Combined Thermal Efficiency Research Articles

Thermodynamic, exergoeconomic evaluation and optimization of S–N2O/t-N2O nuclear power cycle for the construction of the lunar base

With the continuous development of deep space exploration, many planetary exploration schemes and development plans regard the construction of planetary bases as an essential goal, especially the exploration of the Moon. Supercritical and transcritical nitrous oxide (N2O) cycles are compact, low-cost, efficient, and lightweight for nuclear reactors to supply power to the bases on other planets. This paper presents the thermodynamic, exergoeconomic, and mass analyses of a combined cycle consisting of a supercritical N2O recompression Brayton cycle and a transcritical N2O cycle (S–N2O/t-N2O). It is shown that under the optimal conditions, the combined thermal efficiency and exergy efficiency are 45.52 % and 60.13 %, respectively. Based on the exergy analysis, the exergy destruction mainly occurs in the reactor and main compressor. A sensitivity study shows that the split ratio, pressure ratio in the supercritical N2O cycle, main compressor inlet pressure, turbine2 inlet temperature, and turbine2 inlet pressure have significant effects on the net output work, thermal efficiency, specific mass, and levelized cost of electricity. Furthermore, multi-objective optimizations are considered to obtain the Pareto frontier solutions for different multi-objectives, and the optimal design condition is found. These findings could improve the power cycle performance for the construction of the Lunar Base.

Simulation of 15% and 50% Thermal Power Dispatch to an Industrial Facility Using a Flexible Generic Full-Scope Pressurized Water Reactor Plant Simulator

Nuclear power plants in the United States are increasingly challenged to compete in wholesale electricity markets due to the low electricity costs and increasingly dynamic grid conditions from competing generation sources. An alternative market for nuclear power is industrial facilities that can use the thermal and/or electrical power generated by a nuclear power plant to offset the economic losses incurred by electricity market challenges. A generic pressurized water reactor (PWR) simulator was used to show the results of a basic design for a generic thermal power extraction system and tests were run using a set of procedures to show what happens when a nuclear power plant transitions from full electrical power dispatch to 15% and 50% thermal power dispatch. This type of operation leads to losses in turbine performance efficiency due to the deviation from the design operating point, but because the thermal power is also used by the industry load without conversion losses, the combined thermal efficiency of the PWR increases. For the 15% case, the thermal efficiency increased from 32% to 41.9%, while for the 50% case, the efficiency increased up to 60.1%. In addition, for 50% thermal power dispatch, the power dissipated by the condenser decreased from approximately 2000 to approximately 1300 MW (thermal), indicating a substantially diminished impact on the environment in terms of releasing heat into the cooling water reservoir.

Comparative Analysis of Combined Heating Systems Involving the Use of Renewable Energy for Greenhouse Heating

The continued use of fossil fuels is contributing to severe environmental pollution and the establishment of an abnormal climate; consequently, alternative renewable energy sources are being actively investigated worldwide. Further, following global trends, numerous countermeasures aimed at improving carbon neutrality, promoting sustainable agriculture, and reducing fossil fuel dependence are being implemented in the Republic of Korea. Therefore, this study was conducted to investigate the application of renewable energies for greenhouse heating in the Republic of Korea. Three hybrid systems, numbered 1–3, were constructed using a pellet boiler, hydrothermal heat pump, and solar heat collection system, respectively. Thereafter, the heating performance, combined heat efficiency, energy consumption per temperature lifting, and energy cost per temperature lifting of the systems were compared. The combined thermal efficiency results showed no significant differences. However, in terms of energy consumption and cost, hybrid system 1 demonstrated 25.7 and 24.1% savings, respectively, compared with the other systems. Moreover, based on economic analysis via the net present value and life cycle cost analysis methods, the system reduced costs by 29.2 and 27.7%, respectively, compared with conventional fossil fuel boilers. Thus, hybrid system 1 was identified as the most economical system.

Performance analysis and multi-objective optimization of an integrated gas turbine/supercritical CO2 recompression/transcritial CO2 cogeneration system using liquefied natural gas cold energy

A novel power/cooling cogeneration system integrated with a gas turbine, a supercritical CO2 recompression power system (SCRPC) and a transcritical CO2 power system (TCPC) using liquefied natural gas (LNG) cold energy is proposed and investigated. This new combined system can improve the electrical capacity of gas turbine, and it can maximize the electrical output under different gas turbine load conditions by adjusting the split ratio. A steady-state mathematical model is developed to further understand the performance of the proposed system. It is shown that under the given conditions the combined thermal efficiency and the combined exergy efficiency are 52.94% and 30.27%, respectively. And the exergy analysis shows that the exergy destruction mainly occurs in the combustor, followed by condenser and NG terminal, respectively. Parametric study shows that the engine load conditions, the turbine I inlet temperature, the SCRPC and TCPC highest pressures and the effectiveness of HTR, LTR and regenerator have significant effects on the net work output, the cooling capacity, the combined thermal and exergy efficiencics, and the capital investment cost. Furthermore, multi-objective optimizations considering both thermodynamic and economic aspects are carried out to obtain the Pareto frontier solutions for different multi-objectives, and the optimal design condition is found out by means of the TOPSIS method based on entropy weight. These findings could be helpful in improving the utilization rate of the gas turbine exhaust waste heat and thus boost the system efficiency.

Energy and Exergy Analyses of Regenerative Gas Turbine Air-Bottoming Combined Cycle: Optimum Performance

The current paper presents a thermodynamic analysis of an air-bottoming cycle (ABC) operated by the exhaust gasses of a regenerative gas turbine cycle. The partial exhaust heat of a topping gas turbine cycle is utilized to heat the compressed air of the ABC by passing it through a heat exchanger (H.E.2), whereas remaining heat is used to heat the compressed air of the topping cycle before entering a combustion chamber by passing it through a heat exchanger (H.E.1). The effects of the turbine inlet temperature of the topping cycle (1000 K ⩽ $${\text{TIT}}$$ ⩽ 1500 K) and fraction of mass flow rate of the exhaust gas (0 ⩽ $$x$$ ⩽ 1) on the net output, combined thermal efficiency, exergy destruction, exergy loss by exhaust gasses, and specific fuel consumption (SFC) are investigated parametrically for a particular value of the pressure ratio of the topping and bottoming cycles. At $$x = 0$$ , the net output and thermal efficiency of the combined cycle increase by 15.1% and 31.3%, respectively, whereas the SFC decreases by 13.1% and 15.5% at $${\text{TIT}} = 1000\;{\text{K}}$$ and $${\text{TIT}} = 1500\;{\text{K}}$$ , respectively. The exergy destruction of the heat exchanger of the topping cycle increases, whereas that of the bottoming cycle decreases with an increase in x. Overall, in terms of the net output and thermal efficiency, a simple gas turbine cycle with an air-bottoming combined cycle performs better than a simple regenerative gas turbine cycle; however, in view of the exergy loss by exhaust gasses, a simple regenerative gas turbine cycle is better than the combined cycle.

Thermodynamic analysis of Organic Rankine cycle driven by reversed absorber hybrid photovoltaic thermal compound parabolic concentrator system

In current study, an effort is made to improve the overall performance of the solar powered organic Rankine system to meet increasing energy demand and mitigate the resulting menace caused by environmental imbalance. Hourly performance evaluation of Solar powered Organic Rankine Cycle (ORC) system is done for varying concentration ratio in terms of collector output temperature, heat gain in evaporator, combined thermal and exergetic efficiency. The Heptane/R245fa is used as working fluid at fixed (0.1/0.9) fractional mass component. Organic Rankine system is coupled with reversed absorber hybrid photovoltaic thermal compound parabolic concentrator (PVTCPC). The highest collector outlet temperature 125.45 °C, heat gain 3.21 × 105 W, combined thermal efficiency 7.8%, and exergetic efficiency 14.38% is observed at 13:00 h for 6 concentration ratio of the concentrator. This study establishes the utility of low-grade renewable heat source conversion into solar electrification, solar irrigation, solar cooling and solar water purification.

Innovative thermodynamic parametric investigation of gas and steam bottoming cycles with heat exchanger and heat recovery steam generator: Energy and exergy analysis

In this study, gas and steam bottoming cycles, driven by the exhaust gas of Gas turbine cycle, are analyzed thermodynamically. The waste heat of the Gas turbine topping cycle (GT) exhaust gas is used partially to heat the air in the air bottoming cycle and partially to generate steam by passing it through HRSG in the steam bottoming cycle. The topping Gas turbine and air bottoming cycles are coupled with the heat exchanger, whereas the topping and steam bottoming cycles are coupled with Heat Recovery Steam Generator (HRSG). The effects of turbine inlet temperature (1100 K ⩽ TIT ⩽ 1500 K), pressure ratio (6⩽rpt⩽12) and flow rate of exhaust gas on the Net work and combined thermal efficiency and exergy loss of exhaust gas are investigated. It is observed that the Net work of steam bottoming cycle is higher than the Net work of gas bottoming cycle and for higher values of turbine inlet temperature TIT = 1500 K, 90% of power is recovered through the bottoming cycle at lower pressure ratio. The combined thermal efficiency increases by 10% with an increase in the turbine inlet temperature from 1100 to 1500 K. It is found that the combined thermal efficiency increases with all pertinent parameters.

Thermodynamic analysis of a novel combined cooling and power system driven by low-grade heat sources

A novel combined cooling and power system which combines a conventional ammonia-water power/cooling cycle named Goswami cycle and an ejector refrigeration cycle is proposed and investigated. This new combined system can improve the refrigerating capacity of the conventional power/cooling system, and it can also adjust the cooling capacity to power ratio by changing the proportion of the ammonia-water flow into the turbine and the ejector. A mathematical model is developed to study the system performance. It is shown that under the given conditions the combined thermal efficiency and the combined exergy efficiency are 17.49% and 26.15%, respectively. The exergy analysis shows that the exergy destruction mainly occurs in the recovery heat exchanger, followed by boiler and rectifier, respectively. Parametric study shows that the absorber temperature, the cycle highest pressure and low pressure, the boiler temperature and the split ratio have significant effects on the net work output, the cooling capacity, the combined thermal efficiency and the combined exergy efficiency.

Simulation studies on gax based Kalina cycle for both power and cooling applications

A detailed parametric analysis is carried out on both simple and GAX based combined power and cooling cycle. The effect of various parameters such as heat source temperature, refrigeration temperature, sink temperature, split ratio (refrigerant flow ratio between power and cooling systems), split factor (solution flow ratio between absorber and GAX heat exchanger) on the performance of the cycle is studied. The results of the analysis show that using the GAX heat exchanger about 20% of internal heat is recovered within the cycle. The optimum split factor is 0.8–0.9 and the split ratio is 0.5:0.5. The maximum combined thermal efficiency of 35–45% and coefficient of performance of about 0.35 is attained at the optimum conditions.

A prototype photovoltaic/thermal system integrated with transpired collector

Building-integrated photovoltaic/thermal (BIPV/T) systems may be utilized to produce useful heat while simultaneously generating electricity from the same building envelope surface. A well known highly efficient collector is the open-loop unglazed transpired collector (UTC) which consists of dark porous cladding through which outdoor air is drawn and heated by absorbed solar radiation. Commercially available photovoltaic systems typically produce electricity with efficiencies up to about 18%. Thus, it is beneficial to obtain much of the normally wasted heat from the systems, possibly by combining UTC with photovoltaics. Combination of BIPV/T and UTC systems for building facades is considered in this paper – specifically, the design of a prototype façade-integrated photovoltaic/thermal system with transpired collector (BIPV/T). A full scale prototype is constructed with 70% of UTC area covered with PV modules specially designed to enhance heat recovery and compared to a UTC of the same area under outdoor sunny conditions with low wind. The orientation of the corrugations in the UTC is horizontal and the black-framed modules are attached so as to facilitate flow into the UTC plenum. While the overall combined thermal efficiency of the UTC is higher than that of the BIPV/T system, the value of the generated energy – assuming that electricity is at least four times more valuable than heat – is between 7% and 17% higher. Also, the electricity is always useful while the heat is usually utilized only in the heating season. The BIPV/T concept is applied to a full scale office building demonstration project in Montreal, Canada. The ratio of photovoltaic area coverage of the UTC may be selected based on the fresh air heating needs of the building, the value of the electricity generated and the available building surfaces.

Solid oxide fuel cell/gas turbine trigeneration system for marine applications

Shipping contributes 4.5% to global CO2 emissions and is not covered by the Kyoto Agreement. One method of reducing CO2 emissions on land is combined cooling heating and power (CCHP) or trigeneration, with typical combined thermal efficiencies of over 80%. Large luxury yachts are seen as an ideal entry point to the off-shore market for this developing technology considering its current high cost.This paper investigates the feasibility of combining a SOFC-GT system and an absorption heat pump (AHP) in a trigeneration system to drive the heating ventilation and air conditioning (HVAC) and electrical base-load systems. A thermodynamic model is used to simulate the system, with various configurations and cooling loads. Measurement of actual yacht performance data forms the basis of this system simulation.It is found that for the optimum configuration using a double effect absorption chiller in Ship 1, the net electric power increases by 47% relative to the electrical power available for a conventional SOFC-GT-HVAC system. This is due to more air cooled to a lower temperature by absorption cooling; hence less electrical cooling by the conventional HVAC unit is required. The overall efficiency is 12.1% for the conventional system, 34.9% for the system with BROAD single effect absorption chiller, 43.2% for the system with double effect absorption chiller. This shows that the overall efficiency of a trigeneration system is far higher when waste heat recovery happens.The desiccant wheel hardly reduces moisture from the outdoor air due to a relative low mass flow rate of fuel cell exhaust available to dehumidify a very large mass flow rate of HVAC air, Hence, desiccant wheel is not recommended for this application.

447 マイクロコジェネレーションシステムの実測データに基づく総合効率評価

Recently, research and development of micro gas turbine or fuel cell centered micro co-generation system is conducted actively. However, few studies were reported on the combined thermal efficiency based on the actual data measured all through the year. In this paper, we report actual data based combined thermal efficiency evaluation of micro gas turbine centered micro co-generation system especially focused on ambient temperature effect. Measurement was conducted at J-Power Chigasaki R&D Center where oil fueled Capstone 25Kw micro gas turbine was equipped as a central component. We calculated the combined thermal efficiency by counting total heat balance.

629 マイクロコジェネレーションシステムで観察された温度変動の発生機構に関する研究

Recently, research and development of micro co-generation system is conducted actively. However, few studies were reported on the combined thermal efficiency based on the actual data measured all through the year. In this paper, firstly, we report actual data based combined thermal efficiency evaluation of micro gas turbine centered micro co-generation system especially focused on ambient temperature effect. During the measurement we found temperature fluctuation of heat transfer medium under the condition that the ambient temperature is less than 28 degree Celsius. Then, secondly, we report the analysis of this phenomenon by formulating the relation of heat balance taking account of nonlinearity of valve characteristics.