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This study experimentally investigates a Regenerative Organic Rankine Cycle (RORC) system that operated under varied cryogenic conditions using liquid nitrogen (LN2) as the heat sink. A three-fluid heat exchanger (TFHE) is applied to this system instead of a condenser and regenerator to realize the RORC system. The condensing pressure changes between 0.08 MPa and 0.6 MPa, and applying the R290 as the working fluid. The condensing pressure effect on system performances, including electrical power output, cold thermal efficiency, and exergetic efficiency, are investigated under different LN2 flow rates. The comparisons between basic ORC (BORC) and RORC under the same working conditions are conducted. The results demonstrate that as the condensing pressure remains constant, the higher LN2 flow rate is beneficial to the overall performance of the RORC system. The maximum cold thermal efficiency and power generation obtained in the RORC system are 13.35% and 738.81 W, which are obtained at the LN2 flow rate of 120 kg/h and the condensing pressure of 0.25 MPa. Additionally, the RORC shows improved performance with an exergetic efficiency of 10.68%. The results would be a technological guide for the construction and improvement of the system with cold energy recovery. [ABSTRACT FROM AUTHOR]

This work presents an experimental investigation of a small‐scale cryogenic Organic Rankine Cycle (ORC) power generation plant for cold energy utilization using scroll expander and R290. The fresh water and liquid nitrogen were used as heat source and heat sink, respectively. Furthermore, expander gross output power and isentropic efficiency, system thermal efficiency, and cold energy utilization efficiency were calculated as a principle to evaluate the overall system performance. The experimental results demonstrate that increasing pressure drop and heat source temperature will benefit the system performance in some extent, and the pressure drop exhibits a relative sensitivity to heat source temperature about the system performance. Moreover, the expander gross output power will get the peak value while the heat source and heat sink in the best matching. When the mass flow rate of liquid nitrogen at 120 kg/h, optimum pressure drop is 1.02 Mpa, and the corresponding expander gross output power, thermal efficiency, and cold energy utilization efficiency were 638.2W, 0.0586, and 0.0976, respectively. The optimum heat source temperature is 50℃ under liquid nitrogen mass flow rate of 120 kg/h, and the corresponding expander gross output power, thermal efficiency, and cold energy utilization efficiency were 674.2 W, 0.0594, and 0.099, respectively. [ABSTRACT FROM AUTHOR]

Summary: A combined Organic Rankine Cycle (ORC) system with liquefied nature gas (LNG) cold energy and dual‐fuel (DF) marine engine waste heat utilization was proposed. Engine exhaust gas and engine jacket cooling water were adopted as parallel heat sources. Thermo‐economic analyses of the proposed system with 32 working fluids combinations were performed. Two objective functions covering thermal efficiencies and economic index were employed for performance evaluation. Afterward, the effects of operation pressure on the objective functions were investigated. Finally, the optimal conditions were obtained from the Pareto front with the Non‐dominated Sorting Genetic Algorithm‐II (NSGA‐II) method. The results show that the proposed ORC system has better energy recovery performances than the parallel ORC system. R1150‐R600a‐R290, R1150‐R601a‐R600a, and R170‐R601‐R290 are determined as the three most promising working fluids combinations. Under optimized conditions, the output power range is 199.97 to 218.51 kW, the energy efficiency range is 13.64% to 15.62%, and the exergy efficiency range is 25.29% to 27.3%. The payback period ranges from 8.36 to 8.74 years. The working fluids selection helps to reduce the exergy destruction of intermediate heat exchanger, which could be up to 30.59%. [ABSTRACT FROM AUTHOR]

• An experimental RORC system using liquid nitrogen as the cold sink has been built. • Effect of heating and cooling capacities on system performance are examined. • A guidance for the operation of gasification stations has been provided. • MSHE is high efficiency, low cost, but also high exergy destruction. A large amount of available cold energy exists in Liquid Natural Gas (LNG). While it is not efficiently utilized and is released into the ocean. To efficiently utilize LNG cold energy, a power generation test bench based on the organic Rankine cycle has been established with R290 as the working fluid, a scroll expander as the thermal conversion device, and a multi-stream heat exchanger as the high-efficiency heat exchange device. The low-grade heat source and LNG are simulated by electrically heated hot water and −198 °C liquid nitrogen. The following are the main conclusions: (1) Heating and cooling capacities have different degrees of influence on system performance, and there is a matching relationship between the two capacities; (2) system maximum thermal efficiency and cold energy utilization rate are 6.13% and 12.04%, respectively. The comprehensive performance reaches the highest when the ratio of heating-to-cooling capacity is 1.96; (3) among the main components in the system, the increasing proportion of expander exergy destruction plays a positive role in improving the total system exergy efficiency. While the increasing proportion of heat exchangers exergy destruction has a negative influence in system exergy efficiency. [ABSTRACT FROM AUTHOR]

In this paper, a combined organic Rankine cycle (ORC) system that can effectively utilize the cold energy of Liquefied Nature Gas (LNG) and the waste heat of dual fuel (DF) marine engine was proposed. Particularly, the engine exhaust gas and the jacket cooling water of the DF marine engine were used as heat sources. Firstly, a thorough assessment of thermo-economic performance was conducted for the combined ORC system using 11 environmentally friendly working fluids (WFs). Afterwards, the effects of evaporation and condensation pressures on the net output work, energy efficiency, exergy efficiency, total investment cost and payback period were examined. Furthermore, the thermo-economic performances of the ORC system were optimized via multi-objective optimization with a genetic algorithm. Finally, exergy destructions and investment costs of each component under the optimal operating conditions were analyzed to make suggestions for further improvement. The results show that R1150-R1234yf-R600a and R170-R1270-R152a are the two most promising WF combinations. The exergy destruction of the combined ORC system mainly exists in heat exchangers. Through WF optimization, the exergy destruction in the intermediate heat exchanger was reduced by 18.99%. The proportion of expanders investment cost could be greater than 50% and the payback period of the combined ORC system varies in the range of 7.68–9.43 years. This study demonstrated that the selection of WF and the optimization of operating conditions had important potential to improve thermo-economic performances of ORC systems. [ABSTRACT FROM AUTHOR]

• A novel onboard CO 2 capture system is proposed based on zero energy increment. • Ship waste heat and LNG cold energy are recovered for the proposed system. • 4E analyses and multi-objective optimization of the system are carried out. • CO 2 capture cost and payoff period are optimized at 95.6 $/tonCO 2 and 11.3 years. • Zero energy increment CO 2 capture system is feasible in maritime industry. In this paper, a novel zero energy increment onboard carbon capture (ZEIOCC) system was proposed. With LNG cold energy and waste heat recovery, the ZEIOCC system integrated organic Rankine cycle (ORC), CO 2 liquification, and CO 2 capture unit. The ZEIOCC system performances were evaluated via energy, exergy, economic, and environmental (4E) analyses. Parametric studies were performed to investigate the effects of the flue gas mass flow rate (m fg), liquid to gas ratio (L/G), and the pinch point temperature difference at the outlet of the ORC condenser (T pin) on the system performance indicators. Furthermore, multi-optimization was conducted with the product of energy-exergy efficiencies (η en,sys * η ex,sys), the total capital investment cost (C I,tot), and the carbon reduction capacity (ξ) as objective functions. Two decision methods TOPSIS and LINMAP were introduced to find the most optimal point from the Pareto front. Under the basic condition, the proposed system proved its advantages of high efficiency, diversified energy output, fast return on investment, and efficient CO 2 capture capacity. The results of optimization showed that the system performances meet all the requirement of the design goal. The optimal energy-exergy efficiencies is 10.06 %, the carbon reduction capacity is 28.01 %, and the total capital investment cost is 7.06 × 106 $. Under the optimal condition, the system net output power (W net), energy efficiency, and exergy efficiency are 12 kW, 20.53 %, and 49.02 %, respectively. Meanwhile, the payoff period (POP) and the CO 2 capture cost (CCC) are 12.0 year and 99.9 $/tonCO 2 , respectively. [ABSTRACT FROM AUTHOR]

In this paper, three machine learning algorithms (Random Forest (RF), Support Vector Regression (SVR), and Long Short Term Memory (LSTM)) were used to predict and compare the thermodynamic performance of a 1 kW Organic Rankine Cycle (ORC) system under cryogenic operating conditions (i.e., cold source temperature < −160 °C). The cryogenic ORC system uses liquid nitrogen as the cold source, hot water as the heat source, and propane as the working fluid. Ten key operating parameters were selected as input parameters through Variable Importance Measures, and the output work of the expander, the cold exergy efficiency, and the system exergy destruction were used as output parameters. Moreover, the multi-objective optimization of this experimental system was conducted by applying the Non-dominated Sorting Genetic Algorithm III. The results showed that the RF algorithm was the most suitable algorithm among the three machine learning algorithms. According to the optimal results of the prediction model, the maximum error was 5.0251%, which was relatively small compared to the optimal results under experimental conditions. The related results demonstrate the feasibility of machine learning for cryogenic ORC data prediction, which can guide the design and improvement of ORC systems under low-temperature cold source conditions. • Performance of a 1 kW-scale cryogenic Organic Rankine Cycle (ORC) is predicted. • Three machine learning algorithms are used for prediction and system optimization. • Random Forest is more suitable for predicting output work and exergy destruction. • Support Vector Regression is more suitable for predicting cold exergy efficiency. • Maximum error for predicted optimal results and experimental results is 5.0251%. [ABSTRACT FROM AUTHOR]

This paper proposes a solar-ocean thermal energy conversion system (S-OTEC/AC) with integrated air conditioning cycles to provide power, cooling capacity, and fresh water in the South China Sea. Solar energy and surface seawater are used as heat sources in S-OTEC/AC system, the deep-sea water is used to absorb heat. The organic Rankine cycle (ORC) is selected as the main cycle of OTEC, with R134a as the working medium. In order to improve the sustainability of the system, energy, exergy, economic, and environmental (4E) analysis models were proposed for the system. Parametric studies are performed to investigate the effects of R134a temperature at the evaporator outlet, turbine inlet, and outlet pressures, and water flow rate of solar heater on the system performance indicators. Furthermore, multi-optimization is conducted with the Levelized Cost Of Energy (LCOE) and the product of energy-exergy efficiencies (η en,sys * η ex,sys) as objective functions. The linear programming technique of multi-dimensional preference analysis (LINMAP) is introduced to make decisions on the Pareto front. Under basic conditions, the S-OTEC/AC system performs superior to the S-OTEC system in terms of energy, economy, and environmental friendliness. The additional profits of the AC cycle are represented by the annual water fee saving of 3.6x104 $/year and the cooling capacity of 85.8 kW, respectively. Sensitivity results show that water flow rate of solar heaters has the most obvious influence on system performance among the four key parameters. The results of optimizing the non-dominant scheme suggested by Pareto point show that optimized LCOE is 1.18 $/kWh, and η en,sys * η ex,sys is 7.81%. Under this condition, the system's network output, energy efficiency, and exergy efficiency are 89.32 kW,14.09%, and 52.83%, respectively. [Display omitted] • A new S-OTEC/AC system based on the South China Sea is proposed. • The new system is superior to the traditional S-OTEC system in all aspects. • 4E analyses and multi-objective optimization of the system are carried out. • LCOE and the product of energy-exergy efficiency are selected as target functions. • The freshwater revenue reaches 2.28x104 $/year under optimal conditions. [ABSTRACT FROM AUTHOR]

In this study, a recuperative organic Rankine cycle (ORC) was designed with a three-fluid condenser for cryogenic cold energy recovery. An experimental setup with R290 as working fluid was constructed. Hot water and liquid nitrogen were the heat source and heat sink, respectively. The ORC performances were investigated under different heat source temperatures and heat sink flow rates. Both conventional and advanced exergy analyses were carried out based on the obtained experimental data. The optimum working condition was identified as the heat sink flow rate at 100 kg/h and heat source temperature at 45 °C. The results showed that the largest net power of the cryogenic recuperative ORC was 1.02 kW, the maximum thermal efficiency was 8.8%, and the maximum cold energy utilization efficiency was 22.5%. The conventional exergy analysis identified the condenser, which accounted for 62.6% of the total exergy destruction, as the priority of system optimization. However, the priority was ascribed to the expander based on the advanced exergy analysis, which showed that the avoidable endogenous exergy destruction rate of the expander was up to 54.0%. The findings would provide technical guidelines for the development and performance optimization of cryogenic ORCs. • Energy, conventional exergy and advanced exergy analyses were employed. • The highest net power output and thermal efficiency were 1.02 kW and 8.8%. • Exergy destruction of 60.5% in the system were unavoidable. • The improvement potential of condenser was limited by practical factors. [ABSTRACT FROM AUTHOR]

• A one-dimensional model of Tesla turbine for wet working fluids is proposed. • Thermodynamic performance of five wet working fluids in Tesla turbine is analyzed. • Tesla turbine using R22 has the highest efficiency at low rotor speed conditions. • Tesla turbine with R417a has the maximum output power in most operating conditions. • Optimum rotor speed and rotor gap distance exist for each working fluid. In the field of clean energy, Organic Rankine Cycle (ORC) is considered a vital method to utilize low-grade waste heat effectively. Due to certain application advantages in low power level ORC systems, the Tesla turbine is considered one of the essential choices for the core components of ORC systems. Given the inadequacy of the current research on the performance of the Tesla turbine under two-phase flow conditions, a one-dimensional model of the Tesla turbine was constructed in this paper to make it equally applicable to the two-phase flow conditions of wet working fluids. A model of the Tesla turbine and ORC system was constructed from the thermodynamic point of view, and five typical wet working fluids (R22, R417a, R134a, R152a, and R290) were selected to study the effects of the five wet working fluids on the thermal performance of Tesla turbine and ORC system. The effects of the changes in key structural parameters of the Tesla turbine on the performance of the Tesla turbine and the ORC system were further analyzed when different wet working fluids were used in the ORC system. The results showed that the highest turbine efficiency of 42.0 % was achieved when the Tesla turbine used R22 as the working fluid under the design conditions, while the highest turbine output power and the highest system thermal efficiency of 1.19 kW and 3.96 % were achieved when R417a was used as the working fluid. The analysis of the key structural parameters of the system showed that for the five different wet working fluids, the turbine efficiency, turbine output power, and system thermal efficiency increased monotonically with increasing rotor inlet radius. For each of the five wet working fluids, an optimum rotor speed, rotor outlet radius, and rotor gap distance exist, resulting in optimal turbine efficiency and system performance. The related work provides an important reference for the optimal design of Tesla turbines with wet working fluids. [ABSTRACT FROM AUTHOR]

In this paper, a novel negative carbon-emission, cooling, and power generation (NCCP) system was proposed to improve the energy efficiency of the liquid natural gas (LNG)-powered hydrogen production plant. With LNG cold energy and waste heat recovery, the NCCP system integrated organic Rankine cycle (ORC) power generation, data center cooling, and CO 2 capture. The NCCP system could operate under seven scenarios and the system performance evaluations were performed via energy, exergy, economic and environmental (4 E) analysis. It was found that the NCCP system showed the best performance when all subsystems were running simultaneously. The system could produce 31.67 MW of power, 24.92 MW of cooling capacity, and 29.97 t/h of CO 2 capture. The levelized energy cost and the payback period of the NCCP system were 0.071 $/kWh and 7.9 years, respectively. LNG cold energy utilization efficiency, system energy efficiency, and exergy efficiency were 43.20%, 19.08%, and 29.28%, respectively. The environmental profits are validated with the negative carbon index of 29.47 t/h. Moreover, the effects of the LNG pressure, flue gas mass flow rate, and the temperature of the medium temperature shift gas on the NCCP system performances were investigated. The results show that the proposed system is a polygeneration system with the advantages of high efficiency, diversified energy output, fast return on investment, and CO 2 capture. It is expected to be an energy conversion technology that could be used for reference in practical applications. [Display omitted] • A flexible polygeneration system is proposed for LNG cold energy recovery. • The system energy efficiency and exergy efficiency are 19.08% and 46.88%. • Environmental profits are validated with the negative carbon index of 29.47 t/h. • The payback period of the system is 7.9 years. [ABSTRACT FROM AUTHOR]

In this paper, a performance prediction model of the cryogenic ORC was presented based on the back propagation neural network optimized by the genetic algorithm (BPNN-GA). Firstly, an experimental setup was established to obtain the database for BPNN-GA model training and test. Then, the expander output power, working fluid mass flow rate, and the cold energy efficiency were selected as the BPNN-GA model outputs and the model structure was determined as 9-12-3. Finally, the accuracy of the BPNN-GA model was verified, and the parametric study was further conducted. The mean absolute relative errors (MARE) are 1.1876%, 0.9037%, and 2.6464%, the root mean square errors (RMSE) are 5.3789 W, 1.0260 kgh−1, and 0.3151%, and the correlation coefficients (R) are 0.9974, 0.9977, and 0.9665 for the expansion work, the working fluid mass flow rate, and the cold energy efficiency, respectively. The BPNN-GA is proved as a promising methodology, which could provide direct guidance for the determination of relevant parameters in experimental analysis and control strategy optimization. • The performances of a recuperative cryogenic ORC were predicted by BPNN-GA. • 10270 sets of data for BPNN training and test were obtained with experiments. • The effect of hidden neuron number on the BPNN-GA model was discussed. • BPNN was determined as 9-12-3 with the correlation coefficients in 0.9665–0.9977. • Parametric analyses of the recuperative ORC were carried out. [ABSTRACT FROM AUTHOR]

In this paper, experimentally studies of a 1 kW-scale organic Rankine cycle (ORC) with R290 as working medium were carried out for cryogenic cold energy recovery. Specifically, a three-fluid wounded tube heat exchanger was utilized as the condenser and the recuperator, which made the system operate under the basic ORC (bORC) and the recuperative ORC (rORC) working modes. The hot water and the liquid nitrogen were respectively used as the heat source and cold source. The system performances were evaluated at 20–50 °C of the heat source, −170∼-160 °C and 60–120 kg/h of the cold source. The optimal heat source temperatures were obtained for the different cold source conditions. Moreover, the superiority of the rORC was verified. The results demonstrated that the maximum net power outputs were 0.673 kW and 0.894 kW for the bORC and rORC, respectively. For the bORC and the rORC, the maximum energy efficiency was 5.23% and 6.49%, and the maximum exergy efficiency was 21.34% and 28.99%, respectively. The cold energy efficiency varies in the range of 1.73%–14.20% and 1.16%–19.72% for the bORC and rORC, respectively. The three-fluid recuperator occupied the largest exergy loss, which varied in the range of 66.59–84.12%. • An ORC with three-fluid recuperator was proposed for cryogenic cold energy recovery. • The optimal heat source temperatures were obtained under different conditions. • With the recuperator, the maximum energy efficiency increased from 5.23% to 6.49%. • The cold energy efficiency could be increased by 101.7% via the recuperative process. • The three-fluid recuperator occupied the largest exergy loss ratio. [ABSTRACT FROM AUTHOR]