• Current Optics and Photonics
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• v.2 no.5
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• pp.468-473
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• 2018

We investigate the temperature dependence of efficiency droop in InGaN/GaN multiple-quantum-well (MQW) blue light-emitting diodes (LEDs) in the temperature range from 20 to $80^{\circ}C$. When the external quantum efficiency (EQE) and the wall-plug efficiency (WPE) of the LED sample were measured as injection current and temperature varied, the droop of EQE and WPE was found to be reduced with increasing temperature. As the temperature increased from 20 to $80^{\circ}C$, the droop ratio of EQE was decreased from 16% to 14%. This reduction in efficiency droop with temperature can be interpreted by a temperature-dependent carrier distribution in the MQWs. When the carrier distribution and radiative recombination rate in MQWs were simulated and compared for different temperatures, the carrier distribution was found to become increasingly homogeneous as the temperature increased, which is believed to partly contribute to the reduction in efficiency droop with increasing temperature.

• Journal of the Optical Society of Korea
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• v.19 no.3
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• pp.311-316
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• 2015

We investigate the temperature dependence of the phosphor conversion efficiency (PCE) of the phosphor material used in a white light-emitting diode (LED) consisting of a blue LED chip and yellow phosphor. The temperature dependence of the wall-plug efficiency (WPE) of the blue LED chip and the PCE of phosphor are separately determined by analyzing the measured spectrum of the white LED sample. As the ambient temperature increases from 20 to $80^{\circ}C$, WPE and PCE decrease by about 4.5% and 6%, respectively, which means that the contribution of the phosphor to the thermal characteristics of white LEDs can be more important than that of the blue LED chip. When PCE is decomposed into the Stokes-shift efficiency and the phosphor quantum efficiency (QE), it is found that the Stokes-shift efficiency is only weakly dependent on temperature, while the QE decreases rapidly with temperature. From 20 to $80^{\circ}C$ the phosphor QE decreases by about 7% while the Stokes-shift efficiency changes by less than 1%.

• Journal of Korean Society on Water Environment
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• v.35 no.4
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• pp.332-339
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• 2019

A comparative study on the anaerobic digestion efficiency according to the temperature change was conducted considering the characteristics of domestic food wastes with high water content of about 80 % or more. The substrate was tested for anaerobic digestion efficiency in two substrates, a liquid component separated naturally from food waste and food waste itself. In the anaerobic digestion experiments, the digestion efficiency was the highest at $55^{\circ}C$ (thermophilic temperature). However, the digestion efficiency at $45^{\circ}C$(middle high temperature) was lower than that at $35^{\circ}C$(mesophilic temperature). The comparison of general food wastes anaerobic digestion requiring 30 days of hydraulic retention time to the liquid component indicated a stable digestion efficiency even after 15 days of hydraulic retention time.In the experiments conducted on food waste, the digestion efficiency at $55^{\circ}C$ was higher than that at $35^{\circ}C$. When the food waste, especially the liquid component originating from food waste, is treated by anaerobic digestion method, the mesophilic temperature and thermophilic temperature conditions are more favorable in the digestion efficiency than the middle high temperature ($45^{\circ}C$). However, when applying thermophilic or mesophilic temperature anaerobic digestion process operation in the field, the amount of energy input should be considered.

• International Journal of Highway Engineering
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• v.3 no.3 s.9
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• pp.147-158
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• 2001

One of the most important factors accounting for the structural capacity of concrete pavement is load transfer efficiency. Load transfer efficiency is affected by slab temperature gradient, construction of dowel bars, degree of aging, and crack width. The purpose of this study is to determine the patterns of load transfer efficiency of concrete pavement; to determine the factors that affect the load transfer efficiency; and to present the proper measuring method of load transfer efficiency. As a result from this study, load transfer efficiency was affected primarily by the average temperature in concrete slab. Load transfer efficiency decreased with decreasing temperature and increasing crack width. For the sections with dowel bars, there were little differences in load transfer efficiency regardless of temperature changes. For the sections without dowel bars, however, there on great losses of load transfer efficiency at low temperatures. For the old pavement, even in the sections with dowel bars, the load transfer efficiency reduced as the temperature dropped For the sections in this study, 1.4% reduction of the load transfer efficiency was observed for each $1^{\circ}C$ drop in the slab temperature.

• Journal of the Korean Society of Clothing and Textiles
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• v.3 no.1
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• pp.49-56
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• 1979

To investigate detergency of various woven fabrics in relation to the detergents and washing temperature. cotton, polyester/cotton (p/c), nylon, acetate, and polyester were soiled in aqueous artificial ($carbon-CCl_4$) soil. Each fabric was washed with soap, alkaline and neutral synthetic detergents at $30^{\circ}C$, $40^{\circ}C$ and $60^{\circ}C$ respectively. The results obtained may be summerized as follows; 1. In soap, ascension of temperature had the most important effect upon washing efficiency and the higher the temperature was, the higher the washing efficiency was showed in all fabrics. And in case of alkaline synthetic detergent, nylon and p/c fabrics were much more difficult to clean at higher temperature and also acetate and polyester had the best efficiency at $40^{\circ}C$. Detergency of neutral detergent was good but the effect of temperature in neutral detergent was less than in soap. 2. Washing efficiency of cotton was less than that of others. 3. The higher the temperature was, the higher the washing efficiency of cotton in all detergents, and the best was in soap. In p/c, detergency of neutral detergent was good but effect of ascension of temperature was lower than in soap. In nylon, washing efficiencies of alkaline synthetic detergent and neutral detergent were excellent at 30°C but detergency of soap at $60^{\circ}C$ was best. In case of acetate, detergency of all detergents was about the same at $30^{\circ}C$ but that of soap at $60^{\circ}C$ was best. In polyester at $30^{\circ}C$, efficiency of neutral detergent was excellent but that of soap was more excellent at higher temperature and the best detergency of alkaline synthetic detergent showed at $40^{\circ}C$. In general. the higher the temperature is, the higher the washing efficiency of soap is. But when synthetic fibers of nylon and polyester are washed with synthetic detergents, washing at lower temperature is advisable.

• Journal of Power System Engineering
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• v.21 no.6
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• pp.46-55
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• 2017

Due to the arise of natural disasters caused by global warming, consumers have more interest in the fuel efficiency of their vehicles, and fuel efficiency became an important factor in comparing vehicles. In this market situation, methods to measure fuel efficiency has become one of the main interests of vehicle related organizations and laboratories, and the current method to measure fuel efficiency is to follow the notification established by the ministry of trade, industry and energy, ministry of environment, and the ministry of land, infrastructure and transport. In this study, we analyze the influence of vehicle fuel efficiency according to test temperature and cooling fan condition which have the possibility to cause difference in fuel efficiency. The analysis results of the influence of the fuel efficiency according to the test temperature, the difference of the fuel efficiency of the test temperature ($21{\sim}29^{\circ}C$) within the allowable range of the notification showed a maximum difference of 2.9%. Therefore, it is necessary to consider the introduction of a test method that permits only the temperature change based on the reference point as the allowable range even in the test within the allowable range. The analysis of the influence of the fuel efficiency according to the cooling method showed no significant effect, and it seems reasonable to maintain the test method of the current notification.

• Membrane and Water Treatment
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• v.10 no.5
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• pp.387-394
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• 2019

Membrane distillation (MD) is one of the water treatment processes which involves the momentum, heat and mass transfer through channels and membrane. In this study, CFD modeling has been used to simulate the heat and mass transfer in the direct contact membrane distillation (DCMD). Also, the effect of operating parameters on the water flux is investigated. The result shows a good agreement with the experimental result. Results indicated that, while feed temperature is increasing in the feed side, water flux improves in the permeate side. Since higher velocity leads to the higher mixing and turbulence in the feed channel, water flux rises due to this increase in the feed velocity. Moreover, results revealed that temperature polarization coefficient is rising as flow rate (velocity) increases and it is decreasing while the feed temperature increases. Lastly, the thermal efficiency of direct contact membrane distillation is defined, and results confirm that thermal efficiency improves while feed temperature increases. Also, flow rate increment results in enhancement of thermal efficiency.

• Journal of the Korean Solar Energy Society
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• v.28 no.4
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• pp.50-55
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• 2008

The Storage efficiency of concentric evacuated tube solar collector is tested for one year from January 1st to December 31st under the real sun condition. The testing equipment is operated continuously for three days without cooling the storage tank. Daily storage efficiency is obtained from dividing stored energy in the storage tank by solar insolation on the solar collector for each day. Daily averaged temperature of the storage tank is lowest in January and highest in August. Monthly averaged storage efficiency is also lowest in November and highest in June. Therefore, it can be said that the storage temperature and the storage efficiency are roughly proportional to outdoor temperature. Furthermore, the daily storage efficiency is reversely proportional to $(T_s-T_a)/I_c$ where $T_s$ and $T_a$ are daily averaged storage temperature and outdoor temperature from sunrise to sunset, and $I_c$ is total insolation on the solar collector for a day.

• Particle and aerosol research
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• v.10 no.4
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• pp.155-162
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• 2014

The internal temperature will change depending on operation conditions and material of cyclone dust collector. This study compares the results of collection efficiency and temperature distribution on the different heat flux at wall of dust collector. The previous researcher's experiment results were used to confirm the reliability of CFD(Computational Fluid Dynamics) model. Based on this verified CFD model, we extended the analysis on the cyclone dust collectors. In CFD study, we used RNG k-epsilon model for analysis of turbulence flow, fluid is air, the velocity at inlet is 10 m/s, the temperature of air is $600^{\circ}C$. Because of the difference of outer vortex and inner vortex temperature, the collection efficiency will reduce with the increase of heat flux, showed the highest collection efficiency at heat insulation.

• Journal of Power System Engineering
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• v.16 no.1
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• pp.38-43
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• 2012

This paper describes an analysis on performance of R744-R404A cascade refrigeration system with internal heat exchanger to optimize the design for the operating parameters of the system. The operating parameters considered in this study include subcooling and superheating degree, internal heat exchanger and compression efficiency, evaporating and condensing temperature in the R744 low- and R404A high-temperature cycle and temperature difference of cascade heat exchanger. The main results are summarized as follows : COP of cascade refrigeration system increases with the increasing of compression efficiency, but decreases with the increasing temperature difference of cascade heat exchanger. Also, the COP increases with the increasing of internal heat exchanger efficiency in high-temperature cycle, but decreases with that in low-temperature cycle. Therefore, internal heat exchanger efficiency, compressor efficiency and temperature difference of cascade heat exchanger on R744-R404A cascade refrigeration system have an effect on the COP of this system.