HEAT TRANSFER* 7.9
HEAT TRANSFER
Roof
1
Segment gmen t (azimu (a zimuth) th) Gi G i # G s q s / A$ A$ %tu&(h)(ft2 ) q s / A, &m2
2
!
6!
−
341"2 366"2 65"2 2!'
−
! 25 4"5! 14"2
3
4
5
6
7
3!
!
3!
6!
!
34" 5" 1!"' 34"! 34"!
3!"2 55"2 "4 31"3
17"4 42"4 7"63 24"!
−
17"4 42"4 7"63 24"!
3!"2 55"2 "4 31"3
! 25 4"5! 14"2
Sine thi* a+u+ation ,-oe.u-e t-eat* the tan/ a* if it ha. 12 0at *i.e*$ the a+u+ate. i fo*egment* 1 an. 7 i* ze-o" f ou-*e$ G i i* a+*o ze-o fo- the *ha.e. ha+f of the tan/ an. q s / A 4 4.5 %tu&(h)(ft2 )" 2. Calculate the equilibrium temperature of each of the tank surfaces. t an e *ho8n that on.ution et8een the *egment* i* neg+igi+e" Then$ at e9ui+i-ium$ e9ui+i-ium$ eah *egment mu*t *ati*f: the heat;a+ane heat;a+ane e9uation$ that i*$ *o+a-;heat a*o-,tion # net heat in,ut in,ut : -a.iatio -a.iation n # heat t-an*fe--e. in : out*i.e on
# #
a Ra 8 i σ J T 4 − − T 4 h (T
R
−
* o i q / 8 A # σ J T 4 − T 4
T ) # h (T
−
T ) 4 !
o
w
w
8he-e T w i* the tan/;8a++ tem,e-atu-e= *u*-i,t o -efe-* to *u--oun.ing *t-utu-a+ an. othe- e+ement* ha
2 No8$ q s / A 4 65. 65.2 %tu&(h)(ft )$ T o 4 1!5 F 4 565 R (.ue to hot ,i,e* an. othe- e9ui,ment in the
?
#
(!. (!.1713 @ 1!
'
−
# 4(!. 65. 654.2 (!.1713 @ 1! )(!. )(!.75) 465 − T #
w
'
−
4
)(!. )(!.2) 565
w
−
T
4
8
8
!.72(! # 46! − T w ) # !.75('5 # 46! − T w ) 4 !
65. 65.2 # 34. 34.1 − (3. (3.426 @ 1! −
?
?
(!. (!.72 # !.75)T 75)T w
#
1!
−
#
1!
−
12. 12.'4' @ 1!
) T 4 # 6!. 6!.!7 # 36
4!' 4 !
1.6274 @ 1!
−
T 4 # 1.47T 47T w ?
4
65 ?
Thi* i* *o+
7.4
HEAT LOSS !O" A# $#%#S$LATE& S$!ACE TO A%! A *team +ine 8ith a .iamete- of 3"5 in (!"!' m) an. a +ength of 5! ft (15"2 m) t-an*,o-t* *team at 32! F (433 )" The a-on *tee+ ,i,e the-ma+ on.uti
?
?
Downloaded from Digital Engineer ing Library @ McGrawHill !www"digitalengineeringlibrary"com# !www"digitalengineeringlibrary"com# $o%yrig&t ' ()) T&e McGrawHill $om%anie+" All rig&t+ re+er,ed" Any -+e i+ +-b.ect to t&e Term+ Term+ of /+e a+ gi,en at t&e web+ite"
HEAT TRANSFER* 7.10
SEBTN SECEN
Calculation Procedure
'. Calculate the heat loss (ue to ra(iation. %eau*e the oefDient fo- heat t-an*fe- f-om the out*i.e of the ,i,e a* a -e*u+t of -a.iation an. on
Q A
*
T 1!! −
T s
4
!.1713 /
4
4
1!! 8he-e Q i* heat +o** in %-iti*h the-ma+ unit* ,e- hou-$ A i* heat;t-an*fe- a-ea in *9ua-e feet$ T s i* a*o+ute tem,e-atu-e of the *u-fae in .eg-ee* Ran/ine$ T a i* a*o+ute tem,e-atu-e of the ai-$ an. ' ,o-tion of the / i* the emi**i
A
4
Q
!.1713(!.')
46!
32!
#
4
1!! 4 −
46! # 6' 1!!
2 4
4!1 %tu&(h)(ft)
(1264 &m2 ) 2.
Calculate the heat loss as a result of natural con)ection in calm air. *e the fo-mu+a
Q A 8he-e 2
T
2
4
T s
−
4
!.27 T 1.25 D !.25
T a in .eg-ee* Fah-enheit an. D i* ,i,e .iamete- in feet" Thu*$ Q A
4
!.27(32! − 6')1.25 4 36 %tu&(h)(ft ) (1164 &m ) (3.5 / 12)!.25
*. Calculate the total heat loss for the pipe in calm air. No8$ Q 4 ( Q / A) A$ an. A (3.5 / 12) 2 2 @ 5! 4 45.'1 ft (4"26 m )$ *o Q 4 (4!1 # 36)(45.'1) 4 35 27! %tu&h (1!$33! )"
4
π
,
4. Calculate the heat loss b+ con)ection for a ,in( )elocit+ of '- mih. Fi-*t$ .ete-mine the ma** G 4 ρv$ 8he-e ρ i* .en*it: an. v i* +inea-
-. Calculate the total heat loss for the pipe ,hen the ,in( )elocit+ is '- mih. A* in *te, 3$ Q 4 (4!1 # 2!!!.)(45.'1) 4 11! !3! %tu&h (32$24! )" ,
7.-
HEAT LOSS !O" A# %#S$LATE& S$!ACE TO A%! Ba+u+ate the heat +o** f-om the *team +ine in Eam,+e 7"4 if it ha* in*u+ation 2 in (!"!5! m) thi/ ha
Downloaded from Digital Engineer ing Library @ McGrawHill !www"digitalengineeringlibrary"com# $o%yrig&t ' ()) T&e McGrawHill $om%anie+" All rig&t+ re+er,ed" Any -+e i+ +-b.ect to t&e Term+ of /+e a+ gi,en at t&e web+ite"
