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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Transactions of the Korean Society of Mechanical Engineers B
Journal Basic Information
Journal DOI :
The Korean Society of Mechanical Engineers
Editor in Chief :
Volume & Issues
Volume 22, Issue 7 - Jul 1998
Volume 22, Issue 6 - Jun 1998
Volume 22, Issue 5 - May 1998
Volume 22, Issue 4 - Mar 1998
Volume 22, Issue 3 - Mar 1998
Volume 22, Issue 2 - Feb 1998
Volume 22, Issue 1 - Jan 1998
Volume 22, Issue 10 - 00 1998
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An experimental study of flow separation around a circular cylinder with Reynolds number and free stream turbulence intensity variations
Im,Yong-Seop ; Son, Dong-Gi ; Yang, Gyeong-Su ; Lee, Jun-Sik ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 7, 1998, Pages 889~898
DOI : 10.22634/KSME-B.19184.108.40.2069
The influences of the Reynolds number and free-stream turbulence intensity on the flow separation behavior around a circular were investigated experimentally. The range of the Reynolds number and turbulence intensity considered are 10,000 ~ 45,000 and 0.3 ~ 6.8%, respectively. Because of ineffectiveness of using time-mean value of hot-film sensor signals in determining the separation location around the cylinder, a new method using phase-difference of hot-film sensor signals with hot-wire being located in shedding vortex is suggested. The validity of the present method is confirmed by the comparison with flow visualization.
A linear analysis of interfacial instabilities of ferrofluids
Park, Chang-Ho ; Ju, Sang-U ; Lee, Sang-Chun ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 7, 1998, Pages 899~904
DOI : 10.22634/KSME-B.19220.127.116.119
Surface motion of a magnetic fluid is studied by a linear stability analysis. When a thin horizontal magnetic-fluid layer is placed on a nonmagnetic substrate, with a vertical magnetic field applied, the surface of the ferrofluid layer can be severely corrugated, due to the normal-field instability. Based on conservation laws, it is shown that the normal-field instability of thin ferrofluid layers is a long-wave instability and that it is analogous to the interfacial mode of the thermocapillary instability in a thin horizontal layer heated from below.
Hemi-cube algorithm and its application to thermal analysis of crystal growth furnace
Lee, Seung-Bok ; Jeong, Jin-Su ; Go, Sang, Geun ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 7, 1998, Pages 905~914
DOI : 10.22634/KSME-B.1918.104.22.1685
View factor determination is very important in thermal analysis problems with surface radiation but it is very difficult to determine view factors for complex geometries. Exact calculation of view factors for crystal growth furnace is essential due to not only its high surface temperature but the radiation shield, complicated heating system. In this study, view factor calculation algorithm is introduced and applied to cylindrical crystal growth furnace. This algorithm is based on the Hemi-Cube Algorithm and the results obtained with this algorithm show good agreements with those of analytical solution. As an application of this algorithm, temperature profiles and heating value distributions for various furnaces are calculated and the shape criteria for better furnace are suggested.
Effect of fence porosity on the velocity field of wake flow past porous wind fences
Kim, Hyeong-Beom ; Lee, Sang-Jun ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 7, 1998, Pages 915~926
DOI : 10.22634/KSME-B.1922.214.171.1245
Velocity fields of near turbulent was behind a porous wind fence were measured using the 2-frame PTV method in a circulating water channel. The fences used in this study had different geometric porosity(.epsilon.) of 0, 20, 40 and 65%. The fence was embedded in a thin laminar boundary layer, i.e., .delta./H ~ = 0.1. Reynolds number based on the fence height H and free stream velocity(U
o/) was about 8,400. As a result, a recirculating flow region was formed behind the fence for the .epsilon.=0% and 20% wind fence. For the wind fences having porosity larger than .epsilon.=40%, it was difficult to see separation bubbles behind the fence. The .epsilon.=20% porous fence reveals the maximum velocity reduction, however, the turbulent intensity and Reynolds shear stress are much greater than those of .epsilon.=40% fence. Among the wind fence tested in this study, the porous wind fence of .epsilon.=40% porosity is the most effective for abating wind erosion.
Flow characteristics of a cross jet issued in the fully developed pipe flow
Kim, Gyeong-Cheon ; Sin, Dae-Sik ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 7, 1998, Pages 927~936
DOI : 10.22634/KSME-B.19126.96.36.1997
In the fully developed pipe flow, when jet is injected in cross to the flow there are complex transition flows caused by interaction of the cross flow and jet. These interactions are studied by means of the flow visualization methods and frequency analysis using a hot-wire anemometer. The velocity range of cross flow of the pipe is 0.3 m/s ~ 1.2 m/s and the corresponding Reynolds number, R
p/, based on the pipe diameter is 2.25 * 10
3/ ~ 9.02 * 10
3/. The velocity ratio (R), jet velocity/cross flow velocity, is chosen from 2 to 10. A circular cylinder is placed in the pipe instead of jet to observe the vortex shedding from the solid body. To compare the jet and circular cylinder flow, the vortical structure is analyzed in both cases and the structure of vortices and the origin of its formation are investigated, especially. The vortex shedding of the dominant coherent structure is compared between the jet flow and the circular cylinder flow. In the case of the jet flow, the Strouhal numbers are different depending on the existence of the upright vortex as well as the velocity ratio (R).
The characteristics of static pressure recovery in a conical diffuser with a swirling flow
Jeong, Hyo-Min ; Jeong, Han-Sik ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 7, 1998, Pages 937~945
DOI : 10.22634/KSME-B.19188.8.131.527
The purpose of this paper is to investigate the relationship between pressure recovery and turbulent characteristic value of velocity and pressure, in the case where a swirling flow streams into a conical diffuser. The results of both measurements of the wall pressure fluctuation and velocity fluctuation revealed them to role the large part of the total pressure loss of the flow. The cause of the fluctuation of flow was showed to be the flow separation at the inlet of diffuser at low intensity of swirl, but the flow of diffuser center was instable at high intensity of swirl. The static pressure recovery depends strongly on the magnitude of the turbulent energy in the diffuser, and that this magnitude of the turbulent energy varies as the intensity of swirl at the diffuser inlet.
A modeling of in-tube condensation heat transfer considering liquid entrainment
Gwon, Jeong-Tae ; An, Ye-Chan ; Kim, Mu-Hwan ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 7, 1998, Pages 946~955
DOI : 10.22634/KSME-B.19184.108.40.2066
Local condensation heat transfer coefficients in tubes were calculated by solving momentum and energy equations for annular film with liquid entrainment. The turbulent eddy distribution across the liquid film has been proposed and the calculated heat transfer coefficients were presented. Also turbulent Prandtl number effects on condensation heat transfer were discussed from three Pr
t/ models. Finally, the calculated condensation heat transfer coefficients of R22 were compared with some correlations frequency referred to in open literature. This calculation model considering liquid entrainment predicted well the in-tube condensation heat transfer coefficient of R22 than the model not considering liquid entrainment. The effect of entrainment on heat transfer was predominant for high quality and high mass flux when the liquid film was turbulent.
Experimental study of turbulent flow in a U-bend of circular cross-section
Lee, Geon-Hwi ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 7, 1998, Pages 956~965
DOI : 10.22634/KSME-B.19220.127.116.116
Hot-wire measurement of the longitudinal and radial velocity components and Reynolds stresses are reported for developing turbulent flow in a strongly curved 180 deg. pipe and its tangents. Slanted wire is rotated to 6 directions and the voltage outputs of them are combined to obtain the mean velocities and Reynolds stresses. Significant double maxima in the longitudinal velocity component appear in the bend. V-profiles reveal the development of a strong secondary flow. This secondary flow is induced by the transverse pressure gradient set up between the outer(r
o/) and inner(r
i/) wall region of the bend. Another second cross-stream flow develops after .theta.=135 deg. and its direction is opposed to that of main second flow.
Performance analysis of a hermetic reciprocating compressor using the alternative refrigerants, HFC134a and HC600a
Kim, Jeong-U ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 7, 1998, Pages 966~979
DOI : 10.22634/KSME-B.1918.104.22.1686
Thermodynamic and dynamic analysis has been conducted to investigate performance variations induced by substitution of alternative refrigerants, HFC134a or HC600a for CFC12 in hermetic reciprocating compressors. For the thermodynamic analysis, mass and energy conservation laws are applied to the cylinder volume and Helmholtz resonator modeling method is adopted to describe gas pulsations at suction and discharge system. The modeling of the dynamics of the compressor mechanism has been performed with lumped mass method to analyse the bearing loads and friction losses at each bearing. To verify the correctness of this analysis, results of the performance simulation have been compared to those of calorimetric measurrements of compressor operating with CFC12. Analysis of the various losses, noise and reliability as well as performance has been conducted to present the design guideline for the compressor development with alternative refrigerants. It is found that compressors with alternative refrigerants, HFC 134a or HC600a give better COPs than those with CFC12 under the same operating conditions and especially, compressors with HC600a show better reliability and noise characteristics also.
Pool boiling heat transfer coefficients of alternative refrigerants in enhanced tubes
Lee, Jun-Gang ; Go, Yeong-Hwan ; Jeong, Dong-Su ; Song, Gil-Hong ; Kim, Jong-Bo ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 7, 1998, Pages 980~991
DOI : 10.22634/KSME-B.1922.214.171.1240
In this study, nucleate pool boiling heat transfer coefficients of alternative refrigerants on a plain, low fin, and two enhanced tubes were measured and compared against each other. To obtain data at conditions similar to the actual evaporator, a fluid heating method was employed instead of an electric heating method in the experiments. R123, R134a, R22 and R410a were used as working fluids and data were taken at 7 deg.C ar heat fluxes of 20 ~ 100 kW/m
2/. Comparison of the plain tube data against some correlations showed that the simplest correlation of Cooper based on reduced pressure predicted the data for all fluids tested with a 10% deviation. For all refrigerants, enhanced tubes composed of subsurface and subtunnels, especially Thermoexcel-E tube, showed the highest heat transfer coefficients among the tubes tested with one exception that the low fin tube's performance was better than those of enhanced tubes for high vapor pressure fluid such as R410a at high heat flux. Finally, a low fin and enhanced tubes showed higher heat transfer enhancement for low vapor pressure of R123 than for high vapor pressure fluisd. For R123, the enhancement factors for Turbo-B and Thermoexcel-E tubes were 2.8 ~ 4.8 and 4.6 ~ 8.1 respectively.
Effects of interfacial shear stress on laminar-wavy film flow
Kim, Byeong-Ju ; Jeong, Eun-Su ; Kim, Jeong-Heon ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 7, 1998, Pages 992~1000
DOI : 10.22634/KSME-B.19126.96.36.1992
In the present study the behavior of laminar-wavy film flowing down a vertical plate was studied analytically. The effects of film Reynolds number and interfacial shear stress on the mean film thickness, wave amplitude, wave length, and wave celerity were analysed. The anayltical results on the periodic-wave falling film showed good agreements with experimental data for Re < 100. As the film Reynolds number increased, mean film thickness, wave amplitude, and wave celerity increased, but wave length decreased. Depending on the direction of interfacial shear stress, the shape of wavy interface was disturbed significantly, especially for the intermediate-wave. As the interfacial shear stress increased, for the periodic-wave film, wave amplitude and wave celerity increased, but mean film thickness and wave length decreased.
Dynamic characteristics of the compressor-combined condenser system
Kim, Jae-Dol ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 7, 1998, Pages 1001~1012
DOI : 10.22634/KSME-B.19188.8.131.521
This paper reports the analysis of dynamic characteristics of air-cooled condenser. At first, there is an assumption that the superheated vapor flows into the condenser inlet. And in order to consider the effect of pressure change in the dynamic characteristics of the condenser the combined system of condenser and compressor was used. By using the equation of energy balance and the equation of mass balance, the basic equation for describing the dynamic characteristics of condenser can be derived. The transfer function for describing dynamic response of the condenser to flow rate change outlet can be obtained from using linearizations and Laplace transformations of the equation. From this transfer function, analytical investigation which affects the frequency responses of condenser has been made. Through this study, it became possible that the information about the dynamic characteristics of air-cooled condenser is offered. While the average heat transfer coefficient of the refrigerant side necessary for the theoretical calculation of the dynamic characteristics is given by calculation method for the tube length and pressure drop of air-cooled condenser.
Flow Visualization Study on the Turbulent Mixing of Two Fluid Streams(II)
Kim, Gyeong-Cheon ; Sin, Dae-Sik ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 7, 1998, Pages 1013~1021
DOI : 10.22634/KSME-B.19184.108.40.2063
Various vortical structures are investigated by using three kinds of flow visualization methods in branch pipe flows. There are two typical flow patterns when a jet from the branch pipe with various angles is injected to the main pipe cross flow. The velocity range of cross flow of the main pipe is 0.2 m/s ~ 1.2 m/s and the corresponding Reynolds number, R
is of the range 1.5 * 10
~ 9.02 * 10
. The velocity ratio(R), jet velocity/cross flow velocity, is chosen from 1.3 to 4. The subsequent behavior and development of the ring vortices which are created at the jet boundary mainly depend on the velocity ratio. An empirical relation for the shedding frequency of the ring vortices is derived. It is also found that there are two different vortex shedding mechanism in the mixing of two fluid streams.s.
A study on the combustion instability in a bluffbody dump combustor
Lee, Byeong-Jun ; Preston, L.H. ; Santavicca, D.A. ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 7, 1998, Pages 1022~1029
DOI : 10.22634/KSME-B.19220.127.116.112
The relation of the inlet fuel distribution, velocity, and overall equivalence ratio to the stability of a lean burning no-swirl dump combustor was examined. Premixed or partially premixed natural gas was introduced into the air stream, which flowed to the dump region through an annular inlet pipe. Inlet air was preheated upto 400 deg.C. Combustion instability was observed to occur at higher value of equivalence ratio (> 0.6) as the degree of unpremixedness was increased. Instabilities exhibited a dominant frequency of ~ 500 Hz, which corresponded to a half wave mode of combustor. CH chemiluminescence and pressure fluctuations were in-phase when combustion instabilities occurred. Acetone LIF images revealed that there was a strong fuel concentration gradient across the inlet annulus. Phase resolved OH LIF images showed that inlet fuel distribution was affected by the combustion instabilities.
Large-eddy simulation of channel flow using a spectral domain-decomposition grid-embedding technique
Gang, Sang-Mo ; Byeon, Do-Yeong ; Baek, Seung-Uk ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 7, 1998, Pages 1030~1040
DOI : 10.22634/KSME-B.1918.104.22.1680
One of the main unresolved issues in large-eddy simulation(LES) of wall-bounded turbulent flows is the requirement of high spatial resolution in the near-wall region, especially in the spanwise direction. Such high resolution required in the near-wall region is generally used throughout the computational domain, making simulations of high Reynolds number, complex-geometry flows prohibitive. A grid-embedding strategy using a nonconforming spectral domain-decomposition method is proposed to address this limitation. This method provides an efficient way of clustering grid points in the near-wall region with spectral accuracy. LES of transitional and turbulent channel flow has been performed to evaluate the proposed grid-embedding technique. The computational domain is divided into three subdomains to resolve the near-wall regions in the spanwise direction. Spectral patching collocation methods are used for the grid-embedding and appropriate conditions are suggested for the interface matching. Results of LES using the grid-embedding strategy are promising compared to LES of global spectral method and direct numerical simulation. Overall, the results show that the spectral domain-decomposition grid-embedding technique provides an efficient method for resolving the near-wall region in LES of complex flows of engineering interest, allowing significant savings in the computational CPU and memory.