Heat Transfer Properties of Metal Foam and its Application in HVAC Industry
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摘要: 由于泡沫金属具有密度低、体积比大、导热性高等特点,在工程应用领域引起关注。在制热和制冷行业中,紧凑型换热器、太阳能光热设施和热能储存是3大核心方向。换热方面,介绍嵌入金属泡沫的换热器,阐述传热方面金属泡沫基本理论;总结泡沫金属的传热特性中压降、传热系数和性能评价的经验和理论模型;分析其在传热增强和压降增加之间存在权衡;总结了热传导模型。能量转换和储存方面,金属泡沫在太阳能转换设备中有较高的转换效率,包括太阳能集热器中低温利用和高温利用太阳能接收器,并整理了与储能材料结合使用的泡沫金属的主要应用。泡沫金属在热力学领域研究能够为研究者带来新的契机,拓展新的研究方向,推动整个能源领域(暖通)的发展。
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表 1 泡沫金属流体流动模型[4]
流动模型 公式 Darcy $ \dfrac{{\Delta p}}{L} = \dfrac{\mu }{K}u $ Darcy‒Brinkman $ \dfrac{{\Delta p}}{L} = \dfrac{\mu }{K}u + \dfrac{\mu }{\varepsilon }\left( {\dfrac{{{\partial ^2}{u_x}}}{{\partial {x^2}}} + \dfrac{{{\partial ^2}{u_y}}}{{\partial {y^2}}} + \dfrac{{{\partial ^2}{u_z}}}{{\partial {z^2}}}} \right) $ Darcy‒Forchheimer $ \dfrac{{\Delta p}}{L} = \dfrac{\mu }{K}u - \dfrac{{{c_{\text{p}}}\rho }}{{\sqrt K }}{u^2} $ Darcy‒Brinkman‒Forchheimer $ \dfrac{{\Delta p}}{L} = \dfrac{\mu }{K}u + \dfrac{\mu }{\varepsilon }{\nabla ^2}u - \dfrac{{{c_{\text{p}}}\rho }}{{\sqrt K }}{u^2} $ 表 2 泡沫金属材料有效导热系数的5种基本理论边界模型
传热模型 结构示意图 有效导热系数计算公式 并联模型 $ {k_{{\text{eff}}}} = {v_1}{k_1} + {v_2}{k_2} $ Maxwell‒Eucken1 $ {k_{{\text{eff}}}} = \dfrac{{{v_1}{k_1} + {v_2}{k_2}\dfrac{{3{k_1}}}{{2{k_1} + {k_2}}}}}{{{v_1} + {v_2}\dfrac{{3{k_1}}}{{2{k_1} + {k_2}}}}} $ 等效介质理论模型 $ {v_1}\dfrac{{{k_1} - {k_{{\text{eff}}}}}}{{{k_1} + 2{k_{{\text{eff}}}}}} + {v_2}\dfrac{{{k_2} - {k_{{\text{eff}}}}}}{{{k_2} + 2{k_{{\text{eff}}}}}} = 0 $ Maxwell‒Eucken2 $ {k_{{\text{eff}}}} = \dfrac{{{v_1}{k_1} + {v_1}{k_1}\dfrac{{3{k_1}}}{{2{k_1} + {k_2}}}}}{{{v_2} + {v_1}\dfrac{{3{k_2}}}{{2{k_2} + {k_1}}}}} $ 串联模型 $ {k_{{\text{eff}}}} = \dfrac{1}{{\dfrac{{{v_1}}}{{{k_1}}} + \dfrac{{{v_2}}}{{{k_2}}}}} $ 表 3 换热器中泡沫金属与蓄热材料叠加使用应用实例
文献 形状 相变材料 相变材料潜热/(J/g) 研究方法 泡沫金属材料 结论 [13] 矩形 石蜡 184 实验法 铜 不同材质的泡沫金属可使传热速率增加到原有的两倍或者更大 [14] 圆柱形 二十烷 246 实验法 铜 加入相变材料导热系数从0.423 W∙m−1 ∙K−1提升到3.06W∙m−1 ∙K−1 [15] 平板形 石蜡 224 Gibson‒Ashby模型 铝 金属泡沫的加入可以提高纯PCM的固-液相变速率 [16] 矩形 石蜡 181 实验法+ Gibson‒Ashby模型 铜 与纯相变材料相比,泡沫金属在 PCM 固相区的传热具有显著影响。在熔化起始时自然对流可以改善传热性能,降低壁面和PCM 之间的温差。在两相区和纯液相区中,金属泡沫的加入可使总传热速率提高3-10 倍 [17] 矩形 石蜡 181 Gibson‒Ashby模型 铜 大上层小的复合相变材料明显比孔隙率分布为下层小上层大的材料传热效果好 [18] 圆柱形 石蜡 — 实验法 铜 加入泡沫金属不仅能提高蓄热过程中的相变材料的温度均匀性,还可以大大缩短了充热时间。 [19] 矩形 石蜡 181 Gibson‒Ashby模型 铜 泡沫金属铜的加入,提高了石蜡的蓄热性能,缩短了石蜡相变的时间,可缓解自然对流温度不均不熔化现象 [20] 矩形 石蜡 120 Boltzmann模型 铝 泡沫金属铜材料具有较高的导热系数和较大的孔隙率 [21] 矩形 石蜡 180 数值计算 铁 梯度泡沫金属所构成的复合相变材料,可以显著地缩短相变储热单元的充热和放热时间 [22] 壳管式 石蜡 181 Brinkman-extended Darcy模型 铝 泡沫金属可加强传热,但流体的压降也随之增大 [23] 矩形 石蜡 102.1 Boltzmann模型 铜 导热性能与泡沫金属的孔密度有着明显关系,孔密度的增加会在一定程度上削弱蓄热单元内的自然对流作用 [24] 壳管式 石蜡 117 Gibson‒Ashby模型 铝 研究了金属骨架结构不规则排列内嵌石蜡对有效导热系数的影响 [25] 壳管式 — — Brinkman-extended Darcy 模型 — 壳管式换热器传热面积较小,与其他换热器比较,其热熔化速率降低,镶嵌在石墨基体中的 PCM 壳管式换热器具有更好的应用前景 [26] 矩形 硝酸钠 178 Gibson‒Ashby模型 铜 翅片对竖直管壳式蓄能单元传热性能的影响关系可优化;提出在相变材料侧增加翅片可以强化传热 [27] 壳管束式 有机物A164 249.7 Brinkman-extended Darcy 模型 不锈钢316L PCM潜热越大,蓄热越好,温度分布约均匀 [28] 矩形 石蜡 136.4 实验法 铜 以导热为主的实验,金属铜+石蜡内部温度均匀,没有温度分层 [29] 矩形 石蜡 170.4 Gibson‒Ashby模型 铜 装有径向梯度孔隙率铜泡沫的竖直管壳式换热器与均质铜泡沫相比,总熔化时间减少了37.6% [30] 圆柱形 肉豆蔻醇 218.4 实验法 铜+镍 在相变过程中与石蜡相变材料一定差别,潜热越大储热时间越长 [31] 矩形 石蜡 200 实验法+Gibson‒Ashby模型 铝 复合相变材料的熔化速率和温度分布大大优于纯石蜡 [32] 矩形 水 335 实验法+Gibson‒Ashby模型 铝+铜+镍 与空气相比,对泡沫金属中的自然对流使用泡沫后的自然对流对水提高了4倍 -
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