• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.13 no.10
• /
• pp.982-992
• /
• 2001

In this paper, the performance of ventilation equipments in enclosed parking garages were investigated for several air distribution systems by numerical method. Air change effectiveness of the non-mixing system was 0.42. It meant that more supply air as much as the design supply air was needed to maintain good indoor air quality. In the high speed nozzle ventilating system which is most expensive one, air change effectiveness was 0.54. Therefore this system satisfied to ventilation design. In the jet fan ventilating systems, air change effectiveness for jet fan ventilating system-A with 18 jet fans and jet fan ventilating system-B with 6 jet fans in circulation mixing arrangement were 0.565 and 0.42 respectively. Jet fan ventilating system-C with 6 jet fans in transport mixing arrangement was 0.535. Jet fan ventilating system-A and jet fan ventilating system-C met the ventilation design. But velocity in jet fan ventilating system-A was over 2.0m/s which is inappropriate in human comfort. Therefore this system is not proper to ventilation. Jet fan ventilating system-C was the optimum one for enclosed parking garages among 5 systems examined in this paper.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.23 no.1
• /
• pp.80-86
• /
• 2011

Vertical open display cabinets are widely used in shopping mall, supermarkets, retail stores. Maintaining the temperature of foods in the display cabinet is vitally important to retailers to ensure optimal food quality and safety. The purpose of this study is to reduce the infiltration of air and heat loss from ambient space to display cabinet. The three-dimensional Computational Fluid Dynamics(CFD) simulation is used for the analysis of air flow patterns and temperature distribution in refrigerated display cabinets. Under several operating conditions which vary both the inner and outer jet velocities in the range from 0.3 to 1.1 m/s, simulations were carried out. This paper presents a performance of display cabinets with single jet and double jet. The energy consumption due to thermal entrainment ratio is plotted with varying Re. It was found that the double jet system is better than single jet system in terms of temperature distribution and energy saving.

• Transactions of Materials Processing
• /
• v.17 no.8
• /
• pp.594-599
• /
• 2008

This paper presents a micro air pump based on the synthetic jet to supply reactant at the cathode side for micro fuel cells. The synthetic jet is a zero mass flux device that converts electrical energy into the momentum. The synthetic jet actuation is usually generated by a traditional PZT-driven actuator, which consists of a small cylindrical cavity, orifices and PZT diaphragms. Therefore, it is very important that the design parameters are optimized because of the simple configuration. To design the synthetic jet micro air pump, a numerical analysis has been conducted for flow characteristics with respect to various geometries. From results of numerical analysis, the micro air pump has been fabricated by the PDMS replication process. The most important design factors of the micro air pump in micro fuel cells are the small size and low power consumption. To satisfy the design targets, we used SP4423 micro chip that is high voltage output DC-AC converter to control the PZT. The SP4423 micro chips can operate from $2.2{\sim}6V$ power supply(or battery) and is capable of supplying up to 200V signals. So it is possible to make small size controller and low power consumption under 0.1W. The size of micro air pump was $16{\times}13{\times}3mm^3$ and the performance test was conducted. With a voltage of 3V at 800Hz, the air pump's flow rate was 2.4cc/min and its power consumption was only 0.15W.

• Proceedings of the KSME Conference
• /
• 2008.11b
• /
• pp.2834-2838
• /
• 2008

An free breathing proton exchange membrane fuel cell (PEMFC) was developed. This paper presents a study of the several effect on the performance of a fuel cell such as air flow rate, opening ratio, and cathode structures. Especially, an air flow rate is critical condition to improve the fuel cell performance. In this paper, we developed a synthetic jet micro air blower to supply high stoichiometric air. The synthetic jet actuation is usually generated by a traditional PZT-driven actuator, which consists of a small cylindrical cavity, orifices and PZT diaphragms. In comparison with free convection fuel cells, the forced-convection fuel cell which equipped synthetic jet micro air blower brings higher performance and stability for long term test. Also, power consumption of the synthetic jet micro air blower is under 0.3W. The results show that the maximum power density was $188mW/cm^2$ at $400mA/cm^2$. The maximum power density was higher 40% than power density of free convection fuel cell.

• Proceedings of the Korean Fiber Society Conference
• /
• 1998.10a
• /
• pp.394-397
• /
• 1998

Characteristics of air-jet textured yarns are determined by linear density, strength, and instability together with structural properties. Such characteristics are affected by various processing parameters and supply yam properties. In this Paper, specially, we have studied on the effect of air jet texturing conditions not only on texturing characteristics but also on splitting behavior using split-type ultrafine P/N filaments and their draw textured yarns as raw materials. (omitted)

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.2121-2126
• /
• 2003

Supersonic free jets discharging from an orifice or a nozzle have long been research subject with a number of engineering applications and have mainly been investigated using dry air or other gas without any condensation effects. The major characteristics of those supersonic jets are now well known in terms of jet pressure ratio and ratio of specific heats of gas. Recently, the supersonic jets of superheated steam or moist air are being used in many industrial applications, in which case is expected that the condensation effects might alter the fundamental structure of the dry air jet. The present study aims to investigate the supersonic moist air jet and to clarify the condensation effects on the jet structure. An experiment is carried out using an indraft wind tunnel facility. The relative humidity of moist air is controlled at the nozzle supply, and the jet pressure ratio is varied to obtain the moderately under expanded flows at the exit of the nozzle. It is found that the relative humidity of moist air can change the diameter and location of Mach Disk.

• Journal of Biosystems Engineering
• /
• v.8 no.1
• /
• pp.17-29
• /
• 1983

The milling process is considered as causing one of the greatest grain losses among all the processes in rice post-production. Major source of grain losses in the rice milling is considered as the whitening process. This study was attempted to develop an abrasive-type whitener, the whitening chamber of which being supplied by jet-air evenly and continuously. To investigate the milling performance by the new whitener, three kind of emery-stone grit(#36, #41, and #46), and three levels of rotational speed of emery stone roller (950, 1070, and 1200 rpm) were tested. The jet-air abrasive-type whitener was also compared with the conventional abrasive-type having no jet-air blower in terms of their milling performance. In addition, the effect of different combinations of sequential uses of the abrasive- and friction-type whiteners on the milling performance was also experimentally evaluated. The results of this study are summarized as follows; 1. In general, the whitening system combined with the abrasive type whitener with jet-air supply, which was newly designed, and the existing jet-air friction type whiteners produces more milled- and head-rice by about 0.3% points and 2.8% points, respectively than the system combined with the existing abrasive type without the jet-air supply under the same operational conditions. The former also consumed less electricity by 0.024 KwH per 100kg of milled rice production and gave more milling capacity by about 35 kg/hr. As compared with the conventional whitening system consisting of jet-air friction type whiteners only, the former yielded more milled- and head-rice by 1.5% points and 4.4% points, respectively. 2. The abrasive roller having 46 grit emery was better than the roller having 36 grit in aspects of milling performance and machine efficiency, in general. 3. With regard to the effect of combination method of abrasive type and friction type whiteners, one pass in abrasive type plus three passes in friction type gave better milling performance and energy efficiency than the two passes in abrasive type plus two passes in friction type regardless of the designs of the emery stone rollers. 4. The increase in rotational speed of the emery stone roller from 950 rpm to 1200 rpm presented negative effects on milled and head-rice yields and machine efficiency, but slightly positive effect on milling capacity.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2008.05a
• /
• pp.247-251
• /
• 2008

This paper presents a micro air pump actuated by PZT actuator (synthetic jet actuator) for air supply for micro fuel cells. The synthetic jet actuators are usually created by a traditional PZT-driven actuator, which consists of a small cylindrical cavity, in/outlet channel and PZT diaphragms. To design the micro air pump, a numerical analysis has been conducted for flow characteristics with respect to various geometries. A prototype of the micro air pump, with a size of $mm{\times}mm{\times}mm$, was fabricated by PDMS replication process and was conducted performance test. To control the PZT actuator, we used the SP4423 micro chips that can be amplified input voltage to reduce the controller size and the power consumption. With a voltage of 3V at 100Hz, the air pump's pumping pressure is 600pa and its power consumption is only 0.1mW.

• Journal of ILASS-Korea
• /
• v.3 no.2
• /
• pp.14-23
• /
• 1998

The negative pressure as much as 10's mmHg is demanded at nozzle inside, in case of atomizing the large density molten materials. by conventional air jet nozzle. In this study, suction type fluid nozzle is designed by applying the ejector principle in order to clarify the air flow of nozzle inside, mechanism of liquid suction and liquid film formation. The results of this experimental study areas follows. Suction force of liquid is magnified by using liquid nozzle, and it is able to supply the liquid stable. Negative pressure at nozzle inside is varied by throttle angle of liquid nozzle, position and outer diameter of air jet nozzle, and have a influence on liquid suction quantity and liquid film formation.

• Journal of ILASS-Korea
• /
• v.24 no.3
• /
• pp.130-136
• /
• 2019

Spray visualization of a vaporizer fuel injection system of a micro turbo jet engine was experimentally studied. The fuel heating by combustion was simulated by the high pressure steam generator and combustor inlet air from the centrifugal compressor was simulated by compressed air stored in the high pressure air tank. Spray visualization was performed with single vaporizer, and then six vaporizers which are same number of micro turbojet engine were used. As a results, the spray characteristics of the vaporizer were understood with pressure difference of the combustor inlet air and the fuel supply pressure. Spray angles with three types of vaporizer configuration were measured. In the results, guide vane configuration has a wider spray angle than the straight tube and smooth curve tube with a swirler, so it is expected that the fuel will be effectively distributed inside the combustor flame tube.