Second Law Analysis and Synthesis of Solar Collector Systems

1981 ◽  
Vol 103 (1) ◽  
pp. 23-28 ◽  
Author(s):  
A. Bejan ◽  
D. W. Kearney ◽  
F. Kreith
Keyword(s):  
Heat Transfer ◽  
Solar Collector ◽  
Second Law Of Thermodynamics ◽  
Ambient Air ◽  
Operating Conditions ◽  
Optimum Operating ◽  
Second Law ◽  
Second Law Analysis ◽  
Analysis And Synthesis ◽  
Minimum Heat

The second law of thermodynamics is used to analyze the potential for exergy conservation in solar collector systems. It is shown that the amount of useful energy (exergy) delivered by solar collector systems is affected by heat transfer irreversibilities occurring between the sun and the collector, between the collector and the ambient air, and inside the collector. Using as working examples an isothermal collector, a nonisothermal collector, and the design of the collector-user heat exchanger, the optimum operating conditions for minimum heat transfer irreversibility (maximum exergy delivery) are derived.

Analysis of Throttle Opening Variation Impact on a Diesel Engine Performance Using Second Law of Thermodynamics

2009 ◽  
Author(s):  
B. B. Sahoo ◽  
U. K. Saha ◽  
N. Sahoo ◽  
P. Prusty
Keyword(s):  
Diesel Engine ◽  
Direct Injection ◽  
Fuel Efficiency ◽  
Engine Performance ◽  
Second Law Of Thermodynamics ◽  
Operating Conditions ◽  
Second Law ◽  
Engine Fuel ◽  
Availability Analysis ◽  
Second Law Analysis

The fuel efficiency of a modern diesel engine has decreased due to the recent revisions to emission standards. For an engine fuel economy, the engine speed is to be optimum for an exact throttle opening (TO) position. This work presents an analysis of throttle opening variation impact on a multi-cylinder, direct injection diesel engine with the aid of Second Law of thermodynamics. For this purpose, the engine is run for different throttle openings with several load and speed variations. At a steady engine loading condition, variation in the throttle openings has resulted in different engine speeds. The Second Law analysis, also called ‘Exergy’ analysis, is performed for these different engine speeds at their throttle positions. The Second Law analysis includes brake work, coolant heat transfer, exhaust losses, exergy efficiency, and airfuel ratio. The availability analysis is performed for 70%, 80%, and 90% loads of engine maximum power condition with 50%, 75%, and 100% TO variations. The data are recorded using a computerized engine test unit. Results indicate that the optimum engine operating conditions for 70%, 80% and 90% engine loads are 2000 rpm at 50% TO, 2300 rpm at 75% TO and 3250 rpm at 100% TO respectively.

scholarly journals Optimization and Entropy Production: Application to Carnot-Like Refrigeration Machines

Entropy ◽  
2018 ◽  
Vol 20 (12) ◽  
pp. 953 ◽  
Author(s):  
Camelia Stanciu ◽  
Michel Feidt ◽  
Monica Costea ◽  
Dorin Stanciu
Keyword(s):  
Heat Transfer ◽  
Second Law Of Thermodynamics ◽  
Operating Conditions ◽  
Optimum Operating ◽  
System Parameters ◽  
Linear Heat ◽  
Operation Conditions ◽  
Sensitivity Studies ◽  
Actual Operation ◽  
Magnitude Sensitivity

Several optimization models of irreversible reverse cycle machines have been developed based on different optimization criteria in the literature, most of them using linear heat transfer laws at the source and sink. This raises the issue how close to actual operation conditions they are, since the heat transfer law on the phase-change processes is dependent on ΔT3. This paper addresses this issue by proposing a general model for study and optimization of thermal machines with two heat reservoirs applied to a Carnot-like refrigerator, with non-linear heat transfer laws and internal and external irreversibility. The optimization was performed using First and Second Law of Thermodynamics and the Lagrange multipliers method. Thus, several constraints were imposed to the system, also different objective functions were considered, allowing finding the optimum operating conditions, as well as the limited variation ranges of the system parameters. Results show that the nature of the heat transfer laws affects the optimum values of system parameters for obtaining maximum performances and also their magnitude. Sensitivity studies with respect to system several parameters are presented. The results contribute to the understanding of the system limits in operation under different constraints and allow choosing the most convenient variables in given circumstances.

scholarly journals Optimization and Entropy Production: Application to Carnot-Like Refrigeration Machines

2018 ◽  
Author(s):  
Camelia Stanciu ◽  
Michel Feidt ◽  
Monica Costea ◽  
Dorin Stanciu
Keyword(s):  
Heat Transfer ◽  
Second Law Of Thermodynamics ◽  
Operating Conditions ◽  
Optimum Operating ◽  
System Parameters ◽  
Linear Heat ◽  
Operation Conditions ◽  
Sensitivity Studies ◽  
Actual Operation ◽  
Magnitude Sensitivity

Several optimization models of irreversible reverse cycle machines have been developed based on different optimization criteria in the literature, most of them using linear heat transfer laws at the source and sink. This raises the issue how close to actual operation conditions they are, since the heat transfer law on the phase-change processes is dependent on ΔT3. This paper addresses this issue by proposing a general model for study and optimization of thermal machines with two heat reservoirs applied to a Carnot-like refrigerator, with non-linear heat transfer laws and internal and external irreversibility. The optimization was performed using First and Second Law of Thermodynamics and Lagrange multipliers method. Thus, several constraints were imposed to the system, also different objective functions were considered, allowing finding the optimum operating conditions, as well as the limited variation ranges of the system parameters. Results show that the nature of the heat transfer laws affects the optimum values of system parameters for obtaining maximum performances and also their magnitude. Sensitivity studies with respect to system several parameters are presented. The results contribute to the understanding of the system limits in operation under different constraints and allow choosing the most convenient variables in given circumstances.

scholarly journals Analytical Assessment of (Al2O3–Ag/H2O) Hybrid Nanofluid Influenced by Induced Magnetic Field for Second Law Analysis with Mixed Convection, Viscous Dissipation and Heat Generation

Coatings ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 498
Author(s):  
Wasim Ullah Khan ◽  
Muhammad Awais ◽  
Nabeela Parveen ◽  
Aamir Ali ◽  
Saeed Ehsan Awan ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Viscous Dissipation ◽  
Entropy Generation ◽  
Heat Generation ◽  
Transfer Rate ◽  
Second Law ◽  
Hybrid Nanofluid ◽  
Entropy Generation Number ◽  
Generation Number ◽  
Second Law Analysis

The current study is an attempt to analytically characterize the second law analysis and mixed convective rheology of the (Al2O3–Ag/H2O) hybrid nanofluid flow influenced by magnetic induction effects towards a stretching sheet. Viscous dissipation and internal heat generation effects are encountered in the analysis as well. The mathematical model of partial differential equations is fabricated by employing boundary-layer approximation. The transformed system of nonlinear ordinary differential equations is solved using the homotopy analysis method. The entropy generation number is formulated in terms of fluid friction, heat transfer and Joule heating. The effects of dimensionless parameters on flow variables and entropy generation number are examined using graphs and tables. Further, the convergence of HAM solutions is examined in terms of defined physical quantities up to 20th iterations, and confirmed. It is observed that large λ1 upgrades velocity, entropy generation and heat transfer rate, and drops the temperature. High values of δ enlarge velocity and temperature while reducing heat transport and entropy generation number. Viscous dissipation strongly influences an increase in flow and heat transfer rate caused by a no-slip condition on the sheet.

Second Law Analysis of Spray Evaporation

1990 ◽  
Vol 112 (2) ◽  
pp. 130-135 ◽  
Author(s):  
S. K. Som ◽  
A. K. Mitra ◽  
S. P. Sengupta
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Entropy Generation ◽  
Exergy Analysis ◽  
Droplet Evaporation ◽  
Second Law ◽  
Hot Gas ◽  
Second Law Analysis ◽  
Initial Drop ◽  
Parallel Stream

A second law analysis has been developed for an evaporative atomized spray in a uniform parallel stream of hot gas. Using a discrete droplet evaporation model, an equation for entropy balance of a drop has been formulated to determine numerically the entropy generation histories of the evaporative spray. For the exergy analysis of the process, the rate of heat transfer and that of associated irreversibilities for complete evaporation of the spray have been calculated. A second law efficiency (ηII), defined as the ratio of the total exergy transferred to the sum of the total exergy transferred and exergy destroyed, is finally evaluated for various values of pertinent input parameters, namely, the initial Reynolds number (Rei = 2ρgVixi/μg) and the ratio of ambient to initial drop temperature (Θ∞′/Θi′).

Second Law Analysis of Solid Desiccant Rotary Dehumidifiers

1988 ◽  
Vol 110 (1) ◽  
pp. 2-9 ◽  
Author(s):  
E. Van den Bulck ◽  
S. A. Klein ◽  
J. W. Mitchell
Keyword(s):  
Local Maximum ◽  
Operating Conditions ◽  
Second Law ◽  
Transfer Coefficients ◽  
Adiabatic Flow ◽  
Transfer Processes ◽  
Air Stream ◽  
Second Law Analysis ◽  
Pass Through ◽  
Air Streams

This paper presents a second law analysis of solid desiccant rotary dehumidifiers. The equations for entropy generation for adiabatic flow of humid air over a solid desiccant are developed. The generation of entropy during operation of a rotary dehumidifier with infinite transfer coefficients is investigated and the various sources of irreversibility are identified and quantified. As they pass through the dehumidifier, both the process and regeneration air streams acquire nonuniform outlet states, and mixing both of these air streams to deliver homogeneous outlet streams is irreversible. Transfer of mass and energy between the regeneration air stream and the desiccant matrix occurs across finite differences in vapor pressure and temperature and these transfer processes generate entropy. The second law efficiency of the dehumidifier is given as a function of operating conditions and the effect of finite transfer coefficients for an actual dehumidifier is discussed. It is shown that operating the rotary dehumidifier at conditions that minimize regeneration energy also yields a local maximum for the second law efficiency.

Second Law Analysis of Tree-Shaped Fins for the Heat Transfer Enhancement in a PCM Thermal Storage System

2013 ◽  
Author(s):  
Adriano Sciacovelli ◽  
Elisa Guelpa ◽  
Vittorio Verda
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Heat Transfer Enhancement ◽  
Solidification Rate ◽  
High Energy ◽  
Second Law ◽  
Transfer Enhancement ◽  
Energy Storage Devices ◽  
Second Law Analysis ◽  
Melting And Solidification

Latent heat thermal energy storage (LHTES) systems based on phase change materials (PCMs) are a promising option to be employed as effective energy storage devices. PCM allows one to achieve high energy storage density and almost constant temperature energy retrieval, however LHTES systems performance is limited by poor thermal conductivity of the PCMs which leads to unacceptably low melting and solidification rates. Thus, heat transfer enhancement techniques are required in order to obtain acceptable melting and solidification rates. The preliminary design of a shell-and-tube LHTES unit is investigated by means of computational fluid-dynamics (CFD). Three different fin designs are considered: a conventional radial fin, a constructal Y-shaped fin design and a non-constructal Y-shaped configuration previously investigated by the authors. The performances of each fin configuration are evaluated by means of a Second-law analysis. Moreover, local and global entropy generation rates are analyzed in order to show the main source of thermodynamic irreversibilities occurring in the system. The analysis indicates that solidification rate is significantly enhanced when Y-shaped fins are adopted in the LHTES unit, however the constructal Y-shaped geometry is not optimal since further improvements can be achieved by means of a Y-shaped fins with elongated secondary branches.

Second-Law Analysis on Wavy Plate Fin-and-Tube Heat Exchangers

1998 ◽  
Vol 120 (3) ◽  
pp. 797-800 ◽  
Author(s):  
W. W. Lin ◽  
D. J. Lee
Keyword(s):  
Entropy Generation ◽  
Operating Conditions ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Second Law ◽  
Spanwise Direction ◽  
Minimum Entropy ◽  
Tube Heat Exchanger ◽  
Second Law Analysis ◽  
Minimum Entropy Generation

Second-law analysis on the herringbone wavy plate fin-and-tube heat exchanger was conducted on the basis of correlations of Nusselt number and friction factor proposed by Kim et al. (1997), from which the entropy generation rate was evaluated. Optimum Reynolds number and minimum entropy generation rate were found over different operating conditions. At a fixed heat duty, the in-line layout with a large tube spacing along streamwise direction was recommended. Furthermore, within the valid range of Kim et al.’s correlation, effects of the fin spacing and the tube spacing along spanwise direction on the second-law performance are insignificant.

A Parametric Study on a Subcritical CO2/NH3 Cascade Refrigeration System for Low Temperature Applications

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Baris Yilmaz ◽  
Ebru Mancuhan ◽  
Nasuh Erdonmez
Keyword(s):  
Performance Analysis ◽  
Large Scale ◽  
Operating Conditions ◽  
Coefficient Of Performance ◽  
Optimum Operating ◽  
Second Law Analysis ◽  
The Common ◽  
Cascade Refrigeration System ◽  
Cascade Refrigeration ◽  
Thermo Physical Properties

Adverse effects of synthetic refrigerants on the environment have led to replacing them with natural refrigerants. The common candidates are ammonia, carbon dioxide, and several hydrocarbon compounds and their mixtures. Ammonia has been used mainly in large-scale cooling purposes such as large-scale supermarkets and climatic rooms. However, in such systems, leakage of ammonia may arise severe results on human health and may damage products in the cooled space. Recently, in last decade, a well-known refrigerant, CO2, has gained more attention to be applied in refrigeration systems due to having prominent thermo-physical properties. The performance analysis of a CO2/NH3 cascade (CAS) system has been theoretically examined in the current study. The detailed performance analysis of the system and optimization of the operating parameters have been studied extensively. In addition, the second-law analysis of the system with both cycles has been performed. Optimum operating conditions of the system are also determined and correlations are developed. Finally, the coefficient of performance (COP) correlations developed by several researchers in literature and those of current study are compared against available experimental COP results. The comparisons showed that the proposed correlations can be utilized for the accurate prediction of the COP of a cascade CO2/NH3 system within the studied range of operating conditions.

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