• New & Renewable Energy
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• v.7 no.4
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• pp.30-36
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• 2011

The objective of this study is to investigate the effects of the refrigerant charge amount on the performance of a water-to-water ground source heat pump with a variation of compressor speed and the secondary fluid flow rate. The water-to-water ground source heat pump was tested by varying refrigerant charge amount from -40% to 20% of full charge. Compressor speed was changed from 30 Hz to 75 Hz and the secondary fluid flow rate was adjusted from 6 LPM to 14 LPM. For all test conditions, EWTs of an indoor heat exchanger and an outdoor heat exchanger were maintained at standard conditions of ISO 13256-2. The slope of the COP with the variation of charge amount is much steeper at undercharged conditions than that at overcharged conditions. For all compressor speed, the variation of the system performance according to charge amounts showed the similar trends. However, the optimum charge amount of the system increased a little with an increment of compressor speed. When the secondary fluid flow rate decreased, the system was optimized at higher refrigerant charge amount conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.9
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• pp.713-718
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• 2015

The purpose of this study is to realize compressor-performance improvements in the fuel economy of an automotive air-conditioning system. We conduct cooling performance tests in a compressor calorimeter test stand. To improve the cooling performance, we investigate the increase in the suction flow rate and the decrease in the discharge dead volume. Based on the results of the test, we found that the cooling capacity and the coefficient of performance (COP) of the compressors were improved as follows. The cooling performance improved greater at high speeds than low speeds in the case of an increase in the suction flow rate increase, and it improved more at low speeds than at high speed when there was a decrease in the discharge dead volume. When both of the above factors were included, we observed that the improvement effects were generally balanced for both high- and low-speed modes, and there was a significant improvement in the discharge temperature. The improvement was found to be about 3.2% at low speed, 8.3% at high speed during in cooling performance improvement, about 5.8% at low speed and about 6.2% at high speed in COP improvement, and there was a decrease of about $3^{\circ}C$ at low speed and a $5^{\circ}C$ decrease at high speed in discharge temperature.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.11a
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• pp.200-201
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• 2015

The unit modular method is one in which unit modules are prefabricated at a factory and then constructed at a construction site. That is why an important process, transporting unit module, is added in this method. The purpose of this study is to analyse the load for transporting unit module. The results of the analysis of the driving experimental runs revealed that a maximum load of 15 kN was applied on adapter block type A and a maximum load of 25 kN on adapter block type B. These loads were recorded at the points in the road test when the low-bed trailer was driving through unstable sections of the test such as stopping, restarting, passing over a speed bump or taking a left turn at speed.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.117-119
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• 2003

We have designed fabricated, and tested an RSFQ(Rapid Single Flux Quantum) 1-bit ALU (Arithmetic Logic Unit). The 1-bit ALU was composed of a half adder and three SFQ DC switches. Three DC switches were attached to the two output ports of an ALU for the selection of each function from the available functions that were AND, OR, XOR and ADD. And we also attached two DC switches at the input ports of the half adder so that the input data were controlled using the function generators operating at low speed while we tested the circuit at high speed. The test bandwidth was from 1KHz to 5 ㎓. The chip was tested at the liquid helium temperature of 4.2 K.

• Journal of the Korean Society for Heat Treatment
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• v.5 no.2
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• pp.122-132
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• 1992

This study has been performed to investigate into some effects of the power density and traverse speed of laser beam on the optical microstructure, hardness and wear characteristics of medium carbon low alloy steel treated by laser surface hardening technique. The results obtained from the experiment are summarized as follows : (1) Optical micrograph has shown that finer lath martensite is formed and the amount of undissolved complex carbides increases as the traverse speed increases under the condition of a given power density, whereas the coarsening of lath martensite and the reduction of undissolved complex carbides occur with increasing the power density at a given traverse speed. (2) Hardness measurements have revealed that as the traverse speed increases, hardness values of outermost surface layer more of less decrease under low power densities, but are uniformly distributed under high power densities, also showing that they are uniformly distributed at low traverse speeds and more or less decrease at high traverse speeds with increasing the power density. (3) The effective case depth has been found to decrease from 0.26 mm to 0.17 mm with increasing the traverse speed from 1.5 m/min to 3.0 m/min at a given power density of $25.48{\times}10^3w/cm^2$ and to increase from 0.20 mm to 0.36 mm with increasing the power density from $19.11{\times}10^3w/cm^2$ to $38.22{\times}10^3w/cm^2$ at a given traverse speed of 2.0 m/min. (4) Wear test has exhibited that the amount of weight loss of laser surface hardened specimen with respect to sliding distance at a given load increases with increasing traverse speed at a given power density and decreses with increasing power density at a given traverse speed.

• Tribology and Lubricants
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• v.18 no.4
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• pp.305-311
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• 2002

Three different kinds of brake discs including two coated brake discs and one steel disc were tested under the same experimental conditions on a reduced scale braking test bench. A braking test bench was specially designed to analyse thermo-mechanical and frictional behaviors of two types of brake with different sizes in stop and hold braking modes. Plasma spray coating technique was also used to coat the discs with ceramic powder. During the test four commercial brake pads were coupled with discs. Ceramic coated discs showed good stability in friction coefficient at high speed and high energy braking conditions. But they caused large wear loss of pad mass compared with the steel disc. It was shown that thermal barrier effect in ceramic coated discs adjusted the thermal partition between pad and disc. For a steel disc. it showed fluctuating friction coefficient at high speed but small wear loss of pad mass compared with ceramic coated discs.

• Journal of Welding and Joining
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• v.14 no.6
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• pp.48-57
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• 1996

The weldability of high purity aluminum-lithium binary alloys has been investigated using the Varestraint test. Autogenous GTAW (gas-tungsten-arc-welds) were run along specimens of different lithium concentration using three sets of welding parameters. Welding voltage was held constant at 10 volts. Welding current (70∼100 amps) and travel speed (23∼33 cm/min) were the parameter varied. Hot-tearing susceptibility varied with lithium content and exhibited a steep peak at 2.6 weight percent lithium. Depth of penetration increased with increasing heat input and lithium concentration. The susceptibility is influenced by the wettability of dendrites by the interdendritic eutectic liquid as well as the time available for back-Siting by eutectic liquid. The welding condition of welding current 70A and travel speed 23 cm/min was showed good resistance to cracking in aluminum-lithium alloys. Suggestions for improving weld cracking resistance are also provided.

• Aerospace Engineering and Technology
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• v.10 no.1
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• pp.122-128
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• 2011

A series of water tests of a Lox pump for liquid rocket engines are performed at a room temperature. According to the hydraulic test results, the head coefficient is slightly decreased when the rotational speed of the pump is increased. However the efficiency is high at the high-speed test. Also, according to the cavitation test results, the cavitation performance of the pump is found to be decreased when the flow ratio is less than 92%. Furthermore, the vibration characteristic is analyzed using measured high frequency data.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.5
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• pp.127-133
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• 2003

For the purpose of evaluation the damage repairability of a Frame Type Passenger vehicle which experienced a Low Speed 40% Offset front and rear Crash Test. tests were made according to the RCAR testing procedures. Test results concluded ; (1) The deceleration at C.G(center of gravity) off 6.9∼11.39 was similar to that for the vehicle. The airbag system was found to affect neither the passenger's safety nor the savings of the repairing costs. (2) In order to improve the repairability of the Frame Type Passenger vehicle after collision should be a higher crash performance of the bumper on the RCAR standards.

• Journal of the Korean Society of Visualization
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• v.17 no.2
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• pp.32-38
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• 2019

A comparison study between computational-fluid-dynamics simulation and wind tunnel test for a megawatt-class wind turbine is conducted. For the study, flow-field in wake, basic aerodynamic performance, and effect of the yaw error for a 1/86 scaled-down model of the NREL offshore 5 MW wind turbine are numerically calculated using commercial software "FloEFD" with $k-{\varepsilon}$ turbulence model. The computed results are compared to the wind tunnel test performed by the constant-velocity mode for the model. It is shown that discrepancy are found between the two results at lower tip-speed ratio and higher yaw angle, however, the velocity-defection distribution in the wake, the torque coefficient at moderated and high tip-speed ratios are in good agreement with the wind tunnel test.