Modelling of a Two-Phase Thermosyphon Loop for Passive Air-Conditioning of a House in Hot and Dry Climate Countries

The two-phase thermosyphon loop is an efficient solution for space cooling. This paper presents the simulation results of numerical studies on the heat transfer and thermal performance of a two-phase thermosiphon loop for passive air-conditioning of a house. The fluid considered in this study is methanol, which is compatible with copper and is environmentally friendly. These numerical results show that the temperature at the evaporator wall drops from 23°C to 13°C and increases at the condenser. The solar flux density has a strong influence on the condenser temperature. The mass flow rates and masses at the evaporator and condenser increase with temperature. The variation of evaporating and condensing temperature affects the performance of the system. For a constant evaporating and condensing temperature of 2°C and 29°C, the COP is 0.77 and 0.84 respectively. With these results, the use of the two-phase thermosyphon loop in air conditioning is possible to obtain a thermal comfort of the occupants acceptable by the standards but with a large exchange surface of the evaporator.

Characteristics of high-sulfate wastewater treatment by two-phase anaerobic digestion process with Jet-loop anaerobic fluidized bed

A new anaerobic reactor, Jet-loop anaerobic fluidized bed （JLAFB）, was designed for treating high-sulfate wastewater. The treatment characteristics, including the effect of influent COD/SO42 ratio and alkalinity and sulfide inhibition in reactors, were discussed for a JLAFB and a general anaerobic fiuidized bed （AFB） reactor used as sulfate-reducing phase and methane-producing phase, respectively, in two-phase anaerobic digestion process. The formation of granules in the two reactors was also examined. The results indicated that COD and sulfate removal had different demand of influent COD/SO4^2- ratios. When total COD removal was up to 85%, the ratio was only required up to 1.2, whereas, total sulfate removal up to 95% required it exceeding 3.0. The alkalinity in the two reactors increased linearly with the growth of influent alkalinity. Moreover, the change of influent alkalinity had no significant effect on pH and volatile fatty acids （VFA） in the two reactors. Influent alkalinity kept at 400-500 mg/L could meet the requirement of the treating process. The JLAFB reactor had great advantage in avoiding sulfide and free-H2S accumulation and toxicity inhibition on microorganisms. When sulfate loading rate was up to 8. 1 kg/（m^3.d）, the sulfide and free-H2S concentrations in JLAFB reactor were 58.6 and 49.7 mg/L, respectively. Furthermore, the granules, with offwhite color, ellipse shape and diameters of 1.0-3.0 mm, could be developed in JLAFB reactor. In granules, different groups of bacteria were distributed in different layers, and some inorganic metal compounds such as Fe, Ca, Mg etc. were found.

Experimental Investigation of Loop Heat Pipe with Two Evaporators/Two Condensers under Thermal Vacuum Condition

Multiple loop heat pipe is a high-functional thermal transport device. This work was conducted to confirm the working performance of Multiple loop heat pipe under thermal vacuum ambience with the working fluid ammonia. Asmall multiple loop heat pipe with two evaporators and two ra- diators was designed and fabricated. Then thermal vacuum test was conducted. The heaters were fasten on both evaporators, both radiators, both compensation chambers. In the case that both evaporators were heated, the multiple loop heat pipe can transport 120/120 W for 1.5 m, in the case that only one evaporator was heated, evaporator 1 can transport 80 W for 1.5 m, while eva- porator 2 can transport 120 W for 1.5 m. Two flow regulators were installed near the confluence of liquid line to prevent uncondensed vapor penetrating into returning liquid when the tempera- ture difference exists between two radiators. In the case that the heat load at both evaporators were 40/40 W and one radiator was heated, the flow regulator1 can tolerate the 160 W of heat load which was supplied to radiator1 while the flow regulator2 can tolerate the 100 W of heat load which was supplied to radiator2. To demonstrate the multiple loop heat pipe’s startup behavior at lowheat load, each of the compensation chamber was preheated to change the initial distribution of liquid and vapor in the evaporator and compensation chamber, in the result, each evaporator can start up at 5W through preheating.

R1234yf新能源汽车空调电子膨胀阀测试系统研制

针对目前国内现有电子膨胀阀测试系统偏差大、测试范围小、耗能大,研制了一种新型R1234yf新能源汽车空调电子膨胀阀测试系统,该测试系统利用制冷剂节流后气相经压缩机加压、液相经制冷剂循环泵加压,两相充分混合后进入冷凝器,利用排气节流阀直接控制被测电子膨胀阀阀后压力。依据汽车热管理国家标准对该测试系统进行了可行性及热力性能分析,并与实际制冷方法、液环法测试系统冷凝热负荷及耗功总和进行对比。结果表明:该系统利用两相环法,可以减少冷凝后的冷凝热量,通过排气节流阀控制被测阀后压力,取消蒸发器,提高系统性能;在流经被测试电子膨胀阀的工质质量流量为0.02~0.18 kg/s工况下,该系统冷凝热负荷较实际制冷方法减小了71.6%,较液环法降低了37.9%,耗功总和则比实际制冷方法下降了63.7%~38.6%,但比液环法约增加了7.5%。该系统可为新能源汽车空调行业电子膨胀阀性能测试提供可行且节能的测试方法。

环流生物反应器降流区输氧浓度影响因素

环流生物反应器降流区输氧浓度主要受导流筒直径、导流筒溢流堰口高度及曝气量等因素影响,其对反应器污水脱氮除磷处理效果有重要影响。为考察以上影响因素对降流区输氧能力影响,采用数值模拟与实验结合的方法对环流反应器降流区输氧能力进行研究,通过自定义程序耦合Higbie传质理论模拟氧传质,对比不同曝气强度下反应器溶解氧浓度及溢流量模拟与实测值,结果显示误差在8%以内,表明数值模拟模型及方法正确可行。随后探究了曝气量、导流筒直径及导流筒溢流堰口高度对降流区输氧能力的影响。结果表明:曝气量由20 L/min增至50 L/min时,氧体积传质系数由2.04 h^(-1)增至4.45 h^(-1);导流筒直径由325 mm降至250 mm时,氧体积传质系数由3.99 h^(-1)增至4.42 h^(-1);导流筒溢流堰口高度由10 mm增至25 mm时,氧体积传质系数由4.17 h^(-1)降至4.00 h^(-1);增大曝气量和减小导流筒直径能明显提升降流区输氧能力。总之,可通过调整曝气量,导流筒直径及导流筒溢流堰口高度控制降流区输氧能力,以构建耗缺氧区域。通过响应面分析,得到导流筒直径250 mm、导流筒溢流堰口高度10 mm时,反应器降流区输氧能力较优。

应用于新型环路热管的两相引射器数值模拟

环路热管是一种高效被动式相变传热装置,广泛应用于高热流电子器件散热等领域。前期研究发现将小型两相引射器与平板式环路热管耦合,可大幅提高传热性能。然而,小型两相引射器内部流动及传热机理尚不清晰,难以对新型环路热管进行正向设计与理论建模。通过数值模拟研究了汽水参数和混合腔结构对两相引射器性能及内部流场分布的影响。结果表明,喉部下游存在凝结激波,随着背压增加,其位置逐渐向喉部移动;其强度与背压、蒸汽产量、混合腔长度呈正相关,与水温呈负相关。引射器最大工作背压在40~125 kPa,与蒸汽产量和水温呈正相关,与混合腔长度呈负相关。通过大量模拟,得到了设计功率下水温和混合腔长度对引射器工作模式和压比的影响规律。

航天遥感器用泵驱两相流体回路热真空试验研究

针对航天遥感器核心组件的高精度与高稳定度的控温需求,设计并搭建了一套泵驱两相流体回路(MPTL)试验装置,该装置使用了一套具有被动冷却能力的两相控温型储液器。为验证MPTL系统在高真空、极低温与变化外热流条件下的工作能力,在真空罐内对MPTL系统在不同工况点下的散热与控温能力进行了测试,并通过温度和压力等数据研究了主回路的运行特性、储液器内热力学变化特性及两者之间的传热传质过程。结果表明:MPTL系统的控温点可通过储液器进行快速调整,蒸发器温度的变化受外热流与热源开关影响较小;进入毛细管中的过冷液与储液器中的液相形成的温差保证了储液器冷量的供应;主回路发生相态转变时,储液器与主回路工质交换特性引起了系统压力降脉动。

空间大功率热源两相温控系统设计与仿真

为解决未来空间应用中大功率热源带来的温控问题,提出了集微槽道蒸发器、相变装置和热辐射器在内的泵驱两相流体回路热排散系统方案,在此基础上开展了系统仿真工作,对流体回路运行特性和温控能力进行了研究。仿真结果反映了大功率热源短时工作条件下两相流体回路温度、饱和压力和干度的变化特征,两相流体回路工作特性符合设计预期,60 kW分布式大功率热源峰值温度能够控制在70℃以下。对泵驱动能力过剩所带来的不利影响进行了仿真分析,得出了泵驱动能力过剩导致两相回路系统温差增大的结论。分析了蒸发器和相变装置换热性能对温控系统的影响。蒸发器换热性能降低后,热源温度将超出要求范围;相变装置换热性能降低后,泵可能受到气蚀影响。

Numerical Study of Thermal Performance of a Capillary Evaporator in a Loop Heat Pipe with Liquid-Saturated Wick

Heat transfer of a capillary evaporator in a loop heat pipe was analyzed through 3D numerical simulations to study the effects of the thermal conductivity of the wick, the contact area between the casing and the wick, and the subcooling in the compensation chamber (CC) on the thermal performance of the evaporator. A pore network model with a distribution of pore radii was used to simulate liquid flow in the porous structure of the wick. To obtain high accuracy, fine meshes were used at the boundaries among the casing, the wick, and the grooves. Distributions of temperature, pressure, and mass flow rate were compared for polytetra-fluoroethylene (PTFE) and stainless steel wicks. The thermal conductivity of the wick and the contact area between the casing and the wick significantly impacted thermal performance of the evaporator heat-transfer coefficient and the heat leak to the CC. The 3D analysis provided highly accurate values for the heat leak;in some cases, the heat leaks of PTFE and stainless steel wicks showed little differences. In general, the heat flux is concentrated at the boundaries between the casing, the wick, and the grooves;therefore, thermal performance can be optimized by increasing the length of the boundary.

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.

高热流密度航空电子泵驱两相流冷却系统实验研究

航空应用领域正面临着高功率、高热流密度的电子设备冷却难题,传统的单相液冷散热方式已无法应对大于100 W/cm^(2)热流密度的散热需求。本文搭建了泵驱动两相冷却系统地面实验台并设计了系统控制策略,测试系统在多种散热工况下的散热能力和阻力特性并归纳数学模型。结果表明:机械泵驱动两相散热系统散热性能良好,设计的紫铜材质冷板可有效应对热流密度为120 W/cm^(2)的6 kW集中热源。泵驱两相系统可有效冷却10 kW的热源,在相同的运行状态下所需工质质量比单相散热系统所需工质质量减少70%。发热元件表面温度可以稳定在63~70℃之间,满足芯片表面温度要求,且蒸发器整体的温度均匀性良好,各支路间温差在5℃以内。系统相变段阻力在400 kPa以下,阻力特性可由Kim和Mudawar模型描述。

大功率空间激光载荷短时散热系统实验研究

大功率激光载荷在空间应用时具有瞬时热流密度高、工作时间短、间歇性工作的特点。为确保其高性能的工作,需要高效地解决激光载荷的热量获取、传递及排散问题。但受限于航天器有限的散热面面积,其散热能力往往难以满足大功率激光器的瞬时散热需求,而相变储热作为一种利用相变潜热的高效储热方式,可以解决航天器热控系统在供给侧和需求侧时空不匹配的问题。机械泵驱两相流体回路(Mechanically Pumped Two-phase Loop,MPTL)具有高效的传热效率和很强的传热能力,是解决大功率热量获取和传递的先进技术。文章针对大功率空间激光载荷的散热需求,将相变储热和两相传热技术相结合,提出基于固液相变储热和气液相变传热的短时大功率散热方案,完成了散热系统研制及性能测试。实验结果表明,散热系统能够很好的满足大功率激光载荷的散热需求,实现了12kW大功率载荷短时间稳定运行,具有很好的工程应用前景。

分离式热管在暖通空调领域的应用综述

分离式热管作为一种高效传热设备,广泛应用于暖通空调领域,具有制造维护成本低、可靠性高、传热性能好、适用性强等优点。本文综述了分离式热管在暖通空调领域的应用现状,从数据中心和基站、热回收及太阳能系统3个应用场景介绍了国内外对于分离式热管的研究,客观评价了目前研究工作中取得的主要成果及不足,针对未来分离式热管研究的发展方向给出了展望。这一综述将有助于研究人员和工程技术人员了解分离式热管的发展和应用情况,促进热管技术的发展。

连通微小通道环路热虹吸系统换热特性实验研究

针对芯片级散热场景,设计并搭建了两相环路热虹吸实验系统(TPLT),以R245fa作为工质,在冷凝器入口冷水温度为35℃、热流密度为10—162 W/cm2的工况下,研究了充液率对系统运行特性的影响,以及沟槽宽度为0.2—1.2 mm的连通平行微小通道(IPM)与平行微小通道(PPM)的沸腾换热性能。结果表明:40%是系统的合适充液率,过高的充液率导致冷凝器内部积液产生额外的蒸发器入口过冷度,过低的充液率则无法提供足够的循环流量;由于蒸发器水平放置时,TPLT系统流量启动存在滞后性,其瞬态启动特性会影响微小通道的稳态换热性能;0.2 mm槽宽的连通微小通道(IPM02,命名方式下同)具有较好的核态沸腾换热性能,因此启动阶段不存在温度过冲;最高测试热流密度下,IPM02和IPM07的传热系数相比于PPM分别提升约11%和5.7%,IPM12的传热系数则反而低于PPM。

高热流散热泵驱两相流体回路设计及飞行验证

针对激光、雷达等载荷空间应用中存在的超过100 W/cm^2高热流密度散热问题,采用泵驱两相流体回路结合金刚石微槽道的方法实现了271 W/cm^2热流密度的散热。对系统设计及关键部件设计进行了研究,整个系统经过地面和在轨飞行验证,运行平稳。利用储液器控温的方式,实现了系统温度的准确控制。测试结果表明,地面和在轨飞行期间的换热及流阻相当,验证了重力无关设计的正确性。

环管反应器内液固两相流的数值模拟

为了对环管反应器内液固两相的流动形态进行研究,建立了以颗粒动力学为基础的Euler-Euler双流体模型。在浆液流速远大于自由沉降速度的情况下,模拟了不同浆液入口速度时的环管反应器上升段压力降,同时对管道内液固两相流中的一些重要参数进行了数值研究:在入口液固两相体积分布均匀的情况下,环管反应器上升段、弯管段以及下降段液固两相体积分布和液固两相速度均不一样,在弯管段由于离心力存在而引起管道内二次流,使得固相颗粒甩向弯管的外侧壁,引起固相体积分数在弯管外侧壁明显增大,管道内固体颗粒相分布不均。在浆液速度v=3m·s-1时,液相和固相的速度有一定的速度差,随着入口速度增大,速度差变小;当浆液速度v=7m·s-1时,固体颗粒相速度分布与液相速度基本相同,两者之间的滑移速度可以忽略。计算结果与传统经验公式的比较表明模型能有效地描述环管反应器内压力降和反应器内浆液流动形态。

两相控温型储液器进出流量的瞬态数值模拟

两相控温型储液器是泵驱两相流体回路(MPTL)系统中的一个重要部件,承担着工质存储、供给、气液分离及精密控温的作用。采用Navier-Stokes方程建立了MPTL系统瞬态模拟的仿真模型,可用于研究热源功率变化时储液器与主回路的动态传热和传质特性。通过仿真与试验对比发现,数值模型的流量误差在±10%以内,验证了模型的有效性和准确度。数值模拟结果表明:热源开关机时,储液器与主回路发生工质交换,气液两相的温度和压力受到影响,系统的流阻也受到影响;随着热源功率的增加,工质交换速率和交换总量随之增加,储液器内气液两相的温度和压力变化趋势随之增大。该模型可用于研究不同工作条件下的流量、温度和干度的变化特性,指导MPTL设计,并在系统搭建前预测系统特性。

空间两相环路热控系统的动力学特性

针对两种典型的两相环路热控系统——毛细力驱动的平板型环路热管和机械泵驱动的两相环路热控系统(硅微条探测器控温系统,TTCS)展开讨论,分析其工作原理,介绍地面测试实验系统,使用SINDA/FLUINT和Maltab/Simulink软件分别建立其动态模型.研究结果表明,平板型环路热管和TTCS均存在启动问题;平板型环路热管运行时可能有较严重的稳定性问题,而TTCS的稳定性相对较高;重力对平板型环路热管的性能有较大影响,TTCS受重力的影响不大;双通道平板型环路热管可以比单通道环路平板型环路热管有更优异的传热性能,而TTCS的双辐射器结构可以有良好的流量和热量自调节能力.在选择两相环路热控系统时,需考虑热源的分布特点、寿命要求、控温要求以及系统尺寸和质量等因素,这两种两相热控技术未来可交叉借鉴、优势互补.

CCD器件用机械泵驱动两相流体回路仿真与试验

电荷耦合元件(CCD)作为航天光学遥感器的核心部件之一,其工作性能受温度影响很大,传统的热控产品难以满足大功率CCD的精密控温需求。通过仿真与试验系统研究了机械泵驱动两相流体回路(MPTL)用于CCD控温时的启动特性、运行状态、内部工质的流动及传热特性。结果表明:MPTL可以通过干度的调节来吸收冷凝器外热流和CCD工作模式的影响; MPTL的控温精度可以达到±1℃,蒸发器并联支路、蒸发器负载和冷凝器温度在一定范围内变化等均不会对系统运行稳定性产生影响,其仍可将CCD器件控制在所需温度;通过仿真与试验对比,发现仿真模型的误差在±1℃以内,验证了模型的有效性和准确度。MPTL可以很好地满足航天光学遥感器CCD的控温要求,能够保证CCD始终具有较好的温度稳定性和均匀性,且系统具有良好的运行特性和鲁棒性,其在CCD精密控温方面具有很好的应用前景。

嫦娥三号“玉兔”巡视器热控制

根据嫦娥三号'玉兔'巡视器总体构形特点和任务过程中的环境条件,提出了巡视器月昼散热和月夜保温热控设计思路,具体描述了巡视器月昼朝天散热和月夜利用两相流体回路、同位素热源进行设备保温的热控设计方法。经过热平衡试验验证和在轨飞行验证,热控分系统的各项功能和性能均满足总体要求,设备温度均控制在所要求的温度范围内,表明热控设计是合理和可行的。