Question { TATA, 3490 }

In one plant id fan and fd fan are used for boiler. boiler is used to heat water after some days they install one tank to heat water by hot flue gases coming out from boiler and then hot flue gases are used to heat the air coming from fd fan before leaving out from chimney . but hot flue gases are not coming out from id fan what might be the reason?

Answer

before chimney there is RAPH (Roatery air pre heater).so flue gas will pass from half the part of RAPH, and other half part is passing air coming from FD fan.So heat exchanges flue gas to FD fan discharge air .After that RAPH discharge is going to ID fan suction,thats how we are getting low temperature flue gas from ID fan.

Question { Jindal, 2543 }

Steve said that "An eddy-current probe works by passing an alternating
current through a coil of wire and measuring the coil’s
impedance" while we are using -24 Volt DC , So I am confused about DC and AC. Plz .

Answer

We can never generate DC voltage ,we can only change AC to DC ,so no matter you are giving AC or DC input but Addy current will be always AC.