Temperature level optimization for low-grade thermal networks using the exergy method

Low-temperature thermal networks open the field for additional renewable and recovered energy sources to be used. The exploitation of low exergy level resources requires decentralized heat pumps having a significant impact on the network's overall electricity consumption. Thus, a compromise must be found in order to minimize thermal and electrical consumption while integrating a maximum of renewable energy sources. This optimum is governed by the temperature level of the network. This paper aims at determining the optimal network temperature using the exergy criterion. The exergy method is detailed and applied to the multi-source network blueCAD (Fribourg) fed by geothermal energy, and FriCAD, a high temperature district heating network. The optimum temperature decreases as the share of geothermal energy in the production increases. For blueCAD, it ranges from 40 to 55 °C.

Exergy Analysis of an Ejector Cooling System by Modified Gouy–Stodola Equation

In this paper, exergy destruction analysis of a heat-assisted ejector cooling system has been carried out using a modified Gouy–Stodola equation. The modified Gouy–Stodola equation provides a more accurate and realistic irreversibility analysis of the system than the conventional Gouy–Stodola formulation. The coefficient of structural bond (CSB) analysis has also been executed to find the component whose operating variables affect the system’s total irreversibility at the most. Exergy analysis revealed that the maximum exergy loss happens in the ejector followed by the generator and condenser. The model predicted 40.84% of total irreversibility in the ejector at the designed conditions. However, total exergy destruction is found to be the most sensitive to the evaporator temperature. The CSB value of 12.97 is obtained in the evaporator using the modified exergy method. The generator appears to be the second sensitive component with the CSB value of 2.42, followed by the condenser with the CSB value of 1.628. The coefficient of performance of the system is found to be 0.18 at the designed conditions. The refrigerant R1234yf is considered in the system.

APPLICATION OF EXERGETIC METHOD FOR EVALUATION OF PROCESS PERFECTION IN DIESEL ENGINE SUPERCHARGING SYSTEM

One of the most important trends of the modern combat vehicles is increasing their mobility for the security of the crew and for fast movement in different types of terrain. Compliance with these criteria is ensured by the engine of the armored vehicle. The competitiveness of domestic engines for armored vehicles should be ensured by the creation of new structures, their constant modernization and further improvement of performance. One of such engines is a forced diesel engine 6DN12/2x12 with a capacity of 1100 kW. In order to improve its performance and increase the level of forcing, it is proposed to improve the air supply system of the engine. Evaluating the effectiveness of the system can identify nodes that need changing design parameters. Therefore, such a qualitative analysis also indicates the feasibility and the possibility of further modernization of the system design. The qualitative analysis of the turbocharger is carried out on the basis of exergy method, which allows identifying sources of energy losses in the system design and determines the degree of perfection of processes. The application of the exergy method is due to the purpose of determining the reserves to improve the efficiency of the turbocharger elements, the magnitude of the supplied exergy and exergy efficiency in the nodes of the air supply system. According to the method, an exergy scheme of the supercharging system was constructed, on the basis of which the energy-exergy balance of each compressor unit was derived. The results of the analysis allowed to determine the parameters of the flow of the working fluid in the characteristic sections of the compressor and turbine and exergetic efficiency of the supercharging system. The calculated data obtained by exergetic analysis provide an estimate of the distribution of energy losses and allow determining the areas for further improvement of the air supply system and providing an opportunity to choose such design parameters that achieve the most effective improvement of the system.

METHODS FOR EVALUATING THE EFFICIENCY OF TURBOCHARGING SYSTEM OF PISTON ENGINE WITH POWER TURBINE

The analysis of existing methods for assessing the loss of gases performance in the flow part of turbocharging system of piston engine is presented. It is shown that the exergy method provides a complete picture about of local energy transformations in the intake and exhaust systems of a piston engine, which makes it possible to use it to evaluate the efficiency of turbocharging system of piston engine with power turbine when forcing a piston engine by on the average effective pressure.

Analysis of Compressed Air Energy Conversion Processes in a Rotary Piston Pneumatic Engine

This article describes a rotary piston pneumatic engine with a gas exchange system design that minimizes the value of the relative dead volume, as well as ensures the minimum dimensions and weight of the engine. The main purpose of the study is to evaluate the conversion efficiency of compressed air energy in the working cylinder of the rotary piston pneumatic engines using the exergy method of thermodynamic analysis. To achieve the set goal of the study, physical modeling of various operation modes has been performed. The most significant result is that, based on the physical and mathematical modeling, a thermodynamic assessment of the efficiency of the compressed air energy conversion has been performed. The significance of the results obtained lies in the fact that the effect of the main operational parameters of the pneumatic engine on the efficiency of energy conversion is established. The basic equations of the exergy method of the thermodynamic analysis are presented. The results of physical and mathematical modeling of various operation modes are presented. The main reasons for the decrease in the energy conversion efficiency at low and rated loads are emphasized. The amount of exergy supplied with the air flow was established, which, depending on the operation mode, amounted to 2.2…11.4 kW. According to the presented results, the most optimal speed range, based on the achievement of the maximum values of the specific efficient work and exergy efficiency, is 55…70% of the nominal value. It was found that an increase in the operation pressure decreases slightly the exergy efficiency. A twofold increase in the operation pressure of the pneumatic engine increases the efficient power by 46 % at a simultaneous decrease in the exergy efficiency by 8.2 %.

Выбор системы газотурбинного наддува высокооборотного судового дизеля

В статье представлены результаты исследования импульсной и изобарной систем выпуска поршневого двигателя в зависимости от среднего эффективного давления. Целью данной работы является выявление эффективного использования импульсной или изобарной системы выпуска с точки зрения потерь работоспособности газов при движении энергетического потока от цилиндров до турбины при форсировании поршневого двигателя по среднему эффективному давлению. Существующие системы газотурбинного наддува не имеют чёткой области использования в зависимости от среднего эффективного давления. До сих пор на практике в процессе создания более форсированных дизельных двигателей конструкторы вынуждены подбирать многие элементы выпускных систем на основе ранее приобретенного опыта эксплуатации предыдущих конструкций. Причина кроется в отсутствии понимания физической сущности процессов локальных потерь работоспособности рабочего тела, например, при движении газов от цилиндров двигателя к турбине. В работе получены новые результаты расчётов импульсной и изобарной систем выпуска двигателя Caterpillar 3508С в зависимости от уровня форсирования по среднему эффективному давлению с использованием метода характеристик, квазистационарного метода и эксергетического метода. Разработан комплексный подход к решению проблемы выбора оптимальной системы выпуска при форсировании по среднему эффективному давлению поршневого двигателя. Для решения поставленной цели исследования в работе применился современный подход к оценке эффективности различных систем газотурбинного наддува эксергетический метод. Полученные результаты подтверждают возможность использования эксергетического метода для оценки эффективности систем выпуска с точки зрения потерь работоспособности газов. Выбрана оптимальная система выпуска двигателя Caterpillar 3508С с точки зрения потерь работоспособности выпускных газов в зависимости от среднего эффективного давления.The article presents the results of the study of pulse and Isobaric exhaust systems of a piston engine depending on the average effective pressure. The purpose of this work is to identify the effective use of a pulsed or isobaric exhaust system from the point of view of the loss of working capacity of exhaust gases during the movement of the energy flow from cylinders to the turbine when forcing the piston engine according to the average effective pressure. Existing supercharging systems do not have a clear area of use depending on the average effective pressure. Until now, in practice, in the process of creating more forced diesel engines, designers are forced to select many elements of exhaust systems on the basis of previously acquired experience in the operation of previous designs. The reason lies in the lack of understanding of the physical essence of the processes of local losses of the working capacity working fluid, for example, during the movement of gases from the engine cylinders to the turbine. In the work are obtained new results of calculations of impulse and isobaric exhaust systems of Caterpillar 3508C engine depending on the level of forcing on the average effective pressure with the use of the characteristics method, the quasi-stationary method and the exergy method are obtained. A comprehensive approach to solving the problem of choosing the optimal exhaust system when forcing the piston engine according to the average effective pressure is developed. To solve the goal of the study, a modern approach to assessing the efficiency of various supercharging systems exergy method was applied. The obtained results confirm the possibility of using the exergy method to assess the efficiency of exhaust systems from the point of view of the losses of working capacity of exhaust gases. The selected optimum system of exhaust system of the Caterpillar 3508C engine in terms of the losses of working capacity of exhaust gases depending on the average effective pressure.

Advanced Exergetic Assessment of a Vapor Compression Cycle With Alternative Refrigerants

The present study compares the thermal performance of various alternative refrigerants with conventional refrigerant operating on a vapor compression cycle with energetic, exergetic, and advanced exergetic approaches. Appropriate alternative refrigerants are selected for the analysis, and R1234yf is recommended as the best suitable refrigerant to replace the existing refrigerants. By splitting the exergy destruction into endogenous and unavoidable, endogenous and avoidable, exogenous and unavoidable, and exogenous and avoidable parts, an advanced exergy method depicts the real potentials for the improvement in the thermal system. Moreover, a traditional exergy method prefers condenser for performance improvement as it has 18.48% higher exergy destruction than evaporator, whereas the advanced exergy method proposes evaporator rather than condenser since its endogenous and avoidable destruction part is 26.38% more than condenser for R1234yf refrigerant.

Application of exergy analysis for estimation of geotechnical systems stability

The opportunity of application of exergy analysis for estimation of geotechnical systems is considered. The example of use of the exergy method for estimation of pollution of water-producing area of the small rivers is given. Using concept of exergy we have the necessary information about technical object and environment and are able to define current condition and variants of the territory development.