On the heating potential of buried pipes techniques — application in Ireland

The heating potential of a single earth-to-air heat exchanger as well as of a multiple parallel earth tubes system has been investigated in this paper using real climatic data. The heating system consists of a single tube or multiple parallel tubes, buried in the ground, through which ambient air is propelled and heated by the bulk temperature of the natural ground. The dynamic thermal performance of the system during the winter period and its operational limits have been calculated in Ireland using an accurate numerical model. For this reason multi-year ambient air and soil climatic measurements for the city of Dublin have been used as inputs to the model. Furthermore, an extensive sensitivity investigation was carried out in order to evaluate the effect of the main design parameters on the system's heating capacity. The key variables influencing the performance of earth-to-air heat exchangers were considered to be pipe length, pipe radius, air velocity inside the tube and pipe depth below the surface of the earth. Cumulative frequency distributions of the air temperature at the pipe's exit have been developed as a function of all the input parameters.     

蒸发冷却换热贯穿质影响因素分析及实验研究

本文针对管外流体、空气和管内流体耦合换热情况的换热管换热性能进行研究,通过分析各参数的影响,运用控制变量法改变喷淋水流量进行了水平单管外流动水膜与空气之间对流传质系数的实验测定。实验结果表明,喷淋水流量对传质系数有较大的影响,并得到了实验数据拟合关系式。     

Experimental investigations of air and liquid injection by venturi tubes

The venturi system creates a pressure differential that forms a vacuum. As water flows through the tapered venturi orifice, a rapid change in velocity occurs. This velocity change creates a reduced pressure (vacuum), which draws air and liquid to be injected into the system. The air and liquid injection rates vary with the pressure differential across the venturi. Typical applications of venturi tubes are for injecting fertilizers, chemicals, ozone gas, air or oxygen into pressurized water systems. In this paper, experimental studies were conducted to investigate the effects of inlet and throat diameters of the venturi tube, pipe length downstream of the venturi tube, diameter of the suction pipe at the throat portion of the venturi tube, angle of the pipe downstream of the venturi tube, flow velocity at the inlet portion of the venturi tube and density and viscosity of the liquid injected into the venturi tube on air and liquid injection rate. It was observed from the results that venturi tubes had high air and liquid injection efficiencies.     

单U形地埋管换热特性及热作用半径数值分析

针对影响U形地埋管换热能力及热作用半径的典型因素,采用模拟分析,得到了不同入口水温、管内流量、回填料导热系数、岩土体导热系数、体积热容条件下,埋管单位井深换热量和平均热作用半径随之变化的规律。结果表明:地埋管的换热量与入口温度、岩土体导热系数及单位体积热容呈线性变化,与入口流量和回填料导热系数呈指数形式变化,通过拟合分析出单位井深地埋管日平均换热量与五个因素的回归方程;在热物性参数中热扩散系数对地埋管的平均热作用半径影响最显著。     

高温后喷水冷却圆钢管再生混凝土界面黏结性能试验研究

为了研究高温喷水冷却后圆钢管再生混凝土的界面黏结性能变化规律,以历经最高恒温温度、再生粗骨料取代率、界面锚固长度为3个变化参数,进行了27个高温喷水冷却后圆钢管再生混凝土试件和2个自然冷却试件（对照组）的静力推出试验,以位移控制的加载方式为主,使自由端的钢管单独受力（核心混凝土不受力）,圆钢管内的混凝土从下向上推出。通过试验观察了圆钢管再生混凝土试件破坏的全过程和形态,获取了加载端和自由端的荷载-滑移曲线,分析了各个变化参数对黏结性能的影响规律。试验结果表明：经过高温喷水冷却后,圆钢管再生混凝土试件加载端和自由端的荷载-滑移曲线形态相似,且和自然冷却试件的曲线相似,同时也和前期做的钢管普通混凝土的曲线具有相似性;加载端和自由端的荷载-滑移曲线大致分为上升段、缓慢下降段和平缓段;并且自由端的初始滑移晚于加载端。定义了极限黏结强度τu和残余黏结强度τr。圆钢管再生混凝土试件表面上应变沿试件高度方向大致呈指数分布。经历消防喷水冷却后,随历经最高温度的升高,黏结强度先增大后减小,在400 ℃时,黏结强度达到最大值,当大于400 ℃时,黏结强度降低。历经高温后试件的平均残余黏结强度分别是常温下试件的1.25倍、1.75倍、1.38倍和1.50倍。再生粗骨料取代率的变化对黏结强度的影响不明显,常温下γ=50%时,黏结强度达到最大值;温度为200 ℃且γ=75%时,黏结强度也为最大。这和自然冷却下钢管再生混凝土的结论类似。锚固长度的增大也使圆钢管再生混凝土试件平均极限黏结强度和残余黏结强度均有不同程度增大。提出了高温喷水冷却后圆钢管再生混凝土极限黏结强度和残余黏结强度的计算公式,用此公式所得计算结果均比较理想。今后对界面黏结性能的研究,可以从增加钢管内壁的粗糙度、钢管内部加入加劲肋和钢管内增设不同长度的螺栓角度进行探讨,进而进一步丰富界面黏结性能的理论研究,以期为消防喷水后建筑结构构件的其他力学性能提供理论基础,同时为现实生活中火灾后钢-混凝土组合结构的灾后评估和加固提供参考。     

Enhancement of natural ventilation in buildings using a thermal chimney

A new module was developed for and implemented in the EnergyPlus program for the simulation and determination of the energy impact of thermal chimneys. This paper describes the basic concepts, assumptions, and algorithms implemented into the EnergyPlus program to predict the performance of a thermal chimney. Using the new module, the effects of the chimney height, solar absorptance of the absorber wall, solar transmittance of the glass cover and the air gap width are investigated under various conditions. Chimney height, solar absorptance and solar transmittance turned out to have more influence on the ventilation enhancement than the air gap width. The potential energy impacts of a thermal chimney under three different climate conditions are also investigated. It turned out that significant building cooling energy saving can be achieved by properly employing thermal chimneys and that they have more potential for cooling than for heating. In addition, the performance of a thermal chimney was heavily dependent on the climate of the location.     

外掠单排矩形翅片管的强化换热实验研究

本文以冷风机蒸发器普遍采用的矩形平翅片管作为比较对象，对三种不同片型的新型翅片管在吸风式直流风洞中进行了空气外掠单排翅片管的对比性实验研究。     

Thermal performance analysis of evacuated tubes solar air collector in Indian climate conditions

The thermal performance of one-ended evacuated tubes solar air collector is experimentally investigated during the winter season at NIT Kurukshetra, India [29 ° 58^′(latitude) North and 76 ° 53 ^′ (longitude) East]. The collector consists of 15 one-ended evacuated tubes with different lengths of directional inner aluminium tubes (inserted tubes) and a manifold channel, with air used as a working fluid. The inlet air flows through the directional inner aluminium tubes as a result of forced convection. In this experiment, evacuated tubes are used for producing hot air corresponding to different lengths of directional aluminium tubes without using any intermediate fluid. The temperature of the outlet air depends on the air flow rate, length of the directional aluminium tube and solar intensity. The maximum temperature difference between outlet air and inlet air at solar intensity 904 W/m² was found to be 72.7 °C with a flow rate of 5.06 kg/h and length of 0.83 m.     

Hypolimnetic aeration: practical design and application

Hypolimnetic aeration is becoming increasingly important as a fisheries management and water quality improvement technique, however its application has been restricted by a paucity of practical reference material. Hypolimnetic aeration includes partial and full lift designs and several air/oxygen injection systems. Positive displacement compressors flanged to three phase electric motors are the preferred air supply and power for most lake aeration projects. Internal combustion power is adequate for short term use and wind power is in the developmental stage. Rubber compressed air hose is recommended for lake aeration applications. Free air delivery is the air volume taken into the compressor at standard temperature and pressure however actual output volume is regulated by discharge pressure. Performance specifications of full lift hypolimnetic aerators are based on water:air ratios, oxygen increase, transfer efficiencies and oxygenation capacity. An empirical sizing method is proposed using hypolimnetic volume, hypolimnetic oxygen consumption, water flow, air flow and inflow tube radius. Outflow tube radius should equal or exceed inflow tube radius to achieve high flow rates and allow efficient removal of residual bubbles. Floatation requirements are calculated from the total weight of the separator box, inflow and outflow tubes and the theoretical water head.     

空调机制冷运行时室内温度场及温降速率的实验研究

本文以中间侧送风下回风的流场作为实验研究模型,研究柜式空调制冷机在不同送风速度和不同送风角度运行时,室内温度场和温度下降速率,从而确定其主要影响因素。实验结果表明:室内温差主要在高度方向上;送风角度对空调房温度下降速率和温度场有明显影响,送风速度次之;导风板角度大时,温度场的温差较小;当导风板位于90°,送风速度为高速时,室内温度下降最快。另外,本文对其机理也进行了初步探讨。     

大容量多联机空调系统的运行特性分析

利用多联机空调(MSAC)系统仿真平台,以制冷工况下室内机容量连续调节的多联机空调系统为例,探讨了大容量多联机系统的稳态运行特性。结果表明,多联机空调系统随连接管长度的增加,其制冷量有较大的衰减,且制冷能效比COPc的性能域宽度逐渐增大;对于单模块室外机组多联机空调系统而言,采用多台压缩机时,其部分负荷下的COPc优于单台压缩机构成的系统;由多个模块室外机组并联拼装构成的多联机空调系统,随室外机组数量的增加,其COPc逐渐降低,故并联的模块室外机组数量不宜太多,以免削弱多联机系统部分负荷率时的高能效比优势。     

两级蒸发冷却空调机组运行中的问题及改进措施

本文介绍了两级蒸发冷却空调的原理,分析了两级蒸发冷却空调的在实际应用中的优点,针对空调机组实际运行中管式间接段出现的二次风机上方出现较大水雾问题、换热后的喷淋水在接水盘四溅、椭圆换热管出现无淋水、椭圆换热管模块一次出风口出现渗水滴等问题进行分析并提出相应的改进措施,供有关设计、施工及管理人员参考。     

管幕冻结暗挖工法冻结止水效果分析

管幕冻结法是利用管幕配合冻结止水措施解决复杂建设条件下暗挖施工的一种创新性工法,该工法利用管幕顶管内冻结管路对管间土体进行冻结止水,在顶管管幕和冻结土体的超前支护下实施隧道暗挖施工。文章以港珠澳大桥珠海连接线拱北隧道冻结方案为例,利用数值模拟手段对积极冻结期不同土层的冻结效果及圆形冻结管、异形冻结管开启时间进行了研究,结果表明圆形冻结管和异形冻结管宜同步开启。对维护冻结期开挖断面温度、风速进行模拟分析,结果表明开挖断面内空气温度宜控制在25 ℃,风速对冻结效果影响不大。     

Experimental and numerical investigation on bare tube cross flow heat exchanger-using COMSOL

ABSTRACT

In this study, COMSOL multi-physics modelling software was used to make a computational model of a bare helical tube cross flow heat exchanger in order to simulate the temperature changes in the heat exchanger. The computational results of heat transfer are validated by using the analytical models. A conjugate convection/conduction heat transfer model was developed, which exhibited good agreement to the experiments. A different velocity of air taken into the consideration to find out the temperature distribution through the pipe and air temperature inside the duct. The temperature profile, and the overall heat transfer rate from the wall of the tube were calculated and plotted for theoretical, experimental and Numerical method using the k- conjugate heat transfer model. The model is validated through comparison with theoretical relations for single-pass cross-flow arrangements and with experimental results also. Simulation results showed good agreement with experimental values with respect to different mass flow rates.     

椭圆管蒸发冷却器冷却性能的影响因素分析

椭圆管蒸发冷却器具有管子排列紧凑,空气流动阻力小等优点,在高性能的闭式冷却塔内有着广泛应用.本文首先分析了结构参数对椭圆管蒸发冷却器冷却性能的影响,然后分析了运行参数对其冷却性能的影响,通过分析得到了一些有价值的结论,为管式蒸发冷却器的优化设计及运行提供了参考依据.     

Smoke spreading characteristics during a fire in a shallow urban road tunnel with roof openings under a longitudinal external wind blowing

A series of fire experiments was conducted using a 1:12 scale model of a shallow urban road tunnel with roof openings to clarify the flow structure of smoke and fresh air during a fire with a longitudinal external wind blowing above the roof openings. The model tunnel consisted of two road tubes separated by a pillar-type median structure. Five fire test cases were conducted by changing the heat release rate as the experimental parameter. When the smoke produced by a fire in the tunnel tube was exhausted by natural ventilation through the roof openings of the tunnel tube, fresh air was sucked in from the roof openings of the opposite tunnel tube. The flow of exhausted smoke and sucked-in fresh air created a complex three-dimensional flow structure inside the tunnel tubes. Stratified smoke that had formed under the ceiling of the tunnel tube was disturbed by the flow of sucked-in fresh air and was diffused on the upstream side of the fire. Compared to the condition without a longitudinal external wind, when a longitudinal external wind blew over the tunnel with the pillar median structure, the smoke spreading distance on the upstream side was longer than that without the external wind due to the diffusion of smoke. On the other hand, the smoke spreading distance on the downstream side of the fire was shorter than that without the external wind due to the improved smoke extraction performance by the Venturi effect of the longitudinal external wind. Furthermore, the smoke spreading distance on the downstream side was nearly constant and independent of the heat release rate of the fire, within the scope of our experimental conditions.     

PAG润滑油对超临界CO_2换热性能影响的研究

综述了润滑油在气冷器中对超临界CO_2换热特性影响的国内外研究现状,进行了润滑油对超临界CO_2换热性能影响的实验研究,以实验装置为物理原型建立了换热模型,编写了模拟程序,并根据实验得到的结果验证了模拟程序,模拟得出:随着CO_2压力增大,油膜增厚,换热系数反而也增大;随着CO_2质量流量增大,局部换热系数增大。可通过在管道内促进形成无源扰动、管道中设置扰流原件,设计气冷器时适当缩小后半段CO_2换热管管径等方法强化换热。     

加临时浮力塞自平衡浮力法下管技术研究

现有单塞自平衡浮力法下管,塞下充气量较小,并且随着下管深度的增加,塞下空气进一步压缩,提供的浮力逐渐减小,无法满足下管要求。为增加管内储气段长度,设置临时浮力塞。所加临时浮力塞与单塞自平衡下管时的浮力塞处于同一深度,在此处焊接带加强筋的封板作为临时浮力塞,利用常规空管提供浮力。当临时浮力塞上部空管高度达到设计值时,加设混凝土材质浮力塞并充气,随着充气压力的增大,设置在临时浮力塞下部的钢球脱落,空气进入临时浮力塞下部空间。与单塞自平衡浮力法相比,增加了临时浮力塞下这段充气量,因此提供的浮力也增大,从而实现一次性充气下完全布钢管。     

A heat pipe photovoltaic/thermal (PV/T) hybrid system and its performance evaluation

Building-integrated photovoltaic/thermal (BIPV/T) system has been considered as an attractive technology for building integration. The main part of a BIPV/T system is PV/T collector. In order to solve the non-uniform cooling of solar PV cells and control the operating temperature of solar PV cells conveniently, a heat pipe photovoltaic/thermal (PV/T) hybrid system (collector) has been proposed and described by selecting a wick heat pipe to absorb isothermally the excessive heat from solar PV cells. A theoretical model in terms of heat transfer process analysis in PV module panel and introducing the effectiveness-number of transfer unit (?-NTU) method in heat exchanger design was developed to predict the overall thermal-electrical conversion performances of the heat pipe PV/T system. A detailed parametric investigation by varying relevant parameters, i.e., inlet water temperature, water mass flow rate, packing factor of solar cell and heat loss coefficient has been carried out on the basis of the first and second laws of thermodynamics. Results show that the overall thermal, electrical and exergy efficiencies of the heat pipe PV/T hybrid system corresponding to 63.65%, 8.45% and 10.26%, respectively can be achieved under the operating conditions presented in this paper. The varying range of operating temperature for solar cell on the absorber plate is less than 2.5 °C. The heat pipe PV/T hybrid system is viable and exhibits the potential and competitiveness over the other conventional BIPV/T systems.     

垂直粘结矩形斜管沉淀技术的研究

提出了一种新颖的垂直粘结矩形斜管，其斜管具体有平整的顶面和底面。试验研究表明，它还具有良好的沉淀性能、较大的经济效益和斜管全长均起着固液分离作用－－－起端不存在“由紊流变层流”的过渡段。