Concept Of Entransy Research Articles

Comparison of entransy loss analysis and the first law of thermodynamics in the optimization of organic Rankine cycle coupled with parabolic trough collector

Due to the numerous environmental issues associated with fossil fuel power plants, using solar energy to generate electricity is a viable alternative. The organic Rankine cycle (ORC) is a thermodynamic process used to convert low- and medium-temperature heat sources into electricity, often utilizing organic fluids as the working medium. Entransy is a relatively new concept that many readers may not be familiar with. Moreover, entransy loss (Ġloss) is derived from the entransy concept, which quantifies the inefficiency in transferring thermal energy through a system. In this study, (Ġloss) is used for the first time when designing an ORC cycle coupled with parabolic trough collectors. The entransy loss relations were driven with assumption that the heat capacity is a function of temperature. A genetic algorithm is a search heuristic inspired by natural selection. It is used to find optimal or near-optimal solutions to complex problems by evolving a population of candidate solutions. Two scenarios utilized the genetic algorithm in MATLAB to optimize the system (scenario 1: maximizing the output power and scenario 2: maximizing the Ġloss). In addition, the optimization parameters included turbine inlet temperature (Ttur), boiler pressure (Pboil), condenser pressure (Pcond), and the temperature of the collector fluid at the boiler outlet (Thf,out). This optimization was performed for the temperature of the collector fluid at the boiler inlet (Thf,in) in the range 310–400 °C at 10 °C intervals with four working fluids (i.e., toluene, cyclohexane, MM, and water). The land area and the beam solar radiation were considered to be 100 hectares and 800 W/m2, respectively. The results indicated that according to scenario one, at temperatures of 310–320 °C, the maximum power was obtained for the case of toluene fluid with values 59.8 and 63.5 MW. For the collector fluid temperature from 330 to 400 °C, water had the most optimal power with values ranging from 66.2 to 88.2 MW. Furthermore, toluene exhibited superiority to two other organic fluids in the 330–400 °C temperature range after water, with net power values ranged between 65.7 and 76.3 MW. The results indicated that the maximum entransy loss does not correspond to the maximum output power because the application preconditions of the entransy loss concept are not all satisfied. Across all working fluids and Thf,in, scenario 2 resulted in lower optimal output power, cycle efficiency, and system efficiency compared to scenario 1.

Discussion: “A Multi-Objective Comprehensive Evaluation of Heat Transfer Performance of a Direct-Contact Heat Exchanger” [J. Thermal Science and Engineering Applications, 2023, 15 (1), Article No. (011014)

Abstract The units of entransy dissipation (G) in Nomenclature are wrong. Also, an opinion on the concept of entransy is presented.

Derivation of generalized thermoelectric energy equations and the study of thermoelectric irreversible processes based on energy, exergy, and entransy analysis

AbstractThermoelectric (TE) generation is becoming a valuable and promising research direction. Many researchers have carried out system analysis and performance optimization of thermoelectric technologies based on the generalized thermoelectric energy balance equations. However, it is assumed that TE legs have no heat exchange with the ambient except at the junctions of the hot and cold ends where heat flows in and out. Based on basic thermoelectric effects and fundamental theories of heat transfer, a detailed derivation of the revised generalized thermoelectric energy equations considering convective heat transfer between TE legs and the ambient has been carried out. Irreversible heat transfer processes have been analyzed by employing energy analysis based on the first law of thermodynamics and exergy analysis based on the second law of thermodynamics. The results show that convective heat transfer leads to a decrease in both energy and exergy efficiencies: the rate and magnitude of the decrease in exergy efficiency are greater than those of the decrease in energy efficiency. The exergy efficiency is relatively high despite the low energy efficiency in operation, revealing the features and advantages of thermoelectric generators (TEGs) in low‐grade energy utilization. For TEG efficient operation, the load resistance value should match the system's internal resistance, or at least be greater than that, to avoid a sharp drop in power output and efficiencies. In an attempt at theoretical analysis, the concept of entransy was first introduced into thermoelectric analysis, yielding two concise relational equations which reflect the intrinsic link between Carnot cycle efficiency, energy efficiency, exergy efficiency, and entransy flow transfer efficiency. The entransy analysis based on the index of entransy flow transfer efficiency, together with energy analysis and exergy analysis, may be a novel and valuable guideline for the operation and optimization of TEGs, which needs to be further investigated.

Analysis of heat transfer and irreversibility of organic rankine cycle evaporator for selecting working fluid and operating conditions

Organic Rankine cycle (ORC) is suitable to converting the normally hard to utilize low temperature thermal energies, such as geothermal energy, solar energy, and industrial waste heat, to electricity through utilizing low boiling organic working fluids. The performance of ORC system is dramatically affected by the selections of working fluid and working conditions. As a key component of waste heat recovery, the irreversible loss of evaporator also has great influence on the performance of ORC system. In this paper, we study the heat transfer performance in evaporator under the condition that the heat source parameters and pinch point temperature difference are identified. It is found that the heat transfer performance is affected by Cr, the ratio of heat capacity flow rates between the working fluid and the heat source fluid. The equivalent thermal resistance, deducing from the concept of entransy, to measure the irreversability during the heat transfer process is used. Then, the parameter ?r, the ratio between latent heat and sensible heat of working fluid is defined. With the parameters Cr and ?r, we investigate the relationship between the heat transfer and irreversible loss, and deduce the condition that maximum heat transfer and minimum equivalent thermal resistance occurs. Finally, a calculation method is established to choose the optimum working fluid and the evaporation condition.

Entransy analysis of reversible thermodynamic cycles based on the conservation of entransy equation and its application

Entropy analyses and entropy generation analyses have been widely used to analyze and optimize thermal processes. For instance, the entropy generation minimization principle has been used to optimize heat transfer processes, heat transfer systems and thermodynamic cycles. However, some studies have reported that the entropy generation minimization principle cannot derive the optimal results for pure heat transfer processes and heat transfer systems without heat-work conversion processes. The concept of entransy and the principle of the least entransy dissipation-based thermal resistance were proposed for these problems, and they have been widely applied to optimize pure heat transfer processes and systems. Besides, the concept of work entransy was developed for irreversible thermodynamic cycles involving heat-work conversion processes, and it is defined as the product of the work and the temperature. This concept was then used as the entransy analysis approach to optimize thermodynamic cycles. However, previous studies applying the work entransy concept mainly focused on (1) the relation between the work entransy loss and the endoreversible thermodynamic cycle efficiency, and (2) the optimization of practical thermodynamic cycles involving irreversible processes. There have been few such studies of reversible thermodynamic cycles or combined cycles. This article analyzes reversible thermodynamic cycles and combined thermodynamic cycles using the entransy analysis method with a derivation of the conservation of entransy equation. First, the entransy conservation equation for a reversible thermodynamic process is derived, which introduces the concept of heat entransy and heat-work entransy flow. They are both process dependent physical quantities. The corresponding entransy conservation equation is then derived for a reversible thermodynamic cycle. The equation shows that there are two different conservation equations for reversible thermodynamic cycles, i.e. the energy conservation equation (1st law of thermodynamics) and the entransy conservation equation. Meanwhile, according to thermomass theory, the entransy is nothing else but the relative energy. The entransy conservation equation can be used to analyze the performance of reversible thermodynamic cycles. On the other hand, since the entropy returns to the initial value in a reversible thermodynamic cycle, an entropy analysis cannot evaluate the performance of reversible thermodynamic cycles. Second, a combined heat engine-heat pump cycle is taken as an example application of entransy analysis. In the philosophy of entransy analyses, the performance indicator of the combined cycle is its net heat entransy flow. For the properly chosen parameters, the combined cycle can be regarded as an ideal voltage transformer. Therefore, this kind of combined cycle can be referred to as a temperature transformer, which is different from the absorption temperature transformer. A diagram is introduced to show the total effect of the combined cycle to help understand the combined cycle. Finally, two practical cases, i.e. combined cycles for heating and refrigeration, are chosen to show applications of this entransy analysis approach. The concept of entransy efficiency of combined cycles is introduced to evaluate the performance of the combined cycles.

Comparison of entropy generation minimization principle and entransy theory in optimal design of thermal systems

In this study, the relationship among the concepts of entropy generation rate, entransy theory, and generalized thermal resistance to the optimal design of thermal systems is discussed. The equations of entropy and entransy rates are compared and their implications for optimization of conductive heat transfer are analyzed. The theoretical analyses show that based on entropy generation minimization principle by decreasing irreversibility, thermodynamic optimization can be obtained. Significantly, the entransy concept merely describes the heat transfer ability and the minimum and maximum entransy dissipation principle can only lead to thermal optimization. However, due to decreasing thermal resistance both principles are considered as optimization tools for the optimal design of energy and thermal systems. Also, it is shown that the concept of entransy theory is more suitable than the concept of entropy generation for optimizing the performance of heat transfer processes.

Nature of Heat and Thermal Energy: From Caloric to Carnot's Reflections, to Entropy, Exergy, Entransy and Beyond.

The nature of thermal phenomena is still elusive and sometimes misconstrued. Starting from Lavoisier, who presumed that caloric as a weightless substance is conserved, to Sadi Carnot who erroneously assumed that work is extracted while caloric is conserved, to modern day researchers who argue that thermal energy is an indistinguishable part of internal energy, to the generalization of entropy and challengers of the Second Law of thermodynamics, the relevant thermal concepts are critically discussed here. Original reflections about the nature of thermo-mechanical energy transfer, classical and generalized entropy, exergy, and new entransy concept are reasoned and put in historical and contemporary contexts, with the objective of promoting further constructive debates and hopefully resolve some critical issues within the subtle thermal landscape.

Entransy concept and controversies: A critical perspective within elusive thermal landscape

The concept of ‘entransy’, a product of heat and temperature, originally called ‘heat transport potential capacity’, was introduced in 2003, as analogy to product of electrical charge and voltage, as well as other similar quantities. The concept has been extended to entransy property, as integral product of ‘stored heat’ and temperature, MCvT2/2, thus representing quantity and quality of stored heat, or thermal energy in isochoric processes without work interactions. The entransy has been used for analysis and optimization of many heat transfer processes as described in many publications since its introduction, and is under further development. Later, the entransy concept has been criticized and denounced by a group of researchers, thus creating controversies that need to be put in a broader, historical and contemporary perspective, which is the main goal of this paper. Despite the need for further clarifications and development of the new concept, it would be premature and unjust to discredit entransy, based on limited and subjective claims, as if the ‘already established’ concepts and methodologies are perfect, and do not need alternatives and innovations, as if further progress is not needed.

Analyses of thermodynamic performance for the endoreversible Otto cycle with the concepts of entropy generation and entransy

In this paper, the endoreversible Otto cycle is analyzed with the entropy generation minimization and the entransy theory. The output power and the heat-work conversion efficiency are taken as the optimization objectives, and the relationships of the output power, the heat-work conversion efficiency, the entropy generation rate, the entropy generation numbers, the entransy loss rate, the entransy loss coefficient, the entransy dissipation rate and the entransy variation rate associated with work are discussed. The applicability of the entropy generation minimization and the entransy theory to the analyses is also analyzed. It is found that smaller entropy generation rate does not always lead to larger output power, while smaller entropy generation numbers do not always lead to larger heat-work conversion efficiency, either. In our calculations, both larger entransy loss rate and larger entransy variation rate associated with work correspond to larger output power, while larger entransy loss coefficient results in larger heat-work conversion efficiency. It is also found that the concept of entransy dissipation is not always suitable for the analyses because it was developed for heat transfer.

Comments on “Entransy analysis and optimization of performance of nano-scale irreversible Otto cycle operating with Maxwell-Boltzmann ideal gas”

The purpose of this discussion is to increase the awareness of the divergent views on the entransy concept among the readers of chemical physics. Comments are presented in particular on the paper by Ahmadi et al. (2016) where the authors used entransy dissipation in their analysis. Based on the view points of independent different groups of researchers world wide, I draw the attention of readers to the reality that entransy has no physical meaning.

Adjoint optimization of natural convection problems: differentially heated cavity

Optimization of natural convection-driven flows may provide significant improvements to the performance of cooling devices, but a theoretical investigation of such flows has been rarely done. The present paper illustrates an efficient gradient-based optimization method for analyzing such systems. We consider numerically the natural convection-driven flow in a differentially heated cavity with three Prandtl numbers (\(Pr=0.15{-}7\)) at super-critical conditions. All results and implementations were done with the spectral element code Nek5000. The flow is analyzed using linear direct and adjoint computations about a nonlinear base flow, extracting in particular optimal initial conditions using power iteration and the solution of the full adjoint direct eigenproblem. The cost function for both temperature and velocity is based on the kinetic energy and the concept of entransy, which yields a quadratic functional. Results are presented as a function of Prandtl number, time horizons and weights between kinetic energy and entransy. In particular, it is shown that the maximum transient growth is achieved at time horizons on the order of 5 time units for all cases, whereas for larger time horizons the adjoint mode is recovered as optimal initial condition. For smaller time horizons, the influence of the weights leads either to a concentric temperature distribution or to an initial condition pattern that opposes the mean shear and grows according to the Orr mechanism. For specific cases, it could also been shown that the computation of optimal initial conditions leads to a degenerate problem, with a potential loss of symmetry. In these situations, it turns out that any initial condition lying in a specific span of the eigenfunctions will yield exactly the same transient amplification. As a consequence, the power iteration converges very slowly and fails to extract all possible optimal initial conditions. According to the authors’ knowledge, this behavior is illustrated here for the first time.

Comments on “Equivalence between the application of entransy and entropy generation” [Int. J. Heat Mass Transfer 79 (2015): 518–525

This note is our comments to the paper entitled, “Equivalence between the application of entransy and entropy generation” (Oliveira and Milanez, 2015). In this paper, the authors showed the equivalence between the application of the concepts of entransy and entropy by using several application examples including three physical models of solar energy collectors and a physical model of a sensible heat storage system. The main expressions regarding entransy in this paper come from our conference paper entitled, “Entransy transfer analysis and its application to optimizing irreversible thermodynamic cycles” (Wu and Guo, 2007). However, the authors did not distinguish between the entransy, the entransy transfer, and the thermodynamic entransy transfer. The application of which was shown to be equivalent to that of entropy generation by the authors using four examples, is the thermodynamic entransy transfer rather than the entransy transfer. Hence, the conclusion that the applications of entransy and entropy are equivalent is not appropriate.

Entransy and exergy analyses for optimizations of heat-work conversion with carnot cycle

The concept of entransy has been newly proposed in terms of the analogy between heat and electrical conduction and could be useful in analyzing and optimizing the heat-work conversion systems. This work presents comparative analyses of entransy and exergy for optimizations of heat-work conversion. The work production and heat transfer processes in Carnot cycle system are investigated with the formulations of exergy destruction, entransy loss, work entransy, entransy dissipation, and efficiencies for both cases of dumping and non-dumping of used source fluid. The effects of source and condensation temperatures on the system performance are systematically investigated for optimal condition of producing maximum work or work entransy.

Entransy analyses of thermal processes with variable thermophysical properties

Entransy method is developed for the analyses of thermal processes with variable thermophysical properties. The entransy and enthalpy entransy balance equations for thermal processes with variable thermophysical properties are derived based on the definitions of differential entransy and enthalpy entransy. The definitions of the entransy and enthalpy entransy for an object are presented. The optimization principles for heat transfer and heat-work conversion processes with variable thermophysical properties are discussed with the concept of entransy. Entransy analyses for a two-stream heat exchanger and a closed Brayton cycle with variable thermophysical properties are conducted and compared with the entropy generation analyses. For the heat exchanger, the results show that both the minimum entransy-dissipation-based thermal resistance and the minimum revised entropy generation number correspond to the maximum heat exchanger effectiveness when the inlet condition of the heat exchanger is prescribed, but the minimum entropy generation rate and the minimum entropy generation number do not. For the closed Brayton cycle, the results show that both the maximum entransy loss rate and the minimum entropy generation rate correspond to the maximum output power and both the maximum entransy loss coefficient and the minimum entropy generation number correspond to the maximum heat-work conversion efficiency when the inlet conditions of the streams and the environmental temperature are prescribed. When the inlet temperature of the hot stream increases, larger entransy loss rate and larger entransy loss coefficient still correspond to larger output power and larger heat-work conversion efficiency respectively.

A comment on the concept of entransy (versus exergy) for the performance assessment of a desiccant cooling system

The utility of entransy is considered for the performance assessment of an experimental desiccant cooling system, DCS in comparison with the energy and exergy analyses. An increase in the regeneration temperature TR is associated with a decrease in the sensible coefficient of performance COP which has a measurement range of 0.2≤COP≤1.3. The calculated magnitude of COP and system exergetic efficiency, ηDCS is 0.345 and 3.3% respectively. The desiccant wheel, DW has the greatest percentage of the total exergy destruction of DCS. Therefore an entransy effectiveness parameter of DW, ɛDW,ENTRANSY is introduced. This parameter expresses the sensible cooling capacity, CC as a ratio of heat input Q and the regeneration entransy stored in DW, EDW,R. ɛDW,ENTRANSY can be used as an alternative performance parameter since the dependence of ɛDW,ENTRANSY on TR is the same of COP. There exists an acceptable conformity between the calculated magnitudes of ɛDW,ENTRANSY and ηDCS. The cited similarity between the application of entransy and entropy generation is verified for the discussed case. However entransy is of considerable practical importance for the performance analysis of heat transfer processes.

Comparative analyses of energy–exergy–entransy for the optimization of heat-work conversion in power generation systems

A newly proposed concept of entransy as the heat transfer potential could be useful in analyzing and optimizing the heat-work conversion systems. In this study, the work production and heat transfer processes in endoreversible Carnot cycle system are investigated by systematically establishing the balance equation of entransy along with the formulations of entransy loss, work entransy, and entransy dissipations at various positions in the system and environment, which are consistent with energy and exergy balances. Both cases of dumping and non-dumping of used source fluid are considered to analyze the optimal condition of net work production and maximization of total entransy loss. In addition, the several forms of system efficiency are introduced based on entransy input, entransy loss, and work entransy in order to appreciate the system performance. As an illustration of optimization using the concept of entransy, the effects of system parameters on source fluids and heat exchanger are investigated for optimal condition of producing maximum work. In particular, the change of thermal capacity in source fluid leads to different trends of entransy efficiencies when compared to conventional efficiencies of energy and exergy, as it shows another way to assess the effective use of heat source in power generation systems.

Entransy: its physical basis, applications and limitations

In this paper, the physical basis and application conditions of the entransy theory are reviewed and discussed. Entransy can be obtained from the analogy between heat and electrical conductions. It is a state value and the “potential energy” of heat. From the viewpoint of thermomass, it reflects the thermal energy of the thermomass in an object. Furthermore, it was also related to the microstate number and is a single value function of the microstate number. The concepts of entransy, entransy flux and entransy dissipation can be used to express the least action of heat transfer. The entransy balance equations for heat transfer and thermodynamic processes and their applications to thermal systems are also reviewed. The differences between the entransy theory, constructal theory, entropy generation minimization, exergy analyses method, principle of uniformity of temperature difference field and field synergy (coordination) principle are also discussed. The entransy theory is different from the other discussed theories. The limitations of the entransy theory are also discussed.

Equivalence between the application of entransy and entropy generation

Abstract Recently, a group of researchers proposed the concept of entransy by analogy with the electrical energy stored in a capacitor, the entransy being a measure of the ability of a body or a system to transfer heat. In comparative terms, the entransy dissipation rate is related with the loss of heat transfer ability just like the exergy destruction rate is proportional to the loss of work ability, being these losses caused by the irreversibilities related to the thermodynamic processes. Some authors have questioned the need for the concept of entransy, claiming that this concept is only an extension of a well established theory of heat transfer. The objective of this work is show the equivalence between the application of the concepts of entransy and entropy generation rate, which can be verified using various application examples. The application examples used here are the thermodynamic modeling of three physical models of solar energy collectors and a physical model of a sensible heat storage system. Analytical results are shown and compared. The results showed that the application of the concept of entransy provided identical expressions obtained by the concept of entropy generation, indicating a duplication of concepts.

Discussion: “Entransy is Now Clear”

The purpose of this discussion is to place in perspective the concept of entransy, in view of the critiques published by Grazzini et al. (2013, “Entropy Versus Entransy,” J. Non-Equilib. Thermodyn., 38, pp. 259–271), Herwig (2014, “Do We Really Need ‘Entransy’? A Critical Assessment of a New Quantity in Heat Transfer Analysis,” ASME J. Heat Trans., 136(4), 045501), and Bejan 2014, ““Entransy,” and Its Lack of Content in Physics,” ASME J. Heat Trans., 136(5), 055501), and especially the response just published by Guo et al. (2014, “A Response to Do We Really Need ‘Entransy’?” ASME J. Heat Trans., 136(4), 046001). The conclusion is that entransy is improper and not needed, and that Guo et al.'s own response actually confirms this conclusion.

Discussion on the application of entransy theory to heat-work conversion processes

Applications and limitations of the entransy theory for heat-work conversion processes are analyzed and discussed in this paper. Our analyses for the Carnot cycle show that the system entransy of the Carnot cycle is in balance, but the relationship, dG=T2dS, does not exsit between the concepts of entransy and entropy. Therefore, the concept of entropy cannot be replaced by the concept of entransy. For common thermodynamic processes, the analyses show that the present entransy theory is applicable when heat is transferred into an endoreversible thermodynamic cycle to do work. In addition, in the analyses of heat-work conversion processes, the differences between the entransy theory and entropy theory are also discussed. It is shown that the viewpoints and preconditions of the two theories for the analyses and optimizations of heat-work conversion processes are different. The viewpoint of the analyses of entropy generation is the loss of exergy, while that of the analyses of entransy is the consumption of thermal potential. When the input exergy flow of the discussed system is prescribed or the input heat flow and the corresponding thermodynamic forces of the heat flows into and out of the system are prescribed, the entropy generation minimization leads to the maximum output work. For the entransy theory, the maximum entransy loss corresponds to the maximum output work when the input heat flow and the corresponding temperatures of the heat flows into and out of the system are prescribed. Meanwhile, they both have limitations. When the corresponding preconditions are not satisfied, the maximum entransy loss or the minimum entropy generation may not correspond to the maximum output work.