2-D Modeling of a Walking Human-clothing System

Motivation When people are active, the air spacing between the fabric layer of a porous clothing system and the human skin changes with the activity level. This change will cause air penetration in and out of the fabric and from openings. This air penetration will reduce the heat and moisture transfer resistance from the clothing. Some of the previous models didn’t consider the effect of ventilation. Others, developed empirical equations for ventilation that limited its use. Those who developed theoretical models considered the air penetrating through the fabric to be in thermal equilibrium with the fabric, i.e same temperature and humidity ratio which is invalid

Objectives fabric motion (ventilation) on the sensible and latent heat transport In this work, a mathematical and numerical model is developed to study the effect of fabric motion (ventilation) on the sensible and latent heat transport through the fiber clothing system with and without apertures. first principles of mass and energy to accurately predict the dynamic response of clothing systems. The model is based on first principles of mass and energy conservation that made it flexible and widely used to accurately predict the dynamic response of clothing systems. the moving human interacts with environmentally controlled places The model will help us understand how the moving human interacts with environmentally controlled places such as homes and offices, or in harmful environments with protective clothing such as fire fighting, or in work spaces. It also shows how the body behave thermally under different activity levels.

Research development Normal Steady Ventilation of Clothing: Model & Find Transport Coefficients Normal Periodic Ventilation: Applicable to Clothed Walking Human. (Closed Aperture Clothing) Integrated Human Thermoregulatory Model and Ventilation Model for a Walking Human Incorporate Phase Change Material for the Clothing. (Side Application Problem) Extend the Model for 2-D Flow: ( Clothing with Open Apertures) - Combined Ventilation-Diffusion Model Applicable at Low speeds of normal ventilation - Effect of Flow Modulation on air flow that enters from the open boundary.

axial direction is treated as fully developed laminar flow The flow in the axial direction is treated as fully developed laminar flow between two parallel surfaces with constant density and viscosity. The flow at the opening is assumed to be ideal and is calculated by applying Bernoulli’s equation. The axial mass flow rate per unit area can be written as: Governing Equation

Modeling of the Air Mass Flow Rate The fabric sinusoidal motion is represented by: The general air layer mass balance is given by: The mass flow in the normal direction is proportional to the pressure difference. It’s amount depends on the permeability of the fabric material. In this study the permeability of the fabric is considered constant. The airflow rate is then represented by: Governing Equation

axial direction is treated as fully developed laminar flow The flow in the axial direction is treated as fully developed laminar flow between two parallel surfaces with constant density and viscosity. The flow at the opening is assumed to be ideal and is calculated by applying Bernoulli’s equation. The axial mass flow rate per unit area can be written as: Governing Equation

Water Vapor Mass balance: During the upward motion of the fabric, the air flow into the air spacing layer comes from the air void node of the fabric During the downward motion of the fabric, the air flow will be out of the air spacing m ay w void Fabricismovingup ward m ax w a,i m ax w a,i+1 d(ρyW a )/dt H m (P sk -P a ) Governing Equation

Energy balance of the air layer During upward motion: During the Downward motion: Governing Equation

The water vapor mass balance in the air void node is given by: P a (x) < P  P a (x) > P  Governing Equation

Results The variation of axial flow rate as function of time and x.

The variation of normal flow rate as function of time and x.

The temperature variation in time of the internal air layer temperature at x=0, 0.5L, 0.8L and L.

The spatial variation in x-direction of the mean steady periodic temperatures of outer node and the internal air layer.

The space-averaged temperature over the length of the domain L and the air layer temperature of the 1-D model.

The time-average variation in the sensible and latent heat losses from the skin in W/m 2.

Model f = 20 rpmf = 25 rpmf = 30 rpm Q L (Watt/m 2 ) Q S (Watt/m 2 ) Q L (Watt/m 2 ) Q S (Watt/m 2 ) Q L (Watt/m 2 ) Q S (Watt/m 2 ) 1-D Normal flow model (closed aperture) D Flow Model (open aperture) The time-space averaged sensible and latent heat losses at various ventilation frequencies, and the corresponding heat losses of the 1-D normal flow model.

The presence of the opening has resulted in lower sensible and latent heat loss than the 1-D model representing the closed aperture. These results are consistent with published experimental data of Loten and Danielsson (1993). Loten has reported experimentally that vapor resistance from the body at zero walking speed and 0.2 m/s wind is slightly higher for closed aperture than for open aperture. Similar results have been reported by Danielsson on higher heat loss and higher internal convective coefficients for closed aperture clothing over various body parts as compared to respective values for open aperture clothing at walking conditions.