• Journal of Astronomy and Space Sciences
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• v.30 no.2
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• pp.101-106
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• 2013

The length of solar cycle 23 has been prolonged up to about 13 years. Many studies have speculated that the solar cycle 23/24 minimum will indicate the onset of a grand minimum of solar activity, such as the Maunder Minimum. We check the trends of solar (sunspot number, solar magnetic fields, total solar irradiance, solar radio flux, and frequency of solar X-ray flare), interplanetary (interplanetary magnetic field, solar wind and galactic cosmic ray intensity), and geomagnetic (Ap index) parameters (SIG parameters) during solar cycles 21-24. Most SIG parameters during the period of the solar cycle 23/24 minimum have remarkably low values. Since the 1970s, the space environment has been monitored by ground observatories and satellites. Such prevalently low values of SIG parameters have never been seen. We suggest that these unprecedented conditions of SIG parameters originate from the weakened solar magnetic fields. Meanwhile, the deep 23/24 solar cycle minimum might be the portent of a grand minimum in which the global mean temperature of the lower atmosphere is as low as in the period of Dalton or Maunder minimum.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.398-403
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• 2005

The cooling performance of a transcritical $CO_2$ cycle varies significantly with a variation of refrigerant charge amount. In this study, the performance of the $CO_2$ system was measured and analyzed by varying refrigerant charge amount with a change of cycle option. The applied cycle options are the single-stage compression system, two-stage compression with 1-EEV system, and two-stage compression with 2- EEV system. The optimum normalized charge were 0.363, 0.297, and 0.282 for the two-stage compression with 2-EEV system, two-stage compression with 1-EEV system, and single-stage compression system, respectively.

• Journal of Ocean Engineering and Technology
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• v.25 no.1
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• pp.80-84
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• 2011

The cycle performance of closed ocean thermal energy conversion (OTEC) system with 50 kW gross power was evaluated to obtain the basic data for the optimal design of OTEC using waste heat such as solar power, discharged heat from condenser of power plant. The basic thermodynamic model for OTEC is Rankine cycle, and the surface seawater and deep seawater were used for the heat source of evaporator and condenser, respectively. The cycle performance such as efficiency, heat exchanger capacity, etc. was analyzed on the variation of temperature increase by waste heat. The cycle efficiency increased and necessary capacity of evaporator and condenser decreased under 50kW gross power with respect to the temperature increase of working fluid. Also, when the temperature increase is about $13.5^{\circ}C$, the heat which can be used is generated. By generator with 0.9 effectiveness under the simulated condition, the cycle efficiency was improved approximately 3.0% comparing with the basic cycle.

• Journal of ILASS-Korea
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• v.18 no.3
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• pp.132-139
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• 2013

Smoke emissions from light duty diesel vehicles were measured using light extinction method with the free acceleration test mode. The smoke emissions for each measurement cycle of the free acceleration method showed large variations according to driver's pedal pushing pattern. The smoke values for each measurement cycle initially increased and reach a peak value. Integration of the smoke emissions with time for each measurement cycle was performed to get a representative smoke value which was obtained by averaging the integrated results. Two kinds of integration time range were used. One is range over the whole measurement cycle of the free acceleration method. The other is only the acceleration range in the measurement cycle. Overall, variation of the representative smoke values obtained by the integration method was reduced comparing to the traditional representative smoke value which was obtained from a peak smoke value over the measurement cycle. Ten vehicles of the same model with 2.5 liter diesel engines, and seven vehicles of the same model with 2.7 liter diesel engines, were tested using the free acceleration test method.

• Journal of Biosystems Engineering
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• v.27 no.4
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• pp.327-334
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• 2002

In this study, energy conversion from thermal energy to mechanical power by using n-pentane was tested and exergy variation, cycle number, water quantity pumped and thermal efficiency were analyzed. The energy conversion was done and the water head could be ten meters on the experimental conditions. The operating temperature range of cycle was recommended to be around the liquid-vapour saturation temperature of the working fluid on the viewpoint of the maximum work. The cycle diagram was analyzed by the exergy analysis. For the constant water head, the cycle number was decreased and the water quantity per day was increased and thermal efficiency become higher when the water quantity per cycle become increasing. For the constant pumping water quantity per cycle, cycle number and the water quantity per day was decreased and the thermal efficiency become higher because the saturation temperature become higher when the water head become higher.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.43 no.5
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• pp.551-556
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• 2010

The large jellyfish Nemopilema nomurai causes serious damage to fisheries, particularly around the seas of Korea and Japan. Decreasing this damage requires knowledge of the distribution and abundance of jellyfish. Acoustic technology using quantitative echosounders is one method of studying the distribution and abundance of jellyfish. Such methods are commonly used worldwide because they have the advantage of providing substantial information about all water layers in a wide area in a short time. However, in order to conduct an acoustic survey, the acoustic characteristics of the target organism must be known. These can be altered by a number of factors, including pulsation, swimming angle, frequency and size. Accordingly, this study determined the variation in target strength according to pulsation of N. nomurai. Data were analyzed for two jellyfish with bell diameters in air of (a) was 32.0 and (b) 25.0 cm. The pulsation cycle of jellyfish (a) was 1.5~2.0 sec and the target strength (TS) cycle was 1.0~2.5 sec, while jellyfish (b) had a pulsation cycle of 1.0~1.5 sec and TS cycle of 1.0~3.0 sec. The variation width of the TS with the change in pulsation was 7.8 dB (-72.4~-64.6 dB) for jellyfish (a) and 10.3 dB (-71.6~-61.3 dB) for jellyfish (b). The variation in bell diameter was about 0.28 and 0.35, respectively. These results confirmed that the variation in bell diameter caused by pulsation is closely related to the variation in TS.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.6
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• pp.476-483
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• 2016

An organic Rankine cycle for ocean thermal energy conversion system is a generating cycle using the temperature difference between surface water and deep water of the ocean. The working fluid is an important factor in the thermodynamic performance of an organic Rankine cycle. There is pinch point analysis as thermodynamic analysis of an organic Rankine cycle. This study performed a thermodynamic performance analysis according to variation in the pinch point temperature difference in heat exchangers and variation of outlet temperature of heat source and heat sink. It analyzed the thermodynamic performance by applying seven types of simple working fluids in a simple Rankine cycle for ocean thermal energy conversion that was designed according to pinch point analysis. As a result of the performance analysis, cycle irreversibility and total exergy destruction factor more decreased, and second law efficiency more increased in the lower pinch point temperature difference and temperature variation of heat source and heat sink in heat exchangers. In addition, the irreversibility changed greatly at a point that occurred in the thermodynamic variation. Among the selected working fluids, RE245fa2 showed the best thermodynamic performance, and the performance of all working fluids was observed to be similar. It needs a strict theoretical basis about diverse factors with thermodynamic performances in selecting heat exchangers and working fluids.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.2
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• pp.185-193
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• 2005

The present study composed a diesel-atkinson cycle of high expansion as a method of achieving high efficiency in diesel cycle engines. It also interpreted the cycle engine thermodynamically analysis to determine the possibility of the improvement of thermal efficiency and clarified the characteristics of several factors . According to the result of theoretical analysis, heat efficiency was highest when expansion-compression ratio Reど:1. In addition. diesel engines with high apparent compression ratio had higher expansion-compression ratio than otto engines and consequently their effect of high expansion was high. which in turn enhanced thermal efficiency. When the atkinson cycle was implemented in a real diesel engine by applying the miller cycle through the variation of the closing time of the intake valve, the effective compression ratio and the quantify of intake air decreased and as a result, the effect of high expansion was not observed. Accordingly. the atkinson cycle can be implemented when the quantity of intake air is compensated by supercharge and the effective compression ratio is maintained at its initial level through the reduction of the clearance volume. In this case. heat efficiency increased by $4.1\%$ at the same expansion-compression ratio when the apparent compression ratio was 20 and the fuel cut off ratio was 2. As explained above, when the atkinson cycle was used for diesel cycle. heat efficiency was improved. In order to realize high expansion through retarding the intake value closing time, the engine needs to be equipped with variable valve timing equipment, variable compression ratio equipment and supercharged Pressure equipment. Then a diesel-atkinson cycle engine is realized.

• Membrane Journal
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• v.21 no.1
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• pp.13-21
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• 2011

This study investigated the fouling behavior of $Al_2O_3$ colloids on polyethylene microfiltration membrane. To examine the effect of operation variation on fouling, operating pressure was increased from 0.49 to 1.96 bar along with time elapses and then was reduced to 0.49 bar reversely. A hysteresis behavior was observed in the membrane permeate flux over pressure, revealing different fluxes at the same pressure according to the pressure control type, increasing and decreasing. Permeate resistance and its rate of increase was higher in the decreasing pressure cycle than in the increasing pressure cycle. At the initial period of filtration, fouling mechanism for the both cycles was governed by the cake filtration. The degree of fouling was higher in the decreasing pressure cycle compared with in the increasing pressure cycle.

• Journal of Energy Engineering
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• v.22 no.2
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• pp.197-204
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• 2013

A cyclic variability has long been recognized as limiting the range of operating conditions of spark ignition engines, in particular, under idling conditions. The coefficient of variation (COV) in indicated mean effective pressure (IMEP) defines the cyclic variability in indicated work per cycle, and it has been found that vehicle drivability problems usually result. For analysis of the cyclic variations in spark ignition engines at idling, the results show that cyclic variability by the COV, COV of IMEP, the lowest normalized value (LNV), and burn angles can help to design the spark ignition engine.