scholarly journals From Entropy Generation to Exergy Efficiency at Varying Reference Environment Temperature: Case Study of an Air Handling Unit

Entropy ◽  
2019 ◽  
Vol 21 (4) ◽  
pp. 361 ◽  
Author(s):  
Giedrė Streckienė ◽  
Vytautas Martinaitis ◽  
Juozas Bielskus
Keyword(s):  
Heat Pump ◽  
Entropy Generation ◽  
Energy Demand ◽  
Dynamic Modelling ◽  
Second Law Of Thermodynamics ◽  
Exergy Efficiency ◽  
Second Law ◽  
Air Handling Unit ◽  
Individual Character ◽  
Environment Temperature

The continuous energy transformation processes in heating, ventilation, and air conditioning systems of buildings are responsible for 36% of global final energy consumption. Tighter thermal insulation requirements for buildings have significantly reduced heat transfer losses. Unfortunately, this has little effect on energy demand for ventilation. On the basis of the First and the Second Law of Thermodynamics, the concepts of entropy and exergy are applied to the analysis of ventilation air handling unit (AHU) with a heat pump, in this paper. This study aims to develop a consistent approach for this purpose, taking into account the variations of reference temperature and temperatures of working fluids. An analytical investigation on entropy generation and exergy analysis are used, when exergy is determined by calculating coenthalpies and evaluating exergy flows and their directions. The results show that each component of the AHU has its individual character of generated entropy, destroyed exergy, and exergy efficiency variation. However, the evaporator of the heat pump and fans have unabated quantities of exergy destruction. The exergy efficiency of AHU decreases from 45–55% to 12–15% when outdoor air temperature is within the range of −30 to +10 °C, respectively. This helps to determine the conditions and components of improving the exergy efficiency of the AHU at variable real-world local climate conditions. The presented methodological approach could be used in the dynamic modelling software and contribute to a wider application of the Second Law of Thermodynamics in practice.

scholarly journals From Entropy Generation to Exergy Efficiency at Varying Reference Environment Temperature: Case Study of an Air Handling Unit

2019 ◽  
Author(s):  
Giedrė Streckienė ◽  
Vytautas Martinaitis ◽  
Juozas Bielskus
Keyword(s):  
Heat Pump ◽  
Entropy Generation ◽  
Energy Demand ◽  
Dynamic Modelling ◽  
Second Law Of Thermodynamics ◽  
Exergy Efficiency ◽  
Second Law ◽  
Air Handling Unit ◽  
Individual Character ◽  
Environment Temperature

The continuous energy transformation processes in heating, ventilation and air conditioning systems of buildings are responsible for 36% of global final energy consumption. Tighter thermal insulation requirements for buildings have significantly reduced heat transfer losses. Unfortunately, this has little effect on energy demand for ventilation. On the basis of the First and the Second Law of Thermodynamics, the concepts of entropy and exergy are applied to the analysis of ventilation air handling unit (AHU) with a heat pump in this paper. This study aims to develop a consistent approach for this purpose, taking into account the variations of reference temperature and temperatures of working fluids. An analytical investigation on entropy generation and exergy analysis are used, when exergy is determined by calculating coenthalpies and evaluating exergy flows and their directions. The results show that each component of the AHU has its individual character of generated entropy, destroyed exergy and exergy efficiency variation. However, the evaporator of heat pump and fans have unabated quantities of exergy destruction. The exergy efficiency of AHU decreases from 45-55% to 12-15% when outdoor air temperature is within the range of –30°C…+10°C, respectively. This helps to determine conditions and components of improving the exergy efficiency of the AHU at variable real-world local climate conditions. The presented methodological approach could be used in the dynamic modelling software and contribute to a wider application of the Second Law of Thermodynamics in practice.

Thermodynamics as a fundamental science of reliability

2016 ◽  
Vol 230 (6) ◽  
pp. 598-608 ◽  
Author(s):  
Anahita Imanian ◽  
Mohammad Modarres
Keyword(s):  
Energy Dissipation ◽  
Entropy Generation ◽  
Damage Model ◽  
Second Law Of Thermodynamics ◽  
Reliability Function ◽  
Cumulative Damage ◽  
Life Assessment ◽  
Irreversible Processes ◽  
Second Law ◽  
Cumulative Hazard

Cumulative hazard and cumulative damage are important models for reliability and structural integrity assessment. This article reviews a previously developed thermodynamic entropy–based damage model and derives and demonstrates an equivalent reliability function. As such, a thermodynamically inspired approach to developing new definitions of cumulative hazard, cumulative damage, and life models of structures and components based on the second law of thermodynamics is presented. The article defines a new unified measure of damage in terms of energy dissipation associated with multiple interacting irreversible processes that represent the underlying failure mechanisms that cause damage and failure. Since energy dissipation leads to entropy generation in materials, it has been shown and experimentally demonstrated that the use of the total entropy generated in any degradation process is measurable and can ultimately be used to represent the time of failure of structures and components. This description therefore connects the second law of thermodynamics to the conventional models of reliability used in life assessment. Any variability in the entropic endurance to failure and uncertainties about the parameters of the entropic-based damage model lead to the time-to-failure distribution. In comparison with the conventional probabilistic reliability methods, deriving the reliability function in terms of the entropy generation can offer a general and more fundamental approach to representation of reliability. The entropic-based theory of damage and the equivalent reliability approach are demonstrated and confirmed experimentally by applying the complex interactive corrosion-fatigue degradation mechanism to samples of aluminum materials.

A Thermodynamic Efficiency Concept for Heat Exchange Devices

1983 ◽  
Vol 105 (1) ◽  
pp. 199-203 ◽  
Author(s):  
L. C. Witte ◽  
N. Shamsundar
Keyword(s):  
Heat Exchanger ◽  
Heat Exchange ◽  
Energy Use ◽  
Second Law Of Thermodynamics ◽  
Thermodynamic Efficiency ◽  
Second Law ◽  
Two Fluids ◽  
Environment Temperature ◽  
Efficiency And Effectiveness ◽  
The Mean

A thermodynamic efficiency based on the second law of thermodynamics is defined for heat exchange devices. The efficiency can be simply written in terms of the mean absolute temperatures of the two fluids exchanging heat, and the appropriate environment temperature. It is also shown that for a given ratio of hot to cold inlet temperatures, the efficiency and effectiveness for particular heat exchange configurations are related. This efficiency is compared to second-law efficiencies proposed by other authors, and is shown to be superior in its ability to predict the effect of heat exchanger parameter changes upon the efficiency of energy use. The concept is applied to typical heat exchange cases to demonstrate its usefulness and sensitivity.

scholarly journals Diffusive Bejan number and second law of thermodynamics toward a new dimensionless formulation of fluid dynamics laws

2019 ◽  
Vol 23 (6 Part B) ◽  
pp. 4005-4022 ◽  
Author(s):  
Michele Trancossi ◽  
Jose Pascoa
Keyword(s):  
Fluid Dynamics ◽  
Entropy Generation ◽  
Fluid Dynamic ◽  
Second Law Of Thermodynamics ◽  
Integral Form ◽  
Second Law ◽  
Bejan Number ◽  
Definition Of ◽  
New Formulation ◽  
Dimensionless Formulation

In a recent paper, Liversage and Trancossi have defined a new formulation of drag as a function of the dimensionless Bejan and Reynolds numbers. Further analysis of this hypothesis has permitted to obtain a new dimensionless formulation of the fundamental equations of fluid dynamics in their integral form. The resulting equations have been deeply discussed for the thermodynamic definition of Bejan number evidencing that the proposed formulation allows solving fluid dynamic problems in terms of entropy generation, allowing an effective optimization of design in terms of the Second law of thermodynamics. Some samples are discussed evidencing how the new formulation can support the generation of an optimized configuration of fluidic devices and that the optimized configurations allow minimizing the entropy generation.

Introducing a Novel Air Handling Unit Based on Focusing on Turbulent Exhaust Air Energy-Exergy Recovery Potential

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Yuanzhou Zheng ◽  
Rasool Kalbasi ◽  
Arash Karimipour ◽  
Peng Liu ◽  
Quang-Vu Bach
Keyword(s):  
Energy Consumption ◽  
Energy Demand ◽  
Energy Recovery ◽  
Primary Energy ◽  
Second Law ◽  
The Novel ◽  
Heating Coil ◽  
Recovery Potential ◽  
Air Handling Unit ◽  
Second Law Analysis

Abstract A novel air handling unit (AHU) aimed at reducing energy consumption was introduced in this study. In the proposed novel AHU, the heating coil is completely removed, and therefore, no heating coil energy demand is needed. The novel AHU used primary energy recovery as well as secondary one to utilize the return air energy and exergy. Through the first energy recovery unit, the return air exergy was recovered, while in the secondary heat exchanger, return air energy was recycled. Results showed that using the novel AHU leads to a reduction in energy consumption as well as the exergy losses. Three climate zones of A, B, and C were selected to assess the novel AHU performance. From the first law viewpoint, at zone B, using novel AHU has priority over other zones, while in the second law analysis, utilizing the novel AHU at zones B and C is more beneficial. Based on the first law analysis, owing to using novel AHU, energy consumption reduced up to 55.2% at Penang climate zone. Second law analysis revealed that utilizing the novel AHU decreased the irreversibility up to 51.4% in the Vancouver climate region.

scholarly journals Application of the Second Law of Thermodynamics in Brazilian Residential Appliances towards a Rational Use of Energy

Entropy ◽  
2020 ◽  
Vol 22 (6) ◽  
pp. 616 ◽  
Author(s):  
Carlos Eduardo Keutenedjian Mady ◽  
Clara Reis Pinto ◽  
Marina Torelli Reis Martins Pereira
Keyword(s):  
Energy Efficiency ◽  
Natural Resources ◽  
Air Conditioning ◽  
Second Law Of Thermodynamics ◽  
Exergy Efficiency ◽  
Second Law ◽  
Vapor Compression ◽  
Energy Matrix ◽  
Additional Information

This article proposes the utilization of the concepts of destroyed exergy and exergy efficiency for equipment and process performance indicators that are related to the current energy planning scenario in Brazil, more specifically with energy-efficiency labelling. Several indicators associated with these concepts are discussed, including one national program that is based on labeling the energy efficiency of several residential, commercial and industrial appliances. The grades are indicated in the equipment using values from A to G. This labeling system is useful for discriminating similar technologies used for the same function; nevertheless produced by different enterprises. For this complementary analysis, two types of refrigeration methods were compared, absorption and vapor compression; however, these energy indexes alone are not sufficient parameters to select among these two technologies, because their performance indexes definition are different. To address this, our research considers the second law of thermodynamics through exergy analysis as a proper sub-index to obtain a systematic comparison between these various indicators. It is significant to highlight that seldom research studies addressed to this problem so explicitly, in an actual governmental working solution, aiming at discussing to the society the advantage of the usage of the “quality of the energy” as a complementary index to governmental and personal choices. Results indicate that it is possible to use the destroyed exergy and exergy efficiency to help select the technology that better utilizes natural resources, considering the energy matrix of the country. Appliances for water heating and air conditioning were compared from energy and exergy viewpoint, where the last gave additional information about the quality of energy conversion process, giving a completely different trend from the energy analysis alone, without the necessity to think about the energy matrix. Later this issue is addressed from both points of view. Future studies may suggest an exergy based index. The energy efficiency suggests that electrical shower (values higher than 95%) are better than gas water heaters (83% ) in using natural resources, whereas the exergy efficiency shares similar magnitudes (about 3%). A related pattern is shown for the theoretical air conditioning systems. The vapor compression systems have an energy index higher than 3, and absorption systems lower than 1. For these circumstances, the exergy efficiency shows figures nearby 30%.

scholarly journals Teach Second Law of Thermodynamics via Analysis of Flow through Packed Beds and Consolidated Porous Media

Fluids ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 116 ◽  
Author(s):  
Rajinder Pal
Keyword(s):  
Porous Media ◽  
Entropy Generation ◽  
Power Plants ◽  
Mechanical Energy ◽  
Fluid Velocity ◽  
Second Law Of Thermodynamics ◽  
Second Law ◽  
Packed Beds ◽  
Factors Affecting ◽  
Flow Through

The second law of thermodynamics is indispensable in engineering applications. It allows us to determine if a given process is feasible or not, and if the given process is feasible, how efficient or inefficient is the process. Thus, the second law plays a key role in the design and operation of engineering processes, such as steam power plants and refrigeration processes. Nevertheless students often find the second law and its applications most difficult to comprehend. The second law revolves around the concepts of entropy and entropy generation. The feasibility of a process and its efficiency are directly related to entropy generation in the process. As entropy generation occurs in all flow processes due to friction in fluids, fluid mechanics can be used as a tool to teach the second law of thermodynamics and related concepts to students. In this article, flow through packed beds and consolidated porous media is analyzed in terms of entropy generation. The link between entropy generation and mechanical energy dissipation is established in such flows in terms of the directly measurable quantities such as pressure drop. Equations are developed to predict the entropy generation rates in terms of superficial fluid velocity, porous medium characteristics, and fluid properties. The predictions of the proposed equations are presented and discussed. Factors affecting the rate of entropy generation in flow through packed beds and consolidated porous media are identified and explained.

Optimization of turbojet engine cycle with dual-purpose PSO algorithm

2019 ◽  
Vol 20 (6) ◽  
pp. 604 ◽  
Author(s):  
M.R. Ahadi Nasab ◽  
M.A. Ehyaei
Keyword(s):  
Entropy Production ◽  
Pressure Ratio ◽  
Second Law Of Thermodynamics ◽  
Pso Algorithm ◽  
Optimization Method ◽  
Exergy Efficiency ◽  
Second Law ◽  
Turbine Efficiency ◽  
Turbojet Engine ◽  
Compressor Pressure Ratio

In this article, the J85-GE-21 turbojet engine for an altitude of 1000–8000 m, with the speed of 200 m/s and at 10, 20, and 40 °C, was provided, and then, based on the objective functions, the above system was optimized using particle swarm optimization method. For the purpose of optimization, the Mach number, compressor efficiency, turbine efficiency, nozzle efficiency, and compressor pressure ratio were assumed to be in the range of 0.6–1.4, 0.8–0.95, 0.8–0.95, 0.8–0.95, and 7–10, respectively. The highest exergy efficiency of 73.1% for different components of the engine at sea level and speed of 200 m/s belonged to the diffuser. Second and third to it were nozzle and combustion chamber with 68.6 and 51.5%, respectively. The lowest exergy efficiency of 4% belonged to the compressor, and the second to it was the afterburner with 11.6%. Also, the values of entropy production and efficiency of the second law of thermodynamics were 1176.99 and 479 K/W, respectively, prior to optimization, which were respectively changed to 1129 and 51.4 K/W postoptimization. Obviously, the entropy production is reduced, while the efficiency of the second law of thermodynamics is increased.

Exergy Analysis of Transcritical Regenerative Organic Rankine Cycle Using Isobutane

2013 ◽  
Vol 442 ◽  
pp. 183-186
Author(s):  
Kyoung Hoon Kim
Keyword(s):  
Exergy Analysis ◽  
Organic Rankine Cycle ◽  
Internal Heat ◽  
Second Law Of Thermodynamics ◽  
Rankine Cycle ◽  
Exergy Efficiency ◽  
Second Law ◽  
Source Temperature ◽  
Internal Heat Exchanger ◽  
Maximum Value

Exergy analysis is performed for transcritical Organic Rankine Cycle (ORC) with internal heat exchanger based on the second law of thermodynamics. Effects of source temperature as well as turbine inlet pressure (TIP) are investigated on the exergy destructions (or anergies) of the system as well as exergy efficiency. Results show that irreversibility of the system decreases with increasing TIP or decreasing source temperature. Exergy efficiency decreases with increasing source temperature; however has a maximum value with respect to TIP.

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