Chen Lingen

Progress in study on constructal theory and its applications

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.

Improvement of tree-like network constructal method for heat conduction optimization

The analysis of the “tree-like network” construct method has been repeated. The high effective conduction channel distribution has been optimized again, without the premise that the new order assembly construct must be assembled by the optimized last order construct. It is proved that the “tree-like network” construct method is faultiness. A more optimal construct is obtained, and when the thermal conductivity and the proportion of the two heat conduction materials are constant, the limit of the minimum heat resistance is derived. All these conclusions can be used to guide the engineering application.

Thermal insulation constructal optimization for steel rolling reheating furnace wall based on entransy dissipation extremum principle

Analogizing with the heat conduction process, the entransy dissipation extremum principle for thermal insulation process can be described as: for a fixed boundary heat flux (heat loss) with certain constraints, the thermal insulation process is optimized when the entransy dissipation is maximized (maximum average temperature difference), while for a fixed boundary temperature, the thermal insulation process is optimized when the entransy dissipation is minimized (minimum average heat loss rate). Based on the constructal theory, the constructal optimizations of a single plane and cylindrical insulation layers as well as multi-layer insulation layers of the steel rolling reheating furnace walls are carried out for the fixed boundary temperatures and by taking the minimization of entransy dissipation rate as optimization objective. The optimal constructs of these three kinds of insulation structures with distributed thicknesses are obtained. The results show that compared with the insulation layers with uniform thicknesses and the optimal constructs of the insulation layers obtained by minimum heat loss rate, the optimal constructs of the insulation layers obtained by minimum entransy dissipation rate are obviously different from those of the former two insulation layers; the optimal constructs of the insulation layers obtained by minimum entransy dissipation rate can effectively reduce the average heat loss rates of the insulation layers, and can help to improve their global thermal insulation performances. The entransy dissipation extremum principle is applied to the constructal optimizations of insulation systems, which will help to extend the application range of the entransy dissipation extremum principle.

Constructal optimization for H-shaped multi-scale heat exchanger based on entransy theory

Analogizing with the definition of thermal efficiency of a heat exchanger, the entransy dissipation efficiency of a heat exchanger is defined as the ratio of dimensionless entransy dissipation rate to dimensionless pumping power of the heat exchanger. For the constraints of the total tube volume and total tube surface area of the heat exchanger, the constructal optimization of an H-shaped multi-scale heat exchanger is carried out by taking entransy dissipation efficiency maximization as optimization objective, and the optimal construct of the H-shaped multi-scale heat exchanger with maximum entransy dissipation efficiency is obtained. The results show that for the specified total tube volume of the heat exchanger, the optimal constructs of the first order T-shaped heat exchanger based on the maximizations of the thermal efficiency and entransy dissipation efficiency are obviously different with the lower mass flow rates of the cold and hot fluids. For the H-shaped multi-scale heat exchanger, the entransy dissipation efficiency decreases with the increase in mass flow rate when the heat exchanger order is fixed; for the specified dimensionless mass flow rate M (M<32.9), the entransy dissipation efficiency decreases with the increase in the heat exchanger order. The performance of the multi-scale heat exchanger is obviously improved compared with that of the single-scale heat exchanger. Moreover, the heat exchanger subjected to the total tube surface area constraint is also discussed in the paper. The optimization results obtained in this paper can provide a great compromise between the heat transfer and flow performances of the heat exchanger, provide some guidelines for the optimal designs of heat exchangers, and also enrich the connotation of entransy theory.

Cooling Load Density Analysis and Optimization for an Endoreversible Air Refrigerator

The performance analysis and optimization of an endoreversible air refrigerator is carried out by taking the cooling load density, which is defined as the ratio of cooling load to the maximum specific volume in the cycle, as the optimization objective in this paper. The results obtained are different from those with the cooling load objective. Numerical examples show the effects of pressure ratio and allocation of heat exchanger inventory on the cooling load density of the refrigerator.The performance analysis and optimization of an endoreversible air refrigerator is carried out by taking the cooling load density, which is defined as the ratio of cooling load to the maximum specific volume in the cycle, as the optimization objective in this paper. The results obtained are different from those with the cooling load objective. Numerical examples show the effects of pressure ratio and allocation of heat exchanger inventory on the cooling load density of the refrigerator.

Numerical simulation of sinter cooling processes in vertical tank and annular cooler

针对烧结矿冷却的两种基本模式——环冷式和竖罐式, 分别建立了环冷机、竖罐内对流换热过程的非稳态模型, 并运用场协同理论进行了分析比较. 结果表明: 在相同的冷却效果下, 竖罐式冷却过程传热的场协同数明显大于环冷式, 因此可以大大加强热烧结矿高温显热的回收. 同时研究了气料比、料层总高度、料层半径等因素对于竖罐式烧结矿冷却过程场协同数的影响, 从节约能耗的角度, 指出了在兼顾冷却传热性能、实际生产需求的条件下, 应当选择相对较小的气料比, 且冷却竖罐应由“瘦高型”向“矮胖型”发展.

Interaction mechanism among material flows, energy flows and environment and generalized thermodynamic optimizations for iron and steel production processes

Combining modern thermodynamic theories, including finite time thermodynamics, constructal theory and entransy theory, with metallurgical process engineering, a generalized thermodynamic optimization theory for iron and steel production processes is proposed. The simulation platform for the energy consumption and emissions of the iron and steel production process is built, and the evaluation method of the material flows, energy flows and environment combining exergy analysis with life cycle assessment is established. On the basis of the new theory, simulation platform and evaluation method, interaction mechanism investigations for the material flows, energy flows and environment of the elemental packages, working procedure modules, functional subsystems and whole process of the iron and steel production processes are conducted, and multi-disciplinary and multi-objective generalized thermodynamic optimizations of them are also implemented. After optimizations, the selections of the processes and technologies, the distributions of the materials and energies as well as the utilizations of the residual energies and heats are more reasonable. The systems of the whole process are integrated, and the material flows, energy flows and environment are synthetically coordinated. Finally, the efficient allocation of the energies and the cascade utilization of the residual energies are realized, and the energy consumption and emissions of the whole system are significantly decreased. This paper can provide theoretical supports for the designs and operations of the energy and environmental protection center of the iron and steel enterprises by exploring the efficient, energy-saving and low emission technologies of the iron and steel production processes. It also can provide research platforms and lay science and technology bases for solving the common efficient energy-saving problems of the general material transformation processes.

Progress in study on finite time thermodynamic performance optimization for three kinds of microscopic energy conversion systems

With the development of molecular biology technology, nanotechnology and micro electronic technology, more and more attentions have been paid to the microscopic energy conversion systems. The research on energy conversion mechanism and efficiency for micro-energy conversion system is a new subject concerning the interdisciplinary integration of thermodynamics, statistical mechanics, physics theory, etc. Performance optimization is one of the key science problems in revealing the mechanism of energy conversion and improving efficiency of energy utilization for micro-energy conversion system. On the basis of introducing the origin and development of the finite time thermodynamics theory, this paper reviews the recent advances of thermodynamic optimization for three kinds of typical microscopic energy conversion systems, i.e., the thermal Brownian motors, energy selective electron engines and the thermionic energy conversion devices, and proposes the future research prospects.

Entropy generation minimization of steam methane reforming reactor with linear phenomenological heat transfer law

This paper investigates a class of tubular plug flow steam methane reforming reactor coupling among heat exchange, fluid flow and chemical reaction, in which the heat transfer between the heat reservoir outside the conversion tube and the reactants inside the tube is assumed to obey the linear phenomenological heat transfer law [ q ∝ Δ ( T − 1 ) ]. Under the condition that all of the hydrogen production rate, the inlet pressure, the total inlet molar flow rate, the inert gas (N2) molar flow rate are given, and the reservoir temperature is assumed to be controllable completely, both the minimum entropy generation rate of the process and the corresponding optimal reservoir temperature profile are obtained for minimizing the total entropy generation due to heat transfer, fluid flow and chemical reaction and by applying the theory and method of finite time thermodynamics with the help of nonlinear programming method. The obtained results are also compared with other two classes of reference reactors under the heat transfer strategies of constant and linear reservoir temperature operations and the optimization results for the minimum entropy generation of the case with Newtonian heat transfer law [ q ∝ Δ ( T ) ]. The results show that compared to the two classes of the reference reactors, optimizing the reservoir temperature profiles could reduce the entropy generation by more than 58%, which is mainly due to the decrease in the entropy generation caused by heat transfer; a shorter reactor may perform equally well, and the optimal path shows immediate regions of either a constant thermal force or a constant chemical force; heat transfer laws have significant effects on the optimal temperature configurations of both the heat reservoir and the reaction mixture for the minimum entropy generation of the chemical reactor.

Application of Improved BCC Algorithm and RBFNN in Identification of Defect Parameters

The identification of defect parameters in thermal non-destructive test and evaluation (TNDT/E) was considered as a kind of inverse heat transfer problem (IHTP) and a kind of structure design optimization problem, and the design results should meet the surface temperature profile of the apparatus with defects. An improved bacterial colony chemo taxis (IBCC) optimization algorithm and a radial basis function neural network (RBFNN) are applied to the identification of defects parameters. The RBFNN is a precise and convenient surrogate model for the time costly finite element computation, which obtains the surface temperature with different defect parameters. The IBCC optimization algorithm is derivatively-free, and the convergence speed is fast. This method is applied to a simple verification case and the result is acceptable. The algorithm is also compared with the particle swarm optimization (PSO) algorithm, and the IBCC algorithm can access the optimum with faster speed.