Many species, from single-cell bacteria to advanced animals, use molecular communication (MC) to share information with each other via chemical signals. Although MC is mostly studied in microscale, new practical applications emerge in macroscale. It is essential to derive an estimation method for channel parameters such as distance for practical macroscale MC systems which include a sprayer emitting molecules as a transmitter (TX) and a sensor as the receiver (RX). Due to the similarity between sneezing/coughing and spraying mechanisms, these practical systems have the potential to be applied in modeling airborne pathogen (viruses, bacteria, etc.) transmission with a MC perspective where an infected human emitting pathogen-laden droplets is considered as a TX. In this paper, a novel approach based on fluid dynamics is proposed for the derivation of the distance estimation in practical MC systems. According to this approach, transmitted molecules are considered as moving and evaporating droplets in the MC channel. With this approach, the Fluid Dynamics-based Distance Estimation (FDDE) algorithm which predicts the propagation distance of the transmitted droplets by updating the diameter of evaporating droplets at each time step is proposed. FDDE algorithm is validated by experimental data. The results reveal that the distance can be estimated by the fluid dynamics approach which introduces novel parameters such as the volume fraction of droplets in a mixture of air and liquid droplets and the beamwidth of the TX. Furthermore, the effect of the evaporation is shown with the numerical results.

从单细胞细菌到高级动物，许多物种都使用分子通讯（MC）通过化学信号彼此共享信息。尽管MC主要是在微观尺度上进行研究，但在宏观尺度上出现了新的实际应用。对于实用的宏观MC系统，必须得出一种信道参数（例如距离）的估计方法，该系统包括一个将分子作为发射器（TX）发射器和作为接收器（RX）的传感器的喷雾器。由于打喷嚏/咳嗽和喷洒机制之间的相似性，这些实用的系统有可能被用于以MC的观点对空气传播的病原体（病毒，细菌等）传播进行建模，其中被感染的人类散发病原体的飞沫被认为是TX。在本文中，提出了一种基于流体动力学的新颖方法来推导实际MC系统中的距离估计。根据这种方法，传输的分子被认为是MC通道中的运动液滴和蒸发液滴。通过这种方法，提出了一种基于流体动力学的距离估计（FDDE）算法，该算法通过更新每个时间步长上蒸发液滴的直径来预测透射液滴的传播距离。实验数据验证了FDDE算法的有效性。结果表明，可以通过流体动力学方法来估计距离，该方法引入了新的参数，例如空气和液滴混合物中的液滴体积分数以及TX的束宽。此外，通过数值结果显示了蒸发的影响。