• 설비공학논문집
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• 제14권6호
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• pp.441-449
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• 2002

Single-phase convection and partial nucleate boiling in free-surface and submerged jet impingements of subcooled water ejected through a 2-mm-diameter circular pipe nozzle were investigated by local measurements. Effects of jet velocity and nozzle-to-imping-ing surface distance as well as heat flux on distributions of wall temperature and heat transfer coefficients were considered. Incipience of boiling began from far downstream in contrast with the cases of the planar water jets of high Reynolds numbers. Heat flux increase and velocity decrease reduced the temperature difference between stagnation and far downstream regions with the increasing influence of boiling in partial boiling regime. The chance in nozzle-to-impinging surface distance from H/d=1 to 12 had a significant effect on heat transfer around the stagnation point of the submerged jet, but not for the free-surface jet. The submerged jet provided the lower cooling performance than the free-surface jet due to the entrainment of the pool fluid of which temperature increased.

• 설비공학논문집
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• 제22권8호
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• pp.538-544
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• 2010

An experimental investigation is presented to study the effect nozzle spacing, jet to plate spacing and Reynolds number on the local heat transfer to normally upward impinging submerged circular water jets on a flat heated surface. Nozzle arrays are a single jet(nozzle dia. = 8 mm), a row of 3 jets(nozzle dia. = 4.6 mm, nozzle spacing = 37.5 mm) and a row of 5 jets(nozzle dia. = 3.6 mm, nozzle spacing = 25 mm), and jet to plate spacing ranging from 16∼80 mm(H/D = 2∼10) is tested. Reynolds number based on single jet exit condition is varied 30000∼70000($V_o$ = 3∼7 m/s). Except for the condition of H/D = 10, the average Nusselt number of multi-jet is higher than that of single jet. For H/D = 2, average Nusselt number is increased by 50.3∼82.5% for a row of 3 jets and by 52.9∼65.2% on a row of 5 jets when compared to the average Nusselt number on the single jet.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1997년도 추계 학술대회논문집
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• pp.136-142
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• 1997

The present study is aimed to investigate flow characteristics of confined jet flow within circular pipe. Numerical method based upon revised SOLA scheme which secures conservation form of convective terms on irregular grids by interpolating the variables appearing in staggered meshes is adopted on cylindrical coordinate formation. Computation was carried out for two kinds of Reynolds number, $10^5\;and\;1.5{\times}10^5$ defined by diameter of outer pipe and time-mean driving jet velocity. Results show that periodic vortex shedding from the jet mixing layer is profound and related unsteady flow characteristics prevail over the entire region. Spatial distribution of pressure and kinetic energy, fluctuation of static wall pressure, together with radial velocity components are examined in terms of instantaneous and time-mean point of views.

• 대한기계학회논문집
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• 제18권12호
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• pp.3335-3344
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• 1994

The initial flow characteristics of the turbulent circular jet discharging into the sudden expansion pipes have been investigated by the hot wire anemometry. Evolutions of similarity, centerline behavior, jet boundary and typical turbulent quantities were looked into for the expansion ratios. The results show that the spreading rates of discharging jet seem not to be dependent of the expansion ratio and that the velocity profiles in the radial directions exhibit the similarity in the regions, 2-5d, 2-6d and 3-8d for the corresponding expansion rations of 2, 3 and 5, respectively. With the increase of expansion ratio the centerline velocity decays rather slowly. The anisotropic behaviors of the discharging jets into the sudden expansion pipe look stronger than those of the free jet.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2002년도 추계학술대회 논문집
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• pp.109-112
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• 2002

The supersonic jet discharging from a petal nozzle is known to enhance mixing effect with the surrounding gas because it produces strong longitudinal vortices due to the velocity difference from both the major and minor axes of petal nozzle. In the present study, the supersonic free jet discharging from the petal nozzle is investigated experimentally. The nozzles used are 4, 6, and 8 lobed petal nozzles with a design Mach number of 1.7, and the flow fields are compared with a circular nozzle with the same design Mach number. The pitot impact pressures are measured using a fine pilot probe. The flow fields are visualized using a Schlieren optical method. The results show that the petal nozzle has more increased supersonic length compared with the circular jet.

• 대한기계학회논문집B
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• 제27권6호
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• pp.693-700
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• 2003

The effect of the configuration of the nozzle and the impinging surface on the characteristics of the hole-tones has been experimentally investigated. It is found that the plate-tone is a special case of hole-tones, where the hole diameter is zero. The jet velocity range for hole-tones is divided into the low velocity region associated with laminar jet and the high velocity region with turbulent jet. The frequency of the tone is that for the shear layer instability at the nozzle exit or that attainable by a cascade of vortex pairing process with increase of the impinging distance. When the distance is longer than one diameter the frequency decreases to the terminal value near the preferred frequency of the column mode instability, in the range 0.23< $St_d$<0.53, where $St_d$ is the Strouhal number defined by $fd/U_J$, f the frequency, d the nozzle diameter, and $U_J$ the exit velocity. While the convection speed of the downstream vortex, in the present study, is almost constant at low-speed laminar jet, it increases with distance at high-speed turbulent jet. As the frequency increases, the convection speed decreases in the low frequency range corresponding to the preferred mode, in agreement with the existing experimental data for a free jet.

• Advances in aircraft and spacecraft science
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• 제3권4호
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• pp.399-425
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• 2016

The dynamical requirements are obtained for airplanes to travel on inclined circular trajectories. Formulas are provided for determining the load factor, the bank angle, the lift coefficient and the thrust or power required for the motion. The dynamical properties of the airplane are taken into account, for both, airplanes with internal combustion engines and propellers, and airplanes with jet engines. A procedure is presented for the construction of tables from which the flyability of trajectories at a given angle of inclination can be read, together with the corresponding minimum and maximum radii allowed. Sample calculations are shown for the Cessna 182, a Silver Fox like unmanned aerial vehicle, and a F-16 jet airplane.

• 대한기계학회논문집B
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• 제30권12호
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• pp.1147-1154
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• 2006

An experimental investigation was conducted to enhance the heat/mass transfer for impingement/effusion cooling system when the initial crossflow was formed. For the improvement of heat transfer, the circular guide is installed on the injection hole. At the fixed jet Reynolds number of 10,000, the measurements were carried out for blowing ratios ranging from 0.5 to 1.5. The local heat/mass transfer coefficients on the effusion plate are measured using a naphthalene sublimation method. The result presents that the circular guide protects the injected jet from the initial crossflow, increasing the heat/mass transfer. The heat transfer of stagnation region is hardly changed regardless of the blowing ratio. The secondary peak is obviously formed by flow transition to turbulent flow. At high blowing ratio of 1.5, the circular guide produces $26{\sim}30%$ augmentation on the averaged heat/mass transfer while the case without circular guide leads to the low and non-uniform heat/mass transfer. With the increased heat/mass transfer, the installation of circular guide is accompanied by the increase of pressure loss in the channel. However, the pressure drop caused by the circular guide is lower than that for other cooling technique with the circular pin fin.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 춘계 학술대회논문집
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• pp.208-213
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• 2004

The HANARO, multi-purpose research reactor, 30 MWth open-tank-in- pool type, is under normal operation since it reached the initial critical in February 1995. The HANARO is planning to produce a fission moly-99 of radio isotopes, a mother nuclide of Tc-99m, a medical isotope and is under developing a target handling tool for loading and unloading it in a circular flow tube (OR-5). A guide tube is extended from the reactor core to the top of the reactor chimney for easily un/loading a target under the reactor normal operation. But active coolant through the core can be quickly raised up to the top of the chimney through the guide tube by jet flow. This paper is described an analytical analysis to calculate the hole size of a orifice inserted in the circular irradiation hole and to study the flow characteristics through the guide tube under reactor normal operation and loading the target. As results, the results show that the hole size of orifice was 31 mm of the inner diameter to suppress the guide tube jet flow and the coolant safely cooled the target of fission moly after inserting the orifice to the flow tube.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 춘계 학술대회논문집
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• pp.214-219
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• 2004

The HANARO, a multi-purpose research reactor of 30 MWth, open-tank-in-pool type, has been under normal operation since its initial criticality in February, 1995. The HANARO is composed of inlet plenum, grid plate, core channel with flow tubes and chimney. The reactor core channel is located at about twelve m (12 m) depth of the reactor pool and cold by the upward flow that the coolant enters the lower inlet of the plenum, rises up through the grid plate and the core channel and exit through the outlet of chimney. A guide tube is extended from the reactor core to the top of the reactor chimney for easily un/loading a target under the reactor normal operation. But active coolant through the core can be Quickly raised up to the top of the chimney through the guide tube by jet flow. This paper is described an analytical analysis to study the flow behavior through the guide tube under reactor normal operation and unloading the target. As results, it was conformed through the analysis results that the flow rate, about fourteen kilogram per second (14 kg/s) suppressed the guide tube jet and met the design cooling flow rate in a circular flow tube, and that the fission moly target cooling flow rate met the minimum flow rate to cool the target.