A hot-wire anemometer consists of a 5 m diameter platinum wire, 5 mm long. The probe is operated at constant current of 0.03 amp. The electrical resistivity of platinum is 17Wcm at 20°C and increases by 0.385% per °C.
(a) If the voltage across the wire is 1.75 Volts, determine the velocity of the air flowing across it and the wire temperature if the free-stream air temperature is 20°C.
(b) What is the wire temperature and voltage if the air velocity is 10 m/s? Neglect radiation and conduction heat transfer from the wire.
GIVEN
A hot wire in air
Wire diameter (D) = 5 m = 5 x 10–6 m
Wire length (L) 5 mm = 0.005 m
Current (I) = 0.03 A (constant)
Electrical resistivity (rel) = 17 W cm= 17