In applications involving external condensation in the presence of noncondensable gases (NCG), there is a growing interest in horizontal tubes because they minimize condensate resistance, and hence reduce the adverse effects of NCGs. In the literature, experimental heat transfer rates are summarized in empirical correlations that fit the underlying data, but do not cover the spectrum of possible steam-NCG mixtures and thermal conditions. In this work, we aim at developing a general correlation that is applicable to a wide range of physical and geometrical conditions.

We first present a CFD model for laminar free convection regimes, taking into account the resistance of the gas phase and the liquid condensate. The model is validated against recent condensation data on steam-N₂ and steam-CO₂ mixtures. The predictions agree well with the data, being mostly within the experimental uncertainty.

Subsequently, close to 200 parametric CFD simulations are conducted for steam-air mixtures across a wide range of steam mass fraction (0.05–0.99), wall temperature subcooling (5-50 K), pressure (1–5 bar) and tube diameter (0.01–0.04 m). The resulting data are cast in a compact correlation that is compatible with the heat and mass transfer analogy. The proposed correlation is in good agreement with empirical correlations in the literature.

在存在不可冷凝气体（NCG）的情况下涉及外部冷凝的应用中，对水平管的兴趣与日俱增，因为它们最小化了耐冷凝液的能力，因此减少了NCG的不利影响。在文献中，实验传热率是根据经验相关性总结的，这些经验相关性适合基础数据，但未涵盖可能的蒸汽-NCG混合物和热工况的范围。在这项工作中，我们旨在开发适用于广泛的物理和几何条件的一般相关性。

首先，我们考虑了气相和液体冷凝物的阻力，提出了层流自由对流形式的CFD模型。该模型已针对最新的蒸汽-N ₂和蒸汽-CO ₂混合物的冷凝数据进行了验证。这些预测与数据非常吻合，主要是在实验不确定性范围内。

随后，针对广泛范围的蒸汽质量分数（0.05–0.99），壁温过冷（5-50 K），压力（1-5 bar）和管径（ 0.01–0.04 m）。结果数据以紧密的关联关系进行铸造，该关联关系与传热和传质的类比兼容。所提出的相关性与文献中的经验相关性非常吻合。