Nanoporous Membrane Tube Condensing Heat Transfer Enhancement Study
Nanoporous Membrane Tube Condensing Heat Transfer Enhancement Study
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DOI：
10.1115/imece2011-63530
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发表时间：
2015-05
期刊：
影响因子：
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通讯作者：
Ainan Bao;Dexin Wang;Cheng-Xian Lin
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文献类型：
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作者：
Ainan Bao;Dexin Wang;Cheng-Xian Lin
气体技术研究所（GTI）开发了一种由纳米孔膜管束制成的传输膜冷凝器（TMC），用于回收锅炉烟气中的水蒸气及其大量潜热，以提高锅炉效率并节约用水。当膜孔径为纳米级时，膜孔内的水蒸气冷凝现象与表面冷凝有两个不同之处。首先，根据孔隙毛细管凝结机理——开尔文方程，当局部气流相对湿度远低于100%时，就会发生孔隙凝结，因此在相同的表面温度下，与表面凝结相比，可能会出现更多的水凝结。其次，由于膜换热面不断将冷凝水排至透过侧，冷凝面上不会积水，这就消除了传统不透水冷凝面因冷凝液膜（或液滴）而产生的额外传热阻力。通过实验研究了具有相同特征尺寸的纳米多孔膜管束和不渗透不锈钢管束的现象。实验研究采用水蒸气质量分数11.3%、温度范围为65°C至95°C的烟气流，涵盖了典型的TMC余热回收应用参数范围。结果表明，在典型的冷凝换热条件下，膜管束的对流努塞尔数比不渗透不锈钢管束高 50% 至 80%。还进行了更多的参数研究以研究更广泛的参数。冷凝传热增强效应为使用纳米多孔膜表面设计高效冷凝换热器从高含水量低品位废热流中回收水蒸气及其大量潜热提供了良好的前景。版权所有 © 2011 by ASME
A Transport Membrane Condenser (TMC), made from nanoporous membrane tube bundles, was developed by Gas Technology Institute (GTI) to recover the water vapor and its significant amount of latent heat from boiler flue gases to improve boiler efficiency and save water. Water vapor condensing phenomenon inside membrane pores is different in two aspects from surface condensation when the membrane pore size is in the nanometer scale. First, based on the pore capillary condensation mechanism—Kelvin equation, pore condensation can occur when local gas stream relative humidity is well below 100%, so more water condensation is possible at the same surface temperature compared with surface condensation. Second, as membrane heat exchanging surface continues evacuating condensed water to the permeate side, no water will be accumulated on the condensing surface, which eliminates the additional heat transfer resistance caused by the condensed liquid film (or droplets) for a conventional impermeable condensing surface. Experiments have been carried out to study the phenomena for both a nanoporous membrane tube bundle and an impermeable stainless steel tube bundle with the same characteristic dimensions. Flue gas streams with a water vapor mass fraction 11.3%, temperature ranges from 65°C to 95°C were used for the experimental study, which covers the typical TMC waste heat recovery application parameter range. Results show the convection Nusselt number of the membrane tube bundle is 50 to 80% higher than that of the impermeable stainless steel tube counterpart at typical condensation heat transfer conditions. More parameter study was also done to study a wider range of parameters. The condensing heat transfer enhancement effect gives a good perspective for using nanoporous membrane surface to design high efficiency condensing heat exchangers to recover both water vapor and its substantial amount of latent heat from high moisture content low grade waste heat streams.Copyright © 2011 by ASME