The Combined First and Second Laws of Thermodynamics and Exergy Analysis

2000 ◽  
Author(s):  
George A. Adebiyi
Keyword(s):  
Exergy Analysis ◽  
Control Volume ◽  
Novel Approach ◽  
Flow Processes ◽  
Laws Of Thermodynamics ◽  
Closed Systems ◽  
Reversible Processes ◽  
Reference Environment ◽  
Transport Theorem

Abstract A novel approach is proposed for combining the first and second laws of thermodynamics for systems undergoing arbitrary, non-reversible processes. A reference environment at an intensive state (p0, T0) is assumed, and combination of the two laws of thermodynamics yields the familiar equations used in the exergy analysis of processes. The application of the laws of thermodynamics was made first to non-flow processes involving closed systems. An extension to the control volume and flow processes was carried out via the use of the Reynolds transport theorem.

The Impact of Reference Environment Selection on the Exergy Efficiencies of Aerospace Engines

1999 ◽  
Author(s):  
Jason Etele ◽  
Marc A. Rosen
Keyword(s):  
Sea Level ◽  
Exergy Analysis ◽  
Operating Environment ◽  
A Value ◽  
Turbojet Engine ◽  
Reference Environment ◽  
The Impact

Abstract An exergy analysis is applied to a turbojet engine over a range of flight altitudes ranging from sea level to 15,000 m (∼50,000 ft), to examine the effects of using different reference-environment models. The results of this analysis using a variable reference environment (equal to the operating environment at all times) are compared to the results obtained using two constant reference environments (sea level and 15,000 m). The actual rational efficiency of the turbojet decreases with increasing altitude, ranging from a value of 16.9% at sea level to 15.3% at 15,000 m. In the most extreme cases considered, the rational efficiency value calculated using a constant reference environment varies by approximately 2% from the variable reference environment value.

scholarly journals Exergy As a Measure of Sustainable Retrofitting of Buildings

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 3139 ◽  
Author(s):  
Carlos Fernández Bandera ◽  
Ana Muñoz Mardones ◽  
Hu Du ◽  
Juan Echevarría Trueba ◽  
Germán Ramos Ruiz
Keyword(s):  
High Performance ◽  
Exergy Analysis ◽  
Local Contexts ◽  
Primary Selection ◽  
Optimization Methodology ◽  
The One ◽  
Reference Environment ◽  
Architectural Characteristics ◽  
The University

This study presents a novel optimization methodology for choosing optimal building retrofitting strategies based on the concept of exergy analysis. The study demonstrates that the building exergy analysis may open new opportunities in the design of an optimal retrofit solution despite being a theoretical approach based on the high performance of a Carnot reverse cycle. This exergy-based solution is different from the one selected through traditional efficient retrofits where minimizing energy consumption is the primary selection criteria. The new solution connects the building with the reference environment, which acts as “an unlimited sink or unlimited sources of energy”, and it adapts the building to maximize the intake of energy resources from the reference environment. The building hosting the School of Architecture at the University of Navarra has been chosen as the case study building. The unique architectural appearance and bespoke architectural characteristics of the building limit the choices of retrofitting solutions; therefore, retrofitting solutions on the façade, roof, roof skylight and windows are considered in multi-objective optimization using the jEPlus package. It is remarkable that different retrofitting solutions have been obtained for energy-driven and exergy-driven optimization, respectively. Considering the local contexts and all possible reference environments for the building, three “unlimited sinks or unlimited sources of energy” are selected for the case study building to explore exergy-driven optimization: the external air, the ground in the surrounding area and the nearby river. The evidence shows that no matter which reference environment is chosen, an identical envelope retrofitting solution has been obtained.

Exergy Analysis-Potential of Salinity Gradient Energy Source

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Arash Emdadi ◽  
Mansour Zenouzi ◽  
Amir Lak ◽  
Behzad Panahirad ◽  
Yunus Emami ◽  
...  
Keyword(s):  
Sodium Chloride ◽  
Chloride Solution ◽  
Sodium Chloride Solution ◽  
Exergy Analysis ◽  
Salinity Gradient ◽  
Electrical Energy ◽  
Dead State ◽  
Gradient Energy ◽  
Reference Environment ◽  
Faster Development

Mixing of fresh (river) water and salty water (seawater or saline brine) in a controlled environment produces an electrical energy known as salinity gradient energy (SGE). Two main conversion technologies of SGE are membrane-based processes: pressure retarded osmosis (PRO) and reverse electrodialysis (RED). Exergy calculations for a representative river-lake system are investigated using available data in the literature between 2000 and 2008 as a case study. An exergy analysis of an SGE system of sea-river is applied to calculate the maximum potential power for electricity generation. Seawater is taken as reference environment (global dead state) for calculating the exergy of fresh water since the sea is the final reservoir. Aqueous sodium chloride solution model is used to calculate the thermodynamic properties of seawater. This model does not consider seawater as an ideal solution and provides accurate thermodynamics properties of sodium chloride solution. The chemical exergy analysis considers sodium chloride (NaCl) as main salt in the water of this highly saline Lake with concentration of more than 200 g/L. The potential power of this system is between 150 and 329 MW depending on discharge of river and salinity gradient between the Lake and the River based on the exergy results. This result indicates a high potential for constructing power plant for SGE conversion. Semipermeable membranes with lifetime greater than 10 years and power density higher than 5 W/m2 would lead to faster development of this conversion technology.

EXERGY ANALYSIS OF THE PERFORMANCE OF A VARIABLE REFRIGERANT FLOW (VRF) AIR CONDITIONING SYSTEM

2011 ◽  
Vol 19 (01) ◽  
pp. 57-68 ◽  
Author(s):  
MIGUEL PADILLA
Keyword(s):  
System Performance ◽  
Air Conditioning ◽  
Exergy Analysis ◽  
Control Volume ◽  
Hvac Systems ◽  
Coefficient Of Performance ◽  
Cooling Load ◽  
Air Conditioning System ◽  
Operational Conditions ◽  
Highly Sensitive

Commercial multiple evaporators variable refrigerant flow (VRF) HVAC systems present many advantages such as being energy saving and the capability of adjusting refrigerant mass flow rate according to the change of high rises occurrence. This paper deals with an experimental control volume exergy analysis in a VRF air conditioning system. The experimental results show that the brunt of the total exergy destroyed in the whole system occurs in the outdoor unit, where the exergy destroyed in the condenser is more important. The values of coefficient of performance (COP) obtained for the tests increase as the system reaches operational conditions imposed in every indoor unit zone. The VRF system analyzed is highly sensitive to the action of the constant speed compressor. The use of an inverter compressor improves the system performance by adjusting the power consumption according to the cooling load in the evaporators.

Towards an Exergy Analysis of Diffusive and Non-Diffusive Processes in Living Organisms

2016 ◽  
Vol 7 ◽  
pp. 177-184
Author(s):  
Antonio F. Miguel
Keyword(s):  
Exergy Analysis ◽  
Balance Equations ◽  
Physiological Processes ◽  
Performance Of Systems ◽  
Laws Of Thermodynamics ◽  
Living Organisms ◽  
Diffusive Processes ◽  
Cellular Components ◽  
Exergy Balance ◽  
Insight Into

Living organisms are open dissipative thermodynamic systems that rely on mechano-thermo-electrochemical interactions to survive. Plant physiological processes allow plants to survive by converting solar radiation into chemical energy, and store that energy in form that can be used. Mammals catabolize food to obtain energy that is used to fuel, build and repair the cellular components. The exergy balance is a combined statement of the first and second laws of thermodynamics. It provides insight into the performance of systems. In this paper, exergy balance equations for both mammal’s and green plants are presented and analyzed.

scholarly journals Experimental Energy and Exergy Analysis of an Automotive Turbocharger Using a Novel Power-Based Approach

Energies ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6572
Author(s):  
Sina Kazemi Bakhshmand ◽  
Ly Tai Luu ◽  
Clemens Biet
Keyword(s):  
Heat Transfer ◽  
Exergy Analysis ◽  
Test Bench ◽  
Deep Understanding ◽  
Experimental Measurements ◽  
First Law Of Thermodynamics ◽  
Hot Gas ◽  
Energy And Exergy ◽  
Laws Of Thermodynamics ◽  
Energy And Exergy Analysis

The performance of turbochargers is heavily influenced by heat transfer. Conventional investigations are commonly performed under adiabatic assumptions and are based on the first law of thermodynamics, which is insufficient for perceiving the aerothermodynamic performance of turbochargers. This study aims to experimentally investigate the non-adiabatic performance of an automotive turbocharger turbine through energy and exergy analysis, considering heat transfer impacts. It is achieved based on experimental measurements and by implementing a novel innovative power-based approach to extract the amount of heat transfer. The turbocharger is measured on a hot gas test bench in both diabatic and adiabatic conditions. Consequently, by carrying out energy and exergy balances, the amount of lost available work due to heat transfer and internal irreversibilities within the turbine is quantified. The study allows researchers to achieve a deep understanding of the impacts of heat transfer on the aerothermodynamic performance of turbochargers, considering both the first and second laws of thermodynamics.

Exergy Analysis of a Turbojet Engine Over a Complete Flight Cycle

2001 ◽  
Author(s):  
Marc A. Rosen
Keyword(s):  
Sea Level ◽  
Exergy Analysis ◽  
Operating Environment ◽  
Turbojet Engine ◽  
Reference Environment ◽  
Selection Of

Abstract Exergy analysis is used to evaluate the efficiency of a turbojet engine over an entire flight (including climb, cruise and descent), and to assess the sensitivity of these results to the selection of the reference environment. This study is an extension of previous work where the accuracy of an exergy analysis of a turbojet engine is evaluated for different reference environments on an instantaneous basis. The present work evaluates cumulative engine efficiencies. The results show that the use of a constant reference environment set at cruise altitude conditions yields cumulative exergy efficiencies that are within 0.01% of those found using a variable reference environment (equal to the operating environment conditions at all times) over a 3,500 km flight. This result is in contrast to the use of a constant sea-level reference environment where such are 3.7%. This significant cumulative efficiency difference with the choice of reference environment is not observed when using an instantaneous exergy analysis. Care must be exercised when using a constant reference environment, as for both constant sea-level and cruise-altitude reference environments cumulative rational efficiencies increase over the majority of the flight, whereas for a continuously varying reference environment these efficiencies decrease.

scholarly journals On the Reynolds transport theorem for three phase systems with storage in interfaces

2011 ◽  
Vol 32 (1) ◽  
pp. 21-44
Author(s):  
Teodor Skiepko
Keyword(s):  
Control Volume ◽  
Surface Transport ◽  
Spatial Systems ◽  
Three Phase ◽  
Multiphase Systems ◽  
Phase Systems ◽  
Extensive Quantity ◽  
Transport Theorem

On the Reynolds transport theorem for three phase systems with storage in interfacesIn the paper, the Reynolds transport theorem (RTT) for three phase systems is developed, in terms associated with a moving control volume. The basic tools applied to the derivation are the generalized transport theorem by Truesdell and Toupin, and generalized surface transport theorem by Aris as well as Slattery. The final results referenced to a generic extensive quantity demonstrate the theorem in the integral instantaneous form. As a further illustration of applicability of the theorem relation developed some specific forms are deduced from such as for multiphase systems in terms of fixed control volume, surface systems and homogeneous spatial systems.

The balance principle and the Reynolds transport theorem in introductory fluid mechanics

2017 ◽  
Vol 46 (3) ◽  
pp. 195-209
Author(s):  
Donald D Gray ◽  
Wade W Huebsch
Keyword(s):  
United States ◽  
Fluid Dynamics ◽  
Fluid Mechanics ◽  
Control Volume ◽  
The United States ◽  
Balance Principle ◽  
Alternative Approach ◽  
Finite Control ◽  
Transport Theorem ◽  
Volume Equations

This paper traces the evolution of the use of the Reynolds transport theorem to derive finite control volume equations for mass, momentum, and energy in introductory engineering fluid mechanics textbooks used in the United States. The paper demonstrates the superior merits of an alternative approach using the balance principle. The balance principle is easier to teach, to understand, and to apply in more complex situations. It better prepares students to understand the derivation of the partial differential equations of fluid mechanics and the finite volume equations of computational fluid dynamics. For these reasons, instructors should consider using the balance principle instead of (or at minimum in addition to) the Reynolds transport theorem in introductory fluid mechanics courses.

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