• Energy Research
• Closed Access close
• Open Source close
• JP close
• KR close
• Energy Conversion and Management close

Abstract Double and added double stage organic Rankine cycle systems are configured to recover exhaust gas waste heat of dual fuel engines. To evaluate the performance of the models proposed here, energy, exergy and economic analyses are performed. Several working fluids are evaluated for recommendation for double and added double stage organic Rankine cycle systems. In the double stage organic Rankine cycle, cycle 1 and cycle 2 are connected in parallel. Working fluids R123, R141b, and R601 are used in cycle 1, and R245fa, R236ea, and R1233zd in cycle 2. In the double stage organic Rankine cycle, the working fluid combinations of R601-R1233zd, R601-R245fa and R123-R245fa show better performance when considering power, heat transfer area and payback period, which are 1760 kW, 2108.9 m2 and 4.21 year, respectively for R601-R245fa. In the added double stage organic Rankine cycle, cycle 1 and cycle 2 are connected in two stages and cycle 1 and cycle 3 in parallel. The net power of the working fluid combinations of R123-R245fa and R123-R1233zd are 1799 kW and 1782 kW, respectively, which are higher than those of the others. Further, for R123-R245fa, the heat transfer area and payback period are 3352 m2 and 6.20 year, respectively, which is better compared to those of other working fluid combinations.

Abstract A polymer-based flexible pulsating heat pipe (FPHP) as a flexible heat spreader was developed, and a series of experiments were conducted to evaluate the thermal performance and the long-term reliability of the FPHP. The FPHP consisted of a multilayer laminated film and a low-density polyethylene (LDPE) sheet. HFE-7000 was used as the working fluid, and the width, length, and thickness of the FPHP were 53.4 mm, 85.5 mm, and 1 mm, respectively. To minimize the permeation of non-condensable gases (NCGs) in a lateral direction, the heat-sealed flanges were covered with the indium coating. Owing to the indium-coated flanges, the long-term reliability of the FPHP drastically increased. The lifetime of the FPHP was defined to evaluate the long-term reliability. The FPHP had a lifetime of 18.2 days in the acceleration test environment, which was equivalent to 306 days in a standard atmosphere and 17 times longer than the previous polymer-based PHP. The FPHP had the thermal resistance of 2.41 K/W, which is 37% lower than that of the copper reference sample in a vertical orientation. Under bending conditions as well as in a horizontal orientation, the FPHP still operated well as a PHP, but the thermal resistance increased slightly. The fabrication method of the FPHP is effective in minimizing the permeation of NCGs in a lateral direction and can pave the way for fabricating a thin flexible heat spreader that has high flexibility, high thermal performance, and long-term reliability.

Abstract The dynamics of CH 4 replacement in the CH 4 hydrate with saturated liquid CO 2 at 273.2 K was measured with a high pressure optical cell. The results showed that CH 4 in the hydrate gradually moved to the liquid CO 2 phase while CO 2 in the liquid phase penetrated into the hydrate from the quantitative analysis. The decomposing process of the CH 4 hydrate during the replacement was analyzed with in situ Raman spectroscopy, which allowed us to distinguish the cage structure of the CH 4 hydrate and discuss the microscopic view of the replacement in the hydrate. It was found that the decomposition of the medium cage (M-cage) in the CH 4 hydrate proceeded faster than that of the small cage (S-cage). The observed rate difference could be related to the stability of the S-cage in the CH 4 hydrate or the re-formation tendency of CH 4 and water molecules in the S-cage after decomposing the hydrate structure, whereas the guest molecule exchange of CH 4 with CO 2 could occur in the M-cage. Based on the experimental data, we developed a kinetic model for calculation of the CH 4 remaining in the hydrate considering the decomposition rate difference between the M-cage and S-cage in the CH 4 hydrate. The results indicate that the driving force could be the fugacity difference between the fluid phase and the hydrate phase for the replacement process.

Abstract The clathrate hydrate formation at the interface between liquefied carbon dioxide (CO 2 ) and liquid water is one of the key processes in the course of direct CO 2 disposal into deep seas—an option to mitigate the emission of CO 2 into the atmosphere. Eight different models have been proposed so far on the formation and metabolic self-preservation of a hydrate film at the interface and also the mass transfer of CO 2 across the hydrate film. This paper reviews those rival models one by one and illustrates how they are discrepant. Each model is critically examined, and if any, its weakness in physical reality or mathematical formulation is pointed out. The state of the art of hydrate-film modeling thus revealed suggests the necessity of more careful consulting of pertinent experimental observations to establish our physical view about hydrate films, which should serve as the base of any further work on hydrate-film modeling.

Abstract Waste heat recovery has attracted a significant attention because of the world growth in energy demand. In this paper, we report the study on an energy recovery system utilizing low-grade waste heat below 100 °C. This system called a thermal-driven electrochemical generator is composed of reverse electrodialysis (RED) power generation and thermal separation using waste heat. We especially focus on the experimental characterization of the RED process with ammonium bicarbonate (NH4HCO3) solution, which is known to be easily decomposed at the temperature around 60 °C. We characterized this NH4HCO3-RED system with various parameters including the concentration difference, the membrane type, the inlet flow rate, and the compartment thickness. We found the best power density at the concentrated solution of 1.5 mol L−1 and the diluted solution of 0.01 mol L−1. The maximum power density increases as the inlet flow rate increases or the compartment thickness decreases owing to the decrease in the internal resistance. We obtained the excellent power density of 0.77 W m−2, compared with the previous studies.

Abstract In this paper, two robust decentralised proportional integral (PI) control designs are proposed for load frequency control (LFC) with communication delays. In both methodologies, the PI based LFC problem is reduced to a static output feedback (SOF) control synthesis for a multiple delay system. The first one is based on the optimal H ∞ control design using a linear matrix inequalities (LMI) technique. The second control design gives a suboptimal solution using a developed iterative linear matrix inequalities (ILMI) algorithm via the mixed H 2 / H ∞ control technique. The control strategies are suitable for LFC applications that usually employ PI control. The proposed control strategies are applied to a three control area power system with time delays and load disturbance to demonstrate their robustness.

For global survival, we need to launch a rapid regeneration of the nuclear power industry. The replacement of the present fossil fuel industry requires a doubling time for alternative energy sources of 5–7 years and only nuclear energy has the capability to achieve this. The liquid metal cooled fast breeder reactors (LMFBR) have the best breeding criteria but the doubling time exceeds 20 years. Further, the use of plutonium in these systems has the potential of nuclear proliferation. The Thorium Molten-Salt Nuclear Energy Synergetic System [THORIMS-NES], described here is a symbiotic system, based on the thorium–uranium-233 cycle. The production of trans-uranium elements is essentially absent in Th–U system, which simplifies the issue of nuclear waste management. The use of 233 U contaminated with 232 U as fissile material, instead of plutonium/ 235 U makes this system nuclear proliferation resistant. The energy is produced in molten-salt reactors (FUJI) and fissile 233 U is produced by spallation in Accelerator Molten-Salt Breeders (AMSB). This system uses the multi-functional ‘‘single-phase molten-fluoride” circulation system for all operations. There are no difficulties relating to ‘‘radiation-damage”, ‘‘heat-removal” and ‘‘chemical processing” owing to the simple ‘‘idealistic ionic liquid” character of the fuel. FUJI is size-flexible, and can use all kinds of fissile material achieving a nearly fuel self-sustaining condition without continuous chemical processing of fuel salt and without core-graphite replacement for the life of the reactor. The AMSB is based on a single-fluid molten-salt target/blanket concept. Several AMSBs can be accommodated in regional centers for the production of fissile 233 U, with batch chemical processing including radio-waste management. FUJI reactor and the AMSB can also be used for the transmutation of long-lived radioactive elements in the wastes and has a high potential for producing hydrogen-fuel in molten-salt reactors. The development and launching of THORIMS-NES requires the following three programs during the next three decades:

Abstract As NH3 has received extra attention expected to play a key role as an H2 carrier with desirable physical and chemical properties, H2 production via NH3 decomposition becomes a promising way to supply H2 in a cost-competitive and eco-friendly manner. In this study, life cycle techno-economic and carbon footprint analysis is conducted to investigate the feasibility of the NH3 decomposition process in terms of economic performance and CO2 emissions. In particular, the life cycle NH3 supply chain for H2 production is considered including production, transportation, and decomposition back to H2. Based on the classification of NH3 into three different types depending on how the chemical is produced, NH3 price and CO2 emissions are evaluated. In addition, using a commercial process simulator, the decomposition process is modeled and techno-economic analysis for the whole process for H2 production reveals that NH3 price is the most influential economic factor and the H2 production cost can compete with renewable-based H2 but it is still higher than fossil fuel-based H2 production. Moreover, H2 supply via NH3 decomposition is projected based on a domestic implementation plan in the Republic of Korea resulting in estimation of NH3 price, H2 production cost, and corresponding CO2 emissions in the future.

Abstract In this study, performance of R430A is examined numerically and experimentally in an effort to replace HFC134a used in refrigeration system of domestic water purifiers. Even though HFC134a is used predominantly in such a system these days, it needs to be phased out in near future in most of the developed countries due to its high global warming potential. To solve this problem, cycle simulation and experiments are carried out with a new refrigerant mixture of 76%R152a/24%R600a using actual water purifiers. This mixture is numbered and listed as R430A by ASHRAE recently. Test results show that the system performance is greatly influenced by the amount of charge due to the small internal volume of the refrigeration system in water purifiers. With the optimum amount of charge of 21–22 g, about 50% of HFC134a, the energy consumption of R430A is 13.4% lower than that of HFC134a. The compressor dome and discharge temperatures and condenser center temperature of R430A are very similar to those of HFC134a for the optimum charge. Overall, R430A, a new long term environmentally safe refrigerant, is a good alternative for HFC134a in domestic water purifiers requiring no major change in the system.