A tungsten wire used in a constant current hot wire anemometer has the following parameters :
Resistance at $0^\circ C$ is $10\Omega$, Surface area is $10^{-4}m^2$, Linear temperature coefficient of resistance of the tungsten wire is $4.8\times10^{-3}/^\circ C, $ Convective heat transfer coefficient is $25.2W/m^2/^\circ C,$ flowing air temperature is $30^\circ C$, wire current is $100\; mA$, mass-specific heat product is $2.5\times 10^{-5} J/^\circ C$
The thermal time constant of the hot wire under flowing air condition in ms is
- $24.5$
- $12.25$
- $6.125$
- $3.0625$