湿空气焓值计算及其对HAT循环分析的影响

以湿空气焓值为研究对象，按理想混合气体模型和实际混合气体模型分别对含湿量恒定条件下空气的焓值进行计算比较。结果表明：在接近饱和的状态下，实际混合气体效应不可忽略，在HAT循环饱和过程参数范围内两者的最大偏差接近7％。因此，HAT循环饱和器分析应按实际混合气体模型计算湿空气的焓值。图5参5     

燃气轮机工质普朗特数的计算方法

燃气轮机工质的传热计算和温度场分析,需要计算得出工质的定压比热容、动力黏度、导热系数和普朗特数。介绍了混合气体普朗特数的计算方法,给出了湿空气的上述参数的修正方法和计算结果,得出标准烟气的计算修正结果,并采用REFPROP数据库和实验数据分别对湿空气和烟气的计算结果进行了验证。结果表明,采用此普朗特数计算方法和修正方法,结果的相对偏差在工程上是可以接受的,该方法可以用来计算绝大部分燃气轮机工质的普朗特数。研究成果可为燃气轮机工质的传热计算和温度场分析提供参考。     

多元可燃性混合气体最大爆炸压力的简化计算

研究多元可燃性混合气体在定容、绝热情况下发生爆炸时最大爆炸压力的简化计算方法.分析了多元可燃性混合气体煤气的组分及各组分气体的热力学性质,根据热力工程学计算出混合气体的热力学性质,并将该混合气体作为单一气体简化其热化学反应方程式,提出了计算混合气体反应终态温度的方法,在此基础上求解出不同煤气体积分数下最大爆炸压力的理论值;利用爆炸特性参数测试系统实测了对应的不同煤气体积分数下的最大爆炸压力值,并与理论计算值进行了比较分析.结果表明,简化计算方法所得的多元可燃性混合气体最大爆炸压力与实验测试结果基本吻合,为可燃性气体爆炸工程应用提供了一个有效的近似估算方法.     

二元可燃混合气体爆炸上限的理论预测

确定了影响可燃气体爆炸上限的特征理化因素,如化学计量浓度、临界压力和燃烧热等,构建了混合物理化参数来表征混合气体的理化特征.将这些参数作为输入变量,分别应用多元线性回归和多元非线性回归方法对二元可燃混合气体爆炸上限与上述混合物理化参数之间的内在相关性进行研究,建立了根据混合物理化参数预测二元可燃混合气体爆炸上限的数学模型.两种方法对训练集的预测平均绝对误差分别为2.39％和1.272％;对测试集的预测平均绝对误差分别为2.185％和1.888％.结果表明,两种模型爆炸上限的预测值与文献值均符合较好,在可接受误差范围之内.该方法的提出为工程上提供了一种预测二元可燃混合气体爆炸上限的新方法.     

三分仓回转式空气预热器积灰分段监测模型研究

针对三分仓回转式空气预热器热段和冷段积灰分段监测的需求,基于空气预热器的传热模型,定义空气预热器利用系数作为清洁因子并建立积灰分段监测模型.通过分析空气预热器实时运行参数,根据热平衡原理确定了清洁因子计算步骤.以某1 000MW超超临界直流锅炉的三分仓回转式空气预热器为例,研究了热段、冷段清洁因子在空气预热器积灰和吹灰时的变化趋势.结果表明:根据所建模型计算出的分段清洁因子变化趋势在稳定负荷下能够反映此空气预热器的分段积灰情况,而在变负荷情况下虽有一定偏离,但由于电厂变负荷工况下很少吹灰故影响较小;该积灰监测模型可作为三分仓回转式空气预热器热冷分段积灰监测的有效手段.     

燃气轮机的湿空气循环性能分析与试验

对燃气轮机湿空气循环的性能进行了分析,建立了湿化工质的热物性计算模型,并对基于微型分轴燃气轮机湿空气循环装置的性能进行了初步试验.试验结果表明,空气加湿后燃气轮机系统的运行性能有明显改善,与简单循环系统相比,比功和效率都有很大的提高.根据试验条件进行的模拟计算结果与试验结果能很好地吻合.     

湿空气物理性质计算方法研究

为方便热工专业工程技术人员,对不同条件下的湿空气各状态参数的实际查询需要,以IAPWS-IF97和ASHRAE提供的计算公式为基础,提出一种以Excel VBA为计算平台的湿空气露点温度和湿球温度计算方法。计算程序由VBA语言编写,湿球温度的求解采用循环迭代和对比分析为计算模型,通过对初始输入参数进行不断的对比和修正,最终解出正确的湿球温度。结果表明,该计算模块使用方便,可操作性强,其计算精度能满足常规的热力工程设计及计算需要,也可为湿空气参数的查询应用及优化计算提供参考。     

基于遗传算法的电池包高效热管理流道优化

电池包的热管理对于避免过热和热失控等问题至关重要,必须采用主动冷却系统来保持电池的安全温度,提高电池的性能和寿命.液体冷却是一种有效的冷却方法,但是关于结构参数对冷却效果影响的参数化研究仍然缺乏.本文采用了一种基于微通道硅基冷板的液体冷却方法,采用计算流体力学方法建立流-固耦合散热模型.采用拉丁超立方法生成参数组合样本,通过多目标遗传优化方法开发出具有高效散热性能和较低能耗的冷却系统.实验结果表明,优化后的液冷系统能够有效地控制模块的温度低于45℃,单体电池间的温度偏差也可以控制在5℃的小范围内.本研究结果将为电池组件热管理系统的设计和优化提供有效的研究思路,有助于推动电池在实际产品上的应用.     

HAT循环饱和器工质(火用)计算分析及(火用)效率

饱和器是HAT循环中的关键部件,对其性能的认识关系到整个系统的性能分析。运用的方法,计算了饱和器工质湿空气和水的值,分析了不同参考点的温度和湿度对值的影响规律,以及物理和化学扩散随湿空气温度的变化情况。通过建立饱和器平衡模型,采用了目的效率作为饱和器效率。计算结果表明：湿空气值随参考点的温度和湿度变化规律为：先减小,直到最低点为零,然后不断增加,值始终大于(等于)零,并且与参考点参数差距越大,值越大。当湿空气温度增加,物理所占比重减少,而化学扩散的比重增加,在到达一定温度后,化学大于物理。     

太阳能干燥系列讲座(2)太阳能干燥的基础知识——湿空气和湿物料的性质

一湿空气的热力性质 1 湿空气的基本知识 干燥介质是指物料干燥过程中将热量传给物料,同时又将物料中蒸发出来的水分带走的媒介物质.太阳能干燥装置中的干燥介质一般为湿空气.湿空气是指干空气和少量水蒸汽的混合气体.由于自然界中的水分在不断蒸发,空气中或多或少都含有水蒸汽,所以人们通常接触到的空气都是湿空气.不过日常空气中的水蒸汽含量很少,可当作干空气计算.但在干燥作业中,湿空气中水蒸汽的含量及其状态,对物料的干燥速率及干燥质量有很大影响,必须引起重视.这里分别介绍影响湿空气特性的几个主要参数.     

Exergy analysis on throttle reduction efficiency based on real gas equations

This paper proposes an approach to calculate the efficiency of throttling in which the exergy (available energy) is used to evaluate the energy conversion processes. In the exergy calculation for real gases, a difficult part of integration can be removed by judiciously advised thermodynamic paths; the compressibility factor is calculated by using Peng–Robinson (P–R) equation. It is found that the largest deviation between the exergies calculated by the real gas equation and ideal gas assumption is about 1%. Because the exergy is a function of the pressure and temperature, the Joule–Thomson coefficients are used to calculate the temperature changes of throttling, based on the compressibility factors of the Soave–Redlich–Kwong (S–R–K) and P–R equations, and the temperature decreases are compared with those calculated by empirical formula. The result shows that the heat exergy contributes very little in throttling. The simple equation of ideal gas is suggested to calculate the efficiency of throttling for air at atmospheric temperatures.     

Survey of experimental data and assessment of calculation methods of properties for the air–water mixture

Thermodynamic properties of the air–water mixture at elevated temperatures and pressures are of importance in the design and simulation of the advanced gas turbine systems with water addition. In this paper, comprehensive available experimental data and calculation methods for the air–water mixture were reviewed. It is found that the available experimental data are limited, and the determined temperature is within 75 °C. New experimental data are needed to supply in order to verify the model further. Three kinds of models (ideal model, ideal mixing model and real model) were used to calculate saturated vapor composition and enthalpy for the air–water mixture, and the calculated results of these models were compared with experimental data and each other. The comparison shows that for the calculation of saturated vapor composition, the reliable range of the ideal model and ideal mixing model is up to 10 bar. The real model is reliable over a wide temperature and pressure range, and the model proposed by Hyland and Wexler is the best one of today. However, the reliability of the Hyland and Wexler model approved by experimental data is only up to 75 °C and 50 bar, and it is necessary to propose a new predictive model based on the available experimental data to be used up to elevated temperatures and pressures. In the calculation of enthalpy, compared to the ideal model, the calculated results of the ideal mixing model are closer to those of real model.     

考虑空气压缩因子变化影响的地下储气库热力学过程分析CSCD

为了解空气压缩因子变化对压气储能电站地下储气库热力学过程的影响,研究了考虑压缩因子变化条件下的压缩空气热力学过程的计算方法,利用实测数据论证了4种压缩因子计算方法的合理性,结合工程算例,研究了循环充放气状态下地下储气库压缩空气温度及压力变化规律。研究表明,空气压缩因子变化对压缩空气温度和压力计算值有显著影响;循环充放气条件下空气压缩因子、温度和压力均随充放气次数的增加呈现出增大趋势,并逐渐趋于稳定;压缩空气温度计算值对压缩因子的敏感程度大于压缩空气压力计算值。将压缩空气假定为理想气体对储气库温度的估计将产生较大影响,因此,考虑压缩因子的影响是必要的。     

An open heat pump process for moist gases

A heat pump process is proposed for the recovery of the latent heat of water vapour in waste heat gases. The process includes a humidifier where the moist waste gas is additionally humidified. The moist gas leaving the humidifier is pressurized in a turbocompressor. The dew point temperature of the gas is increased by the humidification and the compression. This is utilized by indirect heat exchange for the production of low pressure steam and for the required heat of vaporization in the humidifier. It should be possible to use the process for waste heat recovery from moist flue gases and from process gases such as dryer exhaust air. Performance data have been calculated for production of low pressure steam at 1.2 bar from moist air at atmospheric pressure, dry temperature 100°C and the absolute humidity 0.19 kg water vapour per kg dry air. With these data a coefficient of performance for the heat pump process has been calculated to be 2.8. 85% (m/m) of the waste heat has been recovered from the moisture content. For these calculations the pressurization in the compressor has been set to 4.0 bar. The process should be further investigated to find performance data under optimal operating conditions.     

Influence of quantum degeneracy and regeneration on the performance of Bose-Stirling refrigeration-cycles operated in different temperature regions

The Stirling refrigeration cycle using an ideal Bose-gas as the working substance is called the Bose-Stirling refrigeration cycle, which is different from other thermodynamic cycles such as the Carnot cycle, Ericsson cycle, Brayton cycle, Otto cycle, Diesel cycle and Atkinson cycle working with an ideal Bose gas and may be operated across the critical temperature of Bose–Einstein condensation of the Bose system. The performance of the cycle is investigated, based on the equation of state of an ideal Bose gas. The inherent regenerative losses of the cycle are considered and the coefficient of performance and the amount of refrigeration of the cycle are calculated. The results obtained here are compared with those derived from the classical Stirling refrigeration cycle, using an ideal gas as the working substance. The influence of quantum degeneracy and inherent regenerative losses on the performance of the Bose Stirling refrigeration cycle operated in different temperature regions is discussed in detail, and consequently, general performance characteristics of the cycle are revealed.     

Effect of gas equation of state on CFD predictions for ignition characteristics of hydrogen escaping from a tank

This work involves the investigation of the sensitivity of computational fluid dynamics based models of auto ignition of hydrogen gas escaping into the surroundings to the use of an ideal gas and a real gas Noble–Abel equation of state. Ensuring consistent modeling techniques when the real gas equation of state is implemented, real gas based thermodynamic properties, real gas based property mixture models, and real gas based chemical equilibrium constant formulations are utilized. Within the standard computational fluid dynamics models, a customized chemical kinetic equation integrator is employed. An LES based turbulence model is implemented. For tank pressures of 40, 80, and 120 MPa, differences in the gas conditions, including gas pressures, temperatures, velocities, flow rates, energy, and chemical species mass fractions, are compared. The relationships between the local and time varying gas conditions, chemical reaction indicators, the tank pressure, and the equation of state captured in the simulations are described in detail. The results clearly show the increasing deviation between the ideal gas and Noble–Abel based results as the tank pressure increases, indicating the importance of the use of the proper material model and chemical equilibrium formulation for the conditions of interest.     

Performance analysis of open cycle gas turbines

In this study, the performance of ideal open cycle gas turbine system was examined based on its thermodynamic analysis. The effects of some parameters, such as compressor inlet temperature (CIT), pressure ratio (PR) and the turbine inlet temperature (TIT), on the performance parameters of open cycle gas turbine were discussed. The turbine net power output, the thermal efficiency and the fuel consumption of the turbine were taken as the performance parameters. The values of these parameters were calculated using some basic cycle equations and variables values of thermodynamic properties. Other variables such as lower heating value, combustion efficiency and isentropic efficiencies of compressor and turbine were assumed to be constant. The result showed that the net power output and the thermal efficiency increased by a decrease in the CIT and increase in the TIT and PR values. If it is aimed to have a high net power output and the thermal efficiency for the turbine, the CIT should be chosen as low as possible and the TIT should be chosen as high as possible. Copyright © 2008 John Wiley & Sons, Ltd.     

Thermodynamic modeling and exergy investigation of a hydrogen-based integrated system consisting of SOFC and CO2 capture option

The current study deals with the thermodynamic modeling of an innovative integrated plant based on solid oxide fuel cell (SOFC) with liquefied natural gas (LNG) cold energy supply. For the suggested innovative plant the energy, and exergy simulations are fully extended and the plant comprehensively analyzed. According to mathematical simulations of the proposed plant, a MATLAB code has been extended. The results indicate that under considered initial conditions, the efficiencies of SOFC and net power generation calculated 58% and 78%, respectively and the CO₂-capture rate is obtained 79 kg/h. This study clearly shows that the integrated system reached high efficiency while having zero emissions. In addition, the efficiencies and net amount of power generation, cooling or heating output and SOFC power generation are discussed in detail as a function of different variables such utilization factor, air/fuel ratio, or SOFC inlet temperature. For enhancing the power production efficiency of SOFC, the net electricity, and CCHP exergy efficiency the plant should run in higher utilization factor and lower air/fuel ration also it's important to approximately set SOFC temperature to its ideal temperature.     

Exergetic performance comparison of air and hydrogen gas flowing through the annular curved duct

The main objective of this study is to parametrically compare the exergetic performance of air and hydrogen gas flow through the curved annular duct. For this purpose, it is assumed that, i) air and hydrogen are considered to be ideal gas, ii) the flow of these gases is steady state and laminar fully developed, ii) these gases have constant physical properties, iii) the channel inner and outer walls are exposed to constant wall boundary condition. Moreover, the following important parameters are taken into consideration: i) aspect ratio (four different values which are 5.50, 3.80, 2.90 and 2.36), ii) environment temperature (ranging from ?30 to 30 with 10 °C intervals), iii) Dean number (varying between 24 and 208), and iv) operating pressure (=1 atm). Considering these parameters, exergy destruction and exergy efficiencies are calculated for each aspect ratio. Consequently, exergetic efficiency rises with the increase of Dean number, inner wall temperature, aspect ratio and the decrease of dead state temperature. Also, it is noticed that the gas specie highly affects the volumetric entropy generation rate, exergy destruction rate and exergy efficiency.