Experimental Investigation on the Effection of Flow Regulator in a Multiple Evaporators/Condensers Loop Heat Pipe with Plastic Porous Structure

Multiple loop heat pipes which have two evaporators and two condensers in one loop are a kind of active heat transfer device. Since they have two evaporators and two condensers, the operating mode also becomes multiple. This work discusses the cases that multiple loop heat pipes were operated with one condenser at high temperature and the other at low temperature. To avoid the high temperature returning liquid and keep the multiple loop heat pipes work properly, the flow regulator which was made of polyethylene was designed, fabricated and applied in this test. The effect of flow regulator was confirmed and analyzed. In the test that large temperature difference existed between two sinks, it can be found according to the result that the flow regulator worked effectively and prevented the high temperature vapor to enter the inlet of common liquid line, which can keep the evaporators and returning liquid to operate at low temperature. With the increment of heat loads and the temperature difference between two sinks, the pressure difference between two condensers became larger and larger. When the pressure difference was larger than the flow regulator’s capillary force, the flow regulator could not work properly because the high temperature vapor began to flow through the flow regulator. According to the test data, the flow regulator can work properly within the sinks’ temperature 0°C/60°C and the two evaporators’ heat load 30/30 W.

Operating Characteristics of Multiple Evaporators and Multiple Condensers Loop Heat Pipe with Polytetrafluoroethylene Wicks

This paper presents fabrication and testing of a multiple-evaporator and multiple-condenser loop heat pipe (MLHP) with polytetrafluoroethylene (PTFE) porous media as wicks. The MLHP has two evaporators and two condensers in a loop heat pipe in order to adapt to various changes of thermal condition in spacecraft. The PTFE porous media was used as the primary wicks to reduce heat leak from evaporators to compensation chambers. The tests were conducted under an atmospheric condition. In the tests that heat loads are applied to both evaporators, the MLHP was stably operated as with a LHP with a single evaporator and a single condenser. The relation between the sink temperature and the thermal resistance was experimentally evaluated. In the test with the heat load to one evaporator, the heat transfer from the heated evaporator to the unheated evaporator was confirmed. In the heat load switching test, in which the heat load is switched from one evaporator to another evaporator repeatedly, the MLHP could be stably operated. The loop operation with the large temperature difference between the heat sinks was also tested. From this result, the stable operation of the MLHP in the various conditions was demonstrated. It was also found that a flow regulator which prevents the uncondensed vapor from the condensers is required at the inlet of the common liquid line when one condenser has higher temperature and cannot condense the vapor in it.

Transient Exergy Analysis of the Condenser and Evaporator of an Air Source Heat Pump Water Heater

In this study the performance of an ASHPWH （air source heat pump water heater） is assessed from exergy point of view in component wise. In order to investigate the work potential of energy, the destruction on the exergy is analyzed and results are summarized for the components individually. The exergy destruction of the system is studied by considering real paths of the pressure and temperature data which are collected during the experiments of the ASHPWH under varying environmental conditions. In the following step, the evolution of the exergy destruction of the system is calculated by a code which is compiled on MATLAB along these temperature and pressure paths. The obtained results reveal the importance of the transient exergy analysis by providing detailed information about exergy destruction of the system such as where it drives up and reaches up to its max and where it drops down and evolves on a smooth path.

Numerical simulation of liquid desiccant evaporator driven by heat pump

The standard k-ε turbulence model and discrete phase model (DPM) were used to simulate the heat and mass transfer in a liquid-desiccant evaporator driven by a heat pump using FLUENT software, and the temperature field and velocity field in the device were obtained. The performance of the liquid-desiccant evaporator was studied as the concentration of the inlet solution varied between 21% and 30% and the pipe wall temperature between 30 and 50 ℃. Results show that the humidification rate and the humidification efficiency increased with the inlet air temperature, the solution flow rate, the solution temperature, and the pipe wall temperature. The humidification rate and humidification efficiency decreased with increasing moisture content in inlet air and the concentration of inlet solution. The humidification rate increased substantially but the humidification efficiency decreased as the inlet air flow rate increased. The error between the simulations and experimental results is acceptable, meaning that our model can provide a theoretical basis for optimizing the performance of a humidifying evaporator.

R1234yf在板式蒸发冷凝器中换热过程的数值模拟

通过建立板式蒸发冷凝器的二维数学模型,模拟了新型制冷剂R1234yf在板式蒸发冷凝器的换热过程,总结了冷却水温度、空气含湿量、制冷剂温度在板式蒸发冷凝器中的分布规律,并分析了冷凝温度、降膜雷诺数及空气湿球温度对板式蒸发冷凝器中换热的影响。研究表明:板式蒸发冷凝器的换热能力随冷凝温度升高而增大,随空气湿球温度升高而减小,随着降膜雷诺数的升高先增大后减小。冷凝温度从41℃变化到45℃时,板式蒸发冷凝器的热流密度增加了16.2%;湿球温度从21℃升高到26℃时,板式蒸发冷凝器的热流密度降低了14.6%;在不同冷凝温度下降膜雷诺数由60变化到120,板式蒸发冷凝器的热流密度最大变化率为6.06%。

基于Fluent的板管型蒸发式冷凝器的流动与换热研究

为了研究板管型蒸发式冷凝器的流动和传热特性,并优化其板片凹陷孔的结构,本研究采用商用软件Fluent对气液流动模型进行数值模拟。通过控制变量、逐层优化的方法,研究了各雷诺数(Re)下板片凹陷孔的不同深度(H)和小直径(D_(1))对板片流动与换热效率的影响。研究发现,在所有Re的条件下,努塞尔数(Nu)随着H的增大而增大,且存在一个最佳值——H=3 mm,当H继续增加时,Nu反而开始下降。在确定H的最佳值后,发现在所有Re的条件下,不同D_(1)对Nu的变化影响也存在一个最佳值D_(1)=6 mm,使得换热效果最好。通过实验验证,最佳尺寸下的数值模拟结果与实验结果吻合较好。虽然Re越大,换热效果越好,但也带来了更高的能耗,因此在最佳结构下需要在能耗和效率之间做出取舍。

某电厂脱硫废水蒸发冷凝浓缩(ECS)减量工艺分析

针对某电厂脱硫废水旁路烟道蒸发系统进行改进,利用低成本混合热源进行预浓缩处理,并与烟道蒸发技术相配套,减少烟道蒸发的投资规模。实现了对脱硫废水进行部分回用,测试结果表明,在满足蒸发浓缩进水水质条件下,脱硫废水浓缩量为3~3.75 t/h,处理后产水水质TDS <200 mg/L,蒸发浓缩吨水投资≤100万元,蒸发浓缩吨水运行费用≤85元,为零排放工艺长期稳定的低成本运行打下基础。

椭圆型套管-管翅式蒸发式冷凝器传热传质性能及实验研究

介绍了一种椭圆型套管-管翅式蒸发式冷凝器,通过搭建的蒸发式冷凝器性能测试实验系统,研究该蒸发式冷凝器在不同循环水配比、不同地区环境以及“风冷”“水冷”“蒸发冷凝”和“全工况”4种不同运行模式下的传热传质性能与运行特性的变化规律。结果表明:在相同条件下“全工况”模式的热流密度高于“风冷”和“蒸发冷凝”两种模式,而“水冷”模式由于其传热面积远小于其它模式,所以其热流密度最高;“全工况”模式在保持配风量及循环水总量一定的条件下,热流密度随循环水配比的增大而先增大后减小,喷淋水与冷却水的流量最佳配比为2∶5;“全工况”模式在严寒干燥地区、寒冷地区以及夏热冬暖地区的总热流密度分别为5879.64、3964.28及2933.05 W/m^(2),因此不同地区环境运行的传热性能相差较大,该冷凝器“全工况”模式在空气干燥的地区,喷淋冷却水温度范围为13~18℃运行时传热性能较优。在相同的条件下,“蒸发冷凝”模式的水膜传质系数高于“全工况”模式,且两者均随喷淋密度的增大先增大后减小。

蒸发冷凝长度比对不同微槽平板铝热管热性能的影响

为研究不同蒸发段和冷凝段长度比值对平板铝热管热性能的影响,通过实验分析了相同截面尺寸、相同填充工质、矩形微槽道和三角形微槽道的平板热管90°安装,以及采用连续递增的输入热流和冷凝段强制风冷换热时,9种不同比值对平板热管热性能的影响。研究结果表明:提出的平板微槽道热管蒸发段冷凝段长度比值对平板微槽道热管热性能的影响明显。优选的两种类型蒸发段冷凝段长度比值在0.8~1.25范围内,传热性能良好。对比不同微槽道的平板热管发现,同等条件下矩形微槽道平板热管的传热性能优于三角形微槽道平板热管,并提出蒸发段冷凝段长度比值的最佳值为1,建议应用设计中蒸发段冷凝段长度比值范围为0.8~1.0。研究结果可对平板微槽道热管应用系统的设计提供准确参考。

大型多层地下空间空气品质控制及整体性系统设计初探

通过分析大型多层地下空间项目中车库及快速公共交通区域湿度大、易结露且有害物浓度超标的具体情况,制定了兼顾安全性、舒适性及节能性的空气品质控制策略。依据整体建筑的实际使用需求与实施条件,介绍了与地上建筑相适应的真空垃圾统一收集系统、集中冷热源系统等整体性系统。以满足建筑使用功能为前提,初步探究了大型多层地下空间空气品质控制及整体性系统的设计技术措施。

关于新型节能蒸汽空气预热器汽水系统的研究

垃圾焚烧锅炉、碱回收锅炉等设备通常配套蒸汽空气预热器,利用汽包抽汽、汽机抽汽加热一二次风。减少蒸汽的用量或者更少的消耗高参数蒸汽,可以提高机组的能效指标。空气预热器汽水系统通过采用多级闪蒸设计形式,逐步减小闪蒸汽的压力,实现分段换热,其中高参数蒸汽耗量只需占较小比例。此外汽机的低压抽汽由于压力很小,导致无法疏水回到除氧器。将疏水方向改至凝汽器,可以实现用低压蒸汽加热空气。

Desalination of Seawater by Liquid Columns and Decompression Boiling (Recovery of Condensation Latent Heat)

In this study, the concept of a new seawater desalination method and equipment using liquid columns of seawater and desalinated fresh water, decompression boiling and evaporation, condensation, and recovery of condensation latent heat are proposed. The equipment consists of seawater and freshwater columns approximately 10 m high with top spaces. The pressure of the top space, the evaporation and condensation area, of the seawater column, for example, is reduced approximately 30 mmHg (abs.) using the seawater column, after which it is heated from the general seawater temperature of 25°C to 30°C to boil and evaporate the seawater. The vapor is cooled by the seawater at approximately 25°C in a heat exchanger, and then, it is condensed and sent to the fresh water column. At this time, the condensation latent heat is recovered to preheat the newly flowing seawater. The evaporation or condensation rate, namely, the production rate of freshwater, by the new desalination equipment is also estimated by the results of the existing quadruplex effect vacuum evaporator used in the salt production industry. This new desalination method and its associated equipment also can be used to purify polluted water and waste water.

Thermal transfer experimental research of a horizontal tube evaporative condenser

The thermal resistances distribution in different wet-bulb temperatures, air velocities and spraying water densities were achieved by the experimental test. The fluctuation of the water film convection and the water-air interfacial thermal resistance were reviewed especially. In the distribution of thermal resistance, the rank of the thermal resistance proportion （from max to min） is air flow heat transfer resistance, heat transfer resistance between refrigerant and wall, water film convection resistance and wall heat transfer resistance. When the heat flux is constant, the total resistance lowers nearly along with the increasing of air flow and water spray density. But there are a best air flow value of 2.98 m/s and a best spray water density of 0.064 kg/（m ·s） respectively, if continue to increase them, condensation performance is not significantly improved any more. The test results are available to improve the evaporative condenser performance and the designing lever.

制冷空调用换热器研究进展

为实现制冷空调行业的节能减排目标,研究具有轻量化、小型化和高效化的制冷空调用换热器至关重要。本文主要介绍强化换热技术在制冷空调用换热器中的应用,包括风冷式换热器、水冷式换热器和蒸发式冷凝器,以及适应低制冷剂充注量、低GWP工质的紧凑型高效换热器的研发进展,为换热器的优化设计提供借鉴。

主动气液调配换热器的研究现状

在气液相变过程中实施气液调配来主动调节干度和流量,可实现同时提升传热系数(h)和降低压降(Δp)。本文从气液调配强化传热原理、气液调配单元和气液调配换热器三个方面,总结国内外研究现状。主动气液调配在冷凝过程(分液冷凝)和蒸发过程(配液蒸发)中均需使工质处于高效传热区,但目标干度不同。重点关注了有联箱-小孔型、T型管和金属丝网这三类气液调配单元,发现低质量流量下联箱-小孔型与T型管的分液比率(F L)可达100%,而金属丝网型仅为30%。分液冷凝器的表面传热系数相比常规换热器可提升112%,但蒸发过程的气液调配研究较少,调配机理尚不清晰,需要进一步开展研究。气液调配式换热器的性能与气液分离效率(η)和支管的干度与流量分配紧密相关,基于多维联合仿真法综合考虑气液两相在联箱内的流态(气泡、液膜和液滴)、气液相界面传质和管道压降等影响因素有望提升气液调配换热器模型的预测精度。

竖管渗流降膜蒸发式冷凝器传热特性分析

为研究竖管渗流降膜蒸发式冷凝器,通过仿真和实验相结合的手段,探究了冷凝器单管在不同管外温度、空气雷诺数与液体雷诺数等多工况下的传热特性。结合此前研究中存在的问题,合理选择了物理模型与边界条件,获得了降膜过程的轴向温度、热通量分布等并对径向位置进行了时间序列分析。结果表明逆向通风传热效果优于顺向通风,但易加剧管段下部液膜不稳定甚至出现干壁。通过时间序列分析发现干壁区域会被液膜快速覆盖,因此短暂干壁对整体传热影响并不十分明显,仍需注意逆向通风强度过高会对管子下部液膜的稳定性造成显著影响,本文工况下推荐单管空气雷诺数不宜超过3500。此外,测试结果显示本文单管传热量约为2200W,与模拟结果相差6.7%,单管综合传热系数为1400W/(m^(2)·K)左右。

分离式热管换热技术在井口防冻系统中的应用研究

为解决目前分体式热管规模较小,输送距离短,在煤矿余热回收中应用受限的问题,以赵庄煤矿苏南风井井口供暖项目为工程案例,介绍了分离式热管换热技术在井口防冻系统中的应用。首先在通过对井口供暖热负荷和矿井回风余热的供热能力进行匹配分析的基础上,对分离式热管换热系统蒸发器和冷凝器的换热面积、上升和下降管路循环高差、蒸发器和冷凝器的风阻等进行了设计计算;然后基于供暖季运行的数据,分析了典型工况下两器在换热前后的温度变化情况。工程实践表明:分离式热管换热技术应用于煤矿井口供暖系统是可行的。

蒸发冷凝技术在水泥窑余热发电工程中的应用

水泥窑纯低温余热发电站利用水泥生产过程中产生的废热进行发电,其膨胀做功后的乏汽主要通过水冷和空冷系统进行冷凝,两种冷凝方式在造价、占地、换热效率和节能等方面各有优劣势。针对上述两种冷凝方法的特点,结合福建龙岩地区水泥厂余热发电机组实际运行情况以及当地的气候特点,提出采用蒸发式冷凝技术替代传统的水冷和空冷系统,可节约水资源17.1%,节电27.5%,每年可减少CO_(2)排放量691.2 t。

数据中心园区供冷供热方案浅析

对于同时有供冷供热需求的数据中心园区,有些数据中心会采用冷热源独立设置的方式,例如供冷采用间接蒸发冷却空调系统,供热采用市政热水或燃气锅炉。也有些数据中心会使用冷凝热回收技术,采用热泵机组夏季供冷,冬季同时供冷供热。本文针对冷热都有需求的数据中心园区进行系统分析,通过数据对比,探讨不同方案的可行性和应用场景。

微通道蒸发器高风速湿工况性能试验研究

为了研究微通道蒸发器在高风速湿工况下的热力性能和漂水特性,对不同翅片间距和表面特性的微通道换热器进行了试验研究。结果表明,亲水表面处理的微通道蒸发器不能改善湿工况热力性能和凝水排除效果,相反会恶化。亲水表面处理对换热因子j影响不显著,但使风侧阻力系数f增加。在测试工况条件下,亲水表面处理对换热因子j的影响小于1%,风阻系数增大4%~9%。j和f对翅片密度、空气湿度和风速的变化不敏感。亲水表面微通道换热器增大连续性水桥形成机会,增大漂水风险。常规工况下光箔和亲水箔均未发现漂水现象;高湿工况下光箔未发现漂水,亲水箔在风速4.5 m/s和较小翅片间距1.7 mm时,出现轻微漂水。