• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.14 no.11
• /
• pp.914-922
• /
• 2002

Thermo-acoustic waves can be thermally generated in a compressible flow field by rapid heating and cooling, and chemical reaction near the boundary walls. This mechanism is very important in the space environment in which natural convection does not exist. Also this may be a significant factor for heat transfer when the fluids are close to the thermodynamic critical point. In this study, the generation and transmission characteristics of thermo-acoustic waves in an air-filled confined domain with two-step pulsed heating are studied numerically. The governing equations are discretized using control volume method, and are solved using PISO algorithm and second-order upwind scheme. For the purpose of stable solution, time step was set to the order of $1\times10_-9s,\;and\;grids\;are\;50\times2000$. Results show that temperature and pressure distributions of fluid near the boundary wall subjected to a rapid heating are increased abruptly, and the induced thermo-acoustic wave propagates through the fluid until it decays due to viscous and heat dissipation. Pressure waves have sharp front shape and decay with a long tail in the case of step heating, but these waves have sharp pin shape in the case of pulsed heating.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.17 no.3
• /
• pp.110-116
• /
• 2009

Research for climate control seats is being vigorously pursued because requests for passenger's thermal comfort are increasing. Recently, thermoelectric devices have been applied to automotive seats for both cooling and heating operations. The climate control seats using thermoelectric devices can rapidly control the air temperature passing through the devices and directly affect the thermal comfort of passengers. The performance characteristics of the climate control seats were analyzed by experiments for two different types of a leather covered seat and a mesh applied seat. Experimental results show that the cooling and heating performance for the mesh applied seat by using the discharge port of the shape of nozzle was improved significantly in comparison with that for the leather covered seat. The variation of temperature between the inlet air and the outlet air of the climate control seat for the enhanced mesh applied type was by $-3.5^{\circ}C$ at cooling mode, and was by $15.0^{\circ}C$ at heating mode, after about 30 minutes, respectively. Also, it is possible to provide rapid thermal comfort to passengers sitting on the seat in the vehicle cabin by using the proposed climate control seat.

• The KSFM Journal of Fluid Machinery
• /
• v.17 no.3
• /
• pp.19-24
• /
• 2014

Development of long-term mobile energy sources for mobile robots or small-sized unmanned vehicles are actively increasing. The micro gas turbine generator (MTG) is a good candidate for this purpose because it has both of high energy density and high power density, and 500W class MTG is under development. The designed MTG can be divided into 2 main parts. One part consists of motor/ generator and compressor, and the other one consists of combustor, recuperator and turbine. 500W class MTG is designed to operate at ultra-high speed of 400,000 rpm in high turbine temperature over $700^{\circ}C$ to improve the efficiency. Because the magnetism of NdFeB permanent magnet for the motor/generator could be degraded if the temperature is over $150-200^{\circ}C$, MTG needs the thermal insulation to block the heat transfer from combustor/turbine side to motor/generator side. Moreover, the motor/generator is allocated to get the cooling effect from the rapid air flow by the compressor. This study presents the experimental results to verify whether the thermal insulator and air flow are effective enough to keep the motor/generator part in the low temperature less than $100^{\circ}C$. From the motoring test by using the high temperature test rig, it was confirmed that the motor/generator part could maintain the temperature less than $50^{\circ}C$ under the condition of 1.0 bar compressed air.

• Journal of computational fluids engineering
• /
• v.18 no.1
• /
• pp.58-62
• /
• 2013

Personal Rapid Transit (PRT) is the emerging personal transport vehicle operating on the loop automatically. The PRT system utilize the electrical power from super capacity or battery, it is important to manage the power or energy. In this regards, the management of high temperature occurred by the operation of system is significantly important to prevent from serious damage of component. In this study, we studied the adequate shape of underbody which can reduce the heat accumulation by pickup coil and condenser using natural air cooling. We suggested the additional air pathway, air inlet and flow separator to decrease the temperature of the heat source components. It was found that suggested system can decrease the temperature of PRT under body by 16% during the static mode and by 10% during the running mode at 30km/h. It is expected that the findings of this study will feed into final design of newly built Korean PRT vehicle.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.30 no.2 s.245
• /
• pp.170-176
• /
• 2006

A spark discharge aerosol generator using air as a carrier gas has successfully been applied to silver nanoparticle production. The spark discharge between two silver electrodes, which was periodically obtained by discharging the capacitor, produced sufficient high temperatures to evaporate a small fraction of the silver electrodes. The silver vapor was subsequently supersaturated by rapid cooling and condensed to silver nanoparticles by nucleation and condensation. The morphology of the generated particles observed by transmission electron microscope was spherical. The element composition of the nanoparticles was silver, which was determined by energy dispersive X-ray spectroscopy. The crystal phase of the particles spark-generated under air atmosphere was composed of silver and silver oxides phase, which was determined by Xray diffraction analysis. While the nanoparticles generated under nitrogen atmosphere had only silver phase. This XRD data indicates that some fraction of the evaporated silver vapor could be oxidized in air atmosphere by the reaction with oxygen. A stable operation of the spark discharge generator has been achieved. The size and concentration of the particles can be easily controlled by altering the repetition frequency, capacitance, gap distance and flow rate of the spark discharge system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.21 no.9
• /
• pp.519-526
• /
• 2009

Environmental control system is adopted to control the thermal load from the avionic equipment in the reconnaissance pod which is mounted under a fighter aircraft, undergoing large and rapid environmental changes with the variations of flight altitude and velocity. In this study, an environmental control system was designed and built by adopting vapor compression cycle using R-124. The cooling performance characteristics of the system were measured varying operating parameters: thermal load in the pod, air mass flow rate through evaporator, condenser inlet air temperature, and air mass flow rate through condenser. The effects of the experimental parameters on the system performance were analyzed based on the experimental results. The problems on the designed system were also analyzed and the solutions were suggested to improve system efficiency and to obtain stable operation.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.12
• /
• pp.367-371
• /
• 2019

The molding for hollow products used widely in industry is rotational molding by heating and cooling. Uniform cooling is required to improve the quality of the product, and rapid cooling is required to improve the productivity. In this paper, the cooling condition is largely classified into the case of no forced cooling by the fan and forced cooling by the fan. In addition, when forced cooling by the fan is not performed, the condition for stopping the molding machine horizontally and the condition for stopping the molding machine vertically were classified. To confirm the forced cooling by the fan, the conditions were set such that only the molding machine rotates while the fan is not running and the upper and lower fans operate when only the lower fan is operated. The surface temperature of the rotary molding machine was analyzed by the STAR-CCM+ program for the case of air-cooling. The temperature distribution of the rotary molding machine was analyzed for five conditions and the temperature distribution for cooling was compared under each condition. Among the five cases, Case 4 was lowest at approximately 35 ℃ after 900sec.

• Journal of Energy Engineering
• /
• v.12 no.1
• /
• pp.29-34
• /
• 2003

Thermo-acoustic waves can be generated in a compressible fluid by rapid heating and cooling near the boundary walls. These phenomena are very important mechanism of heat transfer in the space environment in which natural convection does not exist. In this study, the generation and transmission characteristics of thermo-acoustic waves in an air filled enclosure with rapid wall heating are studied numerically. The governing equations were discretized using control volume method, and were solved using PISO algorithm and second-order upwind scheme. For the stable solution time step were considered as t=1$\times$$10^{-9}$ order, and grids are 50$\times$800. The induced thermo-acoustic wave propagates through the fluid until it decays due to viscous and heat dissipation. The wave showed sharp front shape and decreased with long tail.

• Journal of Power Electronics
• /
• v.6 no.1
• /
• pp.29-37
• /
• 2006

A sensorless control for an IPM (Interior Permanent Magnet) synchronous motor in a single piston rotary compressor is presented in this study. The rotor position is estimated from the d-axis and q-axis current errors between the real system and a motor model of the position estimator. The torque pulsation of the single piston rotary compressor is compensated to reduce speed ripples, as well as, mechanical noise and vibration. The proposed sensorless drive enables the compressor to operate at a lower speed which increases energy savings and reduces mechanical noise. It also gives high speed operations by a flux weakening control for rapid air-cooling and heating of the heat pump air-conditioners.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.23 no.1
• /
• pp.100-108
• /
• 2009

Due to rapid economic growth, the usage of residential cooling electrical appliances such as air conditioners and refrigerators has increased dramatically for the last decades. In other to reduce its energy consumption, the authorities have applied energy efficiency standards for principal appliances, including air conditioners. and then it can anticipate environmental effects. In this paper, it presents the actual procedure to analyze the effects for the decline in the $CO_2$ emissions and its methodology for the efficiency improvement of the air conditioner that takes a great portion of the summer power uses.