*5.1.1 Velocity field analysis*

The flow structure in the pipe is characterized by analyzing the velocity field and the pressure distribution in the flow domain. In the current work, there are four different geometrical configurations including plane pipe flow and another three cases with single, triple, and quintuple twisted tape inserts inside the pipe. CFD is a powerful tool to provide flow visualization and assist in the analysis of the flow field structure. Fields of velocity, predicted by computational simulation, in case of water flowing are depicted in **Figure 7**. The velocity contours shown are taken for

Re = 5000 and at different axial locations in the fully developed region. As can be seen in **Figure 7**, frame ii, the velocity is increasing by 50.0% for STT higher than PT. This happens due to secondary flow caused by twisted tape geometry, which increases mean velocity by changing flow type from linear motion to swirl motion and also due to reduction in hydraulic diameter which leads to increase in velocity at constant Reynolds number and the reduction in hydraulic diameter causing a decrease in flow cross sectional area, which resulted in an increment in mean velocity value to satisfy equation of continuity (the rate of mass enters a system is equal to the rate of mass leaves the system).

For TTT and QTT, the velocity increased by 13.3 and 27.4% higher than STT due to narrowing the flow passages. Swirl motion and turbulence fluctuation are also increasing by increases in tape number due to multi-passage flow interactions. In addition, the tapes are breaking the flow field uniformity, and mix fluid flow layers between near wall region and core region lead to the appearance of many regions of high velocity; high velocity region in plain tube appears only at the core of it, which increases as the number of twisted tape increases, and that fission leads to increase in average velocity of fluid flow.

flow and with nanofluid flow. The pressure drop in TTT and QTT is 31.2 and 64.5% higher than STT, respectively. This is due to swirl motion achieved by each one of them, where the secondary motion generated by twisted tapes have an effect on velocity proportionally, where velocity gradient effect on shear forces acting on

*Pressure contours for a longitudinal revolution surface along the computational domains of water flow;*

*Applications of Compound Nanotechnology and Twisted Inserts for Enhanced Heat Transfer*

Pressure drop increases slightly by using nanofluid at 0.1 vol.% TiO2. The numerical results show a percentage difference between water and nanofluid up to 3% for the same model investigated. However, experimental results for pressure agree well with those calculated numerically with a maximum divergence of 6.8%. It is obvious, from **Figure 10**, that pressure drop of water and for nanofluid increases with increasing Reynolds number. The small increase in pressure drop of nanofluid than water illustrates that using nanofluids with higher particle volume

The friction factor is influenced by velocity variation, pressure drop, and contact surface topologies with the fluid flow. The models were examined numerically and

The experimental results of the friction factor are reasonably matching with the results obtained from correlations 12 and 13 for the plain tube with water flow with

*Simulation results of pressure drop obtained from water (w) and 0.1 vol.% TiO2/water nanofluid (nf) for*

experimentally in Reynolds number range varying from 5000 to 20,000.

fluid flow causes pressure drop.

*(a) STT, (b) TTT, and (c) QTT.*

*DOI: http://dx.doi.org/10.5772/intechopen.93359*

*5.1.3 Friction factor*

**Figure 10.**

**37**

*different inserts at various Reynolds numbers.*

**Figure 9.**

fraction may cause small penalty in pressure drop.

Longitudinal vortices in flow fields are shown in **Figure 8**; it was found that the number of vortices generated in the flow equals the number of twisted tapes and formed around it.

Apparently, the velocities of the nanofluid are nearly the same as those of water under the considerable nanoparticle volume fraction, which discloses that nanofluid will not require an added disadvantage over pumping power.

### *5.1.2 Analysis of pressure field and pressure drop*

As a fluid flows through the tube, there will be a pressure drop due to the shear drag at the contact wall in addition to the pressure required to pump the fluid inside the tube which is in tube with inserts higher than those without. The main determinants of pressure drop are fluid viscosity and fluid velocity. Pressure contours are illustrated in **Figure 9** for the computational domains considered at Reynolds number 5000 for water flow and on longitudinal revolution surface along the axial direction.

In the case of STT, **Figure 9**, frame a, pressure drop is 98.7% higher than in PT due to the fact that twisted tape insert increases frictional shear forces within the surface area of the inserts.

**Figure 10** presents the predicted pressure drop for all simulated cases including pure tube and tube with single, triple, and quintuple twisted tape inserts with water

**Figure 8.**

*Longitudinal water vortices for tube fitted with; (a) single twisted tape, (b) triple twisted tapes, and (c) quintuple twisted tapes.*

*Applications of Compound Nanotechnology and Twisted Inserts for Enhanced Heat Transfer DOI: http://dx.doi.org/10.5772/intechopen.93359*

#### **Figure 9.**

Re = 5000 and at different axial locations in the fully developed region. As can be seen in **Figure 7**, frame ii, the velocity is increasing by 50.0% for STT higher than PT. This happens due to secondary flow caused by twisted tape geometry, which increases mean velocity by changing flow type from linear motion to swirl motion and also due to reduction in hydraulic diameter which leads to increase in velocity at constant Reynolds number and the reduction in hydraulic diameter causing a decrease in flow cross sectional area, which resulted in an increment in mean velocity value to satisfy equation of continuity (the rate of mass enters a system is

For TTT and QTT, the velocity increased by 13.3 and 27.4% higher than STT due to narrowing the flow passages. Swirl motion and turbulence fluctuation are also increasing by increases in tape number due to multi-passage flow interactions. In addition, the tapes are breaking the flow field uniformity, and mix fluid flow layers between near wall region and core region lead to the appearance of many regions of high velocity; high velocity region in plain tube appears only at the core of it, which increases as the number of twisted tape increases, and that fission leads to increase

Longitudinal vortices in flow fields are shown in **Figure 8**; it was found that the number of vortices generated in the flow equals the number of twisted tapes and

Apparently, the velocities of the nanofluid are nearly the same as those of water under the considerable nanoparticle volume fraction, which discloses that nanofluid

As a fluid flows through the tube, there will be a pressure drop due to the shear drag at the contact wall in addition to the pressure required to pump the fluid inside the tube which is in tube with inserts higher than those without. The main determinants of pressure drop are fluid viscosity and fluid velocity. Pressure contours are illustrated in **Figure 9** for the computational domains considered at Reynolds number 5000 for water flow and on longitudinal revolution surface along the axial

In the case of STT, **Figure 9**, frame a, pressure drop is 98.7% higher than in PT due to the fact that twisted tape insert increases frictional shear forces within the

**Figure 10** presents the predicted pressure drop for all simulated cases including pure tube and tube with single, triple, and quintuple twisted tape inserts with water

*Longitudinal water vortices for tube fitted with; (a) single twisted tape, (b) triple twisted tapes, and*

will not require an added disadvantage over pumping power.

*5.1.2 Analysis of pressure field and pressure drop*

equal to the rate of mass leaves the system).

*Inverse Heat Conduction and Heat Exchangers*

in average velocity of fluid flow.

formed around it.

direction.

**Figure 8.**

**36**

*(c) quintuple twisted tapes.*

surface area of the inserts.

*Pressure contours for a longitudinal revolution surface along the computational domains of water flow; (a) STT, (b) TTT, and (c) QTT.*

flow and with nanofluid flow. The pressure drop in TTT and QTT is 31.2 and 64.5% higher than STT, respectively. This is due to swirl motion achieved by each one of them, where the secondary motion generated by twisted tapes have an effect on velocity proportionally, where velocity gradient effect on shear forces acting on fluid flow causes pressure drop.

Pressure drop increases slightly by using nanofluid at 0.1 vol.% TiO2. The numerical results show a percentage difference between water and nanofluid up to 3% for the same model investigated. However, experimental results for pressure agree well with those calculated numerically with a maximum divergence of 6.8%. It is obvious, from **Figure 10**, that pressure drop of water and for nanofluid increases with increasing Reynolds number. The small increase in pressure drop of nanofluid than water illustrates that using nanofluids with higher particle volume fraction may cause small penalty in pressure drop.

#### *5.1.3 Friction factor*

The friction factor is influenced by velocity variation, pressure drop, and contact surface topologies with the fluid flow. The models were examined numerically and experimentally in Reynolds number range varying from 5000 to 20,000.

The experimental results of the friction factor are reasonably matching with the results obtained from correlations 12 and 13 for the plain tube with water flow with

#### **Figure 10.**

*Simulation results of pressure drop obtained from water (w) and 0.1 vol.% TiO2/water nanofluid (nf) for different inserts at various Reynolds numbers.*

a maximum deviation of 4.1%. Further verification was carried out by comparing the experimental results of the friction factor of single TT insert in the tube with water flow by comparison with the results gained by a correlation developed by Bergles, as in Eq. (15). The maximum deviation was 3.0%. The verification results are shown in **Figure 11**.

Measured friction factors coincide well with the calculated values from correlations of validation. As the fluid velocity increases, the friction factor decreases. Therefore, friction factor decreases with Reynolds number increasing. This is because Reynolds number increases the momentum, overcomes the viscous force of the fluid, and consequently lowers the shear between the fluid and the tube wall.

Reference [16] developed a correlation for the friction factor prediction for nanofluid flow in a plain tube, shown as Eq. (14). Comparison between the predicted results by Eq. (14) and the experimental results in the current investigations are shown in **Figure 12**. Good match between the experimental and empirical

values has been achieved. Within the tested range of 5000–20,000 Re, the correlation shows overprediction of around 2.0–3.0% in the friction factor values com-

*Experimental measurement results for the friction factor verses Reynolds number for plain tube and tubes with single, triple, and quintuple twisted tape inserts of flow cases of water flow and 0.1 vol.% TiO2/water nanofluid*

*Applications of Compound Nanotechnology and Twisted Inserts for Enhanced Heat Transfer*

The variations of the friction factor with Reynolds number for the tubes with different twisted tape inserts, with flows of water and nanofluid, are compared in **Figure 13**. The friction factors of the nanofluids are slightly higher than those of the base liquid. The tube fitted with plain twisted tape inserts (STT) when water flow has friction factor of 6.6–8.7% higher than plain tube. This is attributed to the flow blockage and swirl flow due to tape insert; for the same case, friction factor

The additional dissipation of pressure of the fluid caused by the fluid disturbance due to increase of tape number results in an increase in pressure drop, which causes increase of friction factor. As the number of inserts increases, the pressure drop significantly increases. For water flow, the friction factors of TTT and QTT are 12.2–17.74% and 18.428–24.65% higher than that in plain tube. For nanofluid flow, the friction factors of TTT are 13.3–18.4% and for QTT are 19.6–25.2% higher than

Results of predicted friction factor from the numerical simulation show the same trend as of the experimental ones, where differentiations between results within 6.04% are considered as an acceptable limit. Numerical simulation results of the friction factors for cases of inserts using water and nanofluid are shown in **Figure 14**. All cases demonstrated a slight increase in the numerically predicted friction factor values when 0.1 vol.% TiO2 is used as working fluid. This is attributed to the slight increase in the viscosity of the nanofluid compared to the viscosity

The heat transfer enhancement, in terms of Nusselt number, is influenced by velocity variation, friction factor, nanoparticles volume fraction, twisted tape dimensions, and other parameters. The four models were examined experimentally and numerically within Reynolds number ranging from 5000 to 20,000. The

pared to the experimental results.

*DOI: http://dx.doi.org/10.5772/intechopen.93359*

increases by 1.2–2.4% using nanofluid.

that in plain tube.

**Figure 13.**

*flow.*

of pure water.

**39**

**5.2 Thermal analysis**

**Figure 11.**

*Verification of experimentally measured friction factors and those predicted from; (a) PT with water flow and prediction by Blasius (Eq. 12) and Petukhov (Eq. 13); (b) STT with water flow and prediction by Bergles (Eq. 15).*

**Figure 12.**

*Verification of experimentally measured friction factors and predicted by Duangthongsuk and Wongwises (Eq. 14) for 0.1 vol.% TiO2/water nanofluid flow in plain tube.*

*Applications of Compound Nanotechnology and Twisted Inserts for Enhanced Heat Transfer DOI: http://dx.doi.org/10.5772/intechopen.93359*

#### **Figure 13.**

a maximum deviation of 4.1%. Further verification was carried out by comparing the experimental results of the friction factor of single TT insert in the tube with water flow by comparison with the results gained by a correlation developed by Bergles, as in Eq. (15). The maximum deviation was 3.0%. The verification results

Measured friction factors coincide well with the calculated values from correlations of validation. As the fluid velocity increases, the friction factor decreases. Therefore, friction factor decreases with Reynolds number increasing. This is because Reynolds number increases the momentum, overcomes the viscous force of the fluid, and consequently lowers the shear between the fluid and the tube wall. Reference [16] developed a correlation for the friction factor prediction for nanofluid flow in a plain tube, shown as Eq. (14). Comparison between the predicted results by Eq. (14) and the experimental results in the current investigations are shown in **Figure 12**. Good match between the experimental and empirical

*Verification of experimentally measured friction factors and those predicted from; (a) PT with water flow and prediction by Blasius (Eq. 12) and Petukhov (Eq. 13); (b) STT with water flow and prediction by Bergles*

*Verification of experimentally measured friction factors and predicted by Duangthongsuk and Wongwises*

*(Eq. 14) for 0.1 vol.% TiO2/water nanofluid flow in plain tube.*

are shown in **Figure 11**.

*Inverse Heat Conduction and Heat Exchangers*

**Figure 11.**

*(Eq. 15).*

**Figure 12.**

**38**

*Experimental measurement results for the friction factor verses Reynolds number for plain tube and tubes with single, triple, and quintuple twisted tape inserts of flow cases of water flow and 0.1 vol.% TiO2/water nanofluid flow.*

values has been achieved. Within the tested range of 5000–20,000 Re, the correlation shows overprediction of around 2.0–3.0% in the friction factor values compared to the experimental results.

The variations of the friction factor with Reynolds number for the tubes with different twisted tape inserts, with flows of water and nanofluid, are compared in **Figure 13**. The friction factors of the nanofluids are slightly higher than those of the base liquid. The tube fitted with plain twisted tape inserts (STT) when water flow has friction factor of 6.6–8.7% higher than plain tube. This is attributed to the flow blockage and swirl flow due to tape insert; for the same case, friction factor increases by 1.2–2.4% using nanofluid.

The additional dissipation of pressure of the fluid caused by the fluid disturbance due to increase of tape number results in an increase in pressure drop, which causes increase of friction factor. As the number of inserts increases, the pressure drop significantly increases. For water flow, the friction factors of TTT and QTT are 12.2–17.74% and 18.428–24.65% higher than that in plain tube. For nanofluid flow, the friction factors of TTT are 13.3–18.4% and for QTT are 19.6–25.2% higher than that in plain tube.

Results of predicted friction factor from the numerical simulation show the same trend as of the experimental ones, where differentiations between results within 6.04% are considered as an acceptable limit. Numerical simulation results of the friction factors for cases of inserts using water and nanofluid are shown in **Figure 14**. All cases demonstrated a slight increase in the numerically predicted friction factor values when 0.1 vol.% TiO2 is used as working fluid. This is attributed to the slight increase in the viscosity of the nanofluid compared to the viscosity of pure water.

#### **5.2 Thermal analysis**

The heat transfer enhancement, in terms of Nusselt number, is influenced by velocity variation, friction factor, nanoparticles volume fraction, twisted tape dimensions, and other parameters. The four models were examined experimentally and numerically within Reynolds number ranging from 5000 to 20,000. The

#### **Figure 14.**

*Numerical simulation results of the friction factor versus Reynolds number for plain tube and tubes with single, triple, and quintuple twisted tape inserts of flow cases of water flow and 0.1 vol.% TiO2/water nanofluid flow.*

measured thermal parameters were verified by comparing the measurement results with well-established correlations to predict Nu. The verification results are shown in **Figure 15a** and **b**. The experimental results are matching those results obtained from correlations 8 and 15 with a deviation of 2.6–7.4%.

Further verification was carried out for the case of nanofluid flow in the pipe by comparing the experimental measurement Nu results with correlation 9 prediction Nu results, as shown in **Figure 16**. Very good agreement between the experimental and correlation results was demonstrated. The predicted results of Nu by the correlation are higher than the experimental results of Nu. As Re increased, a slight increase in the margin of error was observed.

The variations of Nusselt number with Reynolds number for the tubes with different twisted tape inserts are compared in **Figure 17** for both nanofluid and base fluid. It can generally be observed that the Nusselt number increases as the Reynolds number increases. This arises as a result of the momentum that overcomes the viscous force of the fluid as the Reynolds number increases and in effect diminishes the shear between the fluid and the tube wall.

For water flow, the STT has Nusselt numbers of 43.4–63.2% higher than plain tube. This enhancement in heat transfer rate returns to the act of twisted tape that generates swirl motion, which leads to the better temperature distribution at the core region and increases turbulence intensity at near wall region that results in higher temperature gradient there and enhances heat transfer coefficient. Also, secondary

*Variation of Nusselt number with Reynolds number for plain tubes and tubes with single, triple, and quintuple*

*Validation of experimental results for Nusselt number to the plain tube with Duangthongsuk and Wingwiscs*

*Applications of Compound Nanotechnology and Twisted Inserts for Enhanced Heat Transfer*

In case of water flow, Nusselt numbers of TTT and QTT are 50.12–83.74% and 57.48–100.066% higher than that in measured in PT. It is obvious that Nusselt number increases with increasing twisted tape number due to increase in secondary motion violence, which disperses the high temperature region near wall to uniformly distribute all over flow cross sectional area, which is recognized as the key

flow with greater enhancement was realized at higher Reynolds numbers.

*twisted tape inserts operating with water flow and 0.1 vol.% TiO2/water nanofluid flow.*

factor of heat transfer enhancement.

**Figure 16.**

**Figure 17.**

**41**

*correlation for 0.1 vol.% TiO2/water nanofluid flow.*

*DOI: http://dx.doi.org/10.5772/intechopen.93359*

#### **Figure 15.**

*Verification of experimental results for heat exchange performance by: (a) comparison with Gnielinski correlation for water flow in plain tube. (b) Comparison with Bergles correlation for water flow in tube with single TT insert.*

*Applications of Compound Nanotechnology and Twisted Inserts for Enhanced Heat Transfer DOI: http://dx.doi.org/10.5772/intechopen.93359*

#### **Figure 16.**

measured thermal parameters were verified by comparing the measurement results with well-established correlations to predict Nu. The verification results are shown in **Figure 15a** and **b**. The experimental results are matching those results obtained

*Numerical simulation results of the friction factor versus Reynolds number for plain tube and tubes with single, triple, and quintuple twisted tape inserts of flow cases of water flow and 0.1 vol.% TiO2/water nanofluid flow.*

Further verification was carried out for the case of nanofluid flow in the pipe by comparing the experimental measurement Nu results with correlation 9 prediction Nu results, as shown in **Figure 16**. Very good agreement between the experimental and correlation results was demonstrated. The predicted results of Nu by the correlation are higher than the experimental results of Nu. As Re increased, a slight

The variations of Nusselt number with Reynolds number for the tubes with different twisted tape inserts are compared in **Figure 17** for both nanofluid and base

Reynolds number increases. This arises as a result of the momentum that overcomes the viscous force of the fluid as the Reynolds number increases and in effect

fluid. It can generally be observed that the Nusselt number increases as the

*Verification of experimental results for heat exchange performance by: (a) comparison with Gnielinski correlation for water flow in plain tube. (b) Comparison with Bergles correlation for water flow in tube with*

from correlations 8 and 15 with a deviation of 2.6–7.4%.

diminishes the shear between the fluid and the tube wall.

increase in the margin of error was observed.

*Inverse Heat Conduction and Heat Exchangers*

**Figure 14.**

**Figure 15.**

**40**

*single TT insert.*

*Validation of experimental results for Nusselt number to the plain tube with Duangthongsuk and Wingwiscs correlation for 0.1 vol.% TiO2/water nanofluid flow.*

#### **Figure 17.**

*Variation of Nusselt number with Reynolds number for plain tubes and tubes with single, triple, and quintuple twisted tape inserts operating with water flow and 0.1 vol.% TiO2/water nanofluid flow.*

For water flow, the STT has Nusselt numbers of 43.4–63.2% higher than plain tube. This enhancement in heat transfer rate returns to the act of twisted tape that generates swirl motion, which leads to the better temperature distribution at the core region and increases turbulence intensity at near wall region that results in higher temperature gradient there and enhances heat transfer coefficient. Also, secondary flow with greater enhancement was realized at higher Reynolds numbers.

In case of water flow, Nusselt numbers of TTT and QTT are 50.12–83.74% and 57.48–100.066% higher than that in measured in PT. It is obvious that Nusselt number increases with increasing twisted tape number due to increase in secondary motion violence, which disperses the high temperature region near wall to uniformly distribute all over flow cross sectional area, which is recognized as the key factor of heat transfer enhancement.

For 0.1 vol.% TiO2/water nanofluid flow, PT, STT, TTT, and QTT have Nusselt numbers of 1.3–30.4%, 46.1–83.2%, 53.8–97.5%, and 59.9–110.8%, respectively, higher than that in PT with water flow. This behavior is due to the fact that nanoparticles presented in the base liquid increase the thermal conductivity, which leads to an increase in heat transfer performance.

*I* turbulence intensity

*DOI: http://dx.doi.org/10.5772/intechopen.93359*

*L* tube length (mm) *Nu* Nusselt number *Δp* pressure drop (Pa) *Pr* Prandtl number

<sup>¼</sup> heat flux (W/m2

*Re* Reynolds number *V* mean velocity (m/s) w tape width (mm) *y* tape pitch 180° (mm) *δ* tape thickness (mm) *v* kinematic viscosity (m<sup>2</sup>

*ρ* fluid density (kg/m<sup>3</sup>

*q*

**Subscripts**

**Acronyms**

**Author details**

Malaysia

**43**

Hussain H. Al-Kayiem<sup>1</sup>

b bulk h hydraulic in inlet nf nanofluid s surface w water

PT plain tube

*K* thermal conductivity (W/m∙K)

*φ* nanoparticles volume fraction (%)

*μ* fluid dynamic viscosity (kg/m s) *cp* fluid-specific heat (J/kg∙K)

STT tube with single twisted tape TTT tube with triple twisted tapes QTT tube with quintuple twisted tapes

)

/s)

*Applications of Compound Nanotechnology and Twisted Inserts for Enhanced Heat Transfer*

\*, Muna S. Kassim<sup>2</sup> and Saud T. Taher<sup>2</sup>

1 Mechanical Engineering Department, Universiti Teknologi PETRONAS, Perak,

2 Mechanical Engineering Department, Al-Mustansiriyah University, Baghdad, Iraq

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

\*Address all correspondence to: hussain\_kayiem@utp.edu.my

provided the original work is properly cited.

)
