Fluid velocities can be measured using hot-film sen-sors,

Chapter 7, Problem 7.60

(choose chapter or problem)

Fluid velocities can be measured using hot-film sen-sors, and a common design is one for which the sens-ing element forms a thin film about the circumferenceof a quartz rod. The film is typically comprised of athin (100 nm) layer of platinum, whose electricalresistance is proportional to its temperature. Hence,when submerged in a fluid stream, an electric currentmay be passed through the film to maintain itstemperature above that of the fluid. The temperatureof the film is controlled by monitoring its electricresistance, and with concurrent measurement of theelectric current, the power dissipated in the film maybe determined. Proper operation is assured only if the heat generatedin the film is transferred to the fluid, rather than con-ducted from the film into the quartz rod. Thermally,the film should therefore be strongly coupled to thefluid and weakly coupled to the quartz rod. This condi- tion is satisfied if the Biot number is very large, Bi?D/2k?1, where is the convection coefficientbetween the fluid and the film and kis the thermal con-ductivity of the rod.(a) For the following fluids and velocities, calculateand plot the convection coefficient as a functionof velocity: (i) water, 0.5V5 m/s; (ii) air,1V20 m/s.(b) Comment on the suitability of using this hot-filmsensor for the foregoing conditions.

Unfortunately, we don't have that question answered yet. But you can get it answered in just 5 hours by Logging in or Becoming a subscriber.

Becoming a subscriber
Or look for another answer

×

Login

Login or Sign up for access to all of our study tools and educational content!

Forgot password?
Register Now

×

Register

Sign up for access to all content on our site!

Or login if you already have an account

×

Reset password

If you have an active account we’ll send you an e-mail for password recovery

Or login if you have your password back