Numerical investigation of thermal regulation inside firefighter protective clothing

Phase change materials (PCMs) are widely used in heating and cooling applications to reduce the mismatch between the energy production and the demand. PCMs can also be incorporated into the thermal systems to maintain a constant temperature and conduce to increase the thermal comfort. Unlike any human-made thermal system, the thermal comfort of the human body is more crucial since a possible damage may not be recovered. In this study, PCM layers are incorporated into the textile fabric to increase the thermal comfort of a firefighter and protect the skin layers from the thermal burn due to overheating. A transient one-dimensional numerical model is developed in the ANSYS-FLUENT software. The effect of blood perfusion inside skin layers is simulated as an energy source term and defined into the software using user-defined-function (UDF). The validatity of the source term implentation into ANSYS-FLUENT is proven by repoducing a reduced model fom the literature. The predicted time-wise variations of the temperature of the body layers are compared with the ones which are taken from the literature. After the validation procedure, the usage of PCM inside a firefighter protective clothing is numerically investigated by varying the thermal boundary conditions acting on the coating. Results depict that, for the longest fire exposure duration the 1st-degree burn is effective for a depth of 5.29 mm and the 3rd-degree burn is observed for a depth of 2.57 mm. Implementing the PCM inside the clothing inhibits the temperature rise in skin layers and improves the heat storage capacity of the fabric. In the current design and working conditions, firefighter protective clothing with 1 mm of PCM layer prevents the skin burn, even for the longest fire exposure scenario

Measurement of heat capacity and thermal conductivity of HDPE/expanded graphite nanocomposites by differential scanning calorimetry

Purpose: In this study, heat capacity and thermal conductivity of nanocomposites formed by high density polyethylene (HDPE) matrix and expanded graphite (EG) conductive filling material were investigated. Design/methodology/approach: Nanocomposites containing up to 20 weight percent of expanded graphite filler material were prepared by mixing them in a Brabender Plasticorder. Two grades of expanded graphite fillers were used namely expanded graphite with 5 μm (EG5) and 50 μm (EG50) in diameter. Heat capacity and thermal conductivity of pure HDPE and the nanocomposites were measured using differential scanning calorimetry (DSC). Findings: A substantial increase in thermal conductivity was observed with the addition of expanded graphite to HDPE. Thermal conductivity increased from 0.442 W/m.K for pure HDPE to 0.938 W/m.K for nanocomposites containing 7% by weight of expended graphite. Heat capacity increases with the increase in temperature for both pure HDPE and the nanocomposites filled with expanded graphite and no appreciable difference in the values of heat capacity were detected due to particle size. Heat capacity decreased with increasing graphite particle content for both particle size, following the low of mixtures. Practical implications: Layers of expanded graphite have become of intense interest as fillers in polymeric nanocomposites. Upon mixing the expanded graphite intercalates and exfoliates into nanometer thickness sheets due to their sheet-like structure and week bonds normal to the graphite sheets. That way they have very big surface area and high aspect ratio (200-1500) what results in a formation of percolating network at very low filler content. The nanoparticles usage results in significant improvement in thermal, mechanical, and electrical properties of polymers even with very low loading levels compared with microparticles. Originality/value: To see the effect of conducting fillers on thermal conductivity and heat capacity two different sizes of expanded graphite were used. © International OCSCO World Press