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Analysis of frost formation in an evaporator.

机译：分析蒸发器中的霜形成。

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摘要

Fundamental understanding of frost inception and growth on a cold surface shows that the water vapor must be supersaturated for frost to form. This understanding is new, relative to previously published frost growth studies, which assume saturation at the frost surface. The frost nucleation process requires supersaturation of water vapor, and the degree of the supersaturation is strongly dependent on the surface energy. Theoretical analysis of the effect of the surface energy of substrates on frost nucleation was compared to the experimental data. This understanding was applied to a frost growth model. All previously published frost growth models assume that the water vapor is saturated at the frost surface. Using the boundary layer analysis, a procedure to obtain the supersaturation degree at the frost surface was developed, and a simple equation for the supersaturation degree at the frost surface was generated by a regression method using the supersaturation values calculated at the different frosting conditions. This was compared to the experimental results. The saturated interface model results in over-prediction of the mass transfer rate by 4-to-30 times the present experimental values. However, it was found that the present supersaturation model predicts the mass transfer rate within approximately 0∼25% error. It was impossible to compare this finding to the published results because no published data was found for the mass transfer rate at the frost surface from the air stream. Defrosting process by heating the cold surface was analyzed. It was found that the required defrosting time is dependent only on the frost thickness and the temperature of the surface, and that the frost properties (thermal conductive and density) have little affected the defrosting time. Also, it is shown that better time-average evaporator performance will result if the retained water is re-frozen, rather than drying the surface.
机译：对寒冷表面上霜的发生和生长的基本了解表明，水蒸汽必须过饱和才能形成霜。相对于以前发表的霜冻生长研究，这种认识是新的，霜冻生长研究假定霜冻表面处于饱和状态。霜成核过程要求水蒸气过饱和，而过饱和的程度在很大程度上取决于表面能。将基质表面能对霜成核作用的影响的理论分析与实验数据进行了比较。这种理解被应用于霜冻生长模型。以前所有已发布的霜冻生长模型均假定水蒸汽在霜冻表面处饱和。使用边界层分析，开发了获得霜表面的过饱和度的程序，并使用在不同结霜条件下计算出的过饱和度值，通过回归方法生成了霜表面的过饱和度的简单方程式。将其与实验结果进行比较。饱和界面模型导致传质速率的过高预测是当前实验值的4到30倍。然而，发现目前的过饱和模型预测传质速率在大约0〜25％误差内。不可能将这一发现与已发表的结果进行比较，因为未找到已发布的数据来说明气流中霜表面的传质速率。分析了通过加热冷表面的除霜过程。发现所需的除霜时间仅取决于霜的厚度和表面温度，并且霜的性质（导热性和密度）几乎不影响除霜时间。另外，还表明，如果保留的水被重新冷冻而不是干燥表面，则可获得更好的时间平均蒸发器性能。

著录项

  • 作者

    Na, Byeongchul.;

  • 作者单位

    The Pennsylvania State University.;

  • 授予单位 The Pennsylvania State University.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2003
  • 页码 273 p.
  • 总页数 273
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 机械、仪表工业;
  • 关键词

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