Performance of two-layer filters for innovative respiratory protective devices containing granular phase change materials

In this paper, we propose to combine a gas-and-smoke protection element, which consists of granular adsorbing materials, with a thermal protection element consisting of a granular phase change material (PCM) to create multipurpose respiratory protective systems. Such devices can protect the human respiratory system not only from dangerous toxic gaseous substances that cause poisoning, but also from thermal injuries at indoor fires, reducing the temperature of the inhaled air to a safe value for a specified time. Using an original numerical model, we have investigated the effect of various parameters on the efficiency of both two-layer combined filters consisting of a layer of granular PCM and a layer of adsorbing material, and two-layer thermal protection filters consisting of layers of granular PCMs with different properties. It has been shown that commercially available granular PCMs make it possible to create two-layer combined filters with acceptable mass. In particular, a two-layer filter, which is half-filled with PCM and half-filled with activated carbon, should have a mass of only about 190 g in order to cool the inhaled air from 177 °C to less than 50 °C within 10 min. It has been shown that the optimal arrangement of the PCM layer and the gas-and-smoke protection element in the filter, which leads to the longest operating time of the respirator, depends on both the value of the maximum allowable temperature of the inhaled gas and the required operating time of the respiratory protective device, which is determined by the mass of the granular materials.