Methodology for Intrinsic Exergy Analysis as Guide for Process Improvement With a Fuel Droplet Combustion Example

2005 ◽  
Author(s):  
Wladimir Sarmiento-Darkin ◽  
Noam Lior
Keyword(s):  
Process Improvement ◽  
Entropy Generation ◽  
Exergy Analysis ◽  
Combustion Process ◽  
Exergy Efficiency ◽  
Exergy Loss ◽  
System Level ◽  
Base Case ◽  
Droplet Combustion ◽  
Exergy Losses

While exergy analysis is by now commonly used on the system level to identify losses and recommend ways for reducing them, its use on the “intrinsic”, field, level where the exergy of a process is calculated as a function of location and time, is still developing. Intrinsic exergy analysis is a most useful method for identifying and understanding the specific reasons for exergy losses in a process, and in devising methods for their reduction. A good example, which is the sample case of this paper, is the analysis of exergy losses in combustion processes, which are known to be responsible for around 30 % of the fuel potential to produce power. In this paper we develop a methodology for intrinsic exergy analysis and for its use for process improvement, using the case of combustion of a n-heptane droplet as example. The time-dependent continuity, energy and species conservation equations together with the reaction kinetics, state equations, and temperature and concentration dependent transport properties, are solved numerically to determine the temperature and concentrations fields. These results are then used to calculate the rates of local entropy generation to determine the spatial and temporal irreversibilities produced during the combustion process, as well as the exergy efficiency. The results obtained indicate, among other things, that after ignition has taken place, the exergy loss (or entropy generation) component most responsible for the overall exergy loss is the chemical entropy, having the same order of magnitude as the rest of the entropy generation terms combined for all the cases evaluated. The computed exergy efficiency for the base case is 68.4%, in agreement with previous droplet combustion exergy studies. To develop guidelines for the process improvement, the sensitivity of the second law efficiency to the initial gas temperature (Tgi), reaction rate (ω), and combustion duration were analyzed. The results generated several promising improvement avenues.

EXERGY ANALYSIS OF A LiBr–H2O VAPOR ABSORPTION REFRIGERATION PLANT: A CASE STUDY

2014 ◽  
Vol 22 (02) ◽  
pp. 1450010 ◽  
Author(s):  
SANJEEV ANAND ◽  
ANKUSH GUPTA ◽  
SUDHIR KUMAR TYAGI
Keyword(s):  
Performance Optimization ◽  
Exergy Analysis ◽  
Heat Rate ◽  
Exergy Efficiency ◽  
Exergy Loss ◽  
Absorption Refrigeration ◽  
Actual System ◽  
Evaporator Temperature ◽  
Vapor Absorption ◽  
Vapor Absorption Refrigeration

This communication presents the energy and exergy analysis of an actual double effect steam powered LiBr – H 2 O vapor absorption refrigeration plant. Exergy loss, COP, exergy efficiency and heat rate for each component of the system are calculated. The effect of generator as well as evaporator temperature on the COP and exergy efficiency is evaluated and it is found that the irreversibility rate is highest in the generator while it is found to be the lowest in the case of absorber and condenser. It is also found that the COP of the system increases with the increase in the evaporator temperature while it is found to be reverse in case of exergy efficiency. Results revealed that average exergy loss is highest in the generator as compared to other components. The results obtained are helpful for designers to bring changes in the actual system for performance optimization and less wastage of energy. The study clearly explain the operational and maintenance problems in the machine and point out the areas of energy wastage which the operational engineer should look into for the optimum operation of the plant.

Exergy Analysis of Energy Consumption for Central Air Conditioning System

2014 ◽  
Vol 628 ◽  
pp. 332-337
Author(s):  
Xiao Xia Xia ◽  
Nai Jun Zhou ◽  
Zhi Qi Wang
Keyword(s):  
Energy Consumption ◽  
Air Conditioning ◽  
Exergy Analysis ◽  
Exergy Efficiency ◽  
Dew Point ◽  
Exergy Loss ◽  
Air Conditioning System ◽  
Air Cooler ◽  
Central Air Conditioning ◽  
Air Conditioning Systems

The energy consumption of several central air conditioning systems in summer was researched by the method of exergy analysis. Combined with actual example,the exergy loss of all the equipments and the exergy efficiency of three systems were calculated. The results show that the exergy efficiency of three systems is very low. Relatively speaking, the exergy efficiency of primary return air conditioning system with supplying air in dew point is highest. The equipment of highest exergy loss is air-conditioned room, while the exergy loss of surface air cooler is smallest. Based on this, several improvement measures were proposed to reduce exergy loss and improve exergy efficiency.

scholarly journals An exergy analysis for overall hidden losses of energy in solar water heater

2020 ◽  
pp. 343-343
Author(s):  
Sathyakala Ponnusamy ◽  
Sundara Sai Gangadharan ◽  
Balaji Kalaiarasu
Keyword(s):  
Entropy Generation ◽  
Exergy Analysis ◽  
Glass Plate ◽  
Exergy Efficiency ◽  
Solar Water Heater ◽  
Exergy Destruction ◽  
Water Pipe ◽  
Water Heater ◽  
Collector Plate ◽  
Solar Water

This study investigates the hidden thermal losses of glass plate, collector plate, water pipe and storage tank of solar water heater in the process of energy conversion. The present non-conventional energy methods are insufficient, whereas the exergy analysis provides a remarkable solution. Thus, employing the exergy analysis, entropy generation, exergy destruction and exergy efficiency of each subsystem of solar water heater are computed. The obtained results showed that the entropy generation and exergy destruction are high during the heat transfer in each subsystem. Henceforth, the existing solar water heater design is modified placing hexagonal honeycomb structure between the glass plate and the collector plate and also water pipe is insulated to trap huge amount of solar energy. The proposed design exhibits improved exergy efficiency when compared with the existing model, which enhances the performance of the system.

EXERGY ANALYSIS OF GEOTHERMAL POWER PLANT KAMOJANG 68, 3 MW IN CAPACITY

2018 ◽  
Vol 7 (2) ◽  
Author(s):  
Amiral Aziz
Keyword(s):  
Energy Efficiency ◽  
Power Plant ◽  
Exergy Analysis ◽  
Exergy Efficiency ◽  
Preliminary Design ◽  
Exergy Destruction ◽  
Geothermal Power Plant ◽  
Production Wells ◽  
Geothermal Power ◽  
Exergy Losses

The importance of exergy analysis in preliminary design of geothermal power has been proven. An exergy analysis was carried out and the locations and quantities of exergy losses, wastes and destructions in the different processes of the plan were pinpointed. The obtained results show that the total exergy available from production wells KMJ 68 was calculated to be 6967.55 kW. The total exergy received from wells which is connected during the analysis and enter into the separator was found to be 6337.91 kW in which 5808.8 kW is contained in the steam phase. The overall exergy efficiency for the power plant is 43.06% and the overall energy efficiency is 13.05 %, in both cases with respect to the exergy from the connected wells. The parts of the system with largest exergy destruction are the condenser, the turbine, and the disposed waste brinekeywords: exergy, irreversibility, geothermal power plant, KMJ 68

Exergy Analysis of Mine Water Source Heat Pump System

2010 ◽  
Vol 121-122 ◽  
pp. 980-985 ◽  
Author(s):  
Jing Gang Wang ◽  
Mei Xia Du ◽  
Chuan Chuan Du ◽  
Xiao Xia Gao
Keyword(s):  
Energy Saving ◽  
Heat Pump ◽  
Mine Water ◽  
Exergy Analysis ◽  
Water Source ◽  
Exergy Efficiency ◽  
Exergy Loss ◽  
Pump System ◽  
Heat Pump System ◽  
Main Components

This paper analyses exergy of the components of the mine water source heat pump. Evaluate the exergy efficiency and exergy loss of main components of mine water source heat pump. An example that is calculated and analyzed shows that the compressor is the main energy-saving target.

scholarly journals Analysis of Local Exergy Losses in Combustion Systems Using a Hybrid Filtered Eulerian Stochastic Field Coupled with Detailed Chemistry Tabulation: Cases of Flames D and E

Energies ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 6315
Author(s):  
Senda Agrebi ◽  
Louis Dreßler ◽  
Hendrik Nicolai ◽  
Florian Ries ◽  
Kaushal Nishad ◽  
...  
Keyword(s):  
Entropy Generation ◽  
Scalar Fields ◽  
Exergy Loss ◽  
Second Law ◽  
Stochastic Field ◽  
Detailed Chemistry ◽  
Look Up Table ◽  
Second Law Analysis ◽  
Combustion Systems ◽  
Exergy Losses

A second law analysis in combustion systems is performed along with an exergy loss study by quantifying the entropy generation sources using, for the first time, three different approaches: a classical-thermodynamics-based approach, a novel turbulence-based method and a look-up-table-based approach, respectively. The numerical computation is based on a hybrid filtered Eulerian stochastic field (ESF) method coupled with tabulated detailed chemistry according to a Famelet-Generated Manifold (FGM)-based combustion model. In this work, the capability of the three approaches to capture the effect of the Re number on local exergy losses is especially appraised. For this purpose, Sandia flames D and E are selected as application cases. First, the validation of the computed flow and scalar fields is achieved by comparison to available experimental data. For both flames, the flow field results for eight stochastic fields and the associated scalar fields show an excellent agreement. The ESF method reproduces all major features of the flames at a lower numerical cost. Next, the second law analysis carried out with the different approaches for the entropy generation computation provides comparable quantitative results. Using flame D as a reference, for which some results with the thermodynamic-based approach exist in the literature, it turns out that, among the sources of exergy loss, the heat transfer and the chemical reaction emerge notably as the main culprits for entropy production, causing 50% and 35% of it, respectively. This fact-finding increases in Sandia flame E, which features a high Re number compared to Sandia flame D. The computational cost is less once the entropy generation analysis is carried out by using the Large Eddy Simulation (LES) hybrid ESF/FGM approach together with the look-up-table-based or turbulence-based approach.

scholarly journals Exergy Analysis of a Domestic Refrigerator

2018 ◽  
Vol 24 (9) ◽  
pp. 1 ◽  
Author(s):  
Loauy Abd Al-Azez Mahdi ◽  
Wahid S. Mohammad ◽  
Samir Akram Mahmood
Keyword(s):  
Entropy Generation ◽  
Exergy Analysis ◽  
Thermal Conductance ◽  
Internal Surface ◽  
Exergy Efficiency ◽  
System Component ◽  
Minimum Entropy ◽  
Internal Surface Area ◽  
Domestic Refrigerator ◽  
Entropy Generation Minimization

An energy and exergy thermodynamic analysis using EES program was done for a domestic refrigerator working with R-134a using vapor compression refrigeration cycle. The analysis deals with the system component, i.e. compressor, condenser, evaporator and the expansion device. The analysis depends on the entropy generation minimization approach to improve the refrigerator performance by exploring the optimum design points. These design points were derived from three different theories governing the entropy generation minimization using exergy analyzing method. These theories were first applied to find the optimum balance between the hot inner condenser area and the cold inner evaporator area of the refrigerator and between its hot and cold thermal conductances. Nine types of condensers were used according to its internal surface area and thermal conductance, in order to reach the minimum entropy generation in the refrigerator. The results showed that the compressor has the lowest exergy efficiency of 25%. The expansion device was the second component after the compressor with exergy efficiency of 92%, followed by the condenser with an efficiency of 93%. The evaporator was found to have an exergy efficiency of 98 %. The experimental tests were repeated for the nine condensers sizes with three different ambient temperatures 25℃, 30℃ and 35℃.  The exergy analysis showed that the design of the refrigerator mainly depends on thermal conductance calculations rather than the surface inner area estimation.  

scholarly journals Exergy Analysis of Advanced Adsorption Cooling Cycles

Entropy ◽  
2020 ◽  
Vol 22 (10) ◽  
pp. 1082
Author(s):  
Ngoc Vi Cao ◽  
Xuan Quang Duong ◽  
Woo Su Lee ◽  
Moon Yong Park ◽  
Seung Soo Lee ◽  
...  
Keyword(s):  
Recovery Time ◽  
Heat Recovery ◽  
Exergy Analysis ◽  
Exergy Efficiency ◽  
Recovery Cycle ◽  
Adsorption Chiller ◽  
Advanced Cycles ◽  
Heat And Mass Recovery ◽  
Exergy Losses ◽  
Mass Recovery

This study conducted an exergy analysis of advanced adsorption cooling cycles. The possible exergy losses were divided into internal losses and external losses, and the exergy losses of each process in three advanced cycles: a mass recovery cycle, heat recovery cycle and combined heat and mass recovery cycle were calculated. A transient two-dimensional numerical model was used to solve the heat and mass transfer kinetics. The exergy destruction of each component and process in a finned tube type, silica gel/water working paired-adsorption chiller was estimated. The results showed that external loss was significantly reduced at the expense of internal loss. The mass recovery cycle reduced the total loss to 60.95 kJ/kg, which is −2.76% lower than the basic cycle. In the heat recovery cycle, exergy efficiency was significantly enhanced to 23.20%. The optimum value was 0.1248 at a heat recovery time of 60 s. The combined heat and mass recovery cycle resulted in an 11.30% enhancement in exergy efficiency, compared to the heat recovery cycle. The enhancement was much clearer when compared to the basic cycle, with 37.12%. The observed dependency on heat recovery time and heating temperature was similar to that observed for individual mass recovery and heat recovery cycles.

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