A study on cooling efficiency using 1-d analysis code suitable for cooling system of thermoforming

Thermoforming is one of the most versatile and economical processes available for polymer products, but cycle time and production cost must be continuously reduced in order to improve the competitive power of products. In this study, water spray cooling was simulated to apply to a cooling system instead of compressed air cooling in order to shorten the cycle time and reduce the cost of compressed air used in the cooling process. At first, cooling time using compressed air was predicted in order to check the state of mass production. In the following step, the ratio of removed energy by air cooling or water spray cooling among the total removed energy was found by using 1-D analysis code of the cooling system under the condition of checking the possibility of conversion from 2-D to 1-D problem. The analysis results using water spray cooling show that cycle time can be reduced because of high cooling efficiency of water spray, and cost of production caused by using compressed air can be reduced by decreasing the amount of the used compressed air. The 1-D analysis code can be widely used in the design of a thermoforming cooling system, and parameters of the thermoforming process can be modified based on the recommended data suitable for a cooling system of thermoforming. This paper was recommended for publication in revised form by Associate Editor Dongsik Kim Zhen-Zhe Li received his B.S. degree in Mechanical Engineering from Yanbian University, China, in 2002. He then received his M.S. degree in Aerospace Engineering from Konkuk University, South Korea, in 2005. He then received his Ph.D. degree in Mechanical Engineering from Chonnam National University, South Korea, in 2009. Dr. Li is currently a Researcher of the Department of Mechanical Engineering, Chonnam National University, South Korea. Dr. Li’s research interests include applied heat transfer, fluid mechanics and optimal design of thermal and fluid systems. Kwang-Su Heo received his B.S. degree in Mechanical Engineering from Chonnam National University, South Korea, in 1998. He then received his M.S. and Ph.D. degrees in Mechanical Engineering from Chonnam National University, South Korea, in 2003 and 2008, respectively. Dr. Heo is currently a Post-doctorial Researcher of the Department of Mechanical Engineering, KAIST(Korean Advanced Institute of Science and Technology), South Korea. Dr. Heo’s research interests include applied heat transfer, fluid mechanics and thermal analysis of superconductor. Dong-Ji Xuan received his B.S. degree in Mechanical Engineering from Harbin Engineering University, China, in 2000. He then received his M.S. degree in Mechanical Engineering from Chonnam National University, South Korea, in 2006. He is currently a Ph.D. candidate of the Department of Mechanical Engineering, Chonnam National University, South Korea. His research interests include control & optimization of PEM fuel cell system, dynamics & control, mechatronics. Seoung-Yun Seol received his B.S. degree in Mechanical Design from Seoul National University, South Korea, in 1983. He then received his M.S. degree in Mechanical Engineering from KAIST(Korean Advanced Institute of Science and Technology), South Korea, in 1985. He then received his Ph.D. degree in Mechanical Engineering from Texas Tech University, USA, in 1993. Dr. Seol is currently a Professor of the School of Mechanical and Systems Engineering, Chonnam National University, South Korea. Dr. Seol’s research interests include applied heat transfer, fluid mechanics and thermal analysis of superconductor.     

Flow dynamics at the minimum starting condition of a supersonic diffuser to simulate a rocket’s high altitude performance on the ground

A numerical analysis was conducted to investigate and characterize the unsteadiness of the flow structure and oscillatory vacuum pressure inside of a supersonic diffuser equipped to simulate high-altitude rocket performance on the ground. A physical model including a rocket motor, vacuum chamber, and diffuser, which have axisymmetric configurations was employed. Emphasis was placed on investigating the physical phenomena of very complex and oscillatory flow evolutions in the diffuser operating very close to the starting condition, i.e. at a minimum starting condition, which is one of the major important parameters from a diffuser design point of view. This paper was recommended for publication in revised form by Associate Editor Jun Sang Park Hyo-Won Yeom received a B.S. degree in the department of Aerospace & Mechanical Engineering from Korea Aerospace University in 2007. He is currently a master candidate at the school of Aerospace & Mechanical Engi-neering at Korea Aerospace Uni-versity in Goyang-city, Korea. His research interests are in the area of numerical analysis for High-speed propulsion system. Sangkyu Yoon received a B.S. degree in the department of Aerospace & Mechanical Engineering from Korea Aerospace University in 2006 and M.S. degrees in the school of Aerospace & Mecha-nical Engineering from Korea Aerospace University in 2008. He currently works in Hanwha Corporation R&D Center. Hong-Gye Sung received a B.S. degree in the department of Aerospace Engineering from Inha University in 1984 and Ph.D. degree in Nuclear and Mechanical Engineering from The Pennsylvania State University in 1999. Dr. Sung has various research experiences in the fields of high-speed propulsion and rocket propulsion in Agency for Defense Development for 22 years (1984–2006). He is currently a professor at the School of Aerospace and Mechanical Engineering of Korea Aerospace University in Goyang, Korea. Dr. Sung’s research interests are in the area of propulsion, combustion, and its control.     

Phase of acoustic impedance and performance of standing wave thermoacoustic coolers

Investigations on the relations between the phase angle of the acoustic impedance at the driver piston and the system performance of a standing wave thermoacoustic cooler were performed. The system performance measured at a fixed acoustic power showed that the coefficient of performance of the standing wave thermoacoustic cooler increases as the phase angle increases when the stack temperature span is relatively low. The results were consistent with the simulation results obtained from DELTAE, a computer code based on linear thermoacoustic theory. Analysis on the temperature profiles along the stack showed that the cooling efficiency (COP) of the system could be decreased or increased as the phase angle of the acoustic impedance at the driver piston changes depending on the stack temperature spans. This paper was recommended for publication in revised form by Associate Editor Yeon June Kang Insu Paek received the B.S. degree in Mechatronics Engineering from Kangwon National University, Chuncheon, Korea, in 1997, the M.S. degree in Mechanical Engineering from the University of Texas at Austin, USA, in 2000, and the Ph. D. degree in Mechanical Engineering from Purdue University, West Lafayette, USA, in 2005. He worked as a postdoctoral researcher in Purdue University and McGill University in 2006 and 2007. He is currently a faculty member in the Department of Mechatronics Engineering, Kangwon National University, Chuncheon, Korea. His research interests include thermoacoustic cooling and power generation, solar heat driven absorption cooling., and wind power. Luc Mongeau received the B.S. and M.S. degrees in mechanical engineering from the University of Montreal, QC, Canada, in 1984 and 1986, respectively, and the Ph. D. degree in Acoustics from Pennsylvania State University, University Park, USA, in 1990. He is currently a professor in the Department of Mechanical Engineering at McGill University, Montreal, QC, Canada. He has published over 50 archival journal publications on various topics related to acoustics and noise control. His research activities are in the flow and turbomachinery noise areas, as well as in the areas of voice production, and thermoacoustic refrigeration. James E. Braun received the B.S. degree in Mechanical Engineering from the University of Massachusetts, USA, in 1976, and the M.S. and Ph. D. degrees in Mechanical Engineering from the University of Wisconsin, Madison, USA, in 1980 and 1988, respectively. He is currently a professor in the Department of Mechanical Engineering, Purdue University, West Lafayette, USA. Professor Braun’s research combines the use of computer modeling, optimization, and experiments to study and improve the performance of thermal systems. He has published over 140 papers. Professor Braun is currently an associate editor for the international journal of HVAC&R Research. Shin You Kang received the B.S. and M.S. degrees in the Department of Mechanical Design from Seoul National University, Seoul, Korea, in 1982, and 1986, respectively. He then received the Ph.D. in Mechanical Engineering at the same university in 1992. Professor Kang is currently a professor in the Department of Mechatronics Engineering, Kangwon National University, Chuncheon, Korea. His research interests include mechanical structure design, crash analysis, optimal design, computational structure analysis and evaluation.     

A study on performance improvement of corrugated type total heat exchanger considering the structure of flow passage on surface

Three types of flow passage structure of a total heat exchanger (perforated type, slit type, and embossed and perforated type) are studied to enhance the heat exchange performance of a heat recovery ventilation system (total heat exchanger). The perforated type has four punched rows of 6mm holes in the flow passage channel, and the slit type has six processed rows of 40mm length. The embossed and perforated type has holes of about 1mm diameter and protrusions of about 0.2mm height on all surfaces. The heat exchange efficiency of the modified total heat exchanger was compared to that of a general total heat exchanger with a smooth surface. The Korean Standard (KS) heat recovery ventilator test condition was applied for tests. In the case of cooling operation based on a typical Reynolds number of 140 (typical air flow rate of 100 m³/hr), the perforated type, slit type, and embossed and perforated type showed temperature efficiency improvement of 1.2%, 2.5%, and 5.0%; latent efficiency improvement of 18.0%, 32.3%, and 24.5%; and enthalpy efficiency improvement of 7.9%, 11.5%, and 11.2%, respectively. The corresponding improvements of heating operation were 3.0%, 3.4%, and 4.0%; 5.0%, 6.6%, and 18.7%; 3.2%, 4.3%, and 7.7%, respectively. On the other hand, the air pressure drop throughout the modified flow passage of the total heat exchanger increased by up to 1.7% at the typical Reynolds number of 140, from the air pressure drop of the regular total heat exchanger. This paper was recommended for publication in revised form by Associate Editor Dae Hee Lee Kyungmin Kwak received his B.S., M.S. and Ph.D. degrees in Mechanical Engineering from Yeungnam University, Korea, in 1993, 1995 and 1999, respectively. Dr. Kwak is currently a Researcher at the Automotive RIC at Kyungil University, Korea. His research interests include heat transfer, refrigeration and air control. Cheolho Bai received his B.S. and M.S. degrees in Mechanical Engineering from Seoul Na-tional University, Korea, in 1984 and 1986, respectively. He then received his Ph.D. from UCLA, USA, in 1992. Dr. Bai is currently a Professor at the School of Mechanical Engineering at Yeungnam University in Kyungsan, Korea. His research interests include heat transfer, refrigeration and air control.     

Numerical analysis of flow characteristics of fire extinguishing agents in aircraft fire extinguishing systems

If fire breaks out on an airplane, a large amount of fire extinguishing agents should be discharged within a very short time. For effective fire extinguishing, increased discharge velocity of the fire extinguishing agents is required. This can be achieved by using a large-sized vessel in which the fire extinguishing agents are highly pressurized by noncombustible gases. It is important to understand the flow characteristics of a fire extinguishing system for optimal system design. This study reports a numerical analysis of the flow characteristics of an airplane fire extinguishing system using halon-1301 as a fire extinguishing agent. The unsteady flow model was simulated with the general-purpose software package “FLUENT”, to study the flow characteristics of the fire extinguishing agents in the system. The effects of the rupture surface area and tube diameter on the flow characteristics were investigated for optimal system design. From the analysis results, it was clarified that the characteristics of the halon discharge from the end of tube are very sensitive to the rupture surface area and significantly affected by the tube diameter. This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008. Byung-Joon Baek received his B.S. degree in Mechanical Engineering from Seoul National University, KOREA, in 1979. He then received his M.S. and Ph.D. degrees from Seoul National University, KOREA, in 1981 and University of Missouri-Rolla USA, in 1989, respectively. Dr. Baek is currently a Professor at Division of Mechanical System Engineering at Chonbuk National University in Jeonju, Korea. Dr. Baek’s research interests include the thermal control of micro-fluidics. Jee-Keun Lee received his B.S. degree in Precision Mechanical Engineering from Chonbuk National University, KOREA, in 1986. He then received his M.S. and Ph.D. degrees from Chonbuk National University, KOREA, in 1992 and in 1998, respectively. Dr. Lee is currently an associate Professor at Division of Mechanical System Engineering at Chonbuk National University in Jeonju, Korea. Dr. Lee’s research interests include the measurement of a turbulent flow and sprays using the laser diagnostics.     

Numerical simulation on soot deposition process in laminar ethylene diffusion flames under a microgravity condition

A numerical study on soot deposition in ethylene diffusion flames has been conducted to elucidate the effect of thermophoresis on soot particles under a microgravity environment. Time-dependent reactive-flow Navier-Stokes equations coupled with the modeling of soot formation have been solved. The model was validated by comparing the simulation results with the previous experimental data for a laminar diffusion flame of ethylene (C₂H₄) with enriched oxygen (35% O₂ + 65% N₂) along a solid wall. In particular, the effect of surrounding air velocity as a major calculation parameter has been investigated. Especially, the soot deposition length defined as the transverse travel distance to the wall in the streamwise direction is introduced as a parameter to evaluate the soot deposition tendency on the wall. The calculation result exhibits that there existed an optimal air velocity for the early deposition of soot on the surface, which was in good agreement with the previous experimental results. The reason has been attributed to the balance between the effects of the thermophoretic force and convective motion. This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon Jae Hyuk Choi received his B.S. and M.S. degrees in Marine System Engineering from Korea Maritime University in 1996 and 2000, respectively. He then went on to receive a Ph.D. degrees from Hokkaido university in 2005. Dr. Choi is currently a BK21 Assistant Professor at the School of Mechanical and Aerospace Engineering at Seoul National University in Seoul, Korea. Dr. Choi’s research interests are in the area of reduction of pollutant emission (Soot and NOx), high temperature combustion, laser diagnostics, alternative fuel and hydrogen production with high temperature electrolysis steam (HTES). Junhong Kim received his B.S., M.S., and Ph. D degrees in Mechanical Engineering from Seoul National University in 1998, 2000, and 2004, respectively. His research interests include lifted flames, edge flames, and numerical simulation. Sang Kyu Choi received his B.S. degree in Mechanical Engineering from Seoul National University in 2004. He is a Ph. D student in the School of Mechanical Engineering, Seoul National University. His research interests include edge flames, oxy-fuel combustion, and numerical simulation. Byoung ho Jeon received his B.S degrees in Mechanical Engineering from kangwon University in 1998, and M.S., Ph. D. degrees in Mechanical Engineering from Hokkaido University in 2002, 2008, respectively. Dr Jeon is working at Korea Aerospace Research Institute from 2007. June. as Gasturbine engine developer. Jeon’s research interests are in the area of reduction of pollutant emission (Soot and Nox), High temperature combustion, combustion system (Furnace, Combine Generation system, IGCC, CTL), and Fire safety in building. Osamu Fujita received his B.S., M.S., and Ph. D. degrees in Mechanical Engineering from Hokkaido University in 1982, 1984, and 1987, respectively. Prof. Fujita is currently a Professor at the division of Mechanical and space Engineering at Hokkaido University in sapporo, Japan. Prof. Fujita’s research interests are in the area of reduction of pollutant emission (Soot and Nox), solid combustion, catalytic combustion, high temperature combustion, alternative fuel and fire safety in space. Suk Ho Chung received his B.S. degree in Mechanical Engineering in 1976 from Seoul National University, and his M.S. and Ph. D. degree in Mechanical Engineering in 1980 and 1983, respectively from Northwestern University. He is a professor since 1984 in the School of Mechanical and Aerospace Engineering, Seoul National University. His research interests cover combustion fundamentals, pollutant formation, and laser diagnostics.     

Effects of injection type on slot film cooling for a ramjet combustor

A slot film cooling technique has been used to protect a combustor liner from hot combustion gas. This method has been developed for gas turbine combustors. A ramjet combustor exposed to high temperature can be protected properly with a multi-slot film cooling method. An experimental study has been conducted to investigate the change of the first slot angle under recirculation flow and the influence of wiggle strip within a slot, which affects the film cooling effectiveness. The first slot angle has been changed to understand the effect of the injection angle on the film cooling effectiveness in a recirculation zone. The distribution of dimensionless temperature was obtained by a thermocouple rake to investigate the wiggle strip effect, and the adiabatic film cooling effectiveness on downstream wall was measured by a thermochromic liquid crystal (TLC) method. At the first slot position, the film cooling effectiveness decreases significantly because of the effects of recirculation flow. The lip angle of the first slot affects slightly on the film cooling effectiveness. The wiggle strip reinforces the structure of slot and keeps the uniform open area of slot. However, it induces three dimensional flows and enhances the flow mixing between the main flow and the injected slot flow. Therefore, the wiggle strip decreases slightly the overall film cooling effectiveness. This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008. Kwanghoon Park received his M.S degree in Mechanical Engineering from Yonsei University, Seoul, Korea in 2007. He is currently working for an education of an officer as a drillmaster in Army Consolidated Logistics School. Kang Mo Yang joined the Republic of Korea Army in 2004. He is currently working towards the M.S. degree at the Department of Mechanical Engineering, Yonsei University. Keon Woo Lee received his M.S. degree in Mechanical Engineering from Yonsei University, Seoul, Korea in 2008. In 2008, he joined the Doosan heavy industries & Construction Co, LTD, where he is a member of the IGCC Business Team. Hyung Hee Cho received his PhD degree in Mechanical Engineering from University of Minnesota, Minneapolis, MN in 1992. In 1995, he joined the Department of Mechanical Engineering, Yonsei University, Seoul, Korea, where he is currently a full professor in the School of Mechanical Engineering. His research interests include heat transfer in turbomachineries, rocket/ramjet cooling as well as nanoscale heat transfer in thin films, and microfabricated thermal sensors. Hee Cheol Ham received his PhD degree in Mechanical Engineering from Yonsei University, Seoul, Korea in 2001. In 1984, he joined the Agency for Defense Development, Daejeon, Korea, where he is currently a Principal Researcher. Ki Young Hwang received his Ph.D. degree in Mechanical Engineering from Yonsei University, Seoul, Korea in 1994. In 1979, he joined the Agency for Defense Development, Daejon, Korea, where he is currently a principal researcher in the Airbreathing Propulsion Directorate.     

Optimal operating points of PEM fuel cell model with RSM

The output power efficiency of the fuel cell system mainly depends on the required current, stack temperature, air excess ratio, hydrogen excess ratio, and inlet air humidity. Therefore, the operating conditions should be optimized to get maximum output power efficiency. In this paper, a dynamic model for the fuel cell stack was developed, which is comprised of a mass flow model, a gas diffusion layer model, a membrane hydration, and a stack voltage model. Experiments have been performed to calibrate the dynamic Polymer Electrolyte Membrane Fuel Cell (PEMFC) stack model. To achieve the maximum output power and the minimum use of hydrogen in a certain power condition, optimization was carried out using Response Surface Methodology (RSM) based on the proposed PEMFC stack model. Using the developed method, optimal operating conditions can be effectively selected in order to obtain minimum hydrogen consumption. This paper was recommended for publication in revised form by Associate Editor Tong Seop Kim Dong-Ji Xuan received his B.S. degree in Mechanical Engineering from Harbin Engineering University, China in 2000. He then received his M.S. degree in Mechanical Engineering from Chonnam National University, South Korea in 2006. Currently, he is a Ph.D. candidate of the Department of Mechanical Engineering, Chonnam National University, South Korea. His research interests include control and optimization of PEM fuel cell system, dynamics and control, and mechatronics. Zhen-Zhe Li received his B.S. degree in Mechanical Engineering from Yanbian University, China in 2002. He then received his M.S. degree in Aerospace Engineering from Konkuk University, South Korea in 2005 and his Ph.D. degree in Mechanical Engineering from Chonnam National University, South Korea in 2009. Dr. Li is currently a Researcher of the Department of Mechanical Engineering in Chonnam National University, South Korea. Dr. Li’s research interests include applied heat transfer, fluid mechanics, and optimal design of thermal and fluid systems. Jin-Wan Kim received his B.S. degree in Aerospace Engineering from Chosun University, South Korea in 1990. He then received his M.S. degree in Aerospace and Mechanical Engineering from Korea Aerospace University, South Korea in 2003 and his Ph.D degree in Mechanical Engineering from Chonnam National University, South Korea in 2008. He is currently a Post Doctor of the Department of Mechanical Engineering in Chonnam National University, South Korea. His research interests include control of hydraulic systems, dynamics and control, and mechatronics. Young-Bae Kim received his B.S. degree in Mechanical Design from Seoul National University, South Korea in 1980. He then received his M.S. degree in Mechanical Engineering from the Korean Advanced Institute of Science and Technology (KAIST), South Korea in 1982 and his Ph.D. degree in Mechanical Engineering from Texas A&M University, USA in 1990. Dr. Kim is currently a Professor of the School of Mechanical and Systems Engineering in Chonnam National University, South Korea. Dr. Kim’s research interests include mechatronics, dynamics and control, and fuel cell hybrid electric vehicle (FCHEV) systems.     

The effect of blade angle on the flow and pressure distributions in the vicinity of the diffuser blades of a room air conditioner

Many studies on air-conditioning systems are more focused on the individual thermal comfort rather than the thermal efficiency, due to an increase in health concerns. There are several factors influencing the thermal comfort, such as temperature, humidity, convection and air movement, etc. Numerical analyses were performed to investigate the effect of blade angle on the flow characteristics in the vicinity of diffuser blades of a room air conditioner (RAC), with three different blade discharge angles of 45.1°, 58.6° and 116°. We used the commercial code FLUENT to calculate the two-dimensional steady thermal flow fields with different impeller rotational velocities. The angular velocities were located within the range from 900 rpm to 1200 rpm. Turbulence closure was achieved using a standard k-ɛ model. A moving reference frame (MRF) approach was adopted to simulate the flow field generated by the impeller in an RAC. The results were graphically depicted with various geometrical configurations and operating conditions. This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008. Youn-Jea Kim received his B.S. degree in Mechanical Engineering from Sungkyunkwan University, Korea, in 1982. He then received his M.S. and Ph.D. degrees from the State University of New York at Buffalo in 1987 and 1990, respectively. Dr. Kim is currently a Professor at the School of Mechanical Engineering at Sungkyunkwan University in Korea. Dr. Kim’s research interests include gas dynamics, MEMS, and fluid-machineries, etc.     

Solid-liquid mixture flow through a slim hole annulus with rotating inner cylinder

An experimental study was conducted to study solid-liquid mixture upward hydraulic transport of solid particles in vertical and inclined annuli with rotating inner cylinder. Lift forces acting on a fluidized particle play a central role in many important applications, such as the removal of drill cuttings in horizontal drill holes, sand transport in fractured reservoirs and sediment transport, etc. Annular fluid velocities varied from 0.4 m/s to 1.2 m/s. Effect of annulus inclination and drill pipe rotation on the carrying capacity of drilling fluid, particle rising velocity, and pressure drop in the slim hole annulus have been measured for fully developed flows of water and of aqueous solutions of sodium carboxymethyl cellulose (CMC) and bentonite, respectively. For higher particle feed concentration, the hydraulic pressure drop of mixture flow increases due to the friction between the wall and solids or among solids. This paper was recommended for publication in revised form by Associate Editor Gihun Son Sang-Mok Han received a B.S. degree in Mechanical Engineering from Sung-kyunkwan University in 2001. He then went on to receive his M.S. degrees from Sungkyunkwan University in 2003. He is a candidate for Ph.D. from 2006 to the present at the School of Mechanical Engineering at Sungkyunkwan University in Suwon, Korea. His research interests are in the area of Multi-phase flow and drilling. Nam-Sub Woo received a B.S. degree in Mechanical Engineering from Sungkyunkwan University in 1997. He then went on to receive his M.S. and Ph.D. degrees from Sunkyunkwan University in 1999 and 2007, respectively. Dr. Woo is currently a Senior Researcher at the Fire & Engineering Services Research Center at Korea Institute of Construction and Technology in Goyang, Korea. Dr. Woo’s research interests are in the area of fluid dynamics and plant engineering. Young-Kyu Hwang received a B.S. degree in Mechanical Engineering from Sungkyunkwan University in 1977. He then went on to receive his M.S. from University of Wis-consin at Madison in 1980 and Ph.D. degrees from State Uni-versity of New York at Buffalo in 1984, respectively. Dr. Hwang has served as a Professor, from 1984 to the present at the School of Mechanical Engineering at Sungkyunkwan University in Suwon, Korea. His research interests are in the area of drilling hydraulics, molecular gas flow and hydrodynamic instability.     

Experimental study on heat transfer characteristics of internal heat exchangers for CO2 system under cooling condition

This paper presents the heat transfer characteristics of the internal heat exchanger (IHX) for CO₂ heat pump system. The influence on the IHX length, the mass flow rate, the shape of IHX, the operating condition, and the oil concentration was investigated under a cooling condition. Four kinds of IHX with a coaxial type and a micro-channel type, a mass flow meter, a pump, and a measurement system. With increasing of the IHX length, the capacity, the effectiveness, and the pressure drop increased. For the mass flow rate, the capacity of micro-channel IHX are higher about 2 times than those of coaxial IHX. The pressure drop was larger at cold-side than at hot-side. In the transcritical CO₂ cycle, system performance is very sensitive to the IHX design. Design parameters are closely related with the capacity and the pressure drop of CO₂ heat pump system. Along the operating condition, the performance of CO₂ IHXs is different remarkably. For oil concentration 1, 3, 5%, the capacity decreases and the pressure drop increased, as compared with oil concentration 0%. This paper was recommended for publication in revised form by Associate Editor Yong Tae Kang Prof. Young-Chul Kwon received his B.S. degree in Precision Mechanical Engineering from Pusan National University, Korea, in 1989. He then received his M.S. and Ph.D. degrees from POSTECH, in 1991 and 1996, respectively. Dr. Kwon is currently a Professor at the Division of Mechanical Engineering at Sunmoon University in Chungnam, Korea. He serves as a chief of the Institute of Automation and Energy Technology. Dr. Kwon’s research interests include heat exchanger, CO₂ cycle, heat pump, and energy recovery ventilator for HVAC&R. Mr. Dae-Hoon Kim is currently Doctoral student at the Mechanical Engineering from Hanyang University in Seoul, Korea. His research topics include experimental and numerical of CO₂ heatpump system. He has conducted a study on the Analysis of Refrigerating & Air-Conditioning Equipment Industry and Its Forecasting Supervising and Testing for Performance of Refrigerator, Freezer and Air-Conditioner. Prof. Jae-Heon Lee received his B.S. degree in Mechanical Engineering from Seoul National University, Korea, in 1971. He then received his M.S. and Ph. D. degree from Seoul National University in 1977 and 1980, respectively. Dr. Lee is currently a Professor at the school of Mechanical Engineering at Hanyang University in Seoul, Korea. Dr. Lee is currently a president at the Korea Institute research interests include simulation of thermal fluid and Plant engineering and construction. Dr. Jun-Young Choi received his B.S. degree in Mechanical Engineering from Yonsei University, Republic of Korea, in 1989. He then received his M.S. and Ph. D. degrees from Yonsei University in 1991 and 1999, respectively. Dr. Choi is currently a chief researcher with the 18 years experience on the energy performance testing of HVAC/R product. He is now assigned to the Energy Technology Center at Basic Industry Division at Korea Testing Laboratory. He has been involved in the development of Design and Manufacturing Technology for Air-Conditioner E.E.R. and Performance Testing Equipment for Cooling and Heating System with Non-CFCs, and natural refrigerants. He has conducted a study on the Analysis of Refrigerating & Air-Conditioning Equipment Industry and Its Forecasting Supervising and Testing for Performance of Refrigerator, Freezer and Air-Conditioner. Dr. Sang Jae Lee received his Ph.D. degree in Mechanical Engineering from Hanyang University, KOREA, in 2008. Dr. Lee is currently a Researcher at the Korea Institute of Industrial Technology in Cheonan, Korea. Dr. Lee’s research interests CO₂ heatpump system, liquid desiccant air conditioning system and Micro heat exchanger.     

Application of nonlinear integer programming for vibration reduction optimum design of ship structure

This paper presents a hybrid optimization algorithm which combines an external call type optimization method and a general stochastic iterative algorithm for the nonlinear integer programming with genetic algorithm (GA). GA can rapidly search the approximate global optimum under a complicated design environment such as a ship structure. Meanwhile it can handle optimization problems involving discrete design variables. In addition, there are many parameters that have to be set for GA which greatly affect the accuracy and calculation time of the optimum solution. However, the setting process is difficult for users, and there are no rules to decide these parameters. Therefore, to overcome these difficulties, the optimization of these parameters has been also conducted by using GA itself. It is proven using the trial function that the parameters are optimal. Finally, the verification of validity and usefulness of nonlinear integer programming is performed by applying this method to the compass deck of a ship where the vibration problem is frequently occurs. This paper was recommended for publication in revised form by Associate Editor Eung-Soo Shin YoungMo Kong received his B.S. degree, M.S. and Ph.D. degrees in Mechanical Engineering from Pukyong National University, Korea, in 1990, 1992 and 2006, respectively. Dr. Kong is currently a Principal Research Engineer at the Vibration & Noise R&D Team at Daewoo Shipbuilding & Marine Engineering Co.LTD, Korea. His research interests include vibration and noise analysis, optimum design of rotating machinery and structure. SuHyun Choi received his B.S. degree and M.S. degrees in Naval Architecture from Seoul National University, Korea, in 1982 and 1984, respectively and Ph.D. in Mechanical Engineering from The University of Michigan, Ann Arbor in the USA in 1992. Dr. Choi is currently a Vice President at the Commercial Ship Business Management at Daewoo Shipbuilding & Marine Engineering Co.LTD, Korea. His research interests include vibration and noise analysis, optimum design of rotating machinery and structure. Jin Dae Song received his B.S. degree and M.S. degree in Mechanical Engineering from Pukyong National University, Korea, in 2000 and 2002, respectively. Mr. Song is currently a candidate for the Ph.D degree in Mechanical Engineering from Pukyong National University. His research interests include vibration analysis and optimum design of rotating machinery. Bo-Suk Yang is a professor at the Pukyong National University in Korea. He received his Ph.D. degree in Mechanical Engineering from Kobe University, Japan in 1985. His main research fields cover machine dynamics and vibration engineering, intelligent optimum design, and condition monitoring and diagnostics in rotating machinery. He has published well over 190 research papers on vibration analysis, intelligent optimum design and diagnosis of rotating machinery. He is listed in Who’s Who in the World, Who’s Who in Science and Engineering, among others. ByeongKeun Choi is an Associate Professor at the Department of Precision Mechanical Engineering at Gyeongsang National University in Korea. He received his Ph.D. degrees in Mechanical Engineering from Pukyong National University, Korea, in 1999. Dr. Choi worked at Arizona State University as an Academic Professional from 1999 to 2002. His research interests include vibration analysis and optimum design of rotating machinery, machine diagnosis and prognosis and acoustic emission. He is listed in Who’s Who in the World, among others.     

A numerical study on oil retention and migration characteristics in the heat pump system

In HVAC system, the oil circulation is inevitable because the compressor requires the oil for lubrication and sealing. A small portion of the oil circulates with the refrigerant flow through the system components while most of the oil stays or goes back to the compressor. Because oil retention in refrigeration systems can affect system performance and compressor reliability, proper oil management is necessary in order to improve the compressor reliability and increase the overall efficiency of the system. This paper describes a numerical analysis of oil distribution in each component of the commercial air conditioning system including the suction line, discharge line and heat exchanger. In this study, system modeling was conducted for a compressor, discharge line, condenser, expansion valve, evaporator and suction line. Oil separation characteristics of the compressor were taken from the information provided by manufacturer. The working fluid in the system was a mixture of a R-410A refrigerant and PVE oil. When the oil mass fraction (OMF) was assumed, oil mass distribution in each component was obtained under various conditions. The total oil hold-up was also investigated, and the suction line contained the largest oil hold-up per unit length of all components. This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008. Min Soo Kim received his B.S., M.S., and Ph.D. degree at Seoul National University, Korea in 1985, 1987, and 1991, respectively. After Ph.D. degree, Prof. Kim worked at National Institute of Standards and Technology (NIST) in U.S.A. for about three years. He is currently a professor at the School of Mechanical and Aerospace Engineering of Seoul National University, Korea. Jong Won Choi received B.S. degree in Mechanical Engineering from Korea University in Seoul, Korea, in 2004, and then received M.S. degrees from Seoul National University in 2006. He is currently a student in Ph.D. course at the School of Mechanical and Aerospace Engineering of Seoul National University in Seoul, Korea. His research interests include refrigeration system, micro-fluidic devices, and PEM fuel cell as an alternative energy for next generation. Mo Se Kim received B.S. degree in Mechanical and Aerospace Engineering from Seoul National University in Seoul, Korea, in 2007. He is currently a student in M.S. course at the School of Mechanical and Aerospace Engineering of Seoul National University in Seoul, Korea. He had studied on the oil migration in the heat pump system, and now he studies on the refrigeration system using an ejector. Baik-Young Chung received his B.S., M.S., and Ph.D. degrees in Mechanical Engineering from Inha University, Korea in 1984, 1986, and 2001, respectively. He is currently a research fellow of HAC Research Center at LG Electronics. He is responsible for the commercial air conditioner group. Sai-Kee Oh received B.S. degree in Mechanical Engineering from Seoul National University, Korea in 1989, and then received M.S. and Ph.D. degrees from KAIST, Korea in 1991 and 1997, respectively. He is currently a principal research engineer of HAC Research Center at LG Electronics. He is responsible for the residential air conditioner group. Jeong-Seob Shin received B.S. degree in Machine Design and Production Engineering from Hanyang University, Korea in 1988, M.S. degree in Mechanical Engineering from KAIST, Korea in 1991, and Ph.D. degree in Mechanical Engineering from POSTECH, Korea in 2004. He has joined HAC Research Center at LG Electronics since 2006 as a principal research engineer.     

Natural convection heat transfer estimation from a longitudinally finned vertical pipe using CFD

In this study, CFD analysis of air-heating vaporizers was conducted. A longitudinally finned vertical pipe was used to represent the air-heating vaporizer in the CFD model. Nitrogen gas was used as the working fluid inside the vertical pipe, and it was made to flow upward. Ambient air, which was the heat source, was assumed to contain no water vapor. To validate the CFD results, the convective heat transfer coefficients inside the pipe, h_i-c, derived from the CFD results were first compared with the heat transfer coefficients inside the pipe, h_i-p, which were derived from the Perkins correlation. Second, the convection heat transfer coefficients outside the pipe, h_o-c, derived from the CFD results were compared with the convection heat transfer coefficients, h_o-a, which were derived from an analytical solution of the energy equation. Third, the CFD results of both the ambient-air flow pattern and temperature were observed to determine whether they were their reasonability. It was found that all validations showed good results. Subsequently, the heat transfer coefficients for natural convection outside the pipe, h_o-c, were used to determine the Nusselt number outside the pipe, Nu_o.. This was then correlated with the Rayleigh number, R_a. The results show that R_a and Nu_o have a proportional relationship in the range of 2.7414×10¹² ≤ Ra ≤ 2.8263×10¹³. Based on this result, a relation for the Nusselt number outside the pipe, Nu_o, was proposed. This paper was recommended for publication in revised form by Associate Editor Man Yeong Ha Hyomin Jeong is currently a professor of Mechanical and Precision Engineering at Gyeongsang Nation University. He received his ph.D. in mechanical engineering from the University of Tokyo in 1992 and he joined Arizona State University as a visiting professor from 2008 to 2009. His research interests are in fluid engineering, CFD, cryogenic system, cascade refrigeration system and ejector system, mechanical vapor compression Hanshik Chung is a professor of Mechanical and Precision Engineering at Gyeongsang National University. He obtianed his Ph.D. in Mechanical Engineering from Donga University. He joined Changwon Master’s College and Tongyeong Fisher National College as an assistant Professor in 1988 and 1993, respectively. His research fields extend into the thermal engineering, heat transfer, solar heating & cooling system, LNG vaporizer optimum, solar cell, hydrogen compressor for fuel cell and making fresh water system from sea water     

Approximate velocity scale for primary and secondary dual-inlet side-dump flows

Effects of the bulk inlet velocity on the characteristics of dual-inlet side-dump flows are numerically investigated. Non-reacting subsonic turbulent flow is solved by a preconditioned Reynolds-averaged Navier-Stokes equation system with low-Reynolds number k − ɛ turbulence model. The numerical method is properly validated with measured velocity distributions in the head dome and the combustor. With substantial increase in the bulk inlet velocity, general profiles of essential primary and secondary flows normalized by the bulk inlet velocity are quantitatively invariant to the changes in the bulk inlet velocity. This paper was recommended for publication in revised form by Associate Editor Do Hyung Lee Seung-chai Jung received his B.S. degree in Mechanical Engineering from Yonsei University, Korea, in 2001. He then received his M.S. degree in Mechanical Engineering from Yonsei University, Korea, in 2005. Mr. Jung is currently a Ph. D. candidate at Yonsei University, where he is majoring in Mechanical Engineering. Mr. Jung’s research interests include propulsion system and particle-surface collision dynamics. Byung-Hoon Park received his B.S. degree in Mechanical Design and Production Engineering from Yonsei University in 2003. He is currently a Ph.D. candidate in Yonsei University in Seoul, Korea. His research interests include performance design of propulsion systems and nu-merical analysis of instability in multiphase turbulent reacting flow-fields. Hyun Ko received his B.S. degree in Aerospace Engineering from Chonbuk National University, Korea, in 1996. He then received his M.S. degree in Mechanical Design from Chonbuk National University, Korea, in 1998. In 2005, he obtained his Ph.D. degree from Yonsei University, where he majored in mechanical engineering. Dr. Ko is currently a Principal Research Engineer of the MicroFriend Co., Ltd. in Seoul, Korea. His research interests include propulsion related systems and computational fluid dynamics. Woong-sup Yoon received his B.S. degree in Mechanical Engineering from Yonsei University, Korea, in 1985. He then received his M.S. degree from University of Missouri-Rolla in 1989. In 1992, he obtained his Ph.D. degree from the University of Alabama in Huntsville, where he majored in mechanical and aerospace engineering. Dr. Yoon is currently a professor at the School of Mechanical Engineering at Yonsei University in Seoul, Korea. His research interests include propulsion system and particle-related environmental/ thermal engineering.     

Experimental analysis for reducing refrigerant-induced noise of 4-way cassette type air conditioner

Various refrigerant flow patterns can produce a range of noise types according to their cycle conditions. Consequently, the identification of flow patterns in a tube is crucial to reducing refrigerant-induced noise. Because of the obstacles involved in identifying them accurately by experiment, in this paper, these flow patterns are estimated from the flow pattern map. Working from the assumption that the refrigerant-induced noise for an air conditioner in the heating mode comes from slug flow in the condenser-outlet pipe, the reduction of refrigerant-induced noise by avoiding slug flow in a tube is examined. To fully understand the conditions under which the refrigerant-induced noise occurs, cycle simulator equipment for an outdoor unit is developed. With this cycle simulator, noise tests of 4-way cassette type indoor units are performed under the conditions that the refrigerant-induced noise occurs. Increasing the mass flux in a tube by reducing the diameter of the condenser-outlet pipe can avoid slug flow, and the refrigerant-induced noise can therefore be reduced. The results of the cycle simulator can be verified with an outdoor unit 5HP system multi air conditioner and the results are well in line with simulator results. This paper was recommended for publication in revised form by Associate Editor Yeon June Kang Hyung-Suk Han received a B.S. degree in Production and Mechanical Engineering from Pusan National University in 1996. He then went on to receive his M.S. and Ph.D. degrees from Pusan National University in 1998 and 2007, respectively. Dr. Han is currently a Senior Researcher at Defense Agency of Technology and Quality, Pusan, Korea. He is currently serving as a Co-Researcher of Noise and Vibration Analysis Laboratory in Pusan National University. Dr. Han’s research interests are in the area of the mechanical applications of noise and vibration including refrigerant-induced noise. Wei-Bong Jeong received a B.S. degree in Mechanical Engineering from Seoul National University in 1978. He then went on to receive his M.S. and Ph.D. degrees from KAIST in 1980 and from Tokyo Institute of Technology in 1990, respectively. Dr. Jeong is currently a Professor at the Mechanical Engineering at Pusan National University in Busan, Korea. He is currently serving as an Academic Director of the Korean Society for Noise and Vibration Engineering. Dr. Jeong’s research interests are in the area of the measurement and signal processing of noise and vibration, finite/boundary element programming of noise and vibration, fluid-structure interactions and acoustic-structure interactions.     

Investigation of variations of lubricating oil diluted by post-injected fuel for the regeneration of CDPF and its effects on engine wear

The purpose of the present study was to investigate the effects of oil diluted by post-injected fuel for CDPF regeneration on engine wear and to find out the characteristic variation of diluted oil according to operating conditions. Experimental studies were made on a 2700 cc, 5 cylinder engine with an after-treatment system. Fuel content in oil increased according to the increase in the duration of post injection. A fuel dilution chart was made to predict the existing fuel content in used oil. The oil analysis method using this chart was validated through the comparison of the results analyzed by GC. The oil contamination by the post-injected fuel caused the quantity of blow-by gas and engine wear to increase and main gallery pressure to decrease. This paper was recommended for publication in revised form by Associate Editor Kyoung Doug Min Bong-Ha Song received a B.S. degree in Mechanical Engineering from Konkuk University in 1999. He received a M.S. degree from Yonsei University in 2002. He then went to Ajou University to get a Ph.D degree. Bong-Ha Song is currently a student at the School of Mechanical Engineering at Ajou University in Suwon, Korea. Yun-Ho Choi received a B.S. degree in Mechanical Engineering from Seoul National University in 1978. He then went on to receive his M.S. and Ph.D. degrees from Pennsylvania State University in 1984 and 1988, respectively. Dr. Choi is currently a professor at the Division of Mechanical Engineering at Ajou University in Suwon, Korea. Dr. Choi’s research interests are in the area of Computational Fluid Dynamics, Thermal Propulsion Systems Modeling and Two Phase Flows.     

Development of rapid mixing fuel nozzle for premixed combustion

Combustion in high-preheat and low oxygen concentration atmosphere is one of the attractive measures to reduce nitric oxide emission as well as greenhouse gases from combustion devices, and it is expected to be a key technology for the industrial applications in heating devices and furnaces. Before proceeding to the practical applications, we need to elucidate combustion characteristics of non-premixed and premixed flames in high-preheat and low oxygen concentration conditions from scientific point of view. For the purpose, we have developed a special mixing nozzle to create a homogeneous mixture of fuel and air by rapid mixing, and applied this rapidmixing nozzle to a Bunsen-type burner to observe combustion characteristics of the rapid-mixture. As a result, the combustion of rapid-mixture exhibited the same flame structure and combustion characteristics as the perfectly prepared premixed flame, even though the mixing time of the rapid-mixing nozzle was extremely short as a few milliseconds. Therefore, the rapid-mixing nozzle in this paper can be used to create preheated premixed flames as far as the mixing time is shorter than the ignition delay time of the fuel. This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon Masashi Katsuki received his B.E. degree in Mechanical Engineering from Osaka University, Japan, in 1965. He received his Dr. Eng. from O. U. in 1985. Dr. Katsuki is currently a Visiting Professor at the Department of Environmental Engineering at Hoseo University in Chungnam, Korea. He was a Vice President of the Japan Society of Mechanical Engineers. Dr. Katsuki’s research interests include combustion, computational thermo-fluid dynamics, and molecular dynamics. Jin-Do Chung received his B. S., M.S. and Ph.D. degrees in Mechanical Engineering from Chungnam University, Korea in 1983, 1985 and 1990. He then received another Ph.D. in Environmental Engineering from Kanazawa University, Japan in 1996. After that he worked as Post-doc researcher for 1,6 year at KIMM and Senior researcher for 6years at KEPCO Research Center. Dr. Chung is currently a Professor at the Department of Environmental Engineering at Hoseo University in Asan, Korea. Dr. Chung’s research interests include thermal-fluid and environmental engineering. Jang-Woo Kim received his B. S. degree in Mechanical Engineering from Chungnam University, Korea, in 1990. He then received his M. S. and Ph. D. degrees from Kyushu University, Japan in 1994 and 1998, respectively. Dr. Kim is currently a Professor at the School of Display Engineering at Hoseo University in Asan, Korea. Dr. Kim’s research interests include CFD, aerodynamics, and display equipment technology. Seung-Min Hwang received the Ph.D. degree in Mechanical Engineering at Osaka University in 2005. After that he worked as visiting researcher for 3 years at CRIEPI (central research institute of electric power industry) and Osaka University in Japan. He is currently a Professor at the Graduate School of Venture at Hoseo University in Korea. His major research is thermal-fluid, energy issue and environment. Seung-Mo Kim received his Ph. D. degrees in Mechanical engineering from Osaka University, Japan, in 2004. Dr. Kim is currently a research Professor at Pusan Clean Coal Center at Pusan National University in Pusan, South Korea. Dr. Kim’s research interests include coal combustion, oxy-fuel combustion, coal gasification, coal de-watering, power generation plant system and energy issues. Chul-Ju Ahn received his B.S. degree in Mechanical Engineering from Hanyang University, Korea, in 1998. He then received his M.S. and Ph.D. degrees from Osaka University, Japan, in 2001 and 2006, respectively. Dr. Ahn is currently a Senior Research Engineer at Samsung Techwin CO. LTD. in Changwon, Korea. Dr. Ahn’s research interests include gas turbine engine, biomass gasification, and power system.     

A finite thin circular beam element for out-of-plane vibration analysis of curved beams

A finite thin circular beam element for the out-of-plane vibration analysis of curved beams is presented in this paper. Its stiffness matrix and mass matrix are derived, respectively, from the strain energy and the kinetic energy by using the natural shape functions derived from an integration of the differential equations in static equilibrium. The matrices are formulated with respect to the local polar coordinate system or to the global Cartesian coordinate system in consideration of the effects of shear deformation and rotary inertias. Some numerical examples are analyzed to confirm the validity of the element. It is shown that this kind of finite element can describe quite efficiently and accurately the out-of-plane motion of thin curved beams. This paper was recommended for publication in revised form by Associate Editor Seockhyun Kim Chang-Boo Kim received his B.S. degree in Mechanical Engineering from Seoul University, Korea in 1973. He then received his D.E.A., Dr.-Ing. and Dr.-es-Science degrees from Nantes University, France in 1979, 1981 and 1984, respectively. Dr. Kim is currently a Professor at the School of Mechanical Engineering at Inha University in Incheon, Korea. His research interests are in the area of vibrations, structural dynamics, and MEMS.     

The effect of nonequilibrium condensation on hysteresis phenomenon of under-expanded jets

Under-expanded jets which are discharged from an orifice or a nozzle have long been subject of researches for aeronautical and mechanical applications. Provided that the jet pressure ratio and nozzle configuration are known, the major features of the steady jet are now well known. However, the jet pressure ratio is often varied even during the process in many practical applications. Many questions remain unanswered with regard to how the supersonic jet responds to the transient process of the pressure ratio and whether the steady jet data for a specific pressure ratio can still bear the same during the transient process of pressure ratio. In the present study, the hysteric phenomenon of under-expanded jets has been investigated with the help of computational fluid dynamics methods. The under-expanded jets of both dry and moist air have been employed to investigate the transient processes of the pressure ratio. The effects of nonequilibrium condensation occurring in the under-expanded moist air jets are explored on the hysteresis phenomenon. It is known that under-expanded air jet produced during the startup transient of jet behaves differently from the shutdown transient process, leading to the hysteric phenomenon of under-expanded jet. It is also known that the moist air jet reduces the hysteric phenomenon, compared with the dry air jet, and that non-equilibrium condensation which occurs in the underexpanded moist air jet is responsible for these findings. This paper was recommended for publication in revised form by Associate Editor Do Hyung Lee Heuy-Dong Kim received his B.S. and M.S. degrees in Mechanical Engineering from Kyungpook National University, Korea, in 1986 and 1988, respectively. He then received his Ph.D. degree from Kyushu University, Japan, in 1991. Dr. Kim is currently a Professor at the School of Mechanical Engineering, Andong National University, Korea. His research interests include High-Speed Trains, Ramiet and Scramiet, Shock Tube and Technology, Shock Wave Dynamics, Explosions & Blast Waves, Flow Measurement, Aerodynamic Noises and Supersonic Wind Tunnels. Min-Sung Kang received his B.S. and M.S degrees in Mechanical Engineering from Andong National University, Korea, in 2007 and 2009, respectively. Mr. Kang is currently a researcher at the School of Mechanical Engineering at Andong National University, Korea. His research interests include cavity and supersonic nozzle flows. Yumiko Otobe received her B.S. degree in Faculty of Engineering from Yamaguchi University, Japan, in 1978. She then received her Eng. D. degree from Saga University, Japan, in 2007. Dr. Otobe is currently a Research Associate at the Department of Control & Information Systems Engineering, Kitakyushu National College of Technology, Japan. Dr. Otobe’s research interests include sonic and supersonic jets of various gases as well as nonequilibrium condensation phenomena. Toshiaki Setoguchi received his B.S. degree in Mechanical Engineering from Tokyo University of Agriculture and Technology, Japan, in 1976. He then received his M.S. and Ph.D. degrees from Kyushu University, Japan, in 1978 and 1981, respectively. Dr. Setoguchi is currently a Professor at the Department of Mechanical Engineering, Saga University, Japan. His research interests include Nonequilibrium Condensation, Ramiet and Scramiet, Shock Tube and Technology, Shock Wave Dynamics, Explosions & Blast Waves, Aerodynamic Noises and Turbomachinery.