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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
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Volume & Issues
Volume 36, Issue 12 - Dec 2012
Volume 36, Issue 11 - Nov 2012
Volume 36, Issue 10 - Oct 2012
Volume 36, Issue 9 - Sep 2012
Volume 36, Issue 8 - Aug 2012
Volume 36, Issue 7 - Jul 2012
Volume 36, Issue 6 - Jun 2012
Volume 36, Issue 5 - May 2012
Volume 36, Issue 4 - Apr 2012
Volume 36, Issue 3 - Mar 2012
Volume 36, Issue 2 - Feb 2012
Volume 36, Issue 1 - Jan 2012
Selecting the target year
Pool Boiling Heat Transfer in a Vertical Annulus with a Longer Outside Tube
Kang, Myeong-Gie ;
Transactions of the Korean Society of Mechanical Engineers B, volume 36, issue 8, 2012, Pages 775~782
DOI : 10.3795/KSME-B.2012.36.8.775
To investigate pool boiling heat transfer in a vertical annulus with closed bottoms, the length of an outer tube was varied between 0.3 and 0.6 m. For the test, a heated tube of 0.2-m length and 19.1-mm diameter and water at atmospheric pressure were used. To elucidate the effects of the outer tube length on heat transfer, the results for the annulus were compared with data for a single unrestricted tube. The increase in the outer tube length resulted in an increase or decrease in heat transfer depending on the gap size. This tendency is mainly attributed to the difference in the intensity of liquid agitation.
Numerical Study of Turbulent Heat Transfer in Helically Coiled Tubes
Yoon, Dong-Hyeog ; Park, Ju-Yeop ; Seul, Kwang-Won ;
Transactions of the Korean Society of Mechanical Engineers B, volume 36, issue 8, 2012, Pages 783~789
DOI : 10.3795/KSME-B.2012.36.8.783
In this study, turbulent flow and heat transfer characteristics in a helically coiled tube have been numerically investigated. Helically coiled tubes are commonly used in heat exchange systems to enhance the heat transfer rate. Accordingly, they have been widely studied experimentally; however, most studies have focused on the pressure drop and heat transfer correlations. The centrifugal force caused by a helical tube increases the wall shear stress and heat transfer rate on the outer side of the helical tube while decreasing those on the inner side of the tube. Therefore, this study quantitatively shows the variation of the local Nusselt number and friction factor along the circumference at the wall of a helical tube by varying the coil diameter and Reynolds number. It is seen that the local heat transfer rate and wall shear stress greatly decrease near the inner side of the tube, which can affect the safety of the tube materials. Moreover, this study verifies the previous experimental correlations for the friction factor and Nusselt number, and it shows that the correlation between the two in a straight tube can be applied to a helical tube. It is expected that the results of this study can be used as important data for the safety evaluation of heat exchangers and steam generators.
Effect of Sand and Dust Ingestion on Small Gas Turbine Engines
Rhee, Dong-Ho ; Lim, Byeng-Jun ; Ahn, Iee-Ki ; Koo, Hyun-Chul ; Kim, Jee-Hee ;
Transactions of the Korean Society of Mechanical Engineers B, volume 36, issue 8, 2012, Pages 791~796
DOI : 10.3795/KSME-B.2012.36.8.791
Small gas turbine engines are used in aircraft as an auxiliary power unit (APU) to supply compressed air to start the main engine and for emergency electricity. When an aircraft is operating in an environment in which sand and dust is present in the ambient air, the engines as well as the APU ingest the sand and dust. This causes erosion of the engine and a degradation in its performance. The present study investigated the effect of sand and dust ingestion on small gas turbine engines. The concentration of sand and dust was
per unit kg of air, which follows the specification in MIL-E-8593. The test was conducted for 10 h, and the engine performance before and after the test was compared. In addition, a tear-down inspection was conducted to examine the erosion patterns of sub-components such as the impeller and turbine wheel.
Potential Performance Enhancement of Dual Heat Pump Systems through Series Operation
Baik, Young-Jin ; Kim, Min-Sung ; Chang, Ki-Chang ; Lee, Young-Soo ; Kim, Hyeon-Ju ;
Transactions of the Korean Society of Mechanical Engineers B, volume 36, issue 8, 2012, Pages 797~802
DOI : 10.3795/KSME-B.2012.36.8.797
In this study, the potential performance enhancement in a dual heat pump system through series operation was investigated by a comparison between the performance for parallel and series operation for a heating supply temperature of
. To compare the performance of each configuration fairly, the heat transfer surface area of the heat exchangers was fixed. The inlet temperatures and the flow rates of the heat source and the load were also fixed. In addition, the heat transfer and pressure drop characteristics of the working fluids were considered to achieve a more realistic comparison. The results show that the heating coefficient of performance (COP) of the series configuration is approximately 5% higher than that of the parallel configuration under the simulation conditions considered in the present study.
Prediction of Heating Load for Optimum Heat Supply in Apartment Building
Yoo, Seong-Yeon ; Kim, Tae-Ho ; Han, Kyou-Hyun ; Yoon, Hong-Ik ; Kang, Hyung-Chul ; Kim, Kyung-Ho ;
Transactions of the Korean Society of Mechanical Engineers B, volume 36, issue 8, 2012, Pages 803~809
DOI : 10.3795/KSME-B.2012.36.8.803
It is necessary to predict the heating load in order to determine the optimal scheduling control of district heating systems. Heating loads are affected by many complex parameters, and therefore, it is necessary to develop an efficient, flexible, and easy to use prediction method for the heating load. In this study, simple specifications included in a building design document and the estimated temperature and humidity are used to predict the heating load on the next day. To validate the performance of the proposed method, heating load data measured from a benchmark district heating system are compared with the predicted results. The predicted outdoor temperature and humidity show a variation trend that agrees with the measured data. The predicted heating loads show good agreement with the measured hourly, daily, and monthly loads. During the heating period, the monthly load error was estimated to be 4.68%.
Preventing Freezing of Condensate inside Tubes of Air-Cooled Condenser
Joo, Jeong-A ; Hwang, In-Hwan ; Cho, Young-Il ; Lee, Dong-Hwan ;
Transactions of the Korean Society of Mechanical Engineers B, volume 36, issue 8, 2012, Pages 811~819
DOI : 10.3795/KSME-B.2012.36.8.811
An air-cooled condenser is a device that is used for converting steam into condensate by using ambient air. The air-cooled condenser is prone to suffer from a serious explosion when the condensate inside the tubes of a heat exchanger is frozen; in particular, tubes can break during winter. This is primarily due to the structural problem of the tube outlet of an existing conventional air-cooled condenser system, which causes the backflow of residual steam and noncondensable gases. To solve the backflow problem in such condensers, such a system was simulated and a new system was designed and evaluated in this study. The experimental results using the simulated condenser showed the occurrence of freezing because of the backflow inside the tube. On the other hand, no backflow and freezing occurred in the advanced new condenser, and efficient heat exchange occurred.
Numerical Analysis of Thermal Environment Control in High-Density Data Center
Kwon, Oh-Kyung ; Kim, Hyeon-Joong ; Cha, Dong-An ;
Transactions of the Korean Society of Mechanical Engineers B, volume 36, issue 8, 2012, Pages 821~828
DOI : 10.3795/KSME-B.2012.36.8.821
Increasing heat generation in CPUs can hamper effective recirculation and by-pass because of the large temperature difference between the exhaust and the intake air through a server room. This increases the overall temperature inside a data center and decreases the efficiency of the data center's cooling system. The purpose of the data center's cooling system is to separate the intake and exhaust air by controlling the computer room air-conditioner(CRAC). In this study, ICEPAK is used to conduct a numerical analysis of a data center's cooling system. The temperature distribution and the entire room are analyzed for different volumetric flow rates. The optimized volumetric flow rate is found for each CPU power. The heat removal and temperature distribution for CPU powers of 100, 120, and 140 W are found to be the best for a volumetric flow rate of
. The numerical analysis is verified through RTI indicators, and the results appear to be the most reliable when the RTI value is 81.
Reynolds Shear Stress Distribution in Turbulent Channel Flows
Kim, Kyoung-Youn ;
Transactions of the Korean Society of Mechanical Engineers B, volume 36, issue 8, 2012, Pages 829~837
DOI : 10.3795/KSME-B.2012.36.8.829
Direct numerical simulations were carried out for turbulent channel flows with
= 180, 395 and 590 to investigate the turbulent flow structure related to the Reynolds shear stress. By examining the probability density function, the second quadrant (Q2) events with the largest contribution to the mean Reynolds shear stress were identified. The change in the inclination angle of Q2 events varies with wall units in
and with the channel half height in y/h > 0.5. Conditionally averaged flow fields for the Q2 event show that the flow structures associated with Reynolds shear stress are a quasi-streamwise vortex in the buffer layer and a hairpin-shaped vortex in the outer layer. Three-dimensional visualization of the distribution of high Reynolds shear stress reveals that the organization of hairpin vortices in the outer layer having a size of 1.5~3 h is associated with large-scale motions with high Reynolds shear stress in the outer layer.
Process of Hairpin Vortex Packet Generation in Channel Flows
Kim, Kyoung-Youn ;
Transactions of the Korean Society of Mechanical Engineers B, volume 36, issue 8, 2012, Pages 839~847
DOI : 10.3795/KSME-B.2012.36.8.839
Numerical simulations for channel flows with
= 180, 395 and 590 have been performed to investigate the hairpin packet formation process in wall-bounded turbulent flows. Using direct numerical simulation databases, the initial flow fields are given by the conditionally averaged flow field with the second quadrant event specified at the buffer layer. By tracking the initial vortex development, the change in the initial vortex to an
-shaped vortex and th generation of a secondary hairpin vortex were found to occur with time scales based on the wall units. In addition, at the time when the initial vortex has grown to the channel center, the inclination angle of the hairpin vortex packet is approximately
, which is similar for all three Reynolds numbers. Finally, numerical simulations of the evolution of two adjacent hairpin vortices have been performed to examine the interaction between the adjacent vortex packets.
Effect of AC Electric Fields on Counterflow Diffusion Flame of Methane
Choi, Byung-Chul ; Kim, Hyung-Kuk ; Chung, Suk-Ho ;
Transactions of the Korean Society of Mechanical Engineers B, volume 36, issue 8, 2012, Pages 849~855
DOI : 10.3795/KSME-B.2012.36.8.849
The effect of electric fields on the response of diffusion flames in a counterflow has been investigated experimentally by varying the AC voltage and frequency. The result showed that the flame was stationary with high AC frequency above the threshold frequency, and it increased with the applied voltage and then leveled off at 35 Hz. Below the threshold frequency, however, the flame oscillated with a frequency that was synchronized with the applied AC frequency. This oscillation can be attributed to the ionic wind effect due to the generation of bulk flow, which arises from the momentum transfer by molecular collisions between neutral molecules and ions, where the ions in the reaction zone were accelerated by the Lorentz force.
Instability Analysis of Counterflow Diffusion Flames with Radiation Heat Loss
Lee, Su-Ryong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 36, issue 8, 2012, Pages 857~864
DOI : 10.3795/KSME-B.2012.36.8.857
A linear stability analysis of a diffusion flame with radiation heat loss is performed to identify linearly unstable conditions for the Damk
hler number and radiation intensity. We adopt a counterflow diffusion flame with unity Lewis number as a model. Near the kinetic limit extinction regime, the growth rates of disturbances always have real eigenvalues, and a neutral stability condition perfectly falls into the quasi-steady extinction. However, near the radiative limit extinction regime, the eigenvalues are complex, which implies pulsating instability. A stable limit cycle occurs when the temperatures of the pulsating flame exceed the maximum temperature of the steady-state flame with real positive eigenvalues. If the instantaneous temperature of the pulsating flame is below the maximum temperature, the flame cannot recover and goes to extinction. The neutral stability curve of the radiation-induced instability is plotted over a broad range of radiation intensities.
Technical Review of Coal Gasifiers for Production of Synthetic Natural Gas
Lee, Geun-Woo ; Shin, Yong-Seung ;
Transactions of the Korean Society of Mechanical Engineers B, volume 36, issue 8, 2012, Pages 865~871
DOI : 10.3795/KSME-B.2012.36.8.865
Because of the increasing cost of oil and natural gas, energy production technologies using coal, including synthetic natural gas (SNG) and integrated gasification combined cycle (IGCC), have attracted attention because of the relatively low cost of coal. During the early stage of a project, the developer or project owner has many options with regard to the selection of a gasifier. In particular, from the viewpoint of feasibility, the gasifier is a key factor in the economic evaluation. This study compares the technical aspects of gasifiers for a real SNG production project in an early stage. A fixed-bed slagging gasifier, wet-type entrained gasifier, and dry-type entrained gasifier, all of which have specific advantages, can be used for the SNG production project. Base on a comparison of the process descriptions and performances of each gasifier, this study presents a selection guideline for a gasifier for an SNG production project that will be beneficial to project developers and EPC (Engineering, Procurement, Construction) contractors.
Molecular Dynamics Study of [C10mim][Br] Aggregation
Yoon, Hong-Min ; Lee, Joon-Sang ;
Transactions of the Korean Society of Mechanical Engineers B, volume 36, issue 8, 2012, Pages 873~876
DOI : 10.3795/KSME-B.2012.36.8.873
Ionic liquids (ILs) existing in the liquid ion form under standard conditions show a unique properties. 1-10-Alkyl-3-methyl-imidazolium bromide ([C10mim][Br]) is one of the ILs that shows amphiphilic characteristics under specific conditions. This property enables it to function as a surfactant, and therefore, it finds applications in a wide range of areas. In this study, we tried to predict the behavior, especially the aggregation aspect, of [C10mim][Br] in an aqueous solution using molecular dynamics (MD) simulations. The canonical (NVT) ensemble was used to relax the system and trace the trajectory of atoms. Several case studies were simulated and the interaction among [C10mim]+, [Br]-, and water was analyzed using the radial distribution function of each atom. The density distribution function was also used for the structural analysis of the entire system. We used the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code for the present MD simulations.
Characteristics of Multipath Ultrasonic Flowmeter Installed Upstream and Downstream of Flow Disturbance Factors-Contraction, Expansion, and Tee Pipe
Lee, Dong-Keun ; Cho, Yong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 36, issue 8, 2012, Pages 877~883
DOI : 10.3795/KSME-B.2012.36.8.877
Multipath ultrasonic flowmeters are increasingly being used for the purpose of accurate flow measurement. However, an installation standard has not yet been established for these flowmeters, and this can cause considerable confusion during field installation. There is a need for a minimum straight run to ensure the measurement accuracy of a flowmeter installed upstream and downstream of flow disturbance factors-expansion, contraction, and tee pipes. Experiments were performed by using multipath flowmeters that have less than
accuracy-4-paths 1-unit and 2-paths 1-unit are of foreign make, whereas 5-paths 2-units are of domestic make-to determine the straight run under the above conditions. We carried out experiments repeatedly by considering a straight run, velocity, and suggested installation standards for a multipath ultrasonic flowmeter that satisfies the tolerance limits.