Constructal optimization on T-shaped cavity based on entransy dissipation minimization

Based on the relationship between entransy and microstate number, we discuss the variations of the available transport entransy, the unavailable transport entransy, the available conversion entransy and the unavailable conversion entransy with the microstate number. We focus on physical processes in which heat is used for heating/cooling or doing work. When heat is transported for heating or cooling, the available transport entransy increases if the increase in microstate number is due to the increase in internal energy of the system, and decreases if the increase in microstate number is due to spontaneous heat transfer. When heat is used to do work, both the available conversion entransy and the unavailable conversion entransy increase if the increase in microstate number relates to the growth in internal energy of the system. The available conversion entransy decreases and the unavailable conversion entransy increases if the increase in microstate number results from spontaneous heat transfer. microstate number, entransy, available entransy, unavailable entransy

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confidence: 99%

Relationship between microstate number and available entransy

Cheng

Liang

2012

“…Furthermore, Guo et al [17] proposed an alternative criterion for heat transfer optimization: the entransy dissipation extrema correspond to the optimal performance of heat transfer processes not involving a thermodynamic cycle. In [18], the concept of entransy was originally referred to as the heat transfer potential capacity, and this new theory has been applied in studying and optimizing heat conduction [17,19,20], convective heat transfer [21][22][23][24], thermal radiation [25] and the heat transfer performance in a single heat exchanger [26][27][28]. Moreover, some novel heat transfer enhancement technologies have been developed, e.g.…”

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confidence: 99%

A comparison of optimization theories for energy conservation in heat exchanger groups

Chen

Wang

et al. 2011

In general, thermal processes can be classified into two categories: heat-work conversion processes and heat transfer processes. Correspondingly, the optimization of thermal processes has to have two different criteria: the well known entropy generation minimization method and the recently proposed entransy dissipation maximization method. This study analyzes the thermal issues in a heat exchanger group, and optimizes the unit arrangements under different constraints based on a suitable optimization criterion. The result indicates that the principle of minimum entropy generation rate is valid for optimizing heat exchangers in a thermodynamic cycle with given boundary temperatures. In contrast, the entransy dissipation maximization is more suitable in heat exchanger optimizations involving only heat transfer processes. Furthermore, the entropy generation rate induced by dumping used streams into ambient surroundings has to be taken into account, except for that originating from the hot and cold-ends of heat exchangers, when using the entropy generation minimization to optimize heat exchangers undergoing a thermodynamic cycle. Heat exchangers, one of the most important devices in thermal engineering, are being used in more than 80% of energy utilization systems. Improving their effectiveness has often been regarded as the key issue in energy conservation. Consequentially, thermal engineers have developed a large number of passive and active technologies to enhance thermal performance by adding extended or rough surfaces and various inserts to enlarge the exchange surfaces or by introducing surfaces or fluid vibrations and external electric or magnetic field to expedite the process [1][2][3]. Although all of these ideas have been more or less successful in reducing energy consumption, the fundamental physics involved is still not clear. One issue is the relationship between heat exchanger effectiveness and heat *Corresponding author (email: chenqun@tsinghua.edu.cn) transfer irreversibility, noting that heat transfer is an irreversible process [4]. The crucial problem is in understanding why heat exchangers with different flow arrangements lead to diverse heat transfer performances under the same given conditions. Using the entropy generation as a measure of irreversibility for any irreversible process, Bejan [5,6] introduced the concept of irreversibility as being due to finite temperature difference as well as fluid friction in heat transfer processes and optimized the regenerative heat exchanger for a Brayton cycle heat engine based on the criterion of minimum entropy generation. Thereafter several researchers, e.g. Poulikakos [7]

“…With the concept of entransy dissipation or thermal resistance based on entransy dissipation, researchers have conducted many optimization studies of heat conduction, heat convection and mass convection [17][18][19][20][21][22][23]. Chen and co-authors [21][22][23] combined the extremum entransy dissipation principle with the constructal theory and optimized many heat transfer systems based on entransy dissipation rate minimization. In researches of heat exchangers and HENs, Song et al [24] demonstrated the uniformity principle of temperature difference field for one-dimensional heat exchanger based on the extremum entransy dissipation principle.…”

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confidence: 99%

Entransy-dissipation-based thermal resistance analysis of heat exchanger networks

Qian

2011

Heat exchanger network optimization has an important role in high-efficiency energy utilization and energy conservation. The thermal resistance of a heat exchanger network is defined based on its entransy dissipation. In two-stream heat exchanger networks, only heat exchanges between hot and cold fluids are considered. Thermal resistance analysis indicates that the maximum heat transfer rate between two fluids corresponds to the minimum entransy-dissipation-based thermal resistance; i.e. the minimum thermal resistance principle can be exploited in optimizing heat exchanger networks.heat exchanger network, entransy-dissipation-based thermal resistance, optimization, minimum thermal resistance principle Citation:Qian X D, Li Z, Li Z X. Entransy-dissipation-based thermal resistance analysis of heat exchanger networks. Chinese Sci Bull, 2011Bull, , 56: 3289-3295, doi: 10.1007 Heat exchanger networks (HENs) are widely used in energy transport and utilization. Two-stream HENs are a type of HENs in which hot and cold fluids do not exchange thermal energy directly through one heat exchanger due to environmental constraints or practical demands. Trivedi et al. [9] improved on this approach and introduced the dual temperature and pseudo-pinch method in HEN optimization. Analyzing by a mathematical programming method, a HEN is described by an objective function and constraint conditions. Cerda et al. [10] and Floudas et al.[11] solved this HEN optimization problem using linear programming (LP) and mixed-integer nonlinear programming (MINLP) methods respectively.In optimization designs of two-stream HENs, the heat transfer rate is mainly of concern to designers. To maximize the heat recovery or heat transfer rate, much research has been performed. In the research of run-around heat recovery system, Fan et al. [12] found that the system had the highest efficiency when the heat capacity ratio of air and the medial fluid was in the range 0.8-1.2. Zhou et al. [13] found that a ground-coupled liquid loop heat recovery ventilation system had an optimal allocation ratio between heat exchangers and an optimal brine flow rate that provided maximum heat recovery efficiency. These authors found the optimum working condition for the networks but did not explain the phys-