• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1995.04a
• /
• pp.196-201
• /
• 1995

The broadband and discrete sources of sound in small cooling fans of propeller type and centrifugal type were investigated to understand the turbulent vortex structures from many bladed fans using ANSI test plenum for small air-moving devices (AMDs). The noise measurement method uses the plenum as a test apparatus to determine the acoustic source spectral density function at each operating conditions similar to real engineering applications based on acoustic similarity laws. The characteristics of fans including the head rise vs. volumetric flow rate performance were measured using a performance test facility. The sound power spectrum is decomposed into two non-dimensional functions: an acoustic source spectral distribution function F(St,.phi.) and an acoustic system response function G(He,.phi.) where St, He, and .phi. are the Strouhal number, the Helmholtz number, and the volumetric flow rate coefficient, respectively. The autospectra of radiated noise measurements for the fan operating at several volumetric flow rates,.phi., are analyzed using acoustical similarity. The rotating stall in the small propeller fan with a bell-mouth guided is mainly due to a leading edge separation. It creates a blockage in the passage and the reduction in the flow rate. The sound power levels with respect to the rotational speeds were measured to reveal the mechanisms of stall and/or surge for different loading conditions and geometries, for example, fans installed with a impinging plate. Lee and Meecham (1993) studied the effect of the large-scale motions like impinging normally on a flat plate using Large-Eddy Simulation(LES) and Lighthill's analogy.[ASME Winter Annual Meeting 1993, 93-WA/NCA-22]. The dipole and quadrupole sources in the fans tested are shown closely related to the vortex structures involved using cross-correlations of the hot-wire and microphone signals.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.31 no.5
• /
• pp.80-86
• /
• 2003

An anaysis on the discharge performance of an impinging-type injector for cavitating flow has been conducted by both numerical and experimental method. The predicted discharge coefficient for cavitating flow agrees well with the measured data showing less than 1% discrepancy. For the case of non-cavitating flow analysis, the disagreement between CFD results and the experimental data is 8%. The discharge coefficient for the cavitating flow decreases with decrease in the Reynolds number. On the other hand, it increases slightly as the Reynolds number increases for the non-cavitating flow because of the reduced viscous effect. From the present study, it is confirmed that the fact that cavitation phenomena should be included to predict accurately the discharge performance of injectors for cavitating flow regime. The uniformity of density and velocity magnitude degraded at the injector exit, and the secondary flow strength through the injector orifice accentuated due to cavitation.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.12 no.6
• /
• pp.152-158
• /
• 2013

The purpose of this study is to investigate cooling performance of high power LEDs from 100 to 200 W class by using a jet impingement cooling module. The numerical analysis of forced convection cooling inside cooling module is carried out using a multi-purpose CFD software, FLUENT 6.3. In the experiments, the LED cooling system consists of jet impingement module, heat exchanger, water reservoir, and pump. In the present study, the cooling performance of jet impingement cooling module is investigated to determine the effect of the heat sink types on the impinging surface, the space and length of fins. Numerical and experimental studies show the reasonable agreement of LED metal PCB temperature between those results and give the optimized design parameters such as the space of fin and the length of fin. Also, the pin fin type of heat sink is found to be more efficient than the plate type heat sink in jet impingement cooling.

• Journal of ILASS-Korea
• /
• v.15 no.2
• /
• pp.83-93
• /
• 2010

Feedwater heaters of many nuclear power plants have recently experienced severe wall thinning damage, which will increase as operating time progresses. Several nuclear power plants in Korea have experienced wall thinning damage in the area around the impingement baffle inside feedwater heater installed downstream of the turbine extraction stream line. At that point, the extract steam from the turbine is two phase fluid at high temperature, high pressure, and high speed. Since it flows to reverse direction after impinging the impingement baffle, the shell wall of feedwater heaters may be affected by flow-accelerated corrosion. In this paper, to compare degree of shell wall thinning mitigation rate to squared type with mitigation rate of other type baffle plate, four different types of impingement baffle plate-squared, curved, mitigating type and multi-hole type-applied inside the shell. With these comparison data, this paper describes operation of experiments and numerical analysis which is composed similar condition with real feed water heater. And flow visualization is operated for verification of experiments and numerical analysis. In conclusion, this study shows that mitigating type and multi-hole type baffle plate are more effective than other baffle plate about prevention of pressure concentration and pressure value decrease.

• Journal of the Korean Solar Energy Society
• /
• v.25 no.4
• /
• pp.101-110
• /
• 2005

An experimental study of heat transfer of submerged water jet impinging normally on a flat plate is presented. Heat transfer measurements obtained with Reverse cone type nozzle(Rcone) were compared to those obtained with Cone type nozzle(Cone) and Square edged type nozzle(Vert) of the same diameter(D=8mm) for different jet velocities in the range of $3{\sim}7m/s(Re_D=30000{\sim}70000)$ and various nozzle-to target spacings($H/D=2{\sim}10$). The local Nusselt number profiles exhibited a sharp drop for $r/D{\leq}0.5$ and 2nd, 3rd peaks revealed at r/D=2, 3 respectively, followed by a slower decrease there after. The peaks were weakened with increasing the nozzle-to target spacing and decreasing the jet velocity. The stagnation Nusselt number of the Reverse cone type nozzle was larger than those of the other two nozzles for H/D=2. 10, but Cone type nozzle had the highest value for $H/D=4{\sim}8$. Also average Nusselt number of the Reverse cone type nozzle was higher than those of the other two nozzles at $H/D=2{\sim}10$, except for $V_o=7ms$ of H/D=6.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 1998.04a
• /
• pp.16-16
• /
• 1998

로켓의 추진제에는 고체 추진제와 액체 추진제를 사용하는 두 경우로 나눌 수 있는데, 액체 추진제를 사용하는 경우, 액체 연료와 액체 산화제를 다양한 방법으로 연소실내로 분사하게 된다. 이때 사용되는 injector들 중에 impingement type이 있다. 이 type은 injector의 가공이 비교적 용이하고, 혼합성능이 좋기 때문에 LOX/RP-1(Kerosin-based hydrocarbon fuel)을 사용하는 액체 로켓엔진에서 주로 사용되어 왔다. 두 액체 jet의 충돌에 의해 액막이 형성되는데, 이 액막은 가장자리로 갈수록 두께가 얇아지며 액막표면의 파는 충돌점으로부터 멀어질수록 그 진폭의 증가를 이루어 액체의 표면장력과 관성력의 균형을 깨트리며, 이 순간 액막은 rim의 형태로 분열하여 결국에는 액적을 생성하게 된다. 현재까지의 연구내용은 충돌 jet의 형태 laminar jet과 turbulent jet으로 구분된 인젝트에 관해 연구되어왔고, 특히 국내에는 이러한 구분된 충돌 jet의 분열현상에 관한 연구결과가 미흡하다. 동일한 오르피스의 경우에도 laminar jet과 turbulent jet으로 구분되어 지며, 각각의 jet의 형태에 따라 생성되는 액막의 형상 또는 다르게 생성되어 진다. 그러므로 본 연구에서는 두 구분된 jet의 경우의 분열현상을 실험적으로 분석하였다.

• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.6
• /
• pp.55-63
• /
• 2010

Feedwater heaters of many nuclear power plants have recently experienced severe wall thinning damage, which will increase as operating time progresses. Several nuclear power plants in Korea have experienced wall thinning damage in the area around the impingement baffle inside feedwater heater installed downstream of the turbine extraction stream line. At that point, the extract steam from the turbine is two phase fluid at high temperature, high pressure, and high speed. Since it flows to reverse direction after impinging the impingement baffle, the shell wall of feedwater heaters may be affected by flow-accelerated corrosion. In this paper, to compare degree of shell wall thinning mitigation rate to squared type with mitigation rate of other type baffle plate, three different types of impingement baffle plate-squared, curved and mitigating type-applied inside the shell. With these comparison data, this paper describes operation of experiments and numerical analysis which is composed similar condition with real feed water heater. And flow visualization is operated for verification of experiments and numerical analysis. In conclusion, this study shows that mitigating type baffle plate is more effective than other baffle plate about prevention of pressure concentration and pressure value decrease.

• Journal of the Korean Society of Safety
• /
• v.26 no.1
• /
• pp.8-14
• /
• 2011

Noise and vibration are likely to disturb the sensory system of human body leading to psychological stress and thereby property damage. In this research, a cut out switch(COS) with a built-in acoustic absorber along with a COS fuse broken was developed to reduce percussion noise. This new system is based on a design approach that combines existing absorber systems: expansion type, resonator type, and acoustic absorber type silencer The noise performance of the new system was simulated using the $SYSNOISE^{TM}$ software under optimized parameters: the diameter of perforated plate 2 mm, the plate thickness 3 mm, the width of expansion room 25 mm, the impinging vortex room 14 mm, and the noise absorbtion room 10 mm. The results showed that it reduced noise by approximately 41.1 dB compared to the current systems available in the market. Furthermore, it showed reduced noise by approximately 12 dB more than a product with an acoustic absorber of the Fault Tamer(USA).

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.31 no.5
• /
• pp.72-79
• /
• 2003

Spray characteristics were investigated by impinging F-O-O-F type injector with varying the impingement angle through 15, 20 and 30 degree and the mixture ratio(O/F ratio) from 1.5 to 3.0. Experimental results show that the correlation between dispersion and impingement angle is not influenced of the mixture ratio variation, but which has influence on number density, and there is a linear correlation between dispersion and impingement angle. Velocity distribution, standard deviation and SMD of droplets are decreased as the impingement angle increases. Also, it was confirmed that the distribution of droplet size are in accordance with Rosin-Rammler and Upper-limit distribution.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.12 no.1
• /
• pp.50-58
• /
• 2000

Experiments were carried out to obtain the effects of nozzle configuration and jet to jet spacing on the heat transfer characteristics of single line of circular water jets impinging on a constant heat flux plane surface. The nozzle configurations are Cone type, Reverse cone type and Vertical circular type, and the nozzle arrays are single jet(nozzle dia. 8 mm), 1 row of 3 jets and 1 row of 5 jets. Jet velocities ranging from 3m/s to 8m/s were investigated for the nozzle to target plate spacing of 80 mm. For the Cone and Reverse cone type nozzle arrays, the average Nusselt number of 1 row of 5 jets was larger than that of 1 row of 3 jets at Re$_{D}$<45000, but that of 1 row of 3 jets was larger than that of 1 row of 5 jets at $Reo\le45000$. For the Vertical circular type nozzle, however, the average Nusselt number of 1 row of 3 jets was larger than that of 1 row of 5 jets at all jet velocities. In the condition of fixed mass flow rates, the maximum heat transfer augmentation was obtained for 1 row of 5 jets and was over 2 times larger than that of the single jet for all nozzle configurations. The nozzle configurations that produce the maximum average Nusselt number are as follows: For 1 row of 3 jets, the Vertical circular type at $Reo\le45000$ and the Reverse cone type at $Reo\le45000$. But, they are the Reverse cone type at Re$_{D}$<55000 and the Vertical circular type at$Reo\le55000$ for 1 row of 5 jets.