Concept Of Entransy Research Articles

Application of Entransy Analysis in Self-Heat Recuperation Technology

Aside from the introductory and concluding remarks, this article is divided into four sections. Following a brief description of the concepts of entransy and entransy dissipation, which measures th...

Exploring buildings’ secrets: The ideal thermophysical properties of a building’s wall for energy conservation

The thermophysical properties of external walls have an important effect on the energy consumption of buildings. In order to develop a theoretical method to optimize the thermophysical properties, the concepts of entransy and entransy dissipation are used in this paper to study the irreversibility and thereafter deduce the optimization objective of heat transfer in external walls. Furthermore, the corresponding optimization criteria, i.e., the ideal variation functions of thermophysical properties of external walls with temperatures, are obtained by the variational method. The results show that the optimization objective is the extremum of the sum of the entransy stored in external walls and the entransy dissipation during heat transfer from outdoor to indoor. The corresponding optimization criteria, i.e., the ideal heat capacity ρcp(T) of wall, is a δ function in summer or winter, while the ideal thermal conductivity k(T) of wall approaches a staircase function in summer and maintains the available minimal value in winter. Finally, the newly developed entransy dissipation-based optimization method is applied to optimize the thermophysical properties of a practical external wall to show its applications. This work can provide guidelines for the designers of building materials.

Power and heat-work conversion efficiency analyses for the irreversible Carnot engines by entransy and entropy

The concepts of entransy and entropy are applied to the analyses of the irreversible Carnot engines based on the finite time thermodynamics. Taking the maximum output power and the maximum heat-work conversion efficiency (HWCE) as objectives, the applicability of the entransy theory and the entropy generation minimization method to the optimizations is investigated. For the entransy theory, the results show that the maximum entransy loss rate always relates to the maximum output power, while the maximum entransy loss coefficient always leads to the maximum HWCE for all the cases discussed in this paper. For the concept of entropy generation, the maximum entropy generation rate corresponds to the maximum output power when the Carnot engine works between infinite heat reservoirs, while the entropy generation number cannot be defined in this case. When the Carnot engine works between the finite heat reservoirs provided by streams, the minimum entropy generation rate corresponds to the maximum output power with prescribed heat flow capacity rates and inlet temperatures of the streams, while the minimum entropy generation number corresponds to the maximum HWCE. When the heat capacity flow rate of the hot stream is not prescribed, the entropy generation rate increases with increasing output power, while the entropy generation number decreases with increasing HWCE. When the inlet temperature of the hot stream is not prescribed, the entropy generation rate increases with increasing output power, and the entropy generation number also increases with increasing HWCE.

From thermomass to entransy

The concepts of entransy and thermomass have been developed for heat transfer analyses and optimizations. Thermomass is the equivalent mass of heat based on the Einstein’s mass–energy relation. The concept of entransy reflects the energy of thermomass. The entransy balance equations of heat conduction and heat convection, which are the basis of the heat transfer optimization principles, are derived from the energy equation of thermomass in this paper. The relationship between the entransy and the thermomass is discussed.

Entransy analysis of open thermodynamic systems

The concept of entransy developed in recent years can describe the heat transport ability. This paper extends this concept to the open thermodynamic system and defines the concept of enthalpy entransy. The entransy balance equation of steady open thermodynamic systems, as well as the concept of entransy loss, is developed. The entransy balance equation is applied to analyzing and discussing the air standard cycle. It is found that the entransy loss rate can describe the change in net power output from the cycle but the entropy generation rate cannot when the heat absorbed by the working medium is from the combustion reaction of the gas fuel. When the working medium is heated by a high temperature stream, both the maximum entransy loss rate and the minimum entropy generation rate correspond to the maximum net power output from the cycle. Hence, the concept of entransy loss is an appropriate figure of merit that describes the cycle performance.

Entransy decrease principle of heat transfer in an isolated system

The entropy increase principle for an isolated system and the criteria of thermal equilibrium for an isolated system and systems with prescribed temperature and volume can be derived on the basis of the concept of entropy and the first and second laws of thermodynamics. In this paper, the entransy decrease principle for an isolated system is introduced on the basis of the concept of entransy. It is found that the entransy of an isolated system always decreases during heat transfer. This principle can be taken as an expression of the second law of thermodynamics for heat transfer. The thermal equilibrium criteria for an isolated system and a closed system are also introduced. It is found that when an isolated system reaches thermal equilibrium, its entransy is a minimum value. This criterion is referred to as the minimum entransy principle. When a closed system reaches thermal equilibrium, its free entransy is also a minimum value. This criterion is referred to as the minimum free entransy principle. Therefore, like entropy, entransy can be considered an arrow of time in heat transfer and used to describe the thermal equilibrium state.

Moisture transfer resistance method for liquid desiccant dehumidification analysis and optimization

The concepts of entransy, entransy dissipation and transfer resistance are introduced into liquid desiccant dehumidification analysis to reveal the irreversibility and moisture transfer resistance between moist air and liquid desiccant. By analyzing a typical water (vapor) transfer process coupled with heat transfer, we define the concepts of mass entransy of water and its dissipation, derive the expression of moisture transfer resistance (MTR) that reflects the irreversibility of water transfer during dehumidification processes, and also point out the relationship between MTR and dehumidification performance. With these concepts, both adiabatic and internal cooling liquid desiccant dehumidification systems with various operation conditions are analyzed and optimized. It is found that for the adiabatic dehumidification system, increasing the mass transfer coefficient leads to the reduction of MTR, and consequently, the improvement of dehumidification performance. Meanwhile, for the dehumidification system with internal cooling, in order to reduce the MTR and improve the dehumidification performance, pre-cooling should be centralized ahead of the liquid desiccant inlet when the flow rates ratio of air to desiccant is small, whereas, uniform cooling should be applied when the flow rates ratio of air to desiccant is large.

Entransy—A physical quantity describing heat transfer ability

A new physical quantity, E h = 1 2 Q vh T , has been identified as a basis for optimizing heat transfer processes in terms of the analogy between heat and electrical conduction. This quantity, which will be referred to as entransy, corresponds to the electric energy stored in a capacitor. Heat transfer analyses show that the entransy of an object describes its heat transfer ability, as the electrical energy in a capacitor describes its charge transfer ability. Entransy dissipation occurs during heat transfer processes as a measure of the heat transfer irreversibility. The concepts of entransy and entransy dissipation were used to develop the extremum principle of entransy dissipation for heat transfer optimization. For a fixed boundary heat flux, the conduction process is optimized when the entransy dissipation is minimized, while for a fixed boundary temperature the conduction is optimized when the entransy dissipation is maximized. An equivalent thermal resistance for multi-dimensional conduction problems is defined based on the entransy dissipation, so that the extremum principle of entransy dissipation can be related to the minimum thermal resistance principle to optimize conduction. For examples, the optimum thermal conductivity distribution was obtained based on the extremum principle of entransy dissipation for the volume-to-point conduction problem. The domain temperature is substantially reduced relative to the uniform conductivity case. Finally, a brief introduction on the application of the extremum principle of entransy dissipation to heat convection is also provided.