evenly placed on the surface of the tube. Nevertheless, the arrangement of dimples affects the turbulence intensity in the wake behind the tube and the separated flow point, which as a result can influence hydraulic losses.

A thin fluid film formed by withdrawing a vertical plate is being studied theoretically. It is the case of a viscoplastic fluid described by the Bingham model. The boundary-value problem is formulated by the lubrication theory. The analysis presented herein required to solve numerically a system of ordinary differential equations at appropriate boundary conditions. For the viscoplastic fluid, we have predicted a film thickness over a wide range of a capillary number (10−4 to 10), with a particular emphasis on finding the free surface location at various conditions: (a) the unyielded region is much larger than the yielded one; (b) without the yielded region; and (c) the unyielded region is smaller but is compared with the yielded one. For the case of Bingham fluid and the limiting case of Newtonian fluid, the agreement was found between our theory and the experiment for the considered capillary number range.A thin fluid film formed by withdrawing a vertical plate is being studied theoretically. It is the case of a viscoplastic fluid described by the Bingham model. The boundary-value problem is formulated by the lubrication theory. The analysis presented herein required to solve numerically a system of ordinary differential equations at appropriate boundary conditions. For the viscoplastic fluid, we have predicted a film thickness over a wide range of a capillary number (10−4 to 10), with a particular emphasis on finding the free surface location at various conditions: (a) the unyielded region is much larger than the yielded one; (b) without the yielded region; and (c) the unyielded region is smaller but is compared with the yielded one. For the case of Bingham fluid and the limiting case of Newtonian fluid, the agreement was found between our theory and the experiment for the considered capillary number range.