 Open Access
 Total Downloads : 1393
 Authors : Ramesh Vathare , Omprakash Hebbal
 Paper ID : IJERTV2IS80726
 Volume & Issue : Volume 02, Issue 08 (August 2013)
 Published (First Online): 29082013
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
CFD Analysis of Enhancement of Turbulent Flow Heat Transfer in a Horizontal Tube with Different Inserts
Vol. 2 Issue 8, August – 2013
Ramesh Vathare 1*, Omprakash Hebbal2
1*PG Student, Thermal power Engineering, PDA College of Engineering, Gulbarga585102, Karnataka (INDIA)
2Professors, Department of Mechanical Engineering, PDA College of Engineering, Gulbarga585102, Karnataka (INDIA)
ABSTRACT
The present work includes the results of CFD analysis of enhancement of turbulent flow heat transfer in a horizontal circular tube with different inserts (Cylinder, diamond and trapezoidal), with air as working fluid. The Reynolds number ranged from 6000 to 14000. Geometry of tube having inner diameter 27.5 mm and length of the tube is 610 mm. The horizontal tube in the presence of different inserts: (Geometry description of diamond: pitch=50mm, core rod diameter =2mm, diagonal length =20mm, thickness=2mm. Geometry description of cylinder: pitch=50mm, core rod diameter =2mm, diameter of cylinder =20mm, thickness of cylinder=2mm.Geometry description of trapezoidal: pitch=50mm, core rod diameter =2mm, bottom length=15mm, top length=10mm, height=10mm). Improvement of average Nusselt Numbers for tube with 87% for cylinder insert, 85% for diamond insert and 28% of trapezoidal insert, with respect to Plain Tube. Similarly friction factor for tube with cylinder insert is 600% more compared with the plain tube. Overall enhancement ratio is high for cylinder (75%) and low for Trapezoidal insert (65%) and pressure drop is considerably more with different inserts when compared to plain tube, pressure drop is high for cylinder insert and low for trapezoidal insert. Finally we compared results with theoretical results and using tool of package of ANSYSCFX 12.0 version 12.0 version to compare the construction, performance, and economics of tube inserts. Geometries for plain tube and tube with different inserts is developed and meshing in ICEM CFD13.0 (3d dimensional) with and exported to ANSYSCFX 12.0 version12.0 version, then suitable boundary conditions are applied to these models and solved energy momentum and turbulence equations and results obtained are discussed.
Key words : tube, heat transfer, different inserts (Cylinder, diamond and trapezoidal), turbulent flow, pressure drop, augmentation. ICEMCFD13.0 version software, ANSYSCFX 12.0 version12.0 version Software,

introduction
Heat transfer enhancement or intensification is the study of improved heat transfer performance. Recently adequate energy source and material costs have provided significant resources for the development of enhanced energy efficient heat exchangers. As a result, considerable emphasis has been placed on the development of various augmented heat transfer surfaces and devices. Heat transfer enhancement today is characterized by rigorous research activities both in academic and industrial levels. This can be seen from the exponential increase in world technical literature published on heat transfer enhancement devices, growing patents and hundreds of manufacturers offering products ranging from enhanced tubes to entire thermal systems incorporating enhancement technology. Enhancement of turbulent flow heat transfer in a horizontal circular tube with different inserts has drawn great attention, and some experimental and theoretical research work has been carried out in recent years.
ShouShingHsieh ,FengYu Wu,HuangHsiu Tsai et al. [1]: The present result of a study of turbulent flow and pressure drop in a horizontal tube with strip type inserts. Experimental data taken for air for a class of strip type inserts (longitudinal, LS and cross, CS inserts) used as a tube side heat transfer augmentative device for a singlephase cooling mode operation are presented. To broaden the understanding of the underlying physical phenomena responsible for the heat transfer enhancement,flow mechanisms through velocity measurements are combined with pressure drop measurements to develop friction factor correlations for 65006 Re 619500 where Re is the Reynolds number. Friction factor increases were typically between 1.1 and 1.5 from low Re 6500 to high Re 19500 with respect
to bare tubes.
Vol. 2 Issue 8, August – 2013
M Ahmed, L Deju, M. A. R. Sarkar and S. M. Nazrul Islam et al. [2]:Heattransfer and pressure drop characteristics in a circular tube fitted with twisted tape inserts have been investigated experimentally. Experiments were conducted with tape inserts of three different twist ratios (twist ratio, y=23, y=11.5 and y=8).And calculated for tubes with twisted tape inserts to analyze the friction factor, Nusselt Number and the heat transfer coefficient. Reynolds Number was calculated based on inside diameter of the tube and varied from 2.0 Ã— 104 to 5.5 Ã— 104. The result indicated that average heat transfer coefficient is about 1.3 to 3 times higher than that of the smooth tube.
M A R Sarkar, A B M ToufiqueHasan, M Ehsan, M MAlamTalukdar and A MA Huq et al. [3]:An experimental investigation has been carried out to study theconvective heat transfer in a tube with longitudinal inserts with different shapes of strips in turbulent flow. Three different shapes of strip (Y, X and star configuration) were fabricated from mild steel and inserted into the smooth tube successively. And the flow was varied in the range of Reynolds number 2.0×104 to 5.0×104. At comparable Reynolds number, heat transfer coefficient in tube with longitudinal strip inserts is enhanced by 1.4 to 3 times, friction factor increased by 1.2 to 2.2 times while the pumping power increased up to 4 times compared to that of smooth tube.
Hiral N. Prajapati et al. [4]:Present work reports CFD studies of Nusselt number,friction factor and overall enhancement efficiency for a tube fitted with wire coil. The result showed that the wire coil with p/d of 0.434, 0.651 and 0.868 can enhance heattransfer up to 4.98, 5 and 4.3 times respectively and friction factors up to 5.82, 4.06 and
3.3 times respectively, in comparison with plain tube. Wire coil inserts with e/d of 0.038, 0.128 and 0.171 provide heat transfer enhancement around 4.99, 5.92 and 7.6 times respectively and friction factor enhancement up to 5.82,
19.97 and 35.7 times respectively than plain pipe.
S.N. Sarada, A.V.S.R. Raju and K.K. Radha et al. [5]:The present work focuseson experimental and numerical investigations of the augmentation of turbulent flow heat transfer in a horizontal circular tube by means of mesh inserts with air as the working fluid. Sixteen types of mesh inserts with screen diameters of 22 mm, 18 mm, 14 mm and 10 mm for varying distance between the screens of 50 mm, 100 mm, 150 mm and 200 mm in the porosity range of 99.73 to 99.98 were considered for experimentation. The horizontal tube was subjected to constant and uniform heat flux. The Reynolds number varied from 7,000 to 14,000. The results are compared with the clear flow case when no porous material was used. Computational fluid dynamics (CFD) techniques were also employed to perform optimization analysis of the mesh inserts. The horizontal tube along with mesh inserts was modelled in Gambit 2.2.30 with fine meshing and analyzed using FLUENT 6.2.16. CFD analysis was performed initially for plain tube and the results are compared with experimental values for validation.

Methodology. 2.1Mathematical Model Finite Volume Formulation
ANSYSCFX 12.0 version uses a finiteelementbased finite volume method. The governing equations namely the conservation for mass; momentum and energy are expressed in equations (2.1, 2.2 and 2.3).
(2.1)
(2.2)
(2.3)
Where the energy conservation has been replaced by a generic scalar transport equation. The finite vVoollu. 2mIessume 8e,thAougdust – 2013
proceeds by integrating these equations over a fixed control volume, which, using Gauss Theorem, results in equation (2.4, 2.5 and 2.6).
(2.4)
(2.5)
(2.6)
where v and s denote volume and surface integrals respectively and dnj represents the differential Cartesian component of the outward normal surface vector. The equations represent a flux balance in a control volume. The above equations are applied to each control volume or cell in the computational domain. These continuous equations are approximated numerically using discrete functions. Discretisation of the above equations yields the following in equations (2.7, 2.8 and 2.9).
(2.7)
(2.8)
(2.9)
Where
and V is volume of the control volume, the subscript ip denotes the integration point, the summation is overall the integration points of the surface,njis the discrete outward surface vector,t is the time step, the superscript to refers to the old time level, and the overbar on the source terms indicate an average value for the control volume. The fluxes are evaluated at integration points, which are shared by adjacent control volumes and exactly the same flux that leaves one control volume enters the next.
The Standard k Turbulence Model: The k turbulence model utilizes the eddyviscosity assumption to relate the Reynolds stress and turbulent flux terms to the mean flow variables. For the general Reynolds stress tensor is given
by the equations (2.10 and 2.11). Continuity equation
Momentum equation
Here eff =+t t= turbulent viscosity and P* =P+2/3k Turbulent viscosity is related to turbulent kinetic energy k and dissipation rate a sin equation 2.12
(2.10)
(2.11)
(2.12)
Vol. 2 Issue 8, August – 2013
The value so f k and come directly from the differential, transport equations for turbulent kinetic energy and turbulent dissipation rate as in equations (2.13 and 2.14).
(2.13)
(2.14)
Where diffusion coefficients are given by
Wherekand are model constants. Production rate of turbulent kinetic energy Pk is given by equation 2.15.
(2.15)
The values of constants in the model are c= 0.09, c1= 1.44, c2=1.92,k=1.0,= 1.3 and Turbulent Prandtl number Prt = 0.9

Sequence of operation:
Description of the problem and geometry: The primary goal of the present work is to enhance the heat transfer in a tube employing various inserts. Also determine average Nusselt number and friction factors for Reynolds number ranging from 600014000 in the turbulent region. Average Nusselt numbers, friction factors of working fluid (air) flowing in the plain tube are compared with average Nusselt numbers, friction factors of working fluid (air) flowing in tube with diamond, cylinder and trapezoidal inserts which enhance heat transfer. Enhancement Efficiencies of the different inserts also compared.
The geometry of the tube and dimensions of the insert used in this study are listed: Inner Diameter of the test pipe, D = 2.75*102 m
Crosssectional area of the pipe, Ap = 5.939572*104 m2 Length of the Heating Zone, L = 61*102m
Diameter of the Orifice, d0 = 0.014m
Crosssectional area of the Orifice, Ao = 1.54*104 m2
Coefficient of discharge, Cd = 0.64 Thickness of the insert, t=2 mm, Average wall Temperature, Tw
Nusselt numbers and friction numbers are calculated for Reynolds number Ranging from 6000 14000.Equations for calculating Nusselt number & friction factor are given below:
Nu=hDi/k
h= ((Q/A)/(TwTb))
Where Tw= Average Surface Temperature Tb= (Ti+T0)/2
f= (P)/(L/D)V/2)
Enhancement Efficiency is calculated using the following equation: Friction factor ratio = (Nu/Nu0)/(f/fo)1/3
Theoretical calculations:
Nusselt number and friction factor are calculated for Reynolds numbers ranging from 600014000 using
DITTUSBOELTER results are tabulated below:
DITTUSBOELTER for Nusselt number: Vol. 2 Issue 8, August – 2013
Nu=0.023 x Re0.8 x Prnfor6000Re14000 , Where n = 0.4 for Heating fluids.
Friction factor:f= [1.82 log10 Re1.64]2for6000Re1400
Analysis of problem : CFD techniques used to perform the overall performance and optimization analysis of the fluid flow transfer of the tube with/without insert was performed using ANSYSCFX 12.0 version.
Without inserts: Initially the CFD experiment is carried out with air as the moving fluid through pipe section without any inserts. This also termed as PLAIN TUBE CFD experiment.
With insert: In this type case is taken: Trapezoidal, Diamond and Cylinder.
Numerical Investigations in Plain Tube:

Initially numerical analysis was performed on the horizontal plain tube for the estimation of Nusselt number and friction factor of air by using commercially available ANSYSICEM13.0version, and ANSYSCFX 12.0 version software.

Nusselt numbers and friction factors of air obtained from the numerical analysis under turbulent flow are validated with the correlations available in the literature for tube internal flow.

Conducting simulation at a constant heat flux of 759.010 w/m2 at different mass flow rates for calculation of Nusselt numbers, friction factors and pressure drop (across the test section of PLAIN TUBE CFD experiment) of air at different Reynolds numbers by varying the mass flow rate of air.

Nusselt numbers and friction factors values obtained from the numerical analysis are compared with the correlations available in the literature and the percentage deviation is reported.
Numerical Investigations in Plain Tube with Inserts

Simulation of horizontal tube test section (using numerical analysis) in the presence of different inserts like diamond, trapezoidal and cylinder to predict the enhancement of heat transfer rate and generation of pressure drop data across the test section by using commercially available ANSYS ICEM13.0version and ANSYSCFX12.0 version, software.

Simulation of horizontal tube test section (using numerical analysis) in the presence of different inserts: (Geometry description of diamond – pitch=50mm, core rod diameter =2mm, diagonal length =20mm, thickness=2mm. Geometry description of cylinder – pitch=50mm, core rod diameter = 2mm, diameter of cylinder =20mm, thickness of cylinder=2mm. Geometry description of trapezoidal pitch=50mm, core rod diameter = 2mm, bottom length=15mm, top length=10mm, height=10mm) were considered for numerical analysis. CFD techniques are employed to perform optimization analysis of the different inserts. The horizontal tube along with different inserts were modelled and meshing and analysed using ICEM 13.0version and ANSYSCFX 12.0version, software.

Numerical investigations are conducted in plain tube fitted with different inserts of circular, diamond and trapezoidal geometry at a constant heat flux of 759.010 w/m2 to find the Nusselt number and friction factor of air in the presence of different inserts. The diameter of the core rod is 2 mm. The distance between two adjacent insert (pitch) is fixed at 50 mm. The results of investigations using different inserts are compared with those of plain tube to estimate the rate of heat transfer enhancement of air in the presence of different inserts.

Nusselt number ratio (Nui/Nu: Ratio of Nusselt number with insert to that of without insert) for all the inserts like diamond, trapezoidal and cylinder) is calculated.

Friction factor ratio (fi/f: Ratio of friction factor with insert to that of without insert) for all the inserts like diamond, trapezoidal and cylinder) is calculated.

Based on Nusselt number ratio and friction factor ratio, overall enhancement ratio is calculatd individually for each insert.

Overall enhancement ratio is calculated to determine the optimum geometry of inserts that could provide the maximum heat transfer enhancement rate with lesser friction factor.

Based on oveall enhancement ratio, optimum insert geometry is recommended


Model geometry, Boundary conditions and mesh generation
Zone
Type
Boundary Conditions
Tube
Wall
Heat flux = 759.010 w/m2
Inlet temperature
Heat inlet
Temperature = 53.30c
Mass Flow rate
Inlet
0.00334 Kg/sec
Pressure
Outlet
101395.8 Pa
Zone
Type
Boundary Conditions
Tube
Wall
Heat flux = 759.010 w/m2
Inlet temperature
Heat inlet
Temperature = 53.30c
Mass Flow rate
Inlet
0.00334 Kg/sec
Pressure
Outlet
101395.8 Pa
For setting up any CFD problem, the geometry has to be modelled with required details, mesh has to be generated optimally to obtain the results correctly and flow parameters and boundary conditions are to be set up for solving the problem. The discretized domain is solved using solver and results are analyzed in post processor. In the present investigation, CAD model and ANSYSICEM 13.0version software is used for the geometry modelling and mesh generation. ANSYSCFX 12.0version, software is used for defining boundary conditions, solving and post processing. Table 2.1:Boundarycondition specification for ANSYSCFX 12.0version.
Fig. 2.2: Grid for the Tube with trapezoidal insert configuration Grid Info:
Cells: 833004 Pitch = 50 mm
Core rod diameter = 2mm Bottom length = 15 mm Top length = 10 mm Height = 10 mm Thickness = 2mm
Fig. 2.1: Grid for the Plain Tube configuration Fig.2.2
Grid Info: cells 232092
Fig.2.3: Grid for the Tube with cylinder insert configuration Fig2.4: Grid for the tube with diamond insert configuration
Grid Info: Grid Info:
Cells: 852465 Cells: 833722
Pitch = 50 mm Pitch = 50 mm
Core rod diameter = 2mm Core rod diameter = 2mm
Diameter of cylinder = 20 mm Diagonal length = 20 mm
Thickness of cylinder = 2mm Thickness = 2mm

Simulation Scheme
Analysis of problem in ANSYSCFX12 version
Sequence of steps involved in ANSYSCFX 12.0 version and analysis:

Determination of Mean Velocity (V) of working fluid:

Using Reynolds Number considered from [17] the Mean Velocity of working fluid is determined by the following Equation. Re=VDi/

Selection of solver in ANSYSCFX 12.0version: For the current study the type of solver chosen is upwind discretization model

Under model Turbulence model: kepsilon model selected

Under materials tab in ANSYSCFX 12.0version: The working fluid is air.

Defined suitable Operating conditions. Define Boundary Conditions:
InletVelocity
Constant Heat Flux of 759.010 w/m 2on outer surface Pressure Outlet 101395.8 Pa

Assigned suitable Residual values ranging up to 106

Then solve the following equations: Flow

Turbulence Energy

Results and Discussions.
Each case was run using higher order residual schemes for each governing equations. It was ensured that residuals dropped to at least 106 for each case. Nusselt number and friction factor for plain tube are validated with theoretical relations [Table:3.1] and then they are determined for trapezoidal, diamond and cylinder insert. Nusselt number and
friction factor calculated for the plain tube and plain tube with different insert for 6000<Re<14000. The Nusselt number and friction factor obtained for the tube with insert are compared with Nusselt number and friction factor of Plain tube.Each case is solved for 3 equations Energy, Momentum and Turbulence and results are plotted on corresponding graphs as shown below.
Table: 3.1 Theoretical Calculations
case. No
Mass flow rate
Re
F
Nu
1
0.003334
7757.98
0.0338
25.79
2
0.004108
9557.67
0.0316
30.48
3
0.00474
11028.08
0.0303
34.17
4
0.005304
12341.18
0.0295
37.39
ANSYSCFX 12.0 version Calculations:
In ANSYSCFX 12.0version also cases are analyzed separately one for plain tube, other for tube with trapezoidal, diamond and cylinder inserts respectively. The calculations for these cases are tabulated below.
Table 3.2: Plain Tube Calculations in ANSYSCFX 12.0 version
case. NO
Mass flow rate
Tw(Avg. Wall temperature) K
Tb (K)
Q/A
Re
Nu
Pressure drop (Pa)
h (w/m2 K)
F
1
0.003334
363.983
335.406
759.01
7757.98
23.8017
11.4221
24.7266
0.038733
2
0.004108
357.656
334.118
759.01
9557.67
28.4486
16.876
29.5541
0.037694
3
0.00474
354.168
332.848
759.01
11028.08
31.4305
21.7285
32.6519
0.036453
4
0.005304
351.706
332.193
759.01
12341.18
34.2683
26.5954
35.6000
0.035634
Table3.3: Plain Tube with Trapezoidal inserts Calculations in ANSYSCFX 12.0 version
Vol. 2 Issue 8, August – 2013
case.NO
Mass flow rate
Tw(Avg. Wall temperature) K
Tb (K)
Q/A
Re
Nu
Pressure drop (Pa)
h (w/m2 K)
f
1
0.003334
355.796
331.630
759.01
7757.98
30.6313
84.207
31.8216
0.2855
2
0.004108
351.179
328.120
759.01
9557.67
35.9875
123.731
37.3859
0.2763
3
0.00474
348.821
326.920
759.01
11028.08
40.2445
161.399
41.8083
0.2707
4
0.005304
346.460
326.194
759.01
12341.18
43.9761
199.066
45.6849
0.2667
Table3.4: Plain Tube with Diamond inserts Calculations in ANSYSCFX 12.0 verson
case.NO
Mass flow rate
Tw(AvgWall temperature) K
Tb (K)
Q/A
Re
Nu
Pressure drop (Pa)
h (w/m2 K)
f
1
0.003334
348.356
340.591
759.01
7757.98
44.7463
210.720
46.4851
0.7145
2
0.004108
344.797
336.692
759.01
9557.67
52.7770
311.489
54.8279
0.6957
3
0.00474
342.685
334.513
759.01
11028.08
59.1738
407.711
61.4732
0.6840
4
0.005304
341.191
333.100
759.01
12341.18
64.7826
504.144
67.3000
0.6754
Table3.5: Plain Tube with Cylinder inserts Calculations in ANSYSCFX 12.0 version
case.NO
Mass flow rate
Tw(AvgWall temperature) K
Tb (K)
Q/A
Re
Nu
Pressure drop (Pa)
h (w/m2 K)
f
1
0.003334
342.745
343.580
759.01
7757.98
68.8613
641.083
71.5372
2.1739
2
0.004108
339.982
339.640
759.01
9557.67
81.7430
953.987
84.9194
2.1308
3
0.00474
338.357
337.360
759.01
11028.08
91.9827
1253.98
95.5570
2.1037
4
0.005304
337.215
335.842
759.01
12341.18
101.046
1552.22
104.973
2.0797
Table3.6: Enhancement Efficiency calculations for different inserts
Mass flow rate
Re
Trapezoidal (Nu/Nu0)
Diamond (Nu/Nu0)
Cylinder (Nu/Nu0)
0.003334
7757.98
1.286936106
1.879960804
2.893119698
0.004108
9559.023
1.264998522
1.855166685
2.873349743
0.00474
11029.64
1.280426341
1.882684053
2.926539091
0.005304
12342.03
1.283285181
1.890450434
2.948689579
Mass flow rate
Re
Trapezoidal (f/f0)1/3
Diamond (f/f0)1/3
Cylinder (f/f0)1/3
0.003334
7757.98
1.946265665
2.642327227
3.828741986
0.004108
9559.023
1.942687752
2.642760047
3.837876364
0.00474
11029.64
1.95114868
2.657301876
3.864443433
0.005304
12342.03
1.95612613
2.666343054
3.878962515

Flow Simulation of Enhancement of heat transfer in tube with different varying Reynolds numbers such as case1 = 7757.98, case 2 = 9559.023, case 3 = 11029.64, case 4 = 12342.03 Case1 case2 case1 cass2
Case3 case4 case3 case4
Fig3.1 Fig3.2
Fig3.1 and Fig3.2 show that the static temperature variation for the plain tube configuration and on walls configuration.
Case1 case2 case1 case2
Case3 case4
Fig3.3 Case3 case4
Fig3.4 Fig3.3 and Fig3.4 show that pressure and velocity variation for the plain tube configuration.

Flow Simulation of Enhancement of heat transfer in tube with Trapezoidal insert, with varying Reynolds number such as case1 = 7757.98, case 2 = 9559.023, case 3 = 11029.64, case 4 = 12342.03

case1
case1
Case1 case2
Case3
case4
Fig3.5 fig3.6
Fig3.5 and fig3.6 show that the static temperature variation for the tubewith trapezoidal insert
Configuration and on walls configuration.
Case1 case2 case1 case2
Case3 case4 case3 case4 Fig3.7 Fig3.8
Fig3.7and Fig3.8 show that pressure and velocity variation for the tube with trapezoidal insert configuration.

Flow Simulation of Enhancement of heat transfer in tube with Diamond insert, with varying Reynolds number such as case1 = 7757.98, case 2 = 9559.023, case 3 = 11029.64, case 4 = 12342.03
Case1 case2 case1 cass2
Case3 case4 case3 case4
Fig3.9 Fig3.10
Fig3.9 and Fig3.10 show that the static temperature variation for the tube with diamondinsert configuration and on walls configuration.
Case1 case2 case1 case2
Case3 case4
Case3 case4
Fig3.11 fig3.12
Fig3.11and Fig3.12 show that pressure and velocity variation for the tube with diamond insert configuration.

Flow Simulation of Enhancement of heat transfer in tube with cylinder insert, with varying Reynolds number such as case1 = 7757.98, case 2 = 9559.023, case 3 = 11029.64, case 4 = 12342.03
Case1 case2 case1 case2
Case3 case4
Case3 case4
Fig3.13 fig3.14
Fig3.13and Fig3.14show that static temperature variation for the tube with cylinder insert configuration and on walls.
Case1 case2 case1 case2
Case3 case4
Case3 case4
Fig3.15 fig3.16
Fig3.15and Fig3.16 show that pressure and velocity variation for the tube with cylinder insert configuration.
Grapp.1 Grapp.2
Grapp.1 show that the Comparison between Theoretical and CFD Analysis for Variation of Average Nusselt Number with Reynolds number in Plain Tube.
Inference from Grapp.1: the grapp.1 reveals that results obtained through ANSYSCFX 12.0 version are
almost identical with values thorugh DITTUSBOELTER for Nusselt number. The Maximum % varVioalt.i2onIssuoef8C, AFuDgust – 2013
results for Nusslet number is found to be 6.1% with respect to theoretical values.
Grapp.2 show that the Comparison between Theoretical and CFD Analysis for Variation of Friction Factorwith Reynolds number in Plain Tube.
Inference from Grapp.2: the grapp.2 reveals that results obtained through ANSYSCFX 12.0 version are well within the range of values obtained through DITTUSBOELTER for Friction Factor. The Maximum % variation of CFD results for Friction Factor is found to be 10.3% with respect to theoretical values.
Grapp.3 Grapp.4
Grapp.3 show that Comparison between CFD Analysis for Variation of Nusselt Number with Reynolds number in Plain Tube Vs different insert.
Inference from Grapp.3: the grapp.3 reveals that results obtained through ANSYSCFX 12.0 version. The maximum % variation of CFD results for Nusselt Number is found to 87% for cylinder insert, 85% for diamond insert and 28% of trapezoidal insert, with respect to Plain Tube.
Grapp.4 show that Comparison between CFD Analysis for Variation of Friction factor with Reynolds number in Plain Tube Vs different inserts.
Inference from Grapp.4: the grapp.4 reveals that results obtained through ANSYSCFX 12.0 version. The max 600 % variation of CFD results for Friction factor is found for cylinder insert with respect to Plain Tube.
Grapp.5 Grapp.6
Vol. 2 Issue 8, August – 2013
Grapp.5 show that Comparison between the Nusselt Number ratio Vs Reynolds Number of CFD values of different inserts through ANSYSCFX 12.0 version.
Inference from Grapp.5:the grapp.5 reveals that if Reynolds number increases Nusselt number ratio also increasing. Maximum Enhancement of Nusselt Number for cylinder insert is 2.8.
Grapp.6 show that Comparison between the Friction Factor ratio Vs Reynolds Number of CFD values of different inserts through ANSYSCFX 12.0version.
Inference from Grapp.6:the grapp.6 reveals that if Reynolds number increases friction factor is decreasing. Minimum friction factor ratio for trapezoidal insert is 1.95.
NOMENCLATURE
Re Reynolds No
Density in Kg/m3
Di Inner diameter of tube in m
Do outer diameter of tube in m
A Surface area in m2
V Mean velocity of fluid in m/s
L Length of tube in m
Dynamic viscosity of fluid
Nu Nusselt number
F Friction Factor
K Thermal Conductivity in W m/k
Q Heat supplied in w
2
2
H Heat transfer coefficient in W/m k
T1 Inlet temperature in K
T0 outlet temperature in K
Tb Bulk temperature in K
Tw Inner surface temperature in K
p Pressure Drop
uo
uo
N Average Nusselt Number for Plain Tube
ut
ut
N Average Nusselt Number for Tube with insert
F Friction Factor for Plain tube
o
o
f Friction Factor for Tube with insert
Grapp.7
Grapp.7 show that Comparison between the Overall enhancement ratio Vs Reynolds Number of CFD values of different inserts through ANSYSCFX 12.0version.
Inference from Graph: Above graph reveals that overall enhancement ratio is high for cylinder (75%) and low for Trapezoidal insert (65%)
4 CONCLUSIONS
Vol. 2 Issue 8, August – 2013
In the present work CFD Analysis of enhancement of heat transfer of different inserts for improving heat transfer in horizontal tube has been carried out with boundary conditions such as mass inlet and pressure outlet defined with constant heat flux. Mesh is created ANSYSICEM 13.0version(3 dimensional). The variations of Temperatures, average Nusselt Numbers, friction factor and pressure drop on with inserts like diamond, trapezoidal and cylinder has been studied.

Results revelaed that average Nusselt Numbers and friction factors are considerably more with different inserts when compared to plain tube.

Improvement of average Nusselt Numbers for tube with 87% for cylinder insert, 85% for diamond insert and 28% of trapezoidal insert, with respect to Plain Tube.

Similarly friction factor for tube with cylinder insert is 600% more compared with the plain tube. Overall enhancement ratio is high for cylinder (75%) and low for Trapezoidal insert (65%).

The pressure drop is considerably more with different inserts when compared to plain tube, pressure drop is high for cylinder insert and low for trapezoidal insert.
FUTURE WORKCFD simulation can work with different inserts as well as different Reynolds number. Also can carry out the experimental studies to validate the present results
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