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。     

增湿塔圈座肋板变形原因分析

针对国内某2500t/d水泥厂增湿塔圈座肋板弯曲变形加固修复案例,分析了肋板的变形原因,对肋板的设计参数进行了稳定性校核。结果表明:(1)肋板失效的原因并非是强度不足,而是稳定性不够;(2)在重量相等的前提下,在一定范围内,增加肋板厚度比增加肋板数量更为有效;(3)当肋板较长时,增加肋板厚度或增加约束点均能有效提高肋板的承载能力,克服失稳。     

Three-dimensional CFD modeling of a planar membrane humidifier for PEM fuel cell systems

A three-dimensional numerical model is developed to investigate and compare the performance of humidifiers with counter-flow and parallel-flow configurations. This model has a set of coupled equations including conservations of mass, momentum, species and energy. The results indicate that in counter-flow humidifier, water and heat transfer is more than that of the parallel-flow that leads to a higher dew point at dry side outlet, consequently, a better humidifier performance. An increase in temperature and a decrease in mass flow rate at dry side inlet lead to a better humidifier performance. However at the low flow rates the humidifier performance does not change a lot by preheating the inlet dry gas. An increase in relative humidity at dry side inlet does not offer any advantage.     

Mass transfer characteristics of the hydrophilic membrane with the isolation of heat transfer effect by isothermal bath

The efficiency and lifetime of a proton exchange membrane fuel cell (PEMFC) system is critically affected by the humidity of incoming gas which should be maintained properly for normal operating conditions. But the experimental characteristics of the humidifier are rarely reported. Water transport through the hydrophilic membrane is a coupled phenomenon of heat and mass transport. In this study, a laboratory scale test bench is designed to investigate the characteristics of water transport through the hydrophilic membrane. The mass transfer capability of the hydrophilic membrane is evaluated over various flow rates, temperature, pressure, and flow arrangements. In the experiment, the test bench is submerged in a constant temperature bath in order to isolate the effect of temperature variation between dry air and humid air. The results show the water transport of the hydrophilic membrane is significantly affected by operating temperature and operating pressure. Additionally, the flow arrangement demonstrates a minor effect but it should be considered along with the heat transfer effect.     

Effect of inserting obstacles in flow field on a membrane humidifier performance for PEMFC application: A CFD model

In this study, the numerical models are developed to investigate the influence of obstacle shape and number on performance of a planar porous membrane humidifier for proton exchange membrane fuel cell (PEMFC) application. Dew point of dry side outlet and water transfer rate are applied as evaluation parameters of the performance regardless of pressure drop. A dimensionless number named performance evaluation criteria (PEC) is calculated for all models. The higher value of PEC indicates the higher heat transfer rate with lower pressure drop. In humidifier with one rectangular obstacle compared with the simple humidifier, water transfer rate increases by 7.28%. The highest values of water transfer rate, dew point and PEC, also the greatest values of pressure drop are in humidifiers with rectangular, triangular and circular obstacles, in that order. When there is restriction in securing pumping power in fuel cell system, circular obstacle is the best choice. With considering the pressure drop, using one obstacle does not offer any advantage because the PEC is less than one (0.898). At least two obstacles are needed to have PEC number greater than one, consequently an efficient performance. An increment in number of obstacles causes an increment in water transfer rate, dew point and PEC.     

Experimental Investigations on the Performance of a Packed Bed Dehumidifier for Various Climatic Conditions

ABSTRACT

To simulate space cooling or drying systems for various geographical regions (low, moderate, and high humidity regions) a liquid desiccant system consisting of a humidifier and dehumidifier has been designed and constructed. This system consists of two coupled humidifying and dehumidifying packed columns filled with plastic Intalox Snowflake packing material. Experimental measurements of the dehumidifier performance utilizing a new effective liquid desiccant mixture (CELD) total desiccant salt content 40%wt.to 45%wt (salt comprised of equal portions by weight of lithium chloride and calcium chloride ), have. been carried out, The effect of different independent variables such as packing height, air inlet temperature and humidity ratio, and liquid desiccant inlet temperature, flow rate and concentration on the performance of the dehumidifier has been investigated. Experimental results demonstrate that the CELD is a promising desiccant for cooling and drying operations.     

Study of a porous membrane humidification method in polymer electrolyte fuel cells

A gas humidification sub-system that does not add to the parasitic power loss is advantageous for water management in PEMFC. A membrane humidifier was fabricated with porous membrane and the performance of the single cell using this humidifier has been evaluated. The study shows that the performance of the humidifier is comparable to that of the bubble humidifier. It was further found that the humidifier is suitable for both water and exhaust cathode air as the humidifying medium.     

多功能加湿器控制系统的设计与实现

湿度作为空气主要参数之一,与生活生产息息相关,为了快速准确检测湿度值,系统以AT89C52作为微处理器与数据存储器单元,选用合理的温度传感器,将采集的室内环境温度值传送到微处理器,并按比例转化为相应的湿度值,通过LCD1602把相应湿度值显示出来,根据湿度设定值的大小控制加湿器通断。同时,水位传感器对水箱水位可以进行实时检测,并采用C语言编程,设计出一套多功能加湿器控制系统。仿真及测试结果表明,此系统误差小、精度高、结构简单、性价比高,可方便地实现自动加湿与报警等功能。     

Design methodology for membrane-based plate-and-frame fuel cell humidifiers

Currently, polymer electrolyte membrane fuel cells require some method of humidification to operate effectively. External gas-to-gas membrane-based humidifiers can provide an efficient method to recycle exhaust heat and product water from the fuel cell stack. This work describes a design methodology involving a series of design equations for plate-and-frame membrane humidifiers. Humidifiers of different flow channel geometries were created with a rapid prototyping technique. These humidifier units were tested at different operating conditions in an attempt to validate the design equations. The ratio between the residence time of gas in the humidifier over the diffusion time of water from the surface of the membrane into the channel can be used as a design parameter. This ratio was shown to offer a good starting point for humidifier design, and a target range between 2.0 and 4.0 was identified (with a nominal desired value of 3.0). A humidifier design procedure and suggestions are presented based on this parameter and the packaging requirements of the humidifier in a fuel cell system. This algorithm was validated by creating a further prototype humidifier.     

An experimental study and model validation of a membrane humidifier for PEM fuel cell humidification control

This paper presents an experimental study and model validation of an external membrane humidifier for PEM fuel cell humidification control. Membrane humidification behavior was investigated with steady-state and dynamic tests. Steady-state test results show that the membrane vapor transfer rate increases significantly with water channel temperature, air channel temperature, and air flow rate. Water channel pressure has little effect on the vapor transfer rate and thus can be neglected in the system modeling. Dynamic test results reveal that the membrane humidifier has a non-minimum phase (NMP) behavior, which presents extra challenges for control system design. Based on the test data, a new water vapor transfer coefficient for Nafion membrane was obtained. This coefficient increases exponentially with the membrane temperature. The test results were also used to validate a thermodynamic model for membrane humidification. It is shown that the model prediction agrees well with the experimental results. The validated model provides an important tool for external humidifier design and fuel cell humidification control.