evaluating aerodynamic bead shape in a heat exchanger … · enhancement of heat transfer with...

International Journal of Scientific Research and Management Studies (IJSRMS)

ISSN: 23493771 Volume 1 Issue 10, pg: 330-345

http://www.ijsrms.com ©IJSRMS pg. 330

EVALUATING AERODYNAMIC BEAD SHAPE IN A HEAT

EXCHANGER TUBE FOR IMPROVEMENT IN THE RATE OF

HEAT TRANSFER FOR THE SYSTEM

1Rohit R. Jadhao, 2Shylesha Channapattanna, 3Swapnil S. Kulkarni 1ME-H&P Engg, Dr.D.Y.Patil School of Engineering Academy, Ambi-Pune, India

2Asst. Prof., Mechanical Deptt.,

JSPM Rajarshi Shahu College of Engineering, Tathawade, Pune, India 3Director-Able Technologies India Pvt. Ltd., Pune, India

ABSTRACT

The challenges posed to the effort of enhancing the rate of heat transfer includes drop in pressure at the delivery

end of the tube. Generating higher turbulence improves the rate of heat transfer but at the cost of the drop in

pressure in the system. This leads to higher power consumption for the same amount of heat transfer. The study

undertaken for this dissertation work aims to introduce aero-dynamics in the construction of the heat exchanger

that would streamline the flow of air through the channel and eventually reduce the pressure drop in the system.

For deployment of CFD methodology, ANSYS Fluent is proposed as a software tool while validation shall be

pursued using physical experimentation for the benchmark geometry or the proposed solution based on

feasibility of development of prototype for this work.

I. INTRODUCTION

The heat exchanger is an important device in almost all of the mechanical industries as in case of

process industries it is key element. Thus from long time many researchers in this area are working to

improve the performance of these heat exchangers in terms of heat transfer rate, keeping pressure drop

in limit. In order to augment heat transfer and to increase thermal performance of the heat exchangers

heat transfer enhancement techniques are widely used. These techniques are classified in three groups,

active, passive and compound techniques. The literature survey in this area shows that a lot of

research work has been carried out on passive techniques, specially wire coil inserts and twisted tapes.

They have done experimental investigation on wire coil inserts acting alone and by varying wire

thickness, coil pitch, coil separation from tube wall, wire cross section and have developed

correlations for Nusselt number with different variables listed. These techniques when adopted in

Heat exchanger proved that the overall thermal performance improved significantly. These papers

review experimental and numerical works taken by researchers on this technique such as twisted tape,

wire coil, swirl flow generator , dimple surfaces etc. to enhance the thermal efficiency in heat

exchangers and useful to designers implementing passive augmentation techniques in heat exchange.

The authors found that variously developed twisted tape inserts are popular researched and used to

strengthen the heat transfer efficiency for heat exchangers. The other techniques used for specific

work environments are also studied in these papers. The dominant literature study usually mentions

five types: wire coils, twisted tapes, extended surface devices, mesh inserts and displaced elements.

The main advantage of these types in respect to other enhancement techniques such as the artificial

roughness by mechanical deformation or internal fin types is that they allow an easy installation in an

existing smooth-tube heat exchanger. The various single and double twisted tapes are also used to

generate swirl/co-swirl. Due to its low cost, the insert devices which are most frequently used in




engineering applications are wire coils and twisted tapes. A twisted tape insert mixes the bulk flow

well and therefore performs better in laminar flow, because in laminar flow the thermal resistant is not

limited to a thin region. The result also shows twisted tape insert is more effective, if no pressure drop

penalty is considered. Twisted tape in turbulent flow is effective up to a certain Reynolds number

range. It is also concluded that twisted tape insert is not effective in turbulent flow, because it blocks

the flow and therefore pressure drop increases. Hence the thermo hydraulic performance of a twisted

tape is not good in turbulent flow. These conclusions are very useful for the application of heat

transfer enhancement in heat exchanger networks.

The study of the papers is aimed at providing detailed information about the forced convective heat

transfer coefficient and thermal field of aerodynamic bead shape-type insert in a small circular tube.

Experiments carried out with air as the working fluid are presented and discussed in these papers. In

addition, we have examined whether the pressure drop associated with the aerodynamic bead shape

type inserts can be reduced without seriously impairing the heat transfer augmentation. Furthermore,

to verify the present result, flow visualization studies for some different inserts have been

complemented by various authors.

In this section a review of research work in the area of different inserts was carried out and based on

this review certain observation were made;

S.N. Sarada et al. [2010] focuses on 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. He have undertaken detailed experimental investigation of 16 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.

Further, Computational fluid dynamics (CFD) techniques were also employed to perform

optimization analysis of the mesh inserts & its experimental investigations on enhancement of

turbulent flow heat transfer with mesh inserts in a horizontal tube under forced convection with air

flowing inside are carried out along with CFD analysis

Deepali Gaikwad et al. [2014] revealed that the twisted wire brush inserts provided significant

enhancement of heat transfer with the corresponding increase in friction factor, however, the pressure

drop also slightly increases & turbulence, swirl flow is generated. Further, detailed experimental

investigation is carried out by horizontal double pipe heat exchanger for plain tube made from straight

copper tube having inner tube and outer tube diameters of 15 and 25 mm and plain tube with twisted

wire brush inserts. The results can be summarized as, the convective heat transfer obtained from the

tube with twisted wire brush inserts is higher than that with the plain tube without twisted wire brush

inserts & also thermal performance of heat transfer devices can be improved by heat transfer

enhancement techniques.

Pravin Kumar Singh et al. [2012] explained the heat transfer in a horizontal circular tube heat

exchanger with air as the working fluid has been increased by means of rectangular inserts & also

explain determination of friction factor and heat transfer coefficient for rectangular insert in both

counter and parallel flow. In rectangular insert results can be summarized as, the heat transfer

coefficient varied from 0.9 to 1.9 times that of the smooth tube value but the corresponding friction

factor increased by 1 to 1.7 times that of the smooth tube value & also it observed that, an increase in

Reynolds number the heat transfer coefficient increased, whereas the friction factor decreased.

Dr. Sane N.K et al. [2014] focuses on the effects of the coiled wire with conical shapes on the heat

transfer and friction characteristics of air flows in tubes, enhance the rate of heat transfer through an

experiment performed on coiled wire of different pitches and conical shapes inserted in a tube &

studied the detailed investigated experimentally the work of two enhancement heat transfer devices

i.e. conical coil inserts of pitch ratio 2.5 mm & 3.5 mm and full length wire coil inserts of ratio 6 mm,

9 mm and 12 mm spring pitches in which air as working fluid is passed in test tube & also the

Reynolds number is varied from 2000 to 10000. The experimental results revel that, the tube fitted

with the conical coil inserts and full length wire coil inserts provides Nusselt number values of around

5% to 12% and enhancement efficiency varies 0.78 to 0.98 compared with the plain tube.

Prof. Shashank S.Choudhari et al. [2013] investigated the heat transfer characteristics and friction

factor of horizontal double pipe heat exchanger having inner and outer diameters of tubes are 17 mm

and 21.4 mm with coil wire inserts made up of different materials in the range of 4000-13000




Reynolds number. Further, they maintained hot water and cold water flow rates are same and in the

range of 0.033 to 0.1 kg/s on tube side and annulus side & also they discuss the different materials i.e.

aluminum, copper, and stainless steel inserts are of pitches 5, 10, and 15 mm respectively. The

experimental results summarized that, Coil wire has significant effect on heat transfer like Copper,

Aluminum and Stainless Steel insert has higher heat transfer enhancement of 1.58, 1.41 and 1.31

times as compared to plane tube & the friction factor found to be increasing with decreasing coil wire

pitch.

S. Naga Sarada et al. [2010] shows the experimental investigations of the augmentation of turbulent

flow heat transfer in a horizontal tube by means of varying width twisted tape inserts with air as the

working fluid in order to reduce excessive pressure drops associated with full width twisted tape

inserts with less corresponding reduction in heat transfer coefficients & to reduced twisted tapes of

widths ranging from 26 (full width), 22, 18, 14 and 10 mm which are lower than the tube inside

diameter of 27.5 mm. Further, the experiments were carried out, for plain tube with or without twisted

tape insert of three different twist ratios 3, 4 and 5 at constant wall heat flux and different mass flow

rates & it varied from 6000 to 13500 Reynolds number. Both heat transfer coefficient and pressure

drop are calculated and the results are compared with those of plain tube, it was found that the

enhancement of heat transfer with twisted tape inserts as compared to plain tube varied from 36 to

48% for full width (26mm) and 33 to 39% for reduced width (22 mm) inserts.

From the published literature, it can be seen that there is a lot of experimental and numerical data

available on the use of various twisted tape, wire coil inserts, swirl chamber etc. However, there is a

deficient of literature available for aerodynamic bead shape in the Turbulent flow regime inside

circular tube. There is a need to gain a better insight in to the nature of Turbulent flows over

protrusion surface. An investigation to see the effects of different array geometries is also needed.

This study is carried out to see whether aerodynamic bead shape can enhance heat transfer and

thermal performance for turbulent airflows in a circular channel for two different array geometries

using Computational fluid dynamics & experimental work is carried out for the geometry which gives

better performance.

II. EXPERIMENTAL SETUP DESCRIPTION

A schematic drawing of the facility used for heat transfer measurements is shown in Fig. The average

heat transfer coefficient on the circular tube was measured for various rates of air flow through the

annular channel. It consists of an open loop flow circuit having of a centrifugal blower unit fitted with

a circular tube, which is connected to the test tube located in horizontal orientation. The test tube of

about 1 to 2 mm thickness is used for experimentation. Rheostat provide through the input of flexi

glass heater which encloses the test section to a whole length. Four thermo-couples at equal distance

from the origin of the heating zone are embedded on the walls of the tube and one thermocouple is

placed in the air stream at the exit of the test section to measure the temperature of flowing air. The

digital device multi meter is used to display the temperature measured by thermocouple at various

position.

A U tube manometer or electronic multi-meter measures the pressure drop across the test section.

Typically, the pipe system consists of a valve, which controls the airflow rate through it and an orifice

meter to find the volume flow rate of air through the system. The two pressure tapings of the orifice

meter are connected to a water U-tube manometer to indicate the pressure difference between them.

Display unit is a digital multi meter used to indicate temperature indicator. Difference in the levels of

manometer fluid represents the variations in the flow rate of air. The velocity of airflow in the tube is

measured with the help of orifice plate and the water manometer fitted on board.




Fig 1- Schematic diagram & photo of the Experimental Set-up

2.1 Experimental Calculations:

The objective of this investigation was to study the heat transfer characteristics using aerodynamic

bead shape at different Reynolds number flow conditions. Hence, the experimental calculation has

been carried out by;

a) Surface Area of Tube: As = πdoL (1)

b) Cross Section Area of Tube: a1 = 𝜋

4di

2 (2)

c) Orifice Area of Tube: a2 = 𝜋

4d2 (3)

d) Average surface temperature of test tube : (4)

Ts =(T1 + T2 + T3 + T4)

4

e) Mean Temperature of tube: (5)

Tb =(Ti + To)

2

f) Mass flow rate of air through Orifice: (6)

𝑄 =

Cda1a2√2ghρa𝜌𝑤

√𝑎12 − 𝑎2

2

g) Change of Enthalpy : Δ H = 𝑚 𝐶𝑝 (𝑇𝑜 − 𝑇𝑖) (7)

h) heat transfer coefficient of fluid (Theoretical): (8)

ℎ =𝑁𝑢 𝑘

𝐷𝑖

i) By energy balance equation heat transfer coefficient of fluid (Practical): (9)

ℎ =𝑚 𝐶𝑝 (𝑇𝑜 − 𝑇𝑖)

𝐴𝑠 (𝑇𝑤 − 𝑇𝑏)

j) Nusselt numbers calculated from the experimental data for plain tube were compared with the

correlation recommended by Dittus-Boelter.

Theoretical Nusselt number, Nuth=0.023 (Re) 0.8 (Pr) 0.4 (10)

k) Blasius equation of Turbulent Flow,𝑓 = 0.316 (𝑅𝑒)-0.25 (11)

l) Log Mean Temperature Difference LMTD, (12)

∆𝑇𝑙𝑚 =(𝑇𝑤 − 𝑇𝑖𝑛) − (𝑇𝑤 − 𝑇𝑜)

𝑙𝑛(𝑇𝑤 − 𝑇𝑖𝑛)(𝑇𝑤 − 𝑇𝑜)

m) In straight pipe lengths, Pressure drop (P) can be calculated using the Darcy Equation f =

Darcy friction factor (13)

𝑓 =64

𝑅𝑒




n) PressureDrop Δ P: (14)

𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝐷𝑟𝑜𝑝 =𝑓𝑙𝜌𝑣2

2𝐷

o) Enhancement Factor: (15)

𝐸𝑛ℎ𝑎𝑛𝑐𝑒𝑚𝑒𝑛𝑡𝐹𝑎𝑐𝑡𝑜𝑟 =𝐸𝑛𝑡ℎ𝑎𝑙𝑝𝑦 𝐶ℎ𝑎𝑛𝑔𝑒 𝑜𝑓 𝑖𝑛𝑠𝑒𝑟𝑡 𝑡𝑢𝑏𝑒

𝐸𝑛𝑡ℎ𝑎𝑙𝑝𝑦 𝐶ℎ𝑎𝑛𝑔𝑒 𝑜𝑓 𝑝𝑙𝑎𝑖𝑛 𝑡𝑢𝑏𝑒

p) Thermal Performance: (16)

𝑇ℎ𝑒𝑟𝑚𝑎𝑙 𝑃𝑒𝑟𝑓𝑜𝑟𝑚𝑎𝑛𝑐𝑒 =

𝑁𝑢𝑁𝑢0

(𝑓𝑓0

)1

3⁄

q) Electrical power supplied to the heater(Qtotal ) (17)

Qtotal = V I

Where, Qtotal was calculated from V input voltage and I input current to the flexible heater.

III. COMPUTATION PROCEDURE OR SIMULATION SCHEME

The computations of the fluid flow field and heat transfer were performed using CFD by Fluent

software version fluent 14.5 & Gambit 2.2.30 was used for the development of the computational

grid. The geometries of the tube and aerodynamic bead shape employed in the computation are

exactly the same as those used in the experiments. The aerodynamic bead shape geometry and grid

independence with fine meshes are generated inside the aerodynamic bead shape geometry and

around the edges of it to resolve key features in the approximate size of the aerofoil shape.

During the computation, the tube wall is set to the constant wall temperature & the temperature of the

main flow inlet is set to be 303 K and the wall temperature is set to be 353 K. Also the velocity field

is assumed to be independent of temperature.

The computational geometry model and mesh suitable for finite volume method is generated by pre-

processor Ansys Fluent 14.5 & Gambit 2.2.30. Unstructured mixed tetrahedral prism mesh &

triangular surface mesh is generated for the fluid domain which allows greater flexibility, time saving

and easy adaptation. A fine cluster of mesh is generated close to the near-wall regions and in the

vicinity of the injection holes.

Fig 2: 3D Geometry model for Cross arrangement in circular pipe.




Fig 3: 3D Geometry model for aligns arrangement in circular pipe.

Fig 4: Meshing Images- Gambit Software Interface

3.1 Analysis of problem:

CFD techniques used to perform the overall performance and optimization analysis of the fluid flow

transfer of the circular tube with or without bead shape insert was performed using ANSYS-Fluent

14.5 version. The problem is modeled as a steady, 3-dimensional heat transfer problem with a uniform

wall temperature. The k-ԑ model is employed for the calculations. This turbulence model represents

the most sophisticated model available for turbulent flow calculations in FLUENT.

Without Aerodynamic Bead Shape: Initially the CFD experiment is carried out with air as the

moving fluid through pipe section without bead shape insert. This also termed as Plain Tube CFD

experiment.

With Aerodynamic Bead Shape: In this type case, the CFD experiment is carried out in two

forms i.e. align and cross arrangement with air as the moving fluid through pipe section with the

bead shape insert.

3.2 Boundary Conditions:

Boundary conditions are applied to the computational model based on the data collected from the

experiment. The boundary conditions were applied to the mesh used for the present study are as

follows:

• Velocity inlet: The velocity was calculated from the Reynolds number based on the Hydraulic

diameter of the annular channel. The calculated velocity from the Reynolds number was applied to the

inlet of the channel. The applied velocity was used to calculate mass flow. The temperature at the inlet

was set at 303 K.

• Pressure outlet: The outlet of the channel was assigned the zero gauge pressure outlet condition

which is the default in Fluent. All other values are extrapolated from the interior of the domain.




• Wall and thermal boundary conditions: The wall of the tube was assigned constant temperature

boundary condition. A temperature, of 353 K was assigned to this wall to indicate heating at the wall

of the test surface. A no slip boundary condition was assigned to all walls that are the velocity of the

flow at the wall is zero.

Fig 5: Photo of Boundary Condition

3.3 Solution Methods and Controls:

In this step of Fluent, different solution discretization methods i.e. Pressure velocity coupling and

discretization scheme and controls for residual and surface integrals monitors and under relaxation

factors can be set. The solution was then initialized with all values computed from the inlet face &

then calculated until the surface monitors and the residuals flattened out to the set level of accuracy.

IV. RESULTS AND DISCUSSIONS

In order to enhance the heat transfer rates and increase the system efficiency, aerodynamic bead shape

geometry inside the tube have been developed and many experimental investigations have been

conducted to determine their thermodynamic characteristics.

For all the parameters & properties values we have considered in the performance as well as

calculation of experiment and computational methods which are done for the different Reynolds

number in the range of 19000 to 68000, these parameters & its value with its Reynolds numbers are

given in the table:

Table 4.1: Parameters & Properties values table:

Parameter Unit Reynolds Number

19709.59 39419.18 51244.94 67012.61

Inlet temp deg.C 30 30 30 30

Tw deg.C 70 70 70 70

di (inner) m 0.019 0.019 0.019 0.019

do (outer) m 0.022 0.022 0.022 0.022

Length m 1 1 1 1

Cs area m2 0.000284 0.000284 0.000284 0.000284

Surface area m2 0.069115 0.069115 0.069115 0.069115

Velocity m/s 15.056 30.112 39.14559 51.19039

mass kg/s 0.005 0.01 0.013 0.017

density air kg/m3 1.171287 1.171287 1.171287 1.171287

Cp J/kgK 1005 1005 1005 1005




k W/mK 0.0242 0.0242 0.0242 0.0242

viscosity Pa.s 0.000017 0.000017 0.000017 0.000017

Pr 0.705992 0.705992 0.705992 0.705992

Nu 54.5745 95.01972 117.211 145.269

For Plain Tube are validated with theoretical relations are given in;

Table 4.2: Plain Tube Theoretical Calculations table;

Case

No. mf V Re Pr Nuth hth Tanlyt ΔHth Δ P

1 0.005 15.056 19709.59 0.706 54.57 69.51 54.62 123.74 139.74

2 0.01 30.112 39419.18 0.706 95.02 121.02 52.59 227.11 558.97

3 0.013 39.146 51244.94 0.706 117.21 149.28 51.84 285.36 944.67

4 0.017 51.190 67012.60 0.706 145.27 185.02 51.07 360.10 1615.42

For comparisons of Experimental Calculations of Plain tube & Cross arrangement of Aerodynamic

Bead Shape in the tube are tabulated below:

Table 4.3: Comparison of Experimental Calculations for Cross arrangement Aerodynamic Bead Shape & Plain

tube:

Re To ΔH h Δ P f

Plain Cross Plain Cross Plain Cross Plain Cross Plain Cross

19709.59 53.2 55.5 116.58 128.1 59.39 68.04 98.1 245.25 0.014 0.0351

39419.18 51.0 53.0 211.05 231.2 103.5 117.35 117.5 343.35 0.0042 0.0123

51244.94 50.0 51.81 261.30 284.9 126.0 141.70 206.0 588.60 0.0044 0.0125

67012.60 49.2 50.12 328.03 344.6 156.1 166.67 196.2 716.13 0.0024 0.0089

For comparisons of Computational Calculations of Plain tube & Cross or Align arrangement of

Aerodynamic Bead Shape in the tube are tabulated below:

Table 4.4: Comparison of Computational (Temperature based) Calculations for Cross & Align arrangement of

Aerodynamic Bead Shape & Plain tube:

Re To ΔH h

Plain Align Cross Plain Align Cross Plain Align Cross

19709.59 52.24 56.78 54.16 111.76 134.57 121.40 55.99 73.17 62.91

39419.18 49.87 52.74 51.20 199.69 228.54 213.06 96.10 115.49 104.85

51244.94 49.04 51.68 49.81 248.76 283.25 258.76 118.08 140.54 124.39

67012.60 48.27 50.44 48.85 312.14 349.22 322.06 146.32 169.67 152.40

Table 4.5: Comparison of Computational (Pressure based) Calculations for Cross & Align arrangement of

Aerodynamic Bead Shape & Plain tube:

Re ΔP f

Plain Cross Plain Cross

19709.59 253.98 283.842 0.0363 0.0406

39419.18 903.622 957.015 0.0323 0.0342

51244.94 1467.41 1543.88 0.0311 0.0327

67012.60 2413.76 2524.20 0.0299 0.0313

For the performance calculations of Heat transfer Enhancement in Experimental as well as

Computational methods are tabulated below:

Table 4.6: Enhancement Efficiency Experimental calculations for Cross arrangement Aerodynamic Bead

Shape:

Case

No. mf Re Nu / Nuo (f / fo) (f / fo)1/3

TPF or Overall

Enhancement Ratio

1 0.005 19709.59 1.146 2.507 1.358 1.560

2 0.01 39419.18 1.133 2.928 1.431 1.621

3 0.013 51244.94 1.124 2.840 1.416 1.591




4 0.017 67012.60 1.070 3.708 1.548 1.656

Table 4.7: Enhancement Efficiency of Computational calculations for Cross arrangement Aerodynamic Bead

Shape with Plain tube is:

Case

No. mf Re Nu / Nuo (f / fo) (f / fo)1/3

TPF or Overall

Enhancement Ratio

1 0.005 19709.59 1.124 1.059 1.019 1.146

2 0.01 39419.18 1.091 1.118 1.038 1.132

3 0.013 51244.94 1.053 1.052 1.017 1.071

4 0.017 67012.60 1.042 1.046 1.015 1.060

The Experimental & Computational Graphical representation of Nusselt number, Heat transfer

coefficient, Pressure drop and Friction Factor obtained for the aerodynamic bead shape tube compared

with the Nusselt number, Heat transfer coefficient, Pressure drop and Friction Factor for the Plain

tube.

Graph 4.1 shows that Comparison between Variation of Nusselt Number with Reynolds number in all

cases

Graph 4.2 shows that Comparison between Variations of heat transfer coefficient with Reynolds number.

40

60

80

100

120

140

160

0 10000 20000 30000 40000 50000 60000 70000 80000

Nu No.

Re No

Nu No. Vs Re No.

Plain expt

Plain theo

Cross expt

cfd plain

cfd cross

cfd align

20

40

60

80

100

120

140

160

180

200

0 10000 20000 30000 40000 50000 60000 70000 80000

h

Re No

h Vs Re No

h theo plain

h expt plain

h pract cross

h plain cfd

h cross cfd

h align cfd




Graph 4.3 shows that Comparison between the Friction Factor ratios Vs Reynolds Number of CFD values of

plain & cross arrangement insert tube.

Graph 4.4 shows that Comparison between the Overall enhancement ratios Vs Reynolds Number of CFD

values.

Graph 4.5 shows that Comparison between the Pressure Drop Vs Reynolds Number.

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0 10000 20000 30000 40000 50000 60000 70000 80000

f

Re No

Friction factor vs Re No

plain expt

cross expt

plain cfd

cross cfd

plain theo.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 10000 20000 30000 40000 50000 60000 70000 80000

Tpf

Re No

TPF Vs Re No

20

520

1020

1520

2020

2520

0 10000 20000 30000 40000 50000 60000 70000 80000

PD

Re No.

Pressure drop Vs Re No.

Plain Expt

Cross Expt

PD Plain CFD

PD Cross CFD

Plain Theo.




Graph 4.6 shows that Comparison between the Enhancement Factor Vs Re No.

Flow Simulation of Enhancement of heat transfer in tube with different varying Reynolds numbers

such as Case 1 = 19709.59, Case 2 = 39419.18, Case 3 = 51244.94, and Case 4 = 67012.60.

The Pressure contour, velocity contour and static temperature contours for the plain tube, inline

arrangement aerofoil geometry & cross arrangement aerofoil geometry for Reynolds number 19000

and 68000 are shown in above counters Figures.

4.1 Counters of Static Pressure:

Case 1: For Plain tube, Align arrangement aerofoil inserts & Cross arrangement aerofoil insert

at Mass flow rate: 0.005 kg/s

Fig 4.1.1 Fig 4.1.2 Fig 4.1.3

Fig 4.1.1, 4.1.2 and 4.1.3 show that the Static Pressure variations for the plain tube configuration and on align

& cross arrangements aerofoil inserts configuration.

Case 2: For Plain tube, Align arrangement aerofoil inserts & Cross arrangement aerofoil insert at Mass flow rate: 0.001 kg/s

1

1.1

1.2

1.3

0 10000 20000 30000 40000 50000 60000 70000 80000

Enhancement factor

Re No.

Enhancement Factor Vs Re No.

Cfd Cross

Expt. cross

Cfd Align




Fig 4.1.4 Fig 4.1.5 Fig 4.1.6

Fig 4.1.4, 4.1.5 and 4.1.6 show that the Static Pressure variations having pitch 100mm for the plain tube

configuration and on align & cross arrangements aerofoil inserts configuration.

Case 3: For Plain tube, Align arrangement aerofoil inserts & Cross arrangement

aerofoil insert at Mass flow rate: 0.013 kg/s

Fig 4.1.7 Fig 4.1.8 Fig 4.1.9

Fig 4.1.7, 4.1.8 and 4.1.9 show that the Static Pressure variations for the plain tube configuration and on align

& cross arrangements aerofoil inserts configuration.

Case 4: For Plain tube, Align arrangement aerofoil inserts & Cross arrangement aerofoil insert at

Mass flow rate: 0.017 kg/s

Fig 4.1.10 Fig 4.1.11 Fig 4.1.12

4.2 Counters of Static Temperature:



Fig 4.2.1 Fig 4.2.2 Fig 4.2.3

Fig 4.2.1, 4.2.2 and 4.2.3 show that the Static Temperature variations for the plain tube configuration and on

align & cross arrangements aerofoil inserts configuration.






Fig 4.2.4 Fig 4.2.5 Fig 4.2.6

Fig 4.2.4, 4.2.5 and 4.2.6 show that the Static Temperature variations having pitch 100mm for the plain tube

configuration and on align & cross arrangements aerofoil inserts configuration.



Fig 4.2.7 Fig 4.2.8 Fig 4.2.9





Fig 4.2.10 Fig 4.2.11 Fig 4.2.12






V. CONCLUSIONS AND SUMMARY

This study focused on investigating whether the use of cross arrangement aerofoil inserts can enhance

heat transfer characteristics for a annular channel were tested for four different Reynolds numbers

ranging from 19000 to 68000 with experimentally and computationally .

1) Results revealed that; average Nusselt Numbers and friction factors are considerably more with

both arrangements i.e. cross and align of aerodynamic bead shape geometry inserts when

compared to plain tube.

2) Improvement of average Nusselt Numbers for tube with 5 to 20 % for cross arrangement of

aerofoil insert & 16 to 35 % for align arrangement of aerofoil insert for four different Reynolds

numbers ranging from 19000 to 68000 with respect to Plain Tube.

3) The thermal performance factors were plotted for both the cross arrangement & align arrangement

aerofoil geometries. The thermal performance values decreased with increasing Reynolds number

values. The Cross arrangement & Align arrangement of aerodynamic bead shape geometries

proved to give a better thermal performance than the plain tube. Also align arrangement of

aerodynamic bead shape is gives higher thermal performance as compares to cross arrangement in

the cost of pressure drop.

4) The pressure drop is considerably more with aerodynamic bead shape geometry with compared to

plain tube; but cross arrangement of aerodynamic bead shape geometry gives minimize the

pressure drop as compared to align arrangement of aerodynamic bead shape.

5) Similarly friction factor for plain tube is lower than aerodynamic bead shape geometry inserts in

the tube. But results reveal that, if Reynolds number increases friction factor is decreasing.

6) Average Enhancement efficiency ɳ=h/h0 is varied approximately in between 1 to 2 times with

experimentally or computationally for four different Reynolds numbers ranging from 19000 to

68000 in cross arrangement as well as align arrangement of aerodynamic bead shape tube as

compare with plain tube.

7) Variations in experimental, computationally and theoretical values are because of manufacturing

and measuring errors.

8) The numerical computation provides reasonably good accuracy in predicting the heat transfer

enhancement capability of the cross and aligns arrangements compared to the plain tube, which is

essential to the validation of the computation model since heat transfer prediction is the most

important consideration in the heat exchanger device.

9) The secondary vortices generated because of the aerodynamic bead shape is also help in

enhancing convective heat transfer coefficient as the vortices help in mixing the hot and cold

fluids. Thus, the aerodynamic bead shape on the tube found to enhance heat transfer over a plane

tube for turbulent airflows.

VI. FUTURE SCOPE

CFD simulation is ongoing process of research that the present status of the system can be changed by

having certain modification, improvement, innovation etc & it can be work with different geometries

inserts as well as different Reynolds number & also can carry out the experimental studies to validate

the present results.

In the present work the geometrical changes are made configuration of aerodynamic shape

arrangement. For giving the maximum heat transfer enhancement with minimum pressure drop

penalty it can be work with different test tube material.

Whereas the aerodynamic shape present in the tube are of uniform pitch and change the pitch ratio.

One can change the pitch ratio and elongated length of aerofoil shape to understand the behavior and

influence of variations of aerodynamic shape geometries present on the circular tube.

Further work, part of this work will be by making efficient analysis of heat performance parameters,

one can develop a correlation for the critical Reynolds number will derive for the circular tube with

align and cross arrangement of aerodynamic bead shape geometry. Also, friction factor f and Nusselt

number Nu correlations will be derive with respect to the Reynolds number and geometric parameters.




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BIOGRAPHIES

Rohit R. Jadhao received the B.E. degree in Mechanical Engineering from Prof. Ram

Meghe Institute of Technology & Research, Badnera-Amravati in the year 2010. Currently

pursuing M.E (Heat Power) at Dr. D. Y. Patil School of Engineering Academy.




Shylesha Channapattana Received M.E in Mechanical Engineering (Heat Power) in 2005.

Currently pursuing Ph.D & having Administrative experience as Head of Section (Ibra

College of Technology, Oman). Five year teaching experience in abroad.

Swapnil S. Kulkarni, Director, Able Technologies India Pvt. Ltd., Pune. The Company

offers Engineering Services and Manufacturing Solutions to Automotive OEM’s and Tier I

and Tier II Companies. He is a Graduate in Industrial Engineering with PG in Operations

Management. With around 20 years of working experience in the domain of R&D, Product

Design and Tool Engineering, he has executed projects in the Automotive, Medical and

Lighting Industry. His area of interest is Research and Development in the Engineering

Industry as well as the emerging sector of Renewable Energy

evaluating aerodynamic bead shape in a heat exchanger … · enhancement of heat transfer with...

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