heat transfer characteristics of shell and tube heat exchanger

Heat Transfer Characteristics of Shell and Tube Heat Exchanger

07/06/2011

1

Presented By;

Sandeep.S.Thomas

S2 M-Tech

Thermal science

Guided By;

Dr.S.Anil Lal

Dept of Mechanical Engg.

CET

Department of Mechanical Engineering,CET

Objective

Department of Mechanical Engineering,CET2

To determine the heat transfer characteristics of shell and tube heat exchanger in two cases. First case is numerical and experimental analysis by using different tube inserts in tube side of a shell and tube exchanger. Different tube inserts include longitudinal strip inserts (both with and without holes) and twisted-tape inserts with three different twisted angles (15.3, 24.4 and 34.3). Second case is the analysis of heat transfer characteristics of Al2O3/water and TiO2/water nanofluids in a shell and tube heat exchanger. The effects of Peclet number, volume concentration of suspended nanoparticles, and particle type on the heat characteristics were investigated

Shell and Tube Heat Exchanger

This heat exchanger consists of a shell (a large pressure vessel)

with a bundle of tubes inside it. One fluid runs through the tubes,

and another fluid flows over the tubes (through the shell) totransfer

heat between the two fluids

Applications

Oil refineries

Power plants

Chemical processes

Higher-pressure application

Experimental setup

Different strip inserts

•

Equations

Results and Discussion

Velocity distribution for different tube inserts

The boundary layer is repeatedly interrupted by the holes on the longitudinal strip inserts and this causes the flow to re-mix near the holes

Velocity distribution for different tube inserts

The flow for the twisted-tape inserts is accelerated to a value up to 40% higher than the inlet frontal velocity due to the distortion of the flow field

Pressure distribution for different tube inserts

The pressure drop for the inserts with angle 34.3 (type C) is 60% and 109%, higher than that for the inserts with angle 24.4 (type B) and angle 15.3 (type A) respectively.

Pressure drop per unit length vs. Re for different types of tube inserts

The pressure drop for longitudinal strip inserts with holes was 100–120%higher than that of plain tubes and that of longitudinal strip inserts without holes 25–60% higher. The highest-pressure drop occurred when the twisted-tape inserts with a twist angle of 34.3 (type C) was used.

Nusselt number vs. Re for different types of tube inserts.

The heat transfer performance of the twisted tape tube inserts (type C) is the best one among all test samples in this study

Colburn and friction factor for different types of tube inserts.

Corelations

Experimental setup with nanofluids.

Two series of nanofluids were prepared using two types of nanoparticles,Alumina (Al2O3) and Titanium dioxide (TiO2) with mean diameters of 25 and 10 nm, respectively, while water used as base fluid

.

Overall heat transfer coefficient versus Pecletnumber for base fluid water

Overall heat transfer coefficient of nanofluid versus Pecletnumber for various volume concentrations.

The overall heat transfer coefficient of nanofluids increases significantly with Peclet number.

For both nanofluids the overall heat transfer coefficient at a constant Peclet number increases with

nanoparticle concentration compared to the base fluid .

Optimum volume concentration of Al2O3 and TiO2 particles in water are 0.5 and 0.3 vol.%

respectively.

Convective heat transfer coefficient of nanofluid versus Pecletnumber for different volume concentrations

Enhancement of h with Pe. is due to increasing of the fluid thermal conductivity and decreasing ofthermal boundary layer thickness. Thermal conductivity of the nanofluids increases with increasing of the volume concentrations upto an optimum. At concentrations higher than the optimum,nanofluid h enhancement rate is less with nanoparticle volume concentration due to the effect of high viscosity and thickening of thermal boundary layer. •

Nusselt number of nanofluid versus Peclet number fordifferent volume concentrations

Nu increases with Pe because the enhancement of h of both nanofluids is much higher than that of

thermal conductivity. The enhancement of the Nusselt number for both nanofluids is particularly

significant at their optimum nanoparticle concentrations

At lower volume concentrations (<0.3 vol.%) TiO2 nanoparticle possesses better heat

transfer behavior than Al2O3 nanoparticle and at higher volume concentrations (>0.3

vol.%) Al2O3 nanoparticle is more effective than TiO2 nanoparticle.

.

Conclusion

• Heat transfer performance enhances with the use of inserts.• The heat transfer coefficient and the pressure drop using longitudinal strip

inserts with holes are 13–28% and 140–220% higher than those of plain tubes.

• The heat transfer coefficient and the pressure drop of the tubes with twisted-tape inserts are 13–61% and 150–370%, respectively higher than those of plain tubes.

• The heat transfer performance is the best for twisted inserts with the increased twist angle (type C) followed by type B ,type A, longitudinal strip inserts with holes and longitudinal strip inserts without holes.

Pressure drop and Nu increases with increase in Re number Friction factors decrease with in increase in Re number

Conclusion

• The experimental results for both nanofluids indicate that the heat transfer characteristics of nanofluids in shell and tube heat exchanger improve with Peclet number significantly.

• Addition of nanoparticles to the base fluid enhances the heat transfer

performance and results in larger overall and convective heat transfer coefficient and Nusselt number than that of the base fluid at the same Peclet number.

• Both nanofluids have different optimum volume concentration in which the heat transfer characteristics show the maximum enhancement. Optimum volume concentration of Al2O3 and TiO2 particles in water are 0.5 and 0.3 vol.% respectively

At concentrations higher than the optimum,convective heat transfer coefficient

of nanofluid enhancement rate is less.

The nanoparticle with less mean diameter (TiO2 nanoparticle) has a lower optimum volume concentration than Al2O3.

References

[1]B. Farajollahi, S.Gh. Etemad , M. Hojjat, Heat transfer of nanofluids in a shell and tube heat exchanger. International Journal of Heat and Mass Transfer 53 (2010) 12–17

[2] Yu-Wei Chiu, Jiin-Yuh Jang,3D numerical and experimental analysis for thermal–hydraulic characteristics of air flow inside a circular tube with different tube inserts, Applied Thermal Engineering 29 (2009) 250–258

[3] Simin Wang, Jian Wen, Yanzhong Li, An experimental investigation of heat transfer enhancement for a shell-and-tube heat exchanger, Applied Thermal Engineering 29 (2009) 2433–2438

[4]Sepehr Sanaye, Hassan Hajabdollahi, Multi-objective optimization of shell and tube heat exchangers, Applied Thermal Engineering 30 (2010) 1937-1945
