Numerical analysis of thermal performance of breathing air cooler based on granular phase change material

In this paper, we propose to use granular phase change material (PCM) as a heat accumulating material in a thermal protective respirator also called a heat exchanger to cool the breathing air. Such device is needed to protect human respiratory system from thermal injuries at indoor fires. Using the original solver for OpenFOAM software developed and validated previously, the ability of the commercially available granular PCM in the respirator to cool hot air for breathing during the time required for the human evacuation has been shown numerically: mass of 130 g is enough to cool the air from 177 degrees C to a temperature of less than 50 degrees C within 10 min. This result gives hope that such cooling element can be combined with "conventional" gas-and-smoke protective element, resulting in the creation of respirators for the protection of a person from both hot air and toxic combustion products. A parametric study of the performance of the thermal protective respirator is carried out in the paper: effect of PCM melting temperature, time variation of the outlet air flow rate and partial closure of the outlet from the cooling element have been analyzed. It has been shown that an increase in the PCM melting temperature while keeping the other parameters unchanged worsens the thermal performance of the breathing air cooler. The cooling efficiency is also worsened when the cooling element is narrowed or its outlet is partially closed, as this leads to an increase in the maximum temperature of the inhaled air. It has been shown that the time variation of the inhaled air flow rate, which is used in the calculations of the thermal protective respirator, must be close to the parameters of real human breathing, and the use of the assumption of constant air flow rate is unacceptable, since this can significantly affect the output characteristics of the respirator.