shell&tube heat exchanger
DESCRIPTION
Shell&Tube Heat exchanger experiment reportTRANSCRIPT
1
1. INTRODUCTION
The aim of that experiment is to investigate the performance of shell and tube heat
exchanger both operating in counter-current and co-current modes and also to investigate the
effect of Reynolds number on individual heat transfer coefficients by using the experimental
data. To achieve this aim, firstly, the working principles of heat exchangers are researched.
Heat exchangers are devices that are used in wide variety of purposes in engineering
application such as electric resistance heaters, boilers, condensers, radiant heat dryers. Briefly,
they work as a heat transfer medium that is transferred from one matter to the desired one.
Heat exchangers are classified according to type of construction and flow arrangement. As
flow arrangement, heat exchangers classified under two main groups: parallel flow heat
exchangers and counter flow heat exchangers. In parallel flow, hot fluid and cold fluid enter
the exchanger at the same end, and travel in parallel to one another to the other side.
In counter-flow heat exchangers, on the other hand, the fluids enter the exchanger from
opposite ends. In this experiment, these two modes are examined by plotting the temperature
profile of each data. As construction arrangement, there are mainly three types: shell and tube
heat exchanger, concentric tube and compact heat exchanger. [1] In this experiment, a shell
and tube heat exchanger which has 1 pass is studied in both co-current and counter- current
modes. The heat exchanger is made of Borosilicated Glass in the shell side and AISI Stainless
Steel in the tube side and the properties are given in Table 1.1.
Table 1.1: Technical details of examined heat exchanger
2
The shell and tube heat exchangers used widely in industry since they have many
advantages such as having large heat exchange area, having good shape for pressure
operation, using well-established fabrication technique, ability to be constructed from wide
range of materials, ability to be cleaned easily and having well established design
procedures.[2]
Figure 1.1: Shell and tube heat exchanger with counter flow.[2]
In the calculations, the fouling factor effect is neglected since the pipes are said to be
clean. However, baffles are considered in calculation. Baffles are vanes and panels that give a
direction to the flow of fluids in heat exchangers to increase the fluid velocity and improve
rate transfer. The baffle cut term is used for the height of segment removed to form the baffle.
In this project, the designed heat exchanger has 13 baffles and baffles cut at 25% of diameter.
The two correlations for shell side and tube side and overall heat transfer coefficient
equation are given below.
Gnielinski Equation(for tube side)
3
Donohue Equation(for shell side):
Overall heat transfer coefficient calculation by using hi and ho:
4
2. EXPERIMENTAL METHODS
In this experiment, the purposes were to see the effect of Reynolds number on the
individual heat transfer coefficients, to calculate and compare the overall heat transfer
coefficient (U) and to observe the performance of shell and tube heat exchanger for both
cocurrent and counter-current modes.
In the first part of the experiment, the counter-current flow operation was observed
and for this purpose, the valves V1 and V3 are closed and V2 and V4 are opened. For sounter-
current observation, the cold water stream was adjusted to 400, 500 and 600 L/h and hot water
stream was adjusted to 400L/h for three different cold water flow rate values. After the
adjustments were done, the system was operated and each three minutes, the data were
recorded for the temperature values, that is for TI1, TI2, TI3, TI4 and TW1 till the system
reached the steady state. The steady state values of inlet and outlet temperatures of both
streams were also recorded. After the first part finished, in order to compare the performance
of co-current and counter-current operations, co-current operation at a studied value of first
part is chosen which is 500 L/h for cold water stream. The valves V2 and V4 are closed and
V1 and V3 are opened.
Figure 2.1: Experimental setup
5
3. RESULTS
In this experiment, we aimed to calculate and compare the overall heat transfer
coefficients (U) that obtained for both co-current and counter-current modes of shell and tube
heat exchanger. Also, we were able to see the effect of Reynold’s Number on the heat transfer
coefficients.
Temperature profiles of each run in the heat exchanger;
Table 3.1: Temperature and flow rate values for the counter-current flow operation
Flow rate (L/h) Temperature (°C)
Cold Fluid Hot Fluid Tc,i Tc,o Th,i Th,o
400 856 14.7 29.9 62.8 48.7
500 856 14.5 27.1 60.9 46.5
600 856 14.6 24.8 58.2 44.1
Table 3.2: Temperature and flow rate values for the co-current flow operation
Flow rate (L/h) Temperature (°C)
Cold Fluid Hot Fluid Tc,i Tc,o Th,i Th,o
500 856 14.6 26.3 58.8 45.7
Figure 3.1: Temperature profile for the counter-current flow operation for Run 1
6
Figure 3.2: Temperature profile for the counter-current flow operation for Run 2
Figure 3.3: Temperature profile for the counter-current flow operation for Run 3
7
Figure 3.4: Temperature profile for the co-current flow operation for Run 1
Some physical properties that assumed constant at average temperatures;
Table 3.1: Physical Properties of fluid at average temperatures
Counter-current Flow Co-current flow
Run no:1 Run no:2 Run no:3 Run no:1
Tube
Side
Shell
Side
Tube
Side
Shell
Side
Tube
Side
Shell
Side
Tube
Side
Shell
Side
Tav(K) 328.75 295.3 326.7 293.8 324.15 292.7 325.25 293.3
Pr 3.22 6.57 3.33 6.85 3.48 7.05 3.41 6.94
ϻ*10^(-
6)(N.s/m) 498.75 953 515 988 536 1014.6 526 1000
Cp(kj/kgK) 4.184 4.181 4.183 4.182 4.182 4.183 4.182 4.182
k*10^(-3) 648.75 606 646.7 604 644.2 602.3 645.25 603.3
ρ(kg/m3) 985 998 986 998.5 987 998.4 987 998.4
And this table also shows the difference between overall heat transfer coefficients, heat
transfer coefficient with respect to each side of the shell and tube heat exchanger, heat values
of hot and cold fluid, Reynolds and Nussle numbers.
8
Table 3.2: Overall heat transfer coefficients and Reynolds numbers
Counter-current flow Co-current flow
Run no:1 Run no:2 Run no:3 Run no:1
Tube
Side
Shell
Side
Tube
Side
Shell
Side
Tube
Side
Shell
Side
Tube
Side Shell Side
Q(L/h) 856 400 856 500 856 600 856 500
Tcin - 14.7 - 14.5 - 14.6 - 14.6
Tcout - 29.9 - 27.1 - 24.8 - 26
Thin 62.8 - 60.9 - 58.2 - 58.8 -
Thout 48.7 - 46.5 - 44.1 - 45.7 -
m(kg/s) 0.234 0.111 0.234 0.237 0.237 0.166 0.235 0.139
v(m/s) 0.946 0.093 0.946 0.116 0.946 0.139 0.946 0.116
Re 14950 9612 14490 11590 14100 13550 14200 11450
Flow
regime Turbulent Turbulent Turbulent Turbulent Turbulent Turbulent Turbulent Turbulent
Nu 90.087 91.307 88.964 103.601 88.481 114.828 88.305 103.291
hio(W/m2K) 5844 - 5753 - 5344 - 5698 -
ho(W/m2K) - 1197 - 1352 - 1508 - 1344
U(W/m2K) 993.5 1095 1176 1088
q(kW) -13.817 7.047 -14.122 7.308 -14 7.1 -12.857 6.611
These all datas are calculated by mathcad on computer. And sample calculations about all
procedure are given in appendix for shell side and tube side for run1 of counter current flow.
These are the some formulations that we use in results ;
Reynolds Number For Shell Side
9
If we substitute all equations into first one,
where,
fb = 0.1955 P = 20 mm B = 48 mm
D0=10 mm Ds=50mm Nt = 5
Res = ( Do . Ge ) / μ
Reynolds Number For Tube Side
If we substitute all equations into first one,
10
Prandtl Nr. For Shell Side
Or you can find the values for water in cropera [1]
Prandtl Nr. For Tube Side
Or you can find the values for water in cropera [1]
Donohue Equation for Shell Side
Friction Factor Calculation for Tube Side
11
Gnielinski Equation for Tube Side
12
4. DISCUSSION
The aims of this experiment are to investigate the effects of Reynolds number on
individual heat transfer coefficients, while comparing the empirically and experimentally
calculated overall heat transfer coefficients. Both fluids are water; one is heated and the
cold one is simply softened tap water. Shell side water, which is cold one, is fed to the
exchanger at 14.6oC temperature, through piping and the cold fluid gets hotter by the heat
supplied from hot water. However, the gain of cold fluid is less than the amount of supplied
by hot fluid. Therefore, it can be said that there is a heat loss.
Other case is the overall heat transfer coefficients (U), which is both for empirical and
experimental. First of all, to calculate empirical overall heat transfer coefficient, the
individual heat transfer coefficients have to be calculated for each run. The result is in the
Table 3.2. The heat transfer coefficient changes when the flow rate changes. They are
proportional to each other. In theoretically, the heat transfer coefficient increases as
concluded experimentally because of the eddies, due to the turbulent flow regime.
The other assumptions were about the baffle spacing. Again our preliminary
calculations showed that choosing baffle spacing closer to 0.2 of Ds gives better results
which were given as 0.05. If we consider the cost, since baffle spacing affects area for cross
flow and the heat transfer coefficient directly. Moreover, heat transfer coefficient affects
clean overall coefficient and dirt factor.
When results which is listed in Table 3.2 are compared, theoretically, it is expected
that higher heat transfer coefficient for counter-current than for co-current. Similar behavior
is also observed experimentally. As expected that counter-current system is more efficient
with higher heat transfer coefficients.
Finally, while counter current and co-current flows have the same flow rates; their
heat transfer rates are different, because of the effect of log mean temperatures as the
same area. However, the theoretical and calculated values are nearly same in each other.
13
5. CONCLUSION
In this experiment, the performance of heat exchanger for different operating modes
and heat transfer coefficient dependence are investigated. At different flow rates, overall heat
transfer rates, shell side and tube side heat transfer coefficients were calculated and compared.
According to our evaluation of experimental data, heat transfer coefficients are higher
in counter-current flow with respect to co-current flow. Accordingly, we can conclude that
counter-current operating heat exchangers are more efficient.
14
6. REFERENCES
1. Dewitt, D., Incropera, F. & Bergman, T.L. “Fundementals of Heat and Mass Transfer”.
Sixth Edition
2. Shell and tube Heat Exchanger Design. Retrieved from
http://www.engr.iupui.edu/me/courses/shellandtube on May 23, 2012
3. Effectively Design Shell and Tube Heat Exchangers. Retrieved from http://www-
unix.ecs.umass.edu/~rlaurenc/Courses/che333/Reference/exchanger.pdf on May 23, 2012
15
7. APPENDIX
TUBE SIDE (for Run1)
Di 0.008 m Cp 4.184 kj
kgK 985
kg
m3 Pr 3.22
Tcin 14.7 Tcout 29.9
Tincelcius( ) k 648.7510
3
W
mK
Thin 62.8 Thout 48.7
498.75106
Ns
m
Q 856 3600000
Q 2.378 104
m3
s
Tm
Thin Thout
2273
Tm 328.75 TminKelvin
at Di
2
4
Nt 5 nt 1
At
Nt at
nt
m Q
m 0.234 m in kg/s
q m Cp Thout Thin
q 13.817 kW
vm
At
v 0.946
Re v Di
Re 1.495 104
16
0
A Di
2
4
X 4 log
Di
3.7065
5.0452
Relog A( )
f1
X2
f 7.758 103
Nu
f
2Re 1000( ) Pr
1 12.7f
2
1
2
Pr( )
2
31
Nu 90.087
hiNu k
Di
hi 7.306 103
hio hi 0.8
hio 5.844 103
17
SHELL SIDE (for Run1)
Dt 0.01 m Ds 0.05 m Cp 4.181 kj
kgK tav 328.75 K
Tcin 14.7 Tcout 29.9 Tincelcius( ) hio 5844
Thin 62.8 Thout 48.7
Prs 6.57 998 kg
m3 953 10
6
Ns
m k 606 10
3
W
mK
P 0.02 m B 0.048 fb 0.1955
Q 400 3600000
Q 1.111 104
m3
s
Tav
Tcin Tcout
2273
Tav 295.3 Tav inKelvin
m Q
m 0.111 m in kg/s
q m Cp Tcout Tcin
q 7.047 kW
Sc P Dt BDs
P
Sc 1.2 103
m2
v Q Sc
v 0.093 m
s
Gcm
Sc
18
Nb 1
Sb fb
Ds2
4 Nb
Dt2
4
m2
Sb 3.053 104
Gbm
Sb
kg
m2s
Gb 363.185
Ge Gc Gb
Ge 183.197 kg
m2s
Res
Ds Ge
Res 9.612 103
A 0.2Res0.6
Prs0.33
k
Ds
A 1.107 103
where A=hs/ϕ s
tw tavA
hio ATav tav
tw 323.424 Kelvin
w 544 106
Gc 92.407 kg
m2s
19
s
w
0.14
s 1.082
ho A s
W
m2K
ho 1.197 10
3
NuA Ds
k
Nu 91.307
Uhio ho
hio ho
W
m2K
U 993.506