基于泡沫铜/石蜡的动力电池散热性能研究

石蜡作为一种相变材料具有稳定性好、成本低廉等优点,但是其缺点是导热系数较低。利用泡沫铜的多孔结构,将石蜡压入泡沫铜的孔隙中作为相变材料的本体,在此结构中,泡沫铜不仅发挥了多孔连续框架的优势,而且作为强化传热骨架,结合了石蜡相变吸热的性质,在一定程度上弥补了石蜡导热系数较低的不足。实验对电池和电池模块进行不同工况、不同放电倍率的测试,比较各工况下单体电池及电池模块温度分布情况,可以得出泡沫铜/石蜡相变材料冷却系统中动力电池的散热效果非常明显。     

泡沫金属内嵌石蜡水平蓄器内凝固放热实验

蓄能技术,尤其是蓄热技术,与太阳能光热利用系统集成耦合,可有力解决太阳能间隙性问题,提高太阳能热利用品质和利用效率,为光热利用系统提供稳定的能流输出。为解决工程常见的相变材料热导率低、蓄/放热系统效率不高的关键问题,选取石蜡为蓄热介质,设计了一种水平管内填充泡沫金属的蓄热单元,探究相同蓄热工况(70.0℃蓄热)、不同放热流体温度(10.0℃、15.0℃、20.0℃、25.0℃、30.0℃)下泡沫金属内嵌石蜡的凝固相变行为。通过高清相机拍摄得到凝固相界面的实时位置,通过热电偶测量获得凝固过程中内部温度响应规律。实验结果表明,冷流体温度越低,凝固速率越快;相比较30.0℃的放热工况,冷流体为10.0℃时石蜡完全凝固时间缩短了52.0%。同一径向距离测点的竖直高度越高,温降越快,其温度响应率也越大;但轴向位置对凝固测点温度变化影响差异不大。以1b测点的温度响应值为基准进行比较,10.0℃、15.0℃、20.0℃、25.0℃、30.0℃冷却工况下1a点温度响应率分别提高了7.2%、8.8%、10.3%、10.8%、11.7%。本研究有助于推广泡沫金属相变蓄热器的工程应用,为泡沫金属内嵌固液相变材料的结构设计与运行参数选取提供指导和帮助。     

泡沫金属内石蜡相变凝固的数值模拟

研究了泡沫金属中相变材料的相变熔化过程,由于金属骨架和相变材料传热性能的巨大差异,建立了骨架和相变材料的双温度模型,采用显热容法进行了数值模拟。模拟结果显示,相变材料中填充泡沫金属,能有效改善相变材料的温度分布;在相变时,骨架与相变材料的温差较大,局部热不平衡明显;泡沫金属孔隙率越小,石蜡熔化越快。     

泡沫铜强化石蜡相变蓄热特性的数值分析

通过构建泡沫金属内固液相变传热模型,对方腔蓄热单元中泡沫铜强化石蜡相变蓄热特性进行数值分析。数值模型采用考虑泡沫金属真实结构的等效导热系数通用模型,并兼顾石蜡在融化前后与金属骨架之间的热非平衡效应。通过求解模型得到方腔内石蜡固液界面演化规律与温度分布,进而对蓄热过程进行火用分析。结果表明:当前数值模型能较好地预测泡沫铜内固液相变传热;泡沫铜显著改善了石蜡相变的空间均匀性,减小了蓄热区温度梯度,使蓄热速率和火用效率得到有效提高。     

TPS法测定泡沫铜/石蜡复合相变材料热物性

运用瞬态平面热源法(Transient Plane Source-TPS)对4种孔隙率的泡沫铜/石蜡复合材料热物性进行了测量。以10μm厚的镍金属按双螺旋线布置作为测量探头。泡沫铜材料孔隙率分别为ε=97.79%、ε=96.17%、ε=94.94%和ε=93.26%,经线切割加工后向内灌入液态石蜡,凝固后作为测试样品。在室温(25±1℃)和常压下对复合材料的等效导热系数、热容及热扩散率进行了测量。测试结果表明:复合材料导热系数和热扩散率因泡沫铜的加入而大幅提高,在孔隙率ε=93.26%时,等效导热系数已达到单纯石蜡的25倍,而复合材料等效热容则由于铜金属加入的绝对量较少相对原石蜡热容变化较小。以比例加成的方法对泡沫铜/石蜡复合材料的等效热容进行了计算,并利用实验数据拟合了其等效导热系数的计算公式,运用这些公式对复合材料物性的计算结果与实验结果非常吻合。     

基于孔隙尺度的填充床内热态流场数值研究

利用孔隙尺度介观方法对交错排列的固体小球的三维填充床进行数值模拟。研究高温条件下,考虑小球内部的热传导和小球表面的辐射换热时,固体小球和流体之间热的非平衡性以及孔隙内的流动特性。数值计算与实验结果吻合较好。结果表明:除进出口通道外,填充床内同相和异相之间都存在热的非平衡性,气相处的温度变化比气固两相交替处的温度变化更剧烈;无量纲速度分布呈周期性变化,气相处最大无量纲速度在13～14之间,最小无量纲速度约为0.5。     

基于泡沫铜翅片换热器的烟气水分回收实验研究

搭建了以泡沫铜翅片换热器为核心的烟气水分回收实验台,研究了冷却水进口温度、烟气雷诺数及烟气中水蒸气体积分数对该换热器水回收特性和换热特性的影响,基于实验数据,利用多元回归拟合得到对流换热的关联式,其预测值与实验值误差在6%以内。结果表明：水蒸气体积分数增大可以显著提升水回收特性,而冷却水进口温度及烟气雷诺数对其影响很小;冷却水进口温度与烟气雷诺数对换热效率的影响较大,冷却水进口温度与换热效率成反比,烟气雷诺数与之成正比,而水蒸气体积分数对其影响较小;实验获得的最大冷凝水产率为7.68 kg/h,最大冷凝率为56.94%,最大换热效率为96.95%。     

泡沫铜对相变蓄热系统蓄热性能影响的实验研究

石蜡作为一种有机固液相变材料,因其具有高潜热值、无毒、无腐蚀、性能稳定等优点被广泛应用于热蓄存、电子冷却及建筑温控等领域。但在蓄热过程中,因石蜡导热系数较低,导致蓄热时间过长、温差过大。实验按照1∶3的比例将泡沫金属铜均匀分布在石蜡箱体中,探究泡沫铜对石蜡相变速率的影响。结果显示:加入泡沫铜后,有效地提升了石蜡的相变速率,缩短了石蜡相变的时间;同时加入泡沫铜后,石蜡内部温差明显减小,温度分布更加均匀,并且有效缓解了自然对流造成的顶部过热和底部不熔化现象。     

金属泡沫内石蜡固液相变蓄热/放热实验

针对解决太阳能热利用过程中所面临的辐射强度不稳定、不连续和不均匀等关键问题,相变蓄热技术常与太阳能热利用系统耦合协同匹配,以实现稳定连续的热量输出。为了强化固液相变蓄热/放热过程、提高系统热储能效率,对金属泡沫内石蜡类相变材料(PCMs)在不同蓄热流体温度下的固液相变蓄热/放热特性开展了实验研究。设计并搭建了相界面可视化的蓄热/放热实验系统,实验过程中使用高清相机对相变过程中的相界面变化进行了记录。同时,通过在蓄热单元内部布置多个热电偶测点,对蓄热/放热过程中的温度变化规律进行了探究。实验结果表明,受自然对流影响,熔化过程中相界面由上至下变化;而凝固过程中由于初始时蓄热单元下部温度较低且存在自然对流,此时相界面自下而上变化。蓄热流体温度越高,熔化所需时间越短,与蓄热流体温度为65℃的工况相比,蓄热流体温度为85℃、80℃、75℃、70℃工况的完全熔化时间分别减少了56.0%、46.7%、15.4%和26.7%。当采用不同温度的流体进行蓄热工况时,相变材料内部温度呈现出具有明显差别的温升规律。尽管如此,当采用相同温度的换热流体进行放热工况时,相变材料的放热温度仍趋于一致。     

复合相变材料调控机理与强化换热的实验研究

为获取相变温度、潜热和导热性都比较合适的相变材料,本文使用高熔点的固态石蜡(熔点为70℃)和低熔点的液态石蜡(熔点为5℃)按照不同比例进行配比实验,来获得不同相变范围的相变材料,以适应实际应用的要求.制备了五种复合相变材料样品,使用差式扫描量热仪(DSC)测试其参数.并选用孔隙率均为95％,孔隙密度(pores per...     

Role of metal foam in solidification performance for a latent heat storage unit

The current latent heat storage (LHS) units are usually poor in energy charging and discharging efficiency. Given this, a two dimensional (2D) numerical model of the energy discharging process is presented and comprehensively analyzed to predict the role of metal foam in the solidification performance of LHS units. In the model, the fractal geometry reconstructed by the fractal Brownian motion is utilized for the pore characterization of the metal foam. The proposed model is validated through a melting experiment in copper foams from the reference. The temperature dynamic response and the solidification front evolution in metal foam are analyzed and compared to those in a corresponding cavity. The roles of the fractal dimension and porosity in the solidification behaviors are quantitatively analyzed. The results report that the presence of metal foam enhances the solidification performance. For the main goal of maximizing the latent storage, the appropriate porosity of an LHS unit is dependent on the duration time for the heat discharging process in the real application of thermal energy storage. Even if the porosity is the same, the fractal dimension also affects the solidification performance. A decrease in the fractal dimension (lower degree of disorder for pore distribution) provides greater access to heat flow through the phase change material-foam composite and thus leads to improvement in the interstitial heat transfer, which in turn accelerates the rate of heat release. The fractal dimension is expected to be less than 1.5 for superior solidification performance.     

Experimental study of thermal performance improvement in a cross-flow heat exchanger by using copper foam

In this study, copper foam was used as a porous medium in place of traditional aluminum fins. A comparison between the two heat exchangers—one with fins and the other with copper foam—was conducted under various conditions. The air inlet velocity ranged from 0.9 to 9.3 m/s, and the water inlet temperature ranged from 10°C to 18°C. Different water flow rates were tested. A comparison was made between the performance of copper foam and aluminum fins by calculating several parameters, including thermal resistance, heat exchanger effectiveness, Colburn factor, Nusselt number, friction factor, and area goodness factor (AG). The experimental results showed that at low air velocities, the heat transfer coefficient for both types of heat exchangers was almost equal. However, at high air velocities, the copper foam exhibited a higher heat transfer coefficient. The Colburn factor was higher for the heat exchanger with copper foam than in the conventional fins, where it was equal to 0.1959 for the copper foam and 0.1186 for the fins. On the other hand, the AG was higher in the case of fins than in the heat exchanger with copper foam.     

石蜡/泡沫铝复合相变材料对太阳池热性能的影响

传统盐梯度太阳池以显热储热,储热密度较低。提出了在储热层添加石蜡/泡沫铝复合多孔介质相变层的方法,构建了宽度为300mm,长度为400mm,深度为500mm的小型实验太阳池,分别进行了传统盐梯度太阳池和添加石蜡/泡沫铝复合多孔介质相变材料(PCM)的太阳池热性能对比实验。实验研究与理论分析表明:未添加石蜡/泡沫铝复合PCM的下对流层(LCZ)的储存(火用)和(火用)效率的最大值分别13.814 MJ/m³与9.38%;添加4块石蜡/泡沫铝复合PCM的LCZ的储存(火用)和(火用)效率的最大值分别为15.659 MJ/m³与12.05%,同前者对比分别提高了1.845 MJ/m³与2.67%,从而证明石蜡/泡沫铝复合PCM能够有效提高LCZ的储存(火用)与(火用)效率。此外,后者在太阳池LCZ的温度上升期可使其温度提高3℃左右,因此,添加石蜡/泡沫铝复合PCM能够提升太阳池LCZ的蓄热能力。     

Solidification process analysis of a heat storage device containing graphite foam and paraffin

石蜡相变材料的导热系数较小,严重影响了其传热速率和凝固速率。通过对填充石墨泡沫/石蜡的储能系统进行凝固过程的模拟,确定了石墨泡沫对相变储能系统性能的影响。研究结果表明石墨泡沫不仅大大缩短了相变凝固时间,也使储能系统的温度分布更加均匀;通过分析冷却水进口速度和温度对复合相变材料的凝固过程的影响,说明随着冷却水进口速度的增大和温度的降低,传热速率加快,凝固时间缩短。分析了复合材料相变区的自然对流对相变过程的影响,模拟结果证明自然对流能在一定程度上加快相变材料的凝固过程。     

电热式熔融固化垃圾焚烧飞灰的实验研究

对高温管式炉熔融固化垃圾焚烧飞灰的处理效果进行了实验研究.进一步考察了浸出环境对飞灰固化效果的影响.结果表明,根据国家的浸出标准,飞灰熔融固化后就不再是具有浸出毒性的危险废物.酸性（pH≤4.5）和碱性（pH≥1.5）环境对固化效果的影响比较大;潮湿的环境（L/S≤100）对固化效果无明显影响.     

Experimental study on blocking mechanism of nitrogen foam for enhancing oil recovery in heavy oil reservoirs

Foam flooding is one of the effective techniques during thermal recovery process in heavy oil reservoir. Nitrogen is generally co-injection with the foaming agent for the generation of foam. However, the mechanism has not been totally understood, thereby requiring further discussion. In this study, a series of sand pack experiments for nitrogen foam steam flooding were designed and conducted. A comparison of influencing factors, including gas-liquid (foaming agent) ratio, permeability, injection scheme, and oil saturation was used to evaluate the stability and blocking mechanisms of foam. The results show that the blocking capacity of the gas-liquid ratio of 1:1 is the greatest in all cases under high-temperature condition. The blocking mechanism of foam is analyzed, which indicates that foam is selective to block larger pores and throats in porous media with high-permeability. And also, the stability of foam becomes worse while meeting oil. This characteristic is favorable for improving the sweep efficiency to enhance oil recovery in developing heavy oil reservoir.     

Thermal conductivity of aluminum foam based on 3‐D stochastic sphere model

To accurately characterize the geometric structure of closed‐cell aluminum foam, a three‐dimensional stochastic sphere model with adjustable porosity and pore size was established, and its thermal conductivity was studied by numerical simulation. A closed‐cell aluminum foam heat conduction experiment was designed to verify the accuracy of the model. Using this model, the thermal conductivity of aluminum foam with different pore sizes and porosity was calculated, and the variation of thermal conductivity was studied. The results show that with the same porosity, the thermal conductivity increases linearly with the pore size. With the same pore size, the thermal conductivity decreases linearly with the porosity. The equivalent thermal conductivity decreases with the increase of porosity. According to the simulation results, the formula of equivalent thermal conductivity of aluminum foam is .     

水合煅烧改性CaO孔隙的实验分析

水合煅烧是改善CaO脱硫性能的一种有效方式，从改变水钙比和煅烧温度两个影响因素出发，实验研究了高温煅烧后CaO颗粒孔隙特性的变化，并结合TGA实验测定了水合煅烧CaO的脱硫性能的改变效果，最后从孔隙内液体相变析出的膨化作用与毛细作用两个角度解释了实验现象。     

梯度孔密度金属泡沫的池沸腾传热性能研究

实验研究了梯度孔密度通孔金属泡沫的池沸腾传热性能。工质为去离子水,梯度孔密度金属泡沫材质为铜和镍, 孔隙率为0.98,泡沫厚度为4-14 mm。实验结果表明：相比于单层泡沫,梯度孔密度金属泡沫显著的增强了沸腾传热能力,但增强程度受孔密度变化梯度、泡沫厚度和材料的影响;梯度孔密度泡沫的池沸腾传热性能随着表面活性剂SDS浓度的增大而减小,而且SDS降低了梯度孔密度金属泡沫的临界热流密度; 添加Al2O3纳米颗粒严重的削弱了梯度孔密度铜泡沫的池沸腾传热能力。