• The KSFM Journal of Fluid Machinery
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• v.10 no.2 s.41
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• pp.16-21
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• 2007

Potential advantages of using vapor injection in a two stage rotary compressor for a $CO_2$ heat pump water heater system were addressed in this paper by numerical simulation. Vapor separated from a flash tank in the middle of the expansion process can be used for injection into the second stage suction plenum of the compressor to improve the system performance. Vapor injection increases the intermediate pressure between the two stages, thus increasing the first stage compressor work and reducing that of the second stage. As a whole, however, the compressor input power increases due to injected mass flow rate for the second stage. Computer simulation showed that increment of the cooling capacity by vapor injection exceeded that of the compressor work, thus improving the system performance. COP improvement by vapor injection was calculated to be about 5-14% for normal operating conditions. With vapor injection, a maximum COP was found when the displacement volume of the second stage becomes 90-95% of that of the first stage of the compressor.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.7
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• pp.308-314
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• 2014

A heat pump has been considered as a thermal management unit for electric vehicles, including the heating and cooling of the cabin. However, the heat pump shows performance degradation at low outdoor temperatures or high compressor speeds. In this study, a R-134a heat pump for an electric vehicle was designed to improve system efficiency, by applying vapor injection with an internal heat exchanger. The heating performance characteristics of the vapor injection heat pump were analyzed at various compressor speeds and outdoor temperatures. The vapor injection heat pump showed 13.3% COP improvement over the non-injection heat pump, when the heating capacity was fixed at 5.2 kW. In addition, the heating capacity of the vapor injection system increased by 9.6%, as compared to the non-injection system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.8
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• pp.425-432
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• 2009

In this study, the improvement of cooling capacity by applying gas injection technique in a two-stage heat pump using R410A was experimentally investigated. A twin rotary type compressor with gas injection was applied to the heat pump system. The optimum refrigerant charge for the injection and the non-injection cycles was selected to achieve the maximum COP at the cooling standard condition. The injection cycle showed less optimum refrigerant charge than that of the non-injection cycle. The cooling performances of the injection and the non-injection cycles were measured and compared by varying compressor frequency from 40 to 90 Hz. The cooling capacity of the gas injection cycle was 1.6% -11.3% higher than that of the non-injection cycle. The COP of the gas injection cycle was 13.7% to 28.9% higher than that of the non-injection cycle at the same cooling capacity. The heat pump system showed stable operation after 30% of the injection valve opening.

• Korean Journal of Optics and Photonics
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• v.5 no.1
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• pp.84-89
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• 1994

A tunable pulsed dye laser was operated in a single longitudinal mode by injection locking with a cw ring dye laser. A doubled Nd:YAG laser was used as the pumping source. Phase sensitive detection technique was applied to maintain the required match between the master laser frequency and the slave resonator cavity length. The fluctuation of the center frequency of the pulsed laser was < 10 MHz, and the pulse duration (FWHM) was 6 ns. The linewidth measured by scanning confocal interferometer was 130 MHz. When pumped by 50 mJ of the doubled Nd:YAG laser, the output energy of the pulsed dye laser was 2 mJ and the peak power was 330 kW. 30 kW.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.11
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• pp.767-776
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• 2012

In this study, a simulation model for a $CO_2$ heat pump using vapor injection was developed and validated. It was used to predict the improvement of the heating performance of the $CO_2$ heat pump at various operating conditions. The simulation results showed consistent results with the measured data. The heating performances of the vapor injection and non-injection heat pumps were compared by varying the outdoor temperature and compressor frequency. The heating capacity of the vapor injection heat pump was 40% higher than that of the non-injection heat pump at the outdoor temperature of $-8^{\circ}C$. The performance of the vapor injection heat pump was consistently higher than that of the non-injection heat pump even when the compressor frequency was reduced to 35 Hz at the outdoor temperature of $-3^{\circ}C$.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.358-363
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• 2007

In this study, experimental study on the heating performance of a $CO_2$ heat pump with gas injection was performed varying gas injection ratio and outdoor temperature to improve the heating performance of $CO_2$ heat pump. The twin rotary compressor having volume ratio of 0.7 was adopted in the $CO_2$ heat pump. From the test results, the heating capacity and COP were increased and the compressor discharge temperature was decreased with the increase of injection ratio. At the outdoor temperature of $-8^{\circ}C$, the heating capacity and COP with the injection were increased by 45% and 24%, respectively, compared with non-injection condition.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.29 no.2
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• pp.309-320
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• 2019

Blockchain has been developed as a key technology for many cryptocurrency systems such as Bitcoin. These days, blockchain technology attracts many people to adopt it to various fields beyond cryptocurrency systems for their information sharing and processing. However, with the development and increasing adoption of the blockchain, security incidents frequently happen in the blockchain systems due to their implementation flaws. In order to solve this problem, in this paper, we analyze the software vulnerabilities of Bitcoin and Ethereum, which are the most widely used blockchain applications in real world. For that purpose, we conduct an in-depth analysis of source code of them to detect software vulnerabilities, and examine an OS command injection attack exploiting the detected ones.

• Weed & Turfgrass Science
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• v.2 no.4
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• pp.395-401
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• 2013

This study was conducted to evaluate the selective control of creeping bentgrass invaded in Kentucky bluegrass by applying several herbicides and recovery of Kentucky bluegrass by sand injection seeding method. Selective herbicides such as mecoprop, triclopyr-TEA, imazaquin, bentazone and penosulam pyrazosulfuro-ethyl and non-selective herbicides such as glyphosate, paraquat dichloride and glyphsate ammonium oxyflorfen were used. Selective suppression of creeping bentgrass in Kentucky bluegrass was evaluated by turf color, chlorophyll and visual control indexes. Control of creeping bentgrass was most effective with the double dose application of triclopyr-TEA (2 Tri-T) in the selective herbicides and the 1 / 5 dose application of glyphosate ammonium oxyflorfen (1 / 5 GAO) in the non-selective herbicides. Visual control indexes by 2 Tri-T in selective herbicides and 1 / 5 GAOin non-selective herbicides were investigated 6.0 and 7.4, respectively. Treated sites were covered completely in 50 days after seeding Kentucky bluegrass by sand injection method.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.6
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• pp.297-305
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• 2017

Air-source heat pumps are widely used in residential heating systems. However, the decrease in the capacity of the heat pump is unavoidable when operating at very low and high ambient temperatures. The vapor injection technique is considered a promising technology to overcome this problem. Recent research on vapor injection cycles have mainly adopted a scroll compressor with an internal heat exchanger at severe operating conditions. This study measured the COP and EER of a gas injection heat pump using a flash tank with an inverter-driven rotary compressor at severe operating conditions. Compared to non-injection heat pumps, the heating capacity and COP of the gas injection heat pump improved up to 15% and 2.9%, respectively, at outdoor temperatures of $-10^{\circ}C$ to $7^{\circ}C$. The cooling capacity of the gas injection heat pump was 11% higher than the non-injection heat pump at an outdoor temperature of $35^{\circ}C$. At the same time, the EER of the gas injection heat pump was similar to that of the non-injection heat pump.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.2
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• pp.83-93
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• 2013

Generally the capacities of electric power transmission tower's members are improved by increasing their stiffness nature through injection of grout or attachment of other structural stiffeners. Those are for upgrading their axial strength by fulfillment of proper materials into pipe members, increment of member dimension by addition of section, or a combination of the two. However the use of innovative and unusual procedures would be positively recommended for getting more stable state. It is that buckled members are replaced with lengthened and strengthened members. In providing the structural restoration procedures for the existing electric power transform tower whose main members have been damaged due to unequal foundation settlement, structural damage inspection works and numerical analyses for the damaged one and the restored one were done in detail at first. secondarily member-exchanging works using a newly-generated jacking system and strengthened members were achieved. This figures are to point clearly to inherent advantages attending the management of the towers.