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The seals of a Wankel expander produce significant friction and wear, contributing its largest disadvantage. This friction necessitates lubricant to be mixed with the working fluid, increasing the complexity of the device. Removing the seals could therefore produce a significantly more desirable device, if the resulting leakage is acceptable. Currently there are no published studies assessing the performance of a Wankel expander without apex seals, therefore this paper will attempt to address this knowledge gap. A CFD (computational fluid dynamics) model of a Wankel expander without apex seals was developed to assess the performance and leakage amount. Using this model, a parametric study was performed using the apex gap sizes, the rotational speed and the inlet pressure as the variable parameters. Results showed that higher rotational speeds reduced leakage, but resulted in larger pressure drops over the ports, reducing the efficiency. A double-sided ports model helped to counter this, with speeds up to 6000RPM becoming viable. The friction from the apex seals was calculated in order to better compare the cases with and without apex seals. The best efficiency case with apex seals (at 1200RPM, 2 bar inlet pressure) gave 64% isentropic efficiency including apex seal frictional losses. The highest efficiency for the cases without apex seals was 55% (at 6000RPM, 2 bar inlet pressure), however due to the higher rotational speed, the power output was almost four times higher than the case with apex seals above (385 W compared to 100 W).

At present, the economic deterioration of the unit due to solid particle erosion (SPE) at the governing stage has attracted widespread attention. Based on the Euler-Lagrange equation and the Finnie erosion model, the influence of SPE on the safety and the efficiency of the unit are numerically analyzed for different types of notches in the governing stage of a 1000 MW ultra-supercritical steam turbine in this article. The results indicate that the total pressure loss coefficient and the outlet steam angle increase as the depth of the notch goes up. And with the rising of the notch depth, the erosion at the rear edge of the rotor blade increases and the isentropic efficiency decreases rapidly. Furthermore, the decline trend of efficiency differs when notch type is different. When the notch depth is 20 mm, the maximum decline of entropy efficiency is 4.06%.

Geothermal heat mining simulations using supercritical CO2 (sCO2) were performed in this research. Working fluid selection criteria for power generation using sCO2 from a geothermal reservoir are then presented for subcritical, superheated and supercritical organic Rankine cycles (ORCs). Meanwhile, method of working fluid classification for ORC is proposed. To get the most feasible ORC design, this study introduces the concept of “turning point” for isentropic and dry working fluids, as well as minimum turbine inlet temperature for wet working fluids. A thermodynamic model was developed with capabilities to obtain the optimal working fluid mass flow rate, evaporation temperature, superheated temperature, and supercritical pressure, to evaluate the thermal performance of the three ORC approaches using hot produced sCO2. With this model, thirty potential working fluids with critical temperatures in the range from 50 to 225 °C were screened for utilizing hot produced sCO2 considering physical properties, environmental and safety impacts, and thermodynamic performances. Finally, the thermodynamic results were compared for all possible working fluids.

Compressed air energy storage (CAES) systems usually operate under off-design conditions due to load fluctuations, environmental factors, and performance characteristics of the system. Thus, to improve design and operation characteristics, it is important to study off-design performance of CAES systems. The compression process plays an important role in CAES systems. In this paper, we discuss the methodology for modeling off-design operation of a multistage compression process with intercooling of the most promising adiabatic CAES (A-CAES) system. The off-design performances under two proposed kinds of operating regulations are analyzed and compared. These two operating regulations are equal-power-ratio regulation (EPR) and optimizing variable inlet guide vane rotation angle (OVRA) (optimizing all stages simultaneously) regulation. Correlation between parameters such as total power consumption ratio, exergy efficiency, hot water temperature versus mass flow rate ratio, and back pressure is revealed in depth. Based on this research, the optimal operation laws, including pressure ratio distribution and efficiency distribution among all stages, are obtained, and it is found that the primary optimum principle is to enhance the isentropic efficiencies of low-pressure stages to approach design point. Finally, the optimized regulating law for the inlet guide vane rotation angles of the 4 stages is revealed. This study provides strong support for the design, operation, and control of CAES systems.

There are many factors affecting the Organic Rankine Cycle’s (ORC) performance, such as working fluid selection, evaporator and condenser temperatures, pinch point temperature differences (the minimum temperature difference between refrigerant and the waste heat source (PPTDevap) or cooling water (PPTDcon)), superheating temperature, heat exchanger effectiveness, and isentropic efficiencies of the turbine and pump. In this study, the parameters’ impact weights on the cycle’s efficiency are discussed and comparatively examined based on the statistical analyses. First, the system’s thermodynamic model was established, and variation of the cycle’s thermal efficiency was calculated for different parameters and their different ranges. Next, to obtain the contribution ratios and the order of importance of these parameters, the thermodynamic analysis results were evaluated using two statistical methods: Taguchi and ANOVA. In conclusion, the evaporator and condenser temperature and the turbine efficiency have a large effect on the thermal efficiency of the ORC, and the total impact ratio of these parameters is determined as approximately 70%. However, PPTDevap, PPTDcon and pump efficiency are found to be the least effective parameters. In addition, the best and the worst operating conditions are determined from the statistical analysis and in these operating conditions, the thermal efficiencies of the ORC are obtained as 18.1% and 9.6%, respectively.

Compressor in air supply circuit influences flow rate of oxygen in cathode of polymer electrolyte membrane (PEM) fuel cell systems. In this paper, an air-cooled dry oil-free twin-screw compressor for fuel cell systems was developed and adopted successfully in a type of truck with fuel cell system. Extensive experimental investigations including the recording of p-V indicator diagram were carried out to study the performance of the prototype compressor. Rotation speed of the female rotor varied from 5000 rpm to 10,000 rpm, and discharge pressure from 0.14 MPa to 0.22 MPa. It was found that the volume flow rate decreases almost linearly with the reduction of rotation speed and this is beneficial to the fuel cell systems under part-load. Between speed of 7000 rpm and 10,000 rpm at a given discharge pressure, the variations of isentropic efficiency and specific power are very limited. This indicates the twin-screw compressor can operate efficiently in a wide range of power output from the fuel cell systems. Under the design conditions with discharge pressure of 0.2 MPa and female rotor rotation speed of 9000 rpm for a fuel cell output of 50 kW, the volumetric efficiency and isentropic efficiency of the prototype compressor developed are 70% and 55% respectively. And the mechanical efficiency and the polytropic process index regarding to discharge temperature are 80% and 1.58. These values can be used in the design of other air-cooled dry oil-free twin-screw compressors for similar applications.

Over the years, there has been continual increase in the temperature inside a turbine inlet through improvements in the gas turbine efficiency and specific power, and cooling technologies to deal with such temperature increases have been under development for decades. However, the definition of “efficiency” remains ambiguous for cooled turbines, with no consensus achieved on the ideal expansion process. This paper first reviews several proposed definitions, Hartsel, MP (mainstream-pressure), FR (fully reversible), and WP (weighted-pressure) of efficiency and then presents a new one to overcome the existing shortage. The increase in entropy related to mixing is first analysed to demonstrate that FR efficiency consistently provides a significantly lower value than the other definitions, assuming the unavoidable entropy generation to be zero. The flow mixing in a smooth adiabatic channel is then analysed to show that the WP ideal process is not sufficiently “ideal.” A fully mixed (FM) definition is then proposed based on a physical mixing process, followed by isentropic expansion, the value of which does not differ significantly from most of the proposed definitions, and is able to consider the influence of the inlet Mach number on the hypothetical ideal process. Finally, this paper compares several definitions in view of the thermodynamic cycle, and shows that the FM definition can determine the performance potential of an existing turbine better than the other definitions, which means that the FM efficiency can be used as a reliable tool for the performance evaluation and optimization of a cooled turbine.

Partially premixed combustion aims to reduce NOx and particulate matter emission without fuel consumption penalty. Low temperature reactions are important for the partially premixed combustion. In the current study, a self-adaptive strategy is introduced to predict the motoring pressure by means of an equivalent isentropic index. The start of the low temperature reactions is detected when the pressure difference between the measured pressure and the predicted pressure is higher than a threshold value. Experimental results show that the maximum variation between the measured and the predicted motoring pressure before the top dead center is less than 0.02 bar. It is also demonstrated that the presented detection method is able to detect the start of the low temperature reactions under different engine operating conditions with varying injection timing, injection duration, number of injections and exhaust gas recirculation rate.

HFCs are suggested to be banned in 2020 because of high GWP (Global Warming Potential). New type of HFO refrigerant R1233zd(E) is proposed as a drop-in replacement to R245fa for organic Rankine cycle application considering the similar thermo-physical properties. In this paper, a description of previous experimental comparison between two refrigerants is presented in the first section. In the second section, further investigation in expansion procedure is implemented with a semi-empirical expander model, which is validated with experimental data based on ‘Genetic Algorithm’. Internal leakage, mechanical friction and heat transfer are presented as main irreversible losses. Input parameters are assigned to mass flow rate, expander rotational speed, supply temperature and exhaust pressure. Supply pressure, exhaust temperature and net power are computed as output results. The maximum deviation between the measured and predicted results are 3.35%, 2.24 K and 6.09% respectively. In the last section, polynomial curve-fittings of dimensionless expander efficiency are conducted for wider prediction of operating range of the expander. Values of filling factor and expander isentropic efficiency are predicted with R 2 = 99.517 % and R 2 = 97.997 % . Curve-fittings of expander efficiency can be integrated into systematic simulation, which is aimed for further optimization of cycle performance to better take advantage of new refrigerants.

Electricity generation from waste heat by means of Organic Rankine Cycle is a promising method to increase the efficiency of industrial processes. However, due to special boundary conditions, such systems have to be robust, efficient in full load as well as in part load and scalable down to the power range of less than 15 kW. This study presents experimental results on the behaviour of two small-scale turbines, an axial impulse turbine and a radial cantilever turbine with a maximum power of about 12 kW. The turbine characteristics (isentropic efficiency and swallowing capacity) are given with respect to pressure ratio (ranging from 12 to 24) and rotational speed (ranging from 18,000 to 30,000 rotations per minute). For the axial turbine, a maximum isentropic efficiency of 73.4% has been reached in the ORC test bed. The maximum isentropic efficiency of the cantilever turbine is even higher and reaches 76.8%. The values are compared to volumetric expanders and it is shown that micro-turbines can compete even in the power range addressed in this study. As the turbine characteristics are given for full load and part load conditions, they can be implemented in simulation tools to allow for a more realistic calculation of ORCs with fluctuating heat sources.

The objective of this paper is to enhance the refrigeration performance by energy transfer of shock wave. The matching of shock compression and expansion refrigeration is the key to research. Firstly, the efficiency of shock wave transfer energy is discussed. Then, a two dimensional numerical model of wave rotor refrigeration is established. And wave diagram is drawn by numerical calculation, which reveals the principle of refrigeration and the relationship between pressurization and refrigeration. Finally, an experimental platform was established and experiment work is carried out to obtain performance parameters. The results show that shock wave compression is close to isentropic compression. Using the shock wave, the expansion work of refrigeration can be efficiently recovered. Under the design condition, about 50% of pressure energy could be restored. There are three main shock waves in the channels. Only shock wave S1 can be exploited to enhance refrigeration and other shock waves should be avoided. There is an optimum value for the pressure of high temperature port, which observably affects the temperature drop of the novel refrigerator. Under the experimental condition, the performance curves of the refrigerator and temperature distribution in refrigerator are obtained.

The constant pressure combustion of the Joule cycle is a dominant source of losses in gas turbines. One possible improvement is pressure gain combustion through pulse detonation combustion. However, the total pressure increase is the result of a transient periodic process that can adversely affect the performance of adjoining turbo components. The thermodynamic benefits of pressure gain combustion can thus be undermined by low efficiencies of compressor and turbine. In order to account for such unsteady effects early in the design process, suitable methods are essential. Given 3D-CFD simulations’ undue computational demands, an approach with low computation resources is required for first-order estimates. This paper introduces such an approach based on a 1D-Euler method and demonstrates its applicability. A compressor is simulated with 3D-CFD, which serves as a reference, as well as with the 1D-Euler code employing unsteady outlet boundary conditions that approximate those encountered with pulse detonation combustion. The findings suggest that the 1D-Euler code is able to accurately capture the transient compressor behaviour. Though the relative pressure amplitude at the compressor outlet of 3.6% is attenuated by 90% up to the compressor inlet, it still results in a compressor isentropic efficiency loss of 0.8 percentage points.

In order to develop machine learning methods for performance prediction of basic ORC (BORC) and regenerative ORC (RORC), thermodynamic properties of working fluids are used to separately model thermodynamic processes including compression, expansion, evaporation and regeneration by artificial neural network (ANN), based on REFPROP calculation data of 106 working fluids. These properties include critical temperature, critical pressure, acentric factor and ideal gas heat capacity. Other cycle performances can be derived from the predictions of established ANNs. Furthermore, for RORC, considering that dry or isentropic working fluid is usually preferred, vapor slope of temperature-entropy saturation curve is modeled by ANN to determine the working fluid behavior. Meanwhile, for ensuring occurrence of heat exchange in regenerator, temperature difference between outlets of turbine and pump is modeled to judge whether temperature difference is larger than the assumed pinch point temperature difference. Based on the obtained predictions for BORC, average absolute deviations (AADs) of net work and thermal efficiency are 1.3928% and 1.5461%, respectively. As for RORC, AADs of vapor slope, temperature difference, net work and thermal efficiency are 2.3659%, 1.2020% 1.8277% and 2.1047%, respectively. Based on the above models, cycle performances of BORC and RORC can be accurately predicted from thermodynamic properties of any working fluid.

The circulation pump is an important element limiting the development of small-scale Organic Rankine Cycle system which may have a negative efficiency when the power consumption of the pump is considered and if a suitable pump that corresponds to the working fluid is not properly selected. Based on the consideration mentioned above, in this paper, a trapezoid used to represent the power consumption of the pump and a triangle used to represent the degree of subcooling of the working fluid are defined. Using these two models, the perfection of Organic Rankine Cycle at the optimal condensation temperature relative to the Carnot cycle within the same temperature limitation is analyzed when 69 dry and isentropic working fluids are used in Organic Rankine Cycle. The deviation between the real and ideal gas behavior of each working fluid is also obtained. On this basis, the optimal condensation temperature of each dry and isentropic working fluid is determined. Moreover, the applicability of each organic working fluid in Organic Rankine Cycle is discussed from the viewpoint of pump performance. 36 working fluids are suitable and 33 ones not suitable for the application in small-scale Organic Rankine Cycle system. Suitable pump types corresponding to applicable organic working fluids are also analyzed and determined. The graphic method proposed in this paper and the findings about pump performance can provide reference for the operation of practical Organic Rankine Cycle.

Conventional steam power cycles have their limitations on recovering low grade waste heat, therefore other alternatives are required in these cases. Organic Rankine Cycle (ORC) is suitable for power generation based on various heat sources including solar, geothermal, biomass or waste heat. ORC working fluids can be characterized as wet, dry or isentropic. The aim of this paper is to give a method to find novel dry or isentropic working fluids based on simple physical properties, like degree of freedom and isochoric heat capacity.

A new micro radial inflow turbine is developed fora mini organic Rankine cycle (ORC) system in this study. With R123 as the working fluid, the turbine operational characteristics and performance are investigated by experiments. Based on the experimental data, the maximum rotational speed of the radial inflow turbine reaches53564r/min, and the maximum output power of the turbine is3.386kW and the maximum electric power reaches1.884kW. When the turbine rotational speed is34586r/min, the system isentropic and electromechanical efficiencies achieve the maximum values of 83.6% and65.3% respectively. Both the turbine isentropic and thermal efficiencies increase with the heat source temperature.

The Ranque-Hilsch vortex tube (RHVT) is a small interesting extraordinary mechanical device used as refrigeration machine. An experimental setup has been developed for the study of both temperature and relative humidity separation in vortex tube for the two important cases: (a) with insulation and (b) without insulation on vortex tube. Two influential configurations are examined: (1) variations of cold mass fraction (by varying the mass flow at hot outlet) at different pressures and (2) variations of inlet pressures when the hot outlet is fully opened. Over the whole pressure range covered, the cold end temperature drop increases with the cold mass fraction and then decreases for both non-insulated and insulated cases. However, hot end temperature drop increases for whole range of the cold mass fraction for the non-insulated case, whereas it increases to some optimum value, then decreases with the cold mass fraction for the insulated case. Over the range of pressure the relative humidity increases to some optimum value, and then decreases with the cold mass fraction for both non-insulated and insulated cases. The maximum optimum value of relative humidity is found 65% and 67% at 4 bar inlet pressure with and without insulation respectively. Moreover, the correlations for cold end temperature drop, hot end temperature drop, relative humidity and isentropic efficiency have been developed and explained in this paper for the better understanding of the inside behavior of the RHVT. The variation of optimum non-dimensional cold/hot temperature drop with the cold mass fraction at different pressures obeys approximately single cubic equation and also it is true for the case of non-dimensional relative humidity.

The corrosion problem caused by lithium bromide aqueous solution at high temperature limits the construction of multi-effect absorption cooling cycles. In this paper, based on the compressor-assisted absorption cycle as the bottom cycle that the predecessors had put forward to lower generation temperature, the Rankine Cycle (RC) is introduced as the top sub-cycle to supply work and heat to the bottom one in order to utilize high temperature waste heat for refrigeration efficiently. Thermodynamic calculation including exergy analysis is carried out to study the influence of some important factors, mainly high temperature generator deflation range deflation range ( ω H ) and compression ratio (CR), on the performance of the combined cycle. Simulation results show that while the maximum generation temperature is 50 °C lower than that of the traditional triple-effect cycle, the COP and cooling capacity per unit mass flow rate of the heat source still both improve more than 10% at the condition of CR = 2.2 and P vap 1 = 6.3 MPa (the Rankine Cycle evaporation pressure). Comparison with the boosting cycle with additional work input suggests the primary thermal energy conversion factor in the parameter OIR (output/input-rate) of the combined cycle is 1 and reveals the advantage of the combined cycle over the reference cycle. Because of the heat and work couple between the top cycle and the bottom cycle, only the deflation range is not very large ( ω H 0.015 ), could the maximum generation temperature be controlled under 165 °C to get rid of severe corrosion problem. Comparison with the multistage power cycle indicates that the performance of the combined system is similar to that of the series multistage power cycle with the same number of stages.

Scroll compressors converted into expanders represent a good choice in micro-to-small-scale organic Rankine cycle (ORC) applications. Several studies have tested and modeled scroll expanders in ORC systems in the last decade to assess their performance and reliability in off-design conditions. In this work, SANDEN TRS090F scroll compressor is converted into an expander and tested in a micro-scale ORC system using R134a for power generation from low-grade heat. The experimental data are used to modify the available semi-empirical model in the literature considering a polytropic expansion, a more detailed suction pressure drop model, and a variable loss power correlated to the expander pressure ratio. In addition, the two known expander geometrical parameters, the built-in volume ratio, and the swept volume are considered as fixed inputs to the model instead of being determined as part of the model results. In general, the results of the analysis show that the proposed model can predict the expander's overall performance with good accuracy in different operating conditions. The maximum deviation between the model results and most of the measurements is 5% for the mass flow rate and the shaft power, 15% for the overall isentropic efficiency, and 3 K for the discharge temperature. Then, the impact of the different losses is presented, and finally, the validated model is used to generate the performance maps of the studied expander at different working conditions.

High temperature water source heat pumps (HTWSHP) plays an increasingly important role in drying and building heating due to its remarkable energy-saving effect. However, traditional heat pump working fluids such as R134a are not applicable for HTWSHP and the research on alternative working fluids is limited by the complex process of working fluids screening. This paper is aimed to quickly and easily obtain the performance of a large amount of working fluids for screening. A new simple performance predicted model was proposed in a simple vapor compression cycle at condensation temperatures from 70 to 110 °C. By knowing only a working fluid’s critical temperature and pressure, the specific volumetric heating capacity (VHC) and coefficient of performance (COP) can be predicted. Based on the model, the performance prediction for the newer working fluids involving R1336mzz(Z) and R1224yd(Z) was conducted. The results produced by the model were compared with the values calculated by Peng-Robinson equation of state (PR EoS) and the default, high-accuracy equations implemented in REFPROP 10.0. The predicted values in this work show good agreement. Besides, the model can also be applied varying compressor isentropic efficiencies from 60% to 80%, superheats from 0 to 10 °C and sub-coolings from 0 to 8 °C.

Due to the lack of test data of a supercritical CO2 compressor operating under supercritical CO2 conditions, the work of loss model validation for supercritical CO2 compressor could not be conducted successfully before. Therefore, as the first step, this study gathers the existing accessible experiment data as much as possible while conducting additional supercritical CO2 compressor performance experiments to validate the loss models for the supercritical CO2 compressor. To evaluate the reliability of test results, the measurement uncertainty is estimated from the experiment data. Then, three different combinations of loss models based on the mean streamline method are compared with six available experimental cases to find the most suitable combination of loss models for the supercritical CO2 compressor design and analysis. The combination of loss models proposed by Lee was found to predict pressure ratio and isentropic efficiency of supercritical CO2 compressors operating both on-design and off-design conditions successfully. It is expected that the set of loss models presented herein can be utilized as a conceptual design tool in the preliminary design stage of supercritical CO2 compressors.

This thermodynamically based study focuses on the thermal performance of power cycles using CO2 as the working fluid. The work considers numerous aspects that can influence the cycle's performance, such as the type of cycle (i.e., Rankine or Brayton), its configuration (i.e., with and without a recuperator), and different operational conditions (i.e., heat source temperature and the upper and lower operating pressures of the CO2). To account for all possible scenarios, a thermodynamic routine was especially implemented and linked to a library that contained all the thermodynamics properties of CO2. The results are mostly presented in terms of the absolute and relative 1st and 2nd Law efficiencies of CO2 as well as the cycle's scale, here represented by the global conductance (UA) of the heat exchangers used within the cycle. For the relative performance assessment, four other working fluids, commonly used in energy conversion cycles, were considered (i.e., ethane, toluene, D4 siloxane and water). As expected, the absolute performance results indicate a strong dependence of the cycle's efficiencies on the operational conditions. As for the relative performance, the results suggest that while the CO2's 1st Law efficiency might be lower than other fluids, its exergetic efficiency can be significantly higher. Furthermore, the calculations also indicate that the CO2's needed global conductance is potentially lower than competing fluids (e.g., toluene) for certain operational conditions, which suggests that CO2-based power plants can be more compact, since they might require smaller heat exchangers to produce a reference power output of 1 kW.

This article compares constrained system design to non-constrained system design for the basic Organic Rankine Cycle (ORC). The 12 working fluids studied include eight dry-type, three isentropic, and one wet-type fluids. The ORC model was developed using Aspen HYSYS® and validated with data obtained from the literature. The constrained design compared the performance of working fluids for a fixed heat exchanger and turbine configuration. A non-constrained design was studied by altering the design specifications for the heat exchangers and turbine to match the working fluid. An energy and exergy analysis was performed using first and second law efficiency. The exergy analysis was also used to study exergy destruction across the ORC components. Cost analysis was performed by comparing the levelized cost of electricity (LCOE) for each working fluid in both designs. It was observed that non-constrained design favored working fluids with higher critical temperatures. Switching from constrained to non-constrained design lowered the LCOE for higher critical temperature working fluids such as R601, R601a, R123, R245ca, R245fa, R600, and R236ea. R245ca, R601, and R236ea show 11%, 10%, and 9% decrease in LCOE, respectively. No significant change in efficiency is observed for lower critical temperature working fluids such as R236fa and R134a. Also, no increase in net power was observed for lower critical temperature working fluids, suggesting that modifying design does not affect the performance of ORC. LCOE increased for R600a, R152a, and R227ea and remained unchanged for R236fa and R134a.

A rotating spool compressor is a new compressor technology that was recently introduced by Kemp et al. in 2008. To accelerate the development of the technology, a breakdown of the key losses within the 5th generation device is presented. The losses include indicated losses associated with leakage and over/under compression due to valves and porting. These losses are obtained using high-speed pressure measurements to obtain an indicator diagram of the 5th generation device. Additionally, frictional losses associated with the key sealing elements and moving components are calculated. An experimental validation of the spool seal friction sub-model is presented. All of these losses are combined into Pareto of losses for the 5th generation spool compressor. This Pareto identified the spool seals, compression and discharge flow losses, and the friction of the Top Dead Center interface as losses to be addressed in future designs. Using this information efforts to improve these components were integrated into a 6th generation spool compressor. This generation recorded an overall isentropic efficiency of over 80% for a net improvement of nearly 15 percentage points over the 5th generation spool compressor.

The water-injected twin-screw compressor is a key component in the mechanical vapor compression (MVC) desalination system, which is a promising technology for small and medium scale water production. This paper presents an experimental study on a water-injected twin-screw compressor. A prototype is developed and applied in a 50 m3/day double-effect MVC system. The effect of important parameters (including compressor rotation speed, water injection flow rate and compressor inlet temperature) on the compressor performance is experimentally investigated. It is found that the volumetric flow rate and power consumption of the compressor increases almost linearly with the rise in compressor rotation speed. Results also show that the compressor inlet temperature only affects the power consumption of the twin-screw compressor. It has minor effect on the volumetric flow rate, and volumetric and isentropic efficiencies of the compressor. Study further shows that water injection substantially reduces the compressor discharge temperature. As the water injection flow rate increases, the vapor compression process more closely approaches saturation vapor compression and hence the isentropic efficiency of the twin-screw compressor increases. The analyses demonstrate that the water-injected twin-screw compressor can be reliably operated in the MVC system with satisfactory system performance.

A thermodynamic analysis of cogeneration of power and refrigeration activated by low-grade sensible energy is presented in this work. An organic Rankine cycle (ORC) for power production and a vapor compression cycle (VCC) for refrigeration using the same working fluid are linked in the analysis, including the limiting case of cold production without net electricity production. We investigate the effects of key parameters on system performance such as net power production, refrigeration, and thermal and exergy efficiencies. Characteristic indexes proportional to the cost of heat exchangers or of turbines, such as total number of transfer units (NTU tot ), size parameter (SP) and isentropic volumetric flow ratio (VFR) are also examined. Three important system parameters are selected, namely turbine inlet temperature, turbine inlet pressure, and the flow division ratio. The analysis is conducted for several different working fluids. For a few special cases, isobutane is used for a sensitivity analysis due to its relatively high efficiencies. Our results show that the system has the potential to effectively use low grade thermal sources. System performance depends both on the adopted parameters and working fluid.

This study deals with thermodynamic and economic analysis of a combined gas turbine and Organic Rankine Cycle integrated with a biomass gasifier. A modified model is used to increase the precision of the gasifier thermodynamic model. Seven decision variables, namely, biomass gasification temperature (Tgasif), combustion temperature (Tcomb), gas turbine inlet temperature (T3), gas turbine isentropic efficiency (ηGT), compressor isentropic efficiency (ηcomp), compressor pressure ration (rp) and maximum ORC operating pressure (P3R), are selected as the main decision variables of the combined system. The total cost rate and exergy efficiency of the system are chosen as the two main objective functions. A group method of data handling (GMDH) type neural network and evolutionary algorithm (EAs) are used for modeling the effects of the seven decision variables on both objective functions. The result of multi-objective optimization shows that the exergy efficiency of the system is 15.6%, which can be increase to 17.9% in the optimal state, regardless of the total cost rate of system as objective function. In addition, in order to better illustrate the effects of decision variables change in three selected points of the Pareto curve, a sensitive analysis is performed.

In this study, a vapor compression cascade refrigeration cycle was evaluated for the first time by considering the statistical analysis methods, Taguchi and ANOVA approaches, for performance optimization. The analysis was carried out to achieve the optimum operating condition for the maximum COP and exergetic efficiency. The impacts of the operational parameters on the energetic and exergetic performances were investigated. The results show that the most influential parameter on the COP and exergy efficiency was the evaporator temperature, the condenser temperature of the lower cycle, condenser temperature of the overall system and isentropic efficiency of the compressor and the impact ratios were 58.1%, 14.4%, 10.25%, and 7.47%, respectively. The best condition for the multiple performance characteristics was decided to be A3B3C1D1E3F3G3H2J1K2. The COP and exergy efficiency within the range of the operating parameters in the evaluation were found to be 3.274 and 37.63%. These were greater than 27 different combinations of the thermodynamic evaluation results. The temperatures of the evaporator, condenser for the lower cycle, and condenser for the overall system have increment or decrement ratios of 3.92%/°C, 2.2%/°C and 1.61%/°C. The parametric evaluation corroborates the results of the Taguchi and ANOVA methods.

Among different technologies in internal combustion engines, waste heat recovery from the lost energies has great potential to improve fuel economy and reduce CO2 emission. In the present work, to achieve the optimal design parameters for a waste heat recovery system of a gas engine, a multi-objective optimization evolutionary algorithm is employed. The system consists of different types and combinations of the Organic Rankine/Kalina cycle as the waste heat recovery system of gas engine exhaust gas and the waste heat of cooling water is recovered by the trilateral flash cycle. The objective functions are chosen to maximize exergy efficiency and minimize the specific investment cost of the system. Cyclohexane, Toluene, and Benzene have been investigated and compared to the organic Rankine cycle working fluid. To evaluate different cycle configurations and working fluids, the Pareto front solutions related to 18 studied cases are compared. Meanwhile, the “Linear Programming Technique for Multidimensional Analysis of Preference” decision-making approach has been used as an optimal point in all cases. This work is aimed to compare the optimal design operating conditions of the studied configurations to choose the best configuration for waste heat recovery from a gas engine. The results reveal that, among the decision parameters, the organic Rankine cycle turbine inlet temperature is the most important in terms of the specific investment cost of the system. Also, considering the exergy and energy efficiency of the system, organic Rankine cycle turbine inlet temperature as well as organic Rankine cycle and trilateral flash cycle turbine isentropic efficiencies are of great importance. The Pareto front comparison for each configuration indicates that toluene is the most suitable fluid for the organic Rankine cycle in all configurations. Comparing the selected optimal points in different combinations reveals that, the configuration of organic Rankine cycle with internal heat exchanger-trilateral flash cycle, due to its lower payback period and specific investment cost as well as the higher exergy efficiency and net power output in optimal point, is the prominent compared to the other combinations. Furthermore, the optimized configuration of the organic Rankine cycle with the internal heat exchanger-trilateral flash cycle shows a 14.31% increase in the exergy efficiency and an 8.2% decrease in the specific investment cost of the system compared to the base case. Employing the optimized configuration of the organic Rankine cycle with internal heat exchanger-trilateral flash cycle as waste heat recovery of the gas engine leads to a 7.8 kW increment of net power output, equivalent to an increase of 18.85% exergy efficiency of the whole system including engine and bottoming cycle. On the other hand, additional equipment to the engine, impose 3061$/kW specific investment cost which takes 2.2 years to be paid back.

As one of the core components of CAES system, the compressor plays a crucial role in system performance. However, intake humidity can significantly change the performance of the compressor, so it is necessary to accurately evaluate the influence of humidity on the performance. In this paper, the influence of humidity on compressor performance and its mechanism were studied theoretically and experimentally, and an improved humidity correction model based on similarity criterion was proposed. The results showed that the increase of humidity decreases the total pressure ratio and peak isentropic efficiency, and shifts the performance curve towards smaller mass flow. The influence of humidity on compressor performance is essentially the impact of change of gas properties on performance, wherein the gas constant plays a dominant role. Converting the humid air to corresponding dry air by flow similarity, it is founded that the performance variation is mainly attributed to the decrease of rotational speed and increase of mass flow of corresponding dry air. This humidity correction model well agrees with the experimental results and could meet the requirement for assessing the effect of humidity on compressor performance.

In this paper, a trilateral flash cycle (TFC) based system has been developed and studied to find out its prospect for utilizing more energy and enhancing the power generation capacity. To hold simplicity and minimize the cost of system construction, an impulse turbine and a converging-diverging (CD) stationary nozzle setup have been used as the expander. The experimental study introduced impulse turbine incorporates with a stationary CD nozzle and organic working fluid, which showed a promising power generation capability from a heat source below 80 °C in spite of the increasing size of the heat exchanger, condenser, and pump. In addition to the use of proper impulse turbines, however, the power generation capacity of such type of system is basically a function of the nozzle isentropic efficiency, which lies on the nozzle geometry and the alignment with respect to the turbine. A case study on the application of the TFC system for commercial power generation in associate with economic analysis has also been included in this study which shows a payback time less than 10 years with typical operational life of 20 years, considering only 40% nozzle isentropic efficiency and by using more efficient nozzle, the capital cost per unit power generation could be minimized.

Increasing attention has been paid to the axial-flow turbine in supercritical CO2 power cycle and the tip leakage has a significant effect on turbine performance. In the absence of investigation into supercritical CO2 seal on shroud, four types of configurations are established based on a supercritical CO2 axial-flow turbine: the structure without leakage (Without leakage) and the structures with a smooth leakage passage (Smooth), labyrinth seals (Labyrinth) and dry gas seal (DGS). The flow characteristics and aerodynamic performance are discussed in detail. The dry gas seal arranged on the shroud can substantially improve the overall performance. Compared with Labyrinth, the leakage of DGS is reduced by 99.38% while the power and isentropic efficiency are raised by 0.88% and 1.56% respectively. The mass flow rate and leakage increase while the power and isentropic efficiency decrease as seal clearance increases. The mechanical load and thermal load result in converse axial deformation of seal end face while the former performs more remarkably. DGS achieves notable performance close to Without leakage under different inlet pressure and temperature.

A molten carbonate fuel cell (MCFC) is a high-performance electric power generation system, but much research is still required to develop technologies to enhance its power efficiency, because the exhaust gases of an MCFC contain sensible energy. The high level of heat energy in the exhaust gases leads to a poor performance, with an increased electricity rate and decreased efficiency. This study investigated the supercritical carbon dioxide cycle with three different configurations as a bottoming cycle using the exhaust gases of an MCFC stand-alone system and compared the supercritical carbon dioxide cycle with a combined heat and power system in terms of economical operational strategies. The thermodynamic characteristics of each cycle were determined by varying the turbine inlet pressure and isentropic efficiency of the turbomachinery. The results of an analysis found that optimal discharge pressure of compressor, are remarkable parameter for supercritical carbon dioxide cycle. Furthermore, the net power efficiency was increased (3.41%–4.6%) compared to that of the MCFC stand-alone system. In addition, the levelized cost of electricity values for the supercritical carbon dioxide cycle and combined heat and power system were calculated, and sensitivity analyses were conducted for factors such as the heating cost and major equipment cost. The results showed that using the supercritical carbon dioxide cycle as the MCFC bottoming cycle was more economical when the heating cost was less than $28/Gcal and the printed circuit heat exchanger cost was less than $100/kW.

This work presents the aerodynamic design of an 80 kW axial impulse turbine with siloxane MM as working fluid for high-temperature organic Rankine cycle (ORC) applications. Based on the conventional turbine design method, the 1D preliminary design and 3D numerical simulations under both design and off-design conditions are conducted. The numerical results agree well with the preliminary design. The total-to-total isentropic efficiency of the proposed turbine reaches 77.46% with the pressure ratio of 6.54 and rotational speed of 15000 rpm. It can remain a high level in a wide range of operating conditions, especially at high pressure ratios and low rotational speeds. By comparing the maximum decrease value of turbine efficiency depending on the relative tip clearance, the axial impulse turbine shows less sensitivity to the tip clearance than the conventional turbine. The appropriate cascade solidities for the stator and rotor are both higher than the recommended ranges for the conventional turbine, which provide the reference for the further design. Although the axial impulse turbine exhibits slightly lower efficiency than the other ORC turbines in the research, it features great advantages of low cost and wide application which allow the assessment for ORC practical applications.

To clarify the condensation characteristics of natural gas under a high pressure and obtain accurate nucleation parameters, traditional Internal Consistent Classical Nucleation Theory (ICCT) model for single-component gas was improved. A mathematical model for the supersonic condensation flow of methane gas was established based on the improved ICCT model, and the supersonic condensation process was experimentally verified. The field characteristics of condensation flow and isentropic flow were compared, and the low-temperature liquefaction characteristics of methane gas in the Laval nozzle were studied. The results show that the calculation results of improved model considering the real gas effect are more accurate than the results of original ICCT model. When methane gas is condensed, a weak condensation shock wave propagates in the nozzle; compared with the isentropic expansion process, the pressure and temperature at nozzle outlet increase. In a very short distance, the nucleation rate of methane gas sharply increased from 0 to a maximum value of 4.834 × 1021 m−3 s−1 (approximately at x = 0.367 m). The maximum droplet radius, droplet number, and liquid mass fraction are 2.112 × 10−7 m, 4.128 × 1014 kg−1, and 5.437%, respectively.

One of the challenges in swing compressor is how to mitigate or eliminate the impact of the discharge valve. In order to achieve this goal, the swing compressor with no valves (SCNV) has been designed, fabricated, instrumented and tested. This compressor design eliminates the discharge valve and the discharge close volume. A compressor prototype has been tested using R410a as the working fluid and operated at 1800–5400 rev/min. The volumetric efficiency, the isentropic efficiency, and the coefficient of performance (COP) of SCNV have been analyzed. The volumetric efficiency rises with the increase of the shaft speed. However, the isentropic efficiency and the COP increase firstly and then decrease. Additionally, the COP of SCNV is found to be greater than that of the conventional swing compressor when the shaft speed is 1800 rev/min and the reverse is true for the shaft speed at 3600 rev/min and 5400 rev/min.

The current paper investigates the performance behavior of an ORC unit in which the expansion process is realized by two in series scroll expanders. The heating load varies from 50 to 120 kWth and the heat supply temperature to the employed organic fluid (R245fa) from 80 to 130 °C. The two expanders in series configuration is chosen so that to achieve operation as close as possible to the nominal pressure ratio of each scroll machine at high evaporation temperatures where a total pressure ratio in the order of 10 is met. An extensive discussion and analysis is provided on how the key variables, such as pressure ratio, intermediate pressure and filling factor, interact between the two expanders and how this interaction affects each expander separately. This analysis leads to better understanding the overall performance in terms of isentropic and thermal efficiency and power generation. Emphasis is paid in off-design performance comprehension, while useful conclusions on how such split expansion process can be efficiently controlled by speed regulation are extracted. Focus is given on the interpretation of results for the partial heat load of 50 kWth at 130 °C, which show a very large scattering of both isentropic efficiencies of expanders and thermal efficiency. Accordingly, a variation of thermal efficiency is detected from slightly above 3% to about 10%. The results show that there are certain operating conditions where system performance is ameliorated and the maximum thermal efficiency of almost 10% is achieved, while the isentropic efficiency of high pressure expander reaches a maximum of 68% and that of low pressure expander 57%.

This study presents the thermoeconomic optimization of LiBr/H2O-R134a compression-absorption cascade refrigeration cycle. The detailed exergy-based thermoeconomic analyses, thermoeconomic evaluation with exergoeconomic variables, and thermoeconomic optimization by using non-linear simplex direct search method have been performed for the cascade refrigeration cycle. In the sample application, the thermoeconomic optimization reveals the optimum generator temperature, condenser temperature, absorber temperature, condenser temperature of vapour compression section, effectiveness of solution heat exchanger and compressor isentropic efficiency. This analysis points out that the evaporator equipage and solution heat exchanger should be designed carefully according to the exergoeconomic factor values. The exergetic efficiency and minimum cost of objective function are determined as 7.30% and 4.05 ($/h) for the optimum case of sample application. The minimum cost of objective function is reduced about 3.3%, the coefficient of performance (COPcyclegen) and exergetic efficiency of cascade cycle are improved about 7% and 3.1% respectively, according to the base case.

This paper presents the experimental performance of a curved nozzle two-phase reaction turbine design for trilateral flash cycle heat engine. Results from two tests have been presented, for first test the average feed water temperature was maintained around 97 °C under local atmospheric pressure, while for the second test the average feed water temperature was maintained around 115 °C under 200 kPa absolute pressure. For both the tests the initial condenser pressure was maintained around 6 kPa absolute. The maximum power output of the turbine is estimated to be around 1330 W with an isentropic efficiency of around 25%.

An Organic Rankine Cycle (ORC) with a scroll expander with varying displacement is studied. First, to obtain the isentropic efficiency of the scroll expander modified from an automobile air-condition compressor with a displacement of 66 ml/r, the performance is investigated by experiments on a test rig driven by the compressed air. Second, based on the experimentally obtained isentropic efficiency, thermodynamic and heat transfer models of ORC are established on the basis of sub-models of the main apparatuses. Consequently, energy and exergy efficiencies are analyzed. Based on the simulation, an ORC system is constructed and investigated. Experiments show that for a given heat source temperature of 105 °C, the energy efficiency of the system ranges from 1.7% to 3.2% and the exergy efficiency of the system is 8.6%–16.9%. Additionally, another scroll expander with a displacement of 86 ml/r is utilized to investigate how displacement of the scroll expander influences performance of the ORC system. Finally, experiments also show that the IHX deteriorates the performance of ORC system, which is significantly different from simulation results.

The main purpose of this paper is to analyze the sensitivity of system parameters to the performance of the Organic Rankine Cycle (ORC) system quantitatively. A thermodynamic model of the ORC system for binary-cycle geothermal power plants has been developed and verified. The system parameters, such as working fluid, superheat temperature, pinch temperature difference in evaporator and condenser, evaporating temperature, the isentropic efficiencies of the cycle pump and radial inflow turbine are selected as six factors for orthogonal design. The order of factors sensitivity on performance indices of the net power output of the ORC system, the thermal efficiency, the size parameter of radial inflow turbine, the power decrease factor of the pump and the total heat transfer capacity are determined by the range obtained from the orthogonal design. At different geothermal temperatures, the ranges of the six factors corresponding to performance indices are analyzed respectively. The results show that the geothermal temperature influences the range of the factors to the net power output, SP factor of radial inflow turbine, and the total heat transfer capacity, but it has no effect for the range of the factors for the thermal efficiency and the power decrease factor of the pump. The evaporating temperature is always the primary or secondary factor that influence the thermodynamic and economic performance of the ORC system. This study would provide useful references for determining the proper design variables in the performance optimization of the ORC system at different geothermal temperatures.

A method to determine the economic cost of gas turbine compressor fouling was developed. The method is based on the calculation of the influence of the drop of compressor performances (isentropic efficiency, pressure ratio and air mass flow) on Heat Rate and full load power of the gas turbine. A statistical procedure to quantify the drop of compressor performances with fouling and to obtain ambient correction factors for the compressor was also developed. Finally, this method was applied to a real gas turbine in order to check its validity. It was demonstrated that the application of the correction factors obtained worked well. The method was used to check the evolution of the compressor efficiency over time and the effects of off-line washings on compressor performances. It could be concluded that the loss of maximum power is the most important factor to take into account to schedule off-line washings.

This paper investigates the design and operation of a thermal storage refrigerator. Firstly, compressor performance at a range of typical refrigerator operating conditions was analysed. The model results suggest that larger compressors are more efficient when running, with isentropic efficiency increasing by 50% as the displacement increased from 4 to 8 cm3. The impact of compressor performance on the overall refrigerator efficiency was estimated and the results indicated that an energy reduction of 19.5% can be obtained by replacing a conventionally sized, 4 cm3 compressor by a larger 8 cm3 model. However, using a larger compressor will normally lead to more start/stop events, which reduces overall efficiency. A method is proposed for exploiting the superior performance of large compressors by accumulating their high cooling capacity output in a phase change material (PCM), reducing the number of on/off cycles. Numerical modelling and experimental validation were undertaken using a prototype thermal storage refrigerator, incorporating a PCM, to estimate the PCM charge and discharge rate and the corresponding refrigerator on and off cycle durations at different ambient conditions. The results showed that the integration of a 5 mm PCM slab into the refrigerator allowed for 3–5 h of continuous operation without a power supply. The numerical model was found to be in good agreement with the experimental results, with the error between the simulation and tests below 5% for most experiments.

As a major component of cryogenic turboexpander, the design and performance estimation of a radial inflow turbine determines the effectiveness of the system. To explore the performance, this paper focuses on to investigate the effect of mass flow rate and operating temperature on isentropic efficiency, temperature drop, enthalpy drop, pressure variation, and power output of a cryogenic turboexpander. Firstly, the mean-line design of a radial inflow turbine is conducted by considering different loss models. Sobol sensitivity analysis is performed to identify the major geometrical parameters which have a significant effect on the performance of the turbine. Based on the geometrical data sets, an ANN and ANFIS models are developed to predict the ranges in which maximum efficiency of the turbine is obtained with minimum losses. The designed turbine is validated with available data in the literature. Secondly, an experimental set-up with extended measuring points for data collection is developed to investigate the performance of a turboexpander at cryogenic temperature. A detailed experimental analysis is carried out to compare the temperature drop, isentropic efficiency, and power output of the turboexpander for mass flow rate in the range of 0.03–0.08 kg/s and the inlet temperature of 130, 140, and 150 K. It is noticed that the highest temperature drop is obtained for the inlet temperature of 150 K. Thirdly, based on the experimental data, an ANN and ANFIS model is developed to predict the optimal range in which the turboexpander have maximum isentropic efficiency and temperature drop. The results deduce some valuable experimental data and also accumulate the design methodology of radial inflow turbine for cryogenic applications.

Turbine and the working fluid are two key factors that affect the performance of an organic Rankine cycle (ORC). A one-dimensional design for an ORC radial inflow turbine is conducted in this paper. An entire three-dimensional model of the designed turbine including the nozzle, rotor, and volute, is developed and its performance is predicted by Computational Fluid Dynamics. Peng-Robinson equation is employed to predict the properties of working fluids. The simulation shows that the numerical results agree well with the designed value. Additionally, the performance comparison between R245fa and R245fa/R134a is carried out. It is concluded that when R245fa and R134a are mixed with a ratio of 7:3, the power output and isentropic efficiency of the turbine are 9.3% and 2.5% higher than pure R245fa, respectively. What’s more, the off-design performance of the radial turbine using R245fa/R134a is numerically investigated. The results show that there is little change for isentropic efficiency of the radial inflow turbine when the rotational speed varies from 95% rpm to 115% rpm. However, the pressure ratio has a great impact on turbine efficiency. The performance prediction method based on preliminary design and numerical simulation can be applied to the future optimal design of a radial-inflow turbine using zeotropic mixture fluids.

Two-phase expansion is of great interest to enhance the efficiency of conventional sub-critical organic Rankine cycle (ORC). However, the design of highly-efficient expanders to handle two-phase expansion is still an open topic in the literature. In this paper, an experimentally validated thermodynamic model was employed to investigate the two-phase expansion process in a reciprocating expander with a flash chamber for Trilateral Flash Cycle (TFC) applications. An intake ratio, e, defined as the intake time to the expansion time has been proposed to analyze the suction process of saturated liquid and the corresponding intake losses. The evolutions of temperature, pressure, and quality during the expansion process have been simulated, and the intake losses have been quantified from the indicated diagrams. Moreover, parametric analyses on the influence of the intake ratio for different rotational speeds, mean inlet flow velocities, inlet port diameters, and intake mass values have been performed. The isentropic efficiency and the power output of the expander have been calculated and discussed under different operating conditions. Finally, a correlation for estimating the intake losses has been developed.

3E)exergy/exergoeconomic/exergoenvironmental) analysis is considered to evaluate a novel hydrogen liquefaction process. The proposed process is a simple Claude cycle combined with two absorption refrigeration systems (ARSs). The mass flow rate of the liquid hydrogen L H 2 production is about 260 tones per day and the specific energy consumption (SEC) and the exergy efficiency of the system are 12.7 k W h / k g L H 2 and 31.6% respectively. The results show that the HX-201 and HX-203 heat exchangers have the highest total environmental impact and total exergy cost. Therefore, they are in the priority of improving to achieve better performance for overall the process. In addition, the P-101 pump has the highest exergoeconomic and exergoenvairomental coefficient. Therefore, its capital investment cost and its environmental impact should be reduced to decrease the cost and environmental impact of the whole system. Furthermore, the HX-201 heat exchanger has the lowest exergoeconomic and exergoenvairomental coefficient. Therefore, the technical performance of this device should be improved to reduce the cost and environmental impact of the whole system. In addition, a 3D sensitivity analysis is investigated to consider simultaneously the interaction between technical, economic, and environmental aspects of the system. Accordingly, there is an optimum value for the isentropic efficiency of the C-1 compressor that should be examined, and the more/fewer is its pressure ratio, the more/fewer are its exergy costs and/or environmental impacts. Moreover, whilst an optimum pressure ratio should be found out for EXP-2 expander, a higher isentropic efficiency definitely decreases its exergy cost and environmental impact. In addition, the less/more is the temperature approach Δ T min of HX-1 heat exchanger, the less/more are its exergy costs and/or its environmental impacts. As well as, its input pressure should be maximized to achieve minimum exergy costs and environmental impacts of the component. Finally, tower pressure should be raised as much as possible to achieve the least exergy costs and environmental impacts of the T-101 generator. However, its inlet temperature has an optimum value that should be found out.

This paper presents the experimental investigation and development of a general semi empirical scroll expander model for different working fluids. Initially, the characterization and modelling of a scroll expander with R134a working fluid is performed. The influence of key operating variables on the main performance indicators such as isentropic efficiency, filling factor and specific power are investigated. The proposed semi empirical model for the scroll expander predicts mass flow rate, mechanical shaft power and exhaust temperature at accuracies of 3%, 9% and 2 K respectively. The developed semi empirical model is then modified to accommodate different working fluids; validation of the generalization procedure is performed with experimental data using ammonia/water mixture and ammonia as working fluids. The generalized semi-empirical model predicts mass flow rate, mechanical shaft power and exhaust temperature to be less than 5%, 7% and 4 K error margin for both ammonia/water and pure ammonia working fluids. Therefore, the simulation model presented in this study can save the time and material resources for the selected scroll expander solely as a consequence of a change in the working fluid to predict the main performance indicators.

Compression and expansion strokes in internal combustion engines can be characterized by the well-known polytropic process, PVn = constant, which describes the relationship between the in-cylinder volume and the pressure. This process is widely used to estimate the in-cylinder pressure during the compression stroke before combustion occurs; the polytropic index (n) is a key parameter for calculating the pressure accurately when volume data are given. However, the polytropic index changes with different engine operating conditions. Therefore, using the same value for the polytropic index under different operating conditions can decrease the accuracy of the pressure prediction during the compression stroke. It can also affect pressure modelling during combustion in which the pressure at the end of the compression stroke is used as an initial condition. Therefore, it is important to obtain an appropriate polytropic index to predict the in-cylinder pressure precisely. This study focused on a methodology to estimate the polytropic index for real-time applications. Heat loss from the in-cylinder gas was considered a major factor affecting the polytropic index. Therefore, a model of the polytropic index (n) could be established as a simple linear equation, ‘ n = n isen + Q loss T 1 × S ’, where the heat loss (Qloss) is the main variable. nisen means the polytropic index with isentropic condition and T1 is the temperature of the in-cylinder gas when the compression starts. S which indicates the slope of the linear equation is inversely proportional to the compression ratio during the compression stroke. The main variable, heat loss, was modelled to complete the whole model of the polytropic index, and Woschni’s correlation was adopted to estimate the heat loss from the in-cylinder gas. The index model was established with 220 steady-state experimental cases using a 1.6-L compression-ignition (CI) engine. In addition, the pressure at the end of the compression stroke could be predicted using the modelled index with the polytropic process. The model could be validated against 1.6-L CI engine which has different compression ratio and in-cylinder geometry compared with the test engine. This study can contribute to a quantitative understanding of which parameters affect the in-cylinder pressure during the compression stroke. It will also be helpful for establishing a whole in-cylinder pressure prediction model for internal combustion engines; the pressure information obtained from such a model could be used for emissions modelling and combustion control.

With attention to the drawback of specifying isentropic efficiency of expander (or turbine) in Organic Rankine Cycle (ORC) analysis, in order to enhance reliability of analysis results, this article replaces the constant isentropic efficiency by internal efficiency of optimal radial flow turbine for each condition. With both analysis methods, namely internal efficiency analysis method and conventional analysis method, 14 subcritical ORC working fluids are studied with hot water of 90℃, pinch point temperature of 5℃ and condensing temperature of 30℃. Results with both analysis methods are compared. The results show that turbine internal efficiency is determined by expansion ratio in rotor and decreases with the rise of expansion ratio in rotor. There are differences between cycle net power output with internal efficiency analysis method and that with conventional analysis method. The differences can change the results in optimizing fluid. It is significant to apply computational optimal efficiency instead of constant isentropic efficiency in ORC analysis.