• Steel and Composite Structures
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• v.43 no.2
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• pp.201-219
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• 2022

This paper firstly proposed high performance composite columns for cold-region infrastructures using ultra-high performance concrete (UHPC) and ultra-high strength steel (UHSS) Q960E. Then, 24 square UHPC-filled UHSS tubes (UHSTCs) at low temperatures of -80, -60, -30, and 30℃ were performed under axial loads. The key influencing parameters on axial compression performance of UHSS were studied, i.e., temperature level and UHSS-tube wall thickness (t). In addition, mechanical properties of Q960E at low temperatures were also studied. Test results revealed low temperatures improved the yield/ultimate strength of Q960E. Axial compression tests on UHSTCs revealed that the dropping environmental temperature increased the compression strength and stiffness, but compromised the ductility of UHSTCs; increasing t significantly increased the strength, stiffness, and ductility of UHSTCs. This study developed numerical and theoretical models to reproduce axial compression performances of UHSTCs at low temperatures. Validations against 24 tests proved that both two methods provided reasonable simulations on axial compression performance of UHSTCs. Finally, simplified theoretical models (STMs) and modified prediction equations in AISC 360, ACI 318, and Eurocode 4 were developed to estimate the axial load capacity of UHSTCs at low temperatures.

• Macromolecular Research
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• v.17 no.2
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• pp.116-120
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• 2009

The cellulose smart material called electro-active paper (EAPap) is made by regenerating cellulose. However, the actuator performance is degraded at low humidity levels. To solve this drawback, EAPap bending actuators were made by activating wet cellulose films in three different room-temperature ionic liquids: l-butyl-3-methylimidazolium hexaflurophosphate ($BMIPF_6$), 1-butyl-3-methylimidazolium chloride (BMICL) and 1-butyl-3-methylimidazolium tetrafluroborate ($BMIBF_4$). In the results, the actuator performance was dependent on the type of anions in the ionic liquids, in the order of $BF_4$>Cl>$PF_6$. The BMIBF 4-activated actuator showed the maximum displacement of 3.8 mm with low electrical power consumption at relatively low humidity. However, the BMICL-activated actuator showed a slight degradation of actuator performance. Further performance and durability improvement will be possible once various ionic liquids are blended with cellulose.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.2
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• pp.193-204
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• 1999

Performance of a variable-speed, roller-type vane compressor was evaluated at low evaporating temperature. First, an experimental investigation was conducted to examine the performance variation as functions of both outdoor temperature and rotating speed. For this purpose, a typical heat pump was implemented as a test apparatus to measure mass flow rate and power input. Secondly, computational investigations corresponding to the heat pump test conditions were performed to predict compressor performance using ORNL Map-Based compressor model. Results obtained from the heat-pump experiments showed that both mass flow rate and power consumption were sensitively dependent on both evaporating temperature and compressor speed as was predicted from the computational results. From the comparisons of both experimental and computational results, it was well recognized that the ORNL model was subjected to larger error in the accuracy of prediction as outdoor temperature decreased. When the outdoor temperature was above $-5^{\cire}C$, errors of predicted values corresponding to both mass flow rate and power consumption were estimated as $\pm$10% and $\pm$ 15%, respectively. Finally, it is suggested that the ORNL model needs to be re-evaluated if compressor map data tested below $-5^{\cire}C$(in evaporating temperature) are available.

• Transactions of the Korean hydrogen and new energy society
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• v.26 no.6
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• pp.590-599
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• 2015

In this paper a performance analysis is carried out based on the first and second laws of thermodynamics for heat exchanger in organic Rankine cycle (ORC) for the recovery of low-temperature finite thermal energy source. In the analysis, effects of the selection of working fluid and pinch temperature difference are investigated on the performance of the heat exchanger including the effectiveness of the heat exchanger, exergy destruction, second-law efficiency, number of transfer unit (NTU), and pinch point. The temperature distribution are shown depending on the working fluids and the pinch temperature difference. The results show that the performance of the heat exchanger depends on the pinch temperature difference sensitively. As the pinch temperature increases, the exergy destruction in the evaporator increases but the effectiveness, second law efficiency and NTU decreases.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.30 no.2
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• pp.68-82
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• 2018

Radiant floor heating systems with capillary tubes are energy saving systems in which hot water is circulated into capillary tube with a small diameter. In this study, the heating performance of capillary tube system is investigated in an experimental study and a simulation model. The results of the study showed that, the capillary tube radiant floor heating system maintains a more stable floor surface temperature in comparison a PB pipe system. In terms of energy consumption, the capillary tube radiant floor heating system proved to be more efficient than the PB pipe heating system at $40^{\circ}C$ of low temperature hot water supply. The difference between water temperature and room temperature can be held low for heating which saves energy. Low temperature radiant floor heating system with capillary tubes have significant advantages such as health improvement, low energy cost, optimum use of heat source(boiler) and higher operational efficiency.

• Journal of Power System Engineering
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• v.20 no.5
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• pp.92-97
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• 2016

In this study, the seawater Heat Pump System using seawater with temperature of annual domestic conditions ($0^{\circ}C$ to $25^{\circ}C$) is designed in order to compare its performance against the Heat Pump using unused heat of seawater. As a potential replacement for current refrigerants that exacerbate global warming and ozone delpetion, a Low GWP refrigerant's performance is analyzed. The basic water to water Heat Pump system is chosen and three commercial refrigerants - R134a, R410a, R32 - are used to compare against new Low GWP refrigerant R1234ze. When seawater with temperature of $25^{\circ}C$ is used, the performance change showed maximal increase in COP, 38.3%. low GWP refrigerant R1234ze, showed great performance characteristics reach to 5.242 and Existing commercial refrigerant, R134a showed only less than 0.03 performance difference against R1234ze. The study confirms notable performance of R1234ze refrigerant through simulation as environmentally friendly refrigerant for domestic seawater Heat Pump.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.8
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• pp.690-696
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• 2003

This paper presents the heat recovery performance of water fluidized-bed heat exchanger. Temperature and humidity ratio of waste gas are considered as important parameters in this study. Therefore, the heat recovery rate through water fluidized-bed heat exchanger for exhaust gases with various temperatures and humidity ratios can be estimated from the results of this study. Mass flow ratio (the ratio of mass flow rate of water to that of gas) and temperature of inlet water are also considered as important operating variables. Increase of heat recovery rate can be obtained through either high mass flow ratio or low temperature of inlet water with resultant low recovered temperature. The heat recovery performance with the mass flow ratio of about up to 10 has been investigated. The effect of number of stages of water fluidized-bed on the heat recovery performance has been also examined in this study.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.4 no.2
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• pp.119-128
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• 1975

Natural draft and flow which low temperature moist gas produces in the chimney of an Ondol heating system were numerically analysed. Among several factors involved inlet gas temperature has the strongest influence on the chimney performance and then next specific humidity of the gas. Thermal conductivity of the chimney wall, however, has little influence on the performance of such a low temperature chimney. Under given flow conditions there exists an optimum chimney height which gives a maximum flow rate for a given chimney diameter. This optimum value of chimney height inereases with increase in chimney diameter, inlet gas temperature and specific humidity.

• Journal of Biosystems Engineering
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• v.32 no.1 s.120
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• pp.20-29
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• 2007

Korean farmers have purchased agricultural dryer and low temperature storage system apart. In this study, the system was designed and constructed to investigate the practical application possibility of the air to air heat pump as drying and low temperature storage system for agricultural products with providing basic data. The performance and drying characteristics of the system evaluated by drying red pepper. The value of coefficient of performance of the system for heating was from 1.8 to 2.2 when ambient air temperature varied from 13$^{\circ}C$ to 23$^{\circ}C$. For operating the heat pump as dryer for drying red pepper by setting three drying air temperature of 50, 55 and 60$^{\circ}C$, specific moisture extraction rates meaning amount of energy consumption for removing moisture of 1kg from red pepper were 1.095, 1.017 and 1.094 kg$_{water}$/kWh, respectively. The drying period up to moisture ratio of 0.02 were 31, 26 and 21 hour, respectively. The lightness, redness, yellowness and chroma differences of red pepper dried by the heat pump dryer were lowered than those of red pepper dried by conventional heated air dryer except for yellowness difference at drying air temperature of 60$^{\circ}C$.

• Journal of Biosystems Engineering
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• v.24 no.4
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• pp.343-350
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• 1999

The ambient air is commonly used as low-temperature heat source for heat pump operation. However, the coefficient of performance(COP) of the air to water heat pump is decreased with the ambient air temperature drop. In this study to solve this problem, the AVACTHE(Automatic Variable Area Capillary Type Heat Exchanger) with 3 levels of heat exchange area(0, 1,495.4, 1,794.5$\textrm{cm}^2$)was installed in the refrigerant circuit of the heat pump. The AVACTHE effect on the performance of heat pump was tested with the ambient air temperature variation. The COP improvement of the heat pump could be achieved by the AVACTHE installation when below -5$^{\circ}C$ of the ambient air temperature.