In recent years, with the rapid development of tunneling technology in mines, the depth of mining is constantly increasing. Consequently(Fang et al. 2020), hazards such as dust pollution and heat damage becomes more and more severe (Lu et al. 2017a, Ni et al. 2020, Zhang et al. 2021, Zhang et al. 2020). When the dust concentration reaches a certain level, it may cause explosion accidents (Cashdollar et al. 2007, Gao et al. 2021, Liu et al. 2019a, Zheng et al. 2009). According to the statistics, coal dust explosion accidents account for about 9% of all kinds of dust explosion accidents in the world every year, and the proportion reaches up to 35% in China (Lu et al. 2019a, Peng et al. 2019, Yuan et al. 2015, Zhao &Nie 2011). These accidents lead to serious casualties and property losses. In addition, miners who work in a high-concentration dust environment for a long time are prone to pneumoconiosis (Gao et al. 2017, Geng et al. 2014, Hua et al. 2018, Jiang et al. 2017, Lu et al. 2017b, Zhou et al. 2018). According to the statistics of the National Health Commission of China, about 20,000 cases of pneumoconiosis are reported annually in China, accounting for about 90% of the total number of reported cases of occupational diseases(Hassan et al. 2021, Liu et al. 2021). Pneumoconiosis, which mostly occurs in the coal mining and picking industry, the non-ferrous metal mining industry and auxiliary mining activities, is currently the most serious occupational disease in China (Guo et al. 2020, Wang et al. 2021). Statistics of pneumoconiosis cases in China over the recent eight years are shown in Fig. 1.
Heat damage is another problem that cannot be ignored in the mining process. Calculated according to the average geothermal gradient 0.035°C/m in China, the rock temperature will exceed 35°C at a depth of 1,000 m, notably higher than 26°C stipulated in the Coal Mine Safety Regulations(Lu et al. 2021). About 53% of China’s coal reserves are buried below 1,000 m (Zhang et al. 2018, Zhang 2014). As a high-temperature environment will affect people’s physiology and psychology, they may react abnormally and inflexibly and become increasingly prone to accidents in such an environment (Hassan et al. 2021, Ryan &Euler 2017). Based on the survey conducted by Japanese scholars in 1979, the accident rate in a 30–34°C working environment is 3.6 times higher than that in the areas where the temperature is below 30°C (Pretorius et al. 2019). Obviously, these issues endanger miners’ health and pose a considerable threat to safe production in mines (Liu 2010). Therefore, the prevention and control of mine dust and heat damage hazards are major problems that need to be solved urgently for safe production and occupational health(Bao et al. 2020).
Many scholars have conducted extensive research on these two issues. With respect to dust management in mines, the commonly used dust removal technologies include: ventilation dust removal, coal seam water injection, foam dust removal, air curtain dust removal and spray dust suppression (Lu et al. 2019b, Lu et al. 2019c, Ni et al. 2019, Wang et al. 2019, Wang et al. 2020, Xiu et al. 2020, Xu et al. 2019, Yu et al. 2017, Zhou et al. 2019b). Among them, the spray dust suppression technology is the most widely adopted because it is simple, economical and efficient(Hua et al. 2020, Ma et al. 2020). Wang et al. (Wang et al. 2017a) studied the effect of airflow from forced ventilation on the water spray field in the heading face of coal mines. Zhou et al. (Zhou et al. 2019a) investigated in detail the factors that affect the droplet formation pattern, such as injection pressure and nozzle structure, and designed a new nozzle distribution device. Fang et al. (Fang et al. 2020) analyzed the particle size distribution of fine water mist as well as its effect on spray dust suppression, and obtained different laws of water different-sized mist in their main dust capture stages. Their research findings optimized the control scheme of mine spray dust suppression to a certain extent. Peng et al. (Peng et al. 2019) designed an air-assisted PM10 control device, found the distribution law of its fog field, and obtained its optimal spray conditions. These studies have improved the effect of spray dust suppression to varying degrees. However, pure water possesses a limited ability to wet the dust with strong hydrophobicity in mines (Ni et al. 2021, Xie et al. 2020).
Since the early 1980s, Chinese scholars have started the researches on the application of magnetized water. Magnetized water has been widely used in dust removal, scale removal, construction, agriculture, medical treatment and other fields now. Earlier, Liu et al. (Liu 1991), An et al. (An et al. 1998), Zhao (Zhao 2008) proposed that the external magnetic field can reduce the viscosity and surface tension of water. Nie et al. (Nie et al. 2013) and Zhao et al. (Zhao et al. 2019) researched the relevant parameters affecting the performance of magnetized water and came up with partial rules. All these researches indicate that the magnetic field can increase the activity of water molecules, so that the water adsorbs easily on the dust surface. Chen et al. (Chen et al. 2014) further performed an experimental investigation on the dust removal efficiency of magnetized water, concluding that it is 16.36% higher than that of unmagnetized water. Nie et al. (Nie et al. 2015), Qin et al. (Qin et al. 2017) and Liu et al. (Liu &Gu 2020) enhanced the wetting ability of magnetized water by adding surfactants to it, thereby improving the dust removal efficiency. However, these researches only considered the effect of magnetic field on the dust removal performance of water, without shedding light on its effect on the ease of heat damage in mines. In terms of the temperature reduction effect of magnetized water, Huang et al. (Huang &Yao 2019) studied the role of low-temperature magnetized water in dust removal and temperature reduction. Nevertheless, they did not conduct an in-depth study on the change in the cooling properties of water after magnetization.
In summary, the performance of water for dust removal or temperature reduction has been researched on separately in detail. Nevertheless, there is a lack of research on the dust removal and temperature reduction coupling performances of water, especially magnetized water. In this paper, the surface tension, viscosity and specific heat capacity of water under different magnetic fields were experimentally measured. Furthermore, the dust removal and temperature reduction performances of magnetized water were further analyzed through numerical simulation, and the magnetization conditions for achieving the best coupling performance were obtained. Finally, a system was designed to control the magnetization conditions strictly. The research results can provide a theoretical basis for the selection of dust pollution and heat damage control measures in mines.