多孔介质粒径对建筑结构热质传递的影响

汲液式多孔层置于建筑结构中,通过多孔材料的主动吸水、被动蒸发产生制冷效果,减少了外界的动力消耗。应用描述非饱和多孔介质热质迁移的数学模型,在不同环境参数下,分析了床层粒径对多孔床内部非饱和场量的影响;以含湿砂石多孔床层为对象,实验研究了不同粒径床层热湿迁移环境因子特性。数值分析与实验相符合,所获的结果可为含湿多孔填料床制冷性能的开发和利用提供一定的指导。     

含湿多孔介质内热量迁移的研究

文中分析了未饱和含湿多孔介质内热湿耦合作用过程的热迁移机量,提出了热量迁移数学模型,讨论了不同边界条件对多孔介质内温度分布的影响状况。     

多层多孔介质层间界面处的热质耦合传递

为解决多层多孔介质层间界面处含湿量不连续而使含湿量梯度不能直接作为质传递驱动势的问题,该文在仍然以含湿量梯度为质驱动势的条件下,对界面处的质量和能量守恒方程进行适当改进,使对多层多孔介质热质耦合传递的模拟结果更符合实际,通过对已发表文献的实验结果进行验证,利用验证改进后的模拟方法对新建建筑多层多孔介质围护结构进行模拟,并与以界面处的平均体积含湿量梯度作为质驱动势对模拟结果进行对比。对比结果发现:利用改进后的模拟方法模拟的围护结构干燥速度小于后者的模拟结果,模拟结果也更接近实际情况。     

建筑材料多孔介质热物性参数测试实验研究

建立一种操作简单、易推广的实验方法,测试建筑材料多孔介质的导热系数、孔隙率、定压比热以及密度等基础热物性参数。通过实验测试建筑材料混凝土的干燥密度、干燥定压比热容、干燥导热系数及孔隙率等参数值,验证此实验测试方法的可行性,为推动建筑材料多孔介质热湿迁移物性基础数据的进一步完善提供收集依据。     

混凝土多孔介质等温吸湿过程的数值模拟

分析了含湿多孔介质吸湿的主要机理，根据介质吸湿过程中的热湿平衡建立了其吸湿过程的一维数学模型。采用控制容积法及时间显式积分方案对方程进行了数值计算。计算结果表明多孔介质在等温吸湿过程中存在不稳定和相对稳定两个阶段。吸湿处于不稳定阶段时温度梯度势和含湿量梯度势相互作用；吸湿处于相对稳定阶段时仅存在含湿量梯度势。同时比较了轻质混凝土、半轻质混凝土、粘土实心砖三种材料的吸湿性能。     

建筑屋面太阳能被动蒸发冷却研究

提出利用多孔含湿材料太阳能被动蒸发冷却建筑屋面的新方法，建立了多孔含湿材料利用太阳能被动蒸发的热质耦合传递数学模型，通过理论分析，数值计算和实验测试，揭示了热过程规律，结果表明，利用太阳能被动蒸发多孔含湿材料水分降温方法是可行的。     

含湿非饱和多孔介质的完全分形传热研究

为了探究在含湿情况下多孔介质有效导热率的变化,基于分形理论,考虑多孔介质在含湿时加热过程中相变的影响,结合加热过程中的热量守恒方程和傅里叶导热定律推导出计算有效导热率的新公式。将该模型相关数据代入进行计算,分析了孔隙率、含湿率、面积分形维数和迂曲分形维数对有效导热率的影响。研究发现,孔隙率与有效导热率呈负相关,含湿率与有效导热率呈正相关,分形维数与有效导热率呈负相关。该研究能够反映多孔介质内的传热进程,对于探究微孔结构物质的传热具有一定的指导意义。     

严寒地区近零能耗建筑围护结构热湿传递对室内舒适性影响的研究

近零能耗建筑围护结构是复合多孔介质,研究水分透过墙体对建筑物内部环境的影响机理.以沈阳市某近零能耗建筑为例,采用WUFI-Plus软件对建筑内环境参数进行模拟,比较了考虑热湿传递与不考虑热湿传递对该建筑室内舒适性的影响.结果表明:建筑围护结构的热湿传递作用对室内相对湿度情况影响明显,应在空调设备、系统选型和环境预测分析...     

新建建筑围护结构的传热系数变化研究

对严寒地区新建建筑围护结构的干燥过程进行了模拟,建立了不同干燥时期的热质耦合传递质能平衡方程,确立了围护结构各层多孔介质材料导热系数随含湿量和结冰量的变化关系,对围护结构传热系数的变化情况进行了模拟,分析了新建建筑传热系数随着围护结构不断干燥的逐年变化规律。模拟结果表明:在严寒地区,新建建筑围护结构冬季的传热系数由于内部含湿量结冰要高于夏季围护结构传热系数,但围护结构冬季传热系数逐年下降,尤其前三年下降较明显。     

空心喷雾油滴碰撞热多孔介质的数值研究

为加深对多孔介质发动机中均匀混合气形成的了解,用改进的KIVA-3V详细模拟了空心喷雾油滴碰撞热多孔介质的过程。在KIVA-3V中增加了油滴碰撞热多孔介质壁面的碰撞模型、传热模型及空心喷雾的线性不稳定性液膜破碎(LISA)模型。油滴与热壁的碰撞模型和传热模型经检验证明了其合理性。在简化多孔介质结构的基础上,在不同的环境压力及喷雾锥角下,模拟了空心喷雾与热多孔介质的相互作用。计算结果表明:油雾在碰撞到热多孔介质后,发生分裂的油束和多孔介质区域的高温,促使油滴实现快速蒸发并为油蒸汽与空气充分混合创造了前提。不同的空间压力及喷雾锥角直接影响到油滴在多孔介质中的分布。     

Thermal analysis on the cooling performance of a porous evaporative plate for building

In this paper, a wet porous cooling plate has been used for a building wall. Cooling can be achieved due to the evaporation in the porous layer. A mathematical model on the heat and mass transfer in the unsaturated porous media is developed to analyze the influences of ambient conditions and the porous layer thickness on the cooling performance of the porous evaporative plate. With a decrease in ambient relative humidity and an increase in ambient temperature, more cooling of the porous evaporative plate can be supplied for the inside of the room. The heat exchange between the inside surface of the porous plate and the air in the room should be intensified to achieve a higher cooling efficiency of the porous plate. The ambient wind speed and the thickness of the porous plate also have significant influence on the average temperature of the porous plate. All these results should be taken into account for the utilization of the porous evaporative cooling plate. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20284     

多孔介质中的相变传热特性及其在建筑物节能中的应用

将非饱和多孔介质应用于建筑节能，使低品位，低密度的太阳能通过工质的相变得以利用，对实现建筑物的采暖具有应用价值。通过对非饱和多孔材料内的二维流场，温度场以及蒸发量场的数值计算，分析了两端开口的圆柱环型多孔腔内非饱和多孔介质的传热传质特性，研究了流体雷利数及边界条件的变化对多孔床热质迁移的影响。     

Super-high heat flux removal using sintered metal porous media

Introduction Recently there have been a demand for the technique to efficiently and steadily cool down extremely high heat flux of over 10 MW/m2, to fulfill not only the needs for plasma facing components in nuclear fusion reactors, but also the needs associated with sophisticated computers or downsizing of such devices as high-density laser equipment and power devices. However, existing cooling techniques in such high heat loading environment are basically based on high speed and highly subc…     

太阳能喷射/压缩复合制冷循环性能研究

研究了一种太阳能喷射/压缩复合制冷循环,由太阳能集热子系统、喷射制冷子系统及压缩制冷子系统组成,系统充分利用热电两种能源以及两种制冷方法各自的优点,优化喷射制冷子系统工作性能的同时,改善压缩式子系统的工作条件,从而提高复合制冷循环性能的同时节约高品位电能。采用性能较好的高蒸发温度式喷射制冷带走压缩机排气余热具有实际意义。通过数值模拟的手段分析系统性能及其主要影响因素,并优化工作条件。研究表明,与相同工作条件下的单压缩制冷循环相比,复合制冷循环工作日全天候运行时电力性能系数提升约为31.5%,节电优势显著。存在一个最佳的喷射子系统蒸发温度使得复合制冷循环性能系数达到运行工况的最大值。     

旋转式吸附制冷系统冷量输出品质分析

冷量输出的连续性和稳定性是吸附制冷技术能否用于空调领域的关键。本文在介绍双（多）床交替吸附制冷和旋转式吸附制冷基本原理的基础上，提出了吸附制冷冷量输出品质评价指标，即冷量输出的连续性和稳定性。分析表明，双（多）床交替系统冷量输出周期长、连续性和稳定性相对较差，难以满足空调等领域的用冷要求；而旋转式系统冷量输出周期短、连续性和稳定性好，使得吸附制冷方式对空调领域的适用性大为提高。旋转式吸附制冷是一种很有发展潜力的吸附制冷方式。     

MOISTURE EVAPORATION AND MIGRATION IN THIN POROUS PACKED BED INFLUENCED BY AMBIENT AND OPERATING CONDITIONS

The present paper investigates moisture migration in a thin porous bed filled with unconsolidated sand, unsaturated with water, and examines its cooling effect by water evaporation when used as a cooling device for room air-conditioning. An analytical model has been developed to simulate heat and moisture transport phenomena numerically and calculate the evaporation rate of water on which its cooling performance is dependent. For the case of a horizontal thin bed problem, with very small height and a relatively larger surface that is exposed to atmosphere air, one-dimensional, steady-state computation results have been obtained by focusing on the influence of ambient and operating conditions on the physical quantity fields in the porous packed bed. © 1997 by John Wiley & Sons, Ltd.     

Enhanced Evaporation in a Multilayer Porous Media Under Heat Localization: A Numerical Study

Evaporation and steam generation are two of the most vital processes in industry. A new method to advance the efficiency of evaporation involves localizing heat at the water surface where the vapor escapes into the air to minimize energy loss. In this research, we numerically investigate the improvement of a novel evaporation process via solar heat localization in a porous medium. A layer of carbon foam with a combination of interconnected and dead-end pores with a high hydrophilicity surface adjacent to a layer of expanded graphite with known porosity and properties were modeled numerically using a finite volume method. The hydrophilic porous media facilitates the capillary forces for better transportation of the bulk water through the porous media to the top surface of the porous media where the absorbed solar energy is delivered to the water inside the pores for evaporation. Continuity, momentum, heat and mass transfer equations were solved in this modeling effort. The modeling results were validated with the experimental data available in the literature. The findings in this numerical study can shed light on the complex interplay between the fluid dynamics and heat and mass transfer across the porous medium, which are important for efficient evaporation processes.     

废热/动力联合驱动的混合制冷循环特性分析

根据废热驱动的吸收式制冷循环特点以及对汽车制冷系统的技术要求,提出了一种采用直接风冷的,以汽车发动机废热和动力联合驱动的新型吸收/压缩混合制冷循环.在设计工况(空气温度35℃,冷凝温度55℃,制冷剂蒸发温度3℃,制冷负荷30kW)下,对采用R124-DMAC工质的混合制冷循环进行热力计算,其综合性能系数(COPint)为14.85.通过热力循环分析发现发生器负荷率和环境温度变化对混合制冷循环工作特性有较大的影响.     

Experimental study on the impact of mass moisture content on the evaporative cooling effect of porous face brick

Porous face bricks on the outside of a building wall exhibit evaporative cooling after absorbing water. Thus, these bricks are promising for use as a passive energy-saving building technology. Artificial watering is an effective method to ensure a sufficient water supply for effective evaporative cooling. However, improper watering measures may result in the waste of water resources while failing to achieve the evaporative cooling effect. In this paper, studies were conducted on a composite wall composed of a facing layer and a base layer as follows. (1) The mass moisture content variations in the porous face brick with respect to soaking time were measured, and the feasibility of using this type of face brick as an evaporative cooling carrier was investigated. (2) The relationship between mass moisture content and the evaporation capacity of the porous face brick was determined under stable conditions. A critical mass moisture content for the porous face brick was determined through analysis of the measurement data. (3) A field measurement was performed to verify the feasibility of using the critical mass moisture content as a criterion for watering. The results indicate that the temperature and heat flows at the inner and outer surfaces of the composite wall were reduced significantly. However, when the mass moisture content exceeded the critical mass moisture content, the evaporative cooling capability tended to stabilize with further watering. Therefore, the critical mass moisture content of the porous face brick can be used as a criterion for watering to conserve water while facilitating the evaporative cooling effect.     

An exergy analysis of a solar-driven ejector refrigeration system

Exergy analysis is used as a tool to analyse the performance of an ejector refrigeration cycle driven by solar energy. The analysis is based on the following conditions: a solar radiation of 700 W/m², an evaporator temperature of 10 °C, a cooling capacity of 5 kW, butane as the refrigerant in the refrigeration cycle and ambient temperature of 30 °C as the reference temperature. Irreversibilities occur among components and depend on the operating temperatures. The most significant losses in the system are in the solar collector and the ejector. The latter decreases inversely proportional to the evaporation temperature and dominates the total losses within the system. The optimum generating temperature for a specific evaporation temperature is obtained when the total losses in the system are minimized. For the above operating conditions, the optimum generating temperature is about 80 °C.