A three-dimensional,clothed human thermal model

We have developed a three-dimensional clothed human thermal model for predicting physiological responses to temperature and humidity within clothing by considering the thermal properties of fabrics, clothing ensembles, and their designs. The model is a coupled simulation system of a human thermal model and a clothing thermal model. The model performance was investigated by comparing its predictions with experimental data. The following results were obtained. (1) The model predictions of skin temperature distributions and the micro-climate within clothing basically agreed with experimental data. (2) The skin temperatures of clothed body parts were higher than the corresponding body parts in the nude condition, and the skin temperatures of the hand and foot were higher than those in the nude condition, both in the model predictions and in the experimental data. (3) The model prediction of total moisture transfer was almost the same as obtained from the experimental data. 1998 Scripta Technica, Heat Trans Jpn Res, 26(8): 554–566, 1997     

负压对太阳能加湿除湿产淡水性能的影响

为提高淡水产量,设计一种太阳能负压式太阳能加湿除湿海水淡化系统,通过减小加湿腔体内压强来增加湿空气中含湿量,湿空气分别在液环真空泵和除湿腔内冷凝收集得到淡水。湿空气中含湿量上升,日产淡水总量增加。当湿空气温度70 ℃时,加湿腔压强从90 kPa减至70 kPa,含湿量增加154.9 g/kg;加湿腔压强70 kPa时,12：00—14：00可稳定产淡水1.8 kg/h以上,最高可达2.1 kg/h。装置性能系数GOR最高可达1.7。     

湿度对HAT循环燃烧室旋流扩散燃烧特性的影响

为研究湿度对燃烧特性的影响,采用湍流雷诺应力模型和层流小火焰模型,对湿空气透平(HAT)循环燃气轮机带有旋流器的燃烧室内甲烷扩散燃烧过程进行了数值模拟对比了在4种不同空气含湿量(0、100、200、300g／kg(DA))情况下的燃烧室内部温度场、速度场以及NO组分分布的情况,分析了湿度对HAT循环燃烧室扩散燃烧特性的影响结果表明,加湿降低了整个燃烧室的温度,并使其内部温度分布更加均匀;加湿使燃烧室的NO浓度大大降低;加湿减小了回流区长度。     

A basic study on humidity recovery by using micro‐porous media (Effects of thermal condition of fluids and geometrical condition of apparatus on transport performance)

Using an experimental apparatus to examine the performance of heat and mass transfer between constant‐temperature water and dry air through a porous plate having extremely small pores, the effects of the thermal conditions in the fluids and the geometric condition of the apparatus on moisture transport were measured. The effects of water temperature, thickness of the porous plate, and channel height of the flowing air on moisture transport are noticeable. However, the effect of air temperature in the channel inlet on moisture transport is slight. In addition, in order to evaluate the degree of air humidity absorption, a parameter called the moisture absorption rate was introduced. The moisture absorption rate was shown to decrease with increasing air velocity and varies only slightly for a plate thickness of 1 mm and decreases for a plate thickness of 3.5 mm with increasing water temperature. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(8): 568–581, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20133     

Predictions of moisture removal rate and dehumidification effectiveness for structured liquid desiccant air dehumidifier

In hot and humid climates such as in the Sultanate of Oman, the humidity puts extra load on the electric vapor-compression air conditioning (VAC) systems. Liquid and solid desiccants can reduce the moisture content of humid air and thus reduce the latent load imposed on the VAC systems. In the present work, the performance of air dehumidifiers using triethylene glygol (TEG) as desiccant was investigated. Three differently structured packing densities were used (77, 100 and 200 m²/m³). The performance of the dehumidifier was evaluated and expressed in terms of the moisture removal rate (m_cond) and the dehumidifier effectiveness (ε_y). The experimental work was undertaken to study the effects of several influencing design factors on this performance. The design factors covered included the air and TEG flow rates, air and TEG inlet temperatures, inlet air humidity and the inlet TEG concentration. The desiccant flow rate investigated was much less than that covered in previous studies and the range of the inlet temperatures of air and desiccant was significantly wider. The objective this study was to use the multiple regression method and the principal component analysis to obtain statistical prediction models for the water condensation rate and the dehumidification effectiveness in terms of these design factors. The results of both techniques agree with each other affirmed that the desiccant flow rate, desiccant inlet concentration and air inlet temperature are the most significant variables in predicting m_cond, whereas desiccant flow rate, air inlet temperature and packing density are the most significant variables in predicting ε_y.     

Study of humid air turbine cycle with external heat source for air humidification

In this paper, through introducing an external heat source to the conventional humid air turbine (HAT) cycle, we have studied the performances of the improved humid air gas turbine cycle mainly by exergy analysis method. In order to attain the performance of the humid air gas turbine with external heat source, we compare it with the conventional HAT cycle in detail with different factors such as the pressure ratio, turbine inlet temperature (TIT) and the external circulating water mass flow. The results showed that the specific work of the new system and the humidity ratio of saturator are all increased in some degree. For example, in the same pressure ratio and TIT, when the ratio of the external circulating water mass flow rate with that of the internal water is 0.2, the specific work increases more than 15.2 kJ kg⁻¹a, and the humidity raises at least 2.0 percent points. By introducing the external circulating water into the system, though thermal efficiency of the new HAT cycle is lower than that of the conventional HAT cycle, the exergy efficiency exhibits different results. Generally, when the pressure ratio is over 8, the exergy efficiency for the proposed HAT cycle is higher than the conventional HAT cycle; while less than 8, whether or not the exergy efficiency increases will mainly depend on TIT. In addition, the exergy destructions of components in systems were investigated. Through the comparison of the new system with the conventional HAT cycle, it was found that the exergy loss proportion in combustion declines for the new system, and the proportion of exhaust loss increases. From the viewpoint of total energy system, the HAT cycle with utilization of external heat source is a beneficial way to improve the overall performances of energy utilization. Copyright © 2009 John Wiley & Sons, Ltd.     

Experimental investigation on the performance parameters of a helical coil dehumidifier test rig

ABSTRACT

Water scarcity is a major problem faced in different parts of the world due to various reasons. Highly humid places closer to sea offers discomfort to the people and the moisture transport inside the building causes hazards to the interior and exterior over a period of time. However, both the water scarcity and high humidity problem can be addressed with the development of a novel system. Present work focuses on the dehumidification process where highly humid air moves over the copper coils wound helically, with cold water running through it. Vapor compression refrigeration cycle maintains the temperature of the cold water. The dehumidification is enhanced with the condensation of moisture and then dehumidified air enters the room. The fresh water collected is used as drinking water. Thermal parameters like temperature and humidity are measured and the overall dehumidification efficiency is assessed. Water condensation rate is found to be optimum for the air velocity 2 m/s with a dehumidification coil temperature of 2°C. These values are 22% and 31% higher than the water temperatures of 5°C and 10°C. The average water harvesting from the current system is 1.90 kg/hr. or 2.57 liters per hour (l/hr.).     

Moisture buffering capacity of novel solar‐regenerated rotating hygroscopic curtain system

This study proposes a rotating hygroscopic curtain to control indoor relative humidity. The curtain continuously exchanges heat and moisture with the two environments: the internal space where the curtain undergoes absorption and the space between curtain and glass window where it undergoes desorption releasing the collected space moisture to the exhausted airstream. In this work, a theoretical model is developed for the curtain system with an integrated indoor space modal to study the rotating hygroscopic curtain feasibility in performing indoor dehumidification. An experimental setup was built inside climatic chambers for validating the model predictions of room air temperature and moisture removal rate. Experimental data of the curtain‐absorbed moisture and the chamber indoor humidity showed good comparison with the model simulation values. A case study was evaluated to predict the effectiveness of a highly moisture‐absorbing cotton curtain used inside an office in Beirut City having an area of 42 m². At a given load, the hygroscopic curtain maintained an average relative humidity of about 65.7% when rotating continuously at a speed of 1.5 rpm compared with a value of 71.1% when the curtain was stationary. Copyright © 2015 John Wiley & Sons, Ltd.     

Simultaneous heat and mass transport in paper sheets during moisture sorption from humid air

A model of simultaneous heat and mass transfer through a porous material is presented to explain transient moisture sorption by paper sheets from humid air. There are three primary resistances to moisture transport: (1) diffusion through an external boundary layer; (2) diffusion through the pore system and, (3) diffusion from the pore system into the fibers. It is found that diffusion through the fiber phase perpendicular to the plane of the sheet is not significant for the moisture content range considered here. The mass transport model is able to predict the results of transverse moisture gradient experiments which show that moisture content gradients in paper are not as large as previously thought during transient periods. The model shows that the sigmoidal temperature response of paper to a linear change of relative humidity is due to non-linearities of the moisture content isotherm and heat of sorption.     

Investigation of MEA degradation in PEM fuel cell by on/off cyclic operation under different humid conditions

The durability of PEM fuel cells as a function of different humid conditions and MEA degradation were investigated by on/off cyclic operation. The maximum numbers of cycles determined by cycle at 10% of cell voltage loss were 1980, 1650, 1100, 520, and 320 cycles at relative humidity (RH) of 1000, 80, 50, 30, and 10%, respectively. The increases of ohmic resistance were observed at the high humid conditions of RH 100 and 80%. On the other hand, the charge transfer resistance increased at low humid conditions of RH 50, 30, and 10%. The losses of electrochemical surface area were obtained about 21% and 7% under RH 50 and 30% after the on/off cyclic operations, respectively. The thickness of electrode was reduced in the both anode and cathode layer, indicating that carbon corrosion occurred during on/off cycling. At cathode layer, the growth and migration platinum particles into polymer electrolyte were detected by XRD and TEM analyses.     

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。     

Development of design charts for tunnel dryers

A dryer simulation model, comprising a material model and an equipment model, has been developed for the drying of food products in a tunnel dryer. The material model, which deals with the drying kinetics of the product, is based on the receding evaporation front phenomenon while the equipment model describes the dynamics of the dryer. The overall model takes into account the shrinkage of the product. Simulation results of the transient moisture content show good agreement with experimental results for two dryers of different drying capacity. We present a design chart relating air temperature and humidity to the required energy for drying and dryer length, which shows an appreciable effect of setting low humidity for low temperature drying. A reduction in dryer energy consumption and chamber size is obtained under this condition. Multi-stage drying is introduced for situations where saturation of the air is likely to occur in the drying chamber. © 1997 by John Wiley & Sons, Ltd.     

An experimental study of a solar-regenerated liquid desiccant ventilation pre-conditioning system

A solar-regenerated liquid desiccant ventilation pre-conditioning system has been installed and experiments were carried out for a period of nine months covering rainy, cold, and hot seasons in a hot and humid climate (Thailand). A heat exchanger was used to cool the dehumidified air instead of typical evaporative cooling to maintain the dryness of the air. The use of solar energy at the regeneration process and cooling water from a cooling tower makes the system more passive. The evaporation rate at the regeneration process was always greater than the moisture removal rate at the dehumidification process indicating that the concentration of the desiccant in the system would not decrease and so the performance would not drop during continuous operation. The system could reduce the temperature of the delivered air by about 1.2 °C while the humidity ratio was reduced by 0.0042 kg_w/kg_da equivalent to 11.1% relative humidity reduction. The experimental results were also compared with models in literature.     

A basic study on humidity recovery using micro‐porous media: General characteristics and effect of material properties on transport performance

As a first step toward evaluating factors that influence humidity and heat transfer from moist air to dry air through porous media having very small pores, the present paper attempts to clarify factors that influence moisture transport between constant‐temperature water and dry air through a porous media plate. The effect of the pore diameter of the porous plate on the humidity transport through a porous plate was found to depend strongly on the thickness and pore diameter of the porous plate. That is, the smaller the pore diameter and the thicker the plate, the greater the effect of the pore diameter on the humidity transfer. In addition, the performance of heat and mass transfer were confirmed to increase with respect to the increase of air velocity. In addition, a parameter called the humidity absorption rate was introduced to evaluate the utilization degree of the air capacity to absorb humidity. The humidity absorption rate decreased with increases in both air velocity and plate thickness. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(2): 137–151, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20102     

Studies on thin layer drying of bagasse

Thin layer drying experiments of bagasse were carried out to determine the drying kinetics and also to identify a suitable drying model. The drying experiments were conducted in a laboratory scale dryer for a wide range of air temperatures (80–120°C), velocities (0.5–2 m/s), humidity level of air (9–24 g water(kg of d.a)⁻¹) and product thickness (20–60 mm). Air temperature, velocity, humidity and mass of product were recorded continuously during experimentation. The data were fitted to the different semi-theoretical or empirical models and compared based on their correlation coefficient (r), chi-square (χ²), root mean square error and mean bias error values. Among the models considered, the Page model gave accurate predictions with a correlation coefficient of 0.99627. It is found that the drying of bagasse takes place only in the falling rate period, even though the product has high initial moisture content. Copyright © 2006 John Wiley & Sons, Ltd.     

基于Flowmaster的相变空冷器元件开发及应用

基于湿空气热力学理论,以Flowmaster换热元件为基础,通过引入相变计算开发了考虑相变潜热的空冷器元件。经计算验证,所开发的元件计算结果与理论计算值吻合性较好,相同边界条件下,总换热量偏差和含湿量偏差均小于1%。分析表明:在高温、高湿环境条件下,湿空气会在空冷器中形成冷凝水,产生大量相变潜热,而Flowmaster换热元件模型由于未考虑相变因素,气侧出口温度计算结果偏低。采用所开发的相变空冷器元件模型可有效提高气侧出口温度计算的准确性,减小因相变带来的仿真误差。     

Field investigation on hygrothermal performance of full-vent perforated soffit and ceiling

This paper reports on field hygrothermal performance of white full-vent perforated soffit and ceiling compared to common wood soffit and gypsum ceiling. Testing was conducted using a two-story residential house located in Bangkok of 100 m² floor surface area. Data collection included ambient conditions, attic temperatures at various positions, and relative humidity of air in the bathroom and in the attic measured at 30 cm above the ceiling.Experimental results pointed out that perforated ceiling is very effective for reducing attic air temperature and moisture in the bathroom. Due to the solar radiation during daytime, the induced stack ventilation decreased heat and moisture accumulations in the bathroom and the attic. Such performance is extremely significant when compared to the performance of the original ceiling (gypsum board) where moisture removal by a small window took much longer time to achieve the same level of performance. After sunset, the temperatures at all positions in the attic were very close to ambient, which is an additional advantage for energy saving and comfort. Therefore, it is expected that perforated soffit and ceiling will be quickly integrated in the new design of modern houses as a new interesting option that promotes passive moisture ventilation and attic heat gain reduction.     

Performance study of a heat pump dryer system for specialty crops—Part 2: Model verification

The experimental and predicted performance data of a heat pump dryer system is reported. Chopped alfalfa was dried in a cabinet dryer in batches and also by emulating continuous bed drying using two heat pumps operating in parallel. Results showed that alfalfa was dried from an initial moisture content of 70% (wb) to a final moisture content of 10% (wb). The batch drying took about 4.5 h while continuous bed drying took 4 h to dry the same amount of material. The average air velocity inside the dryer was 0.36 m s^?1. Low temperatures (30–45°C) for safe drying of specialty crops were achieved experimentally. The heat pump drying system used in this study was about 50% more efficient in recovering the latent heat from the dryer exhaust compared to the conventional dryers. Specific moisture extraction rate (SMER) was maximum when relative humidity stayed above 40%. The dryer was shown to be capable of SMER of between 0.5 and 1.02 kg kW^?1 h^?1. It was concluded that continuous bed drying is potentially a better option than batch drying because high process air humidity ratios at the entrance of the evaporator and constant moisture extraction rate and specific moisture extraction rate values can be maintained. An uncertainty analysis confirmed the accuracy of the model. Copyright © 2002 John Wiley & Sons, Ltd.     

Heat and mass transfer analysis of a wavy fin-and-tube heat exchanger under fully and partially wet surface conditions

In this study a mathematical model of heat and mass transfer performance of a wavy fin-and-tube heat exchanger under wet surface condition is presented. The heat exchanger is a counterflow heat exchanger in which humid air and liquid are flowing in opposite direction. A water film that causes evaporative cooling of the humid air is circulated on the humid air side. The heat and mass transfer equations are first derived for fully wet heat exchanger and then by defining a wettability parameter, these equations are obtained for partially wet heat exchanger. In modeling, values of Lewis number and wettability parameter are not necessarily specified as unity. The temperature distributions of humid air, liquid and water film, and relative humidity distribution of humid air are obtained numerically. The theoretical results are found to be in good agreement with the available experimental measurements.     

Optical humidity sensing, proton-conducting sol-gel glass monolith

An integrated, crack-free glass monolith is prepared via a modified sol-gel approach. It has an accessible network of channels consisting of anisotropic pores of widths ca. 20-50 nm and lengths ca. 100-250 nm. The glass monolith exhibits a transparency change based on humidity, which is utilized as a basis for optical humidity measurements. On the other hand, the glass monolith shows high proton conduction in humid atmosphere, and its proton conductivity reaches a value of 0.12 S cm⁻¹ at 30 °C and 80% relative humidity.