cfd report group 3
DESCRIPTION
CFD Report Group 3TRANSCRIPT
1
CCB 3033
Advanced Transport Process
May 2015 Semester
CFD SIMULATION OF HEAT EXCHANGE
EQUIPMENT
GROUP 3
TEAM MEMBERS:
Name ID
Muhamad Asyraf Bin Mohd Aris 17670
Hani Zarith Alia Binti Zaharudin 17516
Nor Nadiah Ahmad Hamidi 17154
Syed Amirul Alwi Bin Syed Mohd Zaki 17274
Due Date : 18 August 2015
2
TABLE OF CONTENTS
No. Title Page
1 Introduction about Heat Exchanger 3
2 Governing Equations and Simulation Method 5
3 Flow Regime in Heat Exchanger 8
4 Heat Transfer Coefficient 10
5 Results 12
6 Discussion 26
6 Conclusions 27
7 References 27
3
Introduction About Heat Exchanger
A heat exchanger is a device used to transfer heat between one or more fluids. The fluids
may be separated by a solid wall to prevent mixing or they may be in direct contact. There are
three primary classifications of heat exchangers according to their flow arrangement. For
efficiency, heat exchangers are designed to maximize the surface area of the wall between the
two fluids, while minimizing resistance to fluid flow through the exchanger.
Heat exchanger consists of heat transfer elements such as a core or matrix containing the
heat transfer surface, and fluid distribution elements such as headers, manifolds, tanks, inlet and
outlet nozzles or pipes, or seals. Usually, there are no moving parts in a heat exchanger;
however, there are exceptions, such as a rotary regenerative exchanger (in which the matrix is
mechanically driven to rotate at some design speed) or a scraped surface heat exchanger.
In parallel-flow heat exchangers, the two fluids enter the exchanger at the same end, and
travel in parallel to one another to the other side. In counter-flow heat exchangers the fluids enter
the exchanger from opposite ends. The counter current design is the most efficient, in that it can
transfer the most heat from the heat (transfer) medium per unit mass due to the fact that the
average temperature difference along any unit length is higher. In a cross-flow heat exchanger,
the fluids travel roughly perpendicular to one another through the exchanger.
Types of heat exchangers:
1. Shell-and-Tube Exchanger
This exchanger, shown in Fig. 1.5, is generally built of a bundle of round tubes mounted
in a cylindrical shell with the tube axis parallel to that of the shell. One fluid flows inside
the tubes, the other flows across and along the tubes.
2. Plate Heat Exchanger
These exchangers are composed of many thin, slightly separated plates that have very
large surface areas and small fluid flow passages for heat transfer. Advances
in gasket and brazing technology have made the plate-type heat exchanger increasingly
practical.
4
3. Plate and Shell Heat Exchanger
It combines plate heat exchanger with shell and tube heat exchanger technologies. The
heart of the heat exchanger contains a fully welded circular plate pack made by pressing
and cutting round plates and welding them together. It does completely without gaskets,
which provides security against leakage at high pressures and temperatures.
4. Plate Fin Heat Exchanger
Plate and fin heat exchangers are usually made of aluminium alloys, which provide high
heat transfer efficiency. The material enables the system to operate at a lower temperature
difference and reduce the weight of the equipment. Plate and fin heat exchangers are
mostly used for low temperature services.
5
Governing Equations
1. Convective heat flux equation
q=h(Text-T)
2. Reynolds number
Re = 𝑣𝐷
3. Continuity Equation
𝑆𝐷𝑅= distributed resistance
𝑆𝐷𝑅 = −(𝐾𝑖 +
𝑓𝑑
) 𝜌𝑉2𝑖
2− 𝐶𝑛𝑉𝑖
6
i=u,v and w momentum equation
f= friction factor
d = hydraulic diameter
C= permeability
Note : K-factor term operates on a single momentum equation
Sω= rotating coordinates
𝑺𝝎 = −𝟐𝝆𝝎𝒊 × 𝑽𝒊 − 𝝆𝝎𝒊 × 𝝎𝒊 × 𝒓𝒊
𝜔= rotational speed
r= distance from axis of rotation
4. Energy equation
7
Simulation Method
1. Open COMSOL.
2. Add study Stationary.
3. Add Physics.
a) Non-isothermal
4. Add materials - water to all boundaries.
5. Draw the geometry according to individual values.
6. In Non-Isothermal flow:
a. Add inlet with To=298 K and v=1.11 m/min.
b. Add outlet at boundary.
c. Add heat flux at circles.
7. Compute study.
8. Add study group to build.
a. Temperature profile and velocity field streamline in 2D.
b. Temperature and Velocity profile in revolve-3D (225o).
c. Isosurface plot for temperature.
d. Temperature distribution at different z position.
9. Do a trial and error between heat transfer coefficient and exit temperature.
10. Plot graph.
a. Trial and error process to determine heat transfer coefficient.
b. Relationship between heat transfer coefficient and T2.
8
Flow Regime in Heat Exchanger
Flow regime can be determined from the Reynolds number.
Reynolds number = Inertia force/ Viscous force
(ρvL)/μ
Where ρ = density of the fluid
v = velocity of the fluid
L = Length of the fluid inlet
μ = dynamic Viscosity of the fluid
[999.9(kg/m3)*0.11*105(m/s)*0.05(m)] / [0.896*103] Pa.s
6.26, which is in the limit of Laminar flow.
Hence, the flow regime can be considered as Laminar Flow.
17274
9
17154
17516
17670
10
Heat Transfer Coefficient
By using COMSOL, the heat transfer coefficient for the heat exchanger can be determined.
For the value of X = 0.11m, Y = 0.17m, at T2 = 111°C and v1 = 0.11m/min, the heat transfer
coefficient, h = 104 W/m2K.
For the value of X = 0.11m, Y = 0.156m, at T2 = 111°C and v1 = 0.11m/min, the heat transfer
coefficient, h = 104.
17274
17154
11
For the value of X = 0.16m, Y = 0.128m, at T2 = 111°C and v1 = 0.11m/min, the heat transfer
coefficient, h = 71.75.
For the value of X = 0.21m, Y = 0.128m, at T2 = 111°C and v1 = 0.11m/min, the heat transfer
coefficient, h = 75
17516
17670
12
Results
ID: 17154; X = 0.11m, Y = 0.156m, T2=111OC, v1=0.11m/min
Figure 1 : Temperature profile and velocity field streamline in 2D
Figure 2: Temperature and velocity profile in revolve-3D (225degrees)
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Figure 4: Isosurface plot for temperature
Figure 3: Outlet temperature surface
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Figure 5: Temperature distribution at different z position
Figure 6: Relationship between heat transfer coefficient and T2
15
Figure 7: Trial and error process to determine heat transfer coefficient
ID: 17670; X = 0.21m, Y = 0.128m, T2=111OC, v1=0.11m/min
Figure 3 : Temperature profile and velocity field streamline in 2D
Optimum Point
16
Figure 4: Temperature and velocity profile in revolve-3D (225degrees)
Figure 3: Outlet temperature surface
17
Figure 5: Temperature distribution at different z position
Figure 4: Isosurface plot for temperature
18
Figure 6: Relationship between heat transfer coefficient and T2
Figure 7: Trial and error process to determine heat transfer coefficient
ID: 17516; X = 0.16m, Y = 0.128m, T2=111OC, v1=0.11m/min
0
20
40
60
80
100
120
140
0 20 40 60 80 100 120
Ave
rage
d O
utl
et T
2
Heat Transfer Coefficient
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120
T A
vera
ge O
utl
et T
2
Heat Transfer Coefficient
Optimum Chart
Optimum Point
19
Figure 5 : Temperature profile and velocity field streamline in 2D
Figure 6: Temperature and velocity profile in revolve-3D (225degrees)
20
Figure 4: Isosurface plot for temperature
Figure 3: Outlet temperature surface
21
Figure 5: Temperature distribution at different z position
Figure 6: Relationship between heat transfer coefficient and T2
0
20
40
60
80
100
120
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Ave
rage
d o
utl
et
T2 (
de
gre
e c
els
ius)
Heat transfer coefficient
22
Figure 7: Trial and error process to determine heat transfer coefficient
ID: 17274; X = 0.11m, Y = 0.17m, T2=111OC, v1=0.11m/min
Figure 7 : Temperature profile and velocity field streamline in 2D
0
10
20
30
40
50
60
70
80
90
100
50 55 60 65 70 75 80
T_av
g_o
utl
et-
T2
Heat transfer coefficient
Optimum Chart
Optimum Point
23
Figure 8: Temperature and velocity profile in revolve-3D (225degrees)
Figure 3: Outlet temperature surface
24
Figure 5: Temperature distribution at different z position
Figure 4: Isosurface plot for temperature
25
Figure 6: Relationship between heat transfer coefficient and T2
Figure 7: Trial and error process to determine heat transfer coefficient
Optimum Point
26
Discussion
From the figure of temperature profile and velocity field streamline in 2D, we can observe that
the inlet temperature is approximately 300K and increases up to 500K when it passes through the
heating coil. Maximum temperature is obtained near the heat flux generation region which is the
heating coil. As a much finer mesh is generated in that region, temperature profile is accurately
predicted.
From the velocity profile in revolve 3D, we can observe that the velocity is zero when
approaching the wall due to the no slip condition principle. Maximum velocity is obtained at the
center of the inlet which is 2x10-3
m/s. Velocity is obtained near the inlet and it gradually
decreased due to the fluctuations in the geometry. After achieving a uniform flow, the velocity
raised and headed to a high velocity near the outlet.
From the figure of outlet surface temperature, it can be observed that the temperature is
maximum at the center of the outlet which is 430 K while lowest near the wall which is 370 K.
The same observation can be made from the isosurface plot for temperature.
From the graph of average outlet T2 vs Heat transfer coefficient, we can observe that the
temperature is gradually increasing with the increase of heat transfer coefficient. From the trial
and error process, we can conclude that the optimum heat transfer coefficient is 104 W/m2K.
From the calculations performed, the flow regime is said to be laminar flow. Hence, the velocity
throughout the domain is between 0 to 1 m/s. With respect to the flow, the velocity is zero near
the walls which follows the no slip condition.
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Conclusion
When we compare the three different types of x (in meter) which is 0.11, 0.16, 0.21 given
to us to build the heat exchanger, we found that increase in the length of x (in meter) results in
decrease of overall temperature of the heat exchanger. This can be seen on the surface
temperature profile in results part. Moreover, decrease in x value, makes the velocity streamline
flows easily, shown on the Streamline Velocity field. In addition, the outlet temperature surface
shows higher temperature when x value (in meter) is greater.
Furthermore, when we look at the temperature distribution curve for all the three x
values, we can see that x = 0.11 gives a more consistent curve with less oscillations compare to
the other two values. This shows that the heat exchanger with x = 0.11 has a more stable
temperature distribution compared to the other two.
References
1. Heat Exchanger (n.d). Retrieved from https://en.wikipedia.org/wiki/Heat_exchanger