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- 저자 : Yongtae Jang (검색결과 36 건)
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Jang, Yongtae,Lee, Jaeseon Elsevier 2018 Energy conversion and management Vol.171 No.-
<P><B>Abstract</B></P> <P>The purpose of this study is to investigate the performance characteristics of subcritical organic Rankine cycle (ORC) based combined heat and power (CHP) system according to a variation of major operating parameters and to confirm the possibility of system performance improvement. The CHP system is designed to provide output using a 200 °C heat source, including at least 2 kW of electric power and 25 kW of thermal power with 60 °C of hot water supply. Besides examining a basic ORC-based CHP system, variations of system configurations combined with heat exchangers for additional heat recovery have been considered. The effects of changes in superheat and expander volumetric expansion ratio on system performance were evaluated based on thermodynamic analysis and optimization results for each system and working fluids.</P> <P>Eight candidate working fluids selected for superior thermophysical properties and environmental impacts were classified into three groups according to the magnitude of latent heat, and four types of CHP system configuration with additional heat exchangers were considered. Group A working fluids with the largest latent heat include cyclopentane, isopentane, n-pentane, and diethyl ether, while medium latent heat group B working fluids include R-1233zd and R-245fa. The smallest latent heat group C working fluids include HFE-7000 and HFE-7100. The operating conditions and performance of the CHP systems were calculated considering the fixed heat source temperature (200 °C), the superheat amount, the volumetric expansion ratio and the isentropic efficiency of the expander for parametric analyses.</P> <P>Studies have shown that the group A working fluid systems are superior in performance to other fluid systems. According to the parametric analyses, the increase in superheat has a positive effect regardless of the configuration in the system using the group B working fluids. Other working fluid systems can also be expected to enhance the performance by increasing the degree of superheat in system configurations where an internal heat exchanger (IHE) and a post-heater (PH) are employed together. Increasing the volumetric expansion ratio and the isentropic efficiency of the expander improves the performance of all working fluid systems. Especially, it has been concluded that the addition of the post-heater is essential if the CHP performance is to be improved by increasing the volumetric expansion ratio and the isentropic efficiency of the expander.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Performance characteristics of ORC based CHP system are analyzed according to operating parameters. </LI> <LI> The CHP system was designed with at least 2 kW electric and 25 kW thermal power outputs. </LI> <LI> Eight candidate working fluids and four CHP system variant cases were considered in the analysis. </LI> <LI> It is necessary to add a post heater to improve the performance by employing high efficiency expander. </LI> </UL> </P>
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Optimizations of the organic Rankine cycle-based domestic CHP using biomass fuel
Jang, Yongtae,Lee, Jaeseon Elsevier 2018 Energy conversion and management Vol.160 No.-
<P><B>Abstract</B></P> <P>The purpose of this study is to determine the optimal operating conditions and performance for the design of ORC based biomass compact CHP for 2 kW of electric, 25 kW of thermal power productions and 60 °C warm water supply. Eight organic working fluids were selected based on thermo-physical properties and related environmental regulations: cyclopentane, isopentane, n-pentane, diethyl ether, HFO-1233zd, HFC-245fa, HFE-7000 and HFE-7100. The selected organic fluids were classified into three groups considering latent heat and boiling point. The group A fluids contained cyclopentane, isopentane, n-pentane and diethyl ether. The group B fluids contained HFO-1233zd and HFC-245fa. The group C fluids contained HFE-7000 and HFE-7100. A micro CHP system composed of a biomass boiler (200 °C heat source), an ORC power cycle and a cooling water line (20 °C cooling water supply) was modeled in four variants depending on whether post-heater and IHE were applied or not. The subcritical ORC cycle and saturated vapor state at the inlet of the expander were considered for the analysis. As a result of thermodynamic analyses and optimizations, the group A fluids have the best CHP performance because of the greatest latent heat amount. The systems using the group A fluids have the lowest mass flow rates from 0.053 kg/s to 0.081 kg/s, the lowest required heat supplies from 31.64 kW to 34.61 kW, the highest ORC efficiencies from 5.95% to 7.29% and the CHP efficiencies from 71.83% to 72.32%. The group B fluids have the mass flow rates from 0.157 to 0.215 kg/s, the highest required heat supplies from 36.98 kW to 46.41 kW, the lowest system efficiencies from 4.59% to 6.05% and the highest CHP efficiencies from 72.05% to 73.41%. The group C fluids have the highest mass flow rates from 0.213 kg/s to 0.230 kg/s, the required heat supplies from 32.30 kW to 40.54 kW, the system efficiencies from 5.07% to 6.36% and the lowest CHP efficiencies from 71.31% to 72.33%. In addition, ORC systems using the group A or group C fluids can operate at low pressure and can meet system requirements with low cooling water mass flow rate because of the high boiling points. For the group A fluids, both post-heater and IHE are very effective for the system, and the system using the group B fluids can highly improve the system through the application of the post-heater. For the group C fluids, application of the IHE significantly improves system performance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Optimization of ORC based micro CHP for 2 kW electric, 25 kW thermal power and 60 °C warm water supply. </LI> <LI> The optimal system configuration was identified according to the selection of ORC working fluid. </LI> <LI> After heater and IHE addition, HFO-1233zd can be a good alternative to hydrocarbon fluids. </LI> </UL> </P>
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Comprehensive assessment of the impact of operating parameters on sub 1-kW compact ORC performance
Jang, Yongtae,Lee, Jaeseon Pergamon 2019 Energy Conversion and Management Vol. No.
<P><B>Abstract</B></P> <P>The heat source and sink temperatures are important external variables that determine the performance of power cycles, such as the ideal Carnot cycle and Rankine cycle. In addition to these external operating variables, variations in the mass flow rate within the system can significantly change the operating characteristics of the power cycle. In this study, the combined effects of these operating variables on the compact Rankine cycle performance were investigated experimentally. A compact ORC with R245fa working fluid and scroll expander was experimentally evaluated at 100–140 °C heat source, 10–30 °C heat sink and 0.042–0.060 kg/s mass flow rate conditions.</P> <P>Comprehensive experiments showed that the external parameters have significant effects on ORC operating temperature and pressure. In particular, the electrical output was well predicted by the parameter of change in the pressure difference rather than the expansion ratio of the expander. It was also found that the mechanical efficiency of expander increased nonlinearly when decreasing the heat source temperature and increasing the pressure difference of expander. The generator efficiency was not affected by the operating parameters as the expander rotational speed was linearly proportional to the electrical power. The maximum system performance showed 0.246 kW electrical output and 1.61% thermal efficiency in contrast to 0.796 kW net fluidic output and 5.72% fluidic thermal efficiency where they were in different conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effects of operating parameters are investigated through compact ORC experiments. </LI> <LI> R245fa and a scroll expander were used for the ORC. </LI> <LI> Expander inlet and outlet pressure difference well predicts ORC electrical output. </LI> <LI> ORC operation and performance characteristics are discussed. </LI> <LI> The strategy to find the optimized operation is proposed for high ORC performance. </LI> </UL> </P>
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( Sungjin Jang ),( Jongbae Kim ),( Jungwon Byun ),( Yongtae Shin ) 한국인터넷정보학회 2014 KSII Transactions on Internet and Information Syst Vol.8 No.7
Cognitive Radio (CR) has very promising potential to improve spectrum utilization by allowing unlicensed Secondary Users (SUs) to access the spectrum dynamically without disturbing licensed Primary Users (PUs). Mitigating interference is a fundamental problem in CR scenarios. This is particularly problematic for deploying CR in cellular networks, when users are located at the cell edge, as the inter-cell interference mitigation and frequency reuse are critical requirements for both PUs and SUs. Further cellular networks require higher cell edge performance, then SUs will meet more challenges than PUs. To solve the performance decrease for SUs at the cell edge, a novel Dynamic Spectrum Allocation (DSA) scheme based on Game Theory is proposed in this paper. Full frequency reuse can be realized as well as inter-cell interference mitigated according to SUs` sensing, measurement and interaction in this scheme. A joint power/channel allocation algorithm is proposed to improve both cell-edge user experience and network performance through distributed pricing calculation and exchange based on game theory. Analytical proof is presented and simulation results show that the proposed scheme achieves high efficiency of spectrum usage and improvement of cell edge SUs` performance.
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주용태(Yongtae Joo),강유신(Yoosin Kang),장홍주(Hongjoo Jang) 한국자동차공학회 2020 한국자동차공학회 부문종합 학술대회 Vol.2020 No.7
In order to respond to the increasing global environmental regulations, we are continuously carrying out tire lightening research. Studies conducted to make the thickness of under-tread thin. And the performance of the tread adhesion test method was verified in response to the thickness thinning. As a result of comparing the thinning effect of the cap tread and the under tread under the same weight condition among the tread regions, it was confirmed that thinning the under tread was effective in improving rolling resistance and braking distance compared to the cap tread. Based on this study, it was confirmed that rolling resistance can be improved without loss of driving performance.
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