Supplementary data

Extended surfaces are commonly used to improve heat transfer in shell and tube heat exchangers, increasing manufacturing complicacy and material cost, especially for smaller units. These issues are attempted in the present study through dimensional variations of the tube. Seven model configurations are selected including common straight tubes and each is divided into three zones based on diameter. Both water temperatures and flow directions are also varied for each configuration resulting in 168 combinations. Hot water (30-100℃) flows through the tube and cold air at room temperature flows over the tube. It was observed that heat exchange is much higher compared to straight flow tubes when the hot fluid flows through a narrow neck located at the mid-zone. Comparatively, heat transfer increased by 14.41%, 26.34% and 40.34% during laminar, transition and turbulent conditions respectively. Heat gain by air is much higher during transition flow through tube, regardless of configuration.扩展表面（extended surfaces）常被用于提升管壳式换热器（shell and tube heat exchanger）的换热性能，但会增加制造复杂度与材料成本，对于小型换热装置而言这一问题尤为突出。本研究通过改变管材的尺寸参数来尝试解决上述问题。研究选取了7种模型构型，其中包含普通直管，每种构型均依据管径被划分为三个区域。每种构型还分别调整了水的温度与流动方向，最终得到168组试验组合。试验中，热水（温度范围30~100℃）在管内流动，常温冷空气在管外掠过。结果观察发现，当热流体流经位于中间区域的窄颈结构时，换热性能较直管工况有显著提升。相较而言，在层流、转捩及湍流工况下，换热性能分别提升了14.41%、26.34%与40.34%。无论采用何种构型，当管内为转捩流动时，空气获得的热量均更高。