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Entransy concept and controversies: A critical perspective within elusive thermal landscape
Abstract
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.
... A new property, based on physical analogy between electrical conduction, represented by the Ohm's law (the electrical charge Q ve = I·t = E e /V), and heat conduction, is introduced from Q vh = Z tr /T = E vh /T = G/T (as concept-in-general, if electrical charge and heat are transferred at constant voltage and temperature, respectively), thus, in principle, defining a new physical quantity, "entransy" [15][16][17][18], i.e.,: ...
... Correlations between entransy G, reversible heat Q REV , entransy dissipation or loss G LOSS , and Carnot work-potential loss W LOSS is presented on Figure 8. Furthermore, the "entransy of work", G W , is also essential to be defined for processes when thermal heat is converted to work, such as in heat engines. The work entransy could be defined using the entransy balance for reversible, Carnot cycle relationship, and considering that there is no entransy loss in an ideal reversible process, i.e., G IN = G OUT or G 1 = G W + G 2 (notation in [18]): ...
... . However, this definition is not appropriate since it does not satisfy condition that entransy loss is zero for reversible processes. There is a need for further interpretations of the entransy concept and possible refinements [18]. satisfy condition that entransy loss is zero for reversible processes. ...
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.
... On the other hand, it should be pointed out that the entransy theory is still under developing, and also has some limitations [77]. Therefore, different viewpoints and real academic discussions [144,[147][148][149][150] are very necessary and helpful for the development of the theory. Actually, there are many objective comments and discussions. ...
... Actually, there are many objective comments and discussions. For instance, Kostic [147] wrote that "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." Xu et al. [144] also wrote that "Despite some voices of opposition against entransy, the theory of entransy is still used by researchers from different countries. ...
In engineering, there are different design objectives for heat pump systems, such as the maximum coefficient of performance, the maximum net heat flow rate into the high temperature heat source and the best thermo-economic performance.
As such, the authors provide a comprehensive overview of heat pump technology, focusing on system design, performance, optimization and applications associated with this technology.
Following this, a research study on the optimal operation of a power system in the presence of renewable sources is presented, considering two objectives: decreasing power losses and improving the voltage level in the nodes of the electric network.
A method for detecting short-path wormhole tunnels rather than relying solely on topological features of the network is described. In a wormhole attack, the malicious nodes generally work in pairs and set up a high-speed tunnel for long distances between them.
An approach to multi-objective optimization techniques is presented and applied to either subtractive or additive manufacturing processes. Additionally, the suitability of multi-objective optimization methods is depicted through a case study related to the selective laser melting process.
The performance evaluation of the binary heap tree-based discrete particle swarm optimization is presented and compared with existing Pareto dominance-based multi-objective techniques such as non-dominated sorting genetic algorithm-II and non-dominated sorting particle swarm optimization.
In closing, the authors present a problem that highlights the influence that bidirectional power flows may have on solutions regarding the optimal allocation of energy storage systems in real microgrids in the developing country of Romania.
... Guiding by the entransy theory (ET) [43][44][45][46][47][48][49], many scholars conducted various heat transfer optimizations , which extremely promotes the development of ET. However, some scholars [18,[75][76][77][78][79][80][81][82] criticized the ET as a false science, and the criticisms were replied by the corresponding authors [83][84][85][86][87][88][89][90][91][92][93]. Among them, Vakalis et al. [92] and Kostic [93] given the objective appraisals of the ET who came from Italy and America, respectively. ...
... However, some scholars [18,[75][76][77][78][79][80][81][82] criticized the ET as a false science, and the criticisms were replied by the corresponding authors [83][84][85][86][87][88][89][90][91][92][93]. Among them, Vakalis et al. [92] and Kostic [93] given the objective appraisals of the ET who came from Italy and America, respectively. ET can provide new optimization criteria for various transfer processes and systems, and constructal theory can provide new design method different from traditional method. ...
Constructal optimizations of the elemental and first order “+” shaped high conductivity channels (HCCs) in the square bodies are carried out based on entransy dissipation rate (EDR) minimization. The optimal shapes of the HCCs and minimum EDRs of the bodies are derived. The results show that there exist optimal geometrical parameters of the first order “+” shaped HCC which lead to triple minimum dimensionless EDR of the body. The optimal shape of the first order “+” shaped HCC derived by EDR minimization makes the global heat conduction performance (GHCP) of the square body improve, and the temperature gradient more homogeneous. The optimal design scheme of the “+” shaped HCC with minimum EDR can be adopted in the heat dissipation problem of the electronic device to improve its GHCP.
... Numerous studies have been conducted on applying entransy to heat transfer and energy conversion systems. Some researchers believe that entransy is an original concept, and their findings provide a solid foundation for improving and expanding this concept (Kostic, 2017;Cheng and Liang, 2014). ...
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.
... However, if the heat stored in the cascaded system is used for heat-work conversion, entropy is a better criterion for optimizing the system. The complexity associated with entransy dissipation theory is that the stored heat and transferred heat has not yet been completely defined and tabulated as properties (Kostic, 2017). ...
This paper reviews cascaded or multiple phase change materials (PCMs) approach to provide a fundamental understanding of their thermal behaviors, the performance in terms of heat transfer uniformity, and the influence of input parameters and different geometrical containments on the performance of latent heat thermal energy storage (LHTES) systems. Furthermore, the performance enhancement of energy components through the implementation of cascaded techniques and cascaded arrangements of PCMs accompanied by other enhancement approaches is discussed. The influence of stage numbers affecting the performance of the cascaded LHTES unit is summarized and the range of recommended values for those parameters is provided. Our critical evaluation demonstrates that replacing single PCM by multiple PCMs shows the possibility of improving the performance of TES in terms of energy, exergy and entransy charging/discharging rate along with increased stored/retrieved energy and exergy efficiency. It is also shown that the cascaded LHTES systems opens the doors of opportunity for the seasonal energy sources and extracting the optimum amount of energy within the stipulated time through the proper arrangement of PCMs. Finally, the discussions are extended to the challenges of implementing the cascaded PCMs with some recommendations for future research in this direction.
... In the past years, the new concept of entransy developed under controversies as some scholars confused with entropy and entransy [41]. Nevertheless, the controversies have been clarified and the entransy concept was considered to be inherently suited for the evaluation and optimization of heat transfer processes [42]. Similarly, by the comparison with entropy, a recent review also indicated the superiority of entransy for the optimization of convective heat transfer with the dual objectives of heat transfer enhancement and pumping power reduction [27]. ...
The heat transfer during air cooling of postharvest produce tends to be heterogeneous using either room cooling or forced-air cooling due to airflow maldistribution. The heterogeneity is typically evaluated in terms of temperature. In this study, the thermodynamic indicators, including the rates and the temporal cumulation of entropy generation and entransy dissipation, are proposed for heterogeneity analysis. Based on the experiments with postharvest apples, the heterogeneity is compared between air cooling methods using the proposed thermodynamic indicators. The temporal variation tendencies and spatial distribution characteristics of these thermodynamic indicators are further discussed. Higher heat transfer heterogeneity regarding to the rates of entropy generation and entransy dissipation is observed at the beginning stage and at the end of the process with lower temperature heterogeneity. In comparison with the entropy generation, the entransy dissipation is more appropriate for heterogeneity comparison because of the consistency. The cumulative entransy dissipation is generally higher at the locations with more airflow and higher heat transfer rate. When compared with room cooling, the consistent reduction of standard deviation and coefficient of variation for the cumulative entransy dissipation indicates overall lower heat transfer heterogeneity for forced-air cooling.
... The ability of heat transfer from the heat exchanging device can be understood by entransy and it is used to enhance the performance of heat exchangers. Entransy is denoted by G and can be analysed as (Chen 2012;Chen, Liang, and Guo 2011;Chen, Liang, and Guo 2013;Chen, Xiao, and Feng 2018b;Cheng, Wang, and Liang 2012;Chen, Liang, and Guo 2013;Feng et al. 2016a;Feng et al. 2016;Geete 2017b;GuoJie, BingYang, and ZengYuan 2011;Kostic 2017;Liu et al. 2016;Oliveira and Milanez 2012;Wen, Xue, and Xin 2015;Yang et al. 2016), ...
The optimization of heat exchanger is an important issue. So the optimum size of counter flow surface condenser is found in this research work for MARAL OVERSEAS LTD by entropy, exergy and entransy theories. In this work, effectiveness of heat exchanger, number of transfer units, entropy generation, entransy dissipation, entransy dissipation based thermal resistance, entransy dissipation number and entransy effectiveness for hot/cold fluid sides with outlet temperatures of fluids are found for various 4L/D ratios. And then optimum value of 4L/D ratio is found for surface condenser. Entransy dissipation number and entransy based thermal resistance both must be as low as possible for proper design. It is observed that when 4L/D ratio increases then EDN, entransy dissipation based thermal resistance, outlet temperature of hot fluid and entropy generation decrease but NTU, effectiveness and outlet temperature of cold fluid increase. This research work is concluded as when 4L/D ratio increases with one unit, EDN values decrease with 0.05-0.02 but after some time when 4L/D ratio increases with ten units, EDN values decrease with only 0.01. Finally, optimum condition of 4L/D ratio for surface condenser is found which is 40. Computer software is also developed to eliminate hectic calculations and human errors for performance analyses of heat exchangers.
... Entransy, which is considered as a novelty in heat transfer and thermodynamics, has been rejected or denounced by some researchers. As stated by Kostic (2017) , "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. " The authors sincerely hope that readers could carefully check the development of entransy and its application without any prejudice. ...
This letter is intended to reply to the Letter to the Editor by A. Bejan and closure the discussion on the authors' published article that proposed the temperature–heat (T–Q) diagram methodology for adsorption refrigeration. Dr. Bejan asserted his ownership of the “origin” of this method and reaffirmed the “falsehood” of entransy in his letter. In this reply, the authors give answers and rebuttals to Dr. Bejan's comments and make some points about the academic debate on entransy.
The heat pump integrated with latent heat storage is an efficient heat decarbonization technology for improving of thermal energy storage efficiency in terms of quantity and quality using renewable energy and off-peak electricity.
In this work, a review of the theory and application of heat and mass synergy is carried out. Since the field synergy theory was proposed, it has not only been greatly developed in the field of heat transfer but also has been explored and studied in the field of mass transfer and heat and mass synergy. In order to clarify the development and improvement process of field synergy theory and sort out its application and development trend, this paper conducts theoretical research on the proposal and controversy of field synergy theory and the derivation of the field synergy formula under different conditions. The field synergy equations based on different fluid states such as laminar flow and turbulent flow in the case of heat transfer, mass transfer, and heat–mass synergy are summarized. Optimizing the synergy application of heat–mass in engineering practice can significantly improve its heat and mass transfer capabilities. Although the field synergy principle has certain advantages in enhancing mass and heat transfer, it cannot take into account the power consumption in practical engineering applications. Therefore, combining the principle of field synergy with other theories to improve the comprehensive performance of heat and mass transfer has provided a way of thinking for future research.
Purpose
This study aims to understand the difference between irreversibility in heat and work transfer processes. It also aims to explain that Helmholtz or Gibbs energy does not represent “free” energy but is a measure of loss of Carnot (reversible) work opportunity.
Design/methodology/approach
The entropy of mass is described as the net temperature-standardised heat transfer to mass under ideal conditions measured from a datum value. An expression for the “irreversibility” is derived in terms of work loss (W loss ) in a work transfer process, unaccounted heat dissipation (Q loss ) in a heat transfer process and loss of net Carnot work (CW net ) opportunity resulting from spontaneous heat transfer across a finite temperature difference during the process. The thermal irreversibility is attributed to not exploiting the capability for extracting work by interposing a combination of Carnot engine(s) and/or Carnot heat pump(s) that exchanges heat with the surrounding and operates across the finite temperature difference.
Findings
It is shown, with an example, how the contribution of thermal irreversibility, in estimating reversible input work, amounts to a loss of an opportunity to generate the net work output. The opportunity is created by exchanging heat with surroundings whilst transferring the same amount of heat across finite temperature difference. An entropy change is determined with a numerical simulation, including calculation of local entropy generation values, and results are compared with estimates based on an analytical expression.
Originality/value
A new interpretation of entropy combined with an enhanced mental image of a combination of Carnot engine(s) and/or Carnot heat pump(s) is used to quantify thermal irreversibility.
Despite the importance of variation in depletion index, nothing is known on the changes in the Optimized Exergy Depletion Index (XDI) with cost (USD) and Entransy Depletion Index (NDI) with cost (USD). The aim of this paper is to stablish a new depletion index based on entransy and to applicate this concept to the evaluation of efficiency and sustainability. The efficiency and sustainability of a thermal system can be evaluated through the Depletion Index. It was developed a new mathematical expression for assessing the depletion index based on entransy and it was compared with the conventional index based on exergy. Deductive inductive methods were used to obtain the new depletion index based on entransy theory. A multi-objective optimization is proposed considering as criteria the cost and efficiency based on exergy and entransy. Depletion index values based on entransy dissipation are similar than those ones based on exergy destruction and then the value of efficiency obtained by the two concepts is similar. Until recently, the generation of entropy was used for the Shell and tube heat exchangers optimization, however, the entransy dissipation or some function involving it can also be used for this purpose, being a new approach for assessing the depletion index. The optimization results obtained based on each of the efficiency indices were very similar mainly in relation to the total heat exchange rate. The Pareto fronts obtained in the multi-objective optimization allow to find and match optimum designs adjustable to costs and to the space available to install the equipment and the auxiliary services.
This paper reviews cascaded or multiple phase change materials (PCMs) approach to provide a fundamental understanding of their thermal behaviors, the performance in terms of heat transfer uniformity, and the influence of input parameters and different geometrical containments on the performance of latent heat thermal energy storage (LHTES) systems. Furthermore, the performance enhancement of energy components through the implementation of cascaded techniques and cascaded arrangements of PCMs accompanied by other enhancement approaches is discussed. The influence of stage numbers affecting the performance of the cascaded LHTES unit is summarized and the range of recommended values for those parameters is provided. Our critical evaluation demonstrates that replacing single PCM by multiple PCMs shows the possibility of improving the performance of TES in terms of energy, exergy and entransy charging/discharging rate along with increased stored/retrieved energy and exergy efficiency. It is also shown that the cascaded LHTES systems opens the doors of opportunity for the seasonal energy sources and extracting the optimum amount of energy within the stipulated time through the proper arrangement of PCMs. Finally, the discussions are extended to the challenges of implementing the cascaded PCMs with some recommendations for future research in this direction.
This review paper summarizes constructal design progress performed by the authors for eight types of heat sinks with ten performance indexes being taken as the optimization objectives, respectively, by combining the methods of theoretical analysis and numerical calculation. The eight types of heat sinks are uniform height rectangular fin heat sink, non-uniform height rectangular fin heat sink, inline cylindrical pin-fin heat sink (ICPHS), plate single-row pin fin heat sink (PSRPHS), plate inline pin fin heat sink (PIPHS), plate staggered pin fin heat sink (PSPHS), single-layered microchannel heat sink (SLMCHS) with rectangular cross sections and double-layered microchannel heat sink (DLMCHS) with rectangular cross sections, respectively. And the ten performance indexes are heat transfer rate maximization, maximum thermal resistance minimization, minimization of equivalent thermal resistance which is defined based on the entransy dissipation rate (equivalent thermal resistance for short), field synergy number maximization, entropy generation rate minimization, operation cost minimization, thermo-economic function value minimization, pressure drop minimization, enhanced heat transfer factor maximization and efficiency evaluation criterion number maximization, respectively. The optimal constructs of the eight types of heat sinks with different constraints and based on the different optimization objectives are compared with each other. The results indicated that the optimal constructs mostly are different based on different optimization objectives under the same boundary condition. The optimization objective should be suitable chosen based on the focus when the constructal design for one heat sink is performed. The results obtained herein have some important theoretical significances and application values, and can provide scientific bases and theoretical guidelines for the thermal design of real heat sinks and their applications.
Energy consumption and its associated consequences can be reduced by implementing district cooling strategies that supply low temperature water to a wide range of end users through chillers and distribution networks. Adequate understanding, performance prediction and further optimization of vapor compression chillers used widely in district cooling plants have been a subject of intense research through model-based approaches. In this context, we perform an extensive review of different modeling techniques used for predicting steady-state or dynamic performance of vapor compression liquid chillers. The explored modeling techniques include physical and empirical models. Different physical models used for vapor compression chillers, based on physics laws, are discussed in detail. Furthermore, empirical models (based on artificial neural networks, regression analysis) are elaborated along with their advantages and drawbacks. The physical models can depict both steady- and unsteady-state performance of the vapor compression chiller; however, their accuracy and physical realism can be enhanced by considering the geometrical arrangement of the condenser and evaporator and validating them for various ecofriendly refrigerants and large system size (i.e., cooling capacity). Apparently, empirical models are easy to develop but do not provide the necessary physical realism of the process of vapor compression chiller. It is further observed that DC plants/networks have been modeled from the point of view of optimization or integration but no efforts have been made to model the chillers with multiple VCR cycles. The development of such models will facilitate to optimize the DC plant and provide improved control strategies for effective and efficient operation.
Thermal designs for microchannel heat sinks with laminar flow are conducted numerically by combining constructal theory and entransy theory. Three types of 3-D circular disc heat sink models, i.e. without collection microchannels, with center collection microchannels, and with edge collection microchannels, are established respectively. Compared with the entransy equivalent thermal resistances of circular disc heat sink without collection microchannels and circular disc heat sink with edge collection microchannels, that of circular disc heat sink with center collection microchannels is the minimum, so the overall heat transfer performance of circular disc heat sink with center collection microchannels has obvious advantages. Furthermore, the effects of microchannel branch number on maximum thermal resistance and entransy equivalent thermal resistance of circular disc heat sink with center collection microchannels are investigated under different mass flow rates and heat fluxes. With the mass flow rate increasing, both the maximum thermal resistances and the entransy equivalent thermal resistances of heat sinks with respective fixed microchannel branch number all gradually decrease. With the heat flux increasing, the maximum thermal resistances and the entransy equivalent thermal resistances of heat sinks with respective fixed microchannel branch number remain almost unchanged. With the same mass flow rate and heat flux, the larger the microchannel branch number, the smaller the maximum thermal resistance. While the optimal microchannel branch number corresponding to minimum entransy equivalent thermal resistance is 6.
The aim of this work is to carry a performance analysis based on first and second law of thermodynamics for some operational configurations of feasible gasketed-plate heat exchangers. To achieve this, 40 simulations were done solving the distributed-U differential model proposed by Pinto and Gut, using an adaptive damped secant shooting method. Heat and exergy transfer effectiveness, dimensionless entropy generation, entropic potential loss and energy efficiency index were calculated when both fluids are above and below room temperature, as well as at least one fluid goes across the room temperature. Additionally, four cold fluid inlet port configuration have been studied. Our main conclusion is that countercurrent configurations have better performance than parallel flow configurations due to influence of finite temperature difference in equipment and higher NTU are reached when fluids are above room temperature for the same geometry. Since gasketed-Plate heat exchangers have applications in different industries, our work constitutes a tool and a guide to select operating and installation conditions.
Combining with entransy theory, constructal designs of the X-shaped vascular networks (XSVNs) are implemented with fixed total tube volumes of the XSVNs. The entransy dissipation rates (EDRs) of the XSVNs are minimized, and the optimal constructs of the XSVNs are derived. Comparison of the optimal constructs of the XSVNs with two optimization objectives (EDR minimization and entropy generation rate (EGR) minimization) is conducted. It is found that when the dimensionless mass flow rate (DMFR) is small, the optimal diameter ratio of the elemental XSVN derived by EDR minimization is different from that derived by EGR minimization. For the multilevel XSVN, when the DMFR is 100, compared the XSVN with the corresponding H-shaped vascular network (HSVN), the dimensionless EDRs of the elemental, second and fourth order XSVNs are reduced by 26.39%, 15.34% and 9.81%, respectively. Compared with the entransy dissipation number (EDN) of the second order XSVN before angle optimization, the EDN after optimization is reduced by 26.15%, which illustrates that it is significant to conduct angle optimization of the XSVN. Entransy theory is applied into the constructal design of the vasculature with heat transfer and fluid flow in this paper, which provides new directions for the vasculature designs.
In this research work concentric pipe counter flow heat exchanger (CPCFHEx) is analyzed to optimize the performance
at different conditions. CFD analyses are executed and temperature, pressure, velocity and turbulence profiles are
studied through pipes by CFD simulation method. Effectiveness, overall heat transfer coefficients, pressure drops and
change in velocities for CPCFHEx are found. Entropy, exergy and entransy analyses are also done with different flow rates
and inner pipe materials to find optimum operating conditions. After analyses, maximum temperature difference (i.e.
4.688K) for cold fluid and effectiveness (i.e. 0.1562) are found for copper at low flow rates (i.e. 0.081 and 0.19kg/s
cold/hot) but maximum temperature difference (i.e. 1.595K) for hot fluid is found for steel at high flow rates (i.e. 0.1 and
0.22kg/s cold/hot). Maximum rate of heat transfer (i.e. 1.603W) and overall heat transfer coefficient (i.e. 3.160W/m2K)
but maximum rates of entropy generation (i.e. 1.144J/sec-K) and exergy destruction (i.e. 343.2J/sec) are found for
copper at high flow rates. Minimum rate of entransy dissipation (i.e. 19874.925J-K/sec) and entransy dissipation number
(i.e. 0.4516) are obtained for steel at high flow rates. High conductive material for pipe and low flow rates of fluids are
recommended to get better performance of HExs in terms of rate of heat transfer, effectiveness, entropy generation and
exergy destruction.
Constructal theory has been widely used in performance optimizations of various problems. Among these problems, engineering problem is a hot topic for constructal theory. The developments of constructal theory about engineering problem in China over the past decade are reviewed in this paper. Multi-disciplinary, multi-objective and multi-scale constructal optimizations of various transfer processes in engineering, such as heat conduction and thermal insulation processes, fluid flow processes, convective heat transfer processes of fins, heat sources, cavities, cooling channels, vascular networks and heat exchangers, mass transfer processes of porous mediums, heat and mass transfer processes of solid-gas reactors and solid oxide fuel cells, iron and steel production processes and generalized transfer processes, have been conducted since 2006. Performance improvements are realized, new design requirements are satisfied, and more practical and generalized results are obtained after new research objects, model improvements, optimization objectives, boundary conditions, constraint conditions and transfer extensions are considered. It shows that the developments of constructal theory are still being made in China, which will provide more design guidelines not only for engineering problem, but also for natural and social problems.
This paper proposes a quantity-quality-based optimization method of indoor thermal environment design that emphasizes entransy and exergy analysis. We scrutinized the different focuses of entransy and exergy in examining an energy-related phenomenon or process, and pointed out the need for integrating entransy and exergy for the optimization of indoor thermal environment design. The proposed method contributes to identifying the most energy-efficient solution for attaining the same level of indoor thermal comfort for end users by quantifying the entransy and exergy efficiency of active technologies. With this method, a benchmark technical solution was properly determined and benchmarks for entransy dissipation and exergy loss during the process of thermal environment design were quantified. Entransy dissipation and exergy loss under common technologies were compared with the benchmark values. The concepts of relative entransy savings and relative exergy savings were defined as the evaluation indexes of technical energy efficiency. Referencing winter indoor thermal environment design for residential buildings in hot-summer and cold-winter (HSCW) regions in China, the proposed method was applied to assess the energy efficiency of different heating methods, including an inverter air conditioner, an “air source heat pump + floor radiation,” a “wall-hanging gas heater + floor radiation,” a “wall-hanging gas heater + radiator,” and an oil-filled radiator. This paper recommended that the “air source heat pump + floor radiation” be used for residential buildings in winter in HSCW regions to improve energy efficiency. In addition, the optimization results of the proposed method were compared with that of traditional energy and exergy analysis methods. The results showed that the new method more accurately analyzed the energy flow in indoor thermal environment design, and therefore can serve as an improved way of thinking about follow-up studies on the optimization of heat pump units and the operation strategies of floor radiant heating systems.
A class of finite-time heat transfer processes (HTPs) for entransy dissipation minimization is studied in this paper. Based on optimal control theory, the optimality condition is derived firstly, and then the general characteristics of heat transfer laws (HTLs) for three special temperature distributions including uniform temperature difference field, constant heat transfer rate per unit area, and constant entransy dissipation rate operations are obtained based on the optimality condition. The results show that the condition that the difference of temperature for the minimum entransy dissipation of heat transfer process (EDOHTP) is a constant is not only valid for Newtonian HTL, but also valid for generalized convective HTL [ q∝(ΔT)m] and complex HTL { q∝[(ΔT)+(ΔT)m]}.
There is a growing trend in recently-submitted manuscripts and publications to present calculated results of entropy generation, also known as entropy production, as field quantities in a system or device control volume, based on prior calculation of velocity and temperature fields, frequently using CFD numerical methods. [...]
Recently, a group of scientists introduced a new quantity for the analysis of heat transfer problems. They called it entransy since according to their understanding it is both, an indication of the nature of energy as well as that of the heat transfer ability. This concept is critically assessed on the background of two questions: Is entransy as an extension of the well established theory of heat transfer consistent with this classical approach? And: Is there a real need for the extension of the classical theory by introducing entransy as a quantity that was missing in the past?
Entropy is the most used and often abused concept in science, but also in philosophy and society. Further confusions are produced by some attempts to generalize entropy with similar but not the same concepts in other disciplines. The physical meaning of phenomenological, thermodynamic entropy is reasoned and elaborated by generalizing Clausius definition with inclusion of generated heat, since it is irrelevant if entropy is changed due to reversible heat transfer or irreversible heat generation. Irreversible, caloric heat transfer is introduced as complementing reversible heat transfer. It is also reasoned and thus proven why entropy cannot be destroyed but is always generated (and thus overall increased) locally and globally, at every space and time scales, without any exception. It is concluded that entropy is a thermal displacement (dynamic thermal-volume) of thermal energy due to absolute temperature as a thermal potential (dQ = TdS), and thus associated with thermal heat and absolute temperature, i.e., distribution of thermal energy within thermal micro-particles in space. Entropy is an integral measure of (random) thermal energy redistribution (due to heat transfer and/or irreversible heat generation) within a material system structure in space, per absolute temperature level: dS = dQSys/T = mCSysdT/T, thus logarithmic integral function, with J/K unit. It may be also expressed as a measure of “thermal disorder”, being related to logarithm of number of all thermal, dynamic microstates W (their position and momenta), S = kBlnW, or to the sum of their logarithmic probabilities S = −kB∑pilnpi, that correspond to, or are consistent with the given thermodynamic macro-state. The number of thermal microstates W, is correlated with macro-properties temperature T and volume V for ideal gases. A system form and/or functional order or disorder are not (thermal) energy order/disorder and the former is not related to Thermodynamic entropy. Expanding entropy to any type of disorder or information is a source of many misconceptions. Granted, there are certain benefits of simplified statistical descriptions to better comprehend the randomness of thermal motion and related physical quantities, but the limitations should be stated so the generalizations are not overstretched and the real physics overlooked, or worse discredited.
Sadi Carnot's ingenious reasoning of reversible cycles (1824) laid foundations for The Second Law before The First Law of energy conservation was even known (Joule 1843) and long before Thermodynamic concepts were established in 1850s. A century later, Bridgman (1941) ‘complained’ that “there are almost as many formulations of The Second Law as there have been discussions of it.” Even today, The Second Law remains so obscure, due to the lack of its comprehension, that it continues to attract new efforts at clarification, including this one.
The Laws of Thermodynamics have much wider, including philosophical significance and implication, than their simple expressions based on the experimental observations—they are The Fundamental Laws of Nature: The Zeroth (equilibrium existentialism), The First
(conservational transformationalism), The Second (irreversible directional transformationalism), and The Third (unattainability of emptiness). They are defining and unifying our comprehension of all existence and transformations in the universe. The forces, due to non‐equilibrium of mass‐energy in space (non‐uniform ‘concentrations’), causing the mass‐energy displacement, thus defining the process direction, are manifested by tendency of mass‐energy transfer in time towards common equilibrium—cause‐and‐effect forced tendency of equi‐partition of mass‐energy. It should not be confused with local creation of non‐equilibrium and/or ‘organized structures’ on expense of ‘over‐all’ non‐equilibrium, by spontaneous and irreversible conversion (dissipation) of other energy forms into the thermal energy, always and everywhere accompanied with
entropy
generation (randomized equi‐partition of energy per absolute temperature level).
The fundamental laws of nature are considered to be axiomatic and many believe they could not be explained, proven or questioned. However, everything may and should be questioned, reasoned, explained and possibly proven. The miracles are until they are comprehended and understood.
Here, I show that "entransy" has no meaning in physics, because, at bottom, it rests on the false claim that in order to transfer heat to a solid body of thermodynamic temperature T, the heat transfer must be proportional to T. Entransy "dissipation" is a number proportional to well known measures of irreversibility such as entropy generation and lost exergy (destroyed available work). Furthermore, the "principle of entransy dissipation minimization" adds nothing to existing work based on minimum entropy generation, minimum thermal resistance, and constructal law. The broader trend illustrated by the entransy hoax is that it is becoming easy to take an existing idea, change the keywords, and publish it as new.
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.
Entransy is a function recently introduced in thermodynamics. This
function is analyzed critically in relation to the classical
thermodynamic approach in order to understand its physical fundamentals.
The crucial problem is that thermodynamic analysis shows that entransy
does not contain any new information in comparison with a classical
thermodynamic analysis of systems. Furthermore, entransy dissipation
analysis is a duplicate of entropy generation analysis.
In the present work, the entransy and entransy dissipation are defined from the thermodynamic point of view. It is shown that the entransy is a state variable and can be employed to describe the second law of thermodynamics. For heat conduction, a principle of minimum entransy dissipation is established based on the second law of thermodynamics in terms of entransy dissipation, which leads to the governing equation of the steady Fourier heat conduction without heat source. Furthermore, we derive the expressions of the entransy dissipation in duct flows and heat exchangers from the second law of thermodynamics, which paves the way for applications of the entransy dissipation theory in heat exchanger design.
In the viewpoint of heat transfer, heat transport potential capacity and its dissipation are defined based on the essence
of heat transport phenomenon. Respectively, their physical meanings are the overall heat transfer capability and the dissipation
rate of the heat transfer capacity. Then the least dissipation principle of heat transport potential capacity is presented
to enhance the heat conduction efficiency in the heat conduction optimization. The principle is, for a conduction process
with the constant integral of the thermal conductivity over the region, the optimal distribution of thermal conductivity,
which corresponds to the highest heat conduction efficiency, is characterized by the least dissipation of heat transport potential
capacity. Finally the principle is applied to some cases in heat conduction optimization.
Keywordsheat transfer-heat transport potential capacity-heat conduction optimization-dissipation of heat transport potential capacity
Letter to the editor
- A Bejan
- S Lorente
A. Bejan, S. Lorente, Letter to the editor, Chem. Eng. Process.: Process
Intensification 56 (2012).
Closure to ''Discussion of 'Entransy is Now Clear
- Q Chen
- Z Y Guo
- X G Liang
Q. Chen, Z.Y. Guo, X.G. Liang, Closure to ''Discussion of 'Entransy is Now Clear"
', J. Heat Transf. 136 (9) (2014) 096001-96011.
Controversy about entransy theory
- Z.-Y Guo
- X.-G Liang
- Q Chen
Z.-Y. Guo, X.-G. Liang, Q. Chen, Controversy about entransy theory." Beijing,
China: Institute of Engineering Thermophysics, Department of Engineering
Mechanics, Tsinghua University; June 2015.
Irreversibility and Reversible Heat Transfer: The Quest and Nature of Energy and Entropy
- M Kostic
M. Kostic, Irreversibility and Reversible Heat Transfer: The Quest and Nature of
Energy and Entropy," IMECE2004, ASME Proceedings, ASME, New York, 2004
(PDF).
Reflections on Caloric Theory and Thermal Energy
- M Kostic
Kostic, M. ''Reflections on Caloric Theory and Thermal Energy," Northern
Illinois University, (accessed 2017). <http://niu.edu/kostic/_pdfs/reflectionscaloric-theory-thermal-energy.pdf>.