• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.13 no.3
• /
• pp.209-216
• /
• 2001

A numerical study is peformed to investigate the effect of circumferential velocity generated by the guide vane on the nozzle flow of a jet fan, s a way of increasing the penetration force of jet fan with nozzle of 175mm diameter. For the validation of numerical results. the velocity is measured by a 5-hole pitot tube and flow visualization is conducted by the tuft method. Under the inlet condition that the maximum circumferential velocity in the stator outlet of the present jet fan is 1.8m/s, the axial velocity in the nozzle outlet has the feature that the velocity at the axis is low and the velocity near the wall high. Therefore, to increase the throw length of the jet fan, the configuration of the fairing and nozzle needs to be developed and the precise revise of the stator angle is required, In addition, the bigger the circumferential velocity, the smaller the axial velocity at the axis and the bigger non-uniformity of the flow distribution.

• Proceedings of the KSME Conference
• /
• 2000.11b
• /
• pp.272-277
• /
• 2000

The heat transfer characteristics of confined turbulent slot jet impingement on the flat plate with square rods(turbulence promoter) have been experimentally investigated at different nozzle configuration. The effects of jet Reynolds number (Re=3900, 5800, 7800, 9700), dimensionless slot-to-plate distance(H/B=4, 6, 8) and clearance(c) between square rods and the plate were examined. Measurement of heat transfer rate were conducted using naphthalene sublimation technique. When square rods were inserted over the heat transfer surface, heat transfer rate was slightly increased in the wall jet region and the sharp-edged orifice nozzle was heigher than squared orifice nozzle.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
• /
• v.13 no.1
• /
• pp.14-21
• /
• 1984

The purpose of this investigation is to study heat transfer characteristics in wall jet region on a flat plate caused by upward impinging water jet. In the wall jet region, heat transfer results by impinging water jet are being compared with the ones with supplementary water. As the radius increases, the heat transfer coefficient in the wall jet region consquently decreases, but decreasing nozzle-heat plate distance, the reduction rate increases. The experimental equation is expressed as follows : $$\frac{N_{ur}}{P_r^{0.4}}{\cdot}\overline{\xi}=m(\overline{\eta}{\codt}Re{\delta})^n,\;m=0.034\~0.056,\;n=1.74\~2.007$$ The optimum height of supplementary water is obtained to improve heat transfer effect of wall jet region.

• Fire Science and Engineering
• /
• v.18 no.4
• /
• pp.27-34
• /
• 2004

We have conducted a numerical simulation under three-dimensional unsteady conditions in order to analyze the effect of flow and CO₂ mass transfer according to the distance between the CO₂ nozzle of CO₂ fire fighting system and the rear wall in a protection space. Flow fields and CO₂ concentration fields were measured. The different recirculation flow form and wall jet was developed according to increasing the distance between CO₂ nozzles and rear wall. In all the case, CO₂ mass transfer was generated toward the center of a protection space from each walls, but the CO₂ mass fraction of front and rear areas based on CO₂ nozzles showed higher or lower by increasing the distance between CO₂ nozzle and rear wall.

• International Journal of Aeronautical and Space Sciences
• /
• v.17 no.3
• /
• pp.324-331
• /
• 2016

The present study focuses on the characteristics of a supersonic jet flowing from a rectangular nozzle exit on a flat plate. Flow visualization techniques using schlieren and kerosene-lampblack tracing are utilized to investigate shock reflection structures and boundary-layer separations over a flat plate. Wall pressure measurements are also carried out to quantitatively analyze the flow structures. All observations are repeated for multiple jet flow boundary conditions by varying the flap length and nozzle pressure ratio. The experimental results show that the jet flow structures over the flat plate are highly three-dimensional with strong bleeding flows from the plate sides, and that they are sensitive to plate length and nozzle pressure ratio. A multi-component force measurement device is also utilized to observe the characteristics of the jet flow thrust vectoring over the plate. The maximum thrust deflection angle of the jet is about $8^{\circ}$, demonstrating the applicability of thrust vector control via a flat plate installed at the nozzle exit.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.31 no.12
• /
• pp.1024-1032
• /
• 2007

The flow characteristics with the impinging angles of defrost nozzle jet inside a commercial vehicle passenger compartment were investigated experimentally by using the two-dimensional duct-nozzle model. The shape of the nozzle contraction was designed according to the curved line of cubic equation to the vertical plan of the flow direction. The impinging angles, defined as the angle between nozzle axis and a vertical line to the windshield, were varied from the $0^{\circ}\;to\;80^{\circ}$. The mean velocity distributions, the half-widths, and the momentum distributions with the cases of both the free jet and the impinging jet onto the dummy windshield were measured. The impinging jet flows similarly with wall jet from $X/b_o=20$, and the impinging angle has an effect on the half-width of the impinging jet. The momentum distributions onto the windshield increased with the increase of impinging angle, and then their inflection point was observed around the impinging angle of $60^{\circ}$.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.23 no.2
• /
• pp.175-184
• /
• 1999

A theoretical study on the turbulent round jet diffusion flame impinging on the wall was carried out to predict the characteristics and structure of Impinging jet flame and heat transfer to the wall. Finite chemistry via Arrhenius equation and eddy dissipation model was adopted as a combustion model, and the Favre averaging and $k-{\varepsilon}$ model were Introduced In the theoretical modeling. The SIMPLE algorithm was applied to the calculation. All the transport properties were considered as the variable depending on the temperature and composition. For the parametric study, the distance from nozzle to impinging wall and Reynolds number at nozzle exit were chosen 88 the major parameters. As the results of the present study, the characteristics of flow fields, the distributions of main variables and each chemical species and the flame shapes were obtained. The heat transfer rate from the flame to the wall and the effective heating area were calculated to investigate the Influences of the major parameters on the heat transfer characteristics.

• Journal of Advanced Marine Engineering and Technology
• /
• v.22 no.1
• /
• pp.52-66
• /
• 1998

An experimental study on the flow characteristics was performed for a two-dimensional turbulent wall attaching offset jet at different oblique angles to a surface. The flow characteristics were investigated by using a split film probe with the modified Stock's calibration method. The jet mean velocity, turbulent intensity, wall static pressure coefficient profiles, and time-averaged reattachment point were measured at the Reynolds number Re (based on the nozzle width, D) ranging from 17700 to 53200, the offset ratio H/D from 2.5 to 10, and the inclined angle .alpha. from 0.deg. C to 40.deg. C. The Correlations between the maximum pressure position, minimum pressure position, and reattachment point and offset ratios, and inclined angles are presented.

• Tribology and Lubricants
• /
• v.34 no.5
• /
• pp.175-182
• /
• 2018

Accumulation of coal ash at the boiler wall reduces combustion and fuel efficiency. The design of a wall blower is important to effectively remove coal ash. We present numerical results for the removal of coal ash from boiler walls of domestic coal-fired power plants, associated with the computational fluid dynamics for the flow from spray nozzle to boiler wall. The numerical model simulates an erosion process in which the multiphase fluid comprising saturated vapor and fluid water is sprayed from the nozzle, and the water particles impact the boiler wall. We adopt the Finnie erosion model for water particles. We obtain the erosion rate density as a function of nozzle angle and its injection angle. As excessive coal ash removal usually induces damage to the boiler wall, the removal operation typically focuses on a large area with uniform depth rather than the maximum removal of coal ash at a specific location. In order to estimate the removal performance of the wall blower nozzle considering several functionality and reliability factors, we evaluate the optimal injection and nozzle angles with respect to the biggest cumulative and highest erosion rates, as well as the widest range and lowest standard deviation of the erosion rate distribution.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.26 no.7
• /
• pp.903-910
• /
• 2002

The present study aims to investigate the heat transfer characteristics of a pulsating axisymmetric air jet impinging on a heated wall. An axisymmetric contraction nozzle is used to obtain uniform profiles for the mean velocity and turbulence intensity at the nozzle exit. Measurements of the time averaged temperature on the impingement surface are conducted using a Thermochrornatic Liquid Crystal(TLC) technique for steady and pulsating jets at the jet Reynolds numbers of 20000, 30000 and 40000. Considered are pulsation frequencies of 10 and 20 Hz, corresponding to Strouhal numbers below 0.06 based on nozzle width and jet discharge velocity. In addition, the effect of nozzle-to-plate distances in the range of 2 to 10 on heat transfer characteristics is assessed. The pulsating impinging jet provides more uniform heat transfer coefficient near the impingement region, irrespective of H/D. Based on the measured data, a good correlation as a function of the jet Reynolds and Nusselt numbers is reported. It is also found that an exponent m in the relation of Nu ${\propto}\;Re^m$ depends on both r/D and H/D, by which the impinging jet flows are highly affected.