Second Law Analysis of a Stirling Cryocooler With Optimal Design of the Regenerator and Losses

2001 ◽  
Author(s):  
E. D. Rogdakis ◽  
N. A. Bormpilas
Keyword(s):  
Gas Flow ◽  
Optimization Technique ◽  
Internal Heat ◽  
Thermodynamic Characteristics ◽  
Coefficient Of Performance ◽  
Solid Matrix ◽  
Second Law ◽  
External Temperature ◽  
Technical Requirements ◽  
Second Law Analysis

Abstract The aim of the research in this paper is a second law analysis of a Stirling cryocooler. A one-dimensional model is proposed for the simulation of the gas flow in the expansion space, the regenerator, the warm-end, the compression space and the compressor. Helium gas is selected as the working medium. An algorithm has been developed considering parametrically the most from the main operational tasks of the thermodynamic cycle. Performance indices such as heat input, efficiency, external dimensions of the engine and technical requirements are taken into account as constraints. Engine operating parameters i.e. speed, external temperature, mean pressure are fixed. The regenerator loss has a critical influence on the cryocooler efficiency and the reduction of this kind of internal irreversibilities is extremely difficult due to the generator is subject to rapidly cycling flows accompanied by steep temperature gradients and large pressure variations. The second flow analysis of the regenerator identifies two principal losses, the irreversible internal heat transfer into the solid matrix and the hydraulic resistance. An optimization technique leads to entropy generation charts, extremely useful for a good design of the regenerator. Finally the main thermodynamic characteristics (net refrigeration, power input and the coefficient of performance) of the cryocooler are given both cases with and without external and internal irreversibilities.

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 optimization of two-stage transcritical CO2 refrigeration cycles in the cooling mode operation

2009 ◽  
Vol 223 (5) ◽  
pp. 551-561 ◽  
Author(s):  
M Yari
Keyword(s):  
Geometric Mean ◽  
Internal Heat ◽  
Coefficient Of Performance ◽  
Second Law ◽  
Refrigeration Cycle ◽  
Cooling Mode ◽  
Two Stage ◽  
Entrainment Ratio ◽  
Cycle Simulation ◽  
Mean Pressure

Second law optimization studies of two-stage transcritical CO2 (TRCC) refrigeration cycles, incorporating options such as a new ejector-expansion with internal heat exchanger (IHE) and intercooler (IC), flash gas bypass, flash gas intercooling, compressor intercooling with IHE, are presented based on cycle simulation. To validate the simulations, the available numerical data in open literature are used. It is found that the coefficient of performance (COP) and second law efficiency of the new two-stage TRCC cycle are on average 16.5, 18.4, and 28.4 per cent higher than that of the two-stage TRCC with IHE and IC, the two-stage TRCC with flash gas bypass, and the two-stage TRCC with flash gas intercooling cycles, respectively. Hence, the new two-stage refrigeration cycle is a promising refrigeration cycle from the thermodynamic point of view. It is also concluded that for cases of the flash gas bypass and flash gas intercooling the optimum inter-stage pressure deviates significantly from the geometric mean pressure of the gas cooler and evaporator pressure. While for the new two-stage TRCC and the two-stage TRCC with IHE and IC, the optimum inter-stage pressure is approximately equal to geometric mean pressure. Finally, a regression analysis was employed in terms of evaporator and gas cooler exit temperatures to develop mathematical expressions for maximum COP, optimum discharge, and inter-stage pressures and entrainment ratio.

scholarly journals Second Law Analysis of a Mobile Air Conditioning System with Internal Heat Exchanger Using Low GWP Refrigerants

Entropy ◽  
2017 ◽  
Vol 19 (4) ◽  
pp. 175 ◽  
Author(s):  
Vicente Pérez-García ◽  
Juan Belman-Flores ◽  
José Rodríguez-Muñoz ◽  
Víctor. Rangel-Hernández ◽  
Armando Gallegos-Muñoz
Keyword(s):  
Heat Exchanger ◽  
Air Conditioning ◽  
Internal Heat ◽  
Second Law ◽  
Air Conditioning System ◽  
Internal Heat Exchanger ◽  
Second Law Analysis

Modeling of a Solid/Liquid Thermal Storage System

2003 ◽  
Author(s):  
J. S. Mulvey ◽  
R. F. Boehm
Keyword(s):  
Storage System ◽  
Heat Removal ◽  
Thermal Storage ◽  
Heat Transfer Fluid ◽  
Solid Matrix ◽  
Second Law ◽  
Second Law Analysis ◽  
The Finite Difference Method ◽  
Design Options ◽  
Solid Liquid

A computational model utilizing the finite difference method was developed to simulate the behavior of a simple thermal storage system. The system analyzed utilizes the deposition of heat from a fluid to a solid matrix in the initial part of cycle followed by heat removal in the latter part. The storage system was divided into perpendicular slices with respect to the direction of the heat transfer fluid (HTF) flow. To further reduce the area of the slice on which the calculations were performed, the symmetry of the design was then used. Two dimensional conduction and convection calculations were performed within the plane generated by each slice. Interaction between the slices was limited to only the HTF flow rate. It was assumed that the system would experience no losses to the ambient and the HTF contained in each slice would be fully mixed. First and Second Law analysis were incorporated as a means of evaluating different configurations of the storage system design. A technique that allows the designer to choose between design options is discussed.

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′).

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