Finite-Time Thermodynamic Simulation of Circulating Direct Condensation Heat Recovery on Chillers

A time series model is used in this paper to describe the progress of circulating direct condensation heat recovery of the compound condensing process (CCP) which is made of two water cooling condensing processes in series for a centrifugal chiller in the paper. A finite-time thermodynamics method is used to set up the time series simulation model. As a result, an upper bound of recoverable condensation heat for the compound condensing process is obtained which is in good agreement with experimental result. And the result is valuable and useful to optimization design of condensing heat recovery.

Thermodynamics of a Shallow Solar Still

A detailed summary of the most relevant aspects of the thermodynamics of a shallow solar still is presented, including historical features not often found in the literature. Solar distillation has grown from applying empirical knowledge to advanced modeling and simulation. Geometrical, environmental and operational parameters of the solar still to heat transfer phenomena including evaporation and condensation, are taken into account in this overview, giving a comprehensive structure and classification to the study of solar stills from the thermodynamic point of view. The article describes global parameters, such as solar radiation, wind speed and thermal insulation among others and how they have been taken into account in the literature. Also, a distinction between internal and external heat transfer phenomena is proposed for clarification. Exergy balance is included to account for thermodynamic imperfections in the several processes inside the solar still.

关于CA效率、不可逆热机和有限时间热力学发展

著名的Curzon-Ahlborn效率η_(CA)是由El-Wakil于1962年最先导出的,不可逆热机的概念也是El-Wakil最早建立的,有限时间热力学正在由物理学向工程学发展,并将使工程热力学产生巨大变革。

混凝土热力学特性和收缩特性的宏细观研究

介绍了三种有代表性的混凝土细观力学数值模型,总结了混凝土热力学特性的影响因素及新兴预测技术的研究情况,阐述了温度收缩和自收缩两种变形的发生机理、模型预测及近年研究热点。评述了研究中存在的问题并对未来发展趋势提出了建议。

Consistency of optimizing finite-time Carnot engines with the low-dissipation model in the two-level atomic heat engine

The efficiency at the maximum power(EMP)for finite-time Carnot engines established with the low-dissipation model,relies significantly on the assumption of the inverse proportion scaling of the irreversible entropy generationΔS^(ir)on the operation timeτ,i.e.ΔS^(ir)∝1/τ.The optimal operation time of the finite-time isothermal process for EMP has to be within the valid regime of the inverse proportion scaling.Yet,such consistency was not tested due to the unknown coefficient of the 1/τ-scaling.In this paper,we reveal that the optimization of the finite-time two-level atomic Carnot engines with the low-dissipation model is consistent only in the regime ofη_(C)<<2(1-δ)/(1+δ),whereη_(C)is the Carnot efficiency,andδis the compression ratio in energy level difference of the heat engine cycle.In the large-η_(C)regime,the operation time for EMP obtained with the low-dissipation model is not within the valid regime of the 1/τ-scaling,and the exact EMP of the engine is found to surpass the well-known boundη_(C)=η_(C)/(2-η_(C)).

“W”型火焰锅炉屏过爆管原因分析及对策

针对于某发电厂新进投产的600 MW机组"W"火焰锅炉在运行过程中遇到的受热面超温爆管、减温水量不足以及氧量偏低、飞灰可燃物含量偏高的问题,提出了一系列相应的解决方案来防止锅炉受热面超温和增加减温水流量,并对锅炉进行了一定的燃烧调整,为同类型锅炉的可靠稳定运行提供了依据。

Thermodynamic Analysis and Experimental Research of Water-Cooled Small Space Thermoelectric Air-Conditioner

This paper aims to find a more general analysis method for the refrigeration performance,and to design a high efficiency modular cooling structure of water-cooled plate.A new analysis method,namely current and refrigeration rate density analysis,is proposed.The general refrigeration performance calculation equations are obtained.A finite-time thermodynamic model of the thermoelectric device is established considering Thomson effect.The basic structure of water-cooled thermoelectric air-conditioner is designed and the specific calculation method is given.The influences of input current density,filling factor and heat transfer conditions on refrigeration performance of the thermoelectric air-conditioner are analyzed,which is compared with refrigeration performance of air-cooled thermoelectric air-conditioner.The results show that the maximum refrigeration rate density of the water-cooled thermoelectric air-conditioner is 8.65 k W/m^(2),and the maximum coefficient of performance(COP)is 2.27 in the case of the cooling temperature differenceΔT=5 K.Compared withΔT=5 K,the maximum refrigeration rate density and the maximum COP ofΔT=15 K decreases by 27.98%and 76.65%,respectively.At the filling factorθ=0.43,the refrigeration rate density and COP are 2.57 k W/m~2 and 1.24,respectively.The experimental device of thermoelectric air-conditioner is established to verify the model.The experimental results show that the maximum value of input current and COP is 4 A and 0.95 with the efficient water-cooling method,respectively.The experimental data coincides with the theoretical calculation,which shows the validity of the analysis method and cooling method.

Thermodynamic Analysis and Optimization of an Irreversible Maisotsenko-Diesel Cycle

So far,Maisotsenko cycle has been applied to many fields such as heating ventilation and air-conditioning,power industry,chemical production,and so on.A lot of researches about classical thermodynamic analyses of Maisotsenko cycle have been made.A new cycle model of combined Diesel and Maisotsenko cycles considering heat transfer loss(HTL),piston friction loss(PFL)and internal irreversible loss(IIL)was proposed in this paper.By using the finite time thermodynamic(FTT)theory,the power and efficiency performances of the Maisotsenko-Diesel cycle(MDC)were studied.Effects of mass flow rate(MFR)of water injection in the Maisotsenko air saturator(MAS)and the other parameters related to the design of Diesel engine on the optimal cycle performances were analyzed.Furthermore,it was testified that irreversible MDC was superior than conventional irreversible Diesel cycle in both power output and thermal efficiency.The results can expand the application of Maisotsenko cycle(M-cycle)and provide some theoretical guidelines for the practical devices.

Power and efficiency optimizations for an open cycle two-shaft gas turbine power plant

In finite-time thermodynamic analyses for various gas turbine cycles,there are two common models:one is closed-cycle model with thermal conductance optimization of heat exchangers,and another is open-cycle model with optimization of pressure drop(PD)distributions.Both of optimization also with searching optimal compressor pressure ratio(PR).This paper focuses on an open-cycle model.A two-shaft open-cycle gas turbine power plant(OCGTPP)is modeled in this paper.Expressions of power output(PP)and thermal conversion efficiency(TCE)are deduced,and these performances are optimized by varying the relative PD and compressor PR.The results show that there exist the optimal values(0.32 and 14.0)of PD and PR which lead to double maximum dimensionless PP(1.75).There also exists an optimal value(0.38)of area allocation ratio which leads to maximum TCE(0.37).Moreover,the performances of three types of gas turbine cycles,such as one-shaft and two-shaft ones,are compared.When the relative pressure drop at the compressor inlet is small,the TCE of third cycle is the biggest one;when this pressure drop is large,the PP of second cycle is the biggest one.The results herein can be applied to guide the preliminary designs of OCGTPPs.

Abstract models for heat engines

We retrospect three abstract models for heat engines which include a classic abstract model in textbook of thermal physics,a primary abstract model for finite-time heat engines,and a refined abstract model for finite-time heat engines.The detailed models of heat engines in literature of finite-time thermodynamics may be mapped into the refined abstract model.The future developments based on the refined abstract model are also surveyed.

Optimization of the power, efficiency and ecological function for an air-standard irreversible Dual-Miller cycle

This paper establishes an irreversible DualMiller cycle (DMC) model with the heat transfer (HT) loss, friction loss (FL) and other internal irreversible losses. To analyze the effects of the cut-off ratio (ρ) and Miller cycle ratio (rM) on the power output (P), thermal efficiency (η) and ecological function (E), obtain the optimal popt and optimal rMopt, and compare the performance characteristics of DMC with its simplified cycles and with different optimization objective functions, the P,η and E of irreversible DMC are analyzed and optimized by applying the finite time thermodynamic (FTT) theory. Expressions of P,η and E are derived. The relationships among P,η, E and compression ratio (ε) are obtained by numerical examples. The effects of ρ and rM on P,η, E, maximum power output (MP), maximum efficiency (MEF) and maximum ecological function (ME) are analyzed. Performance differences among the DMC, the Otto cycle (OC), the Dual cycle (DDC), and the Otto-Miller cycle (OMC) are compared for fixed design parameters. Performance characteristics of irreversible DMC with the choice of P,η and E as optimization objective functions are analyzed and compared. The results show that the irreversible DMC engine can reach a twice-maximum power, a twicemaximum efficiency, and a twice-maximum ecological fiinction, respectively. Moreover, when choosing E as the optimization objective, there is a 5.2% of improvement in η while there is a drop of only 2.7% in P compared to choosing P as the optimization objective. However, there is a 5.6% of improvement in P while there is a drop of only 1.3% in rj compared to choosing as the optimization objective.

Minimum mass-entransy dissipation profile for one-way isothermal diffusive mass-transfer process with mass-resistance and massleakage

As a new concept,mass-entransy is one of the twins in the core of entransy theory.It can describe mass-transfer ability for masstransfer 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.