Search

There has been an increasing interest in solar-driven combined energy supply systems for low-temperate applications, particularly those based on the Organic Rankine Cycle (ORC), Kalina Cycle (KC), or Trilateral Cycle (TLC). However, systems based on these thermodynamic cycles usually employ large area collectors that stand alone or are placed on the roof, without considering integration with the building facade. This research presents a solution to large-scale photothermal utilization integrated with facades for co-generated systems. The current study is the first to conduct performance and economic assessment for four novel solar cooling and power (SCP) co-generated systems driven by evacuated tube solar collectors (ETCs) or semi-transparent photovoltaic (STPV) integrated into the building facades. The suggested systems were simulated using TRNSYS to forecast their performance metrics when used in four Chinese cities with various climate zones. As indicators, a solar fraction (SF) and unit energy cost (UEC) were used to evaluate the technical and financial aspects of each system. The STPV-vapor compression cycle (VCC) system had the highest SF (100%, except Haikou), as well as the lowest UEC (0.211$/kWh on average) among the four cities, according to the results. Among the three solar-thermal co-generation systems, ETC-ORC-VCC had the best performance (SF,37.9%; UEC,0.597$/kWh on average). [ABSTRACT FROM AUTHOR]

Though the trilateral cycle (TLC) is a promising heat recovery-to-power cycle, its application has not been widely accepted or commercialised due to some thermodynamic feasibility concerns. This study examined the performance analysis and sensitivity of the system parameters on the thermodynamic performance of the TLC power generator systems for waste heat recovery-to-power generation. Thermodynamic models of the simple, recuperative, reheat and regenerative TLCs were established. Performance analysis and sensitivity of the system parameters on the cycles' performance were conducted at the expander inlet temperature of 453 to 473 K, expander pressure of 2 to 3 MPa and expander isentropic efficiency of 50% to 100%. The expander inlet temperatures, pressures, and its isentropic efficiencies have significant effects on the thermodynamic efficiencies and net work output of the cycles. At 473 K cycle high temperature, the thermal efficiencies of the cycles increase from 20.13% to 21.97%, 23.29% to 23.91%, 20.62% to 22.07% and 20.66% to 22.9% for the simple, recuperative, reheat and regenerative TLCs, respectively. Their corresponding net power outputs varied from 131.6 to 134.1 kW, 145.9 to 152.2 kW, 113.8 to 124.1 kW and 124.9 to 130.5 kW, respectively. The cycles' thermodynamic performance increased with an increase in expander inlet temperature, expander pressure and expander isentropic efficiencies. [ABSTRACT FROM AUTHOR]

In this study, the ideal cycles with finite heat capacity rates is investigated theoretically to maximize power generation using a sequential Carnot cycle model. Although the Carnot efficiency is important, it is limited to evaluating only in terms of heat source/sink temperatures. For the actual heat engine, maximization of power generation is more important than cycle thermal efficiency when utilizing low-grade heat sources such as a waste heat. In this study, power generation optimization is numerically simulated under the fixed conditions of heat source temperatures, heat source flow rate and heat sink temperature. Effect by two design variables, compressor exit temperature and evaporator size ratio, were evaluated during cycle optimization. The optimization was performed using the pattern search algorithm (PSA) under a given thermal capacitance rate ratios and size of heat exchanger (UA) conditions. As a result, designing compressor exit temperature for maximizing the heat received from heat sources does not always maximize the power, but the higher the UA makes the optimum temperature lower, and the power output higher. These idealistic approaches can be useful in designing of cycle where the power maximization is crucial.

In a total flow geothermal system, the two-phase turbine can generate output power and recover fresh water for the water-deficient area. The performance of the two-phase turbine under various working conditions is significantly affected by operation parameters of the geothermal system. This paper presented performance evaluation methods of two-phase turbines, including one-dimensional (1D) method, two-dimensional (2D) method and three-dimensional (3D) method. The 1D method was a fast iteration approach and could reflect average flow parameters along the impeller channel. The 2D method included nonuniform effects in the rotational direction and the 3D method could derive the complete 3D flow in the channel using CFD methods. The three models were validated with experimental results under various rotational speeds. Compared with the 3D method, the 1D method and the 2D method could significantly reduce computational time. The performance of the two-phase reaction turbine was evaluated under various working conditions. A correction method based on 1D and 3D results was proposed to generate the performance map and evaluate the influence of operation parameters of the geothermal system on the turbine performance. Proposed methods and analysis can be widely used in the design, selection and operation of two-phase reaction turbines for various thermal systems. • The 1D, 2D and 3D methods of two-phase turbine are presented and validated. • The 1D method predicts the turbines' average flow and performance rapidly. • The 2D method considers the nonuniform effects in the rotational direction. • The performance map can guide the design and operation of two-phase turbines. [ABSTRACT FROM AUTHOR]

Abstract A combined Trilateral Cycle-Organic Rankine Cycle (TLC-ORC) system for waste heat recovery is proposed in this paper in order to obtain a better matching performance between the heat source and working fluid. Working fluid selection including Cyclohexane, Toluene, Benzene and water for the high temperature cycle is analyzed based on thermodynamic model under different evaporating temperature of high temperature cycle and low temperature cycle. Results show that Toluene has the best performance among the studied four high temperature working fluid. The net power output, thermal efficiency and exergy efficiency increases with T evap,HT or T evap,LT increasing at any a high temperature working fluid. The maximum net power output 11.3 kW, thermal efficiency 24.2% and exergy efficiency 63.2% are achieved by Toluene at T evap,HT =530 K and T evap,LT =373 K at the same time. It is also found that evaporator 1 has the largest exergy destruction while condenser 1 has the smallest one among all the components. Meanwhile, the condenser 2 has the lowest exergy efficiency while condenser 1 has the highest one. These results show us the direction to optimize the system parameters to improve the total efficiency of the whole system. [ABSTRACT FROM AUTHOR]

Abstract This paper selects the working fluids for Trilateral cycle from two unique perspectives. The first aspect is to match the heat sources temperature with the critical temperature of working fluids, in which the thermal efficiency, exergy efficiency and utilization of heat source are chosen as the evaluation indicators. A better performance can be achieved when the heat source temperature approaches to the critical temperature of working fluid. From the aspect of expander, working fluids are selected to reduce volumetric flow ratio of expander and the size of expander, which have the lager vapor pressure at condensing temperature (VP), lager density at expander outlet and lower critical temperature. N-butane and R152a show higher net power output and lower volumetric flow ratio of expander among 13 studied working fluids. Two functions of expander volumetric flow ratio with respect to critical temperature of working fluid and VP have been gotten respectively. Furthermore, it can be concluded the suitable heat source temperature range of a TLC system is moderate temperature. [ABSTRACT FROM AUTHOR]

The transition in the energy market and the growing share of renewable energy sources have been boosting the research in new power cycles. For example, the concept of batch evaporation in the Misselhorn Cycle promises to increase the overall efficiency in low-temperature applications and therefore saves resources. In this paper, a dynamic evaporator model was extended in order to prove the feasibility of the Misselhorn Cycle despite its transient character. In this context, the thermal capacity of the wall material as well as the residence time of the heat source medium were added. The previous, underlying model predicted an improved system efficiency for the Misselhorn Cycle of about 50% compared to an Organic Rankine Cycle (ORC) at 100 C ∘ . Initially, the results of the extended model showed a negative influence of the inertial effects on the possible net power output (advantage over ORC only 10%). However, an unheated discharge phase and reduced dimensions of the heat exchanger could compensate these drawbacks and achieved results (about 40% better than ORC) in the same range as the previous, simple model predicted. These findings prove the general practical feasibility of the Misselhorn Cycle. [ABSTRACT FROM AUTHOR]

Wastewater Treatment Plants (WWTP) have a significant role in both processing wastewaters to return to the water cycle and in transforming between 40% and 60% of the dissolved organic matter into a non-fossil combustible gas (biogas) with a methane content of around 50–70 vol %. Significant energy cost savings can be achieved using combined cooling, heat and power (CCHP) systems in small-scale distributed power system wastewater treatment plants. In this study, feasibility of a trigeneration system in a real wastewater treatment plant is studied. A mathematical model has been developed to evaluate system performance from the thermodynamics point of view. Based on the simulation results, fuel consumption, power production, and thermal efficiency of the system were analyzed. For the proposed configuration, the electricity coverage is increased by 27% and the produced cooling load of around 20 kW in summer season is obtained. The results also reveal that integration of the trilateral cycle (TLC) and the absorption chiller system in the reference WWTP offers a 17.2% more efficient plant from the viewpoint of first law efficiency. [ABSTRACT FROM AUTHOR]

Numerous innovative heat recovery-to-power technologies have been resourcefully and technologically exploited to bridge the growing gap between energy needs and its sustainable and affordable supply. Among them, the proposed trilateral-cycle (TLC) power system exhibits high thermodynamic efficiency during heat recovery-to-power from low-to-medium temperature heat sources. The TLCs are proposed and analysed using n-pentane as working fluid for waste heat recovery-to-power generation from low-grade heat source to evaluate the thermodynamic efficiency of the cycles. Four different single stage TLC configurations with distinct working principles are modelled thermodynamically using engineering equation solver. Based on the thermodynamic framework, thermodynamic performance simulation and efficiency analysis of the cycles as well as the exergy efficiencies of the heating and condensing processes are carried out and compared in their efficiency. The results show that the simple TLC, recuperated TLC, reheat TLC and regenerative TLC operating at subcritical conditions with cycle high temperature of 473 K can attain thermal efficiencies of 21.97%, 23.91%, 22.07% and 22.9%, respectively. The recuperated TLC attains the highest thermodynamic efficiency at the cycle high temperature because of its lowest exergy destruction rates in the heat exchanger and condenser. The efficiency analysis carried out would assist in guiding thermodynamic process development and thermal integration of the proposed cycles. [ABSTRACT FROM AUTHOR]

An innovative cascade cycle combining a trilateral cycle and an organic Rankine cycle (TLC-ORC) system is proposed in this paper. The proposed TLC-ORC system aims at obtaining better performance of temperature matching between working fluid and heat source, leading to better overall system performance than that of the conventional dual-loop ORC system. The proposed cascade cycle adopts TLC to replace the High-Temperature (HT) cycle of the conventional dual-loop ORC system. The comprehensive comparisons between the conventional dual-loop ORC and the proposed TLC-ORC system have been conducted using the first and second law analysis. Effects of evaporating temperature for HT and Low-Temperature (LT) cycle, as well as different HT and LT working fluids, are systematically investigated. The comparisons of exergy destruction and exergy efficiency of each component in the two systems have been studied. Results illustrate that the maximum net power output, thermal efficiency, and exergy efficiency of a conventional dual-loop ORC are 8.8 kW, 18.7%, and 50.0%, respectively, obtained by the system using cyclohexane as HT working fluid at THT,evap = 470 K and TLT,evap = 343 K. While for the TLC-ORC, the corresponding values are 11.8 kW, 25.0%, and 65.6%, obtained by the system using toluene as a HT working fluid at THT,evap = 470 K and TLT,evap = 343 K, which are 34.1%, 33.7%, and 31.2% higher than that of a conventional dual-loop ORC.

Based on organic Rankine cycle (ORC), a trapezoidal cycle with theoretical model is proposed and built according to the trapezoidal configuration and the thermodynamic relation in T-s diagram. Simulations show that the relative deviation between trapezoidal cycle and ORC is lower than 5% within evaporation temperature of 5 °C lower than the critical temperature of the working fluids. Empirical equations to calculate the optimal evaporation temperature, the maximum net power output and the corresponding thermal efficiency are built, which relative deviations from ORC are lower than 4%. Trapezoidal cycle can break through the restrictions of the actual working fluids and the configuration of the ORC to extend the study of the ORC and investigate the general principle of the ORC (or the trapezoidal cycle). Trapezoidal cycle can develop to trilateral cycle or Carnot cycle, which are the boundary cycles of the trapezoidal cycle. Trapezoidal cycle can be used as a general cycle to investigate the relations and principles among the trilateral cycle, Carnot cycle and trapezoidal cycle (or ORC). The performance of these three cycles at maximum power and their relations are investigated in the same conditions of finite heat source. Results show that the maximum power and the corresponding thermal efficiency of the trapezoidal cycle are bounded between Carnot cycle and trilateral cycle. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A vast amount of heat energy is available at low cost within the range of medium and low temperatures. Existing thermal cycles cannot make efficient use of such available low grade heat because they are mainly based on conventional organic Rankine cycles which are limited by Carnot constraints. However, recent developments related to the performance of thermal cycles composed of closed processes have led to the exceeding of the Carnot factor. Consequently, once the viability of closed process based thermal cycles that surpass the Carnot factor operating at low and medium temperatures is globally accepted, research work will aim at looking into the consequences that lead from surpassing the Carnot factor while fulfilling the 2nd law, its impact on the 2nd law efficiency definition as well as the impact on the exergy transfer from thermal power sources to any heat consumer, including thermal cycles. The methodology used to meet the proposed objectives involves the analysis of energy and entropy on trilateral closed process based thermal cycles. Thus, such energy and entropy analysis is carried out upon non-condensing mode trilateral thermal cycles (TCs) characterised by the conversion of low grade heat into mechanical work undergoing closed adiabatic path functions: isochoric heat absorption, adiabatic heat to mechanical work conversion and isobaric heat rejection. Firstly, cycle energy analysis is performed to determine the range of some relevant cycle parameters, such as the operating temperatures and their associated pressures, entropies, internal energies and specific volumes. In this way, the ranges of temperatures within which the Carnot factor is exceeded are determined, where carbon dioxide, nitrogen, helium and hydrogen are considered as real working fluids, followed by an entropic analysis in order to verify 2nd law fulfilment. The results of the analysis show that within a range of relatively low operating temperatures, high thermal efficiency is achieved, reaching 44.9% for helium when the Carnot factor is 33.3% under a ratio of temperatures of 450/300 K. With respect to entropy analysis, it is verified that the results of the latter demonstrate compliance with the second principle, while violating Carnot constraints, since the Carnot factor is constrained only by the Carnot, Stirling and Ericsson cycles and its associated Carnot engine characteristics. However, the most relevant findings through the performed analysis concern the detection of some inconsistencies regarding the conventional 2nd law efficiency definition and the exergy transfer definition from thermal power sources to thermal cycles. In summary, a TC undergoing isochoric heat absorption, adiabatic expansion and isobaric heat rejection under closed transformations can yield improved performance over traditional thermal cycles, even exceeding the Carnot factor under relatively low top temperatures, for which Carnot efficiency is lower. Furthermore, the concept of 2nd law efficiency, defined as the ratio of the thermal to the Carnot efficiency, has been reconsidered in agreement with the results achieved. That is, the definition of 2nd law efficiency lacks both theoretical and practical sense. In the same way, as a result of discarding the Carnot factor as limiting the thermal efficiency, the definition of the exergy transfer to a thermal cycle (the maximum available energy) must be defined as the product of the transferred heat from a heat source and the thermal efficiency. [ABSTRACT FROM AUTHOR]

Trilateral cycle is one of the heat cycles for waste heat recovery system. In the heat exchange process of the trilateral cycle, pressurized working fluid is kept as a single liquid phase. Therefore, temperature-profile matching between the heat source and the working fluid should be improved, and exergy loss can be minimized. In the present study, thermodynamic performances of Rankine, trilateral and supercritical cycles are assessed. In the cycle simulation, maximum pressures of these three cycles are optimized to give the highest exergy efficiency. Cycle performance criteria are sink-temperature-based exergy efficiency, isentropic expansion ratio and maximum pressure. Exhaust gas (400℃) and hot water (80℃) are assumed for the heat sources. Simulation results show that the sink-temperature-based exergy efficiency of trilateral cycle is 78 %, which is 1.36 times larger than that of Rankine cycle for the hot water case. For the exhaust gas case, water is the optimal working fluid for the trilateral cycle, and the sink-temperature-based exergy efficiency is 80 %. Especially in the trilateral cycle, the optimum expansion ratio shows large variation depending on the working fluids and working conditions. Thus, a reciprocating expander should be suitable from the view point of adaptability to various working conditions. In the present study, the effect of volumetric expansion ratio with reciprocating expander is also investigated. Simulation results show that the volumetric expansion ratio of 100 or even higher is needed to reduce the expander loss.

The trilateral cycle (TLC) is one of the most promising alternatives among the heat recovery-to-power technologies, due to its compact system configuration and high performance at relatively low compression work and low-to-moderate expander inlet temperature. These feats make the TLC beneficial for off-grid applications particularly in remote or offshore applications where power-to-weight ratio of the power plant is of significance. This study presents the thermodynamic performance simulation and design optimisation of the TLCs using unconventional working fluid for heat recovery-to-power generation from low-grade waste heat, which is considered for process development and integration of the TLC. Four system configurations, comprising the simple TLC, recuperated TLC, reheat TLC and regenerative TLC are analysed and compared their performance metrics. Based on the theory of steady-state steady-flow thermodynamics, the simulation models of the TLC power plants, corresponding to their thermodynamic processes are established and implemented using engineering equation solver. The results show that the thermal efficiencies of the simple TLC, recuperated TLC, reheat TLC and regenerative TLC employing n -pentane are 11.85–21.97%, 12.32–23.91%, 11.86–22.07% and 12.01–22.9% respectively at subcritical operating conditions with low-grade heat in the temperature limit of 393–473 K. These suggest that the thermal integration of the optimised design of the simple TLC enhanced heat exchange efficiencies as well as the performance metrics. A comparative study among these cycles shows that the proposed recuperated TLC achieved the best performance metrics. [ABSTRACT FROM AUTHOR]

Recently, the TLC (trilateral power cycle) has attracted significant interest as it provides better matching between the temperature profiles in the evaporator compared to conventional power cycles. This article investigates the performance of this cycle and compares it with those for the ORC (organic Rankine cycle) and the Kalina cycle, from the viewpoints of thermodynamics and thermoeconomics. A low-grade heat source with a temperature of 120 °C is considered for all the three systems. Parametric studies are performed for the systems for several working fluids in the ORC and TLC. The systems are then optimized for either maximum net output power or minimum product cost, using the EES (engineering equation solver) software. The results for the TLC indicate that an increase in the expander inlet temperature leads to an increase in net output power and a decrease in product cost for this power plant, whereas this is not the case for the ORC system. It is found that, although the TLC can achieve a higher net output power compared with the ORC and Kalina (KCS11 (Kalina cycle system 11)) systems, its product cost is greatly affected by the expander isentropic efficiency. It is also revealed that using n-butane as the working fluid can result in the lowest product cost in the ORC and the TLC. In addition, it is observed that, for both the ORC and Kalina systems, the optimum operating condition for maximum net output power differs from that for minimum product cost. [ABSTRACT FROM AUTHOR]

Abstract: A dual loop waste heat recovery power generation system that comprises an upper trilateral cycle and a lower organic Rankine cycle, in which discharged exhaust gas heat is recovered and re-used for propulsion power, was theoretically applied to an internal combustion engine for propulsion in a 6800 TEU container ship. The thermodynamic properties of this exhaust gas heat recovery system, which vary depending on the boundary temperature between the upper and lower cycles, were also investigated. The results confirmed that this dual loop exhaust gas heat recovery power generation system exhibited a maximum net output of 2069.8 kW, and a maximum system efficiency of 10.93% according to the first law of thermodynamics and a maximum system exergy efficiency of 58.77% according to the second law of thermodynamics. In this case, the energy and exergy efficiencies of the dual loop system were larger than those of the single loop trilateral cycle. Further, in the upper trilateral cycle, the volumetric expansion ratio of the turbine could be considerably reduced to an adequate level to be employed in the practical system. When this dual loop exhaust gas heat recovery power generation system was applied to the main engine of the container ship, which was actually in operation, a 2.824% improvement in propulsion efficiency was confirmed in comparison to the case of a base engine. This improvement in propulsion efficiency resulted in about 6.06% reduction in the specific fuel oil consumption and specific CO2 emissions of the main engine during actual operation. [Copyright &y& Elsevier]

Power flash cycles (PFC) are a generalization of trilateral cycles (TLC) in which the compressed liquid is heated up to its boiling point and then performs a flash expansion during which it delivers power. The end point of the expansion may be in the wet vapour region (TLC) or in the dry vapour region. Here model results are presented for PFC-systems including the heat transfer to and from the cycles with aromates, siloxanes, and alkanes as working fluids. Optimization criterion is the exergy efficiency for power production at different pairs of heat carrier and cooling agent inlet temperatures ranging from (350 °C, 62 °C) to (150 °C, 15 °C). Comparisons with TLC for water, organic Rankine cycles (ORC) and water Clausius-Rankine cycles are made. General findings are that PFC has higher power production efficiencies than ORC but larger volume flows at the expander outlet. Moreover, TLC with water have in all cases the highest or nearly highest power production efficiencies. The disadvantage of water are the large outlet volume flows at low temperatures. For these cases alkanes like cyclopentane are to be preferred in PFC which can have significantly smaller outlet volume flows and rather high power production efficiencies. [ABSTRACT FROM AUTHOR]

Abstract: A comparison of optimized trilateral cycle (TLC) - systems with water as working fluid and optimized organic Rankine cycle (ORC) – systems with pure organic working fluids is presented. The study includes the heat transfer to and from the cycles. The TLC - systems were optimized by the selection of the maximum water temperature, the ORC - systems by the selection of the working fluid and the process parameters. The optimization criterion is the exergy efficiency for power production being the ratio of the net power output to the incoming exergy flow of the heat carrier. Results will be presented for five different cases specified by the inlet temperature of the heat carrier and the inlet temperature of the cooling agent. The inlet temperature pairs are (350 °C, 62 °C), (280 °C, 62 °C), (280 °C, 15 °C), (220 °C, 15 °C) and (150 °C, 15 °C). It is found that the exergy efficiency for power production is larger by 14%–29% for the TLC than for the ORC. On the other hand, the outgoing volume flows from the expander are larger for the TLC than for the ORC by a factor ranging from 2.8 for the first case to 70 for the last case. [Copyright &y& Elsevier]

Abstract: The Carnot cycle is reviewed as to its appropriateness to serve as the ideal model for geothermal binary power plants. It is shown that the Carnot cycle sets an unrealistically high upper limit on the thermal efficiency of these plants. A more useful model is the triangular (or trilateral) cycle because binary plants operating on geothermal hot water use a non-isothermal heat source. The triangular cycle imposes a lower upper bound on the thermal efficiency and serves as a more meaningful ideal cycle against which to measure the performance of real binary cycles. Carnot and triangular cycle efficiencies are contrasted and the thermal efficiencies of several actual binary cycles are weighed against those of the ideal triangular cycle to determine their relative efficiencies. It is found that actual binary plants can achieve relative efficiencies as high as 85%. The paper briefly discusses cycles using two-phase expanders that in principle come close to the ideal triangular cycle. [Copyright &y& Elsevier]

• Introduces the novel organic Rankine flash cycle (ORFC); • Evaluates its thermodynamic and economic performance; • Demonstrates the ORFC potential for low-grade heat recovery. Growing environmental concerns are driving the energy market toward the development of thermodynamic cycles to harness renewable energy and waste heat. This manuscript introduces the novel organic Rankine flash cycle, which combines the organic Rankine cycle with the trilateral cycle, merging their advantages in terms of high specific power output and low heat transfer irreversibility, respectively. By comparing the organic Rankine flash cycle to the organic flash cycle, it was found that the proposed architecture reaches a peak exergy efficiency at a more realistic value of two-phase expansion volume flow ratio, consistently achieves higher energy and exergy efficiencies, presents a lower cost, and is not constrained to operate close to the working fluid saturation temperature, promising easier operability. Considering pentane as working fluid, the exergy efficiency of the organic Rankine flash cycle is 18%p higher for a heat source temperature of 150 °C, 12%p for 175 °C, and 4%p for 200 °C. The attractive thermoeconomic performance of the proposed organic Rankine flash cycle highlights the potential of such a cycle as a new paradigm in the ORC panorama, encouraging further investigation towards practical demonstration. [ABSTRACT FROM AUTHOR]

When organic Rankine cycles (ORC) are employed to convert waste heat into work, the thermal efficiency is not recommended as a key performance metric because waste heat recovery and power output are not generally maximized at the point of peak efficiency. In such an application, maximization of the net power output should be the objective. Two alternative cycle configurations that can increase the net power output from a heat source with a given temperature and flow rate are analyzed and compared to a baseline ORC. These cycle configurations are: an ORC with two-phase flash expansion (TFC) and an ORC with a zeotropic working fluid mixture (ZRC). A design-stage ORC model allowed a consistent comparison of multiple ORC configurations with finite capacity of the source and heat sink fluids. Simulation results indicated that the TFC offered the most improvement over the baseline ORC, but required a highly efficient two-phase expansion. The ZRC shows improvement over the baseline as long as the condenser fan power requirement is not negligible. At the highest estimated condenser fan power, the TFC is no longer beneficial. Finally, a partial-evaporating ZRC (PE-ZRC) has also been considered to reduce the volume ratio requirements of a flash expansion. • A systematic comparison between traditional ORC and different cycles architectures is proposed. • The ORC with two-phase flash expansion and zeotropic mixtures have been thoroughly analyzed. • At high heat source temperatures, ZRC leads to limited benefits compared to TFC. • At low heat source temperatures and higher condenser fan powers, ZRC offers greater improvements over TFC. • At low source temperatures, the ZRC with flash-expansion allows better performance than a TFC except when water is used as working fluid. [ABSTRACT FROM AUTHOR]

An innovative cascade cycle combining a trilateral cycle and an organic Rankine cycle (TLC-ORC) system is proposed in this paper. The proposed TLC-ORC system aims at obtaining better performance of temperature matching between working fluid and heat source, leading to better overall system performance than that of the conventional dual-loop ORC system. The proposed cascade cycle adopts TLC to replace the High-Temperature (HT) cycle of the conventional dual-loop ORC system. The comprehensive comparisons between the conventional dual-loop ORC and the proposed TLC-ORC system have been conducted using the first and second law analysis. Effects of evaporating temperature for HT and Low-Temperature (LT) cycle, as well as different HT and LT working fluids, are systematically investigated. The comparisons of exergy destruction and exergy efficiency of each component in the two systems have been studied. Results illustrate that the maximum net power output, thermal efficiency, and exergy efficiency of a conventional dual-loop ORC are 8.8 kW, 18.7%, and 50.0%, respectively, obtained by the system using cyclohexane as HT working fluid at THT,evap = 470 K and TLT,evap = 343 K. While for the TLC-ORC, the corresponding values are 11.8 kW, 25.0%, and 65.6%, obtained by the system using toluene as a HT working fluid at THT,evap = 470 K and TLT,evap = 343 K, which are 34.1%, 33.7%, and 31.2% higher than that of a conventional dual-loop ORC. [ABSTRACT FROM AUTHOR]