ABSTRACT

For

the optimization of energy, the devices used in industries and household

application must be design very carefully. The enhancement in the heat transfer

is the major factor in design of heat exchanger. Helical coil heat exchanger is

used in power plant, automobiles, food industries and aerospace due to

advantages such as large heat transfer area, high heat transfer capabilities

and compact structure. In present study the simulation has been performed on

horizontal shell and coil heat exchanger injecting air bubbles of five

different diameters at constant temperature inlet. If air inject into a liquid

fluid, many ambulant air bubbles are formed inside the fluid. Due to buoyancy

force air bubbles move inside the liquid fluid. The mobility of these air bubbles

makes turbulence inside the fluid. The ANSYS FLUENT 14.5 has been used for

numerical analysis using multiphase- Eulerian and energy. The k-? standard

turbulent model has been used. The graph has been plotted for Nusselt number,

NTU, effectiveness and overall heat transfer for different diameter of air

bubbles. It has been observed that the 0.1mm diameter of air bubbles has best

heat transfer.

Keyword:

shell and coil heat exchanger, air bubbles injection, NTU, Nusselt number,

effectiveness, heat transfer coefficient, CFD.

3.1.

JUSTIFICATION OF

PRESENT WORK

Khorasani

et.al.(2017): in their work on titled “Effect of

air bubble injection on the performance of a horizontal helical shell and

coiled tube heat exchanger: an experimental study” performed air bubbles

injection with different air flow rates (1 l/min – 5 l/min) on a horizontal

helical shell and coiled heat exchanger and got results:

(i)

NTU Vs air flow rate.

(ii)

NTU Vs effectiveness.

The

authors performed an experimental work on shell and helical coil heat exchanger

at 0.3 mm diameter of bubbles.

From the above

works it can be observed that further research as follows can be taken up:

(i)

Above work shows an experimental study & the

current work is based on a simulation study.

(ii)

In the present work the diameter of air bubbles

is varied from 0.05mm, 0.1mm, 0.3mm, 0.5mm and 0.7mm.

(iii)

Similar graph will be drawn for different air

flow rate (1 l/mm – 5 l/mm) and comparison will be done with experimental data.

(iv)

Validation of experimental result will be done

by simulation and changes will be represented.

3.2 OBJECTIVE

The main objectives of the dissertation are as follows:

The

design of a helical coil tube in tube heat exchanger has been facing problems

because of the lack of experimental data available regarding the behavior of

the fluid in helical coils and also in case of the required data for heat

transfer, unlike the shell and helical

coil heat exchanger. So to the best of

our effort, numerical analysis on ANSYS software was carried out:

1.

To develop model of horizontal

shell and helical coiled tube heat exchanger, injecting air bubbles in shell

side.

2.

Validation will be carried on CFD model with comparison of previous

experimental model.

3.

To improve effectiveness and

NTU of model.

3.3CONCLUSION

The present study propose to investigate effect of different diameter of

air bubbles (0.05mm, 0.1mm, 0.3mm, 0.5mm and 0.7mm) in shell and helical coil heat

exchanger and improve the NTU and effectiveness.

5.4

CALCULATION AN ANALYSIS OF NUSSLTE NUMBER

The value of Nusselt number calculate with the help

of equation no. 5.6

Nu = =

(5.6)

Where k = thermal conductive

h= coefficient

of convective heat transfer

from above calculation of Nusselt number from

equation (5.6), NTU from equation (5.5) and overall heat transfer from equation

(5.4) is calculated and shown in Table 5.2.

Table

5.2: NTU, effectiveness and Nusselt

number

Diameter of air

bubbles (mm)

NTU

Effectiveness

Nusselt number

Overall heat

transfer

0.05

1.215492

0.68645

21.8858

1180.15

0.1

1.312881

0.714575

23.8743

1274.71

0.3

1.307064

0.710505

24.3037

1269.06

0.5

1.30596

0.70455

24.4434

1267.99

0.7

1.263182

0.70415

25.2778

1226.46

5.5 Discussion

There

are many parameters, which are taken into account while performing current

analysis. After the analysis, result has been generated within 500 iterations

by ANSYS fluent software. Result show that as air bubbles diameter increases Nusselt

number increases subsequently. But NTU and effectiveness decreases with

increasing diameter.

·

From the above analysis

it has been observed that increasing the air bubbles diameter Nusselt number

increase.

·

As per Figure 5.27 it

has been observed that 0.1mm diameter of air bubbles have maximum effectiveness.

·

As per figure 5.28: it

has been observed that 0.1 mm diameter of air bubbles have maximum NTU.

·

From this analysis it

is concluded that 0.1 mm diameter of air bubbles best for using, because it

give maximum heat transfer.

CHAPTER

VI

CONCLUSION

In

this analysis, the effect of air bubbles diameter on the effectiveness, NTU and

Nusselt number of shell and helical coil heat exchanger has been investigated

using CFD analysis. Based on the results, obtained by the CFD and mathematical

calculations it is found that;

·

The percentage

variation observed between experimental result and simulation result is 2.15 –

4.15%.

·

From the above analysis

it has been observed that at 0.05, 0.1, 0.3, 0.5and 0.7 mm diameter of air bubbles

Nusselt number increase.

·

From Fig 5.29 it has

been observed that NTU at 0.05mm to 0.1 mm increase and then it decrease.

·

Fig 5.29 it is

concluded that 0.1 mm diameter of air bubbles is better than 0.3mm 0.7mm.

CHAPTER VII

FUTURE

SCOPE

Optimum

utilization of energy the equipment’s used in industries, household and

commercials must be efficient. By using helically coiled heat exchanger

injecting air bubbles at optimum diameter, heat transfer from the system can be

increased to a great extent. The works that can be done in future are as

following: –

·

Use Nano fluids flow

inside shell and helical coil heat exchanger besides water so that performance

of the heat exchanger can be compared and enhanced.

·

To improve air inlet

geometry like use air flow inside helical coil or whole shell of the shell.

·

Use different material

of coil and shell for analysis.

·

It can be seen clearly

from results that as diameter of air bubbles increasing effectiveness and NTU

increase rapidly. Therefore, it can be suggested that more work can be done in

the field of increasing the air bubbles diameter up to certain limit to find

the optimum value.

·

Analysis can be

performed by varying mass flow rate of helical coil.

·

Use different heat

exchanger for analysis air bubble injection.