土壤空气换热器换热特性的模拟研究

文章针对日光温室环境下土壤空气换热器的换热特性进行了研究。首先通过监测土壤空气换热器沿程空气温度的全天变化,分析了试验工况下土壤空气换热器的动态换热过程及系统性能变化规律。研究结果表明,在试验工况下,土壤空气换热器系统的性能系数(COP)可高达24.1。在此基础上,通过建立土壤空气换热器的非稳态换热模型,模拟研究不同的入口风速对土壤空气换热器换热性能的影响。研究结果表明,当换热管入口空气温度相同时,随着入口风速的增加,土壤空气换热器进出口空气温度差逐渐减小,出口处空气温度与土壤温度差值逐渐增大,这意味着土壤空气换热器有效换热长度逐渐变长。在此过程中,土壤空气换热器系统的换热量和COP随着入口空气风速的增加呈现出先增后减的规律。通过模拟结果可知,当入口风速达到5.5 m/s时,土壤空气换热器系统的换热量与COP均达到最大值。     

低气压环境下开缝翅片管换热器换热性能研究

利用低气压环境模拟装置对开缝翅片管换热器在不同气压下的换热性能进行实验研究.研究结果表明:随着气压不断降低,换热器周围空气密度逐渐降低,换热器空气侧换热系数以及显热换热量逐渐降低,而空气含湿量随着气压降低逐渐升高,导致潜热换热量逐渐增加;当气压降至0.058 MPa以下时,换热器空气侧潜热换热量占主要部分,当气压为0.04 MPa时,换热器换热能力与常压下相比下降了36.63%.     

汽车空调性能试验台总成——主机及风洞系统的研制与试验分析

针对微通道换热器用作汽车空调冷凝器的特点,研制了一套冷凝器单体性能测试试验台,即主机及风洞试验台.该试验台主测风洞系统的换热量采用空气焓差法测试,辅测主机系统的换热量采用制冷剂流量计法测试,并选取两款微通道冷凝器对其进行冷凝换热试验,以验证该试验台的稳定性和准确性.结果表明,该试验台空气侧和制冷剂侧所测得的换热量偏差均在5%以内,满足冷凝器测控要求.根据实验数据得到了冷凝器迎面风速对换热量、空气压降和制冷剂压降的影响规律,为微通道换热器的优化设计及企业的相关研究提供参考.     

湿工况下低气压对翅片管换热器换热特性的影响

在高空低气压环境下模拟舱内对开缝翅片管换热器在湿工况下的换热特性进行了实验研究,分析了不同环境压力对空气侧换热特性的影响,包括显热换热、潜热换热和努赛尔数的变化规律。实验结果表明,当干球温度和相对湿度不变时,湿工况下空气侧显热换热量、潜热换热量和空气侧传热系数均随着环境压力的降低而减小;而单位质量潜热换热量几乎不变,潜热换热所占比例略微增大。同一个环境压力下,入口空气的相对湿度对换热器的显热换热量影响不大,而对潜热换热量影响显著。当相对湿度分别为40%、60%和80%时,显热换热量差异小于5%;而潜热换热量当相对湿度为80%时,是相对湿度为40%时的5.9~6.8倍。     

椭圆管翅式换热器空气侧传热和流动特性的数值模拟

建立了椭圆管百叶窗翅片换热器三维模型,对椭圆管翅式换热器空气侧传热和流动特性进行了数值模拟,分析管径、管排数、翅片间距对椭圆管翅式换热器空气侧传热流动的影响。结果表明:管排数为1～3时,椭圆管百叶窗翅片换热器空气侧换热系数随换热器管排数的增加而降低,最大降幅达17.1%;椭圆率为2:3的椭圆管翅式换热器综合性能最好,与同周长圆管管翅式换热器相比,换热性能提高了10.1%,降阻幅度达32.3%;随着风速的提高,翅间距对管翅式换热器换热性能及阻力影响逐渐降低。     

相关参数对增强型冷却塔换热性能影响的研究

以增强型冷却塔为研究对象,通过数值模拟的方法,对其在不同环境温度、湿度及不同换热器布置下的换热性能进行计算与分析,得到不同条件下空气流量和换热量的分布。研究表明:系统换热量随空气湿度增加小幅度增加,而随温度的增加却有较大幅度的下降;在换热面积一定且换热器均匀分组条件下,如换热器间隙有填塞物,换热量随着覆盖率的增加而减小;若换热器间隙无填塞物,换热量随着覆盖率的增加而增加至覆盖率为93%达到最大值,随后减小。最优换热器布置为:覆盖率93%,换热器分组均匀且尽量细分,间隙内无填塞物。     

汽车空调换热器性能试验台的研制及实验分析

根据换热器性能测试的空气焓差法和制冷剂流量剂法,设计了汽车空调换热器性能测试试验台的制冷剂工况系统和焓差室测试系统。该试验装置不仅可以对汽车空调换热器在实际运行状态下的换热量和阻力特性进行试验研究,还可以进行整机性能试验。为验证试验台的稳定性和可靠性,分别进行了环境室工况条件试验以及冷凝器和蒸发器的样件的单体性能测试试验。通过对试验数据的计算分析,得出实验台的主测空气侧和辅测制冷剂侧换热量偏差均在3%的范围内,满足国标和企业技术要求。     

利用寒冷空气自然冷量的翅片管式换热器设计与分析

为了充分利用我国西北地区冬季丰富的自然冷量,设计了能够利用冷空气对盐水降温的翅片管式换热器。对换热器进行了结构设计,采用计算流体动力学Fluent软件对换热器空气侧的温度场和速度场进行了模拟,分析了空气流量和盐水流量变化对传热性能的影响。结果表明:当环境温度变化时,换热器空气侧的温度场和速度场整体分布较为均匀;总传热系数随空气流量和盐水流量的增加而增大,但幅度越来越小;实际换热量随空气流量的增加先增大后减小,随盐水流量的增加逐渐增大,但幅度越来越小。     

不同流程平行流换热器换热性能分析

采用3个不同流程布置的微通道换热器进行循环水冷散热实验,研究不同流程及风速布置下的微通道换热器的换热性能。换热器的水冷介质为乙二醇溶液,具有凝固点低、比热高的特点,能够满足不同地区室外环境温度需求。结果显示：不同流程布置对微通道换热器的换热量和压降有影响,随着流程数的增加,换热器的换热量和压降都随之增加,4流程换热器比1流程换热器换热量最多增加了11.1%,增长速率随着风速和流量的升高逐渐减小;而4流程换热器比1流程换热器的压降最多增大了150%,增长幅度随着流量的增加而增加。     

新型液压油冷却系统换热器优化设计

板翅式换热器在液压油冷却系统中体积较大,制造成本高,接触热阻大,换热效果不佳。因此,将平行流换热器应用到液压油冷却系统中,提高换热效率。本设计在换热量相同的工况下,利用VB编写应用程序,对不同的扁管孔数平行流换热器进行优化设计,得出质量最轻、换热效果最佳的换热器,并将优化后的换热器与目前重型机械中所使用的板翅式换热器进行对比分析。     

空气横掠矩形翅片椭圆管束换热规律的数值研究

采用Fluent软件对矩形翅片椭圆管束空气侧的对流换热情况进行了三维数值模拟,获得了不同流速下翅片表面温度分布,分析了迎面风速与换热系数之间的关系,随着速度的增大,空气侧的换热系数增加,并拟合了换热计算公式。同时分析了不同翅片间距对换热的影响因素,随着翅片间距的增大,空气侧换热系数增加,而且随着Rg数的增加,换热的强化更加明显。     

Heat extraction characteristic of embedded heat exchanger in honeycomb ceramic packed bed

On the basis of experimental verification of mathematical model, the influence of honeycomb ceramic on heat extraction is numerically studied under the steady state condition. The calculation results show the packed honeycomb ceramic influences the extracted heat of heat exchanger by changing the flow field while not radiation heat transfer of heat exchanger outer wall, and the difference between the extracted heat of heat exchanger embedded in packed bed and that of heat exchanger in empty bad is gradually obvious with gas temperature increasing under the condition of the same gas mass flow rate. In addition, under the same operating condition, when the two characteristic sizes of heat extraction zone honeycomb ceramic in the vertical gas flow direction increase, the extracted heat of embedded heat exchanger shows a trend of first increase while extracted heat of embedded heat exchanger shows a trend of decrease because the decreasing of the windward and leeward side gas flow velocity of heat exchanger results into weakening of convective heat transfer of embedded heat exchanger outer wall.     

结构参数对电厂翅片管散热器动态特性的影响

散热器经常处于变化的工作条件中,研究散热器的动态特性有助于改善间接空冷系统的安全和经济运行,而散热器的结构参数会影响其动态特性。根据能量守恒建立了散热器空气、管壁和循环水的热平衡偏微分方程,采用改进欧拉法对偏微分方程组进行求解。以迎面风速阶跃变化为典型工况,研究了换热面积、换热系数和工质体积对散热器动态特性的影响。结果如下:当空气侧换热面积增加时,散热器换热量增大,两个稳态之间的空气出口温度差值不变,循环水出口温度差值增加,空气侧响应时间增加,循环水侧响应时间不变。当循环水侧换热面积增加时,散热器换热量增大,两个稳态之间的空气和循环水出口温度差值不变,空气侧和循环水侧的响应时间也不变。换热系数变化时,散热器动态过程的变化规律与换热面积变化时类似。空气侧工质体积变化对散热器动态特性没有影响。循环水侧工质体积增大会使得动态响应时间变长。     

Heat pipe heat exchanger for heat recovery in air conditioning

The heat pipe heat exchangers are used in heat recovery applications to cool the incoming fresh air in air conditioning applications. Two streams of fresh and return air have been connected with heat pipe heat exchanger to investigate the thermal performance and effectiveness of heat recovery system. Ratios of mass flow rate between return and fresh air of 1, 1.5 and 2.3 have been adapted to validate the heat transfer and the temperature change of fresh air. Fresh air inlet temperature of 32–40 °C has been controlled, while the inlet return air temperature is kept constant at about 26 °C. The results showed that the temperature changes of fresh and return air are increased with the increase of inlet temperature of fresh air. The effectiveness and heat transfer for both evaporator and condenser sections are also increased to about 48%, when the inlet fresh air temperature is increased to 40 °C. The effect of mass flow rate ratio on effectiveness is positive for evaporator side and negative for condenser side. The enthalpy ratio between the heat recovery and conventional air mixing is increased to about 85% with increasing fresh air inlet temperature. The optimum effectiveness of heat pipe heat exchanger is estimated and compared with the present experimental data. The results showed that the effectiveness is close to the optimum effectiveness at fresh air inlet temperature near the fluid operating temperature of heat pipes.     

螺旋扭曲椭圆管换热器壳程数值模拟

以水为介质,采用k-ε模型,用数值模拟方法研究了5种不同结构的螺旋扭曲椭圆管换热器的管外壳程传热与流阻性能,并和采用椭圆管作为换热部件的换热器进行了比较.研究结果表明,螺旋扭曲椭圆管换热器壳程有较好的强化换热特性,螺旋扭曲椭圆管的几何尺寸和流体流动速度对壳程传热与流阻性能有重要影响.通过数值模拟所获得的规律为螺旋扭曲椭...     

氢化物车用空调模拟换热器传热试验研究

对作者自行设计制造的氢化物空调模拟换热器,进行了非吸放氢循环下的传热试验,获得了传热系数,空气流阻和Ｎｕ与Ｒｅ的关系式,提出了进一步提高反应器传热系数的方法。为实际车用氢化物空调反应器的设计提供了依据。     

同轴径向热管换热器壳程流场数值模拟

基于多孔介质模型和分布阻力方法,引入Al-sanea和Taborek两种阻力关系式模拟同轴径向热管换热器壳程的流场。结果表明:换热器壳程静压沿烟气流动方向呈线性分布;随入口烟气速度的增加,换热器阻力损失增大、压降增大;且随入口烟气速度的增加,压降增加的速率增大。     

Numerical studies on flow and heat transfer in membrane helical-coil heat exchanger and membrane serpentine-tube heat exchanger

The flow and heat transfer characteristics of synthesis gas (syngas) in membrane helical-coil heat exchanger and membrane serpentine-tube heat exchanger under different operating pressures, inlet velocities and pitches are investigated numerically. The three-dimensional governing equations for mass, momentum and heat transfer are solved using a control volume finite difference method. The realizable k-ε model is adopted to simulate the turbulent flow and heat transfer in heat exchangers. There flows syngas in the channels consisting of the membrane helical coils or membrane serpentine tubes, where the operating pressure varies from 0.5 to 3.0 MPa. The numerically obtained heat transfer coefficients for heat exchangers are in good agreement with experimental values. The results show that the syngas tangential flow in the channel consisting of membrane helical coils is significant to the heat transfer enhancement to lead to the higher average heat transfer coefficient of membrane helical-coil heat exchanger compared to membrane serpentine-tube heat exchanger. The syngas tangential velocity in the membrane helical-coil heat exchanger increases along the axial direction, and it is independent of the gas pressure, increasing with the axial velocity and axial pitch rise and decreasing with the radial pitch rise.