• Advances in materials Research
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• 제7권3호
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• pp.195-201
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• 2018

High Strength low alloy steels containing various levels of C, Nb and Mn were used and for each of which, a simulated double thermal cycle was applied with the same first peak temperature and different second peak temperatures to produce HAZ microstructure corresponding to multi-pass weld. Effect of double cycle second temperature on the microstructure was observed and compared with single cycle results obtained from previous works, it was found that the percentage of martensite austenite constituent (MA) increases by Nb addition for all steels with the same Mn content and the increase in Mn content at the same Nb content shows an increase in MA area fraction as well. MA area fraction obtained for the double cycle is larger than that obtained for the single cycle for all steels used which imply that MA will have great role in the brittle fracture initiation for double cycle and the inter-pass temperature should be controlled for medium and high-carbon Mn steel to avoid large area fraction of MA. The beneficial effects of Niobium obtained in single pass weld were not observed for the double cycle or multi pass welds.

• 설비공학논문집
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• 제12권3호
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• pp.267-276
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• 2000

A numerical study has been carried out to find out the optimal design condition of a solar absorption cooling system. The system was composed of solar collectors and an absorption chiller with LiBr/water The System performance with commercial single effect(SE) cycle and a new single effect/double lift(SE/DL) cycle utilizing low temperature hot water was calculated and compared. It was found that the required solar collector area grew exponentially as the overall heat loss coefficient of solar collectors increased. For instance, the required area for cooling capacity of 1 USRT was $17m^2$ if heat loss coefficient was 4 W/$m^2\;cdot\;K$. If heat loss coefficient was doubled($8\;W/m^2\;cdot\;$K), the required collector area was increased by 6 times($100m^2$) .It was also found that the SE-cycle as the heat loss coefficient of solar collectors increased. Generally, a SE/DL-cycle seems to be more advantageous than a SE-cycle if loss coefficient of solar collector is greater than 4 W/$m^2\;cdot\;K$.

• 한국태양에너지학회 논문집
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• 제27권4호
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• pp.19-26
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• 2007

This paper concerns the study of absorption refrigeration and heat pump cycle to use sewage. Simulation analysis on the double-effect absorption refrigeration cycle with parallel and two-stage heat pump cycle has been performed. The working fluid is Lithium Bromide and water solution. The absorption refrigeration cycle use sewage as a cooling water for the absorber and condenser, and absorption refrigeration cycle does that as a chilled water for the evaporator of the first stage cycle. And the two-stage cycle consists of coupling double-effect with parallel and single effect cycle so that the first stage absorber and condenser produces heating water to evaporate refrigerant in the evaporator of the second stage. The effects of operating variables such as a absorber temperature on the coefficient of performance have been studied for absorption refrigeration and heat pump cycle.

• 태양에너지
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• 제17권3호
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• pp.43-49
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• 1997

본 연구는 저온재생기에서 용액 재생 열원으로 저온열을 보조열원으로 이용가능한 2열원 2중효용 흡수 사이클특성을 규명하기 위한 방법으로 병렬 용액 순환형 2중 효용 흡수 사이클 해석을 수행한다. 본 해석은 저온 재생기에서 필요한 재생열의 일부를 태양열 또는 배열 등과 같은 저온 보조 가열원을 이용하여 열의 유용성 검증을 위한 기초 수단으로 가열원 입구 온도, 용액 순환량을 변화시켜 2중효용 parallel flow cycle 의 특성을 규명한다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.668-672
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• 2009

This is to report the result of Development of Single effect/Double lift absorption chiller & heater which is used in the district heating net work. The heating cycle was newly developed to make the secondary hot water from evaporator and the cycle change-over function was added for the heating to the cooling mode and the cooling to the heating mode. Finally, it was assured through the site trial operation that the outlet temperature of primary hot water can be produced lower than $68^{\circ}C$ when the outlet temperature of secondary hot water is $60^{\circ}C$.

• 대한물리치료과학회지
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• 제18권3호
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• pp.33-39
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• 2011

Background : The purpose of this study was to apply cervical orthosis for temporal parameters of gait was to evaluate the effect. Methods : Seven normal adults participated in this study. Before and after applying a cervical orthosis compared to gait. Outcome measure were: general characteristics, temporal parameters of gait. General chacteristics included age, gender, height, weight. Temporal parameters included the Velocity cycle, Stride length, Step length, Cadence cycle, Initial double support time. Temporal parameters of gait, using the motion analysis system for cervical orthosis were evaluated before and after applying. The data was analyzed using SPSS 12.0 software and the Wilcoxon's signed-ranks test. Results : Velocity cycle and Step length were no significant differences(p>0.05). But Stride length, Cadence cycle, Initial double support time were significant(p<0.05). After apply Cervical orthosis in gait, Stride length and Initial double support time was decreased and Cadence cycle was increased. Conclusion : Changes in temporal of temporal parameters of gait was apply a cervical orthosis with the limitations of vision due to take effect. Therefore, Cervical orthosis does not interfere with the normal gait pattern by limiting the Range of Motion so that we consider to apply.

• 대한기계학회논문집B
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• 제23권2호
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• pp.272-280
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• 1999

A cycle analysis was achieved to predict the characteristics by comprehensive modeling and simulation of an air-cooled, double-effect absorption system using a new $H_2O/LiBr+HO(CH_2)_3OH$ solution. The simulation results showed that the new working fluid may provide the crystallization limit 8% higher than the conventional $H_2O/LiBr$ solution. With a crystallization margin of 3wt%(weight%), the optimal solution distribution ratio was found in the range of 36 to 40%. Variation of cooling air Inlet temperature has a sensitive effect on the cooling COP and corrosion problem. The simulation of heat exchangers with UA value revealed that the absorber and the evaporator are relatively important for an air-cooled system compared with the condenser and the low temperature generator. The effect of cooling air flow rate, circulation weak solution flow rate and chilled water inlet temperature were also examined. The new working fluid may provide the COP approximately 5% higher than the conventional $H_2O/LiBr$ solution.

• 대한기계학회논문집
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• 제17권8호
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• pp.2099-2109
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• 1993

A gas-fired 4RT absorption heat pump was designed as an air-conditioner for domestic use during the summer. The absorption heat pump is air-cooled. double-effect, $LiBr-H_{2}O$ system with parallel flow type. The performance of the absorption heat pump in the cooling mode of operation was investigated through cycle modeling and simulation to obtain the system characteristics with parameter changes. System parameters considered in this analysis were the inlet temperature of cooling air to the absorber, the working solution concentrations, the ratio of the amount of the weak solution from the absorber, and the LTD's of each heat exchange component. The optimum designs and operating conditions were determined based on the operating constraints and the coefficient of performance.

• Journal of Advanced Marine Engineering and Technology
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• 제22권6호
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• pp.792-799
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• 1998

Further improvement of existing $H_{2}O/LiBr$ absorption refrigeration machine is absolutely neces-sary to promote the utilization of gas-cooling system Among various methods to improve the per-formance of the absorption refrigeration machine this research has focused on the use of a new working fluid that has better properties than the existing $H_{2}O/LiBr$ working fluid. In the series of the research, $H_{2}O/LiBr+HO{(CH_{2})}_{3}OH$ system was selected as the most promisable candidate. The absorption refrigeration machine is water-cooled double-effect, $H_{2}O/LiBr+HO{(CH_{2})}_{3}OH$ sys-tem with series flow type. In this study we found out the characteristic of new working solution through the cycle simulation and compared the result with that of LiBr solution to evaluate. Theoptimum designs and operating conditions were determined based on the operating constraints and the coefficient of performance. Results demonstrate that new working fluid subsrantially increases COP by as much as 10% and has a wider working range with 8% higher crystallization limits compared to the conventional $H_{2}O/LiBr$.

• 설비공학논문집
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• 제29권7호
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• pp.360-365
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• 2017

Recently, development efforts of triple-effect absorption chiller have been increased in order to improve the efficiency of double-effect absorption chiller. However, triple-effect absorption chiller has some disadvantages, including high corrosion characteristic of LiBr solution at high temperature of $200^{\circ}C$. Moreover, it is necessary to develop new components for operation under high pressure of 2 bars even though COP is increased to 1.6 or 1.7. The objective of this study was to introduce a new system by combining double effect absorption chiller with single effect absorption chiller with multi-generators using bypass flow of LiBr dilute solution to $3^{rd}$ generator to overcome the disadvantages of triple-effect chiller and improve energy efficiency. Results indicate that the new absorption cycle had a much higher efficiency than double-effect chiller system, showing significant improvement when bypass solution flow rate of 25% was applied to the $3^{rd}$ generator using the main dilute solution of the absorber. The COP of the new chiller system was found to be 1.438, which was 21.7% higher than that (1.18) of the present double-effect system. The COP was decreased when solution by-pass rate to the $3^{rd}$ generator was increased. In addition, lower cooling water temperature caused higher COP. Therefore, the multi-generator system with by-pass solution might be an excellent chiller alternative to triple-effect absorption chiller with higher efficiency.