Thermodynamic Power Cycle Research Articles

Thermodynamic investigation and 4Es analysis of a VCR diesel engine using emulsified diesel with catalytic co-pyrolysis fuel derived from waste LDPE and Pongamia pinnata seeds

Global challenges for massive plastic waste disposal and regular decrement of conventional resources, converting plastic and biomass seeds waste into transportation-grade fuels through co-pyrolysis offer a better option for providing a promising solution. This investigation signifies a thermodynamic power cycle model, and 4Es (Energy, Exergy, Environmental, Economic) analysis of a direct injection unmodified diesel engine powered with various blends of test fuels derived from thermo-catalytic co-pyrolysis of low-density polyethylene (LDPE) wastes and Pongamia pinnata seeds at 500 °C with calcium oxide as catalyst, mixed with diesel. The fuel mixtures of pure diesel and pyrolytic test fuels are utilized for diesel engine testing with varying compression ratio. The synergistic effects of major parameters such as full engine load, varying compression ratios (16:1, 17:1, 18:1, and 19:1), and fuel blends (10, 20, 30, and 40 %) are considered for engine run. The Brake thermal energy was found to increase for the 20 % blend at 6.6 % (40 % load) in comparison to pure diesel. Also, the Brake specific fuel consumption was the least for the same blend, 0.31 kg/kWh at 18:1 CR. The smoke was also found to have lowered by 22 % for the 20 % blend in comparison to pure diesel. At a compression ratio of 18:1, the NOx formation also decreased by approximately 1.4 % in comparison to the pure diesel for almost all considered fuel blends. The fuel efficiency was observed to increase for the 20 % blend compared to pure diesel by 20 %. The cost and exergy destruction analysis also confirmed the D80PB20 to have the least and maximum values respectively for both parameters. The energy, exergy, emission, and economic (4Es) analysis confirmed the suitability of blended fuels for achieving improved engine performance and emissions. In addition, the economic and fuel sustainability analysis foster the techno-economic feasibility of the test fuels as compared to conventional diesel fuel.

Power Generation with Renewable Energy and Advanced Supercritical CO2 Thermodynamic Power Cycles: A Review

Supercritical CO2 (S-CO2) thermodynamic power cycles have been considerably investigated in the applications of fossil fuel and nuclear power generation systems, considering their superior characteristics such as compactness, sustainability, cost-effectiveness, environmentally friendly working fluid and high thermal efficiency. They can be potentially integrated and applied with various renewable energy systems for low-carbon power generation, so extensive studies in these areas have also been conducted substantially. However, there is a shortage of reviews that specifically concentrate on the integrations of S-CO2 with renewable energy, encompassing biomass, solar, geothermal and waste heat. It is thus necessary to provide an update and overview of the development of S-CO2 renewable energy systems and identify technology and integration opportunities for different types of renewable resources. Correspondingly, this paper not only summarizes the advantages of CO2 working fluid, design layouts of S-CO2 cycles and classifications of renewable energies to be integrated but also reviews the recent research activities and studies carried out worldwide on advanced S-CO2 power cycles with renewable energy. Moreover, the performance and development of various systems are well grouped and discussed.

Development of a Semi-Empirical Model for Estimating the Efficiency of Thermodynamic Power Cycles

Power plants constitute the main sources of electricity production, and the calculation of their efficiency is a critical factor that is needed in energy studies. The efficiency improvement of power plants through the optimization of the cycle is a critical means of reducing fuel consumption and leading to more sustainable designs. The goal of the present work is the development of semi-empirical models for estimating the thermodynamic efficiency of power cycles. The developed model uses only the lower and the high operating temperature levels, which makes it flexible and easily applicable. The final expression is found by using the literature data for different power cycles, named as: organic Rankine cycles, water-steam Rankine cycles, gas turbines, combined cycles and Stirling engines. According to the results, the real operation of the different cases was found to be a bit lower compared to the respective endoreversible cycle. Specifically, the present global model indicates that the thermodynamic efficiency is a function of the temperature ratio (low cycle temperature to high cycle temperature). The suggested equation can be exploited as a quick and accurate tool for calculating the thermodynamic efficiency of power plants by using the operating temperature levels. Moreover, separate equations are provided for all of the examined thermodynamic cycles.

Techno-economic and 4E comparisons of various thermodynamic power cycles for low-medium grade heat recovery

Various thermodynamic power cycles can be utilized to convert the low-to-medium temperature heat (available from many sources and has huge potential) to electricity and a detailed comparison between all of them is essential to identify the suitable one. Hence, to fulfill this research gap, six thermodynamic power cycles (Organic Rankine cycle with dry fluid, Organic Rankine cycle with wet fluid, Transcritical CO2 Rankine cycle, Kalina cycle, Organic flash cycle and Trilateral flash cycle) have been compared for various heat source and sink temperatures. Objective functions are power generation, efficiency, irreversibility, cost, profit, environmental benefit, techno-economic parameters, etc. Study shows that the trilateral flash cycle is best for medium heat source temperature and the CO2 cycle is best for low heat source temperature. The trilateral flash cycle shows an 11.5% higher exergy efficiency and 16.16% increment in annual profit at 160 °C heat source temperature as compared to the organic Rankine cycle with dry fluid. A decrease in condenser temperature is more advantageous than an increase. The study reveals that the CO2 Rankine cycle would be advantageous for low-grade heat sources while the trilateral flash cycle for medium-grade heat sources in terms of performance, cost, design, operation and environmental benefits.

Analytical study of the absorber performance of a Hygroscopic cycle for low concentrations of LiBr solutions

Nowadays, higher ambient temperatures and water scarcity, primarily due to climate change, represent a challenge for the refrigeration systems of traditional thermodynamic power cycles. The novel Hygroscopic Cycle Technology arises as a solution to mitigate those drawbacks by means of hygroscopic compounds, which lead to a condensation process by absorption in a mixing chamber, called absorber. Consequently, heat rejection can be achieved at higher cold sink temperatures in a closed loop, avoiding water consumption. In this work, the influence of the concentration of the hygroscopic salt LiBr in the condensation process inside the absorber, key element of the cycle, has been analyzed with EES software. The analysis is divided into very low (0% to 0.01%) and low (0.01% to 5%) concentrations of LiBr-H2O solutions. Absolute pressure at the absorber ranges between 3 kPa and 21 kPa. Results show that properties of very low concentration mixtures can be approximated to those of pure water, showing errors lower than 0.11%. As concentration rises from 0.01 to 5 % specific enthalpy decreases, leading to lower consumption of the refrigeration system of the cycle.

Thermodynamic optimization and performance study of supercritical CO2 thermodynamic power cycles with dry cooling using response surface method

This paper deals with thermodynamic optimization of supercritical CO2 recompression and partial cooling cycles operating at cycle maximum temperature of 680°C and maximum pressure of 250 bar. The primary goal to investigate the effects of variation in heat sink temperature (ambient air temperature), mass split fraction (X), and cycle minimum pressure (Pmin) on the thermal efficiency of the power cycles. Response surface method (RSM) is adopted to create a second-order polynomial equation in order to develop the relationship between cycle thermal efficiency and selected decision variables and to find global optimum cycle efficiency. In addition, classification of most influencing cycle parameter is carried out using ANOVA approach. In the case of a recompression cycle, the results demonstrate that heat sink temperature has the greatest impact on thermal efficiency, owing to low p-value and high F-value, followed by mass split fraction and minimum pressure. In a partial cooling cycle, the minimum pressure has the most significant impact on cycle thermal efficiency, followed by the mass split fraction and heat sink temperature. The global optimum combination for the recompression cycle is at heat sink temperature of 20°C, the mass split fraction of 0.3182, and a minimum pressure of 89 bar to obtain the highest thermal efficiency of 0.4963. In addition, the global optimum combination for partial cooling cycle is at heat sink temperature of 32.8 °C, mass split fraction of 0.34, and minimum pressure of 76 bar, which results in an optimum thermal efficiency of 0.4708.

Dispatch optimization of electric thermal energy storage within System Advisor Model

A stand-alone electric thermal energy storage (ETES) system converts low-value electricity into heat using resistance heating elements. During periods of high-value electricity, an ETES system uses a thermodynamic power cycle to convert stored thermal energy back to electricity. These dispatchable systems derive value from their ability to store energy when prices are low and generate electricity when prices are favorable, i.e., energy arbitrage. Consequently, dispatch optimization of system operations, through maximizing revenue subject to system constraints, is essential to evaluate the economic value of a particular system design. While stand-alone ETES systems offer potential advantages as dispatchable grid storage technologies, there is a lack of a neutral third-party, publicly available, open-source model to evaluate the performance, dispatch, and financial viability of these systems. To address this problem, we have developed a techno-economic model for stand-alone ETES systems, within National Renewable Energy Laboratory’s (NREL’s) System Advisor Model (SAM). We implement a mixed-integer linear program to determine an ETES optimal operating schedule that maximizes electricity sales less maintenance costs caused by operation and cycling given temporal-varying grid electricity prices. Our contributions include a mixed-integer linear program for energy arbitrage of an ETES system, an ETES performance model through a publicly-available software (i.e., SAM), and an exercise of our model through case studies that compare ETES operational strategies and annual financial metrics. With our dispatch optimization model, we were able to improve revenue by 20% compared to a myopic heuristic while reducing the operational cost of the ETES system through decreases in cycle starts, cycles per day, and heater starts.

The effect of circumferentially non-uniform heat flux on flow boiling heat transfer in a horizontal tube

Flow boiling is an important energy transfer mechanism in several thermodynamic power cycles. In direct steam generation concentrated solar power applications, flow boiling occurs under non-uniform heat flux conditions, such as in horizontal tubes which are predominantly heated from below. This can influence the local and average heat transfer coefficient. In this experimental study the heat transfer characteristics of saturated flow boiling under different circumferentially non-uniform heat fluxes were determined. To demonstrate the influence of a non-uniform heat flux, tests were conducted on R245fa in an 8.5 mm inner diameter tube at a mass fluxes of 200 kg/m²s and 300 kg/m²s, at saturation temperatures of 35 °C and 40 °C, for vapour qualities between 0.2 and 0.7, and for an averaged heat flux of approximately 6.8 kW/m2. Eight non-uniform heat flux distributions, including variations of heating from above, from the side and below, were considered and their results were compared against those of a uniform heat flux distribution. In all cases, the same or comparable total heat rate was maintained. It was found that uniform heat flux conditions exhibited the highest inner wall heat transfer coefficients, irrespective of the mass flux, saturation temperature or vapour quality under consideration. Compared to the uniform heat flux cases, non-uniform heat flux conditions exhibited a significantly reduced average heat transfer which became worse at higher vapour qualities. Depending on the heat flux scenario, heat transfer performances reduced by up to approximately 45%, and for conditions where heating was applied from below, a reduction of approximately 25% was observed. Based on the circumferential local heat transfer coefficients, that were solved via an inverse problem model, it was concluded that the applied heat flux distribution needs more attention and research. The overall pressure drop was not affected by the heat flux condition.

Stress Distribution on Turbine Blade along with Root at Several Operating Speeds

Steam turbine blades are a very important element in the thermal power generation station and these blades are exposed to higher temperatures and pressure in the thermodynamic power cycle. The designing of such turbine blades and roots is one of the crucial components; most of the failures occurring in the power plant are at blade sections/roots of the sections. The stress distribution is a very important parameter for designing such blades In this research paper, the turbine blade along with an inverted fire tree root is considered for stress analysis. Blade and roots are divided into no of section based up the load acting on it. The stress distribution analysis can be done by different rpm for the X20Cr13 material. The original operating speed as 6728 rpm, the analysis is extended up to 30% of increased speed along with original conditions. The failure of the turbine blade occurs at 15 % of increased speed from the original speed condition, in section1 for QT 650 (material1), and for QT 750 (material 2) it is increased up to 25% for the safest operating conditions.

Multiphase Marine Ramjet Using Liquefied Gas as a Source of Bubbles

An innovative variant of a multiphase marine ramjet is investigated analytically and experimentally. Pressure liquefied gas (LG) is injected, boiling under superheat conditions in the water stream within the propulsion unit, and serving as an on-board bubble source necessary for the ramjet operation. Experiments were conducted in a 10 m diameter tow pool at a speed range of 7–18 m/s (approximately 14–35 knots). For the laboratory concept demonstration and process characterization, two liquefied gases, butane and R134a (synthetic refrigerant gas), were employed. In practical applications, non-polluting LGs such as liquid air may be used. The results reveal the overall performance comparable to the operation with pressurized air, with some thrust advantage of the LG at high-speed tests, attributed to the volume increase of gas during phase change, in accordance with the thermodynamic power cycle analysis.

Determination of optimal compositions and properties for phase change materials in a solar electric generating station

Thermal Energy Storage (TES) systems coupled to thermodynamic power cycles capable of generating electrical work are becoming strategic technologies of the future. The efficiency of TES fluids is a function of several thermodynamic and physical properties such as their heat capacity, latent enthalpy of melting and thermal conductivity. The stored thermal energy in these materials can be delivered to heat transfer fluids either by sensible heat or latent heat interactions. Challenges in the design of TES-based technologies are linked to the thermal stability and corrosivity of the selected heat storage fluid that needs to be encapsulated in metallic tubes/containers as well as the heat transfer efficiency. Latent heat storage materials, also known as Phase Change Materials (PCMs) offer high specific heat storage capacity and can operate at a constant temperature if their chemistry is adjusted so that they represent minima on liquidus surfaces. Working at a constant and minimal temperature is highly desirable from an engineering perspective as it limits corrosion degradation and temperature cycling stresses experienced by the container materials. Up to now, the identification of optimal PCMs has been mostly done via experimental trial-and-error based on limited amounts of thermodynamic data. Being able to theoretically identify PCM candidates and fine-tune their thermo-physical behavior would drastically improve their design. We present here an efficient tool specifically developed for the design of PCMs. This tool was used to identify 30 PCM candidates found in high-order anhydrous chloride-based salt systems that can operate at a temperature of 390±10∘ C.

A quantitative engineering study of ecosystem robustness using thermodynamic power cycles as case studies.

Human networks and engineered systems are traditionally designed to maximize efficiency. Ecosystems on the other hand, achieve long-term robustness and sustainability by maintaining a unique balance between pathway efficiency and redundancy, measured in terms of the number of flow pathways available for a given unit of flow at any node in the network. Translating this flow-based ecosystem robustness into an engineering context supports the creation of new robust and sustainable design guidelines for engineered systems. Thermodynamic cycles provide good examples of human systems where simple and clearly defined modifications can be made to increase efficiency. Twenty-three variations on the Brayton and Rankine cycles are used to understand the relationship between design decisions that maximize a system’s efficient use of energy (measured by thermodynamic first law efficiency) and ecological measures of robustness and structural efficiency. The results reveal that thermodynamic efficiency and ecological pathway efficiency do not always correlate and that while on average modifications to increase energy efficiency reduce the robustness of the system, the engineering understanding of ecological network design presented here can enable decisions that are able to increase both energy efficiency and robustness.

Sodium receiver designs for integration with high temperature power cycles

A variety of tube materials and geometries are considered in an analysis that identifies suitable sodium receiver designs for integration with next-generation thermodynamic power cycles. Sodium is capable of delivering outlet temperatures of >750∘C, however the net power output diminishes with rising temperatures due to tube material limitations on allowable flux density and increasing heat losses. Small tube diameters facilitate large thermal efficiencies and heat fluxes for all materials, however a large pressure drop penalty can somewhat mitigate these advantages. Traditional heat exchanger alloys perform quite poorly in comparison to Inconel 617 and Haynes 230, with allowable heat flux decreasing significantly as temperatures are increased beyond 600∘C. Multi-pass concepts offer greater control of flow-path exposure to the heat flux boundary condition than straightforward single-pass designs. A triple-panel design with small diameter Inconel 617 tubes balances thermal, hydraulic, and mechanical performance most effectively across all temperatures. For all candidate materials, sodium can augment power plant efficiency when integrated with a high temperature cycle (>600∘C). A combined receiver and power cycle efficiency percentage point improvement of 1.5% is possible using Ni-based superalloys at ∼650−700∘C compared to a baseline outlet temperature of 550∘C, resulting in a solar-to-electric power output increase of over 4%.

Trilateral Flash Cycle (TFC): a promising thermodynamic cycle for low grade heat to power generation

Energy crisis, fossil fuel depletion and growing environmental concern pushing not only for new source of energy but also developing advance technology for power generation. Besides conventional heat sources, low grade heat source of below 100 °C temperature like solar thermal, geothermal or waste heat has a good potential to become a sustainable source of power. Organic Rankine Cycle is the widely use thermodynamic power cycle for low grade heat to power generation where low boiling point pressurised organic working fluid is vaporised and expands through a turbine fed generator thus outputting usable electrical energy. The used fluid then returns to a reservoir before it is condensed and forced through the same process again via a high-pressure pump. Another thermodynamic cycle namely Trilateral Flash Cycle (TFC) which is nothing but a modified ORC where the organic working fluid is heated up to the saturation temperature under high pressure rather than evaporated. In this paper, an analytical comparative study on ORC and TFC shows that TFC has about at least 50% more power generation potential than that of conventional ORC for the same heat source and heat sink conditions if the heat source temperature is just below 100 °C. TFC even has the potential of power generation from the heat source below 80 °C where ORC is not economically viable.

Study and Prediction the Performance of an Integrated Solar Combined Cycle Power Plant

Concentrating solar thermal systems (CSP) have recently introduced as solar technologies that used for electrical power generation by heating a working fluid to high operating temperature range (≥300 oC) and combining it with a thermodynamic power cycle. This study is carried out to develop a Mathcad mathematical model for simulation and analyzing the performance of a pre-design integrated solar combined cycle power plant (ISCC). The system performance analysis results show that the ISCC operation mode raises the plant capacity from 503 MW to 555.23 MW in summer months. The annual solar share of electrical energy is approximately 85.77 GWh and the annual reduction in CO2 emission are approximately 51670.8 tons.

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.

Techno-economic assessment of Joule-Brayton cycle architectures for heat to power conversion from high-grade heat sources using CO2 in the supercritical state

Bottoming thermodynamic power cycles using supercritical carbon dioxide (sCO2) are a promising technology to exploit high temperature waste heat sources. CO2 is a non-flammable and thermally stable compound, and due to its favourable thermophysical properties in the supercritical state, it can achieve high cycle efficiencies and a substantial reduction in size and cost compared to alternative heat to power conversion technologies. Eight variants of the sCO2 Joule-Brayton cycle have been investigated. Cycle modelling and sensitivity analysis identified the Turbine Inlet Temperature (TIT) as the most influencing variable on cycle performance, with reference to a heat source gas flow rate of 1.0 kg/s and 650 °C. Energy, exergy and cost metrics for different cycle layouts have been compared for varying TIT in the range between 250 °C and 600 °C. The analysis has shown that the most complex sCO2 cycle configurations lead to higher overall efficiency and net power output but also to higher investment costs. Conversely, more basic architectures, such as the simple regenerative cycle, with a TIT of 425 °C, would be able to achieve an overall efficiency of 25.2%, power output of 93.7 kWe and a payback period of less than two years.

Parabolic trough solar collectors integrated with a Kalina cycle for high temperature applications: Energy, exergy and economic analyses

Asa promising option for future power generation is the concentrating solar power systems with various types, among which Parabolic Trough Solar Collectors (PTSC) are the most proven technology with lowest cost available today. Benefits of this renewable energy source are challenged by means of relatively low energy conversion efficiency. To overcome the dilemma, one approach is employing an efficient thermodynamic power cycle in order to enhance the overall power plant efficiency. The Kalina cycle (KC) is considered asan efficient alternative over the conventional or organic Rankine cycles in last few years. In the present work, the integration of a novel configuration of the KC, which is proper for utilizing high temperature heat sources, with PTSC is proposed and analyzed. Thermal, thermodynamic and economic models are developed to investigate the integrated system performance from the viewpoints of energy, exergy and economics. The results indicate that, exergy efficiencies of around 64% is achievable for power cycle unit while the overall power plant exergy efficiency reaches to around 14%. The results of economic analysis revealed that if a lower LCOE is to be reached increment of the number of collectors per row is more beneficial than the increment of parallel rows of the collectors.

Thermodynamic potential of Rankine and flash cycles for waste heat recovery in a heavy duty Diesel engine

In heavy duty Diesel engines more than 50% of the fuel energy is not converted to brake power, but is lost as heat. One promising way to recapture a portion of this heat and convert it to power is by using thermodynamic power cycles. Using the heavy duty Diesel engine as the waste heat source, this paper evaluates and compares the thermodynamic potential of different working fluids in four power cycles: the Rankine cycle (RC), the transcritical Rankine cycle (TRC), the trilateral flash cycle (TFC) and the single flash cycle (SFC). To establish the heat input into the cycle, operating conditions from an actual heavy duty Diesel engine are used as boundary conditions for the cycle heat source. A GT-Power model of the engine was previously developed and experimentally validated for the stationary points in the European Stationary Cycle (ESC). An energy analysis of this engine revealed that it has four heat sources with the potential for waste heat recovery: the charge air cooler (CAC), the coolant flow, the exhaust gas recirculation cooler (EGRC), and the exhaust flow. Using fixed heat input conditions determined by the selected engine operating mode, the TFC performed best for the CAC with a net power increase of around 2 kW, while the RC performed best for the coolant flow, with a net power increase of 5 kW. For the EGRC, ethanol performed especially well with both the RC and TRC, leading to an 8 kW net power increase. When using the exhaust as heat source, all four cycles provided a power output of around 5 kW with some variation depending on the working fluid. This study shows that for most cases, considering the different heat sources, the choice of cycle has a larger impact on the cycle performance than the choice of working fluid.

Initial Design of an Optical-Access Piston Expansion Chamber for Wet-Expansion

High efficiency expanders which can cope with fluid-vapour mixtures (i.e wet expansion) at the inlet and during expansion have the potential to increase the power output from thermodynamic power cycles. Volumetric expanders are considered suitable, yet experimental results are scarce and there is no model that can predict the performance of the expansion process. This is mainly due to the knowledge gap on the fundamental aspects off two-phase expansion and the non-equilibrium effects. Therefore, in this work, a variable volume piston expansion chamber is designed. The influence of the main design parameters are investigated by means of a simple deterministic model. Based on initial figures of merit, the component selection and technical layout is presented. The optical access in a later stage will be crucial to allow investigating the mechanistic process of the nucleation and the interfacial effects. This understanding is essential for generalization of the results to other working fluids and geometries.