• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.12
• /
• pp.8165-8175
• /
• 2015

In Korea, summer is hot and humid, and air-conditioners consume lots of electricity. In such case, simultaneous usage of indirect evaporative cooler may reduce the sensible heat and save the electricity. In this study, heat transfer and pressure drop characteristics of indirect evaporative cooler made of aluminum, plastic, plastic/paper are investigated both under dry or wet condition. Results show that indirect evaporation efficiencies of the plastic/paper sample (38.5% ~ 51.4%) are approximately the same as those of the aluminum sample (41.9% ~ 47.5%), and are larger than those of the plastic sample (29.0% ~ 37.4%). This suggests that the plastic/paper sample could be a good substitute to the aluminum sample. However, the pressure drops across the paper channel are 92% ~ 106% larger than those across the aluminum channel. The heat transfer coefficients of the paper channel under dry condition are 15% ~ 44% larger than those of the plastic channel. The increases are 185% ~ 203% for the aluminum channel. The pressure drops of the paper channel are 34% ~ 48% larger than those of the plastic channel and 93% ~ 106% larger than those of the aluminum channel. Rigorous heat transfer analysis reveals that, for the plastic sample, 30% ~ 37% of the wet channels remain dry, whereas all the channels are wet for plastic/paper sample. For aluminum sample, the ratio is 17% ~ 23%.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.11 no.12
• /
• pp.4721-4726
• /
• 2010

The performance characteristics of water-chilling heat pump using CO2 for the control of inverter frequency was investigated experimentally. An experimental apparatus is consisted of a compressor, a gas cooler, an expansion valve, an evaporator and a liquid receiver. All heat exchangers used in the test rig are counter flow type heat exchangers with concentric dual tubes, which are made of copper. The gas cooler and the evaporator consist of 6 and 4 straight sections respectively arranged in parallel, each has 2.4m length. The experimental results summarize as the following: for constant inlet temperature of evaporator and gas cooler, as mass flow rate, compression ratio and discharge pressure increases with the inverter frequency. And heating capacity and compressor work increases, but coefficient of performance(COP) decreases with the inverter frequency of compressor. As inlet temperature of secondary fluid in the evaporator increases from $15^{\circ}C$ to $25^{\circ}C$, compression ratio and compressor work decreases, but mass flow rate, heating capacity and COP increases with the inverter frequency of compressor. The above tendency is similar with performance variation with respect to the variation of inverter frequency in the conventional vapor compression refrigeration cycle.

• Journal of Advanced Marine Engineering and Technology
• /
• v.28 no.6
• /
• pp.894-905
• /
• 2004

The closed cycle diesel propulsion system is free from the problem of the intake air, exhaust gas and their control that are associated with the conventional diesel propulsion system. The system is composed of a main engine, an exhaust cooler. a $CO_2$ scrubber and a $O_2$ mixer. In this paper, a hardware using microprocessor is proposed in order to monitor and control the oxygen and ratio of specific heat for underwater diesel propulsion system. Also simulation is carried out to ascertain the performance of proposed system.

• 한국신재생에너지학회:학술대회논문집
• /
• 2005.06a
• /
• pp.353-356
• /
• 2005

We developed a dynamic model of PEM fuel cell system which can analyze its transient response to dynamic load current. System components such as compressor, air cooler, humidifier, and stack were modeled based on their dynamic equations and performance maps by using Matlab Simulink platform. Through this simulation model, dynamic characteristics of fuel cell system including oxygen excess rat io, stack voltage, and system efficiency were shown. In addition to that, we briefly analyzed the humidity effect on cathode pressure and system efficiency, expecting that this model can be further used to optimize fuel cell system parameters just like operating pressure and temperature, humidity and oxygen excess ratio.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.64 no.4
• /
• pp.251-255
• /
• 2015

Chiller system plays an important role of maintaining room temperature constantly by supplying chilled water to Heating, Ventilating and Air Conditioning(HVAC)or area room cooler equipment during plant normal operation or accident condition. Chiller failures are one of the most frequently occurring equipment failures. If the types of chiller failures are analyzed and grouped thoroughly, it would be helpful to make chiller maintenance strategy at the plants. That would enhance equipment reliability of chiller in the end. In this paper, chiller failure data during three years were analyzed and categorized by specific failure code. In addition, the various proposals to improve equipment reliability of chiller were suggested such as Preventive Maintenance Optimization(PMO) strategy and performance monitoring reinforcement and so on.

• Journal of Advanced Marine Engineering and Technology
• /
• v.31 no.6
• /
• pp.723-728
• /
• 2007

In order to evaluate the performance of carbon dioxide cycle with a sub-cooling loop. a simulation system was developed to predict the steady state of $CO_2$ trans-critical cycle. Mathematical models are derived to describe the relationships between the system's coefficient of performance and other operating parameters The mathematical models are based entirely on the basic mass and energy conservation law and thermodynamic and transport properties of carbon dioxide A parametric study has been conducted in order to investigate the effect of sub-cooling loop and various operating conditions on the cycle performance. An optimal mass fraction of a refrigerant flowing through sub-cooling cycle existed for the given evaporating temperature, high pressure and air inlet temperature through gas cooler.

• Transactions of the Korean hydrogen and new energy society
• /
• v.15 no.4
• /
• pp.341-347
• /
• 2004

An experimental study has been carried out on cooling perfonnance of a thennoelectric module. This problem is of particular interest in the design of the refrigeration systems using thermoelectric module, such as cosmetic refrigerator, wine cellar and air cooler. The effect of the input voltage and the hot side temperature on the cooling performance is studied in detail. The $\Delta$T, temperature difference between cold side and hot side surface of thermoelectric module, is described in terms of the input voltage and the hot side temperature. It is found that the cooling capacity can be improved by increasing the input voltage and by reducing the heat from the hot side of the thermoelectric module. However, COP is decreased with an increase in the input voltage, since power consumption is also increased. Thus, optimum input voltage can be selected based on cooling capacity and COP.

• Proceedings of the SAREK Conference
• /
• 2006.06a
• /
• pp.156-161
• /
• 2006

The rivulet is a narrow stream of liquid flowing down a solid surface. Heat transfer of rivulet flow over on inclined heated surface has been investigated experimentally. This problem is of particular interest in the understanding of fundamental mechanism on rivulet heat transfer as well as in the design of a regenerative evaporative cooler. The rivulet is seem to be meandering flow, single wide flat flow. and film flow as rivulet flow rate is increased. Even though the wetted surface area is increased with an increase in the rivulet flow rate, the absorbed heat transfer of rivulet flow from a heated surface strongly depends on the flow pattern of rivulet.

• Journal of Power System Engineering
• /
• v.17 no.6
• /
• pp.102-107
• /
• 2013

In this paper, the performance analysis for evaporation capacity, total work and efficiency of the ocean thermal energy conversion(OTEC) power system using mixed refrigerant(R32,R152a) is conducted to find the effect of hot wasted water on OTEC power system. The system in this study is applied with two stage turbine, regenerator, cooler and separator on Organic Rankine Cycle. The commercial program HYSYS is used for the performance analysis. The main results were summarized as follows : The efficiency of the OTEC power cycle has a largely effect on the evaporation capacity and total work. As increasing temperature of heat source water, evaporator's capacity is decreased but total work increase. Otherwise, using hot wasted water bring effects not only increasing system efficiency but also declining evaporator's capacity. Thus With a thorough grasp of these effect, it is necessary to find way to use hot wasted water emitted by power plant and so on.

• Clean Technology
• /
• v.14 no.4
• /
• pp.265-270
• /
• 2008

In this study, the flow and heat transfer of the aligned pin-fin array of the air cooling module for electronic packaging application were numerically analyzed with various fin shapes. The geometric cross-sectional shapes of pin-fins considered in this study were ellipse, wing and circle. The fins had same cross-sectional area and height, but they had different surface areas. As the results, the surface area, the heat transfer coefficient, and the heat transfer performance of pin-fins greatly depended on their shapes. Of the three types of pin-fins, the wing type pin-fin with suitable shape produced the best heat transfer performance. This result implies that the cooling capacity of the pin-fin cooler can be significantly enhanced only by the change of fin shape without increasing air flow-rate or fin density.