8/13/2019 HMT-M12
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Con. 4748 12.
06 D 6 .1 L .GN-938
[Total Marks:
N.B.: 1 Quest ion No .1 is compulsory.
2 Answer any four quest ions from the rema ining six quest ions
. 3 Assume suitable data wherever necessary . 4 Figures to t he
right indicate full ma rks .
1. Answer any four of the following :-
a Overal l heat transfer coefficient in heat exchanger .
b Velocity boundary layer c Critical radius of insulation d
Weins displacement law and its use e What is heat exchanger? Where
they are used?
20
2. a Hot o il is be ing cooled from 160 C to 110 C in a paral
lel flow heat ex ch an ger b y 10
wa ter enter ing at 24 C and exiting at 60 C. Determ ine the out
let tem p. of both stre am sif the hea t exchanger is made Counter
flow .
b Exp la in me thods used for d ime ns ional analysis. 6
c Exp la in Reynolds analogy . 4
3. a Fo r na tur a l convec tion heat t ra nsfe r prove t ha t-
Nu = C. Gr. P r 10
b The n e t rad ia tion from the surf ace of two p a rallel p
lates main ta ined at temp . T, and 10
T2 is to b e re duced by 80 tim es . Ca lcu late the num bers o
f s cree ns to be pl a ce dbet wee n 1f1etw o surfaces to a ch ie
ve th is red uc tion in h ea t e xcha ng e . As s um ing thee miss
ivity of sc reens as 0.05 and that of surfaces as 0 .8.
4. a A n egg w ith mean diameter of 40 mm and initially at 25 C
is p laced in a b oiling 10
water pan for 4 min . and found to be boiled to th e consumers t
aste . For how long
should a s imilar egg for same consumer be boiled wh e n ta ke n
from a re frigerator at5C.Takethefoliowing properties of egg. K = 1
W m DC,h = 1 W m 2 DC,C
p= 2000J /kg DC,
P = 1200 kg /m 3 Use lump syst e m analysis . b Der ive express
ion for the effectiveness of a count e r flow typ e heat exchanger
. 6
c Expla in des ign of heat exchan ge r. 4
5. a Fo r trans ien t heat conduct ion , with negli gible in te
rna l resist a nce with us ua l notation s 10
s how th a t, = exp - Bi.Fo
b S how tha t tota l emiss ive po we r is rt times th e inten
sity rad iation. 6
c Expla in bo iling heat tra nsfer . 4
[ TURN OVER
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