HAT循环后冷湿化过程的传热传质性能研究

为了提升湿空气燃气轮机循环的调控灵活性,自主设计和搭建了后冷湿化器一体化实验系统,通过实验获得不同水气比下后冷湿化器出口空气的温湿度和出口水温,利用实验数据修正表面化学反应速率,基于表面化学反应模型建立了后冷湿化过程三维数值模型,分析了水气比和进口水温对后冷湿化器性能的影响。结果表明：建立的后冷湿化器传热传质模型能高精度模拟后冷湿化过程,空气温度沿流动方向呈逐渐降低的趋势,空气的含湿量和相对湿度沿流动方向逐渐升高;水气比和进口水温均对后冷湿化器的性能有较大影响,随着水气比和进口水温增大出口空气湿度提高,湿化性能提升,而降低水气比有利于提升空气后冷性能。     

逆流式空气湿化器热力性能的(火用)效率分析

为了详细研究HAT循环关键部件湿化器的热力学性能，用[火用]分析的方法定义了湿化器的[火用]效率的概念，并结合实验得出了不同进口参数，如湿空气合湿量、水气比和进口水温（水气温差）对[火用]效率的影响规律，为提高湿化器性能和确定合理的运行工作状态提供了依据。     

HAT循环湿化器内部传热传质实验研究

为了研究湿空气透平(HAT)循环湿化器内部气液两相间的传热传质规律,搭建了高压填料湿化器实验系统,并自主开发了加压气液两相温度和相对湿度测量装置,得到15个工况下湿化器内湿空气温度(气温)、水的温度(水温)以及相对湿度沿湿化器高度的分布规律,研究了水气比、进口水温对湿化器内湿化过程的影响规律。结果表明:气液两相温度分别沿流动方向先降低后升高,湿空气在湿化器底部就已达到饱和状态;水气比对湿化器性能和内部气液参数的影响较大,水气比增大,进口水温升高,同一位置的水温和气温均升高,总体加湿量增大;进口水温升高时,底部湿空气更快达到饱和状态。     

泡沫陶瓷填料湿化器加湿性能实验研究

温化器是湿空气透平(HAT)循环的关键部件,其性能优劣对于循环的性能有着重要的影响.对采用新型SiC泡沫陶瓷填料的湿化器在加压条件下的湿化性能进行了实验研究,分析了水气比、进口水温、操作压力以及进口空气温度对湿化过程的影响,研究表明,提高水气比或进口水温会使进出口空气温差、含湿量差相应增加,湿化器节点温差增大.操作压力...     

HAT循环逆流式湿化器的热力性能实验研究及冷却数计算

在理论分析湿化器内部传热传质机理的基础上，进行了湿化器总体热力性能试验，得出了在不同实验工况下，各测量参数对湿化器热力性能的影响规律，同时计算了冷却数，得出了其变化规律。结果表明：随水气质量比的增大，湿化器出口湿空气的温度、温升和出口水温都增大，而冷却数减少。在同一水气质量比下，随进口水温升高，出口湿空气温度、温升和出口水温都增大，冷却数减少。在各实验工况下，湿化器的出口湿空气都具有很高的相对湿度，达到或接近饱和状态。冷却数降低对系统有利，但不是越低越好，应该优化选择最佳值。     

逆流式空气湿化器实验系统的研制

增湿湿化器是HAT循环的关键部件，本文利用相位多普勒分析仪Dual PDA(Phase Doppler Analyzer)详细测量湿化器内气液两相流场和内部温度场、相对湿度分布等，掌握传热传质机理以及研究分析影响湿化器性能的主要因素，从而进一步研制设计和改进、完善了湿化器实验系统。     

逆流喷雾式饱和器内湿化过程的实验研究

对逆流喷雾式饱和器内部空气的湿化过程进行实验研究,实验中不仅测量了饱和器进出口湿空气的相对湿度、温度和水的温度,而且也测量了饱和器内部几个高度截面上湿空气的相对湿度和气相、液相的温度。根据实验测量的湿空气的相对湿度和温度,计算出了饱和器内湿空气的含湿量和测量高度间湿空气的加湿量。由实验结果可见,随水气质量比的增大,饱和器出口湿空气的温度和温升也相应增大。湿空气的含湿量和水的蒸发量、出口温度随进口水温升高、水气质量比增大而增大。在所有实验工况下,饱和器出口湿空气接近或达到饱和。随空气速度增大水滴逃逸量增大。总体上饱和器内部下部主要是加湿进口空气,上部是加湿和加热空气。     

基于散堆填料的空气湿化塔性能实验研究

搭建了内径约600mm的空气湿化塔性能实验台,以塑料阶梯环散装填料塔为研究对象,实验并分析了气速、水气比、填料总高度对湿化塔的压力损失、加湿效果和传质单元高度的影响,以及进水温度对后两者的影响,同时获得了空气湿化填料塔精细设计数据,并对结果进行了拟合,得到填料的传质单元高度经验关联式。     

湿化器的传热传质机理和性能分析

从传热传质基本原理出发,建立了ＨＡＴ循环的重要部件－湿化器的数学模型,研究了湿化器的工作性能,并指出了目前某些处理方法的不合理之处。     

有无后冷器的微燃气轮机HAT循环性能比较

基于某80kW微燃气轮机回热循环改造工作,比较了有后冷器和无后冷器的HAT(Humid Air Turbine)循环性能和需要增加的换热器面积。研究结果表明,对于所研究的微燃气轮机,有、无后冷器的HAT循环系统折合效率和折合输出功相当,与有后冷器的HAT循环相比,无后冷器的HAT循环湿化器更高,体积更大,但是由于省掉了后冷器,其总换热面积(后冷器、湿化器、省煤器换热面积之和)更小,即意味着其投资更低,且无后冷器的HAT循环系统结构更简单,将使系统更加紧凑且控制更容易。     

耦合有机朗肯循环的液化空气储能系统性能研究

为解决液化空气储能系统(LAES)压缩热利用不完全的问题,构建了耦合有机朗肯循环的液化空气储能系统(ORC-LAES)。对ORC-LAES系统建立热力学性能计算模型,在设计参数下分析压缩机出口压力、膨胀机入口压力、加压水初温、加压水流量比及膨胀机级数对ORC-LAES系统性能的影响。结果表明,当压缩机出口压力由6 MPa上升到16 MPa、加压水初温从293 K上升到323 K时,系统的循环效率、火用效率和液化率均下降;当膨胀机入口压力由8 MPa上升到18 MPa时,系统循环效率和火用效率均增加;当加压水流量比由0.51上升到0.96时,系统循环效率和火用效率先增加再减少,流量比为0.71时,系统的循环效率和火用效率达到最大;在压缩热利用上耦合有机朗肯循环要优于增加膨胀机级数;ORC-LAES系统与LAES系统相比,循环效率提高4.8%,火用效率提升5.1%。     

Exergetic analysis of a double stage LiBr–H2O thermal compressor cooled by air/water and driven by low grade heat

In the present paper, an exergetic analysis of a double stage thermal compressor using the lithium bromide–water solution is performed. The double stage system considered allows obtaining evaporation temperatures equal to 5 °C using solar heat coming from flat plate collectors and other low grade thermal sources. In this study, ambient air and water are alternatively used as cooling fluids without crystallization problems up to condensation–absorption temperatures equal to 50 °C. The results obtained give the entropy generated, the exergy destroyed and the exergetic efficiency of the double stage thermal compressor as a function of the absorption temperature. The conclusions obtained show that the irreversibilities generated by the double stage thermal compressor will tend to increase with the absorption temperature up to 45 °C. The maximum value corresponds to 1.35 kJ kg⁻¹ K⁻¹. The entropy generated and the exergy destroyed by the air cooled system are higher than those by the water cooled one. The difference between the values increases when the absorption temperature increases. For an absorption temperature equal to 50 °C, the air cooled mode generates 14% more entropy and destroys 14% more exergy than the water cooled one. Also, the results are compared with those of previous studies for single and double effect air cooled and water cooled thermal compressors. The conclusions show that the double stage system has about 22% less exergetic efficiency than the single effect one and 32% less exergetic efficiency than the double effect one.     

A review of heat pump water heating systems

A heat pump water heater (HPWH) operates on an electrically driven vapor-compression cycle and pumps energy from the air in its surroundings to water in a storage tank, thus raising the temperature of the water. HPWHs are a promising technology in both residential and commercial applications due to both improved efficiency and air conditioning benefits.Residential HPWH units have been available for more than 20 years, but have experienced limited success in the marketplace. Commercial-scale HPWHs are also a very promising technology, while their present market share is extremely low.This study dealt with reviewing HPWH systems in terms of energetic and exergetic aspects. In this context, HPWH technology along with its historical development was briefly given first. Next, a comprehensive review of studies conducted on them were classified and presented in tables. HPWHs were then modeled for performance evaluation purposes by using energy and exergy analysis methods. Finally, the results obtained were discussed. It is expected that this comprehensive review will be very beneficial to everyone involved or interested in the energetic and exergetic design, simulation, analysis, performance assessment and applications of various types of HPWH systems.     

Exergy analysis of two phase change materials storage system for solar thermal power with finite-time thermodynamics

A mathematical model for the overall exergetic efficiency of two phase change materials named PCM1 and PCM2 storage system with a concentrating collector for solar thermal power based on finite-time thermodynamics is developed. The model takes into consideration the effects of melting temperatures and number of heat transfer unit of PCM1 and PCM2 on the overall exergetic efficiency. The analysis is based on a lumped model for the PCMs which assumes that a PCM is a thermal reservoir with a constant temperature of its melting point and a distributed model for the air which assumes that the temperature of the air varies in its flow path. The results show that the overall exergetic efficiency can be improved by 19.0-53.8% using two PCMs compared with a single PCM. It is found that melting temperatures of PCM1 and PCM2 have different influences on the overall exergetic efficiency, and the overall exergetic efficiency decreases with increasing the melting temperature of PCM1, increases with increasing the melting temperature of PCM2. It is also found that for PCM1, increasing its number of heat transfer unit can increase the overall exergetic efficiency, however, for PCM2, only when the melting temperature of PCM1 is less than 1150 K and the melting temperature of PCM2 is more than 750 K, increasing the number of heat transfer unit of PCM2 can increase the overall exergetic efficiency. Considering actual application of solar thermal power, we suggest that the optimum melting temperature range of PCM1 is 1000-1150 K and that of PCM2 is 750-900 K. The present analysis provides theoretical guidance for applications of two PCMs storage system for solar thermal power.     

Determination of optimum working conditions R22 and R404A refrigerant mixtures in heat-pumps using Taguchi method

In this study, refrigerants R22 and R404A five of their binary mixtures which contain about 0%, 25%, 50%, 75% and 100% mass fractions of R404A were tested. It is investigated experimentally the effects of gas mixture rate, evaporator air inlet temperature (from 24 to 32 °C), evaporator air mass flow rate (from 0.58 to 0.74 kg/s), condenser air inlet temperature (from 22 to 34 °C) and condenser air mass flow rate (from 0.57 to 0.73 kg/s) on the coefficient of performance (COP) and exergetic efficiency values of vapor compression heat-pump systems. To determine the effect of the chosen parameters on the system and optimum working conditions, an experimental design method suggested by Genichi Taguchi was used. In this study, it was observed that the most effective parameters are found to be the condenser air inlet temperature for COP and exergetic efficiency.     

Thermodynamic performance assessment of wind energy systems: An application

In this paper, the performance of wind energy system is assessed thermodynamically, from resource and technology perspectives. The thermodynamic characteristics of wind through energy and exergy analyses are considered and both energetic and exergetic efficiencies are studied. Wind speed is affected by air temperature and pressure and has a subsequent effect on wind turbine performance based on wind reference temperature and Bernoulli’s equation. VESTAS V52 wind turbine is selected for (Sharjah/UAE). Energy and exergy efficiency equations for wind energy systems are further developed for practical applications. The results show that there are noticeable differences between energy and exergy efficiencies and that exergetic efficiency reflects the right/actual performance. Finally, exergy analysis has been proven to be the right tool used in design, simulation, and performance evaluation of all renewable energy systems.     

Theoretical analysis of LiBr/H2O absorption refrigeration systems

A computational model is developed for the parametric investigation of single‐effect and series flow double‐effect LiBr/H₂O absorption refrigeration systems. The effects of generator, absorber, condenser, evaporator and dead state temperatures are examined on the performance of these systems. The parameters computed are coefficient of performance (COP), exergy destruction rates, thermal exergy loss rates, irreversibility and exergetic efficiency. The results indicate that COP and exergetic efficiency of both the systems increase with increase in the generator temperature. There exist different optimum values of generator temperature for maximum COP and maximum exergetic efficiency. The optimum generator temperature is lower corresponding to maximum exergetic efficiency as compared to optimum generator temperature corresponding to maximum COP. The effect of increase in absorber, condenser and evaporator temperatures is to decrease the exergetic efficiency of both the systems. The irreversibility is highest in absorber in both systems. Copyright © 2009 John Wiley & Sons, Ltd.     

Comprehensive investigation of membrane sorption and CFD modeling of a tube membrane humidifier with experimental validation

The humidification of PEM fuel cells is critical for their performance and efficiency and for ensuring a long durability. In most PEM fuel cell systems for mobile applications membrane humidifiers are used to humidify the fresh air. In this process, the water contained in the cathode exhaust gas is used to increase the humidity of the supply air. Despite the simple design of membrane humidifiers, the simulation of the water transfer is difficult and so far there exist hardly any precise models to calculate the absorption and desorption processes. Common approaches that use the Sherwood number to determine the sorption rates cannot account for the influence of the local water content of the membrane. This ultimately leads to an inaccurate simulation of humidifier behavior, as these models cannot consider the fact that desorption is nearly ten times faster than absorption.In this study, an empirical formula for an accurate determination of the sorption rate is derived based on experimental data. This function accounts for the different absorption and desorption rates by finding a sorption rate coefficient as a function of the local membrane water content, temperature, pressure and flow velocity.Furthermore, a CFD model is derived from the geometry of a commercially available membrane humidifier, which is also investigated on a test bench. Using the experimental data, the CFD model is validated and it is shown that the developed sorption rate formula leads to good agreements between simulations and experiments at steady-state operating points of the humidifier.     

Exergetic analysis of transcritical CO2 residential air-conditioning system based on experimental data

The experimental system for the transcritical CO₂ residential air-conditioning with an internal heat exchanger was built. The effects of working conditions on system performance were experimentally studied. Based on the experimental dada, the second law analysis on the transcritical CO₂ system was performed. The effects of working conditions on the total exergetic efficiency of the system were investigated. The results show that in the studied parameter ranges, the exergetic efficiency of the system increases with the increases of gas cooler side air inlet temperature, gas cooler side air inlet velocity and evaporating temperature. And it will decrease with the increases of evaporator side air inlet temperature and velocity. Then, a complete exergetic analysis was performed for the entire CO₂ transcritical cycle including compressor, gas cooler, expansion valve, evaporator and internal heat exchanger under different working conditions. The average exergy loss in gas cooler is the highest one under all working conditions which is about 30.7% of the total exergy loss in the system. The second is the average exergy loss in expansion valve which is about 24.9% of the total exergy loss, followed by the exergy losses in evaporator and compressor, which account for 21.9% and 19.5%, respectively. The exergy loss in internal heat exchanger is the lowest one which is only about 3.0%. So in the optimization design of the transcritical CO₂ residential air-conditioning system more attentions should be paid to the gas cooler and expansion valve.