• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
• /
• pp.33.1-33.1
• /
• 2005

• 설비공학논문집
• /
• 제14권6호
• /
• pp.477-484
• /
• 2002

A numerical investigation of the performance of the plate heat exchanger with rectangular winglet is conducted to examine the combined effect of vortex generator and louver fins. Velocity and temperature fields and spanwise averaged Nu and friction factor are presented. Enhancement of heat transfer and flow loss penalty is evident. A Parametric study of three factors (Re, angle of attack and louver angle) with levels of 5 (Re= 300, 500, 700, 900, 1100), 4($\alpha=15^{\circ}, 30^{\circ}, 45^{\circ}, 90^{\circ},$), and 4($\beta=0^{\circ}, 15^{\circ}, 30^{\circ}, 45^{\circ}$), respectively, indicates the performance defined by the ratio of heat transfer enhancement to flow loss penalty shows monotonic behavior for each parameter alone but the interactions between parameters is found to be considerable effect on the performance of heat exchanger and should be considered in design. The effect of stamping is also examined.

• Journal of Mechanical Science and Technology
• /
• 제20권3호
• /
• pp.418-425
• /
• 2006

The present investigation deals with the study of the internal flow phenomena of the counterflow type vortex tube using experimental testing and numerical simulation. Visualization was carried out using the surface tracing method, injecting dye on the vortex tube wall using a needle. Vortex tube is made of acrylic to visualize the surface particle tracing and the input air pressure was varied from 0.1MPa to 0.3MPa. The experimentally visualized results on the tube show that there is an apparent sudden changing of the trajectory on the vortex tube wall which was observed in every experimental test case. This may indicate the stagnation position of the vortex flow. The visualized stagnation position moves towards the vortex generator with increase in cold flow ratio and input pressure. Three-dimensional computational study is also conducted to obtain more detailed flow information in the vortex tube. Calculated total pressure, static pressure and total temperature distributions in the vortex tube were in good agreement with the experimental data. The computational particle trace on the vortex tube wall is very similar to that observed in experiments.

• 설비공학논문집
• /
• 제17권9호
• /
• pp.789-798
• /
• 2005

This paper is a numerical study concerning how the interactions between a pair of the vortices effect flow field and heat transfer. The flow field (common flow down) behind a vortex generator is modeled by the information that is available from studies on a half-delta winglet. Also, the energy equation and the Reynolds-averaged Wavier-Stokes equation for three-dimensional turbulent flows, together with a two-layer turbulence model to resolve the near-wall flow, are solved by the method of AF-ADI. The present results predict that the boundary layer is thinned in the regions where the secondary flow is directed toward the wall and thickened where it Is directed away from the wall. Although some discrepancies are observed near the center of the vortex core, the overall performance of the computational model is found to be satisfactory.

• 대한기계학회논문집B
• /
• 제20권3호
• /
• pp.1061-1073
• /
• 1996

Vortex tube is a simple device which splits a compressed gas stream into a cold stream and a hot stream without any chemical reactions. The phenomena of energy separation taking place in a vortex tube has been investigated experimentally. Recently, vortex tube is widely used to local cooler of industrial equipments and air conditioner of special purpose. In this study, experimental study on vortex tube efficiency was performed with various cold end orifices and nozzles type. The experimental results indicate that there is an optimum diameter of cold end orifice and nozzle type for the best cooling performance. The variation of the maximum wall temperature along the vortex tube surface provides useful information about the location of the stagnation point of the flow field at the axis of the vortex tube. The similarity relation for the prediction of the temperature of the cold exit air was obtained.

• Wind and Structures
• /
• 제28권6호
• /
• pp.355-367
• /
• 2019

Control of horseshoe vortex in the circular cylinder-plate juncture using vortex generator (VG) was studied at $Re_D$(where D is the diameter of the cylinder) = $2.05{\times}10^5$. Impact of a number of parameters e.g., the shape of the VG's, number of VG pairs (n), spacing between the VG and the cylinder leading edge (L), lateral gap between the trailing edges of a VG pair (g), streamwise gap between two VG pairs ($S_{VG}$) and the spacing between the two VG's in parallel arrangement ($Z_{VG}$) etc. were investigated on the horseshoe vortex control. The study is conducted using surface oil flow visualization and surface pressure measurements in low speed wind tunnel. It is observed that all the parameters studied have significant control effect, either by reduction in separation region or by lowering the adverse pressure along the symmetric axis upstream of the juncture.

• 대한기계학회논문집B
• /
• 제27권11호
• /
• pp.1618-1629
• /
• 2003

The effects of the interaction between flow field and heat transfer caused by the longitudinal vortices are experimentally investigated using a five hole probe and a transient liquid crystal technique. The test facility consists of a wind tunnel with vortex generators protruding from a bottom surface and a mesh heater. In order to control the strength of the longitudinal vortices, the angle of attack of vortex generators used in the present experiment is 20$^{\circ}$, and the spacing between the vortex generators is 25mm. The height and cord length of the vortex generator is 20mm and 50mm, respectively. Three-component mean velocity measurements are made using a f-hole probe system, and the surface temperature distribution is measured by the hue capturing method using a transient liquid crystal technique. The transient liquid crystal technique in measuring heat transfer has become one of the most effective ways in determining the full surface distributions of heat transfer coefficients. The key point of this technique is to convert the inlet flow temperature into an exponential temperature profile using the mesh heater set up in the wind tunnel. The conclusions obtained in the present experiment are as follows: The two maximum heat transfer values exist over the whole domain, and as the longitudinal vortices move to the farther downstream region, these peak values show the decreasing trends. These trends are also observed in the experimental results of other researchers to have used the uniform heat flux method.

• Nuclear Engineering and Technology
• /
• 제52권8호
• /
• pp.1677-1688
• /
• 2020

In the sodium-cooled fast reactor, the steam generator is a heat exchange device between sodium and water, which may cause leakage, resulting in a sodium-water reaction accident, which in turn affects the safe operation of the entire nuclear reactor. To this end, the electromagnetic vortex flowmeter is used to detect leakage of the steam generator and its signal processing method is studied in this paper. The hydraulic experiment was carried out by using water instead of liquid sodium, and the sensor output signal of the electromagnetic vortex flowmeter under different gas injection volumes was collected. The bubble noise signal is reflected by the base line of the sensor output signal. According to the relationship between the proportion of the bubble noise signal in the sensor output signal and the gas injection volume, a signal processing method based on the energy ratio calculation is proposed to detect whether the water contains bubbles. The gas injection experiment of liquid sodium was conducted to verify the effectiveness of the signal processing method in the detection of bubbles in sodium, and the minimum detectable leak rate of water in the steam generator was detected to be 0.2 g/s.

• Journal of Advanced Marine Engineering and Technology
• /
• 제27권5호
• /
• pp.581-588
• /
• 2003

Heat transfer characteristics of a pair of longitudinal vortices using a transient liquid crystal technique are studied experimentally. In order to control the strength of longitudinal vortices, angle of attack of the vortex generators is $20^{\circ}$and the length of space from the centerline the vortex generations is 25mm apart. The heat transfer measurements using a transfer coefficients. The following conclusions are obtained from the present experiment. When any vortex generators are not set up in wind tunnel test, heat transfer rate is low respectively. However, with the vortex generators of rectangular winglet, the heat transfer on the local surface can be enhanced.

• Journal of Advanced Marine Engineering and Technology
• /
• 제29권6호
• /
• pp.637-644
• /
• 2005

This paper describes the numerical simulation of the interaction between longitudinal vortices ("common flow up") and a 3-D turbulent boundary layer over a flat plate To analyze the common flow up Produced from vortex generators. the flow field behind the vortex generators Is modeled by the information that is available from studies on a half-delta winglet. Also. the Reynolds-averaged Navier-Stokes equation for three-dimensional turbulent flows. together with a two-layer turbulence model to resolve the near-wall flow, is solved by the method of AF-ADI. The computational results predict that the boundary layer is thinned in the regions where the secondary flow is directed toward the wall and thickened where it is directed away from the wall Also. the numerical results. such as Reynolds stresses. turbulent kinetic energy and skin friction characteristics generated from the vortex generators . are reasonably close to the experimental data.