Abstract Harnessing waste thermal energy from greywater (GW) in non-industrial buildings is becoming necessary to reduce energy demands, make heating/cooling technologies more efficient and to increase the share of renewables in the consumption. Harnessing this low grade energy to heat incoming cold water (CW) linked with phase change materials (PCMs) would decouple demand and supply along with integrating heat recovery with storage in a single unit, unlike technologies of the past. Radially installed rectangular copper fins around the GW and CW pipes of such heat exchanger (HE) enhance the thermal conductivity of the PCM which is the biggest obstacle in this high-impulse application, with the flow rate being high only for a short duration of time. Initially an experimental test rig is used to validate a numerical model as the basis of a sensitivity analysis to find the optimum geometric parameters of the finned HE for this application. A 40 × 90 mm fin with a 10 mm pitch provides complete phase change for both melting and freezing in the constrained time duration of 900s. Compared to a non-finned geometry this optimized fin configuration enhances the effective thermal conductivity of the PCM by a factor of 1.38 for melting and 4.75 for freezing. Although the development of buoyancy induced natural convection vortices are inhibited by fins the eventual heat transfer is enhanced due to a lower overall thermal resistance compared to a non-finned configuration. The GW to CW energy transfer efficiency is 72.4% with higher fluid flow temperature increments, compared to only 47.3% for a non-finned version.

中文翻译：

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用于低等级热利用的 PCM 中矩形翅片的数值分析

摘要 在非工业建筑中利用来自灰水 (GW) 的废热能来减少能源需求、提高加热/冷却技术的效率以及增加可再生能源在消费中的份额变得必要。与过去的技术不同，利用这种低等级能源来加热与相变材料 (PCM) 相关的进入冷水 (CW) 将使需求和供应脱钩，同时将热回收与存储集成在一个单元中。这种换热器 (HE) 的 GW 和 CW 管周围径向安装的矩形铜翅片增强了 PCM 的导热性，这是这种高脉冲应用中的最大障碍，流速仅在短时间内较高. 最初，实验测试台用于验证作为灵敏度分析基础的数值模型，以找到适合该应用的翅片 HE 的最佳几何参数。具有 10 mm 节距的 40 × 90 mm 翅片在 900 秒的受限持续时间内为熔化和冻结提供了完整的相变。与非翅片几何结构相比，这种优化的翅片配置将 PCM 的有效热导率提高了 1.38 倍（熔化）和 4.75 倍（冻结）。虽然浮力引起的自然对流涡流的发展受到翅片的抑制，但由于与非翅片配置相比较低的总热阻，最终的热传递得到了增强。GW 到 CW 的能量传输效率为 72.4%，流体流动温度增量更高，而只有 47%。