ABSTRACT bubbles of five different diameters at constant temperature

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.

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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.