Thermodynamic Simulation Model Research Articles

Thermodynamic simulation and mathematical model for single and double flash cycles of Cerro Prieto geothermal power plants

Geothermal power generation technologies are well established and there are numerous power plants operating worldwide. The Cerro Prieto geothermal field is located in northwestern Mexico, approximately 32 km from the US-México border. A single flash and double flash cycle have been selected for power generation. The study is aimed to thermodynamic simulation and mathematical model development for the single and double flash cycles. Thermodynamic Simulation for energy flows were developed and implemented in Aspen Hysys software, while the multiple linear regression analysis was developed in IBM SPSS software. The single flash cycle thermodynamic simulation of the proposed design shows the plant’s maximum net power output can reach 36.667 MW if the separator and condenser pressures are 650 kPa and 11.5 kPa, respectively. In the double flash cycle, the optimum pressure value for high pressure (HP) separation is 1200 kPa, low pressure (LP) separation is 385 kPa and the pressure for condenser was determined to be 11.5 kPa, the maximum net power output of the plant is 102.112 MW. The multiple linear regression shows mathematical model to predict the net power and thermal efficiency for single flash and double flash cycles, using the independent variables of the well temperature, separator pressure and condenser pressure to obtain a mathematical expression that predicts the behavior of this cycle. While for the double flash cycles, the well temperature, the pressures in the separators and the condenser pressure are used. The mathematical models to predict the net power and the thermal efficiency of the cycles shows a very good approximation to the thermodynamic analysis, the single flash cycle shows ANOVA results net power (r=0.999885, R2=0.999769, p<0.0001) and thermal efficiency (r=0.999628, R2=0.999256, p<0.0001), while the double flash cycle ANOVA results net power (r=0.999861, R2=0.999722, p<0.0001) and thermal efficiency (r=0.999806, R2=0.999612, p<0.0001).

Thermodynamic analysis of waste heat recovery using Organic Rankine Cycle (ORC) for a two-stroke low speed marine Diesel engine in IMO Tier II and Tier III operation

In the present study, a complete thermodynamic model of a two-stroke, low speed, 13.6 MW marine Diesel engine of Winterthur Gas & Diesel has been developed using the engine simulation software Ricardo WAVE. The model has been first validated against experimental data. A Low Pressure (LP) EGR architecture has then been implemented in order to assess the engine performance in the frame of the IMO Tier III regulations. The computational results have been used as inputs to a thermodynamic process simulation model, developed in Engineering Equation Solver, able to quantify the performance of different Organic Rankine Cycle (ORC) architectures and working fluids, with the scope of obtaining the maximum net power output for all engine operating points considered. The outcome of the present study is that, through the combined use of innovative emission reduction strategies, such as LP EGR, and waste heat recovery systems, such as ORC, it is possible to develop marine Diesel engines which exhibit fuel consumption levels comparable to those of Tier II operation, at substantially reduced levels of pollutant emissions. A preliminary economic analysis has yielded annual financial savings in fuel cost of the order of 5% for operation with ORC, as compared to operation without ORC.

Water clarity and temperature effects on walleye safe harvest: an empirical test of the safe operating space concept

AbstractSuccessful management of natural resources requires local action that adapts to larger‐scale environmental changes in order to maintain populations within the safe operating space (SOS) of acceptable conditions. Here, we identify the boundaries of the SOS for a managed freshwater fishery in the first empirical test of the SOS concept applied to management of harvested resources. Walleye (Sander vitreus) are popular sport fish with declining populations in many North American lakes, and understanding the causes of and responding to these changes is a high priority for fisheries management. We evaluated the role of changing water clarity and temperature in the decline of a high‐profile walleye population in Mille Lacs, Minnesota, USA, and estimated safe harvest under changing conditions from 1987 to 2017. Thermal–optical habitat area (TOHA)—the proportion of lake area in which the optimal thermal and optical conditions for walleye overlap—was estimated using a thermodynamic simulation model of daily water temperatures and light conditions. We then used a SOS model to analyze how walleye carrying capacity and safe harvest relate to walleye thermal–optical habitat. Thermal–optical habitat area varied annually and declined over time due to increased water clarity, and maximum safe harvest estimated by the SOS model varied by nearly an order of magnitude. Maximum safe harvest levels of walleye declined with declining TOHA. Walleye harvest exceeded safe harvest estimated by the SOS model in 16 out of the 30 yr of our dataset, and walleye abundance declined following 14 of those years, suggesting that walleye harvest should be managed to accommodate changing habitat conditions. By quantifying harvest trade‐offs associated with loss of walleye habitat, this study provides a framework for managing walleye in the context of ecosystem change.

Performance Analysis and Simulation of a Diesel-Miller Cycle (DiMC) Engine

A comprehensive performance examination of an engine running on combination of the Diesel and Miller cycles called Diesel-Miller cycle in terms of effective power, density of the effective power, and effective thermal efficiency, which will be called engine performance (ENPER) characteristics, is conducted using a novel thermodynamic simulation model. The impacts of cycle design parameters such as cycle pressure ratio, equivalence ratio, effective compression ratio (r), bore/stroke ratio (d / L), average piston speed, friction coefficient, engine speed (N), stroke (L), and air inlet temperature and air inlet pressure on the ENPER characteristics have been investigated. Additionally, the energy losses depending on exhaust output, friction, incomplete combustion, heat transfer have been defined as a ratio of energy provided by fuel injection. Variable specific heat values with respect to temperature variation for working fluid are used to get realistic results. The results of the study are reasonable and unique, and they could be utilized by researchers and engineers studying on internal combustion engines.

Optimization Simulation, Using Steel Plant Off-Gas for Power Generation: A Life-Cycle Cost Analysis Approach

This research aims to contribute to the international desires of greenhouse gas mitigation through a study on the optimization of 100 MW off-gas power plants’ subcritical steam cycle, operating in conjunction with steel plants. The performance and fiscal efficiency of the off-gas power plants are based on data collected from Krakatau Steel plants in Indonesia, simulated and analyzed through thermodynamic simulation model (PEPSE). The three scenarios simulated for comparison are: (1) 100 MW off-gas power plant as-is operation, (2) 100 MW off-gas power plant optimized, and (3) 100 MW cogeneration off-gas power plant. The optimization of the off-gas power plant and use of steam extraction was found to have a 45 M and 26 M USD savings in comparison to the base power plant, assuming a 5.5% discount rate and 400 Million USD capital expenditure. The theoretical findings are of use to academia and industry in providing proof of potential cost-savings of integrating off-gas into existing power generation operations.

Study on the Method of Improving Efficiency of Natural Gas Engine

A one-dimensional thermodynamic simulation model was built based on the test data and using the system dynamics method to study the effects of geometric compression ratio, late intake valve closing (LIVC), air fuel ratio, exhaust gas recirculation (EGR) and ignition advance on the thermal efficiency of a straight line 6 cylinder miller cycle natural gas engine. The result shows that improve engine geometry compression ratio appropriately can effectively improve engine energy distribution, engine power and fuel economy. And compared with LIVC setting, ignition advance setting has a more obvious effect on engine performance. Proper ignition advance ensures high efficiency of the engine. Moderately increasing EGR rate can effectively guarantee the low NOx emission, and further increase LIVC can reduce exhaust gas dilution effect on inhibition of engine combustion rate, to ensure that the engine has good thermal efficiency.

Thermodynamic Simulation of CCP in Air-Cooled Heat Pump Unit with HFCs and CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; Trans-Critical

The exergy analysis and finite time thermodynamic methods had been employed to analyze the compound condensation process (CCP). It was based on the air-cooling heat pump unit. The cooling capacity of the chiller unit is about 1 kW, and the work refrigerant is R22/R407C/R410A/CO2. The MATLAB/SIMULINK software was employed to build the simulation model. The thermodynamic simulation model is significant for the optimization of parameters of the unit, such as condensation and evaporation temperature and mass flow of the sanitary hot water and size of hot water storage tank. The COP of the CCP of R410A system is about 3% - 5% higher than the CCP of the R22 system, while CCP of the R407C system is a little lower than the CCP of R22 system. And the CCP of CO2 trans-critical system has advantage in the hot supply mode. The simulation method provided a theoretical reference for developing the production of CCP with substitute refrigerant R407C/R410A/CO2.

Simulation of SOFCs based power generation system using Aspen

Abstract This study presents a thermodynamic Aspen simulation model for Solid Oxide Fuel Cells, SOFCs, based power generation system. In the first step, a steady-state SOFCs system model was developed. The model includes the electrochemistry and the diffusion phenomena. The electrochemical model gives good agreement with experimental data in a wide operating range. Then, a parametric study has been conducted to estimate effects of the oxygen to carbon ratio, O/C, on reformer temperature, fuel cell temperature, fuel utilization, overall fuel cell performance, and the results are discussed in this paper. In the second step, a dynamic analysis of SOFCs characteristic has been developed. The aim of dynamic modelling was to find the response of the system against the fuel utilization and the O/C ratio variations. From the simulations, it was concluded that both developed models in the steady and dynamic state were reasonably accurate and can be used for system level optimization studies of the SOFC based power generation system.

Diesel and Spark Ignition Engines Emissions and After-Treatment Control: Research and Advancements

One of the major risks mankind has encountered during recent years is, without a doubt, the anthropogenic contribution to environmental pollution [...]

Thermodynamic simulation model for predicting the performance of spark ignition engines using biogas as fuel

Biogas found its way from developing countries and is now an alternative to fossil fuels in internal combustion engines and with the advantage of lower greenhouse gas emissions. However, its use in gas engines requires engine modifications or adaptations that may be costly. This paper reports the results of experimental performance and emissions tests of an engine-generator unit fueled with biogas produced in a sewage plant in Brazil, operating under different loads, and with suitable engine modifications. These emissions and performance results were in agreement with the literature and it was confirmed that the penalties to engine performance were more significant than emission reduction in the operating range tested. Furthermore, a zero dimensional simulation model was employed to predict performance characteristics. Moreover, a differential thermodynamic equation system was solved, obtaining the pressure inside the cylinder as a function of the crank angle for different engine conditions. Mean effective pressure and indicated power were also obtained. The results of simulation and experimental tests of the engine in similar conditions were compared and the model validated. Although several simplifying assumptions were adopted and empirical correlations were used for Wiebe function, the model was adequate in predicting engine performance as the relative difference between simulated and experimental values was lower than 5%. The model can be adapted for use with different raw or enriched biogas compositions and could prove to be a valuable tool to guide experimentation, reducing time and resources needed. As such, it is suitable for use with biogas supplies in developing regions, such as Brazil, for small-scale power generation in rural areas.

Simulation of a Diesel Engine with Variable Geometry Turbocharger and Parametric Study of Variable Vane Position on Engine Performance

Modelling of a turbocharger is of interest to the engine designer as the work developed by the turbine can be used to drive a compressor coupled to it. This positively influences charge air density and engine power to weight ratio. Variable geometry turbocharger (VGT) additionally has a controllable nozzle ring which is normally electro-pneumatically actuated. This additional degree of freedom offers efficient matching of the effective turbine area for a wide range of engine mass flow rates. Closing of the nozzle ring (vanes tangential to rotor) result in more turbine work and deliver higher boost pressure but it also increases the back pressure on the engine induced by reduced turbine effective area. This adversely affects the net engine torque as the pumping work required increases. Hence, the optimum vane position for a given engine operating point is to be found through simulations or experimentation. A thermodynamic simulation model of a 2.2l 4 cylinder diesel engine was developed for investigation of different control strategies. Model features map based performance prediction of the VGT. Performance of the engine was simulated for steady state operation and validated with experimentation. The results of the parametric study of VGT’s vane position on the engine performance are discussed.

Quasi dimensional numerical investigation of syngas fuelled engine operation: MBT operation and parametric sensitivity analysis

The formulation, validation and application of a thermodynamic quasi dimensional SI engine simulation model for syngas fuelled operation is reported. The QD approach establishes the dependence of turbulent combustion on mixture thermo-physical properties and fluid domain average turbulent parameters, eliminating the need for domain discretization (unlike in multi-dimensional models). Turbulent combustion is formulated along the Eddy Entrainment Laminar Burn-up concept (Williams-Klimov criterion) with non-linear dependence of mixture burn rate on local laminar flame speed and turbulent intensity. Simulations are reported for syngas fuelled operation of a six cylinder engine and compared with experimental pressure and heat release traces. Maximum brake torque stoichiometric operation pressure and heat release simulation traces evolve closely with corresponding experimental traces. The simulation peak pressure and IMEP deviations remain within 5% and 2% of experimental traces respectively while the position of peak pressure overlaps within ±0.5deg. Parametric sensitivity analysis for load, mixture quality and ignition timing are also addressed. Overall, the simulation results are in accordance within 5% of experimental results as long as the parametric variations are within the regimes of tuning of empirical correlations. In general, the versatility and robustness of quasi dimensional approach to simulate non-regular bio-derived alternative fuels is established.

Analysis of thermodynamic scope engine simulation model empirical coefficients: Suitability assessment and tuning of conventional hydrocarbon fuel coefficients for bio syngas

The sensitivity of empirical correlations and coefficients of thermodynamic quasi and zero dimensional SI engine models to mixture thermo-chemistry and engine thermo-kinematic response variations is addressed. Mixture thermo-chemistry alterations, as in case engine operation with non-regular alternatives, and accompanying in-cylinder fluid flow and combustion dynamics perturbations induce variations in full cycle thermodynamic and process thermo-kinematic response with potential influence on empirical coefficients. As an example, producer gas and natural gas thermo-physical properties differ significantly, extending to thermo-kinematic response over a range of operating conditions. Literature indicates monotonous adoptions of conventional fuel coefficients for simulation studies with non-regular fuels and tuning efforts are directed at initial and boundary conditions, which are many times thermodynamically untenable. The current work evaluates the suitability of empirical correlations and coefficients tuned for conventional hydrocarbon fuels, for numerical simulation of producer gas fuelled operation. Producer gas specific coefficients are evolved, following a generic approach, wherever necessary.Assessment of producer gas thermo-physical properties indicates four times higher thermal conductivity of producer gas (40.0 mW/mK) compared to gasoline (11.2 mW/mK), attributed to the presence of hydrogen. The influence is on convective cooling which is reflected in about 32% cooling load as against 25% for spark ignited engines. In response, the Reynolds number power coefficient of convective heat transfer correlation nearly doubles from 0.35 to 0.76. Analysing laminar flame speed coefficients, the inability of CHEMKIN-III to accurately predict laminar flame speed of hydrogen containing gases requiring adoption of CHEMKIN-II is a key observation. Substantial deviations are also observed for apparent heat release profiles with extended terminal stage combustion duration for producer gas, attributed to enhanced convective cooling. Curve fit analysis evolves producer gas specific shape and efficiency coefficients of 0.71 and 2.23 as against 2.0 and 5.0 for conventional fuels. The terminal combustion duration also changes from 1.22 to 2.12 ms. Using tuned coefficients permits near concurrent evolution of simulation and experimental pressure and heat release profiles establishing the need for fuel specific coefficients.

A Damage Evaluation Model of Turbine Blade for Gas Turbine

Current maintenance, having a great impact on the safety, reliability and economics of a gas turbine, becomes the major obstacle for the application of gas turbines in energy field. An effective solution is to process condition based maintenance (CBM) thoroughly for gas turbines. Maintenance of high temperature blade, accounting for the most of the maintenance costs and time, is the crucial section of gas turbine maintenance. The suggested life of high temperature blade by original equipment manufacturer (OEM) is based on several certain operating conditions, which is used for time based maintenance (TBM). Thus, for the requirement of gas turbine CBM, a damage evaluation model is demanded to estimate the life consumption online. A physics-based model is built, consisting of thermodynamic performance simulation model, stress estimation model, thermal estimation model, and interactive damage analysis model. Unmeasured parameters are simulated by the thermodynamic performance simulation model, as the input of the stress estimation model and the thermal estimation model. Due to the ability to analyze online data, this model can be used to calculate online damage and support CBM decision. Then the stress and temperature distribution of blades will become as the input of the creep damage analysis model and the fatigue damage analysis model. The interactive damage of blades will be evaluated based on the creep and fatigue analysis results. To validate this physics-based model, it is used to calculate the lifes of high temperature blade under several certain operating conditions. And the results are compared to the suggestion value of OEM. An application case is designed to evaluate the application effect of this model. The result shows that the relative error of this model is less than 10.4% in selected cases. And it can cut overhaul costs and increase the availability of gas turbines significantly. Finally, a simple application of this model is proposed to show its functions. The physical-based damage evaluation model proposed in this paper is found to be a useful tool to tracing the online life consumption of a high temperature blade, to support the implementation of CBM for gas turbines, and to guarantee the reliability of gas turbines with lowest maintenance costs.

Simulation of a reversible SOFC with Aspen Plus

A thermodynamic Aspen Plus simulation model for a reversible solid oxide fuel cell (RSOFC) is presented and evaluated. It is composed of an electrolysis and a fuel cell module. The latter is based on an existing non reversible SOFC model. The electrolysis model simulates water electrolysis as well as catalytic reactions of inlet gases. The model has been validated using data from literature. It has been found that the support layer on fuel electrode supported cells has to be treated differently in terms of diffusion than the active layer. Simulation results show that for the investigated cell parameters, the positive effect of adding CO2 to the steam feed on the electrolysis process is due to water–gas-shift reactions and not CO2 electrolysis. An analysis of outlet gas compositions in electrolysis mode showed that the assumption of the cell as an equilibrium reactor was justified. A parameter study has been conducted, showing that increasing the operation temperature and pressure can improve the overall performance, while changing the inlet gas compositions in general improves either fuel cell or electrolysis mode and deteriorates performance for the other mode.

Innovative Calibration Method for System Level Simulation Models of Internal Combustion Engines

The paper outlines a procedure for the computer-controlled calibration of the combined zero-dimensional (0D) and one-dimensional (1D) thermodynamic simulation model of a turbocharged internal combustion engine (ICE). The main purpose of the calibration is to determine input parameters of the simulation model in such a way as to achieve the smallest difference between the results of the measurements and the results of the numerical simulations with minimum consumption of the computing time. An innovative calibration methodology is based on a novel interaction between optimization methods and physically based methods of the selected ICE sub-systems. Therein physically based methods were used for steering the division of the integral ICE to several sub-models and for determining parameters of selected components considering their governing equations. Innovative multistage interaction between optimization methods and physically based methods allows, unlike the use of well-established methods that rely only on the optimization techniques, for successful calibration of a large number of input parameters with low time consumption. Therefore, the proposed method is suitable for efficient calibration of simulation models of advanced ICEs.

A kernel principal component analysis–based degradation model and remaining useful life estimation for the turbofan engine

Remaining useful life estimation of the prognostics and health management technique is a complicated and difficult research question for maintenance. In this article, we consider the problem of prognostics modeling and estimation of the turbofan engine under complicated circumstances and propose a kernel principal component analysis–based degradation model and remaining useful life estimation method for such aircraft engine. We first analyze the output data created by the turbofan engine thermodynamic simulation that is based on the kernel principal component analysis method and then distinguish the qualitative and quantitative relationships between the key factors. Next, we build a degradation model for the engine fault based on the following assumptions: the engine has only had constant failure (i.e. no sudden failure is included), and the engine has a Wiener process, which is a covariate stand for the engine system drift. To predict the remaining useful life of the turbofan engine, we built a health index based on the degradation model and used the method of maximum likelihood and the data from the thermodynamic simulation model to estimate the parameters of this degradation model. Through the data analysis, we obtained a trend model of the regression curve line that fits with the actual statistical data. Based on the predicted health index model and the data trend model, we estimate the remaining useful life of the aircraft engine as the index reaches zero. At last, a case study involving engine simulation data demonstrates the precision and performance advantages of this prediction method that we propose. At last, a case study involving engine simulation data demonstrates the precision and performance advantages of this proposed method, the precision of the method can reach to 98.9% and the average precision is 95.8%.

Potential for efficiency improvement of four-stroke marine diesel gensets by utilisation of exhaust gas energy

In the present paper, it is examined the potential application of a Rankine cycle exhaust gas heat recovery system which recovers and utilises energy from the exhaust gas of four-stroke marine diesel auxiliary unit before it is released to the atmosphere, increasing thus its total efficiency. For this purpose, a thermodynamic simulation model of the Rankine bottoming cycle is used. Heat utilisation is initially considered only from the main exhaust gas stream after the T/C turbine. As reference for the investigation are used the values from the official shop tests at various loads ranging from 25% up to 100%. From these using the Rankine cycle simulation model, it is investigated the potential for increase of generated cycle power output and optimisation of its efficiency. In addition, it is examined the effect of working media by considering steam and an organic. The results derived reveal that there exists a significant potential for fuel saving by utilisation of exhaust gas energy of auxiliary engines installed on commercial vessels.

Simulation Study of Sludge Precipitation in Spent Fuel Reprocessing

A simulation technology with electrolyte thermodynamic model has been developed to evaluate the precipitation behavior in reprocessing solution. In this study, we have chosen the model of OLI system Inc. which combines an excess Gibbs energy model for mixed-solvent electrolyte systems with a comprehensive treatment of chemical equilibrium. The simulation results of precipitation were compared with the experiment data from non-radioactive simulated HLLW and Pu-Zr-Mo solution, and they showed good agreement each other. Most of the precipitation species was zirconium molybdate hydrate (ZMH) from the both data. This study has shown the thermodynamic simulation model is one of the useful tools to estimate the behavior of precipitation species from the reprocessing solution.

Development of a Gas Dynamic and Thermodynamic Simulation Model of the Lontra Blade Compressor™

The Lontra Blade Compressor™ is a patented double acting, internally compressing, positive displacement rotary compressor of innovative design. The Blade Compressor is in production for waste-water treatment, and will soon be launched for a range of applications at higher pressure ratios.In order to aid the design and development process, a thermodynamic and gas dynamic simulation program has been written in house. The software has been successfully used to optimise geometries and running conditions of current designs, and is also being used to evaluate future designs for different applications and markets.The simulation code has three main elements. A positive displacement chamber model, a leakage model and a gas dynamic model to simulate gas flow through ports and to track pressure waves in the inlet and outlet pipes. All three of these models are interlinked in order to track mass and energy flows within the system.A correlation study has been carried out to verify the software. The main correlation markers used were mass flow, chamber pressure, pressure wave tracking in the outlet pipe, and volumetric efficiency. It will be shown that excellent correlation has been achieved between measured and simulated data. Mass flow predictions were to within 2% of measured data, and the timings and magnitudes of all major gas dynamic effects were well replicated.The simulation will be further developed in the near future to help with the optimisation of exhaust and inlet silencers.