Minimum Entransy Dissipation Research Articles

Simulation and Optimization of the Operation Efficiency of Heat Exchange Units in Intelligent Heating Systems Based on Entransy Dissipation Thermal Resistance

So as to investigate heat exchange efficiency of heat exchange units under different operating conditions, this paper builds a simulation analysis model for heat exchange units in the framework of intelligent district heating systems based on the Modelica unified modeling language and the MWorks platform. Analyze the real-time operating efficiency of heat exchange units using entransy dissipation thermal resistance as an evaluation indicator of heat exchange efficiency. This paper analyzes the trend of heat exchange efficiency changes of heat exchange units when the primary side flow rate, secondary side flow rate, primary side inlet temperature, secondary side inlet temperature, and secondary side bypass pipeline valve opening change. The simulation results verify that when the primary side and the secondary side flow match, the entransy dissipation thermal resistance is the smallest, and its heat transfer efficiency is the highest. Under the simulation condition where the convective heat transfer coefficient is constant, the entransy dissipation thermal resistance is independent of the inlet temperature changes on the primary and secondary sides. The minimum entransy dissipation thermal resistance could be achieved, which represents the optimal real-time heat exchange efficiency state, when the valve opening of the mixed water heat exchange unit is 45% under the specific flow conditions.

Minimizing entransy dissipation for heat transfer processes withq∝Δ(Tn)and heat leakage

Heat transfer process with heat leakage and generalized radiative heat transfer law (HTL) [q∝Δ(Tn)] is investigated. Optimality condition for the minimum entransy dissipation (MED) is derived by applying average optimal control theory. On the basis of the general optimization result, the results for four special cases of Newtonian [q∝Δ(T)], linear phenomenological [q∝Δ(T−1)], radiative [q∝Δ(T4)], and mixed [q∝Δ(T4) with q∝Δ(T)] HTLs are further obtained. Optimal paths are compared with the common strategies of constant heat flux rate and constant hot fluid temperature operation. Numerical examples are presented, and influences of heat transferred amount and heat leakage on optimization performances are analyzed.

Constructal optimization of heat conduction with minimum entransy dissipation rate for leaf-shaped quadrilateral heat-generating body

<p indent=0mm>In this work, a constructal study of a leaf-shaped quadrilateral heat-generating body based on the bionic quadrilateral of the common leaf vein shape was performed by combining the constructal and entransy theories, thus allowing the optimal construct of the leaf quadrilateral heat-generating body to be derived. The effect of the number of intervals, i.e., the number of branches containing high thermal conductivity materials, <italic>n</italic>, and angle <italic>θ</italic> between the high thermal conductivity material in the branch and the center, on the optimal construction of the heat-generating body was also studied. The constructal differences of the heat-generating body were compared under the minimum entransy dissipation rate and minimum temperature difference. The results show that the mean heat transfer temperature difference of the heat-generating body is the smallest in the optimal constructal when the entransy dissipation rate is the lowest. With the increase in the number of intervals (<italic>n</italic>≥20), the optimal aspect ratio and minimum mean temperature difference of the heat-generating body decreased slightly. Therefore, increasing the complexity of the high heat conduction passage in the heat-generating body can decrease the mean heat transfer temperature difference. Different optimal constructs of the heat-generating body were obtained using the entransy dissipation rate and maximum temperature difference as the optimization objective; both provide more optimal solutions when the high thermal conductivity material of the branch and center are perpendicular. Furthermore, minimizing the entransy dissipation rate allowed for a smaller mean temperature difference to be obtained. Therefore, using the minimum entransy dissipation rate as the optimization objective can reduce the mean heat transfer temperature difference more effectively in a leaf-shaped quadrilateral heat-generating body.

From thermomass energy to dark energy: Re-exploration to the origin of dark energy

Dark energy constitutes 68% of the matter of our universe, which has been successfully used in the standard cosmological model to explain the phenomenon of cosmic acceleration. However, the scholars still have different opinions in the origin of dark energy, making it one of the most important unsolved problems in the modern cosmology. There are several candidates to explain the origin of dark energy, such as vacuum energy, scalar field theory, light pressure, etc. However, all these models are still in debate and we are far from a commonly agreed theory to understand the true nature of dark energy. In this report, we intend to re-explore some fundamental properties and the origin of dark energy from the perspective of thermomass theory in the framework of energy conservation principle. Thermomass theory is a newly developed theory in the field of heat transfer, including some new physical quantities, such as thermomass, thermomass velocity, thermomass energy, etc. Thermomass is the relativistic mass of heat and thermomass energy is the relativistic energy. Based on the thermomass theory, the heat transfer can be understood as the direct flow of thermomass under a certain temperature gradient. Then the principle of fluid mechanics can be used to solve the heat transfer problems and a general heat conduction law has been established. Some non-Fourier heat transfer phenomena under the extreme conditions, such as ultrafast laser heating, ultrahigh heat flux at nanoscales, can be well explained by using the general heat conduction law. Meanwhile, a simplified expression of thermomass energy was defined as entransy. Guided by a minimum entransy dissipation principle, the structure of a complicated heat exchanger network can be optimized to increase the energy efficiency. Both the general heat conduction law and entransy model have been experimentally validated. The thermomass theory have been widely accepted and applied in the field of thermal science. But a question still remains: The thermomass energy dissipates during the heat transfer process, where does it go? Actually, we find an answer that the dissipated thermomass energy is closely related with the dark energy. Under the normal temperature and pressure conditions, the order of magnitude of thermomass and its energy is much smaller than that of the static mass and its energy. In the beginning of the Big Bang, the temperature exceeds 1015°C and the thermomass energy equals to or even is larger than the energy of static mass. According to the energy conservation principle, the energy at high level, i.e., electrical energy, optical energy, mechanical energy, etc., will dissipate into the energy at low level, i.e., heat. But in the heat transfer process, heat (thermomass) is conserved, while the thermomass energy will dissipate into a lower level, “invisible” energy. This kind of energy has four features: Filling the whole space, ultra-low energy density, negative pressure and gradually accumulated with time. All these features are in consistence with the performance of dark energy. Hence, we hypothesize that the dark energy comes from the dissipated thermomass energy, which is the motivating force of the cosmic acceleration and forms the main body of our universe.

Analysis of elliptical thermal cloak based on entropy generation and entransy dissipation approach**Project supported by the National Natural Science Foundation of China (Grant Nos. 51606074 and 51625601) and the Fund from the Ministry of Science and Technology of China (Grant No. 2017YFE0100600).

In this work, we designed the elliptical thermal cloak based on the transformation thermotics. The local entropy generation rate distribution and entransy dissipation rate distribution were obtained, and the total entropy generation and entransy dissipation of different types of elliptical cloaks were evaluated. We used entropy generation approach and entransy dissipation approach to evaluate the performance of the thermal cloak, and heat dissipation analysis was carried out for models with different parameters. Finally, the optimized elliptical thermal cloak with minimum entropy generation and minimum entransy dissipation is found, and some suggestions on optimizing the structure of elliptical thermal cloak were given.

An inverse optimisation for heat exchangers with entransy dissipation minimisation

ABSTRACT A class of finite-time heat transfer processes (HTPs) for entransy dissipation minimisation is studied in this paper. Based on optimal control theory, the optimality condition is derived firstly, and then the general characteristics of heat transfer laws (HTLs) for three special temperature distributions including uniform temperature difference field, constant heat transfer rate per unit area, and constant entransy dissipation rate operations are obtained based on the optimality condition. The results show that the condition that the difference of temperature for the minimum entransy dissipation of heat transfer process (EDOHTP) is a constant is not only valid for Newtonian HTL, but also valid for generalised convective HTL and complex HTL .

Experiment and simulation method to investigate the flow within porous ceramic membrane

It is efficient to recover water and latent heat from flue gas by using a porous ceramic membrane. In this paper, an experimental and numerical simulation is used for studying the heat transfer and flow of fluid in the ceramic tube in a porous membrane. The experimental data shows that the inlet velocity of feed gas and porosity of membrane enhance the heat and mass transfer performance of membranes when the range of which is 0.65–2.87 m/s and 60–78% respectively. Based on the minimum entransy dissipation, the Lagrange multiplier method is used to deduce the optimal momentum equation, which is interpreted by user definition functions (UDF) of FLUENT 15.0. A numerical study is carried out by varying Reynolds number, thickness of condensate, and values of momentum loss in this paper. The results show that the mass flux of water recovery is 0.25 kg/m2.h when Re was in range of 2.17 × 102~1.13 × 103, thickness of condensation film (δcon) is close to 0.02 mm, and membrane porosity (ф) is close to 70%.

New thermodynamic analysis and optimization of performance of an irreversible diesel cycle

In this study, an irreversible Diesel cycle is investigated based on entransy method and optimization conducted by considering various scenarios. Entransy expressed as a heat transfer potential of a subject and it has begun to investigate as a new thermodynamic assessment parameter. This paper presents thermodynamical study of an irreversible Diesel cycle in order to optimize its performance. Moreover, four different strategies in the process of multiobjective optimization are proposed, and the outcomes are assessing separately. The first strategy is proposed to minimize the entransy dissipation rate and maximize the ecological coefficient of performance along with the maximum available work. Furthermore, the second one is suggested to minimize the entransy dissipation rate and maximize the ecological function along with the exergetic performance criteria. The third strategy is proposed to minimize ethe entransy dissipation rate and maximize the ecological function along with the thermal efficiency. Moreover, the fourth strategy is suggested to achieve the minimum entransy dissipation rate and maximum ecological function along with the entransy efficiency. Finally, the values of objective functions were obtained at the optimum conditions of each scenario; afterwards, compared with other scenarios to select the most appropriate one. Based on obtained results, maximizing ecological coefficient of performance is the most appropriate approach for optimization, since it leads to the maximum values of ecological function, exergetic performance criteria and thermal efficiency. In addition, in the fourth scenario the lowest entransy dissipation rate was achieved. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 1475–1490, 2018

Theoretical analysis of heat and mass transfer characteristics of a counter-flow packing tower and liquid desiccant dehumidification systems based on entransy theory

Abstract Dehumidifier and regenerator are the key components of a liquid desiccant dehumidification system. This paper examines the heat and mass transfer processes of a counter-flow packing tower using entransy analysis. Under ideal thermodynamic conditions, if NTUm of the counter-flow packing tower is infinite, the reversible process only exists when the inlet states of air and solution lie on the same iso-relative humidity line. In actual heat and mass transfer processes, the relative position of the inlet parameters of air and solution in the psychrometric chart will influence the entransy dissipation in the packing tower. Based on the analytic solution of temperature difference and humidity ratio difference between air and solution, minimum entransy dissipation is determined when the states of inlet air and solution lie on the same iso-relative humidity line. The influence of inlet characteristics can be quantified using an unmatched coefficient of inlet parameter (γ). This parameter is an indicator of the flow-path design and the system optimization. Furthermore, a practical application is presented by comparing three typical flow paths. The flow path with the smallest γ value reduces the required temperature of heat sources from 60 °C to 45 °C. The realization of such low-grade heat sources not only means high/efficient utilization of heat or solar energy, but also results in less waste heat.

Entransy dissipation minimization for generalized heat exchange processes

This paper investigates the MED (Minimum Entransy Dissipation) optimization of heat transfer processes with the generalized heat transfer law q ∝ (Δ(Tn))m. For the fixed amount of heat transfer, the optimal temperature paths for the MED are obtained. The results show that the strategy of the MED with generalized convective law q ∝ (ΔT)m is that the temperature difference keeps constant, which is in accordance with the famous temperature-difference-field uniformity principle, while the strategy of the MED with linear phenomenological law q ∝ Δ(T−1) is that the temperature ratio keeps constant. For special cases with Dulong-Petit law q ∝ (ΔT)1.25 and an imaginary complex law q ∝ (Δ(T4))1.25, numerical examples are provided and further compared with the strategies of the MEG (Minimum Entropy Generation), CHF (Constant Heat Flux) and CRT (Constant Reservoir Temperature) operations. Besides, influences of the change of the heat transfer amount on the optimization results with various heat resistance models are discussed in detail.

Optimization of equimolar reverse constant-temperature mass-diffusion process for minimum entransy dissipation

The mass entransy describes the mass-diffusion ability of the solution system, and the mass-diffusion process with the finite concentration difference always leads to the mass-entransy dissipation. This paper studies the equimolar reverse constant-temperature mass-diffusion process with Fick’s law (g ∝ Δ(c)). The optimal concentration paths for the MED (Minimum Entransy Dissipation) are derived and compared with those for the MEG (Minimum Entropy Generation) and CCR (Constant Concentration Ratio) operations. It is indicated that the strategy of the MED is equivalent to that of the CCD (Constant Concentration Difference) of the same component; whether the MED or the MEG is selected as the optimization objective, the strategy of the CCD is much better than that of the CCR.

Constructal design for blast furnace wall based on the entransy theory

Based on the entransy dissipation extremum principle for thermal insulation process, constructal design of blast furnace wall is performed in this paper. Optimal construct of the cooling stave in the furnace wall is obtained by using finite element method. The results show that there exists twice optimal axial diameter ratio and optimal cooling water velocity which makes the entransy dissipation rate of the blast furnace wall reach its critical minimum. Moreover, the optimal cross-section shape of the cooling pipe is approximately round. Within the discussed variation range of the axial diameter ratios, the minimum entransy dissipation rate is 2.73% less than the maximum entransy dissipation rate when the cooling water velocity is preset. Within the discussed variation range of the cooling water velocities, the minimum entransy dissipation rate is 2.09% less than the maximum entransy dissipation rate. Besides, increasing inlet temperature of cooling water appropriately is propitious to improve the global thermal insulation performance of the blast furnace wall while it cannot reduce the cooling water. The global thermal insulation performance of the furnace wall with approximately round cooling pipe is higher than that with composite-oblate cooling pipe.

Improvement of constructal tree-like network for “volume-point” heat conduction with variable cross-section conducting path and without the premise of optimal last-order construct

The constructal “tree-like” network has been proved an effective way for “volume-point” heat conduction. This paper aims to further improve the constructal “tree-like” network with the optimization objectives of minimizations of maximum thermal resistance and entransy dissipation rate respectively. By removing the constraint that the last-order construct must be optimal, and using variable cross-section conducting path, the maximum thermal resistance and entransy dissipation rate can be greatly reduced. It is also found that the optimal construct for minimum peak temperature is similar to the optimal one for minimum entransy dissipation rate. They hold the same shape and configuration, and the main difference of them is the shape of high-conductivity path.

Constructal optimization of variable cross-section insulation layer of steel rolling reheating furnace wall based on entransy theory

Based on the entransy dissipation extremum principle for thermal insulation process, the constructal optimizations of a variable cross-sectional insulation layer of the steel rolling reheating furnace wall with convective and compound heat transfer (mixed convective and radiative heat transfer) boundary conditions are carried out. An optimal construct of the insulation layer with minimum entransy dissipation rate can be obtained. Results show that the global thermal insulation performance of the variable cross-sectional insulation layer at minimum entransy dissipation rate is better than that of the constant cross-sectional one. The optimal constructs of the insulation layer obtained based respectively on the minimizations of the entransy dissipation rate and heat loss rate are different. The optimal construct of the insulation layer at minimum heat loss rate leads to a reduction of the energy loss, and that at minimum entransy dissipation rate leads to an improvement of the global thermal insulation performance. The difference between the optimal constructs of the variable cross-sectional insulation layer based on the minimizations of the entransy dissipation rate and the maximum temperature gradient is small. This makes the global thermal insulation performance and thermal safety of the insulation layer improved simultaneously. The constructal optimization of the insulation layer based on entransy theory can provide some new guidelines for the optimal designs of the insulation systems.

Performance optimization of two-stage latent heat storage unit based on entransy theory

In order to enhance the performance of the latent heat storage (LHS) process and provide the criterion for the selection and match of the multistage PCMs, the effects of PCMs melting temperatures on the heat storage rate, entransy dissipation rate and heat storage quality were numerically analyzed based on the entransy theory. For the single stage LHS unit, although decreasing the PCM melting temperature can augment the heat storage rate, the lower melting temperature causes larger entransy dissipation and reduces the heat storage quality. The larger heat storage rate results in the larger entransy dissipation rate, which is accordant with the entransy dissipation extremum theory. For the two-stage LHS unit with reasonably matching the PCMs melting temperature, the heat storage rate can be augmented and the entransy dissipation rate can be reduced. Then the optimization for the match of the two-stage PCMs melting temperatures was performed based on the entransy theory. The results show that there is an optimal match of the two-stage PCMs melting temperatures to achieve the maximum heat transfer rate or the minimum entransy dissipation rate. And the formulas for the optimum two-stage PCMs temperatures were presented, which can provide the criterions for the selection and match of the PCMs.

Numerical studies on the inherent interrelationship between field synergy principle and entransy dissipation extreme principle for enhancing convective heat transfer

In 1998 Guo et al. integrated the boundary-layer energy equation along the thermal boundary layer thickness, and noted that at outside boundary the temperature gradient is zero and the convection term is actually the inner production of vector velocity and temperature gradient, they found that for a fixed flow rate and temperature difference, the smaller the intersection angle between velocity and temperature gradient the larger the heat transfer rate. This idea is called field synergy principle (FSP). Later it has been shown that FSP can unify all mechanisms for enhancing single phase heat transfer. In 2007 Guo and his co-workers proposed a new concept: entransy to describe the potential of a body to transfer thermal energy and the entransy dissipation extreme principle (EDEP). It is indicated that for any heat transfer process the entransy of the system is always dissipated, which can be regarded as the indication of the irreversibility of the transport process. For a heat transfer process with given boundary temperature condition the best one has the maximum entransy dissipation, while for that with given boundary heat flux condition the best one has minimum entransy dissipation. The combination of the two cases is called the entransy dissipation extremum principle.The purpose of this paper is to reveal the inherent interrelationship between the ideas of field synergy principle and the entransy extremum principle. Numerical simulations are conducted for five examples of convective heat transfer. All the numerical results demonstrate the inherent consistency between FSP and EDEP.

Convective heat transfer optimization based on minimum entransy dissipation in the circular tube

Convective heat transfer optimization based on minimum entransy dissipation is studied in this paper. By setting entransy dissipation as optimization objective and power consumption as constraint condition, optimized fluid momentum equation with additional volume force for convective heat transfer are deduced by variational principle. Numerical investigations for convective heat transfer in a straight circular tube based on optimized governing equations are conducted. The results show that there exist longitudinal swirl flows with multi-vortexes in the tube, which leads to heat transfer enhancement at relatively small flow resistance. The present analysis for heat transfer and flow shows that this kind of optimized flow field can realize a far greater increase in heat transfer than that in flow resistance, which indicates that the investigated optimization method is useful in design of heat transfer enhancement.

Constructal entransy dissipation rate minimization for variable cross-section insulation layer of the steel rolling reheating furnace wall

A variable cross-section (distributed thickness and width) insulation layer of the steel rolling reheating furnace wall is investigated subjected to the constraints of the total volume and cross-sectional area of the insulation material. According to the entransy dissipation extremum principle of the thermal insulation process, the thickness of the insulation layer is optimized by taking minimum entransy dissipation rate as optimization objective, and the optimal construct of the insulation layer is obtained. The results show that when the temperature distribution of the furnace is linear with the length, the optimal thickness of the insulation layer with minimum entransy dissipation rate is linear with the dimensionless longitudinal position, which is evidently different from that with minimum heat loss rate. When the dimensionless temperature at the low temperature side ε=0, the minimum entransy dissipation rate of the insulation layer with distributed thickness is decreased by 33.33% than that with uniform thickness, and is decreased by 8.85% than that based on minimum heat loss rate. Essentially, the temperature gradient field obtained based on minimum entransy dissipation rate is more homogenous than that based on minimum heat loss rate, and the corresponding thermal stress performance is better. The decrement of the entransy dissipation rate tends to increase for the exponential temperature distribution case with a large exponent. Moreover, the insulation layer with triangular cross-section has a better global thermal insulation performance derived from entransy dissipation than those with rectangular and trapezoidal cross-sections. Therefore, the optimal construct obtained by adopting variable cross-section insulation layer (distributed thickness and width) and based on minimum entransy dissipation rate can improve the global thermal insulation performance of the insulation layer derived from entransy dissipation, and can reduce its average heat loss rate defined based on entransy dissipation simultaneously. The optimal construct obtained based on minimum entransy dissipation rate can provide a new scheme for the design of practical thermal insulation system different from that based on minimum heat loss rate, which can satisfy the different requirements in the design of practical thermal insulation systems.

Constructal optimization for &amp;ldquo;disc-point&amp;rdquo; vascular networks based on minimum entransy dissipation rate

For the specified total area of the disc and total volume of the vascular network, the constructal optimizations of the first order, second order and third order vascular networks are carried out by taking the minimizations of the entransy dissipation rate and entransy dissipation number, caused by heat transfer with finite temperature difference and flow resistance, as optimization objectives. The optimal constructs for each order vascular network with minimum entransy dissipation rate and entransy dissipation number are obtained. The results show that when the parameter B 1≥10-4, for the same dimensionless mass flow rate M *(1≤ M *≤102), the optimal constructs of the first order vascular network based on the minimizations of entransy dissipation rate and entropy generation rate are obviously different. For the second order vascular network, when the dimensionless mass flow rate locates at the range of 1≤ M *≤102, the magnitude orders of the entransy dissipations caused by heat transfer and flow resistance locate at the same level, and the optimal construct of the vascular network varies obviously with the change of the mass flow rate. For the same total volume of the vascular network and radius of the disc, when the dimensionless mass flow rates of the vascular networks are equal, the first order, second order and third order vascular networks almost exhibit the same performances of the entransy dissipation number; when the dimensionless pumping power satisfies , the minimum entransy dissipation number of the vascular network decreases with the increase in the order of the vascular network, and the performance of the vascular network can be improved by increasing the complexity of the vascular network in this case. Moreover, the performance of the vascular network is also optimized by taking complex index of entransy dissipation rate as optimization objective in this paper. The optimal results obtained in this paper can provide some guidelines for the designs of the vasculature from the point of view of heat transfer optimization.

Constructal Entransy Dissipation Rate Minimization for Gas-turbine Blade Cooling

Based on constructal theory, the construct of an elemental gas-turbine blade is optimized by taking minimum entransy dissipation rate as optimization objective. The optimal construct of the elemental gas-turbine blade is obtained. The results show that for the fixed total cross-sectional area and cavity faction of the elemental gas-turbine blade, there exists an optimal ratio of the cavity diameter to the thickness of the elemental blade which leads to the minimum dimensionless equivalent thermal resistance of the elemental blade; but there do not exist the optimal ratios of the cavity edge distance to the thickness, as well as the length to the thickness of the elemental blade which lead to the minimum dimensionless equivalent thermal resistance of the elemental blade. On the premise that the structural strength of the blade is allowed, the increase of the cavity fraction, the decrease of the cavity edge distance, and the slenderness of the elemental blade will help to improve the global heat transfer performance of the elemental blade. The optimal constructs of the elemental blade based on the minimizations of entransy dissipation rate and maximum temperature difference are different. The average heat transfer temperature difference of the elemental blade based on the minimization of entransy dissipation rate can be more effectively reduced compared with that based on the minimization of maximum temperature difference, and its global heat transfer performance is obviously improved. Moreover, the global heat transfer performance of the elemental blade can also be obviously improved by using the multi-scale constructal optimization of the cooling cavity of the elemental blade.