Question:-
A thermocouple in a thermowell measures the temperature of hot gas flowing through the pipe. For the most accurate measurement of temperature, the thermowell should be made of
Option (A)
Steel
Option (B)
brass
Option(C)
Copper
Option(D)
aluminum
Correct Option:
(A)
Question Solution:
(tl - ta)/(t0-ta) = (1/coshmL)
\ Error = tl-ta = ((t0-ta)/cosh(mL))
Where m = Ö(hp/KAc)
t0 = temperature of pipe wall
ta = temperature of gas or air flowing through pipe
tl = temperature recorded by the thermometer at the bottom of the wall so to have better thermo well K should be minimum






Material K(W/m2-K)
Steel 16-20
Brass 100
Copper 380
Aluminimum 225

So steel will be the better material for thermo well
question-answer-faq-3067