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.

Experimental Investigation of Composite Desiccant Wheel Dehumidifier

2015 ◽  
Vol 813-814 ◽  
pp. 1080-1084
Author(s):  
P.D. Dipinlal ◽  
S. Shankara Narayanan ◽  
Seranthian Ramanathan ◽  
S. Prabhu
Keyword(s):  
Honeycomb Structure ◽  
Coefficient Of Performance ◽  
Work Study ◽  
Performance Indices ◽  
Desiccant Wheel ◽  
Air Stream ◽  
Inlet Conditions ◽  
Pass Through ◽  
Air Streams ◽  
Study Performance

Desiccant wheel dehumidifier is filled with solid desiccants, looks like a honeycomb structure which is open on both ends. Air is allowed to pass through the honeycomb passages, giving moisture to the solid desiccant contained in the wheel. The wheel constantly rotates through two separate air streams. The first air stream, called the process air is dried by the desiccant. The second air stream, called reactivation or regeneration air is heated and dries the desiccant. The combination of desiccant materials such as chloride desiccant and organic desiccant is used here and dehumidification in the composite desiccant wheel has been studied experimentally. In this work, study performance of composite desiccant wheel with different air velocities, regeneration temperatures and at different inlet conditions was conducted and calculated the different performance indices of the desiccant wheel dehumidifier such as Dehumidification Effectiveness and Dehumidification Coefficient of Performance (DCOP).

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.

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 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.

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.

Heat Transfer From Rotating Discs With Finite Thickness Subjected to Outer Air Streams

2010 ◽  
Author(s):  
Stefan aus der Wiesche
Keyword(s):  
Heat Transfer ◽  
Large Range ◽  
Finite Thickness ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Rotating Disc ◽  
Heat Transfer Coefficients ◽  
Rotating Discs ◽  
Air Stream ◽  
Air Streams

The heat transfer from rotating discs in an outer air stream is of major importance for many technical applications. Experimentally determined heat transfer coefficients are presented for a large range of rotational and crossflow Reynolds numbers including also the effects of finite disc thickness and incidence to the uniform air stream. The extreme conditions of a rotating disc in still air and a stationary disc in an air crossflow are considered, too.

Second Law Analysis and Optimization of Organic Rankine Cycle

2006 ◽  
Author(s):  
C. Somayaji ◽  
P. J. Mago ◽  
L. M. Chamra
Keyword(s):  
Waste Heat ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Operating Conditions ◽  
Working Fluid ◽  
Second Law ◽  
Low Grade ◽  
Heat Sources ◽  
Working Fluids ◽  
Second Law Analysis

This paper presents a second law analysis and optimization for the use of Organic Rankine Cycle “ORC” to convert waste energy to power from low grade heat sources. The working fluids used in this study are organic substances which have a low boiling point and a low latent heat for using low grade waste heat sources. The organic working fluids under investigation are R134a and R113 and their results are compared with those of ammonia and water under similar operating conditions. A combined first and second law analysis is performed by varying some system operating parameters at various reference temperatures. Some of the results show that the efficiency of ORC is typically below 20% depending on the temperatures and matched working fluid. In addition, it has been found that organic working fluids are more suited for heat recovery than water for low temperature applications, which justifies the use of organic working fluids at the lower waste source temperatures.

The Role of Entropy Generation in Momentum and Heat Transfer

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Heinz Herwig
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Entropy Generation ◽  
Second Law ◽  
Transfer Processes ◽  
Second Law Analysis ◽  
Momentum And Heat Transfer ◽  
Transfer Problems

Entropy generation in a velocity and temperature field is shown to be very significant in momentum and heat transfer problems. After the determination of this postprocessing quantity, many details about the physics of a problem are available. This second law analysis (SLA) is a tool for conceptual considerations, for the determination of losses, both in the velocity and the temperature field, and it helps to assess complex convective heat transfer processes. These three aspects in conjunction with entropy generation are discussed in detail and illustrated by several examples.

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