Second Law Analysis of Condensing Steam Flows

2018 ◽  
Author(s):  
Marius Grübel ◽  
Markus Schatz ◽  
Damian M. Vogt
Keyword(s):  
Entropy Production ◽  
Turbulent Flows ◽  
Operating Conditions ◽  
Second Law ◽  
Test Case ◽  
Relaxation Processes ◽  
Minor Importance ◽  
Two Phase ◽  
Second Law Analysis ◽  
Aerodynamic Losses

A numerical second law analysis is performed to determine the entropy production due to irreversibilities in condensing steam flows. In the present work the classical approach to calculate entropy production rates in turbulent flows based on velocity and temperature gradients is extended to two-phase condensing flows modeled within an Eulerian-Eulerian framework. This requires some modifications of the general approach and the inclusion of additional models to account for thermodynamic and kinematic relaxation processes. With this approach, the entropy production within each mesh element is obtained. In addition to the quantification of thermodynamic and kinematic wetness losses, a breakdown of aerodynamic losses is possible to allow for a detailed loss analysis. The aerodynamic losses are classified into wake mixing, boundary layer and shock losses. The application of the method is demonstrated by means of the flow through a well known steam turbine cascade test case. Predicted variations of loss coefficients for different operating conditions can be confirmed by experimental observations. For the investigated test cases, the thermodynamic relaxation contributes the most to the total losses and the losses due to droplet inertia are only of minor importance. The variation of the predicted aerodynamic losses for different operating conditions is as expected and demonstrates the suitability of the approach.

Second Law Analysis of Condensing Steam Flows

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Marius Grübel ◽  
Markus Schatz ◽  
Damian M. Vogt
Keyword(s):  
Entropy Production ◽  
Turbulent Flows ◽  
Operating Conditions ◽  
Second Law ◽  
Test Case ◽  
Relaxation Processes ◽  
Minor Importance ◽  
Two Phase ◽  
Second Law Analysis ◽  
Aerodynamic Losses

A numerical second law analysis is performed to determine the entropy production due to irreversibilities in condensing steam flows. In the present work, the classical approach to calculate entropy production rates in turbulent flows based on velocity and temperature gradients is extended to two-phase condensing flows modeled within an Eulerian–Eulerian framework. This requires some modifications of the general approach and the inclusion of additional models to account for thermodynamic and kinematic relaxation processes. With this approach, the entropy production within each mesh element is obtained. In addition to the quantification of thermodynamic and kinematic wetness losses, a breakdown of aerodynamic losses is possible to allow for a detailed loss analysis. The aerodynamic losses are classified into wake mixing, boundary layer, and shock losses. The application of the method is demonstrated by means of the flow through a well-known steam turbine cascade test case. Predicted variations of loss coefficients for different operating conditions can be confirmed by experimental observations. For the investigated test cases, the thermodynamic relaxation contributes the most to the total losses and the losses due to droplet inertia are only of minor importance. The variation of the predicted aerodynamic losses for different operating conditions is as expected and demonstrates the suitability of the approach.

Determination of Loss Coefficients for Micro-Flow Devices: A Method Based on the Second Law Analysis (SLA)

2009 ◽  
Author(s):  
H.-C. Zhang ◽  
B. Schmandt ◽  
H. Herwig
Keyword(s):  
Laminar Flow ◽  
Entropy Production ◽  
Turbulent Flows ◽  
Head Loss ◽  
Second Law ◽  
Second Law Analysis ◽  
Micro Flow ◽  
Loss Coefficients ◽  
Flow Devices

The concept of head loss coefficients K for the determination of losses in conduit components is discussed in detail. While so far it has only been applied to fully turbulent flows it is extended here to also cover the laminar flow regime. Specific numbers of K can be determined by integration of the entropy production field (second law analysis). This general approach is discussed and illustrated with the specific example of a conical diffusor.

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 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.

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 Evaluación de irreversibilidades en un sistema de refrigeración por absorción amoniaco-agua empleando tres modelos matemáticos diferentes para calcular las propiedades termodinámicas

2018 ◽  
Vol 27 (47) ◽  
Author(s):  
Iván Vera-Romero ◽  
Christopher Lionel Heard-Wade
Keyword(s):  
Individual Component ◽  
Operating Conditions ◽  
Coefficient Of Performance ◽  
Second Law ◽  
Base Case ◽  
Water Mixture ◽  
Absorption Refrigeration ◽  
Second Law Analysis ◽  
Exergy Analyses

Second Law or Exergy Analyses of Absorption Refrigeration Systems (ARS) are very important for optimisations based on available work; these analyses are derived from the operating conditions and property calculations. There are several methods available for calculating the thermodynamic properties used in modelling these systems. A thermodynamic study on an ARS with the ammonia-water mixture (base case) was carried out with the objective of analysing the sensitivity of the overall and individual component irreversibility to the thermodynamic property. To this end, three existing methods were used: (M1), a model proposed by Ibrahim and Klein (1993) and used in the Engineering Equation Solver (EES) commercial software; (M2), a model proposed by Tillner-Roth and Friend (1998) and embodied in REFPROP v.8.0 developed by the National Institute of Standards and Technology (NIST); and (M3), a method proposed by Xu and Goswami (1999) that was programmed for this analysis. The obtained differences in the properties and the first law performance of the ARS are insignificant in the determination of the coefficient of performance (COP) (base case: 0.595, M1: 0.596, M2: 0.594, M3: 0.599). For the second law analysis, the overall irreversibility was the same (123.339kW) despite the irreversibilities per component had important differences: the solution heat exchanger (M1: 5.783kW, M2: 6.122kW, M3: 8.701kW), the desorber (generator) (M1: 51.302kW, M2: 45.713kW, M3: 49.098kW) and the rectifier (M1: 0.766kW, M2: 3.565kW, M3: 0.427kW). The components that destroy exergy the most are the desorber, the absorber and the condenser.

Second Law Analysis of Aerodynamic Losses: Results for a Cambered Vane With and Without Film Cooling

2012 ◽  
Author(s):  
Phil Ligrani ◽  
Jae Sik Jin
Keyword(s):  
Surface Roughness ◽  
Mach Number ◽  
Turbulence Intensity ◽  
Film Cooling ◽  
Chord Length ◽  
Second Law ◽  
Exergy Destruction ◽  
Freestream Turbulence ◽  
Second Law Analysis ◽  
Aerodynamic Losses

Results of second law analysis of experimentally-measured aerodynamic losses are presented for a cambered vane with and without film cooling, including comparisons with similar results from a symmetric airfoil. Included are distributions of local entropy creation, as well as mass-averaged magnitudes of global exergy destruction. The axial chord length of the cambered vane is 4.85 cm, the true chord length is 7.27 cm, and the effective pitch is 6.35 cm. Data are presented for three airfoil Mex distributions (including one wherein the flow is transonic), magnitudes of inlet turbulence intensity from 1.1 percent to 8.2 percent, and ks/cx surface roughness values of 0, 0.00108, and 0.00258. The associated second law aerodynamics losses are presented for two different measurement locations downstream of the vane trailing edge (one axial chord length and 0.25 axial chord length). The surface roughness, when present, simulates characteristics of the actual roughness which develops on operating turbine airfoils from a utility power engine, over long operating times, due to particulate deposition and to spallation of thermal barrier coatings (TBCs). Quantitative surface roughness characteristics which are matched include equivalent sandgrain roughness size, as well as the irregularity, non-uniformity, and the three-dimensional irregular arrangement of the roughness. Relative to a smooth, symmetric airfoil with no film cooling at low Mach number and low freestream turbulence intensity, overall, the largest increases in exergy destruction occur with increasing Mach number, and increasing surface roughness. Important variations are also observed as airfoil camber changes. Progressively smaller mass-averaged exergy destruction increases are then observed with changes of freestream turbulence intensity, and different film cooling conditions. In addition, the dependences of overall exergy destruction magnitudes on mainstream turbulence intensity and freestream Mach number are vastly different as level of vane surface roughness changes. When film cooling is present, overall mass-averaged exergy destruction magnitudes are significantly less than values associated with increased airfoil surface roughness for both the cambered vane and the symmetric airfoil. Exergy destruction values (associated with wake aerodynamic losses) for the symmetric airfoil with film cooling are then significantly higher than data from the cambered vane with film cooling, when compared at a particular blowing ratio.

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