Heat and Mass Transfer in a Permeable Fabric System under Hot Air Jet Impingement

Heat and mass transfer in a permeable fabric system used for Personal Protective Equipment (PPE) was investigated using hot air jet impingement conditions to mimic the jet exhaust of Short Take-Off and Vertical Landing (STOVL) aircraft. The STOVL aircraft uses a thrust-vectoring nozzle of the jet engine and a lift fan in order to vertically land and take off a short runaway. The jet engine exhaust is a new kind of thermal hazard for military personnel operating within an affected zone of the jet exhaust. An experimental approach was used to measure the thermal response of a fabric system consisting of permeable fabric samples and air pocket using a high-speed jet impingement. The jet impingement conditions consisted of two different temperatures: one of 100°C and another of 200°C at a jet impingement velocity of 32 m/s. Air was used as the working fluid. In this study, two permeable fabrics, (NOMEX IIIA and Cotton) commonly used for the Personal Protective Equipment (PPE) were investigated. The physical properties (porosity, permeability, Ergun coefficient, and density) and the thermo-physical properties (thermal diffusivity, thermal conductivity, and specific heat) of the fabrics were measured. A one-dimensional, two-medium formulation assuming thermal non-equilibrium between solid (fabric) and gas (air) phases in the fabric layer was used for the numerical analysis. The measurement results from the fabric experiment were used to define boundary conditions and adjust various heat transfer correlations and input data used in the numerical model. The experimental and numerical results of the temperatures of the fabric system were compared. The effects of the air temperature of the jet impingement on the thermal response of the fabric system were discussed.