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Heat and mass transfer from a single horizontal tube of an evaporative tubular heat exchanger
INT. (X]F~. HEAT MASS TRANSFER 0735-1933/83 $3.00 + .00 Vol. I0, pp. 403-412, 1983 @PergamonPre~s Ltd. Printed in the United States
HEAT A~!D MASS TR~ZFEIi FROM A SIi[GLE HORIZOflTAL TUBE O F AI~ EVAPORATIVE TUBULA~R HEAT EXCHA~GER R. S. Rana, V. ~haran Mechanical and Industrial Engineering Department University of Roorkee, Roorkee, U.P.-247672, Ih~DIA (Ccmmm/cated by J.H. Whitelaw) ABSTRACT In this investigation, water side heat transfer coefficients without air flow from a single horizontal t u b e are determined. Mass transfer coefficients are determine~ with water and air flow from the same tube. The total energy dis~ipated by inside hot fluid when only water is falling is compared with that when both the air and water flow past the tube. The water side heat transfer coef±icient and mass trsmsfer coefficient are given by empirical rela= 6.0(Rep)O'lS(Rew)O'87 and K=3.5(Re p-)o.I~ t ions (i~ea)O •z~ (Rew)0"54 , respectively. The ratio of energies dissipated with water and air flow sad with only water flow increases with Ke w and Re a and its maximum value is 1.72 in the range of variables u~e<~.
Intr od uct ion I~ sr~ evaporative tubular heat exchanger, the water is made to fall over horizontal tubes inside which hot fluid pasties.
Water reaching over the tube is cooled
evapor~tively by the air blown from bottom to top.
Simul-
taneous he~t and mass transfer t~kes place in the equipment and the energy transfer depends upon these mechanisms. Most of the earlier work [1-7] on evaporative heat exchangers considers a nest of tubes in the form of a coil stag~;ered in different planes as a model for their experimental investigation.
In order to understand the mechanism of heat
and mass transfer in such units, it is considered desirable to investigate first the behaviour of a sin!~le horizontal tube.
This simple study can be used to compare 403
404
R.S. Rana and V. Charan
Vol. I0, No. 5
its perfoz~nance ~,,ith that, of ~ stni~;le vertical
plane/bauk
The rate o£ he~t ~nd mass t._-~,~sf~_showu in Fig. p#oeess
1 depends
fluid,
o:g the tube.
studies of feZling ~,,at,~ on horizontal heat ~[ssipatoz
by the authors without
in the ~aodel of
coolinz v~t,,n and sin ar~ ~,ell as on spae:rg
mal tube have been repo~ted isothermal
tu a
upon flow r~te ~nd temperature
between the tubes and outside diamet,r perimental
of tubes
row
of tubes.
[13].
[8-12].
7~]~-
isother-
The case of non-
foul t(~be has also been
Water' side heat transfez
studied
coefgicient
ai~ flow is found to increase ~,~ith coolins ~,,ate=
flow rate in all the above studies.
Qualitative
of tube spacing and the inlet temperature water fil,~ on heat transfe~ coefficient breakdown
effect
of the cooling
prior to film
from an elect;cicelly heated horizontal tube
experimentally
investigated by Ganic
ence of temper~,tu~:e difference
et al [12].
ofthe
[13].
coeffLcient
When a non-coudensir~
passes through a heat exchanger f~om outside,
Influ-
inside h6t fluid
and the cooling wate~ on heat transfer studied by autho=s
is
hot fluid
tube ~,,hlch is being
the outside wall temperatu=e
a. function of flow ~ate and temperature
is cooled
of the tube is
of hot fluid flo~r-
ing i#side the tub~. Therefo~tte, it seems lo~icP1 to study the effect of these pa2a~,~et~s on heat ~nd mass transl,# quately
~t~s
from the tube.
reoortea
and needs
The Reynolds
Such a ~ u d y
number of a fluid
includes the effect
of mass flow hate and the temper~ture Therefore, culated
an atte~pt
is ~ot ade-
b~vesttgatiou.
of the fl~id.
has b e e n r~lade to e:rprec~ the c~l-
heat and mass tr~nsf,~r coefficients
as ~ function-:
of l~eynolds numbers of the v~rious f]utd~ ~lo~:in,~i t n ~h~, sy;te~;l ,qnd the developed co,:t:,_'el~biop:~ ",~e ~:c~orted. The functional is to dissipate unit.
r~dv~ntzze of an ewq >oz:,tLve eooltu, 7 unit more
energy than a si~.:ple water cooled
The ratio of these two eue~gies
ss 'Ev~po~otive
~.~e beLns defrayed
Effecttvr~e,~ ' ~u~ c)e,qLg:,.pte,i
::~:: '!:~]'.
Vo1. 10, NO. 5
HEAT TRANSFER F~3M A HEAT EXCHANGER
lh!~l~t~tlve study o.~ e v ~ o r ~ t i v e t~ken ,~p in the p ~ e n t
effectiveness is ~Iso
investigation.
Experimental Set-up_ The .qoper.~tus used is shown in Fif~. 2.
The detail
description of this e~)~?ar~tus is ~iven in [13]. The flo~: rates ~nd te~uper~tures of outside cooling watAr and the hot wat,n flowing inside the tube are messuzed by rota~neters ~nd cop~e= constmnt~n therL~ocouples, respectively at locations given in the figure. The velocity of air is measured at the top of the test section by a velometer. The d.b.t, and w.b.t, of the air are measured at the entry and exit of the test section with the help of a dry and wet bulb thermomet~r set. Test Procedure In this investigation for tube with long usage, heroafter designated as 'foul tube', the data is recorded when w ~ t e r flow~ over it for 36 hours and no cleaning operation is performed, so that it is adequately fouled by the onflowing water. For studyin~r~ the influence of Reynolds numbers of hot process fluid and cooling ~ater on water ~ide he~t transfer coefficient without air flow, the procedure followed is now described. In the first set of observations the flow rate of cooling water is fixed at 12 kg/h and the flow rate of hot fluid is varied from 60 kg/h to 600 kg/h in steps of 60 kg/h. The temperature of cooling water is kept around 298 K and the temperature of hot fluid is adjusted so that A t is 35+1 K in all the observations. The heat dissipated by the tube is calculated from the flow rate and temperature difference of hot fluid at entry and exit of the test tube.
Outside
wall temperature of the tube is recorded by the=mocouples. In second set of observations the flow rate of cooling water is varied from 12 kg/h to 36 kg/h in steps of 12 kg/h and from 36 kg/h to 216 kg/h in st~ps of 36 kg/h.
405
406
R.S. Rana and V. Charan
Vol. I0, No. 5
The first set is repeated fo~ each flow rate of cooling waten. In o~den to study the influence of Reynolds numbers of hot fluid, cooling ~ t ~ n and air on the mass transfew coefficient with ai~ ~nd water flowing, set 1 and 2 a~e repeated fo= ain velocities 171 m/min, 80 m/mln and 53 ~ m i n . Au~lysls The heat dissipation rste from the tube is given by: Q = G
Cp(t P
- t Pl
)
..(1)
P2
The oversll heat transfer coefficient based on outer surf~c~ ar~n is given by: Uw = QI(AoAt )
.. (2)
where, at = (tpl + tp2)/2 - twl The inside, film heat transfer coefficient is calculated by McAd~ms equation • hi =
0,023(kp/Di)(Rep)0"8
(Prp) 0"4
..(3)
The ~ater side heat transf~n coefficient is indirectly calculated by " 1
..(4)
Uw = Dot ( Di h~.)+~,. +l/h., It is assumed that from the vet~ed surface of the tube msss transfer vould t~ke place due to enthalpy potential ~iv~n by ~if~erenee of enth~lDy of s~tu~ot~d air at tube te~neratune ~nd enthe~lpy of air at inlet of the heat dissipator.
The mass t_v~ms~r coefficient K is F~iven by"
'~ = The
ev,~.poc~",:tve
r ,'~o(is,tc-il) ~ ; f .... c , , . . z
=_~ = % a /%
.... e .....
..(5) ic
!-'i
,
. by
.
.. (6)
Vol. i0, NO. 5
HEAT TRANSFER FIK3M A HEAT EXCHANGER
407
The Reynolds number is calculated by : Re a
=
(Do ,ma )l a
..(7)
where, G' is b~sed on the minimum free area of air flow a.,max (obtained by subtracting projected area of tube from cross section area of the test section) and its units are kg/h m 2. Results, Development of Correlation and Discussion --Water Side He&t Trans_f~r Coef~icient Without Air Flow As shown in Fig. 3, the values of water side heat transfer coefficient, h w , are plotted for 3.1xlO3
..(81
The above correlation predicts values of hw with an accuracy of + 20% in the range of 3.1xi03< Rep<2.5xl04 and 13 < Re w
..(9)
408
R.S. Rana and V. Charan
The above correlation predicts value~
Vol. 10, No. 5 ~f K with an accuracy
of + 15;~ in the r~ng:e of parameters used.
However,
it
starts decreasing slightly at hi~her values of Rep ~nd Rew d~e to dry patch formation but the effect is not as l~rge as in the csse of h w. Evaporative _Effectiveness In Fig. 6, the values of 'Evaporative Effectiveness', EE, are plotted for 60 kg/h< Gp<600 kg/h, 12 kg/h
The values of ~]~ lie between 1.3 and 1.72 for Gw<_36 kg/h,
between 1.1 and 1.22 for 72 kg/h < Gw_< 104 kg/h and is around 1 for Gw _> 144 kg/h. For Gp/360 kg/h, EE starts decreasing for all flow rates of cooling water ~ue to greater influence of dry patch formation.
For other flow rates of
air having values of Re a around 1127 and 750, the values of ~E are also calculated.
In general, they are smaller in
magnitude and their maximum values are 1.45 and 1.38, respectively for these two Re a. C oncl us ions i.
The water side heet transfer coefficient without air flow increases with flow rates of process fluid and coolin~ water.
Eq (8) correlates the value~ of hw with
an accuracy of _+ 20~ in the range of 3.1xl03< Rep< 2.5x104 and 13< 1~ew< 1.7xl02. 2.
The mass transfer coefficient with air and water flow increases with flow rate of process fluid, cooling water and air. Eq. (9) correlates its values with an accuracy of +_ 15~$ in the r~uge of variables used.
3.
EvaporatiVe Effectiveness decreases with flow rate of cooling water, increases with flow rate of air and is not affected by flow rate of process fluid.
Its
maximum w~lue is 1.72 for the range of varidbles used in this investigation.
Vol. 10, NO. 5
HEAT TRANSFER FROM A HEAT EXCHANGER Nomenclature
A
surface area
G
specific heat capacity
D
diameter of test tube
EE
Evaporative Effectiveness
G
mass flow rate
h
heat transfer coefficient
H
tube spacing, distance between cooling water tube and test tube
i
enthalpy
k
thermal conductivity
K
mass transfer coefficient
Pr
Prandtl number
Q
hes.t transfer rate
Re
reynolds number, 4 G p / ( D i ~ ) f o r fluid flowing inside a tube or 4 F /~ for cooling water flowing over the tube
t At
temperature difference of mean temperature of hot flui~ and temperature of cooling water
U
overall heat transfer coefficient
x
thickness of tube ~,:all
F
mass flow rate of cooling water per side per unit axial length of test tube
dynamic viscosity
Subscripts a
moist
c
tube surface
i
ins ide
m
metal
o
outside
p
process fluid, (hot water)
s
saturated air
w
cooling water
wa
cooling water and air
1
inlet
2
outlet
409
410
R.S. Rana and V. Charan
Vol. i0, No. 5
Re fe renc e s
1.
Byron E.James, Refriger~:tion Engg., ~ ,
169 (1937).
2.
E.G~Thomson, Refriger:~tion Sh~g~., ~.~, 425 (1946).
5.
D.D. Wile, Refrigeration E n ~ . ,
4.
~obert O.Parker and Robert E.Treybal, A.I.Ch.E. Progress Symposium series, 57, 138 (1961).
5.
T.Mizushims, R. Ito ~ud H.Miyashita, Int.Chem. Eng~., Z, 727 (1967).
6.
T.Oshima, S.Iuchi, A.Yoshida, and K.Takamatsu, Heat Transfer Japanese Research ~=, 47 (1972).
7.
V. Charan snd M.R. Wasek~r,XV Int. Congress of Refrigeration, B1-58 (1979).
8.
L.S.Fletcher, V. Sernas and L.Golowin, Ind. Eng!;.Chem. Process Des. Development, 13, 265 (1974).
9.
L.S.Fletcher, V. Sernas and W.H.Perken, Ind. ~agc. Jhem. Process De~. Development, 14, 411 (1975).
58, 55 (1950).
lO.
W.H.Psrken Jr., ph.D.The~is, Rutgers University, 1975.
ll.
V. Sernas, Trans. A3;.~ t J.Heat Transfer, lO1, 176
12.
E.N.Ganic and M.N.Roppo, Trans. ASME " J.Heat Transfer ~,Q2, 342 (1980).
13.
R.S.R~na, V.Char~.~n, Letters in Heat and Mass Tr~nsfer, 9_, 25~ (1982).
~
Coating Water
Cooling
Hot
Fluid ~
Tube
water
TestTube
TTTTTT Air
FIG. 1 Physical Model
Vol. i0, NO. 5
HEAT TRANSFER FROM A HEAT EXCHANGER
Measured Loco+ion Ouontit y A : GD B,C,D,E,F : tp , tc J K,L
,,
: ;
Gw tw
":':: B
C O E
F
TEST SECTION t
.
22
23
+ +
9. Rypol$ VOlve
16 By P01S Valve
2,
Wheel Valves 3. Coolino Water Tube
I
T e l l Tube
I0 Cooli.g Water Regulating Valve
17. Hot Water
4. Adjustment for 3
I I Rotomelee for COoling Water 12. Hot Water Reservoir
18. Rolometlr for Hot Water 19.Collecting Troy
13 .Heotmp ElemenlS
20.BOlance 21 Container
5+ COOling Woter Sump 6, Healil~l EIImefll$ 7 CooliflQ Water Pump 8 ..........
Reguloting Valve
Wo+er Pump IS . . . . . . . . . 4 14Hal
22321 . . . . . . . . . . 24. I
FIG. 2 Line Diagram of the Experimental Setup
Sym~o~ '~
R%
symbol
l&_+1
[]
Rew ll'P ++5
P+
z6~i
o
150 ++I0
o
42:2
V
206".17
+
79:6
@
2s2:e
~+t, 3 + i l k H , 2$,Amm
j,10 3 0
0
•
ev
V m
s
o
m
~
A
a
m
~
mm
m
o
e
a
A
AA
a
~IO 7
o
t 3 • ~03
o
°
o
o
0
I
I
104
0 °
i
.104
m,+
FIG. 3 Effect of Rep e n d
Re w
on
411
412
R.S. Rana and V. Charan
Vol. i0, No. 5
5x103 ~ %0 o /
.....
-" 20 "/. e r r o r
/~
o
//
o
/
/ (~o /o o
=~,0
o/
////°
~
/
o
//"
2xi02 3 XlO 2
IO 3
4x103 hw
~. 4 Comparison of Tes% Dato ~ith Developed Correlation
5ymOol
0
14_*l
[:]
117-'5
~t
=)$~IK
?.2 ~2
~"
2136~17
Re~ ; 2370+-35
7~ ~ 6
®
~sz~e
o 2~4
o
q
o ~o?
~.
0 tee
o ~'
z 9z8 ~ 66o
, : 35 :
IK
%
r~
tO
l~2
10) %
~glh,
) I
~
L
I
l
.--L
1
Re;~
? IG.
5
i~ffect of .:ep and Re w on ~.~
FIG. Effect of G
and U P
on
~
HEAT A~!D MASS TR~ZFEIi FROM A SIi[GLE HORIZOflTAL TUBE O F AI~ EVAPORATIVE TUBULA~R HEAT EXCHA~GER R. S. Rana, V. ~haran Mechanical and Industrial Engineering Department University of Roorkee, Roorkee, U.P.-247672, Ih~DIA (Ccmmm/cated by J.H. Whitelaw) ABSTRACT In this investigation, water side heat transfer coefficients without air flow from a single horizontal t u b e are determined. Mass transfer coefficients are determine~ with water and air flow from the same tube. The total energy dis~ipated by inside hot fluid when only water is falling is compared with that when both the air and water flow past the tube. The water side heat transfer coef±icient and mass trsmsfer coefficient are given by empirical rela= 6.0(Rep)O'lS(Rew)O'87 and K=3.5(Re p-)o.I~ t ions (i~ea)O •z~ (Rew)0"54 , respectively. The ratio of energies dissipated with water and air flow sad with only water flow increases with Ke w and Re a and its maximum value is 1.72 in the range of variables u~e<~.
Intr od uct ion I~ sr~ evaporative tubular heat exchanger, the water is made to fall over horizontal tubes inside which hot fluid pasties.
Water reaching over the tube is cooled
evapor~tively by the air blown from bottom to top.
Simul-
taneous he~t and mass transfer t~kes place in the equipment and the energy transfer depends upon these mechanisms. Most of the earlier work [1-7] on evaporative heat exchangers considers a nest of tubes in the form of a coil stag~;ered in different planes as a model for their experimental investigation.
In order to understand the mechanism of heat
and mass transfer in such units, it is considered desirable to investigate first the behaviour of a sin!~le horizontal tube.
This simple study can be used to compare 403
404
R.S. Rana and V. Charan
Vol. I0, No. 5
its perfoz~nance ~,,ith that, of ~ stni~;le vertical
plane/bauk
The rate o£ he~t ~nd mass t._-~,~sf~_showu in Fig. p#oeess
1 depends
fluid,
o:g the tube.
studies of feZling ~,,at,~ on horizontal heat ~[ssipatoz
by the authors without
in the ~aodel of
coolinz v~t,,n and sin ar~ ~,ell as on spae:rg
mal tube have been repo~ted isothermal
tu a
upon flow r~te ~nd temperature
between the tubes and outside diamet,r perimental
of tubes
row
of tubes.
[13].
[8-12].
7~]~-
isother-
The case of non-
foul t(~be has also been
Water' side heat transfez
studied
coefgicient
ai~ flow is found to increase ~,~ith coolins ~,,ate=
flow rate in all the above studies.
Qualitative
of tube spacing and the inlet temperature water fil,~ on heat transfe~ coefficient breakdown
effect
of the cooling
prior to film
from an elect;cicelly heated horizontal tube
experimentally
investigated by Ganic
ence of temper~,tu~:e difference
et al [12].
ofthe
[13].
coeffLcient
When a non-coudensir~
passes through a heat exchanger f~om outside,
Influ-
inside h6t fluid
and the cooling wate~ on heat transfer studied by autho=s
is
hot fluid
tube ~,,hlch is being
the outside wall temperatu=e
a. function of flow ~ate and temperature
is cooled
of the tube is
of hot fluid flo~r-
ing i#side the tub~. Therefo~tte, it seems lo~icP1 to study the effect of these pa2a~,~et~s on heat ~nd mass transl,# quately
~t~s
from the tube.
reoortea
and needs
The Reynolds
Such a ~ u d y
number of a fluid
includes the effect
of mass flow hate and the temper~ture Therefore, culated
an atte~pt
is ~ot ade-
b~vesttgatiou.
of the fl~id.
has b e e n r~lade to e:rprec~ the c~l-
heat and mass tr~nsf,~r coefficients
as ~ function-:
of l~eynolds numbers of the v~rious f]utd~ ~lo~:in,~i t n ~h~, sy;te~;l ,qnd the developed co,:t:,_'el~biop:~ ",~e ~:c~orted. The functional is to dissipate unit.
r~dv~ntzze of an ewq >oz:,tLve eooltu, 7 unit more
energy than a si~.:ple water cooled
The ratio of these two eue~gies
ss 'Ev~po~otive
~.~e beLns defrayed
Effecttvr~e,~ ' ~u~ c)e,qLg:,.pte,i
::~:: '!:~]'.
Vo1. 10, NO. 5
HEAT TRANSFER F~3M A HEAT EXCHANGER
lh!~l~t~tlve study o.~ e v ~ o r ~ t i v e t~ken ,~p in the p ~ e n t
effectiveness is ~Iso
investigation.
Experimental Set-up_ The .qoper.~tus used is shown in Fif~. 2.
The detail
description of this e~)~?ar~tus is ~iven in [13]. The flo~: rates ~nd te~uper~tures of outside cooling watAr and the hot wat,n flowing inside the tube are messuzed by rota~neters ~nd cop~e= constmnt~n therL~ocouples, respectively at locations given in the figure. The velocity of air is measured at the top of the test section by a velometer. The d.b.t, and w.b.t, of the air are measured at the entry and exit of the test section with the help of a dry and wet bulb thermomet~r set. Test Procedure In this investigation for tube with long usage, heroafter designated as 'foul tube', the data is recorded when w ~ t e r flow~ over it for 36 hours and no cleaning operation is performed, so that it is adequately fouled by the onflowing water. For studyin~r~ the influence of Reynolds numbers of hot process fluid and cooling ~ater on water ~ide he~t transfer coefficient without air flow, the procedure followed is now described. In the first set of observations the flow rate of cooling water is fixed at 12 kg/h and the flow rate of hot fluid is varied from 60 kg/h to 600 kg/h in steps of 60 kg/h. The temperature of cooling water is kept around 298 K and the temperature of hot fluid is adjusted so that A t is 35+1 K in all the observations. The heat dissipated by the tube is calculated from the flow rate and temperature difference of hot fluid at entry and exit of the test tube.
Outside
wall temperature of the tube is recorded by the=mocouples. In second set of observations the flow rate of cooling water is varied from 12 kg/h to 36 kg/h in steps of 12 kg/h and from 36 kg/h to 216 kg/h in st~ps of 36 kg/h.
405
406
R.S. Rana and V. Charan
Vol. I0, No. 5
The first set is repeated fo~ each flow rate of cooling waten. In o~den to study the influence of Reynolds numbers of hot fluid, cooling ~ t ~ n and air on the mass transfew coefficient with ai~ ~nd water flowing, set 1 and 2 a~e repeated fo= ain velocities 171 m/min, 80 m/mln and 53 ~ m i n . Au~lysls The heat dissipation rste from the tube is given by: Q = G
Cp(t P
- t Pl
)
..(1)
P2
The oversll heat transfer coefficient based on outer surf~c~ ar~n is given by: Uw = QI(AoAt )
.. (2)
where, at = (tpl + tp2)/2 - twl The inside, film heat transfer coefficient is calculated by McAd~ms equation • hi =
0,023(kp/Di)(Rep)0"8
(Prp) 0"4
..(3)
The ~ater side heat transf~n coefficient is indirectly calculated by " 1
..(4)
Uw = Dot ( Di h~.)+~,. +l/h., It is assumed that from the vet~ed surface of the tube msss transfer vould t~ke place due to enthalpy potential ~iv~n by ~if~erenee of enth~lDy of s~tu~ot~d air at tube te~neratune ~nd enthe~lpy of air at inlet of the heat dissipator.
The mass t_v~ms~r coefficient K is F~iven by"
'~ = The
ev,~.poc~",:tve
r ,'~o(is,tc-il) ~ ; f .... c , , . . z
=_~ = % a /%
.... e .....
..(5) ic
!-'i
,
. by
.
.. (6)
Vol. i0, NO. 5
HEAT TRANSFER FIK3M A HEAT EXCHANGER
407
The Reynolds number is calculated by : Re a
=
(Do ,ma )l a
..(7)
where, G' is b~sed on the minimum free area of air flow a.,max (obtained by subtracting projected area of tube from cross section area of the test section) and its units are kg/h m 2. Results, Development of Correlation and Discussion --Water Side He&t Trans_f~r Coef~icient Without Air Flow As shown in Fig. 3, the values of water side heat transfer coefficient, h w , are plotted for 3.1xlO3
..(81
The above correlation predicts values of hw with an accuracy of + 20% in the range of 3.1xi03< Rep<2.5xl04 and 13 < Re w
..(9)
408
R.S. Rana and V. Charan
The above correlation predicts value~
Vol. 10, No. 5 ~f K with an accuracy
of + 15;~ in the r~ng:e of parameters used.
However,
it
starts decreasing slightly at hi~her values of Rep ~nd Rew d~e to dry patch formation but the effect is not as l~rge as in the csse of h w. Evaporative _Effectiveness In Fig. 6, the values of 'Evaporative Effectiveness', EE, are plotted for 60 kg/h< Gp<600 kg/h, 12 kg/h
The values of ~]~ lie between 1.3 and 1.72 for Gw<_36 kg/h,
between 1.1 and 1.22 for 72 kg/h < Gw_< 104 kg/h and is around 1 for Gw _> 144 kg/h. For Gp/360 kg/h, EE starts decreasing for all flow rates of cooling water ~ue to greater influence of dry patch formation.
For other flow rates of
air having values of Re a around 1127 and 750, the values of ~E are also calculated.
In general, they are smaller in
magnitude and their maximum values are 1.45 and 1.38, respectively for these two Re a. C oncl us ions i.
The water side heet transfer coefficient without air flow increases with flow rates of process fluid and coolin~ water.
Eq (8) correlates the value~ of hw with
an accuracy of _+ 20~ in the range of 3.1xl03< Rep< 2.5x104 and 13< 1~ew< 1.7xl02. 2.
The mass transfer coefficient with air and water flow increases with flow rate of process fluid, cooling water and air. Eq. (9) correlates its values with an accuracy of +_ 15~$ in the r~uge of variables used.
3.
EvaporatiVe Effectiveness decreases with flow rate of cooling water, increases with flow rate of air and is not affected by flow rate of process fluid.
Its
maximum w~lue is 1.72 for the range of varidbles used in this investigation.
Vol. 10, NO. 5
HEAT TRANSFER FROM A HEAT EXCHANGER Nomenclature
A
surface area
G
specific heat capacity
D
diameter of test tube
EE
Evaporative Effectiveness
G
mass flow rate
h
heat transfer coefficient
H
tube spacing, distance between cooling water tube and test tube
i
enthalpy
k
thermal conductivity
K
mass transfer coefficient
Pr
Prandtl number
Q
hes.t transfer rate
Re
reynolds number, 4 G p / ( D i ~ ) f o r fluid flowing inside a tube or 4 F /~ for cooling water flowing over the tube
t At
temperature difference of mean temperature of hot flui~ and temperature of cooling water
U
overall heat transfer coefficient
x
thickness of tube ~,:all
F
mass flow rate of cooling water per side per unit axial length of test tube
dynamic viscosity
Subscripts a
moist
c
tube surface
i
ins ide
m
metal
o
outside
p
process fluid, (hot water)
s
saturated air
w
cooling water
wa
cooling water and air
1
inlet
2
outlet
409
410
R.S. Rana and V. Charan
Vol. i0, No. 5
Re fe renc e s
1.
Byron E.James, Refriger~:tion Engg., ~ ,
169 (1937).
2.
E.G~Thomson, Refriger:~tion Sh~g~., ~.~, 425 (1946).
5.
D.D. Wile, Refrigeration E n ~ . ,
4.
~obert O.Parker and Robert E.Treybal, A.I.Ch.E. Progress Symposium series, 57, 138 (1961).
5.
T.Mizushims, R. Ito ~ud H.Miyashita, Int.Chem. Eng~., Z, 727 (1967).
6.
T.Oshima, S.Iuchi, A.Yoshida, and K.Takamatsu, Heat Transfer Japanese Research ~=, 47 (1972).
7.
V. Charan snd M.R. Wasek~r,XV Int. Congress of Refrigeration, B1-58 (1979).
8.
L.S.Fletcher, V. Sernas and L.Golowin, Ind. Eng!;.Chem. Process Des. Development, 13, 265 (1974).
9.
L.S.Fletcher, V. Sernas and W.H.Perken, Ind. ~agc. Jhem. Process De~. Development, 14, 411 (1975).
58, 55 (1950).
lO.
W.H.Psrken Jr., ph.D.The~is, Rutgers University, 1975.
ll.
V. Sernas, Trans. A3;.~ t J.Heat Transfer, lO1, 176
12.
E.N.Ganic and M.N.Roppo, Trans. ASME " J.Heat Transfer ~,Q2, 342 (1980).
13.
R.S.R~na, V.Char~.~n, Letters in Heat and Mass Tr~nsfer, 9_, 25~ (1982).
~
Coating Water
Cooling
Hot
Fluid ~
Tube
water
TestTube
TTTTTT Air
FIG. 1 Physical Model
Vol. i0, NO. 5
HEAT TRANSFER FROM A HEAT EXCHANGER
Measured Loco+ion Ouontit y A : GD B,C,D,E,F : tp , tc J K,L
,,
: ;
Gw tw
":':: B
C O E
F
TEST SECTION t
.
22
23
+ +
9. Rypol$ VOlve
16 By P01S Valve
2,
Wheel Valves 3. Coolino Water Tube
I
T e l l Tube
I0 Cooli.g Water Regulating Valve
17. Hot Water
4. Adjustment for 3
I I Rotomelee for COoling Water 12. Hot Water Reservoir
18. Rolometlr for Hot Water 19.Collecting Troy
13 .Heotmp ElemenlS
20.BOlance 21 Container
5+ COOling Woter Sump 6, Healil~l EIImefll$ 7 CooliflQ Water Pump 8 ..........
Reguloting Valve
Wo+er Pump IS . . . . . . . . . 4 14Hal
22321 . . . . . . . . . . 24. I
FIG. 2 Line Diagram of the Experimental Setup
Sym~o~ '~
R%
symbol
l&_+1
[]
Rew ll'P ++5
P+
z6~i
o
150 ++I0
o
42:2
V
206".17
+
79:6
@
2s2:e
~+t, 3 + i l k H , 2$,Amm
j,10 3 0
0
•
ev
V m
s
o
m
~
A
a
m
~
mm
m
o
e
a
A
AA
a
~IO 7
o
t 3 • ~03
o
°
o
o
0
I
I
104
0 °
i
.104
m,+
FIG. 3 Effect of Rep e n d
Re w
on
411
412
R.S. Rana and V. Charan
Vol. i0, No. 5
5x103 ~ %0 o /
.....
-" 20 "/. e r r o r
/~
o
//
o
/
/ (~o /o o
=~,0
o/
////°
~
/
o
//"
2xi02 3 XlO 2
IO 3
4x103 hw
~. 4 Comparison of Tes% Dato ~ith Developed Correlation
5ymOol
0
14_*l
[:]
117-'5
~t
=)$~IK
?.2 ~2
~"
2136~17
Re~ ; 2370+-35
7~ ~ 6
®
~sz~e
o 2~4
o
q
o ~o?
~.
0 tee
o ~'
z 9z8 ~ 66o
, : 35 :
IK
%
r~
tO
l~2
10) %
~glh,
) I
~
L
I
l
.--L
1
Re;~
? IG.
5
i~ffect of .:ep and Re w on ~.~
FIG. Effect of G
and U P
on
~