Thermodynamics Cycle Analysis

This work presents a computer simulation of the exhaust nitric oxide and soot emission histories from a four stroke, naturally aspirated, Diesel engine with a swirl prechamber (divided chamber). The simulation is based on a thermodynamic analysis, which was validated successfully concerning the performance of the engine (load, fuel consumption, maximum pressures, etc). The analysis includes the calculation of the heat exchange between gas and walls in both the main chamber and (swirl) prechamber, after computing the relevant characteristic velocities and lengths, while combustion in both the main chamber and the swirl prechamber is attacked by proposing a two-zone combustion model. The concentration of the constituents in the exhaust gases is calculated by incorporating a complete chemical equilibrium scheme for the C-H-0 system of the eleven species considered, together with chemical rate equations for the calculation of nitric oxide (NO). A model for the evaluation of soot formation and oxidation rates is also included, in order to compute the net soot concentration. The contribution of each chamber to the formation of NO and soot is given by presenting time (crank angle) diagrams of the net NO and soot formation inside each chamber (histories of formation). To validate the analysis, an extensive experimental investigation is undertaken at the authors' laboratory on a Diesel engine of this type by evaluating its exhaust emission characteristics in a wide range of operating conditions. The experimental results are found to be in good agreement with the theoretical results obtained from the computer program implementing the analysis, while the detailed NO and soot net formation histories provide insight into the mechanisms involved.

This paper considers carbon dioxide transcritical and supercritical power cycles driven by low temperature flue gases exhaust from a gas turbine. Transcritical CO2 Rankine and supercritical CO2 Brayton cycles were studied at steady state conditions and their performance were compared. Furthermore, the study carried out parametric analysis to investigate the cycles' performance in terms of thermal efficiency and the network output at different turbine inlet temperatures. A mathematical model was developed to carry out the analysis based on the first law of thermodynamics. In order to simulate cycle performance and generate parametric tables a simulation model was developed using Engineering Equations Solver (EES). The efficiencies of the cycles were compared and it was found that transcritical Rankine cycle generates higher efficiency and net power output compared to supercritical Braytoncycle for the same turbine inlet conditions. Parametric analysis showed that as the turbine inlet temperature increases, the gas heater pressure that gives optimum efficiency increases.

Siklus Brayton dengan intercooling adalah salah satu konfigurasi yang umum digunakan dalam
sistem pembangkit listrik tenaga gas untuk meningkatkan efisiensi termal dan kinerja
keseluruhan. Efisiensi siklus Brayton dengan intercooling merupakan salah satu parameter
penting dalam desain dan operasi turbin gas untuk aplikasi berbagai industri, seperti
pembangkit listrik dan propulsi. Penelitian ini bertujuan untuk menganalisis pengaruh tekanan
masuk ruang bakar (RB) dan temperatur masuk turbin terhadap efisiensi siklus Brayton dengan
intercooling. Metode simulasi numerik digunakan untuk memodelkan siklus Brayton dengan
intercooling. Variasi tekanan masuk RB dan temperatur masuk turbin dievaluasi dalam rentang
yang relevan dengan aplikasi industri. Hasil simulasi menunjukkan bahwa peningkatan tekanan
masuk RB menyebabkan peningkatan efisiensi siklus secara signifikan. Selain itu, temperatur
masuk turbin juga mempengaruhi efisiensi siklus, dengan penurunan temperatur masuk turbin
menghasilkan peningkatan efisiensi siklus yang berarti. Analisis sensitivitas menunjukkan
bahwa interaksi antara tekanan masuk RB dan temperatur masuk turbin memiliki dampak yang
signifikan terhadap efisiensi siklus. Kombinasi optimal dari tekanan masuk RB dan temperatur
masuk turbin harus dipertimbangkan untuk mencapai efisiensi siklus maksimum. Studi ini
memberikan wawasan yang berharga bagi desainer turbin gas dalam memilih parameter
operasional yang optimal untuk meningkatkan efisiensi siklus Brayton dengan intercooling.
Pemahaman yang lebih baik tentang pengaruh tekanan masuk RB dan temperatur masuk turbin
dapat membantu mengoptimalkan kinerja sistem dan mengurangi konsumsi energi dalam
aplikasi industri.

The main idea of generalized intelligent tutoring system (ITS) development tools like Generalized Intelligent Framework for Tutoring (GIFT) is to provide authors with high-level standards and a readily reusable structure within different domains. Hence, adapting such a tool could be the best way to boost an underdeveloped tutor. In this paper we propose the design for a new GIFTbased tutor for undergraduate thermodynamics. An existing Thermodynamics Cycle Tutor has been designed that is meant to facilitate problem framing for undergraduate students. We describe the advantages of integrating this tutor with GIFT to add student models. Also an approach for evaluating the pedagogical performance of the GIFT-enhanced tutor is described.

Students learn when they connect new information to existing understanding or when they modify existing understanding to accept new information. Most current teaching methods focus on trying to get students to solve problems in a manner identical to that of an expert. This study investigates the effectiveness of assessing student understanding related to context specific problem solving decisions, prescribing feedback based on the assessment, and improving student understanding to the point where they can make correct decisions. Students were given a refrigeration problem unlike their prior problems and were asked to draw the cycle on a Tv diagram using a tutor system. Every group tested (a total of 373 students) showed a significant improvement in their understanding (p<0.0001, Cohen's d>0.8) using a single 40 minute tutor activity.

The performance of the supercritical CO2 (sCO2) Brayton cycle deteriorates due to the mismatch between critical temperature and cold source temperature. An innovative solution based on ternary CO2 mixtures with adjustable compositions is proposed to expand the variation range of the critical temperature. An in-house MATLAB code is developed to investigate the design-point performance of the proposed system. The results indicate that the effect of improving cycle efficiency by using the modified floating critical point method becomes increasingly significant as the target critical temperature deviates from that of CO2. The CO2–H2S–Kr is screened out as the best ternary mixture, with the cycle efficiency being increased by over 8 % compared to the sCO2 cycle at very high (45 °C) and low (−15 °C) temperatures. The long-term performance is also evaluated based on the hourly historical weather data of two typical climate regions. The annual performance depends on both the average value and the distribution characteristics of the local ambient temperature. A relative improvement in annual average efficiency of 7%–9.56 % can be obtained depending on the regions. The present work is helpful to make the supercritical Brayton cycle give full play to its efficiency advantage in a wide cold source temperature range.

h i g h l i g h t s SAFT-VR Mie produces highly accurate thermodynamic properties of ORC fluid systems. Limiting superheating to a minimum leads to cycles with superior performance. Generally, cycles with pure working fluids are more powerful and cost effective. Large-glide fluid mixtures are attractive in applications with limited cooling resources.

District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

Heat exchangers and other heat transfer devices/systems play vital roles of heat transfer in thermal fluid flow systems for industrial application. Sodium cooled fast reactors are normally designed to have two loops of sodium coolants and one loop of water coolant which generates steam for power production. The two loops of sodium coolants consist of primary cooling system of sodium which cools the fuel rods of the reactor core and secondary cooling system of sodium transferring heat from the sodium primary cooling system. The water-cooling system transfers heat from the secondary cooling system of sodium for steam generation. Lead cooled fast reactors on the other hand are designed to have primary cooling system of lead cooling the fuel rods in the reactor core and secondary cooling system of water transferring heat from the lead cooling primary system for steam generation. Water cooled Nuclear Power Plants used water to cool the reactor core in the primary system and the heat remo...

Heat exchangers and other heat transfer devices/systems play vital roles of heat transfer in thermal fluid flow systems for industrial application. Sodium cooled fast reactors are normally designed to have two loops of sodium coolants and one loop of water coolant which generates steam for power production. The two loops of sodium coolants consist of primary cooling system of sodium which cools the fuel rods of the reactor core and secondary cooling system of sodium transferring heat from the sodium primary cooling system. The water-cooling system transfers heat from the secondary cooling system of sodium for steam generation. Lead cooled fast reactors on the other hand are designed to have primary cooling system of lead cooling the fuel rods in the reactor core and secondary cooling system of water transferring heat from the lead cooling primary system for steam generation. Water cooled Nuclear Power Plants used water to cool the reactor core in the primary system and the heat remo...

Refrigeration and air conditioning are essential applications nowadays. It has a wide range of applications in domestic and industrial VARS, VCRs & VADRS systems that are used nowadays. VARS system is an eco-friendly refrigeration system, and it has a wide range of refrigerants for working. In this paper, we reviewed the most essential 15 refrigerants, studied their thermal characteristics, and tried to find out the best suitable, eco-friendly, nonflammable, and suitable for the VARS system.

إن المعدل الحراري للوحدة Heat Rate (HR) مؤشر مهم جدا لتقييم كفاءة الوحدة الحرارية لذا يجب أن يكون هدف ومسعى أية محطة تشغيل الوحدة التوليدية ضمن الحدود التصميمية للمعدل الحراري قدر الإمكان ، إضافة إلى أن تحسين المعدل الحراري للمحطة يساعد على تقليل التلوث الناجم من تشغيل الوحدات .
تقليل معدل الحرارة يؤدي إلى تقليل أستهلاك الوقود وتوفير الوقود

Doping CO2 with an additional fluid to produce a CO2-based mixture is predicted to enhance the performance of the super critical CO2 power cycle and lower its cost when adapted to Concentrated Solar Power plants. A consistent fluid mixture modelling process is necessary to reliably design and predict the performance of turbines operating with CO2-based working fluids. This paper aims to quantify the significance of the choice of an Equation of State (EoS) and the uncertainty in the binary interaction parameter (

Titanium tetrachloride is proposed as new fluid in high temperature Rankine cycles. We show experimentally that it is remarkably stable at temperatures up to 500°C. Resulting plant efficiencies of 35-40% are higher than state-of-the-art ORCs. Its high reactivity with water poses some concerns in the design of a power plant.

District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

The objective of this research is to validate properties of mixtures relevant to supercritical carbon dioxide (sCO2) power cycles. Direct-fired sCO2 cycles are a promising technology for the future power generation systems. The working fluid of sCO2 cycles will be near and above critical point of CO2. One of the challenges is that the simulation of mixtures should consider real gas behavior. Expected operating conditions of Allam cycles reach up to 300 bar and 1000 °C. Characterizing the mixtures at the extreme conditions is an important issue in current researches and industrial applications. Thermophysical properties of mixtures may be beyond the valid range of the widely used database such as NIST REFPROP. Experimental data of mixture properties in the literature are limited which is necessary to develop high-fidelity design tools for sCO2 power cycles. We measured the density and sound speed of several multi-component mixtures. A temperature-controlled high-pressure test cell wa...

District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

Titanium tetrachloride is proposed as new fluid in high temperature Rankine cycles. We show experimentally that it is remarkably stable at temperatures up to 500°C. Resulting plant efficiencies of 35-40% are higher than state-of-the-art ORCs. Its high reactivity with water poses some concerns in the design of a power plant.

District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

In this study CHP (Combine Heat And Power) systems are used in commercial buildings in the world are studied thermodynamically and economically. It has been told in cogeneration and trigeneration systems turbine efficiencies are very low while system is operating in partial load. Additionally, absorption cooling systems are not designed to cycle on and off quickly, starting up and reaching equilibrium temperatures is taking time. Using hourly energy consumption values of the university hospital, the total benefit respect to existing situation and the capacity, which can provide maximum benefit, has been determined.

Supercritical Carbon Dioxide (sCO2) power cycles have been proposed for Concentrated Solar Power (CSP) applications as a means to increase the performance and reduce the cost of state-of-the-art CSP systems. Nevertheless, the sensitivity of sCO2 systems to the usually hot ambient temperatures found in solar sites compromises the actual thermodynamic and economic gains that were originally anticipated by researchers of this innovative power cycle. In order to exploit the actual potential of sCO2 cycles, the utilization of dopants to shift the (pseudo)critical temperature of the working fluid to higher values is proposed here as a solution towards enabling exactly the same features of supercritical CO2 cycles even when ambient temperatures compromise the feasibility of the latter technology. To this end, this work explores the impact of adopting a CO2-based working mixture on the performance of a CSP power block, considering hexafluorobenzene (C6F6) and titanium tetrachloride (TiCl4) as possible dopants. Different cycle options and operating conditions are studied (250-300 bar and 550-700ºC) as well as molar fractions ranging between 10 and 25%. The results in this work confirm that CO2 blends with 15-25%(v) of the cited dopants enable efficiencies that are well in excess of 50% for minimum cycle temperatures as high as 50 or even 55ºC. It is also confirmed that, for these cycles, turbine inlet temperature and pressure hardly have any effect on the characteristics of the cycle that yields the best performance possible. In this regard, the last part of this work also shows that cycle layout should be an additional degree of freedom in the optimisation process inasmuch as the best performing layout changes depending on boundary conditions.

In the last years, several fluids have been proposed to replace steam as working fluid in power cycle for con-verting thermal power into electricity. This paper describes the procedure to be adopted for the selection of any
innovative fluid which can be even mixtures of fluids. The first step consists of the working fluid characterization
in terms of thermodynamic properties through equations of state. The equations of state have to be calibrated on
experimental Vapour-Liquid Equilibrium measurements while, in the second step, the maximum operating
temperature is identified through thermal stability tests. Finally, the impact of the fluid thermodynamic prop-erties on the performance of the power cycle in which it is implemented must be assessed through modelling
tools. In this work, the procedure is discussed for the mixture of CO2and C6F14as a potential working fluid for
gas thermodynamic cycles with liquid phase compression. Results of the application of this mixture in a closed
cycle show the benefit of using a CO2/C6F14mixture which provides 3% points efficiency increase at 400 °C with
respect to the pure CO2together with a preliminary design of the expander.