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Heat and Mass Transfer

Heat and Mass Transfer
Question:-
Option (A)
k1 + k2
Option (B)
k1k2
Option (C)
(2k1k2/(k1+k2))
Option (D)
((k1+k2)/k1k2)
Correct Option:
C
Question Solution:

Or T1-T2 = (2Qb/KA)
Or T1 - T3 = (Qb/K1A)
Or T3 -T2 = (Qb/K2A)
Or (2Qb/KA) = (Qb/K1A)+(Qb/K2A)
\ K = (2K1K2 / (K1+K2))
Question:-
Option (A)
Increase
Option (B)
Decrease
Option (C)
Remain the same
Option (D)
Very depending upon the electrical conductivity of the wire
Correct Option:
A
Question Solution:
rc = (K/h) = (0.5/10) = 0.05 mm = 50 mm
New radius = 0.5 + 1 + 10 mm = 11.5 mm

The heat flow will increases because it is less then critical radius
Question:-
Option (A)
80°C
Option (B)
110°C
Option (C)
60°C
Option (D)
Not determinable as zero is involved
Correct Option:
C
Question Solution:
We use L-hospital rule for differentiation
q1 = q2 = q
Let (q1/q2) = x
qm = ((q1-q2)/in(q1/q2))={q2(x-21)/in x}
qm = ltx®1{(q2) /(1/x)}= q2
\ qm = q2 = q1
Question:-
Option (A)
1000
Option (B)
500
Option (C)
5
Option (D)
0.2
Correct Option:
C
Question Solution:
NTU = (UA/Cmin) = ((50 x 100) /1000)= 5
Cmin is minimum of heat capacity of cold and heat fluid
Question:-
Option (A)
h1 + h2 + h3
Option (B)
(h1h2h3)1/3
Option (C)
(1/h1) + (1/h2) – (1/h3)
Option (D)
None of these
Correct Option:
D
Question Solution:
Q = (h1AΔT + h2AΔT + h34AΔT)
Q = hav x 6.A.ΔT.
\ hav = ((h1+h2+4h3)/6)