An improved FFR design.

<p>(a) the experimental prototype of improved FFR worn by subject (b) sensor position for temperature measurement.</p

Temperature of FFR deadspace with and without a ventilation fan.

<p>Temperature of FFR deadspace with and without a ventilation fan.</p

Grid Independency and speed sensibility test of the ventilation fan.

<p>Grid Independency and speed sensibility test of the ventilation fan.</p

Air velocity contours of an axial fan.

<p>(a) Outtake side (b) Intake side.</p

Official technical parameters of the ventilation fan: Delta 3010 series.

<p>(<a href="http://www.delta-china.com.cn/" target="_blank">http://www.delta-china.com.cn/</a>)</p

FFR deadspace temperature when FFRs with/without a ventilation fan.

<p>FFR deadspace temperature when FFRs with/without a ventilation fan.</p

Streamline distribution around the object's head when the FFR with a ventilation fan.

<p>(a) Outward-blowing fan (b) Inward-blowing fan.</p

CO2 volume fraction in the FFR deadspace when FFRs used with/without a ventilation fan.

<p>CO2 volume fraction in the FFR deadspace when FFRs used with/without a ventilation fan.</p

Temperature distribution when FFRs without a ventilation fan (a), (b) and with a ventilation fan (c), (d).

<p>Temperature distribution when FFRs without a ventilation fan (a), (b) and with a ventilation fan (c), (d).</p

Simulation model:

<p>(a) 3D geometric model (b) finite element mesh for CFD simulation (c) the respiratory flow rate.</p