Entransy Analysis Research Articles

Theoretical perfection and application of entransy analysis method on absorption systems

In thermal energy utilization scenarios, absorption systems have been widely and effectively utilized as heat exchange devices. However, existing thermal research methods on absorption systems for these scenarios have limitations. Therefore, the entransy parameter, which is applicable for analyzing the heat exchange process is chosen to study. The entransy balance relationship of the absorption system is theoretically analyzed, and the entransy analysis method is further perfected to break through the limitations. First, the entransy imbalance of the reversible absorption cycle is proved, and the reason for this imbalance is clarified that two heat-work conversion processes at different temperatures occur inside the cycle. Then, the working fluid's entransy change during the conversion process is theoretically derived and defined, and a new parameter: conversion entransy is defined based on it. Moreover, the comprehensive entransy balance equation and comprehensive entransy analysis method of absorption systems are further proposed. Finally, a specific case study is carried out, and this method is compared with the existing exergy analysis method and entransy analysis method without considering the conversion entransy respectively. By using this method, the optimal process form of the absorption heat exchanger can be directly obtained without numerical simulation calculations, demonstrating significant advantages.

Experimental investigation on thermodynamic performance of a copper foam-based cascaded latent heat storage tubes

Cascaded latent heat storage (CLHS) systems offer an effective means for energy storage from moderate to medium and low temperature heat sources (100-200℃). In this study, a three-stage shell-and-tube cascaded latent heat storage system was designed and fabricated. Three types of paraffin wax with distinct melting points were employed as phase change materials (PCMs), and foam copper was utilized to enhance heat transfer. By adjusting the inlet temperature and flow rate of heat transfer fluid (HTF), the thermodynamic performance of each LHS stage and the entire system under different operating conditions were investigated. Exergy analysis, entransy analysis, and sensitivity analysis were employed to study the primary influential factors on system performance and the impact weights of diverse operating conditions. Experimental results highlighted the crucial significance of maintaining consistency in the physical parameters of PCMs across different stages in the CLHS system for its thermodynamic performance. The high thermal conductivity and low latent heat of PCM#2 in the second stage result in substantial energy losses during the heat storage process, reducing the efficiency of energy cascaded utilization within the system. With an increase in the HTF inlet temperature and flow rate, the energy storage capacity and rate increase, while the energy storage efficiency exhibits a decreasing trend. Moreover, the effect of varying inlet temperature on the energy storage efficiency is much smaller compared to that of inlet flow rate. This study emphasizes that heat dissipation is a critical factor affecting the thermodynamic performance of the cascaded latent heat storage system. For CLHS systems targeting high-temperature and high-flow rate heat sources, enhancing insulation is crucial for ensuring the sustained high-efficiency operation.

Comparison analysis of entropy and entransy under various conditions of a hollow fiber membrane humidifier (HFMH)

The hollow fiber membrane heat and moisture transfer model is converted equivalently into a series of parallel-plate membranes stacked along the z-axis to simplify the model. A detailed modeling process is described based on the concept of finite difference method. The comparison of experimental values with calculated values ensures the validity of the model. Subsequently, an entransy dissipation model for the heat and moisture transfer process in a hollow fiber membrane humidifier (HFMH) is developed by analogizing heat and moisture conduction to electrical conduction. The variation of heat/moisture transfer capability within the HFMH is investigated from the perspective of “heat/moisture potential energy”. In addition, an entropy generation model for the HFMH is established to study the irreversible losses in the heat and moisture transfer process caused by irreversibility. The performance, entropy generation rate, and entransy dissipation rate of the HFMH under different conditions are comparatively analyzed. It can be found that the heat/moisture transfer performance of the humidifier can be improved by adjusting the operating conditions to increase the heat/moisture transfer driving force. However, the irreversible losses increase due to a higher heat/moisture transfer energy grade. The sensible and latent effectiveness can be enhanced by 20.9%–85.2 %, while the equivalent resistance can be reduced by 16.2%–42.0 % via optimizing the geometry structures and membrane properties. In the hot-dry region, the heat and moisture transfer increase by 25.9%–89.8 %, while the equivalent resistances decrease by 20.8%–66.0 %. In addition, the minimum equivalent resistances correspond to the optimal HFMH performance. The entransy analysis avoids the “paradox” of entropy analysis.

Thermohydraulic and Irreversibility Analyses of Swirl Flows Utilizing Distorted Radial Fins: Entropy Generation and Entransy Dissipation Evaluation

The current investigation analyses the convective heat transfer performance, entropy generation, and entransy evaluation of swirl flows generated by distorted radial fins (DRF). As swirl flows and various vortical structures induce large temperature gradients, second law and entransy analyses are necessary to thoroughly evaluate their true thermodynamic influence on heat transfer enhancement. The results indicated that due to the influence of swirl flows and vortices, all angles of the DRF were capable of inducing intense fluid mixing, thinner thermal boundary layers, and turbulent eddies. It was found that overaggressive swirl flows may hinder local heat transfer performances, by enclosing low-velocity heated fluids within the thermal boundary layers. However, as these overaggressive swirl flows and strong vortices propagate downstream, beneficial fluid mixing was eventuated, favouring heat transport over large regions. In terms of thermal performances, the maximum heat transfer enhancement was exhibited by the α=45° DRF, improving the Nusselt numbers up to 59.3%. Accordingly, the highest performance evaluation criterion (PEC) of 1.269 was obtained by the α=45° DRF at the Reynolds number 2389, attributed to the centrifugal effects of the swirl flows. Optimal entropy generation numbers were also exhibited by the α=45° DRF at the highest studied Reynolds number, reducing total entropy generation by 36.81%. Lower entransy thermal resistances were also accredited to greater DRF angles due to the intense swirl effects. In essence, the study concludes that the effects of swirl flows and vortices significantly enhance heat transfer, whilst reducing both entropy generation and entransy dissipation rates, leading to optimal thermal performances.

Entransy based heat exchange irreversibility analysis for a hybrid absorption-compression heat pump cycle

Thermally-coupled hybrid absorption-compression heat pump cycle could achieve large temperature lift and high output temperature, which is promising for the decarbonization of industrial heat demand. However, the cycle also has many heat exchange processes, resulting in irreversible losses in different components and performance degradation. In this study, entransy dissipation is used for the heat exchange irreversibility analysis of different components in the cycle. Heat and mass transfer model and entransy dissipation model for combined heat and mass transfer components such as absorber and generator are proposed. By comparing with the exergy loss, it proved that the entransy dissipation calculation model is reasonable. In addition, the T-Q diagram obtained by entransy dissipation analysis visually illustrates the heat exchange processes in each heat exchange component, which shows that entransy dissipation analysis has the characteristics of focusing on heat exchange, process-oriented and visualization. Results of entransy dissipation analysis are then used to guide the heat exchange enhancement of different components, thus optimizing the performance of whole heat pump cycle. Reducing the heat exchange irreversibility in internal heat recovery part can obtain the maximize improvement on COP by 3.92 %. The effect of thermal coupling temperature on exergy based and entransy based parameters of the heat pump cycle is investigated. The entransy increment states the optimal coupling temperature as 73.9 °C, in agreement with the COP and exergy analysis results. Therefore, from entransy dissipation to entransy increment, entransy analysis is expected to be a powerful tool to guide from the heat transfer optimization to the thermodynamic system optimization.

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.

Experimental study of air source heat pump water heater: Energy, exergy, and entransy analysis

Experimental study of air source heat pump water heater: Energy, exergy, and entransy analysis

Dynamic thermal environment management technologies for data center: A review

The energy demand of the data center (DC) industry has accounted for 2% of the total global energy consumption, and its operating power consumption has reached 50 times that of the commercial buildings. Therefore, improving the thermal environment performance to reduce the energy cost is major trend to realize the energy savings of DC. It has become a positive measure to integrate smart technologies to improve the operating efficiency of HVAC systems, especially due to the development of informatization and intelligence. This study provides detailed overview of the dynamic thermal environment management technologies of the DCs. The requirements of thermal environment in DCs were reviewed by different levels, which are the basis of the design and operation. Accordingly, various dynamic prediction technologies were presented concerning the theoretical mechanics, the computation efficiency and the applicable circumstances. The performance of the PID, the model predictive control and the reinforcement learning in the dynamic thermal environment control of DC were analyzed. Moreover, the evaluation systems based on cooling capacity, exergy analysis and entransy analysis were introduced respectively to measure the performance of the thermal environment. By investigating the knowledge related to the “requirement, prediction, control, and evaluation” of the DC dynamic thermal environment, this study aims to provide reference and guidance for energy conservation, airflow organization and smart operation of DCs.

Thermodynamic performance of cascaded latent heat storage systems for building heating

Decarbonization of building space heating is essential for China to meet its carbon neutrality goal by 2060. Cascaded latent heat storage (CLHS) coupled with electric heating is a promising technology to promote renewable energy consumption, reduce carbon emissions, and save on heating bills. However, few studies have focused on the thorough investigation of the superiority of the CLHS system over a non-cascaded system. This study investigated the effects of heat transfer fluid (HTF) flow rates, HTF inlet temperatures, and number of stages on the thermodynamic performance of non-cascaded and CLHS systems based on energy and entransy analysis. Results showed that, compared with the non-cascaded system, the charged thermal energy and discharged thermal energy of the two-stage CLHS system increased by 26.5%–44.6% and 19.8%–74.5%, respectively, and the entransy increase of cold HTF increased by 20.0%–75.7%; while, in heating systems, it is not guaranteed that thermodynamic performance improves by using more stages in the CLHS system.

3E investigation and artificial neural network optimization of a new triple-flash geothermally-powered configuration

Geothermal systems are among the world's most well-appreciated sources for providing heat to generate power and exploit in numerous ways, attracting attention worldwide due to abundancy and renewability. The present investigation is dedicated to a cogeneration system providing power and hot water for domestic use. The novel system consists of three flash chambers and three turbines intended for power production. The heat source is geothermal subterranean reservoir. Furthermore, thermoelectric generators were creatively implemented as substitutions for condensers so to produce surplus power by utilizing waste heat. The proposed cycle was primarily analyzed with respect to the first and second laws of thermodynamics. As an additional novelty, entransy analysis was also included. After which, the findings were validated in accordance to previously verified scientific resources. The study revealed that the overall power production in the basic mode was 133 kW, 35.62 kW of which was generated by the TEGs. Further, the first and second law efficiencies for the integrated cycle were 26.8% and 64.8, respectively. The sum of entransy loss throughout the integrated system was 8.77MWK. Eventually, an artificial neural network optimization was performed to identify the optimum states of the system, where exergy efficiency and entransy loss were assigned as the objectives.

Energy-Saving Analysis of Epichlorohydrin Plant Based on Entransy

To improve energy efficiency and to recover energy, various mathematical models, such as pinch analysis, entropy analysis, exergy analysis, and entransy analysis, have been established to analyze heat transfer networks. In this study, these methods were applied to analyze the energy-saving effect of the epichlorohydrin unit in a certain enterprise. The results showed that when the minimum heat transfer temperature difference (ΔTmin) was 10K, 15K, and 20K, the efficiencies of the second law of thermodynamics calculated by entropy analysis were 88.02%, 93.52%, and 99.49%, respectively. The analytical method calculated an efficiency of 61.01%, 59.28%, and 57.27%, respectively, with public works’ savings of 16.59%, 14.86%, and 12.02%. The pinch analysis method achieved public works’ savings of 22.80%, 21.50%, and 19.35%. The entransy analysis method calculated an entransy transfer efficiency of 42.81%, 42.13%, and 41.00%, respectively, with public works’ savings of 19.41%, 18.01%, and 15.70%. Based on the results, entropy analysis was found to be contrary to the principle of minimum entropy production. Exergy analysis was not able to establish a heat transfer network. The pinch analysis method was not suitable for determining the thermal efficiency of a heat transfer network as the criterion for evaluating energy saving. On the other hand, the entransy analysis method was able to establish a heat transfer network and evaluate the heat utilization of the network by entransy transfer efficiency. Overall, the data analysis was reasonable.

Study on the performance of a miniscale channel heat sink with Y-shaped unit channels based on entransy analysis

Liquid-cooled miniscale channel heat sink has been widely used in electronic chip cooling due to its characteristics of energy saving, high heat dissipation, and easy integration. Although the cooling performance of the miniscale channel heat sinks can be further improved by the optimization of channel structures, the study on the characteristics of the heat transfer process not only help to improve the cooling performance, but also provide the guiding significance for the optimization of heat sinks. This paper conducts an experimental study on the optimization of the heat transfer performance for the proposed liquid-cooled miniscale channel heat sink with Y-shaped unit channels (MCHSYC) based on the constructal law and entransy theory. The models of entransy transfer are developed for the MCHSYC to analyze the effects of the flowrate and heat flux on the entransy dissipation rate, entransy dissipation-based thermal resistance, and efficiency of entransy. And then the models to determine the optimal flowrate of the MCHSYC is proposed by considering both heat transfer ability and average surface temperature. The results show that the optimal heat dissipation performance of the MCHSYC is obtained under the flowrate of 0.055 m3/h by considering both the amount of heat transfer and the heat transfer ability. Furthermore, a higher heat transfer ability and a lower average surface temperature of the MCHSYC can be achieved simultaneously from the estimated optimal range of flowrate using the proposed optimization models.

Fluid Friction Effects on the Thermodynamic Performance of Spiral Plate Heat Exchangers

This paper presents a detailed analysis of the thermodynamic performance of spiral plate heat exchangers (SPHEs) and their channels by considering the fluid friction effect and no heat leakage to the environment. An optimal design algorithm for SPHEs is developed to find higher compactness and the overall heat transfer coefficient by increasing channels pressure drops, maintaining the geometric aspect ratio, and minimizing total costs. To determine the internal temperature distributions and the rates of heat transfer, a mathematical model is proposed. Fluid friction effects are examined as viscous heating; for this purpose, new parameters of the viscous heating entransy number and viscous heating entransy resistance are defined. Finally, various single-phase countercurrent SPHEs assuming a constant heat transfer rate, are modeled and compared in terms of energy, entropy generation, and entransy criteria. The results show the fluid friction effects as pressure drop effects in entropy generation are insignificant when compared to those caused by heat transfer. However, fluid effects as viscous heating in entransy analysis show that these effects can be rather significant in SPHEs with large spiral turn numbers or small values of heat capacity rate ratios. The obtained data suggest the significant role of entransy methods and their reliability to entropy generation methods in thermodynamic performance evaluation of SPHEs.

The entransy analysis in the wet channel of dew point evaporative cooler

A method to calculate entransy change (ΔE) and thermal resistance (R) was proposed firstly in this paper. The experimental results showed that in the wet channel the R was decreased and the total heat exchange capacity (Qt) was increased gradually along the air flow at the condition of Turpan and Shanghai, but showed a different trend in Lanzhou. Meanwhile, in the dry channel the cooling capacity (Q) and temperature drop (ΔT) were decreased along the air flow in all three regions. As inlet temperature increased, the R was decreased and Qt was increased in wet channel, thus the Q and the cooling rate in dry channel were increased. With inlet humidity ratio and air velocity decreased in dry channel, the R in wet channel was increased firstly and then decreased. The lowest inlet humidity ratio was, the smallest R in wet channel was, the highest Q and temperature drop rate in dry channel were. At the velocity 1.8 m/s, the R dropped to the lowest point, after that, Q was increased slowly and the temperature drop rate was reduced in the dry channel, therefore, high air velocity would only make Q increased but attribute to poor cooling effect. Then, some improved methods of the experimental device were proposed by the theory and experiment. Finally, some comparisons were made between conventional evaluation indicators and the new one proposed in this paper, it can be concluded that each indicator has its own strength and shortages, in the practical application, the proper indicator should be selected according to the demand.

Heat-transfer optimization of fluid loop radiator based on entransy analysis

Heat-transfer optimization of fluid loop radiator based on entransy analysis

Entropy, Exergy and Entransy Analyses on Fabricated Shell and Spiral Tube Heat Exchanger

Entropy, Exergy and Entransy Analyses on Fabricated Shell and Spiral Tube Heat Exchanger

Application and discussion on entransy analysis of ammonia/salt absorption heat pump systems

Abstract This study investigates the application of the entransy analysis in ammonia/salt absorption heat pump (AHP) systems. The results of the entransy analysis are compared with those of energy analysis and exergy analysis under typical and various operating conditions. Entransy dissipation and exergy loss in each component, as well as coefficient of performance (COP), exergy efficiency and entransy efficiency of systems, are discussed. The changing trends of entransy dissipation in each component are similar under various operating conditions. However, the entransy analysis performs better than the exergy analysis in evaluating the irreversible loss of each component. Moreover, the differences between the exergy analysis and entransy analysis are mainly in absorber, generator and SHE. Especially in the NH3/NaSCN system, the proportion of entransy dissipation in generator is 60.8%, which is almost twice of the proportion of exergy loss (34.9%). In addition, under various operating conditions, entransy efficiency and COP have roughly the same changing trend. Meanwhile, entransy efficiency is more reasonable than exergy efficiency in evaluating the performance of systems under the absorption temperature, which varies from 30°C to 50°C. These comparison results demonstrate that the entransy analysis is appropriate to evaluate the performance of ammonia/salt AHP systems and suitable for analyzing the irreversibility of each component.

Secondary heat transfer enhancement design of variable cross-section microchannels based on entransy analysis

Convective heat transfer enhancement is a trade-off between heat transfer enhancement and pumping power reduction. Entransy theory, evaluating the heat transfer efficiency from the viewpoint of irreversibility, is an ideal way to evaluate convective heat transfer performance. In this paper, the entransy dissipation is re-recognized from the viewpoints of heat transfer and fluid flow to explain the contradiction between heat transfer entransy dissipation (HTED) and fluid flow entransy dissipation (FFED). The concept of local entransy is introduced to analyze the heat transfer enhancement mechanism of variable cross-section microchannels (VC-Ms). Based on the analysis, a secondary design was used to further enhance heat transfer performance. The results found that the secondary design of VC-Ms showed lower entransy dissipation and higher convective heat transfer efficiency, which provided data supporting the optimization and active design of the microchannel heat sink.

Performance and Irreversibility Analysis of Spiral Plate Heat Exchangers

Herein, a model is developed based on energy balance equations to analyze and improve the performance of single‐phase counter‐current and co‐current flow spiral plate heat exchangers (SPHEs). The aim is to comprehensively check the performance and irreversibility factors based on energy, entropy, and entransy methods. First, a new optimization algorithm is proposed to maximize pressure drops and minimize the total cost by considering the geometric proportion of the SPHE. Second, the SPHE spiral turns are modeled as a series‐connected equivalent internal heat exchangers network to determine the temperature boundaries and develop the temperature–enthalpy diagram in analysis. The algorithm and modeling is validated in two stages for different flow arrangement SPHEs. Performance and irreversibility analysis shows similar result trends in different flow patterns. In third stage, a wide range of counter‐current flow SPHEs with constant heat transfer rate is designed, modeled, and analyzed by energy, entropy, and entransy methods. To recapitulate, results assert that SPHEs designed by new algorithm have higher overall heat‐transfer coefficient and compactness. Although entropy and entransy analyses reveal irreversibility trends with effectiveness in SPHEs, entransy analysis is more effective and reliable to analyze the SPHEs.

Experimental exergy and entransy analyses on designed and fabricated crossflow heat exchanger

AbstractA crossflow heat exchanger (CFHEx) is designed and fabricated in a workshop. For designing this heat exchanger (HEx), the number of passes, frontal areas, HEx volumes, heat transfer areas, free‐flow areas, ratios of minimum free‐flow area to frontal area, densities, mass flow rates of flowing fluids, maximum/minimum heat capacities, heat capacity ratio, outlet temperatures of hot/cold fluids, average temperatures, mass velocities, Reynolds numbers, and convective heat transfer coefficients are evaluated by considering Colburn/friction factors. After fabrication of the HEx, effectiveness, exergy destruction, entransy dissipation, entransy dissipation‐based thermal resistance, entransy dissipation number, and entransy effectiveness for hot/cold fluids sides are found at different flow rates and inlet temperatures of fluids. By experimental results, optimum operating conditions are found, which gives maximum effectiveness and entransy effectiveness but minimum rates of exergy destruction, entransy dissipation, entransy dissipation‐based thermal resistance, and entransy dissipation number for the fabricated CFHEx. This study is concluded as follows: minimum exergy destruction and entransy dissipation rates (ie, 3.061 kJ/s·K and 1125.44 kJ·K/s, respectively) are found during experiment 2. Maximum entransy effectiveness of hot/cold fluids (ie, 0.689/0.21) is achieved in experiment 1. Moderate values of entransy dissipation number (ie, 4.689), entransy dissipation‐based thermal resistance (ie, 0.04 s·K/J), exergy destruction (ie, 3.845 kJ/s·K), and entransy dissipation (ie, 1374.04 kJ·K/s) rates are found during experiment 1. Maximum effectiveness (ie, 0.4) for the fabricated HEx is also obtained through experiment 1. After comparative analyses, it is found that experiment 1 provides optimum results, which shows the best performance of the fabricated HEx.