Expander Power Output Research Articles

Novel multi-helical coil heat exchanger-based small-scale organic Rankine cycle: A detailed heat transfer analysis

This paper discusses a prototype of the ORC, which is developed utilizing a novel multi-coil evaporator and condenser for the waste heat source with a temperature below 100 °C. R123 acts as a working fluid for the ORC. The thermal performance of a multi-helical coil is evaluated experimentally and compared to the single-helical coil heat exchanger available in the literature.The performance of a novel multi-coil heat exchanger depicts that when the Reynolds Number varies from 60000 to 120000, the heat transfer coefficient varies from 1560 W/(m2K) to 2900 W/(m2K) for a single coil heat exchanger and 3014 W/(m2K) to 4531 W/(m2K) for multi helical coil evaporator. The Nusselt Number varies from 300 to 570 for single-coil heat exchangers and 715 to 1076 for multi-helical coil heat exchangers. The results show that the expander's power output is around 2.14 kW and proportional to the evaporator temperature and pressure increase. The high condensing temperature decreases the expander power output. The main contribution of the present work is developing a small ORC system with novel multi-helical coil heat exchangers and testing them on a lab scale for the most probable application to fulfill the electricity requirement in remote areas in the future.

The Influence of Condenser Temperature on the Energy and Exergy Efficiencies of the ORC

From low-grade heat sources, the organic Rankine cycle may be exploited to create power. The thermal efficiency of the organic Rankine cycle is affected by the value of the lowest cycle temperature, which is the condensation temperature. This study looks at the effect of condensation temperature on the efficiency of energy systems that use organic Rankine cycles. At a condensing temperature of 10–20 °C, the ORC thermal efficiency is calculated. R134a working fluid was used in the study. The expander's power output was boosted to 0.09765 kW by decreasing the condensing temperature. Additionally, the thermal efficiency has been enhanced by 3.826 %. At a minimum temperature of 10 °C, the expander speed at 595 rpm. Exergy efficiency has an 18.26 %. is shown that lowering the condensing temperature increased the ORC system's thermal efficiency and energy output.

Experimental testing of scroll machine driven by compressed air for power generation and its integration in small scale organic Rankine cycle

Organic Rankine Cycle (ORC) is a proven technology in the field of waste heat recovery and present days ORC is extensively being used in exploiting biomass, geothermal and solar energy. The overall performance of ORC depends on the expander, making it a core component of the system. Generally, these expanders are classified into velocity type and displacement type. The velocity type expanders find their applications in large scale power generation and are not preferred in small scale power applications as their rotational speeds exponentially increase with a decrease in expander power output. As a result, the displacement type expanders are best suited for small scale power generation in ORC. Yet, till date expanders capable of producing power at small scale are not commercially available in the market for ORC application. As an effect commercially available scroll compressors are modified to work as expanders in ORC systems. The present study aims to examine the feasibility of using one such scroll compressor as an expander in ORC with and without modification. A test rig was developed to test the compressor running in reverse as expander using compressed air, before and after modifications. The scroll machine was tested for operating conditions consisting of pressure varying from 0.5 bar to 4.5 bar and the load varying from 0.2 kg to 2.2 kg for a constant airflow rate. The configurations tested were, scroll compressor with the suction port as inlet, modified scroll compressor with the suction port as inlet and modified scroll compressor with discharge port as an inlet. Based on the experimental test data obtained it is observed that, in all three configurations, for various loading conditions at given inlet air pressure there exists a maximum power generation point and a further increase in the load at given pressure has a negative effect on power output. Also, a significant increase in speed is observed from 300 to 4250 rpm at no load condition with increasing inlet air pressures. Maximum power of 210 W was achieved at a load of 1.1 kg with the inlet pressure of 4.5 bar for modified scroll machine when the discharge port was used as an inlet. Finally, it is recommended to use a modified scroll machine with discharge port as inlet as it gives more power when compared with other configurations for the same operating conditions.

Experimental investigation of an organic Rankine cycle with liquid-flooded expansion and R1233zd(E) as working fluid

A new concept of liquid-flooded expansion has been proposed as a performance increasing modification of the basic ORC targeted at low-temperature heat sources. However, little research demonstrates the potential of this technology especially experimentally. In this paper, an experimental test facility based on a conventional recuperative ORC system was constructed with an independent liquid flooding loop that enables testing the influence of liquid flooding on a modified single-screw expander as well as on the cycle itself. Experiments were performed at various pressure ratios (3.3–4.1) over the expander and flooding ratios (0–0.3) with R1233zd(E) as the working fluid and a standard lubricant oil as the flooding medium. The data reduction and uncertainty analysis were also discussed in depth. In total, 142 steady-state points were obtained. Compared with the baseline organic Rankine cycle, the maximum improvement of the liquid-flooded expansion on the expander power output can be 9.1%, although at slightly worse expander inlet conditions. The maximum enhancement of the isothermal efficiency of the expander was 9.5%. Results also showed that the expander power output, the net power output and the thermal efficiency were enhanced with the increase of the flooding liquid amount. The potential of an organic Rankine cycle system with liquid-flooded expansion can be further examined if over-expansion losses can be reduced and larger amount of oil can be injected, i.e., with higher pressure ratios and higher flooding ratios. Overall, this study provides insights into performance improvement by means of modifying the cycle thermodynamics itself.

Dynamic analysis of a low-temperature Adiabatic Compressed Air Energy Storage system

Adiabatic Compressed Air Energy Storage (A-CAES) systems have received wide attention in the last decade. The variations of the air pressure and temperature in the storage cavern substantially affect the expander power output and overall system efficiency. In this paper, the dynamic performance of a low-temperature A-CAES system is studied under real-time operation. A comprehensive dynamic model is developed and validated using experimental data. The dynamic analysis shows that the predicted system efficiency agrees well with the experimental data and is about 10% lower than that obtained from the steady-state analysis. The effect of operating parameters (e.g. compression/expansion flow rate, cavern initial and storage pressure, and number of compression/expansion stages) on the A-CAES system performance is further investigated. High compressor flow rate leads to a cavern air temperature above 521 K and reduces the system efficiency relatively by 9.1%. This indicates that the compressor flow rate must be carefully selected to ensure the cavern safety and reliability and overall system performance. It is also found that increasing the expander flow rate reduces the system and heat recovery efficiencies by up to 8.8% and 40.3%, respectively under the studied flow rates. The results also show that the cavern storage and initial pressure have a large effect on the overall system efficiency. The practical cavern storage and initial pressure were around 66 and 25 bars, respectively, to achieve a good system performance.

Prediction and optimization of power output of single screw expander in organic Rankine cycle (ORC) for diesel engine waste heat recovery

The output characteristics of single screw expander has a direct and crucial influence on the performance of organic Rankine cycle (ORC) system. In this paper, a machine learning prediction model driven by experimental data is developed and applied to predict the power output of single screw expander. After screening different structural parameters of the model, genetic algorithm (GA) is used to optimize the initial weights and thresholds of the model, so as to further improve the generalization ability of the model. In addition, the generalization ability of the model is compared with that of the model not optimized by GA. Furthermore, the influence of operating parameters on the power output of single screw expander is analyzed by fitting algorithm in three-dimensional space. The optimization boundary value needed for prediction and optimization is determined by fitting algorithm in four-dimensional space. Finally, a prediction and optimization model is created by coupling the machine learning prediction model with GA, and the maximum power output and corresponding operating parameters of the single screw expander under full operating conditions are predicted and optimized. The results show that with the application of machine learning and GA, the maximum power output of single screw expander can be predicted and optimized precisely under full operating conditions. So as to directly guide the selection of relevant parameters in the process of theoretical analysis and experimental research.

Experimental study and energy loss analysis of an R245fa organic Rankine cycle prototype system with a radial piston expander

In this paper, an R245fa organic Rankine cycle experimental prototype system with a 5-cylinders radial piston expander is presented to recovery waste heat from exhaust gas of diesel engine. In order to explore the system behavior and research the effective adjustment method, the performance was tested and analyzed with multiple operating parameters: pump speed, generator load, energy of waste heat source and working fluid filling quantity. Moreover, energy and exergy analysis were provided to evaluate the system energy loss. Combining simulation study of expander in GT-SUITE, the internal friction and leakage were calculated to illuminate the energy degradation processes of expansion. The experiments proved the feasibility of radial piston expander for organic Rankine cycle coupled to vehicle engine. The results demonstrate that expander power output can be optimized by adjusting pump speed under different heat sources and moderate filling quantity indicates the largest expander power output. The gross thermal efficiency and exergy efficiency of the organic Rankine cycle system can reach up to 2.02% and 10.5%, respectively. Overall system exergy losses are 4.24–4.63 kW and expander contributes about 1 kW. In the processes of expansion, entropy increment leads to larger energy degradation than working fluid flow loss and mechanical frictional loss. Under the influences of multiple energy losses, the maximum expander mechanical power output 279 W can be obtained.

Experimental and Techno-Economic Analysis of Solar-Geothermal Organic Rankine Cycle Technology for Power Generation in Nepal

The current research study focuses on the feasibility of stand-alone hybrid solar-geothermal organic Rankine cycle (ORC) technology for power generation from hot springs of Bhurung Tatopani, Myagdi, Nepal. For the study, the temperature of the hot spring was measured on the particular site of the heat source of the hot spring. The measured temperature could be used for operating the ORC system. Temperature of hot spring can also further be increased by adopting the solar collector for rising the temperature. This hybrid type of the system can have a high-temperature heat source which could power more energy from ORC technology. There are various types of organic working fluids available on the market, but R134a and R245fa are environmentally friendly and have low global warming potential candidates. The thermodynamic models have been developed for predicting the performance analysis of the system. The input parameter for the model is the temperature which was measured experimentally. The maximum temperature of the hot spring was found to be 69.7°C. Expander power output, thermal efficiency, heat of evaporation, solar collector area, and hybrid solar ORC system power output and efficiency are the outputs from the developed model. From the simulation, it was found that 1 kg/s of working fluid could produce 17.5 kW and 22.5 kW power output for R134a and R245fa, respectively, when the geothermal source temperature was around 70°C. Later when the hot spring was heated with a solar collector, the power output produced were 25 kW and 30 kW for R134a and R245fa, respectively, when the heat source was 99°C. The study also further determines the cost of electricity generation for the system with working fluids R134a and R245fa to be $0.17/kWh and $0.14/kWh, respectively. The levelised cost of the electricity (LCOE) was $0.38/kWh in order to be highly feasible investment. The payback period for such hybrid system was found to have 7.5 years and 10.5 years for R245fa and R134a, respectively.

Dynamic simulation and experiments of a low-cost small ORC unit for market applications

Organic Rankine Cycle is one of the most efficient, profitable and feasible technology for low-to-medium temperature heat recovery. The boost to the development of small-scale systems that could easily enter the market poses challenges in the design and selection of components, and in the choice of the operating conditions. This work deals with a micro-scale Organic Rankine Cycle (ORC) unit that has been designed to be cheap, efficient and compact, and tested to analyze performance and transient response under large variations of the heat source temperature. A dynamic model is also built and validated against two sets of experimental data: the first one refers to maximum power operation of the system and the second one to partial load operation close to the occurrence of two-phase expansion. The goal is to understand the potential of the system to face market applications, for which best design choices, operational limits and response time to variable heat sources must be identified. The choice of scroll expander, volumetric pump and plate heat exchangers has been made according to the lowest cost-to-efficiency ratio to keep the investment cost below 2500 euro/kW, already in the pre-market phase, in the power range of 3–4 kW. Results of the experiments show a fast time response, with a prompt reaction of the system to variations of the heat source temperature. Simulations demonstrated the ability of the model to capture with good accuracy the system dynamics. In particular, the validation process at maximum power operation (expander power output of 3300 W) shows maximum relative errors of about 4% in the prediction of measurements, whereas, the validation process at partial load operation yields slightly higher errors, namely 5.2% and 6.6% in the prediction of the evaporation pressure and the expander power output, respectively.

Working fluids selection from perspectives of heat source and expander for a Trilateral cycle

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.

Experimental and numerical analyses of a 5 kWe oil-free open-drive scroll expander for small-scale organic Rankine cycle (ORC) applications

Organic Rankine cycles (ORCs) are thermodynamic power cycles designed to generate work from a wide range of heat source conditions. In particular, low-grade waste heat recovery (WHR) (<150 °C) can be effectively exploited with such systems. The efficiency of an ORC is highly dependent on its expander performance. In the low power output range (<10 kW), scroll expanders are cost-effective. Although a number of researchers have investigated the use of scroll compressors as expanders, very little work has been carried out in modeling and investigating the performance of oil-free expanders. In this work, an experimental evaluation of a newly designed open-drive oil-free scroll expander was performed. The expander had a nominal capacity of 5 kW, built-in volume ratio of 3.5, and was integrated into an ORC test-rig with R245fa as working fluid. The experimental data consisted of 75 data points that were used to map the oil-free operation of the scroll expander over five expander rotational speeds (from 800 rpm to 3000 rpm). Two heat sources inlet temperature, i.e. 85 °C and 110 °C, were investigated. The scroll expander achieved a maximum overall isentropic efficiency of 0.58 for the temperature source of 110 °C, for the imposed specific volume ratio of 6.12 at rotational speed of 1600 rpm. For the same heat source, the maximum expander power output was 3.75 kW for an imposed specific volume ratio of 6.55 and rotational speed of 2500 rpm. Besides the experimental work, the performance of the expander was characterized by means of a semi-empirical model to break-down the different loss terms. A well known model available in the literature was extended to account for the major frictional losses in a scroll machine, i.e. bearings, tip-seals and other sources of friction. Additionally, an Artificial Neural Network (ANN) modeling approach was also proposed to achieve higher accuracy in mapping expander performance for use in system simulation. The experimental data and model source codes are provided as supplementary materials.

Simulation of a scroll expander using R1233zd(E), R1234ze(Z) and their mixtures as drop-in replacements for R245fa

This paper presents simulations of the performance of a 2 kW hermetic scroll expander, based on a model reported in literature, when replacing the original working fluid (R245fa) with fourth-generation refrigerants.Calculations of micro organic Rankine cycles, equipped with the selected expander, show a slightly better performance when using R1234ze(Z) or R1233zd(E), as drop-in replacements of R245fa. Binary mixtures, characterized by a non-isothermal phase-change behavior, are considered as well. In particular, results of mixtures depend on the fluid temperature at the expander inlet. The most relevant result is that the mixture process for some hydrofluoroolefins causes a decrease of the maximum cycle temperature, after setting a fixed expander power output, and therefore the possibility of exploiting heat sources at lower temperatures.

Simulation and Performance Analysis of Organic Rankine Systems for Stationary Compressed Natural Gas Engine

The organic Rankine cycle (ORC) can be used to recover the waste heat from a stationary compressed natural gas (CNG) engine. However, the exhaust energy rate varies with engine load, which can influence the operating performance of the ORC system, therefore, it is necessary to study the running state of the ORC system. In this paper, first, the numerical simulation model of the ORC system is built by using GT-Suite software, with R245fa selected as the working fluid of the ORC system. The boundary conditions of the numerical simulation model are specified according to the measured data obtained by the stationary CNG engine test. Subsequently, the power output and dynamic characteristics of expander are analyzed to determine the running state of the ORC system. Investigations indicate that the fluctuation of refrigerant mass flow rate in the expander is obvious in the engine’s low-load regions (from 20% engine load to 40% engine load). The performances of ORC system and stationary CNG engine-ORC combined system (combined system) are finally investigated, respectively. The results show that the thermal efficiency of the combined system can be increased by a maximum 5.0% (at the engine rated condition), while the brake specific fuel consumption (BSFC) can be reduced by a maximum 4.0% (at the engine rated condition).

Heat source temperature control investigation of a hydraulic retarder based organic Rankine cycle

In the paper, a hydraulic retarder based organic Rankine cycle (ORC) system is investigated. In order to achieve stable oil output temperature in the evaporator under different hydraulic retarder operating conditions, evaporating pressure is studied to match with a specified evaporator heat transfer area through iterative calculations. An experiment test is a setup to conduct the validation. The results show that regulating evaporating pressure can achieve a target evaporator oil output temperature. However, expander load moment and working fluid mass flow rate (MFR) need to be controlled precisely. With the increase of retarder rotor speed, required evaporating pressure generally decreases, while working fluid MFR increases dramatically. Effects of the changed evaporating pressures and MFR s on expander power output increases from 2.52 kW to 31.43 kW, while cycle thermal efficiency changes slightly in low filling rate condition, from 10.2% to 10.7% for 25% filling condition.

Experimental and Potential Analysis of a Single-Valve Expander for Waste Heat Recovery of a Gasoline Engine

In this paper, a Rankine cycle test system is established to recover exhaust energy from a 2.0 L gasoline engine. Experiments on the system’s performance are carried out under various working conditions. The experimental results indicate that the recovery power of the expander is strongly related to the load and speed of the gasoline engine. It is found that when the output power of the gasoline engine is 39.8–76.6 kW, the net power of the expander is 1.8–2.97 kW, which is equivalent to 3.9%–4.9% of the engine power. The performance simulation shows that the mass flow rate, power output, and isentropic efficiency of the piston expander are directly determined by the intake valve timing. Selecting a suitable intake valve timing can optimize the performance of the expander. The simulation results show that a 1 kW increment in power can be obtained only by selecting an optimum intake open timing. The experimental results further verify that the single-valve piston expander, because of its small dimensions, simple structure, and high speed, is appropriate, and has great potential for energy recovery of gasoline engine exhaust and has good prospects for engineering applications.

Performance Analysis of a Reciprocating Piston Expander and a Plate Type Exhaust Gas Recirculation Boiler in a Water-Based Rankine Cycle for Heat Recovery from a Heavy Duty Diesel Engine

The exhaust gas in an internal combustion engine provides favorable conditions for a waste-heat recovery (WHR) system. The highest potential is achieved by the Rankine cycle as a heat recovery technology. There are only few experimental studies that investigate full-scale systems using water-based working fluids and their effects on the performance and operation of a Rankine cycle heat recovery system. This paper discusses experimental results and practical challenges with a WHR system when utilizing heat from the exhaust gas recirculation system of a truck engine. The results showed that the boiler’s pinch point necessitated trade-offs between maintaining adequate boiling pressure while achieving acceptable cooling of the EGR and superheating of the water. The expander used in the system had a geometric compression ratio of 21 together with a steam outlet timing that caused high re-compression. Inlet pressures of up to 30 bar were therefore required for a stable expander power output. Such high pressures increased the pump power, and reduced the EGR cooling in the boiler because of pinch-point effects. Simulations indicated that reducing the expander’s compression ratio from 21 to 13 would allow 30% lower steam supply pressures without adversely affecting the expander’s power output.

Effect of resistive load on the performance of an organic Rankine cycle with a scroll expander

An experimental investigation is performed for an organic Rankine cycle system with different electrical resistive loads. The test rig is set up with a small scroll expander-generator unit, a boiler and a magnetically coupled pump. R134a is used as the working fluid in the system. The experimental results reveal that the resistive load coupled to the scroll expander-generator unit affects the expander performance and power output characteristics. It is found that an optimum pressure ratio exists for the maximum power output. The optimal pressure ratio of the expander decreases markedly as the resistive load gets higher. The optimum pressure ratio of the scroll expander is 3.6 at a rotation speed of 3450 r/min for a resistive load of 18.6 Ω. The maximum electrical power output is 564.5 W and corresponding isentropic and volumetric efficiencies are 78% and 83% respectively.

Experimental study on the performance of single-screw expander with different inlet vapor dryness

A single-screw expander with 155 mm diameter screw has been developed. In order to investigate the performance of this prototype with different inlet vapor dryness, an organic Rankine cycle experimental system was built, and experiments were conducted at different inlet vapor dryness by adjusting the mass flow rate of working fluid into evaporator. The results indicated that with the increase of inlet vapor dryness, the power output and expansion ratio were increased，however， the volume efficiency and overall efficiency were decreased. The maximums of power output, expansion ratio, volumetric efficiency and total efficiency of single-screw expander were 5.12 kW, 4.55, 80.5% and 49.5%, respectively.

Energy, Exergy and Performance Analysis of Small-Scale Organic Rankine Cycle Systems for Electrical Power Generation Applicable in Rural Areas of Developing Countries

This paper introduces the concept of installing a small-scale organic Rankine cycle system for the generation of electricity in remote areas of developing countries. The Organic Rankine Cycle Systems (ORC) system uses a commercial magnetically-coupled scroll expander, plate type heat exchangers and plunger type working fluid feed pump. The heat source for the ORC system can be solar energy. A series of laboratory tests were conducted to confirm the cycle efficiency and expander power output of the system. Using the actual system data, the exergy destruction on the system components and exergy efficiency were assessed. Furthermore, the results of the variations of system energy and exergy efficiencies with different operating parameters, such as the evaporating and condensing pressures, degree of superheating, dead state temperature, expander inlet temperature and pressure ratio were illustrated. The system exhibited acceptable operational characteristics with good performance under a wide range of conditions. A heat source temperature of 121 °C is expected to deliver a power output of approximately 1.4 kW. In addition, the system cost analysis and financing mechanisms for the installation of the ORC system were discussed.

Investigation of Thermodynamic Parameters of Organic Rankine Cycle (ORC) Designed Exclusively to Improve Generating Large-Scale Electricity Purpose

In present ORC thermodynamic cycle, R245fa, NOVEC700, and R141b as refrigerant working fluids sent to a Heat Exchanger then sent to an Expander to produce electricity, separately. Finally, the remaining working fluid is condensed by a Cooler and it is sent back to the ORC thermodynamic cycle. Current study conducted and analyzed the net power output of Expander, which R141b has a highest amount compare with R245fa, and NOVEC7000. The optimum pressure of working fluids at inlet of Expander has linear relationship with temperature of working fluids at inlet of Expander, with increasing the optimum pressure of working fluids at inlet of Expander, the temperature of working fluids at inlet of Expander is increasing slightly, and then net power Electricity of Expander is increasing, significantly. The efficiency of ORC and thermal efficiency for R245fa, NOVEC7000, and R141b measured at influence of inlet pressure of Expander differences which due to specific different inlet temperature of Expander. The highest, middle, and lowest of ORC efficiency belongs to the R245fa, R141b, and NOVEC7000, respectively. And the highest, middle, and lowest of thermal efficiency belongs to the R141b, NOVEC7000, and R245fa, respectively.