Finite Time Thermodynamic Analysis Research Articles

Finite time thermodynamic optimization for performance of absorption energy storage systems

Absorption energy storage (AES) has attracted worldwide attention due to the high energy storage density and environmental friendliness. To optimize the performance of the AES system, a finite time thermodynamic (FTT) model considering some influencing factors such as time, heat transfer area, heat transfer temperature difference, internal friction and dissipation has been developed in this paper. A new concept of ratio of charging and discharging time is proposed. The general relation of the energy storage efficiency, energy storage rate and energy release rate are induced based on FTT analysis. The distribution of the total thermal conductivity was optimized under the condition of a certain total thermal conductivity and the optimized maximum cooldown release rate has been increased by 14%. The optimal operating conditions of the AES system are obtained. Furthermore, the influences of the internal irreversibility, ratio of charging and discharging time and heat source temperatures on the performance of the AES system are analyzed. The research results can provide theoretical basis and guidance for the AES system design and optimization.

Finite-time thermodynamic and economic analysis of Rankine Carnot battery based on life-cycle method

Rankine Carnot battery (R-CB) has a great potential in renewable energy-to-grid integration, and the theoretical thermodynamic performance is inaccurate because of the dynamic heat transfer processes and system performance. In this paper, an R-CB system consisting of a heat pump, a heat engine cycle, and a sensible heat storage tank was established. The finite-time thermodynamic model considering the irreversible loss of energy transfer and conversion processes was proposed. Based on the combination of finite-time thermodynamic model and life-cycle method, the levelized cost of energy storage model was established for the combination of economic and energy performance. Furthermore, evaporation temperature, heat storage temperature, temperature difference of shared heat exchanger, and shared heat transfer area were adopted as main variables to conduct the global optimization and parametric analysis of the system. The simulation is based on an R-CB system with a storage capacity of 10 MW/6h, and the results showed the optimized system roundtrip efficiency was 78.1%, and the levelized cost of storage (LCOS) was 0.329 $/kWh with an evaporation temperature of 100 ℃. The roundtrip efficiency increased from 25.6% to 78.1% with the evaporation temperature rising from 60 to 100 ℃, while LCOS decreased by 45.8 %. Reducing the highest heat storage temperature effectively increased the roundtrip efficiency and reduced the heat storage cost, while decreasing the LCOS. The increase in roundtrip efficiency, which was obtained by reducing the shared heat exchange temperature difference and increasing the shared heat transfer area, was the primary factor in reducing the LCOS. The combination of finite-time thermodynamics and the life-cycle method in this paper may provide a more realistic evaluation approach for measuring the technical and economic potential of R-CB systems.

Finite time thermodynamic analysis and optimization of water cooled multi-spilit heat pipe system (MSHPS)

• Energy saving in data centers is increasingly with the developing IT industry. • An accurate performance and evaluation model based on time cycle is proposed. • An periodic integral energy efficiency model is proposed. • The refrigerant flow distribution characteristic of MSHPS was built and tested. • The proposed method is fit for analysis of MSHPS and the real pipe-net systems. This study focuses on the heat transfer characteristics of the evaporation terminal, the cool distribute unit (CDU) and refrigerant flow distribution of a water cooled multi-spilit heat pipe system (MSHPS) used in data center. The finite time thermodynamic analysis, the exergy method and the software SIMULINK was employed to build the simulation model of the combined system. The results show that the IT servers should concentrate on arranging at the location below 1.3 m. The CDU has a heat transfer of about 74 J in a period of 6 s. And the optimum flow rate of the CDU is 0.82 kg/s. The flow distribution characteristic of a CDU which connect 2 heat pipe evaporator terminals of 6 kW was calculated, and the working fluid is R22. Then the free cooling time,part time free cooling and energy saving potential in major cities of China were analysised. The energy saving potential is from 61% to 25%. The results are of great significance for the operational control and practical application of a MSHPS and other pipe-net systems.

Finite time thermodynamics analysis and research of pulsating heat pipe cold storage device

Phase change energy storage technology can effectively solve the energy mismatch in space and time. There are many disadvantages of phase change materials (PCMs), such as high supercooling, phase separation and poor heat transfer performance. As a new type of heat exchange structure, pulsating heat pipe has the advantages of simple structure, high heat transfer coefficient and good economic behavior. The system efficiency can be greatly improved by using pulsating heat pipe combined with cold storage technology. A set of pulsating heat pipe type cold storage device is developed, the finite time thermodynamic analysis is carried out, and the correlation between heat pipe efficiency and power is established. The three-dimensional physical model of pulsating heat pipe is simulated and verified by experiments. The experimental results show that in the cold storage stage, with the increase of the filling rate, the greater the pressure is, the better the heat transfer effect is; in the cold release stage, with the decrease of the filling rate, the smaller the pressure is, the better the heat transfer effect is.

Finite time thermodynamic analysis of water cooled multi-spilit heat pipe system

Finite time thermodynamic analysis of water cooled multi-spilit heat pipe system

Finite-time thermodynamics modeling and analysis on compressed air energy storage systems with thermal storage

The charging and discharging processes of compressed air energy storage (CAES) systems are operated separately, and their characteristics depend on time strongly. In addition, CAES systems typically consist of certain scales of thermal storage and air storage units. The size of these units has a significant effect on system performance. As time and size factors are usually involved and analyzed through finite-time thermodynamics, it can be applied for analyzing and optimizing CAES systems properly. In this paper, the finite-time thermodynamics models for CAES systems with thermal storage (TS-CAES) including single-stage and multi-stage configurations are first established. Equations of TS-CAES system efficiency are innovatively derived, with time and size items being clearly expressed and decoupled. Moreover, the well-built unbalanced factors among compressor/expander stages are used for investigating the coupling relationship. The system efficiencies with charging/discharging time, heat exchange area, unbalanced factors and other key parameters are calculated. The finite-time thermodynamic boundary of TS-CAES system is obtained. It is found that the effect of finite time and finite size on the system efficiency is in a certain range, and the optimal heat transfer conductance under a certain finite storage/release time is attained. System efficiency decreases obviously with the increase of pressure/expansion ratio unbalance. The equilibrium of the pressure loss coefficient rather than the absolute value of the pressure loss can achieve higher efficiency. Positive matching of pressure ratio/expansion ratio and compressor efficiency/expander efficiency can result in obvious positive effects.

English

English

Finite time thermodynamic analysis of water cooled multi-spilit heat pipe system

Energy saving in data centers is increasingly important along with the rapidly developing IT industry. A integrated heat pipe air conditioning (AC) system which used chilled water unit and heat pipe heat exchanger (HPHE) was proposed.With the meteorological parameter of Changde city (31°53′N and 117°15′E) as the reference. The thermodynamic simulation software SIMULINK was employed in build the simulation model of the combined system. And it is compared with the traditional air-conditional system. The system include heat pipe evaporator cooling deliver unit (CDU) and the cold source. A time integral model for heat transfer of heat pipe evaporator is proposed. A heat pipe evaporator of a 12KW in the company was taking as an example. The results show that the time period of working fluid passing through the heat exchanger is about 6 seconds. When the dry degree is greater than 0.72, the heat transfer efficiency is low. When arranging the IT server, we should concentrate on the location below 1.3 meters. The CDU was treated as a condenser. Then, the cooling source is vapor compressor. The finite time thermodynamic and the exergy method were employed to analysis the heat exchanger and the compress processes.The results show that the former one has saved 26% of the energy. Then the using time and energy saving potential in major cities of China were investigated and studied.

Exergetic, ecological and thermo-economic (3E) optimization of an absorption heat pump with heat resistance, heat leakage and two internal irreversibilities: Comparison

The multi-objective optimization of a three-heat-reservoir absorption heat pump (THR AHP) is used mainly considering three objective functions: exergetic performance criterion (EPC), exergy-based ecological criterion (E) and thermo-economic criterion (F). Indeed, the exergy, ecological and thermo-economic criteria are highlighted analytically. This is done by using the law of convective heat exchanges between the working fluid and the different components and finite time thermodynamics analysis. This is to determine the optimum operating points of the system by minimizing exergy destruction rate, the environmental impact and the costs of capital and energy consumed. Also, the parameters taken into account influencing the performance of the absorption heat pump are the heat resistances, the heat leakages, the thermo-economic parameter and the two internal irreversibility factors in particular that between the evaporator-condenser assembly. However, the Flowchart optimization methodology made it possible to deduce that the system presents a significant advantage at the maxima of the F and the EPC criteria in terms of coefficient of performance. Nevertheless, the THR AHP presents a significant advantage at the maximum of the EPC in terms of exergy destruction rate and at the maximum of the E in terms of specific heating load and exergy output rate.

Finite time thermodynamic analysis of quantum Otto heat engine with squeezed thermal bath

We investigate the finite time performance of reciprocating quantum Otto heat engine coupled to squeezed hot reservoir. We emphasize the converged limit cycle where each stroke is performed in finite time. To fully exploit the quantum availability provided by the squeezed bath, an optimal frequency protocol in the work extraction stroke is explicitly proposed. The power output is optimized with respect to the hot and cold isochore times. Thermodynamic analysis shows that for a wide range of squeezing parameters, efficiency at maximum power exceeds the generalized Curzon–Ahlborn efficiency defined by the effective temperature of the squeezed bath.

Efficiency at Maximum Power of Dissipative Thermoelectric Generators: A Finite-time Thermodynamic Analysis

In this paper we analyze the thermodynamic efficiency expected for a fully dissipative thermoelectric generator (TEG) operating under stationary conditions at a finite rate. Although a finite-time thermodynamic analysis of TEGs has been aimed at since long time, no complete theory is available yet. The state of the art of theory is reviewed, and a simple expression for the maximum achievable efficiency of TEGs operating under fully irreversible conditions is obtained. This also sets a reference efficiency for forthcoming studies of nonstationary operation of TEGs.

Finite Time Thermodynamic Analysis of a Real Vapour Absorption Refrigeration System with and without Heat Leak

This article presents finite time thermodynamic analysis of a real vapour absorption refrigeration system taking into account both external as well as internal irreversibility. The complete VAR model is assumed to be consisting of two sub-systems. One sub-system (generator-absorber assembly) is assumed as an irreversible heat engine cycle whereas another sub-system (evaporator-condenser assembly) is assumed as an irreversible refrigeration cycle. This study analyzes the effect of presence of heat leak on performance of irreversible (real) vapour absorption refrigeration (VAR) system. This is achieved by adding a heat leakage term into an irreversible model of VAR system. Overall coefficient of performance (COP) of the VAR system is optimized with respect to source/sink side heat exchanger areas using Langrangian multiplier method. Furthermore, the effects of the variations in the cycle parameters on performance deviation of the VAR system are compared with and without heat leak. Results show that effect of rate of heat leak is significant along with the other irreversibilities variations on performance deviation of the VAR system.

Multi-objective optimization in a finite time thermodynamic method for dish-Stirling by branch and bound method and MOPSO algorithm

There are various analyses for a solar system with the dish Stirling technology. One of those analyses is the finite time thermodynamic analysis. By the finite time thermodynamic analysis, the total power of system can be obtained by calculating the process time. In this study, the convection and radiation heat transfer losses from collector surface, the conduction heat transfer between hot and cold cylinders and cold side heat exchanger have been considered. During this investigation, the four objective functions have been optimized simultaneously. These objective functions are included of the power, efficiency, entropy and economic factors. In addition to the four-objective optimization, three-objective, two-objective and single-objective optimizations have been done on the dish-Stirling model. In this study, the algorithm of MOPSO with post-expression of preferences is used for multi-objective optimizations while the Branch and Bound algorithm with Pre-expression of preferences is used for single-objective and multi-objective optimizations. In case of multi-objective optimizations with post-expression of preferences, Pareto optimal front are obtained, afterward by implementing the Fuzzy, LINMAP and TOPSIS decision making algorithms, the single optimum results can be achieved. At the end, the comparison of the results shows the benefits of MOPSO in optimizing dish Stirling finite time thermodynamic equations.

Finite time thermodynamic analysis of small alpha-type Stirling engine in non-ideal polytropic conditions for recovery of LNG cryogenic exergy

Abstract In the paper, a second order thermodynamic analysis of a small scale alpha-type Stirling engine is presented. The developed mathematical model is based on the Finite Time Thermodynamics (FFT) approach and it is derived from the differential time dependent equations of energy and mass conservation. The engine model consists of three spaces: compression, expansion and regenerator. In contrast to available models, the model presented in this paper assumes polytropic processes in the compression and expansion spaces, which corresponds to the non-ideal heat transfer in these spaces. The results, obtained using the developed second order model, were compared with the results obtained using the Computational Fluid Dynamics (CFD) analysis of the same engine. A very good agreement between the second order model and the CFD model was achieved. Finally, the developed model was applied to analyse potential to recover cryogenic exergy of the Liquefied Natural Gas (LNG). The paper presents the results of the dimensional upscaling of the engine and the influence of the average working pressure. It was revealed that increasing the size of the engine or the average working pressure moves the engine to practically unachievable working conditions.

A parameter optimization method for actual thermal system

The objective of the parameter optimization of thermal system is to increase the system efficiency and decrease the cost of unit output power under the condition which the total output power can meet the actual requirements in energy applications. In this paper, a new parameter optimization method for actual thermal system was proposed, which was called the Equivalent Transformation Constant State Finite-time Thermodynamic Analysis Method and had two calculation steps. The first step was choosing the optimum efficiency under the principle of taking into account both output power and efficiency weights, and the second step was calculating the optimum total heat transfer coefficient ratio and other concerned parameters with the optimum efficiency fixed. The related calculation principles and formulas for parameter optimizations of this method were given. That provided the guiding theoretical basis for actual thermal system efficiency increase and cost decrease of unit output power.

Soft computing based multi-objective optimization of Brayton cycle power plant with isothermal heat addition using evolutionary algorithm and decision making

An irreversible regenerative Brayton cycle model considering internal and external irreversibilities is developed in matrix laboratory (MATLAB) simulink environment and thermodynamic optimization based on finite time thermodynamic analysis along with multiple criteria is implemented. Evolutionary algorithms based on second version of non-dominated sorting genetic algorithm (NSGA-II) and multi-objective evolutionary algorithm based on decomposition (MOEA/D) are employed to optimize power output and thermal efficiency simultaneously where isobaric-side heat exchanger effectiveness (εH), isothermal-side effectiveness (εH1), sink-side effectiveness (εL), regenerator-side effectiveness (εR), and working medium temperature (T5) are taken as design variables. The optimal values of aforementioned design variables are investigated. Pareto optimal frontiers between dual objectives are obtained and the final optimal values of power output and thermal efficiency are chosen via LINMAP, fuzzy Bellman–Zadeh, Shannon’s entropy and TOPSIS decision making approaches. The obtained results are compared and the best one is preferred. An improvement in thermal efficiency from 18.29% to 21.10% is reported. In addition to this, variations of different input parameters on the power output and thermal efficiency are conferred and presented graphically. With the goal of error investigation, the maximum and average errors for the obtained results are designed at last.

Thermodynamic modeling and multi-objective optimization of two stage thermoelectric generator in electrically series and parallel configuration

Two-stage exo-reversible thermoelectric generator considering internal irreversibilties is developed in electrically series and electrically parallel configurations in matrix laboratory simulink environment based on finite time thermodynamic analysis. Simultaneous optimization of proposed system for maximizing power output, thermal efficiency and minimizing entropy generation is employed based on second version of non-dominated sorting genetic algorithm, where working electrical current, number of thermoelectric elements in top and bottom stage, temperature of hot side and cold side are considered as design variables. The present work explores optimal values of above performance parameters and design variables with the comparison of two-stage thermoelectric generator in two modes. For triple and dual objective functions, Pareto frontier is obtained and using four decision variable techniques viz. Fuzzy Bellman–Zadeh, Shannon’s entropy, LINMAP and TOPSIS best optimal solution is selected. With the current study, it has been proved that triple-objective optimization gives much lower difference between ideal and obtained solution, termed as deviation index, as compared to the dual objective optimization.

Finite-time thermodynamic analysis for a chemically driven heat engine based on probability theory

This paper studies the problem of power optimization of chemically driven heat engine obeying Arrhenius law kinetics. Respectively, the first and second order reaction kinetics models taking the rate coefficients of the chemical reaction as finite-time constraints has been analyzed by the methods of finite-time thermodynamics with the synthetical consideration about the optimal configuration of the coupling process between chemical reaction and heat engines, and the effects of the finite-time thermodynamic characteristics of the coupling relation between chemical reaction and heat engine on the power optimization has been obtained. Combining the numerical results of this paper and the previous analysis, there is always a finite optimal flow rate in the reactor that yields maximum power when chemical reactions drive these three kinds of heat engine models, but a generalized Carnot heat engine driven by a chemical reaction can obtain the maximum power output in the practical case, the optimal flow rate in which the model of a generalized Carnot engine obtains the maximum power output can make the fuel efficiency of the system approaches the optimal value simultaneously. The finite-time thermodynamic method based on probability analysis can more accurately describe various performance parameters of thermodynamic system, this paper establishes the probability model of the first order reaction kinetics theory by using the probability analysis method, and obtains the power and fuel efficiency fluctuation bounds of the chemically driven heat engines. The results can not only include the mean value that is the only information obtained by classical method, but also take the fluctuations in microscale into account. The probabilistic method can provide more abundant information in the prediction of practical performance for the micro-size systems.

Optimization of powered Stirling heat engine with finite speed thermodynamics

Popular thermodynamic analyses including finite time thermodynamic analysis was lately developed based upon external irreversibilities while internal irreversibilities such as friction, pressure drop and entropy generation were not considered. The aforementioned disadvantage reduces the reliability of the finite time thermodynamic analysis in the design of an accurate Stirling engine model. Consequently, the finite time thermodynamic analysis could not sufficiently satisfy researchers for implementing in design and optimization issues. In this study, finite speed thermodynamic analysis was employed instead of finite time thermodynamic analysis for studying Stirling heat engine. The finite speed thermodynamic analysis approach is based on the first law of thermodynamics for a closed system with finite speed and the direct method. The effects of heat source temperature, regenerating effectiveness, volumetric ratio, piston stroke as well as rotational speed are included in the analysis. Moreover, maximum output power in optimal rotational speed was calculated while pressure losses in the Stirling engine were systematically considered. The result reveals the accuracy and the reliability of the finite speed thermodynamic method in thermodynamic analysis of Stirling heat engine. The outcomes can help researchers in the design of an appropriate and efficient Stirling engine.

Multi-objective thermodynamic optimization of an irreversible regenerative Brayton cycle using evolutionary algorithm and decision making

Abstract Brayton heat engine model is developed in MATLAB simulink environment and thermodynamic optimization based on finite time thermodynamic analysis along with multiple criteria is implemented. The proposed work investigates optimal values of various decision variables that simultaneously optimize power output, thermal efficiency and ecological function using evolutionary algorithm based on NSGA-II. Pareto optimal frontier between triple and dual objectives is obtained and best optimal value is selected using Fuzzy, TOPSIS, LINMAP and Shannon’s entropy decision making methods. Triple objective evolutionary approach applied to the proposed model gives power output, thermal efficiency, ecological function as (53.89 kW, 0.1611, −142 kW) which are 29.78%, 25.86% and 21.13% lower in comparison with reversible system. Furthermore, the present study reflects the effect of various heat capacitance rates and component efficiencies on triple objectives in graphical custom. Finally, with the aim of error investigation, average and maximum errors of obtained results are computed.