Speed distribution in the exhaust diffuser of the air fan

A perfect connection between the column and the fan is that which ensures an air inlet in the fan, evenly distributed, over the entire surface of the suction mouth and an air outlet from the fan outlet made in a way that allows the full use of developed pressure. For both suction and exhaust, fans must be equipped with a device/diffuser. When the fan discharges freely into the atmosphere without any connection, a loss equivalent to 50% of the average dynamic pressure at the discharge port occurs. If the fan discharges into a speaker, the loss depends on its angle. At a peak angle of 30° corresponds to a loss of ≈ 25% of the average dynamic pressure in the discharge mouth, and to reduce air vortices the speakers must be built at an angle of inclination to vertical or horizontal between 12- 15°, in order to reduce the aerodynamic resistances. The paper will present the speed field distribution of an axial fan located on a circular duct, provided on the air discharge side with a diffuser with a length of 1.5 m, at an angle of inclination to the vertical or horizontal of 12°.

Bubble behavior in liquid-gas two-phase flow behind a cross-shaped obstacle in a vertical circular duct

Grid spacers installed in subchannels of fuel assemblies for nuclear reactors can promote heat transfer. However, the fluid velocity and bubble behavior are greatly affected as the cross-sectional area of the flow passage changes. Therefore, the void fraction distribution behind the obstacle that simulates the grid spacer shape simply was measured by using a wire mesh sensor (WMS) system. Moreover, a two-phase flow analysis was performed to investigate the effect of the obstacle on the bubble behavior in a vertical duct.

Numerical Analysis of Flow and Heat Transfer Enhancement in A Horizontal Pipe with Plain and Dimple Twisted Tape

In order to improve thermo-hydraulic performance of laminar flow various techniques has been used among which a plain tube with twisted tape insert is widely used. The main objective is to numerically study flow field in order to enhance heat transfer, through a circular pipe built in with/without Dimples on twisted strip. Effect of plain and dimple strip on thermo hydraulic performance discussed. The analysis results for laminar range of 800<Re<2000 is obtained with twist ratio of the strip is 3.0. Analysis is carried for full length tape with constant heat flux. The simulation results of Nusselt number versus Reynolds number of the plain, plain twisted tape and Dimple twisted tape with the experimental data give variation of 2.5, 5.75 and 9.5%. The friction factor of Dimple twisted tape tube is 6 to 13 times that of the plain tube. The thermal performance factor of the Dimple twisted tape and plain twisted tape tube is 4 to 15% and 3 to 12 % respectively higher than that of plain tube. Due to increase in thermal performance factor of induced strip with dimples there is an intensification of heat transfer obtained through circular duct with dimple twisted tape insert than that of plain twisted tape and plain pipe. The use of a twisted tube compounded with dimples is feasible in terms of energy saving at lower Reynolds numbers. Present study is applicable for design of compact heat exchanger in order to optimize energy consumption.

Analysis of the Magnetohydrodynamic Behavior of the Fully Developed Flow of Conducting Fluid

Important industrial applications are based on magnetohydrodynamics (MHD), which concerns the flow of electrically conducting fluids immersed in external magnetic fields. Using the Finite Volume Method, we performed a 3D numerical study of the MHD flow of a conducting fluid in a circular duct. The flow considered was laminar and fully developed. Along the initial section of the duct, there were magnets placed around the duct producing magnetic fields in the radial direction. Two arrangements of magnetic field orientation were considered: fields pointing toward and away from the duct’s center alternately, and all fields pointing toward the duct’s center. For each arrangement of magnets, various intensities of magnetic fields were considered to evaluate two effects: the influence of the magnetic field on the flow velocity, and the influence of the flow velocity on magnetic field induction. It was found that for the second arrangement of magnets and Hartmann numbers larger than 10, the flow velocity was reduced by as much as 35%, and the axial magnetic induction was as high as the field intensity applied by each magnet. Those effects were negligible for the first arrangement and low fields because of the distribution of field lines inside the duct for these situations.