scholarly journals Second-Law Analysis of a Double-Effect Evaporator with Thermal Vapor Compression

2021 ◽  
Vol 8 ◽  
pp. 50-61
Author(s):  
Ali Snoussi ◽  
Maha BenHamad
Keyword(s):  
Theoretical Work ◽  
Double Effect ◽  
Performance Criterion ◽  
Second Law ◽  
Vapor Compression ◽  
Future Design ◽  
Second Law Analysis ◽  
Work Input ◽  
Energy Balances

In this paper, we present a steady-state analysis of a double-effect evaporator with thermal vapor compression (MED-TVC) installed in the Tunisian Chemical Group (GCT) factory. A thermodynamic model including mass and energy balances of the system is developed and integrated in a Matlab program. The model resolution yields to the determination of the operating parameters of the plant and the Gain Output Rate (GOR) was found to be roughly equal to 5. In a second step, the simulation results served to conduct a second law analysis of the unit. The performance criterion used in this analysis is the second law efficiency, i.e., the ratio of the least theoretical work of separation to the actual work input to the plant. The second law efficiency was found to be 2.4%. The distribution of the irreversibility between the different components of the plant was, in addition, assessed. As a conclusion, it was established that the most irreversibility occurs in the thermo-compressor which contributes with more than 50% to the global imperfection and which presents an exergy efficiency of less than 77%. The remaining irreversibility comes from the three exchangers (the two evaporators and the condenser) with an average contribution of 16%. As it is very difficult to introduce modifications into an existing unit, we assume that the importance of the results is not limited to the studied unit. They serve, rather, as an aid to the future design of a MED-TVC plant.

Second-Law Analysis of Vapor Compression Heat Pumps With Solution Circuit

1994 ◽  
Vol 116 (3) ◽  
pp. 453-461
Author(s):  
K. Amrane ◽  
R. Radermacher
Keyword(s):  
Heat Pump ◽  
Heat Pumps ◽  
Single Stage ◽  
Heat Transfer Fluid ◽  
Second Law ◽  
Fluid Temperature ◽  
Ammonia Vapor ◽  
Vapor Compression ◽  
Second Law Analysis ◽  
Work Input

A second-law analysis is conducted on both the single-stage vapor compression heat pump with solution circuit (VCHSC) and its modified version, the cycle with a preheater and additional desorber. The results are compared to a conventional heat pump cycle operating with pure ammonia. The location and magnitude of the irreversibilities of the individual components constituting the cycles are determined. The entropic average temperature is used in computing the irreversibilities. The total work input to the heat pumps is then conveniently decomposed into two parts: the minimum work input or the work of a reversible cycle operating between the desorber and absorber entropic average temperatures, plus an additional input of work caused by the irreversibilities of the different processes of the cycles. The analysis reveals that the compressor is the most inefficient component of the heat pumps with losses accounting for about one fourth of the work input. The irreversibilities in the desorber and absorber are found to be minimum when there is a good match in both the solution and heat transfer fluid temperature glides. By adding a preheater and an additional desorber, the irreversibilities in the single-stage VCHSC are considerably reduced. However, it is shown that it is the preheater and not the additional desorber that has by far the most significant impact on the heat pump’s efficiency improvements. Compared to a conventional ammonia vapor compression cycle, the modified VCHSC, which has twice as many sources of irreversibility, shows nevertheless a maximum improvement of 56.1 percent in second-law efficiency.

Second Law Analysis of Separation Processes of Mixtures

1999 ◽  
Author(s):  
Yunus A. Çengel ◽  
Yunus Çerçi ◽  
Byard Wood
Keyword(s):  
Second Law ◽  
Exergy Destruction ◽  
Mixing Processes ◽  
Separation Processes ◽  
Wide Range ◽  
Ideal Solutions ◽  
Second Law Analysis ◽  
Work Input ◽  
Minimum Work

Abstract Mixing and separation processes are commonly encountered in a wide range of industries in practice. Separation processes require a work (more generally, exergy) input, and minimizing this required work input is an important part of the design process of separation plants. The presence of dissimilar molecules in a mixture affect each other, and therefore the influence of composition on the properties must be taken into consideration in any thermodynamic analysis. Below we first analyze the general mixtures and the mixing processes, with particular attention to ideal solutions, and determine the entropy generation and the corresponding exergy destruction. We then consider the reverse process of separation, and determine the minimum (or reversible) work input needed for separation. The results presented can readily be used in the calculation of minimum work input and the determination of the second law efficiency of separation processes.

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.

scholarly journals Determination of the Real Loss of Power for a Condensing and a Backpressure Turbine by Means of Second Law Analysis

Entropy ◽  
2009 ◽  
Vol 11 (4) ◽  
pp. 702-712 ◽  
Author(s):  
Henrik Holmberg ◽  
Pekka Ruohonen ◽  
Pekka Ahtila
Keyword(s):  
Second Law ◽  
The Real ◽  
Second Law Analysis ◽  
Backpressure Turbine

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.

Loss Coefficients in Laminar Flows: Indispensable for the Design of Micro Flow Systems

2010 ◽  
Author(s):  
H. Herwig ◽  
B. Schmandt ◽  
M.-F. Uth
Keyword(s):  
Numerical Simulation ◽  
Laminar Flow ◽  
Turbulent Flows ◽  
Head Loss ◽  
Laminar Flows ◽  
Second Law ◽  
Second Law Analysis ◽  
Micro Flow ◽  
Loss Coefficients

The concept of head loss coefficients K for the determination of losses in conduit components is discussed in detail. While so far it has mainly 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 generation field (second law analysis) obtained from a numerical simulation. This general approach is discussed and illustrated for various conduit components.

The Role of Entropy Generation in Momentum and Heat Transfer

2010 ◽  
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 post-processing 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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