Internal Irreversibility Research Articles

Thermodynamic optimization of an irreversible Carnot refrigerator with heat recovery reservoir

A thermodynamic model of an irreversible Carnot refrigerator with heat recovery (CRHR) working between two high temperature reservoirs (TH and TR) and one low temperature heat reservoir (TL) has been established in this paper for optimization of allocation of heat transfer areas. For the CRHR distinguishing from the Carnot refrigerator working between two heat reservoirs (TH and TL), there are two important performance parameters, including refrigeration coefficient (ε) and heat recovery coefficient (εR), existing in the cycle. The comprehensive coefficient of performance (COPint) and the optimal value range (U) have been put forward to reflect the combined influence of ε and εR. A numerical example of the CRHR has been studied and the effect of the heat leakages (q and q0) and internal irreversibility factor (Φ) have been analyzed. The exergy efficiency optimization based on the thermodynamic model has also been researched. This work provides a theoretical value range for optimal allocation of heat transfer areas of the CRHR. And it is helpful to the design and optimization and related standard forming of the refrigerator with heat recovery.

Performance augmentation in flat plate solar collector using MgO/water nanofluid

In present work, testing of solar collector has been performed for MgO/water working fluid having particle size ∼40nm and particle volume concentration at 0.25, 0.5, 0.75, 1.0, 1.25 and 1.5% at 0.5, 1.0, 1.5, 2.0, 2.5lpm respectively. Performance analysis of solar collector is based on first law of energy balance and qualitative nature of energy flow based on second law analysis. Parameters of performance analysis are chosen in order to examine both quantitative and qualitative characteristics of system performance. These parameters are thermal efficiency, energetic efficiency, pumping power, entropy generation; Bejan number and reduction in surface area. Experimental observation establishes thermal efficiency enhancement 9.34% for 0.75% particle volume concentration at flow rate 1.5lpm. Exergetic efficiency enhancement observed 32.23% for same concentration and flow rate. Bejan number also reaches closer to unity (0.97) which throws light on systems qualitative response in terms of decline in entropy generation contribution due to internal irreversibilities and frictional heat loss. Entropy generation is 0.0611W/K for 0.75% particle concentration compare to 0.1394W/K for same flow rate and 0.071W/K for 1.5% particle volume concentration. In this endeavor some penalty in form of rise in pumping power loss also incurred. 6.84% enhancement in pumping power loss observed for optimum flow rate and particle volume concentration which has not as much pronounced effect as enhancement in thermal efficiency and exergetic efficiency.

SPLITTING THE TOTAL EXERGY DESTRUCTION INTO THE ENDOGENOUS AND EXOGENOUS PARTS OF THE THERMAL PROCESSES IN A REAL INDUSTRIAL PLANT

The total exergy destruction occurring in a component is not only due to the component itself (endogenous exergy destruction) but is also caused by the inefficiencies of the remaining system components (exogenous exergy destruction). Hence care must be taken in using the total exergy destruction of a component for making decisions to optimize the overall energy system. In this paper, a complex industrial plant is analyzed by splitting the component’s exergy destruction into its endogenous part (the part resulting totally from the component’s irreversibilities) and its exogenous part (resulting from the irreversibilities of the other components within the system). It is observed that the steam generator has the dominant effect. From the total exergy destruction in the steam generator, 1,097.63 kW or 96.95% come from internal irreversibilities in the component, while the influence of other components on the loss of useful work in the steam generator is only 3.05%.

Thermodynamic assessment of an integrated molten carbonate fuel cell and absorption refrigerator hybrid system for combined power and cooling applications

A hybrid system is proposed to harvest the waste heat released in MCFC through integrating an absorption refrigerator as a bottoming cycle. A thermo-electrochemical model is used to describe the main irreversible losses in the system. The operating current density interval of the MCFC that enables the bottoming absorption refrigerator to effectively cool is determined. Numerical expressions for the equivalent power output and efficiency are derived to evaluate the performance of the hybrid system under different operating conditions. Compared to the stand-alone MCFC, the maximum power density and the corresponding efficiency of the hybrid system are found to have increased by 3.2% and 3.8%, respectively. The general performance characteristics and optimum operating regions for the hybrid system are revealed. Comprehensive parametric analyses are conducted to investigate how the hybrid system performance depends on various physical properties and working conditions such as working fluid internal irreversibility inside the absorption refrigerator, heat transfer coefficients, some thermodynamic losses related parameters, and the operating current density, temperature and pressure of the MCFC.

ОПТИМАЛЬНЫЕ ТЕМПЕРАТУРЫ ОХЛАЖДЕНИЯ В ЦИКЛАХ ПАРОКОМПРЕССОРНОЙ ХОЛОДИЛЬНОЙ МАШИНЫ

Vapor compression refrigeration machines (VCRM) are used in numerous and various cooling systems. While manufacturing them, there is a tendency to reduce specific energy consumption for cold production. One of the ways of reducing costs in the operation of the VCRM is organization of its work with an optimum cooling temperature. To develop an effective VCRM, we need to have a two-parameter model of the compressor, which describes its volume and power characteristics. Development of such a model based on experimental study of a hermetic reciprocating compressor has been reported. These data were used in determining the optimum cooling temperature corresponding to the maximum values of exergetic efficiency of VCRM cycles with different losses from internal and external irreversibility. It has been established that considering these losses, optimum R134a refrigerant boiling temperature is the same, equal to 243 K. There is detected conservatism of optimal cooling temperature in case of significant losses from irreversibility in the VCRM cycle.

Electromagnetic waves and living cells: A kinetic thermodynamic approach

Abstract Cells are complex thermodynamic systems. Their energy transfer, thermo-electro-chemical processes and transports phenomena can occur across the cells membranes, the border of the complex system. Moreover, cells can also actively modify their behaviours in relation to any change of their environment. All the living systems waste heat, which is no more than the result of their internal irreversibility. This heat is dissipated into their environment. But, this wasted heat represents also a sort of information, which outflows from the cell towards its environment, completely accessible to any observer. The analysis of irreversibility related to this wasted heat can represent a new useful approach to the study of the cells behaviour. This approach allows us to consider the living systems as black boxes and analyse only the inflows and outflows and their changes in relation to any environmental change. This analysis allows also the explanation of the effects of electromagnetic fields on the cell behaviour.

On reversible, endoreversible, and irreversible heat device cycles versus the Carnot cycle: a pedagogical approach to account for losses

In this work we analyze the deviations of reversible cycles (for both heat engines and refrigerators) from the corresponding Carnot cycle operating between the same extreme temperatures, and deviations of irreversible cycles from their corresponding reversible realization while putting emphasis on the corresponding losses. The endoreversible models fit in the proposed framework. Two suitable loss factors, which do not need the explicit calculation of entropy variations, are introduced. The behavior of these factors and their interplay allow for a clear and pedagogical visualization of where external and internal irreversibilities are located, and their intensities in terms of the main variables describing the cycle. The analysis could be used as a starting point for more advanced studies on modeling and optimization of real devices and installations.

Soft computing based multi-objective optimization of Brayton cycle power plant with isothermal heat addition using evolutionary algorithm and decision making

An irreversible regenerative Brayton cycle model considering internal and external irreversibilities is developed in matrix laboratory (MATLAB) simulink environment and thermodynamic optimization based on finite time thermodynamic analysis along with multiple criteria is implemented. Evolutionary algorithms based on second version of non-dominated sorting genetic algorithm (NSGA-II) and multi-objective evolutionary algorithm based on decomposition (MOEA/D) are employed to optimize power output and thermal efficiency simultaneously where isobaric-side heat exchanger effectiveness (εH), isothermal-side effectiveness (εH1), sink-side effectiveness (εL), regenerator-side effectiveness (εR), and working medium temperature (T5) are taken as design variables. The optimal values of aforementioned design variables are investigated. Pareto optimal frontiers between dual objectives are obtained and the final optimal values of power output and thermal efficiency are chosen via LINMAP, fuzzy Bellman–Zadeh, Shannon’s entropy and TOPSIS decision making approaches. The obtained results are compared and the best one is preferred. An improvement in thermal efficiency from 18.29% to 21.10% is reported. In addition to this, variations of different input parameters on the power output and thermal efficiency are conferred and presented graphically. With the goal of error investigation, the maximum and average errors for the obtained results are designed at last.

The effects of the engine design and running parameters on the performance of a Otto–Miller Cycle engine

In this paper, a thermodynamic analysis for an irreversible Otto–Miller Cycle (OMC) has been presented by taking into consideration heat transfer effects, frictions, time-dependent specific heats, internal irreversibility resulting from compression and expansion processes. In the analyses, the influences of the engine design parameters such as cycle temperature ratio, cycle pressure ratio, friction coefficient, engine speed, mean piston speed, stroke length, inlet temperature, inlet pressure, equivalence ratio, compression ratio, and bore-stroke length ratio on the effective power, effective power density and effective efficiency have been investigated relations with efficiency in dimensionless form. The dimensionless power output and power density and thermal efficiency relations have been computationally obtained versus the engine design parameters. The results demonstrate that the engine design and running parameters have considerable effects on the cycle thermodynamic performance. of a OMC. The results showed that the cycle efficiency increased up to 50%, as cycle temperature ratio increases from 6 to 8, the effective power raised to 11 kW from 5 kW at this range. Other parameters such as engine speed, mean piston speed, cycle pressure ratio affected the performance up to 30%, positively. However, friction coefficient and inlet temperature have negative effect on the performance. As the friction coefficient increases from 12.9 to 16.9, a performance reduction was seen up to 5%. Increase of the inlet temperature abated the performance by 40%.

Thermo-ecological performance analyses and optimizations of irreversible gas cycle engines

This paper reports ecological performance analyses and optimization of irreversible gas cycle engines such as Joule–Brayton cycle (JB), Atkinson cycle (AC), Otto cycle (OC), Diesel cycle (DC), Miller cycle (MC), Dual-Atkinson cycle (DAC), Dual-Diesel cycle (DDC), Dual-Miller cycle (DMC) engines based on the ecological coefficient of performance (ECOP) criterion which covers internal irreversibility, heat leak and finite-rate of heat transfer. Comprehensive computational analyses have been conducted to investigate the global and optimal performances of the gas cycle engines. The results obtained based on the ECOP criterion are compared with a different ecological function which is named as the ecologic objective-function and with the maximum power output conditions. The results have been acquired introducing the compression ratio, cut-off ratio, pressure ratio, air recharging ratio, source temperature ratio and internal irreversibility parameter. The changes of cycle performances with respect to these parameters are examined and demonstrated with figures.

Finite-time thermodynamics optimization of an irreversible parallel flow double-effect absorption refrigerator

Finite-time thermodynamics optimization analysis based on the coefficient of performance and the ecological coefficient of performance criteria has been carried out. This was done analytically and numerically for a double-effect parallel flow absorption refrigerator with losses of heat resistance, heat leakage and internal irreversibility. The maximum of the coefficient of performance and the corresponding optimal conditions have been derived analytically. The optimum performance parameters, which maximize the coefficient of performance objective function have been investigated. The effects of irreversibility parameters on the general and optimal performances on the basis of COP and ECOP functions have been discussed. The results obtained may provide the basis for designing real double-effect parallel flow absorption refrigerators.

Performance analysis and optimization of irreversible Dual–Atkinson cycle engine (DACE) with heat transfer effects under maximum power and maximum power density conditions

This study presents an analysis considering the effects of heat transfer loss and internal irreversibility due to adiabatic compression and expansion processes on the performance of an irreversible Dual–Atkinson cycle engine (DACE) under non-dimensional maximum power (MP), non-dimensional maximum power density (MPD) and maximum thermal efficiency (MEF) conditions. The effects of the inlet temperature, combustion constant and heat transfer constant on the engine performance are investigated. The results could be used by engine designers to optimize the performance of the internal combustion engines (ICEs).

Thermodynamic analysis and evolutionary algorithm based on multi-objective optimization performance of actual power generating thermal cycles

The key objective of this research is to find out the best assessment principles for irreversible power generating thermal cycles. These approaches, which can be found through previous works, are the ecological coefficient of performance, exergetic performance coefficient and maximum available work. Irreversible Carnot power cycle is defined as system. External and internal irreversibilities are encompassed in the thermodynamic analysis. In this paper, two scenarios are defined in the optimization progression. The outputs of each scenarios are studied individually. Throughout the first scenario, with the aim of maximize the ecological coefficient of performance (ECOP), the exergetic performance criteria (EPC) and maximum available work (MAW), multi-objective optimization algorithms is engaged. Furthermore, throughout the second scenario, three objective functions comprising the first law efficiency (η), the exergetic performance criteria (EPC) and maximum available work (MAW) are maximized at the same time via multi objective optimization approaches. The multi objective evolutionary approaches (MOEAs) coupled with non-dominated sorting genetic algorithm (NSGA-II) approach is applied in the present paper. Decision making is performed via three well-known approaches comprising LINAMP and TOPSIS and FUZZY. Finally, error analysis of the outputs are accomplished for the aforementioned system.

Parametric study of a hybrid system integrating a phosphoric acid fuel cell with an absorption refrigerator for cooling purposes

A hybrid system that integrates an absorption refrigerator and a PAFC (phosphoric acid fuel cell) is proposed to recover waste heat for cooling purposes. The operating current density interval of the PAFC that enables the absorption refrigerator to cool effectively is determined. The numerical expressions for the equivalent power output and efficiency of the hybrid system are specified at different operating conditions. Calculations show that the maximum power density and corresponding efficiency using the hybrid system can be increased by 2.6% and 3.0%, respectively, compared to system only using a PAFC. The general performance characteristics and optimum criteria for the hybrid system are revealed. Comprehensive parametric analyses were conducted to determine the effects of internal irreversibilities in the absorption refrigerator, some integrated parameters related to the thermodynamic losses, and the operating current density, temperature and pressure of the PAFC on the performance of the hybrid system.

Thermodynamic analysis and performance maps for the irreversible Dual–Atkinson cycle engine (DACE) with considerations of temperature-dependent specific heats, heat transfer and friction losses

A comprehensive performance analysis depending on the non-dimensional power output, effective power, non-dimensional power density, effective power density, thermal efficiency, effective efficiency, maximum power output (MP), maximum power density (MPD) and maximum thermal efficiency (MEF) criteria has been conducted for the irreversible Dual–Atkinson cycle engine (DACE) which includes internal irreversibilities by virtue of the irreversible-adiabatic compression process, expansion process, heat transfer and friction losses. In the analyses, Classical Thermodynamics Modeling (CTM) and a new realistic Finite-Time Thermodynamics Modeling (FTTM) have been used. The power output, power density and thermal efficiency are obtained with respect to the variation of the pressure ratio, cut-off ratio, stroke ratio, Atkinson cycle ratio, cycle pressure ratio and cycle temperature ratio. The effects of the engine design and operating parameters on the general and maximum performances of the DACE have been investigated with respect to the variation of the cycle pressure ratio and cycle temperature ratio in the CTM section. The influences of the other engine design and operating parameters such as engine speed, mean piston speed, stroke length, equivalence ratio, compression ratio and bore–stroke length ratio on the engine performance have been investigated in the FTTM section. In addition, the energy losses depending on incomplete combustion, friction, heat transfer and exhaust output have been described as fuel input energy. In order to obtain realistic results, temperature-dependent specific heats for working fluid have been used. The DACE is a new concept for internal combustion engines and just a few studies have been carried out. This study presents new contributions to the analysis of the Dual–Atkinson cycle engines in terms of the effects of engine design and operating parameters on the engine performance. Because CTM, FTTM, energy losses, power density and MPD analyses, for the DACE are newly presented just in this study.

Performance optimisation of two-stage exoreversible thermoelectric heat pump in electrically series, parallel and isolated configurations

A configuration of the behaviour of an exoreversible two-stage semiconductor thermoelectric heat pump (TEHP) in three different modes, i.e., electrically series, electrically parallel and electrically separated is devised. The TEHP performance assuming Newton's heat transfer law is evaluated through a combination of finite time thermodynamics (FTT) and non-equilibrium thermodynamics. A formulation based on the heating load versus working electrical current and coefficient of performance (COP) versus working electrical current is applied in this study. For fixed total number of thermoelectric elements, optimisation of number of thermoelectric elements of the top stage for maximising the heating load and COP is done here. The complete analysis of effects of various design parameters on the performance of TEHP is formulated. Three thermodynamic models for multi-stage TEHP system considering internal irreversibilities are developed in the matrix laboratory Simulink environment. For typical operating conditions of TEHP system with total 30 thermocouples, the maximum value of COP is improved from 4.56 to 5.20 for same current in electrically parallel mode. This analysis will be helpful in designing the actual multistage TEHPs.

Thermodynamic Analysis of Stirling Heat Pump based on Thermoeconomic Optimization Criteria

A connectionist investigation of irreversible Stirling heat pump cycles that includes both internal and external irreversibilities together finite heat capacities of external reservoirs was carried out. The thermoeconomic optimization for Stirling heat pump is reported. The heating load per unit total cost for the heat pump is proposed as objective functions for the optimization. The optimum performance parameters which maximize the objective functions are investigated. Since the optimization technique consists of both investment and energy consumption costs, the obtained results are more general and realistic.

Second Law Based Thermodynamic Performance analysis of Steam Power Cycle

The generation of mechanical power had been a challenge for mechanical engineers and a great deal of attention has been focused on designing system for power generation. Thermal power cycles are important devices used in practical engineering application for thermal power generation and control of environment. Several thermodynamic approaches are possible to analyze the performance of these cycles. The most traditional approach is the first law of thermodynamics or energy balance analysis; however, this concerned only with the conversion of energy, and therefore it can not be show how or where irreversibility in a system or process occur. Second law analysis is another well-known method used to analyze thermodynamic cycles, but to some, it may be still new. Unlike first law analysis, second law analysis determines the magnitude of irreversible processes in a system, and thereby provides an indicator that the points the direction in which the engineers should concentrate their efforts to improve the performance of thermodynamic systems. This thesis is an attempt to physically understand and evaluate the internal irreversibilities due to heat transfer and fluid flow in various thermal power cycle used for power generation. This thesis present investigations on thermodynamic modelling and effects of irreversibilities in thermal power cycles using the concept of exrgy analysis and entropy generation. Detail literature review on second law analysis of thermal power cycles is reported in Section I.0 First and second law analysis of stem power cycle, gas turbine cycle, combine Brayton/Rankine power cycle, indirect fired air turbine multi stage…. have been carried out. Analytical expressions for the performance parameters involving the relevant variables for these systems under given conditions, corresponding to available power output and exergy destruction in the system, have been obtained. Detailed parametric study has been done and result are presented. This study include the effect of pressure ratio, cycle temperature ratio, number of reheat stages, pressutre drop in heat transfer devices, and the refrigeration temperature on the performance parameters of the thermal power cycles. Second law based performance assessment of regenerative-reheat steam power cycle has been carried out in terms of irreversibility analysis. The reduction in irreversible losses with the addition of backward, cascade type feed water heater and a reheat options are compared with a conventional first-law assessment. The second law indicate that the maximum exergy is destroyed in the boiler and that these thermodynamic losses are significantly reduced by incorporating feed water heater. The incorporation of feed water heating results in a reduction of total irreversility rate of the plant by 18%. The corresponding improvement in thermal efficiencies is 12%. These two values are enhanced to 24% and 14% respectively, by the incorporation of reheat in addition to regeneration.

Local Stability Analysis for a Thermo-Economic Irreversible Heat Engine Model under Different Performance Regimes

A recent work reported a local stability analysis of a thermo-economical model of an irreversible heat engine working under maximum power conditions. That work showed that after small perturbations to the working temperatures, the system decreases exponentially to the steady state characterized by two different relaxation times. This work extends the local stability analysis considering other performance regimes: the Maximum Efficient Power (MEP) and the Ecological Function (EF) regimes. The relaxation time was shown under different performance regimes as functions of the temperature ratio τ = T2/T1, with T1 > T2, the fractional fuel cost f and a lumped parameter R related to the internal irreversibilities degree. Under Maximum Efficient Power conditions the relaxation times are less than the relaxation times under both Maximum Ecological function and Maximum Power. At Maximum Power Efficient conditions, the model gives better stability conditions than for the other two regimes.

Bioengineering thermodynamics of biological cells.

BackgroundCells are open complex thermodynamic systems. They can be also regarded as complex engines that execute a series of chemical reactions. Energy transformations, thermo-electro-chemical processes and transports phenomena can occur across the cells membranes. Moreover, cells can also actively modify their behaviours in relation to changes in their environment.MethodsDifferent thermo-electro-biochemical behaviours occur between health and disease states. But, all the living systems waste heat, which is no more than the result of their internal irreversibility. This heat is dissipated into the environment. But, this wasted heat represent also a sort of information, which outflows from the cell toward its environment, completely accessible to any observer.ResultsThe analysis of irreversibility related to this wasted heat can represent a new approach to study the behaviour of the cells themselves and to control their behaviours. So, this approach allows us to consider the living systems as black boxes and analyze only the inflows and outflows and their changes in relation to the modification of the environment. Therefore, information on the systems can be obtained by analyzing the changes in the cell heat wasted in relation to external perturbations.ConclusionsThe bioengineering thermodynamics bases are summarized and used to analyse possible controls of the calls behaviours based on the control of the ions fluxes across the cells membranes.