جستجوی مقالات مرتبط با کلیدواژه « Vertical Tube » در نشریات گروه « مکانیک »

The present research aims to investigate the two-phase air/water flow in a vertical pipe using an electrical resistance sensor and a high-speed camera. An electrical resistance sensor is designed and embedded in the inner wall of the tube. A flow pattern map is drawn at the height of 270 cm from the testbed inlet for 320 different phase velocities using a high-speed camera. By measuring the output voltage of the electrical resistance sensor and using the Maxwell relation, the volume fraction in bubbly and slug flow regimes are calculated for different phase velocities. The volume fraction values detected from the output signal of the electrical resistance sensor are compared with the results obtained from the high-speed camera images. The width of the output signal from the electrical resistance sensor indicates the length of the Taylor bubble. The output signal width is compared to the obtained Taylor bubble length from high-speed camera images, for several different velocities of the phases. It is noticed that at a constant velocity of the phases, the output signal width from the sensor is linearly related to the length of the Taylor bubble. The variations of the output signal width are plotted in terms of the ratio of the Taylor bubble length to the summation of air and water superficial velocities. By linear fitting of the available data, a novel equation is presented to calculate the Taylor bubble length in terms of the signal output from the electrical resistance sensor and the total superficial velocity of the phases.

To examine the flow characteristics of particles in the vertical tube corresponding to different curvature radius bends, the particle velocity is measured at the Minimum Pressure Drop (MPD) using a high-speed Particle Image Velocimeter (PIV). This experiment explores the effects of particle flow characteristics at different curvature radius bends and their corresponding vertical tubes with pressure drop, power consumption, the intensity of particle fluctuation velocity, power spectrum and time-frequency characteristics. It is observed that the pressure drop and power consumption can be reduced with the help of a large curvature radius bend. Besides, the reduction of particle velocity in the large curvature radius bend and its corresponding vertical tube is less, and the particle possesses a larger intensity of fluctuation velocity in its corresponding vertical tube. The particles in the vertical tube corresponding to the large curvature radius bend lead to large peaks of the power spectrum in the low-frequency region, which is closely linked to the pressure drop. Eventually, the dynamics of particles in a vertical tube are revealed from the perspective of time-frequency analysis by using a continuous wavelet transform.

In the present work, the critical heat flux measurements were performed for the subcooled flow boiling of pure water and magnetic nanofluids (i.e., water + 0.01 and 0.1 vol.% Fe 3O4) in a vertical tube. The effect of applying an external magnetic field on the CHF variation was studied experimentally as well. The obtained results indicated that the subcooled flow boiling CHF in the vertical tube is increased by using the nanofluid as the working fluid, especially in lower volume concentration of nanoparticles. The nanoparticles deposition on the tube inner surface and consequently improvement of the surface characteristics such as nucleation site density, wettability and re-wetting properties could be mentioned as the main reasons of this incident. Moreover, it was seen that applying the magnetic field leads to the additional enhancement in the CHF of ferrofluids. It could be clarified as the attraction of the nanoparticles into the magnets and increasing the surface wettability resulted in the CHF enhancement.

The problem of laminar film condensation from binary vapours mixture with the presence of non-condensable gas (air) flowing in a vertical tube is numerically investigated. The set of the non-linear parabolic equations expressing the mass conservation, momentum, energy, and species diffusion in both phases with the boundary conditions are resolved by using a finite difference numerical scheme. A comparative study between the results obtained for three cases (water-ethanol-air, water-methanol-air, and ethanol-methanol-air) under the same conditions is made. The impact of varying the wall temperature, the inlet vapour mass fractions, and the inlet liquid mass flow rate on the conjugate the heat and mass transfer during the condensation of the studied mixtures are examined. It is found that the condensation of water-methanol-air corresponds to a higher latent heat flux QL2 and accumulated condensation rate Mr2 when compared with water-ethanol-air and ethanol-methanol-air. Moreover, the nature of the fluid plays an important role in the heat and mass exchanges.