This paper describes a new heat transfer parameterisation between wastewater and in-sewer air based on understanding the physical phenomena observed in free surface wastewater and in-sewer air. Long-term wastewater and in-sewer air temperature data were collected and studied to indicate the importance of considering the heat exchange with in-sewer air and the relevant seasonal changes. The new parameterisation was based on the physical flow condition variations. Accurate modelling of wastewater temperature in linked combined sewers is needed to assess the feasibility of in-sewer heat recovery. Historically, the heat transfer coefficient between wastewater and in-sewer air has been estimated using simple empirical relationships. The newly developed parameterisation was implemented and validated using independent long-term flow and temperature datasets. Predictive accuracy of wastewater temperatures was investigated using a Taylor diagram, where absolute errors and correlations between modelled and observed values were plotted for different site sizes and seasons. The newly developed coefficient improved wastewater temperature modelling accuracy, compared with the older empirical approaches, which resulted in predicting more potential for heat recovery from large sewer networks. For individual locations, the RMSE between observed and predicted temperatures ranged between 0.15 and 0.5 °C with an overall average of 0.27 °C. Previous studies showed higher RMSE ranges, e.g., between 0.12 and 7.8 °C, with overall averages of 0.35, 0.42 and 2 °C. The new coefficient has also provided stable values at various seasons and minimised the number of required model inputs.

中文翻译：

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使用长期模拟来了解组合下水道稳定流动条件下的传热过程

本文基于了解在自由表面废水和下水道中观察到的物理现象，描述了废水和下水道之间的新传热参数。收集并研究了长期废水和下水道温度数据，以表明考虑与下水道热交换和相关季节变化的重要性。新的参数化基于物理流动条件的变化。需要对链接的联合下水道中的废水温度进行精确建模，以评估下水道内热回收的可行性。从历史上看，废水和下水道之间的传热系数已使用简单的经验关系进行了估算。使用独立的长期流量和温度数据集实施并验证了新开发的参数设置。使用泰勒图研究了废水温度的预测精度，其中绘制了不同站点大小和季节的绝对误差以及模型值和观测值之间的关系。与旧的经验方法相比，新开发的系数提高了废水温度建模的准确性，从而预测了从大型下水道网络回收热量的潜力。对于各个位置，观测到的温度与预测温度之间的RMSE在0.15至0.5°C之间，整体平均为0.27°C。先前的研究显示较高的RMSE范围，例如，介于0.12和7.8°C之间，总体平均值为0.35、0.42和2°C。