Entransy Theory Research Articles

Study on the optimization of heat loss during operation of air source heat pump based on entransy theory

Existing research on the analysis heat pump operation generally focuses on the efficiency of doing work while ignores heat loss in the transfer process. Hence, heat pumps are often studied based on theory of minimum entropy production. However, this theory is rarely applied to optimizing heat transfer process with?out heat work conversion. Taking the air source heat pump hot water supply sys?tem of a hotel building as an example, this paper simulates the heat production, power and COP of the air source heat pump during operation based on the the?ory of entransy and entransy dissipation proposed by Professor Zengyuan Guo. The findings show that heat pump operates best at inlet water temperatures of 293 K and 298 K, with a COP of 4.8. In the water at a temperature of 298 K, water temperature can be adjusted by the function of heating capacity between 30 kW and 40 kW to minimize the system?s entransy dissipation, where the system?s unit power consumption reaches its minimum at 9 kW, corresponding to an entransy dissipation of 245.4 kJK. This study provides a good research idea to optimize the thermal power conversion process using the theory of entransy and entransy dissipation.

Useful entransy—A physical quantity describing the useful heat transfer ability for heating/cooling

The existing entransy theory does not consider the usefulness of heat transfer ability. This leads to the fact that the heat transfer ability described by entransy is not completely consistent with the heat/cold utilization, and the entransy efficiency analysis also has certain limitations. Hence, this paper first studies the usefulness of heat transfer ability. Under the ambient air with infinite heat capacity, only the exothermic ability of the object above ambient temperature T0 is useful for heating, and only the endothermic ability of the object below T0 is useful for cooling. On this basis, with T0 as the reference point, the useful entransy is proposed to describe the useful heat transfer ability of an object for heating/cooling. It is demonstrated that heating/cooling mainly utilizes the heat transfer ability of an object relative to T0 (useful entransy), rather than its heat transfer ability relative to 0 K (entransy). Moreover, taking latent heat storage as an example, it is proved that the useful entransy efficiency is more accurate than the entransy efficiency to evaluate the heat transfer irreversibility. And the guidance based on useful entransy efficiency is more practical. Furthermore, useful entransy efficiency analysis and entransy dissipation analysis are complementary. The combination of the two can evaluate and analyze the heat transfer performance more comprehensively. In summary, the useful entransy is an important improvement of entransy theory.

Optimization of tree-shaped fin structures towards enhanced discharging performance of metal hydride reactor for thermochemical heat storage based on entransy theory

Integrating fin structures into metal hydride (MH) bed can enhance heat discharging performance of the reactor for thermochemical heat storage. In this study, based on the entransy theory, the entransy dissipation rate (Eh,st) or the entransy dissipation (Eh,tr) of a simplified two-dimensional (2D) steady-state or transient heat conduction model for the MH bed was used to be an objective to optimize the tree-shaped fin (TSF) structures. Furthermore, response surface method (RSM) was adopted to explore the relationship between Eh,st or Eh,tr and structural parameters (i.e., branch number N, branch level M, length ratio α, width index β, and angle ratio γ). The results show that RSM can effectively predict influences of structural parameters of TSFs on heat discharging performance. Based on RSM with entransy theory, the obtained optimal combination parameters were N = 8, M = 3, α = 1, β = 0.5, and γ = 1, corresponding to the maximum gravimetric exergy-output rate (GEOR) of 20.98 W/kg. Furthermore, the GEOR with optimized fins was 11.5 % higher than that with unoptimized TSFs. The optimization method based on the entransy theory was effective to optimize the TSF structures by solving 2D model instead of three-dimensional model, and shorten the calculation time for optimization.

Improvement of Constructal Optimization for “Volume-Point” Heat Conduction Based on Uniformity Principle of Temperature Difference Fields

The uniformity principle of temperature difference fields (TDFs) is applied in this study to improve the constructal optimization for “volume-point” heat conduction based on entransy dissipation rate (EDR) minimization without the premise of an optimal last-order construct, and the constructal optimization algorithm based on EDR minimization is simplified in this paper. The results further prove that the uniformity principle of TDF is consistent with entransy theory. The constructal optimization of “volume-point” heat conduction based on EDR minimization is conducted not only to lower the average temperature but also to obtain a more uniform TDF distribution. Through comparing the optimal results based on EDR minimization without the premise of an optimal last-order construct with those based on maximum temperature difference (MTD) minimization, some criteria and formulas for designing conductivity paths based on EDR minimization and MTD minimization are proposed, and the idea and method of improving constructal optimization via the variational principle are proposed.

A novel design for fin profile in metal hydride reactor towards heat transfer enhancement: Theoretical derivations and analysis

Hydrogen storage using metal hydrides is one of the research hotspots in the field of energy storage. However, metal hydride powders are known to have low thermal conductivity, which causes significant temperature fluctuation and hinders further reaction, hence efficient thermal management is a must for hydrogen storage using metal hydrides. In this paper, based on the principle of entransy dissipation, the optimal profile of fin in a cylindrical reactor under steady-state conditions is deduced. The expression for the temperature distribution of the bed is also obtained, which could clearly account for the influences of multiple involving factors, such as fin thickness, fin spacing, and radius of reactor. Through simulation, the characteristic time of hydrogen absorption for reactor inserting the optimized fin, is shortened by 19.1 % compared with the conventional uniform thickness fin. The influence of the geometric parameters of storage reactor was further discussed. When the ratio of the inner and outer radius of the reactor is confined (rr/rt≤2), linear thinning fin can be seen as a reasonable simplification of the optimized fin with comparable heat transfer enhancement effect. This study proves that the thermal management of metal hydride reactors, particularly those inserting high thermal conductivity materials like graphite, can be optimized quantitatively by entransy theory.

Performance enhancement of a horizontal latent thermal energy storage unit with elliptical fins

The practical use of latent thermal energy storage (LTES) system is limited by the low thermal conductivity of the available Phase Change Materials (PCMs). In this study, the elliptical fin is proposed and applied to Horizontal Double Tube LTES Unit (HDT-LTESU) for improving the performance of thermal storage. Paraffin wax is used as PCM that is placed in the annulus between tube and shell. Three-dimensional numerical simulation based on enthalpy porosity method is performed to study the characteristics of the PCM melting/solidification and the performance of charging/discharging thermal energy of HDT-LTESU with different aspect ratios elliptical fins. The mechanism of enhanced thermal energy storage is also verified and analyzed by the entransy theory. It was found that the addition of elliptical fins can effectively improve convection heat transfer of PCM at the top and bottom of the annulus. Further, the high aspect ratio fins are more favorable for improving the comprehensive performance enhancement, and enhancement ratio can reach up to maximum 16.9% and 13.8% for melting and solidification, respectively. The entransy dissipation is reduced, and the phase change process of heat transfer is improved.

Effect of Geometric Parameters on the Performance of a Membrane‐Based Enthalpy Exchanger

AbstractA membrane‐based enthalpy exchanger (MBEE) with partial inlet is proposed. Numerical simulations were conducted to investigate the effect of Reynolds number (Re), the ratio of entrance area to channel cross‐sectional area Re−c, and channel length/width ratio Rl−w on the performance of the MBEE. Effectiveness, pressure loss, and flow patterns were evaluated for optimization. Moreover, the entransy theory was applied to analyze the mechanism of the heat transfer enhancement of the MBEE. The results indicate that the larger the Re–c, the higher the effectiveness and lesser pressure drop of the MBEE at the same volumetric flow rate. The total heat exchange rate per unit area and the pressure drop per unit length are reduced with the increasing of Rl–w .

Symmetric Heat Transfer Pattern of Fuel Assembly Subchannels in a Sodium-Cooled Fast Reactor

The method outlined in this paper is convenient and effective for studying the thermal performance of fuel assemblies cooled with sodium fast reactors using the subchannel procedure. To initially study an optimization model for a symmetric single fuel assembly heat transfer pattern analysis in a fast sodium-cooled reactor based on subchannel calculations, this paper innovatively proposes a subchannel heat transfer analysis method with the entransy dissipation theory, which can solve the limitations and inaccuracies of the traditional entropy method such as poor applicability for heat transfer processes without functional conversion and the paradox of entropy production of heat exchangers. The symmetric distributions of the thermal-hydraulic parameters such as coolant flow rate, coolant temperature, cladding temperature, and fuel pellet temperature were calculated, and the entransy dissipation calculation method corresponding to the fuel assembly subchannels was derived based on the entransy theory. The effect of subchannel differences on the thermal-hydraulic parameters and the symmetric distribution pattern of entransy dissipation during the cooling process of the fuel assembly was analyzed and compared from the symmetrical arrangement of subchannels in the axial and radial directions.

Research on Performance Optimization of Gravity Heat Pipe for Mine Return Air

The mine return air flow has the characteristics of basically constant temperature and humidity all year round and is a high-quality waste heat resource. Its direct discharge not only wastes energy but also causes environment pollution. It has important economic value and application prospect to solve the problem of shaft antifreeze using new technology to recover the waste heat of mine return air. Gravity heat pipe is widely used in the heat recovery of mine return air. Its heat transfer process is a complex process with multiple parameters. The current research focuses on the influence of a single factor on heat transfer, which has many limitations. To analyze the effects of different parameters on the heat recovery effect of gravity heat pipe in mine return air and to optimize heat pipe heat exchanger parameters in the heat exchange system, mathematical models of gas–water countercurrent heat and mass transfer, entransy dissipation and exergy efficiency were established in this paper, based on the entransy dissipation theory. Under the condition of the given initial parameters, the effects of different parameters on the dimensionless factor, β, of heat transfer, total heat transfer, and entransy dissipation thermal resistance were analyzed. The experimental and calculation results show the entransy dissipation theory can be used to evaluate the heat transfer performance of the gravity heat pipe. When the entransy dissipation thermal resistance was minimum, the heat transfer performance was optimal. During the heat transfer process between the mine return air and the gravity heat pipe with high humidity under a given working condition, increasing the Reynolds number was beneficial to increase the heat transfer dimensionless factor, β.

Entransy performance analysis of the sulfuric acid wastewater treatment process using a vacuum membrane distillation system

Industrial sulfuric acid wastewater treatment using vacuum membrane distillation (VMD) technology has attracted worldwide attention. However, high energy loss and low membrane flux seriously hinder the industrialization of VMD technology. This paper novelly introduced an entransy theory to improve the VMD system performance. Mathematical models were built and verified via an experimental setup. System performance was investigated through the experiment and simulation from entransy dissipation standpoint. Experimental results indicated that an excellent separation performance with a membrane flux of 1.8 kg·m−2·h−1 and condensate conductivity within 20 μS·cm−1 were obtained at feed concentration of 10 %, feed temperature of 353.0 K, feed velocity of 1.0 m·s−1and vacuum side pressure of 24 kPa. Moreover, a thermal efficiency of 57.8 % was obtained with an entransy dissipation resistance of 0.00012 K·W−1. Simulation results showed that decreasing feed concentration and vacuum side pressure or increasing feed temperature and feed velocity decrease entransy dissipation resistance and improve heat transfer capability. More importantly, the prediction model of entransy dissipation resistance was established by a multiple linear regression method, and influence degrees of operation parameters on entransy dissipation resistance were obtained by a single factor analysis method. These findings are beneficial to optimize the VMD system in the future.

Performance study on multiple phase change materials heat storage system during melting process based on entransy theory

Performance study on multiple phase change materials heat storage system during melting process based on entransy theory

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.

Progress in theoretical study on constructal optimization of marine steam power plants

<p indent="0mm">Theoretical research of the constructal optimization of marine steam power plants is introduced in this study from two aspects: ship steam power plants and ocean thermal energy conversion plants. First, reviews are conducted on the main heat exchange component models of ship steam power plants, including the evaporator, superheater, economizer, whole boiler and condenser, main heat exchange, and energy conversion components, and system models of ocean thermal energy conversion plants, including the evaporator, condenser, dual-pressure turbine, and whole system. Then, constructal optimization of the main components of the two power plants and constructal thermodynamic optimization of the ocean thermal energy conversion plant based on modern thermal theories such as entropy generation minimization theory, finite time thermodynamics theory, entransy theory, and constructal theory are introduced. The similarities and differences in the results obtained before and after optimization, as well as the different optimization objectives and system structures, are extensively compared. Finally, the application prospects of constructal thermodynamic optimization to the optimal designs of energy transfer and conversion processes are made considering theoretical research on reduced energy consumption of power plants.

Field synergy principle: Its scientific beauty and relationship with entransy theory

Field synergy principle: Its scientific beauty and relationship with entransy theory

Entransy-based optimization on the energy-saving potentials of thermal power generation

Improving the efficiency of energy utilization is a necessary way to control the total amount of fossil energy and thus, achieve the goal of carbon peaking by 2030 and carbon neutrality by 2060. Thermal power generation accounts for nearly 50% of the total installed power generation capacity. The optimization of energy savings of existing thermal power-generating units under full working conditions has a key role in energy efficiency improvement. The introduction of a new physical quantity, entransy, provides a new perspective for connections of operating parameters of the system with the multifields and structural parameters of heat- and mass-transfer surfaces. This paper summarizes the results of the application of the entransy theory in thermal power generation systems recently, focusing on the heat, flow, and mass entransy dissipation-based optimization on the tail flue of boiler and cold-end systems. Then, an outlook on the problems to be solved and the energy-saving potentials, as well as optimization targets of each key subsystem, is provided to offer references for further improving the operating conditions of thermal power units during the energy transition period.

Heat current method for integrated analysis and optimization of thermodynamic systems

Performance analysis and optimization of thermodynamic systems are important in increasing the efficiency of energy systems, but traditional approaches cannot meet the demand of high-efficiency performance analysis for complex thermodynamic systems. Based on the entransy theory, the recently developed heat current method, combined with the specialized simulation algorithm, offers a new and attractive solution for performance analysis of thermodynamic systems. This paper first presents the standardized heat current modeling strategy for thermodynamic systems, taking a Rankine cycle power generation system as an example to present the modeling procedure. Combining flow constraints and physical property constraints of working fluids, the framework of construction of a global system mathematical model is then presented. In the proposed framework, linear, nonlinear explicit, and nonlinear implicit system constraints can be separated. Consequently, the number of constraints needing to be solved iteratively is minimized. Based on this separation feature, this paper further proposes and presents a hierarchical and categorized algorithm that could reduce calculation time greatly and improve calculation stability significantly. Finally, a triple-pressure steam power generation system is investigated to demonstrate the advantages of the proposed hierarchical and categorized algorithm compared with conventional methods from the aspects of the time required for calculation and the initial values required.

Entransy &amp;middot; Thermomass energy &amp;middot; Relativistic kinetomass energy

This paper is divided into five parts. The first part is the introduction, and it briefly reviews the three stages of the development of the entransy theory. The second part relates the entransy theory in heat transfer, introducing the necessity for, the definition of, the physical meaning of, and the applications of entransy. The third part concerns thermomass and thermomass energy, giving the concepts and their definitions, establishes the general heat conduction law, and clarifies that the nature of heat is the duality of “energy and mass”. The fourth part introduces the concepts of relativistic kinetomass and relativistic kinetomass energy, distinguishing them from the existing concepts of relativistic mass and relativistic energy. Some forms of relativistic kinetomass energy, except for thermomass energy, are introduced, including mechanical kinetomass energy, information energy, and dark energy. Following a brief introduction of energetics, the fifth section presents an idea of establishing a new discipline, Neo-energetics, based on a class of new energy forms (relativistic kinetomass energy) and new law of energy conservations.

Constructal optimization for a marine boiler based on entransy theory

<p indent="0mm">Based on entransy theory and constructal theory, performance optimization of a marine boiler is conducted by taking the outer diameters of the third convection evaporation tube, superheater tube, and economizer tube as the design variables with the total heat transfer area constraint of three main heat exchange components (evaporator, superheater, and economizer). The optimal construct and performance of the whole boiler are obtained. First, the optimization is performed by taking a complex function comprising the linear weighted sum of entransy dissipation rate and power consumption rate as the optimization objective. The influences of initial design parameters, such as heat preservation coefficient, weighting coefficient for the composite function, and heat transfer rate, on the constructal optimization results of the whole boiler, are analyzed. Results show that the optimal dimensionless tube outer diameters of the evaporator, superheater, and economizer are 1.2, 1.3, and 1.1, respectively, which make the composite function obtain the cubic minimum value of 0.737. Compared with the initial design point, the composite function of the overall boiler is reduced by 26.3%, and the comprehensive performance of the boiler is significantly improved. Second, the bi-objective optimization of the overall boiler based on the composite function is conducted based on the NSGA-II algorithm, and the corresponding Pareto frontier and optimal construct of the boiler are obtained, which can provide a wider selection space for the performance optimization and parameter design of the overall boiler. The results of this paper can provide a certain degree of theoretical guidelines for the overall performance optimization design of marine boilers.

Heat-Storage Performance Optimization for Packed Bed Using Cascaded PCMs Capsules

The design, in which the capsules are packed in the bed at different sections based on the Phase Change Material (PCM) melting temperature, is an effective method to improve the heat-storage performance of the latent heat energy storage system. A latent heat storage system was established in the present study in order to optimize the arrangement of cascaded PCM capsules. Four kinds of paraffin with different melting temperatures were selected as the PCM for the experiment. The effects of stage number, cascade ratio and melting temperature on the heat-storage performance of the latent heat storage system were investigated during the charging and discharging operations. The complete time of charge and discharge, heat storage-release capacity, energy efficiency, exergy efficiency and entransy dissipation (based on a new entransy theory) were computed for different arrangement cases, in order to analyze and evaluate the heat-storage performance of the system under different stage numbers and cascade ratios of PCMs. The results revealed that the arrangement of cascaded PCM capsules has an obvious effect on the heat-storage performance of the system. When more high melting PCMs are adopted, the heat storage-release capacity, energy efficiency and exergy efficiency increases, while the entransy dissipation decreases. However, the temperature increase becomes slow, and the charging or discharging process becomes long.

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.