The emergence and development of constructal theory, which has been a new discipline branch to research sorts of structures in nature and engineering, are reviewed. The core of the constructal theory ...is that various shapes and structures of the matters in nature are generated from the tendency to obtain optimal performance. Constructal theory and its application are summarized, from disciplines such as heat, mechanism, fluid flow, electricity, magnetism and chemistry, to life and non-life systems in nature.
The mass entransy and its dissipation extremum principle have opened up a new direction for the mass transfer optimization. Firstly, the emergence and development process of both the mass entransy ...and its dissipation extremum principle are reviewed. Secondly, the combination of the mass entransy dissipation extremum principle and the finite-time thermodynamics for optimizing the mass transfer processes of one-way isothermal mass transfer, two-way isothermal equimolar mass transfer, and isothermal throttling and isothermal crystallization are summarized. Thirdly, the combination of the mass entransy dissipation extremum principle and the constructal theory for optimizing the mass transfer processes of disc-to-point and volume-to-point problems are summarized. The scientific features of the mass entransy dissipation extremum principle are emphasized.
The research on the output rate performance limit of the multi-stage energy conversion system based on modern optimal control theory is one of the hot spots of finite time thermodynamics. The ...existing research mainly focuses on the multi-stage heat engine system with pure heat transfer and the multi-stage isothermal chemical engine (ICE) system with pure mass transfer, while the multi-stage non ICE system with heat and mass transfer coupling is less involved. A multistage endoreversible non-isothermal chemical engine (ENICE) system with a finite high-chemical-potential (HCP) source (driving fluid) and an infinite low-chemical-potential sink (environment) is researched. The multistage continuous system is treated as infinitesimal ENICEs located continuously. Each infinitesimal ENICE is assumed to be a single-stage ENICE with stationary reservoirs. Extending single-stage results, the maximum power output (MPO) of the multistage system is obtained. Heat and mass transfer processes between the reservoir and working fluid are assumed to obey Onsager equations. For the fixed initial time, fixed initial fluid temperature, and fixed initial concentration of key component (CKC) in the HCP source, continuous and discrete models of the multistage system are optimized. With given initial reservoir temperature, initial CKC, and total process time, the MPO of the multistage ENICE system is optimized with fixed and free final temperature and final concentration. If the final concentration and final temperature are free, there are optimal final temperature and optimal final concentration for the multistage ENICE system to achieve MPO; meanwhile, there are low limit values for final fluid temperature and final concentration. Special cases for multistage endoreversible Carnot heat engines and ICE systems are further obtained. For the model in this paper, the minimum entropy generation objective is not equivalent to MPO objective.
Compared with endoreversible heat engine with pure heat transfer and endoreversible isothermal chemical engine with pure mass transfer, endoreversible non-isothermal chemical engine (ENICE) is a more ...reasonable model of practical mass exchanger, solid device and chemo-electric systems. There exists heat and mass transfer (HMT) simultaneously between working fluid and chemical potential reservoir in ENICE. There is coupled HMT effect that in ENICE should be considered. There are two ways to consider this coupled effect. One is based on Onsager equations, and another is based on Lewis analogy. For the mathematical and physical description of the above HMT process, the model using Onsager equations are more appropriate in the linear HMT region not far from the equilibrium state, while that based on Lewis analogy is more appropriate in nonlinear HMT region far from the equilibrium state. Different from the previous research on the power optimization of ENICEs with Onsager equations, this paper optimizes power and efficiency of ENICE based on Lewis analogy. HMT processes are assumed to obey Newtonian heat transfer law (
q
∝ Δ
T
, and
T
is temperature) and Fick’s diffusive mass transfer law (
g
∝ Δ
c
, and
c
is concentration), respectively. Analytical results of power output and corresponding vector efficiency (
η
T
and
η
μ
) of ENICE are obtained, which provide important parallel results with those based on Onsager equations. They include special cases for endoreversible Carnot heat engine with
q
∝ Δ
T
and endoreversible isothermal chemical engine with
g
∝ Δ
c
. Adopting Lewis analogy in the modelling of ENICEs with simultaneous HMT is an important work. It provides important analytical and numerical results different from those with Onsager equations obtained previously and enriches the research contents of FTT. The research results in this paper have a certain guiding significance for the optimal designs of single irreversible NICEs, multistage NICE systems, practical mass exchangers, solid devices, chemo-electric systems, and so on.
Models of multi-element thermoelectric refrigerator (TER) with radiative heat transfer law (RHT) and Newtonian heat transfer law (NHT) are established based on finite time thermodynamics. The ...sameness and difference of the characteristics with different form of heat transfer are compared by numerical examples. It is found that for two heat transfer models, there is a set of optimal variables, i.e., an optimal working electrical current (WEC) and an optimal ratio of thermal conductance (RTC) of heat exchangers corresponding to the maximum cooling load, and there is another set of optimal variables corresponding to the maximum coefficient of performance (COP). For the same heat reservoir temperature difference (HRTD), both the cooling load and COP with RHT is larger than that with NHT, the optimal WEC at maximum cooling load with RTH is lager than that with NTH, and the optimal WEC at maximum COP with RTH is almost the same as that with NTH. With the increase of HRTD, both of the optimal WECs at maximum cooling load with RTH and NTH decrease, and both of the optimal WECs at maximum COP with RTH and NTH increase. The study with different heat transfer model for TER is necessary.
Thermoelectric effect is the most efficient way to convert electric energy directly from the temperature gradient. Thermoelec- tric effect-based power generation, cooling and heating devices are ...solid-stated, environmentally friendly, reliable, long-lived, easily maintainable, and easy to achieve miniaturization and integration. So they have unparalleled advantages in the aerospace vehicle industry, waste heat recovery, electronic cooling, etc. This paper reviews the progress in thermodynamic analyses and optimizations for single- and multiple-element, single- and multiple-stage, and combined thermoelectric generators, thermoe- lectric refrigerators and thermoelectric heat pumps, especially in the aspects of non-equilibrium thermodynamics and finite time thermodynamics. It also discusses the developing trends of thermoelectric devices, such as the heat sources of thermoe- lectric generators, multi-stage thermoelectric devices, combined thermoelectric devices, and heat transfer enhancement of thermoelectric devices.
Increasing the production of energy in line with industry development, transportation, and life quality improvement is an interesting topic needs to be addressed. Energy policymakers and researchers ...have aimed at energy management, particularly by improving energy systems performance. This review paper explains the rising interest of thermoelectric technology and applications. Nowadays, thermoelectric technology such as thermoelectric generators (TEGs) and thermoelectric cooling systems (TECs) provide heat loss recovery of thermodynamic units for power production of remote areas. Unlimited solar energy can also be employed for thermoelectric power production. This paper describes the principles of thermoelectricity and presents an explanation of current and upcoming materials. Developed models and various performed optimization of thermoelectric applications by using non-equilibrium thermodynamics and finite time thermodynamics are discussed as well. Additionally, a number of topical applications and energy resources are introduced. The main goal of this study is to give a clear overview of thermoelectric technology and applications.
•Explains the rising interest of thermoelectric technology and applications.•Describes thermoelectricity principles and current and upcoming materials.•Developed models and various performed optimization are discussed.•Includes non-equilibrium thermodynamics and finite time thermodynamics.•A number of topical applications and energy resources are introduced.
On the basis of introducing the origin and development of finite time thermodynamics (FTT), this paper reviews the progress in FTT optimization for internal combustion engine (ICE) cycles from the ...following four aspects: the studies on the optimum performances of air standard endoreversible (with only the irreversibility of heat resistance) and irreversible ICE cycles, including Otto, Diesel, Atkinson, Brayton, Dual, Miller, Porous Medium and Universal cycles with constant specific heats, variable specific heats, and variable specific ratio of the conventional and quantum working fluids (WFs); the studies on the optimum piston motion (OPM) trajectories of ICE cycles, including Otto and Diesel cycles with Newtonian and other heat transfer laws; the studies on the performance limits of ICE cycles with non-uniform WF with Newtonian and other heat transfer laws; as well as the studies on the performance simulation of ICE cycles. In the studies, the optimization objectives include work, power, power density, efficiency, entropy generation rate, ecological function, and so on. The further direction for the studies is explored.
An improved irreversible closed modified simple Brayton cycle model with one isothermal heating process is established in this paper by using finite time thermodynamics. The heat reservoirs are ...variable-temperature ones. The irreversible losses in the compressor, turbine, and heat exchangers are considered. Firstly, the cycle performance is optimized by taking four performance indicators, including the dimensionless power output, thermal efficiency, dimensionless power density, and dimensionless ecological function, as the optimization objectives. The impacts of the irreversible losses on the optimization results are analyzed. The results indicate that four objective functions increase as the compressor and turbine efficiencies increase. The influences of the latter efficiency on the cycle performances are more significant than those of the former efficiency. Then, the NSGA-II algorithm is applied for multi-objective optimization, and three different decision methods are used to select the optimal solution from the Pareto frontier. The results show that the dimensionless power density and dimensionless ecological function compromise dimensionless power output and thermal efficiency. The corresponding deviation index of the Shannon Entropy method is equal to the corresponding deviation index of the maximum ecological function.
As a new concept, mass-entransy is one of the twins in the core of entransy theory. It can describe mass-transfer ability for mass-transfer processes (MTPes), just as thermal-entransy for describing ...heat-transfer ability. Accordingly, mass-entransy dissipation can be utilized to evaluate the loss of mass-transfer ability. Minimum mass-entransy dissipation (MMED) is utilized to optimize one-way isothermal diffusive MTPes with mass-leakage and mass-transfer law (g ∝ Δ(
c
), where
c
means concentration). For a given net amount of mass-transferred key components at the low-concentration side, optimality-condition for the MMED of isothermal diffusive MTPes is obtained by using the averaged-optimization-method. Effects of the amount of mass-transferred and mass-leakage on optimal results are analyzed, and the obtained optimization profiles are compared with those for MTP profiles of constant-concentration-difference (
c
1
−
c
2
= const) and constant-concentration-ratio (
c
1
/
c
2
= const). The product of square of key-component-concentration (KCC) difference between high- and low-concentration sides and inert component concentration at high-concentration side for the MMED of the MTP with no mass-leakage is a constant, and the optimal relationship of the KCCs between high- and low-concentration sides with mass-leakage is significantly different from the former. When mass-leakage is relatively small, the MTP with
c
1
−
c
2
= const strategy is superior to that with
c
1
/
c
2
= const strategy, and the latter is superior to the former with an increase in mass-leakage. A combination of mass-entransy concept, finite-time thermodynamics, and averaged-optimization-method is a meaningful tool for optimizing MTPes.
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