The heat transfer coefficient in a plane channel was estimated theoretically. In the framework of assumptions made in the present research, a correlation in the form of Lyon’s integral was obtained for energy equation. It was employed for analytical estimation of heat transfer coefficient in laminar flows and liquid metal flows, in which molecular heat transfers prevail over turbulent one. The computational results comply with the literature.
Spanwise heterogeneous surface roughness can induce secondary flows of Prandtl’s second kind, which significantly affect momentum and heat transfer. Despite a large number of numerical studies of such flows, experimental data remain rather limited. In this paper, an experimental study of turbulent flow in a rectangular channel with walls formed by alternating smooth sections and strips of discrete roughness is performed. The fields of mean velocities and turbulence characteristics are obtained using the SIV method, and the structure of secondary flows is reconstructed. Measurements of hydraulic resistance are carried out for various surface configurations and Reynolds numbers. It is shown that heterogeneous roughness leads to the formation of large-scale secondary flows in the form of counter-rotating vortices with a transverse velocity of up to 5
In this paper, we investigate the occurrence of Majorana zero modes in carbon nanotubes in contact with a conventional superconductor and placed in a longitudinal magnetic field. The influence of nanotube geometry, determined by chirality indices (n,m) , on the conditions for the formation of the topological superconducting phase is considered. It is shown that chirality changes the electronic structure of the nanotube, the spin–orbit interaction and the effective chemical potential, which determine the conditions of the topological phase transition. To describe the system, an effective model based on the Bogolyubov–de Gennes Hamiltonian is constructed, which allows one to obtain a criterion for the occurrence of Majorana null modes. Based on the developed model, a method for selecting the most favorable geometries of carbon nanotubes is proposed. Numerical results show that certain chiralities minimize the effective chemical potential and facilitate the transition of the system to the topological phase. The obtained results show that the geometry of the carbon nanotube is an effective parameter for controlling the topological properties of the system and can serve as a criterion for choosing the chiralities that are most promising for the experimental implementation of Majorana zero modes.
The paper presents a methodology for experimental research and a test bench for determining the flow coefficient during the flow of a two-phase working fluid through cracks. The dependences of the influence of the degree of dryness of the wet refrigerant vapor and the gap resistance on the flow coefficient during the outflow of the working fluid through the gap were established. A method for determining the coefficient of flow of wet vapor through cracks is proposed, implemented on the basis of the method of S.E. Zakharenko for dry saturated vapor and a correction function for the degree of dryness of the vapor. Artificial refrigerants used in air conditioning systems, such as R32 and R410a, which belong to the HFC class, and R22, which belongs to the HCFC class, are considered as the working fluid.
The efficiency of four modifications of flow conditioners in terms of smoothing velocity profiles and ensuring their reproducibility with varying flow history and turbulence intensity at low Reynolds numbers was experimentally studied. The relevance of the work is due to the problem of increasing the accuracy of gas flow measurement in complex gas-dynamic conditions, especially in the region of laminar–turbulent transition. An approach has been identified that allows for the leveling of velocity profile deformations in a wide range of flow histories with a flow turbulence level not exceeding 14
