Heat Source Temperature Research Articles

Development and experimental study of a 3-dimensional enhanced heat pipe radiator for cooling high-power electronic devices

A 3-dimensional enhanced heat pipe radiator (HPR) is developed to meet the requirements of heat dissipation and temperature uniformity in the cooling of high-power electronic components. The radiator is composed of a conventional flat heat pipe base and roll-bond flat heat pipe fins, which can enhance heat transfer in three dimensions. By means of experiments, the heat transfer characteristic is firstly studied under different filling ratios for a single roll bond flat heat pipe. Then, a comparison is performed of the heat transfer performance between the HPR and the conventional aluminum fin radiator (CAFR) under different heating powers and wind speed conditions experimentally. In this research, HPR demonstrates obvious advantages in the heat transfer. Results show that the optimum filling ratio is 35% for the roll-bond flat heat pipe. The start-up time of HPR is shorter (25 mins), and the start-up performance is not affected by power variation. HPR has a low thermal resistance of less than 0.48 °C/W compared with CAFR, which can effectively control the heat source temperature difference is about 1.7 °C–1.8 °C. The maximum heat dissipation of HPR and CAFR is almost the same under natural convection condition. But when the wind speed is 4 m/s, the maximum heat dissipation of HPR increased by 58.2% compared to the maximum heat dissipation of CAFR.

Advanced exergy analysis of a double absorption heat transformer recovering industrial waste heat for pure water production

Conventional and advanced exergy analyses are applied for a double absorption heat transformer system utilizing low-grade industrial waste heat for water purification. The conventional method provides information about the location and magnitude of inefficiencies and does not consider any interaction among components regarding the irreversibility occurring in them. The advanced exergy technique however, exposes the real origins of irreversibilities and latent potential for enhancement of each system component, along with reflecting mutual interaction between components. The simulation of the cycle is carried out with engineering equation solver software. The results show that the overall improvement potential of the cycle is only 16%. Also, the mutual interdependency between components is found to be weak as 97% of the total exergy destruction appeared as endogenous. Furthermore, considering endogenous avoidable exergy destruction, the improvement strategy of components obtained by advanced exergy method is disparate from conventional one. Results of the advanced exergy suggest this order: condenser, absorber, evaporator, absorber/evaporator assembly, generator assembly, economizer 1, and economizer 2. Additionally, a parametric investigation is performed to assess the sensitivity of splitting exergy destruction to the variation of heat source temperature for highlighting improvement opportunities. The results indicate that the condenser yields the highest amount of avoidable endogenous exergy destruction in the entire studied temperature range.

Global sensitivity analysis and optimization of a multistage thermoelectric generator based on failure probability

Thermoelectric generator (TEG) is a thermoelectric conversion device that mainly utilizes the Seebeck effect, and the electrical energy generated is usually directly converted from thermal energy. However, research on the global sensitivity analysis and optimization of three-stage TEG systems is currently lacking. In this study, a multistage semiconductor TEG system model based on functional failure probability and a global sensitivity analysis model were established. These models are first used to compare the performance of TEG configurations with different stages. Then, based on the double random uncertainties of design variables, a series of studies were conducted. The results showed that the performance parameters of the all TEG configurations exhibited similar performance variation trends. An first-best working current was identified to obtain the first-best output power and conversion efficiency. Next, as the sample size used to determine the variable uncertainty for a three-stage TEG increased, it increased to 4 × 106, the sensitivity indicators of the output response (P and η) tended to constant values of 0.02322 and 0.02039. Among the 11 considered design parameters, the uncertainties of the heat and cold source temperatures had the most significant influence on the functional failure probability of the three-stage TEG system, followed by the working current, Zeebek coefficient, number of temperature difference components in each stage, and heat transfer coefficient of the cold source. The remaining variables had negligible influence. Finally, small changes in the mean heat and cold source temperatures changed the sensitivity of the output response of the three-stage TEG to each critical design variable, but did not affect the relative ranking of the sensitivity indicators corresponding to each. The results of this study can provide some basis for the further development of TEG systems.

Modelling and performance assessment of a two-bed adsorption chiller at different operating conditions

The study aims to assess the performance of an adsorption chiller using the Maxsorb III-methanol as an adsorbent pair. A modified transient lumped parameter model was developed to evaluate the dynamic behavior of the system at various operating parameters. Methanol is used as refrigerant as it has a significant latent heat of evaporation, high normal boiling point, low melting point and environmentally friendly. The results showed that the modified transient lumped parameter model can predict well the dynamic behavior of the adsorption chiller under different operating conditions. The system was able to produce about 13.65 kW (227 W kg-1) cooling capacity with a thermal COP of 0.73 at 85 and 30 oC driving source and cooling temperatures respectively. In addition, simulation tests were made to compare the performance of the Maxsorb III-methanol system with the different working pairs at the same physical dimensions of the present system components and operating parameters. At heat source temperatures of 85 oC which can be gained from waste heat or solar energy, the COP of the Maxsorb III-methanol cycle was about 12.0%, 44.0% and 6.6% higher than that of ACF-ethanol, silica-gel-water and activated charcoal/methanol cycles. The Maxsorb III/methanol adsorption cycle can work effectively with low grade heat sources, which can be gained from renewable energy or waste heat sources.

Modelling and performance assessment of a two-bed adsorption chiller at different operating conditions

The study aims to assess the performance of an adsorption chiller using the Maxsorb III-methanol as an adsorbent pair. A modified transient lumped parameter model was developed to evaluate the dynamic behavior of the system at various operating parameters. Methanol is used as refrigerant as it has a significant latent heat of evaporation, high normal boiling point, low melting point and environmentally friendly. The results showed that the modified transient lumped parameter model can predict well the dynamic behavior of the adsorption chiller under different operating conditions. The system was able to produce about 13.65 kW (227 W kg-1) cooling capacity with a thermal COP of 0.73 at 85 and 30 oC driving source and cooling temperatures respectively. In addition, simulation tests were made to compare the performance of the Maxsorb III-methanol system with the different working pairs at the same physical dimensions of the present system components and operating parameters. At heat source temperatures of 85 oC which can be gained from waste heat or solar energy, the COP of the Maxsorb III-methanol cycle was about 12.0%, 44.0% and 6.6% higher than that of ACF-ethanol, silica-gel-water and activated charcoal/methanol cycles. The Maxsorb III/methanol adsorption cycle can work effectively with low grade heat sources, which can be gained from renewable energy or waste heat sources.

Experimental investigation and thermodynamic modeling of adsorption equilibria of MSC30 with R32 for supercritical adsorption cooling systems

In the present study, the adsorption isotherms of difluoromethane (R32) on the activated carbon (MSC 30) throughout a temperature range of 25 °C to 150 °C and pressures up to 3000 kPa are measured for possible application in adsorption cooling systems. The Dubinin-Astakhov model was used to fit the experimental data. A thermodynamic model is proposed in this study to investigate the adsorption potential under supercritical conditions. The model is validated using the isotherm data from the experiments and literatures for different working pairs. The validation results exhibited a good agreement between the proposed model and the experimental data, signifying the precision and dependability of the model. The corresponding adsorption isosteric heat model was derived and verified, taking into account both the inclusion and exclusion of the adsorbed volume correction. Furthermore, the developed models were utilized in the equilibrium analysis of an adsorption heat pump to evaluate the performance of the system in terms of the theoretical coefficient of performance (COP) and specific cooling energy (SCE). The analysis covered the driving heat source temperature ranging from 30 °C to 150 °C, with different evaporation temperatures and adsorption temperatures. The results showed that the maximum COP value of 0.47 for the adsorption heat pump system employing the MSC30+R32 pair was achieved at a desorption temperature of 115 °C, at which the SCE was 315.5 kJ·kg−1. The results can potentially improve the accuracy of predicting adsorption behavior and contribute to the development of more efficient and effective adsorption systems.

Thermodynamic and economic analysis of a novel thermoelectric-hydrogen co-generation system combining compressed air energy storage and chemical energy

With the adjustment of energy structure, the proportion of renewable energy is gradually increasing, and how to solve the problem of renewable energy consumption is becoming more and more prominent. Therefore, a novel thermoelectric-hydrogen co-generation system combining compressed air energy storage (CAES) and chemical energy (CE) is proposed. For energy storage, the system uses adiabatic compression with liquid piston to reduce the generation of compression heat, while using the generated compression heat to preheat the methanol. For energy release, the methanol is fed into the methanol steam reforming reactor (MSR) and the methanol decomposition reactor (MDR) in certain proportions for the hydrogen production reaction; the unreacted methanol and the carbon monoxide produced by the MDR are used as make-up heat for the reactors and the high-pressure air before the turbine, while the exhaust waste heat supplies heat to the customer. The thermodynamic, economic and environmental performances of the system were investigated separately by developing a mathematical model describing the system. The results show that under the design conditions, the system has an energy storage density of 12.00 kWh/m3, an energy efficiency of 88.47 %, an exergy efficiency of 77.04 %, a lifetime net present value of 59.20 M$, a payback period of 4 years, and a CO2 emission per unit of energy output of 227.85 kg/MWh. Increasing the thermostatic heat source temperature and increasing the reactor diameter and length increased the methanol conversion rate. Increasing heat exchange effectiveness of the heat exchanger and heat source temperature can all improve system thermodynamic and economic performance. The energy storage density, energy efficiency, net present value and profitability of the system varied parabolically with the reactor tube diameter. The system energy storage density had a maximum value of 12.03 kWh/m3 at a reactor diameter of 0.040 m.

Experimental and numerical study on transportation performance of ionic wind generator with distributed auxiliary heat source

Ionic wind technology can be used to achieve directional airflow transportation and local heat and mass transfer enhancement, which are suitable in the field of food drying. Ionic wind can be coupled with medium- and low-temperature heat sources to achieve collaborative heat and mass transfer while satisfying the requirements of efficient drying and maintaining food quality. However, the distributed heat source introduces ambient temperature gradients. Notably, different ambient temperature gradients of the generator exert obvious effects on the local molecular number as well as particle energy; this can affect the gas transportation performance of the generator, which has not been clarified thus far. Herein, the gas transportation performance of a wire-mesh ionic wind generator operating at different heat-source temperatures is experimentally and numerically investigated. The experimental results show that ionic wind generators operating at normal atmospheric temperature are more beneficial to obtaining a high mass flow rate and local velocity of ionic wind. Additionally, continuously increasing the heat source temperature can improve the transportation performance of ionic wind generators. In the simulation, an electrohydrodynamic (EHD) force is introduced to indicate ionic wind strength. The simulated EHD force reaches the highest value without a temperature difference between the two electrodes. The variation trend of the simulation results is consistent with that of the experimental results. The simulation results emphasize the combined effects of particle energy and air molecule number on ionic wind strength, which can explain the phenomena observed in the experiments. This study thus provides a theoretical guideline for the design and combined application of ionic wind generators and distributed auxiliary heat sources.

Experimental validation of a 0.3 kW ORC for the future purposes in the study of low-grade thermal to power conversion

Organic Rankine cycle (ORC) is a promising development direction for energy conservation and environmental protection, as it can effectively convert low-temperature waste heat into mechanical work. This article focuses on the experimental performance study of what is likely the world's smallest scroll expander used in a 0.3 kW micro-ORC system. The system uses R1233zd-E as the working fluid, and the expander is repurposed from a scroll compressor of an air conditioner, with a displacement of 11.1 mL/rev. In the first part of the experiments, the influence of the system pressure difference and the expander rotational speed on the system performance is investigated while keeping the expander inlet superheating fixed. The maximum system efficiency, expander efficiency, and power output were 5.46 %, 72.4 %, and 0.266 kW, respectively. In the second part of experiments, the effect of changing the heating source temperature on the system is explored while keeping the expander rotational speed and inlet pressure fixed. As the superheat increased, both the expander and cycle efficiency increased. In addition, this study combines the experimental results with previous data on small-scale ORC systems and discusses the similar trends, indirectly demonstrating that the 0.3 kW micro-ORC can achieve similar behavior as predicted in a large-scale ORC.

Investigation of the thermal response characteristics of the loop thermosyphon under convective boundary conditions

The two-phase loop thermosyphon (TPLT) is a highly efficient passive heat transfer device that is widely applied in various fields. This paper experimentally and numerically investigates the thermal response performance of a large-scale TPLT under various convective boundary conditions. Experimental studies have been carried out to explore the effects of different working fluids, filling ratios, cold and heat source temperatures, and mass flow rates on the thermosyphon’s performance. Meanwhile, a two-dimensional Computational Fluid Dynamics (CFD) simulation model of the TPLT is established and validated. The results indicate that the start-up procedure of the TPLT is highly dependent on the heat source temperature and the working fluid. Normally, the TPLT can start when the heat source reaches a certain temperature. In general, using methanol as the working fluid is more favorable to start-up compared to the water and ethanol TPLTs. The experimental results also show that the heat transfer capacity of the TPLT increases with increasing heat source temperature while increasing cooling temperature decreases heat transfer capacity. The best heat transfer performance of a TPLT charging methanol is observed at a filling ratio of 70 % with a heating mass flow rate of 1 L/min. At that point, the convective heat transfer coefficient of outside the evaporator is 1036.7 W/(m2·K). Moreover, the simulation results reveal that the average wall heat flux of the TPLT’s evaporator initially decreases and then gradually stabilizes with time. During stable operation, the wall heat flux density of the evaporator exhibits an initial increase in the pool section followed by a subsequent decrease with increasing wall height. This work provides insight into the heat and fluid flow characteristics of the TPLT under convective boundary conditions.

Synergetic characteristic of a novel thermally-driven CCHP system based on supercritical and transcritical CO2 cycles

A novel poly-generation system is proposed based on supercritical carbon dioxide (SCO2) Brayton cycle and transcritical carbon dioxide (TCO2) refrigeration cycle to meet the seasonal energy demand in buildings. The thermodynamic model of the combined cooling, heating and power (CCHP) system was constructed based on the laws of thermodynamics, and seasonal operation modes were also analyzed. The Techno-economic performance of CCHP system was analyzed and compared with the single output systems and organic working fluids. The results show that the temperature of the turbine inlet in SCO2 cycle should be close to the heat source temperature and the temperature of the condenser outlet should be close to the critical temperature. The optimal pressure of the condenser outlet for coefficient of performance is about 9.3 MPa, while it is 8.6 MPa for power generation. The optimum thermodynamic and economic performance cannot be achieved simultaneously. The power generation of CO2 is 13.13% worse than that of organic working fluids and coefficient of performance of former is worse than that of latter. As the manufacturing cost goes down over time, the CCHP system based on CO2 will further improve its economic performance in the future.

Thermo-economic evaluations of novel dual-heater regenerative organic flash cycle (DROFC)

Organic Flash Cycle (OFC) is a promising waste heat utilization technique for low and medium temperature. However, throttling exergy loss in the flash and throttling processes substantially reduces the efficiency of basic organic flash cycle (BOFC). The regenerative organic flash cycle (ROFC) can avoid the exergy loss in the throttling process and enhance the thermodynamic performance of OFC. This paper proposes a novel dual-heater regenerative organic flash cycle (DROFC), which can obtain more power output by reducing the flash process exergy loss and eliminating the mixer exergy loss in ROFC. The thermo-economic performance of DROFC was compared with BOFC and ROFC to evaluate its application potential. Eight low-GWP pure organic fluids were selected and the heat sources were 100–200 °C. Results indicate that DROFC could produce more net power output than BOFC and ROFC with a lower specific investment cost. Specifically, with R600 as an example, the maximum net power output percentage gain of DROFC is 41.19% and 29.09%, respectively. DROFC is more suitable for application scenarios where the heat source temperature exceeds the critical temperature of organic fluid. To balance the net power output and levelized cost of electricity, Hydrocarbons with a high critical temperature are appropriate for DROFC.

Experimental study on heat transfer during melting in metal and carbon foam saturated with phase-change materials for temperature control in electronic devices

Porous media embedded in phase-change materials (PCMs) have been widely applied to thermal management of electronic devices, whereas the influence mechanisms of the suppression of the natural convection of liquid PCM by the porous skeleton and anisotropy of the skeleton on the temperature response of the heat source are still unclear. In this study, an isotropic metal foam and several anisotropic carbon foams are embedded in paraffin and higher alcohol, respectively. The influences of copper-foam skeleton on the PCM natural convection, the evolution of PCM melting front, and the variation of heat-source temperature are studied. The effects of carbon-foam skeleton on the directionality of phase-change heat transfer and the variation of heat-source temperature are investigated. The embedding of metal foam can reduce the heat-source temperature, postpone the onset of PCM melting and the appearance of natural convection, and shorten the PCM melting duration mildly. The anisotropy of carbon foams causes the out-of-plane thermal conductivities of carbon-foam/PCM composites to be larger than the in-plane thermal conductivities. The composite with a low porosity possesses a low melting temperature and short duration of PCM melting process. The increase in ambient temperature causes the time required to trigger the melting of the carbon-foam/PCM composite to decrease but does not affect the melting duration. Conversely, an increase in heat flux reduces the melting duration.

Thermally regenerative electrochemically cycled flow battery coupled with radiative cooling for low-grade heat harvesting

Low-grade heat sources below 100 °C provide a vast quantity of energy, yet harvesting them has been a longstanding challenge due to the limited and fluctuating temperature difference between the low-grade heat sources and the environment. Through thermo-electrochemical modeling, this work shows that coupling a thermally regenerative electrochemically cycled flow battery (TREC-FB) with radiative coolers can lead to an additional operating temperature difference of 11.8 °C, a 36.9% enhancement in energy density, and a maximum efficiency of 3.7% when the heat-source temperature fluctuates between 20 and 60 °C with a heat recuperation effectiveness of 70%. Our model also captures the coupled effects of mass transfer and electrochemical kinetics in affecting power density and efficiency, and we showed that ohmic losses due to internal resistances, and mass transfer overpotential inside the porous electrode are the major factors limiting the power density and efficiency. Finally, we predict that if the effective thermopower of electrolytes can reach 5 mV/K, a maximum power density of 8 W/m2, and a relative efficiency (ηth/ηC) of 20.5% can be achieved, with ηth and ηC denoting the efficiency and the Carnot limit respectively.

Performance analysis of zeotropic mixture as a working fluid for medium temperature in regenerative Organic Rankine cycle

Energy consumption is a never-ending need so, for levelizing the energy demands the efficient recovery of waste heat is a crucial mechanism to address energy and environmental problems. Organic Rankine cycle is the most technically feasible and promising approaches for recovering waste heat. To augment the system performance and technology economic viability, the opted fluid plays a vital role. So, zeotropic fluid acts as a best candidate by showing a proper match with the temperature of heat source as a result enhances the thermodynamic performance of Organic Rankine cycle system. In this study a detailed thermo-economic analysis of regenerative Organic Rankine cycle to recover medium temperature waste heat from glass industry employing zeotropic mixtures of cyclohexane + benzene, toluene + benzene, toluene + nonane and cyclohexane + nonane as a viable working fluid at 0.5 mass fraction. Result reveals that, at 375 °C hot gas inlet temperature the maximum power, energy and exergy at respective parameters are 1132.96 kW, 50.15 % and 75.53 % by using cyclohexane + benzene. Economic analysis shows the maximum operating cost of 118.8 $/h. Likewise, the impact of hot gas input temperatures are investigated for the best mixture at a mass fraction of 0.1–0.9.

Performance analysis of the Thermo Osmotic Energy Conversion (TOEC) process for harvesting low-grade heat

Low-grade heat energy from resources below 100 °C is readily available in massive quantities worldwide. However, existing technologies face challenges in converting this heat power into usable forms of energy, such as electricity. This is primarily due to temperature fluctuations in these heat sources and the limited temperature gradient with the surrounding environment. To address this issue, a recently developed technology called thermo-osmotic energy conversion (TOEC) offers a promising solution for harvesting electrical energy from low-grade heat sources. In the TOEC method, a hydrophobic membrane facilitates the transfer of water vapor molecules from a moderately hot aqueous solution to a cold water stream. The resulting hydraulic pressure in the compressed water on the cold side can be harnessed using a hydro-turbine. Despite the many interesting features of TOEC technology, a comprehensive analysis of its performance under various operating conditions and membrane properties is currently lacking in the literature. In this study, we conducted a theoretical evaluation of the TOEC process based on mass and heat transfer phenomena, and we validated our findings with experimental data. Our results indicate that employing membranes with smaller pore size, low thickness, and high porosity, along with higher feed temperature and flowrates, can significantly enhance energy efficiency and power density. Specifically, we demonstrate that the utilization of hydrophobic membranes with nanometer-sized pores, coupled with hydraulic pressures ranging from 6.2 bar to 11.8 bar, enables us to achieve power densities exceeding 5 W/m2, given a 20 °C heat sink and a heat source temperature above 65 °C. Furthermore, we have determined that an applied hydraulic pressure of 9.4 bar yields the maximum energy efficiency value of 0.016%.

Simulation study of R134a based vapour compression-adsorption hybrid chiller with activated carbon as adsorbent

Vapour adsorption is one of the viable routes for producing refrigeration from low-grade thermal energy. This paper presents the simulation study of a proposed novel hybrid chiller combining a R134a based vapour compression refrigeration (VCR) chiller with a single-bed vapour adsorption (VAd) chiller. The proposed system layout leads to minimal thermal inventory and it also ensures that the VAd system can be integrated with any pre-existing R134a VCR system. The performance of proposed hybrid chiller is compared with the standalone VCR system. Maxsorb-III (MX-III) and a low cost Coconut shell based activated carbon (CSAC) are chosen as the two adsorbents for this comparative study. When compared to standalone VCR system, the hybrid system shows a maximum increment of 50% and 9% in peak refrigeration capacity for 30 kg MX-III and CSAC as adsorbents respectively. Time-averaged specific cooling capacity (SCC) and COP ratio of hybrid to standalone VCR system is used as performance parameters in the present study to evaluate optimum adsorption time, which lies between 450 and 750 s. This paper also presents the evaluation of practical minimum desorption heat source temperature of the hybrid system. For both the adsorbents, minimum desorption temperature lies in the range of 62–71 °C making this hybrid system suitable for both industrial waste heat as well as non-concentrating type solar based heat source.

Daily sorption thermal battery cycle for building applications

The study propose firstly an absorption thermal energy storage (ATES) system designed for repeated operations on a daily base without any additional manipulation. The performance of the sorption thermal battery was analyzed by varying four parameters (mass flow ratio, number of exchanger heat transfer units (NTU), heat source, and cooling water temperature). The lower the cooling water temperature, the better was the performance, particularly for improving the energy storage density (ESD). Additionally, if low-temperature cooling water is used, the coefficient of performance (COP) with a 65 °C heat source is comparable to that with 95 °C. ESD increased with the increasing the heat source temperature, and the maximum COP was obtained when using a 75–85 °C heat source. To solve the crystallization problem, [DMIM][DMP], a type of ionic liquid, was applied as an absorbent. However, the COP of H2O-[DMIM][DMP] with a heat source temperature of 120 °C was lower that of H2O–LiBr with 95–100 °C. Therefore, it is advantageous to use H2O–LiBr to improve the sorption thermal battery performance. ESD and COP of the sorption thermal battery are 451.13 kJ/kg and 0.728, respectively, when using a 95 °C heat source and 32 °C cooling water.

Comparison Of The Electricity Generation Potentials Of Solar ORC Designed With Different Fluids Depending On Instantaneous Solar Radiation In Four Districts Of Türkiye

In this study, the solar Organic Rankine Cycle (ORC) system was analyzed to meet some of the electrical energy needed in large and medium-sized buildings and large enterprises such as hotels from solar energy. A simulation study was conducted for different districts in Türkiye that are rich in solar energy potential. These counties and the provinces they are affiliated with; Silifke-İçel, Alanya-Antalya, Bodrum-Muğla, Çeşme-İzmir. The power value transferred to the ORC was determined by considering the instantaneous radiation values and sunshine durations for the districts. The performance of solar ORC was determined by comparing fluids from three different organic fluid types. Organic fluids and types used in design; benzene-aromatic hydrocarbon, cyclohexane-alkane, octamethylcyclotetrasiloxane (D4)-siloxane. Considering the maximum electrical energy values obtained from Solar ORC in the summer months, it was seen that 205 MWh electricity generated was obtained for Silifke with benzene at a heat source temperature of 223 oC in July. Maximum solar parabolic trough collector (PTC) specific electric power value was determined as 59.52 W/m2 in Alanya district with benzene in June. When the four districts are evaluated together, it has been determined that benzene performs better than cyclohexane by 3.8% on average and 23% better than D4. When the annual electrical energy values are examined, the highest production was determined as 1625 MWh with benzene fluid in Alanya district.

Thermodynamic and economic analysis of organic Rankine cycle combined with flash cycle and ejector

Increasing the net output power of the Organic Rankine Cycle (ORC) can increase the possibility of developing low-medium temperature heat sources. It is equally important to effectively control the system's economy. So, subcritical double-pressure ORC combined with flash cycle and ejector (S-EFDPORC) and transcritical ORC combined with flash cycle and ejector (T-EFDPORC) are proposed in present work. The thermodynamic and economic analyses on five proposed systems within the heat source temperature range of 100 °C–200 °C are conducted. The net output power and levelized energy cost (LEC) are treated as optimization objectives in thermodynamic and economic performance comparisons, respectively. The non-dominated sorting and three multi-objective optimization methods (LINMAP, TOPSIS, and Shannon Entropy) are used to perform the multi-objective optimization. The results show that S-EFDPORC and T-EFDPORC can both effectively improve the net output power compared with subcritical double-pressure ORC (S-DPORC) and transcritical double-pressure ORC (T-DPORC), while subcritical ORC combined with flash cycle and ejector (S-EFORC) can only improve the net output power within a certain temperature range. When the optimization objective is the net output power, compared with S-DPORC and T-DPORC, the growth rate of net output power in S-EFORC is more than 20% when the temperature is below 160 °C. When the temperature of the heat source is below 160 °C or above 180 °C, the growth rates of net output power of S-EFDPORC and T-EFDPORC increase more than 25%. When LEC is treated as optimization objective, compared with S-DPORC and T-DPORC, S-EFORC reduces LEC by more than 10%. S-EFDPORC and T-EFDPORC increase the LEC of the system, and the maximum growth rates of LEC are 30% and 60% respectively, resulting in worse economic performance. With three multi-objective optimization methods, both S-EFDPORC and T-EFDPORC can increase net output power, but their economy will deteriorate at most heat source temperatures. Although S-EFORC increase the net output power when the heat source temperature is below than 177 °C, LEC reduces throughout the heat source temperature range.