**3. Experimental approach to evaluate the effect of nanoparticles concentration in nanofluid to the heat exchanger effectiveness**

The effectiveness of heat transfer using different nanofluids was assessed in the laboratory scale of experimental heat transfer system (automobile radiator training kit) which includes a closed loop of hot and cold flow (**Figure 3**). The heat exchanger was finned-tube cross flow heat exchanger (Suzuki). The nanoparticle used was Al2O3 and SiO2@TiO2. The SiO2@TiO2 in a mixture of EG:water (1:1 v/v) nanofluid was utilized as the hot fluid in the system. The concentration was varied in the range of 0–0.025% mass fraction of SiO2@TiO2 to EG:water base fluids. The system was functionalized with the calibrated thermocouples, flow meter and

*∂ ∂t*

momentum:

**200**

**Figure 2.**

**Table 1.**

ð Þþ *ρE* ∇*: υ*

*Boundary conditions of shell and tube heat exchangers.*

*exchanger. Figures from Ref. [27] used with permission.*

*Heat Transfer - Design, Experimentation and Applications*

the energy transfer was calculated as follow [17, 18]: *∂ ∂t*

!ð Þ *ρE* þ *p* 

ð Þþ *ρh* ∇*: v*

*ρ du*

where *k*eff is the effective conductivity which is the sum of *k* and *k*<sup>t</sup> (thermal conductivity for the presence of turbulence). The two terms on the right side represent the energy transfer by conduction and viscosity dissipation. Meanwhile,

*(a) The 3D model of shell and tube heat exchanger meshed with tetrahedral/hexahedral meshing type at different angle, and the corresponding (b) horizontal and (c) vertical cross-sectional 3D model of heat*

**No. Specification Boundary conditions** Inlet Mass flow inlet Shell Adiabatic wall Tube Convection wall Baffle Adiabatic wall Outlet Outflow

> !*ρh*

where *ρ* was the density, *h* was the sensible enthalpy, *k* was the conductivity constant, T was the surface temperature, and *Sh* was the volumetric heat source. The Eq. (1) and (2) were complemented by the continuity and conservation of

*dt* <sup>¼</sup> *<sup>F</sup>* � <sup>∇</sup>*<sup>p</sup>* <sup>þ</sup> *<sup>μ</sup>*∇<sup>2</sup>

<sup>¼</sup> <sup>∇</sup>*:keff* <sup>∇</sup>*<sup>T</sup>* <sup>þ</sup> <sup>∇</sup>*: <sup>τ</sup>eff :<sup>υ</sup>*

!

¼ ∇*:*ð Þþ *k*∇*T Sh* (2)

∇*:u* ¼ 0 (3)

*u* (4)

þ *Sh* (1)

• Nusselt number (*Nu*) of internal flow

*DOI: http://dx.doi.org/10.5772/intechopen.96996*

• Convection coefficient (*hnf*) of nanofluids

• Convection coefficient (*h*) of air

evaluated by the following:

where

**203**

*Nu* <sup>¼</sup> <sup>0</sup>*:*<sup>0265</sup> � Re <sup>0</sup>*:*<sup>8</sup>

*Nanofluid-Enhancing Shell and Tube Heat Exchanger Effectiveness with Modified Baffle…*

*Dh*

*<sup>h</sup>* <sup>¼</sup> *Nu* � *<sup>k</sup> <sup>f</sup> Dh*

*<sup>U</sup>* <sup>¼</sup> <sup>1</sup> 1 *hi* <sup>þ</sup> <sup>Δ</sup>*<sup>x</sup> kw* <sup>þ</sup> <sup>1</sup> *ho*

Finally, the heat transfer rate which involves convection and conduction was

<sup>Δ</sup>T*LMTD* <sup>¼</sup> <sup>ð</sup>*Th*,*in* � *Tc*,*out*Þ � ð Þ *Th*,*out* � *Tc*,*in*

As previously mentioned, in this section effect of baffle architecture, including type, angle, and distance, and the nanoparticle type and concentration in nanofluids

As stated in the introduction, the baffle arrangement plays significant role in the

Regarding the baffle selection, in this work helical and double segmental baffle were evaluated. While the baffle distance is different for both, *i.e.,* 1.64 and 1 cm for helical and double-segmental baffle, respectively, the baffle distance does not give significant effect to the performance. **Table 2** gives the experimental results and indicates that the ΔTc for heat exchanger with helical baffles is higher than that with double segmental baffles, i.e., 17.7°C vs. 14.4°C. This condition in turn yields

operation of heat exchanger. All thermal properties and performance of heat exchanger upon modification of baffle type, angle and distance are summarized in **Table 2**. In general, the efficiency of heat transfer process can be indicated by the temperature difference in either the hot or the cold fluid flow in the shell and tube

heat exchanger, which is later used to determine the effectiveness.

**4. Improvement of heat exchanger effectiveness**

toward the heat exchange effectiveness will be discussed.

**4.1 Effect of baffle arrangement**

ln ð Þ *Th*,*in*�*Tc*,*out*

Once all above parameters were determined, the overall heat transfer coefficient (*U*) was estimated. For a single tube heat exchanger, *U* was determined as follows:

Re <sup>0</sup>*:*64Pr0*:*<sup>32</sup> *<sup>π</sup>*

2

*Q* ¼ *U* � Α � ΔT*LMTD* (24)

ð Þ *Th*,*out*�*Tc*,*in* (25)

*hnf* <sup>¼</sup> <sup>0</sup>*:*<sup>295</sup> *kw*

Pr0*:*<sup>36</sup> (20)

(21)

(22)

(23)

**Figure 3.** *The schematic of heat exchanger system for investigating the effect nanofluid concentration to its effectiveness.*

pressure gauges. The schematic diagram of the automobile radiator training kit is shown in **Figure 1**.

Performance of heat exchanger using different concentration of SiO2@TiO2 was evaluated by the heat transfer effectiveness. Heat transfer parameters of nanofluids were determined by joint experimental and theoretical approach*, i.e.* only conductivity is directly determined from transient hot wire measurements. The other parameters are determined as follows:

• Density of nanofluids

$$
\rho\_{\eta f} = (\mathbf{1} - \mathbf{q})\rho\_{bf} + \mathbf{q}\rho\_{bf} \tag{16}
$$

• Viscosity of nanofluids (Einstein equation)

$$
\mu\_{nf} = (\mathbf{1} + \mathbf{2.5p})\mu\_{bf} \tag{17}
$$

• Reynolds number (Re)

$$\text{Re} = \frac{\rho \times V \times D\_h}{\mu} \tag{18}$$

• Nusselt number (*Nu*) of external flow

$$Nu = 0.683 \times \text{Re}^{0.38} \times \text{Pr}^{0.37} \times \left(\frac{\text{Pr}}{\text{Pr}\_t}\right)^{0.25} \tag{19}$$

*Nanofluid-Enhancing Shell and Tube Heat Exchanger Effectiveness with Modified Baffle… DOI: http://dx.doi.org/10.5772/intechopen.96996*

• Nusselt number (*Nu*) of internal flow

$$Nu = 0.0265 \times \text{Re}^{0.8} \text{Pr}^{0.36} \tag{20}$$

• Convection coefficient (*hnf*) of nanofluids

$$h\_{\eta f} = 0.295 \left(\frac{k\_w}{D\_h}\right) \text{Re}^{0.64} \text{Pr}^{0.32} \left(\frac{\pi}{2}\right) \tag{21}$$

• Convection coefficient (*h*) of air

$$h = \frac{\mathbf{N}\boldsymbol{\mu} \times \mathbf{k}\_f}{D\_h} \tag{22}$$

Once all above parameters were determined, the overall heat transfer coefficient (*U*) was estimated. For a single tube heat exchanger, *U* was determined as follows:

$$U = \frac{1}{\frac{1}{h\_i} + \frac{\Delta x}{k\_w} + \frac{1}{h\_o}} \tag{23}$$

Finally, the heat transfer rate which involves convection and conduction was evaluated by the following:

$$Q = U \times \mathbf{A} \times \Delta \mathbf{T}\_{LMTD} \tag{24}$$

where

pressure gauges. The schematic diagram of the automobile radiator training kit is

*The schematic of heat exchanger system for investigating the effect nanofluid concentration to its effectiveness.*

Performance of heat exchanger using different concentration of SiO2@TiO2 was evaluated by the heat transfer effectiveness. Heat transfer parameters of nanofluids were determined by joint experimental and theoretical approach*, i.e.* only conductivity is directly determined from transient hot wire measurements. The other

> Re <sup>¼</sup> <sup>ρ</sup> � *<sup>V</sup>* � *Dh* μ

*Nu* <sup>¼</sup> <sup>0</sup>*:*<sup>683</sup> � Re <sup>0</sup>*:*<sup>38</sup> � Pr<sup>0</sup>*:*<sup>37</sup> �

ρ*nf* ¼ ð Þ 1 � φ ρ*bf* þ φρ*bf* (16)

μ*nf* ¼ ð Þ 1 þ 2*:*5φ μ*bf* (17)

Pr Pr*<sup>s</sup>* <sup>0</sup>*:*<sup>25</sup> (18)

(19)

shown in **Figure 1**.

**Figure 3.**

**202**

parameters are determined as follows:

• Viscosity of nanofluids (Einstein equation)

*Heat Transfer - Design, Experimentation and Applications*

• Nusselt number (*Nu*) of external flow

• Density of nanofluids

• Reynolds number (Re)

$$\Delta T\_{LMTD} = \frac{(T\_{h,in} - T\_{c,out}) - (T\_{h,out} - T\_{c,in})}{\ln \left[ \frac{(T\_{h,in} - T\_{c,out})}{(T\_{h,out} - T\_{c,in})} \right]} \tag{25}$$

#### **4. Improvement of heat exchanger effectiveness**

As previously mentioned, in this section effect of baffle architecture, including type, angle, and distance, and the nanoparticle type and concentration in nanofluids toward the heat exchange effectiveness will be discussed.

#### **4.1 Effect of baffle arrangement**

As stated in the introduction, the baffle arrangement plays significant role in the operation of heat exchanger. All thermal properties and performance of heat exchanger upon modification of baffle type, angle and distance are summarized in **Table 2**. In general, the efficiency of heat transfer process can be indicated by the temperature difference in either the hot or the cold fluid flow in the shell and tube heat exchanger, which is later used to determine the effectiveness.

Regarding the baffle selection, in this work helical and double segmental baffle were evaluated. While the baffle distance is different for both, *i.e.,* 1.64 and 1 cm for helical and double-segmental baffle, respectively, the baffle distance does not give significant effect to the performance. **Table 2** gives the experimental results and indicates that the ΔTc for heat exchanger with helical baffles is higher than that with double segmental baffles, i.e., 17.7°C vs. 14.4°C. This condition in turn yields


it is clear that the temperature profile of the fluid flow in the heat exchanger with a baffle distance of 30 mm is substantially different from others. The non-uniform temperature distribution is observed in the first quarter of the heat exchanger due to the turbulence flow as there are dead spaces and recirculation zones. Nonetheless, this phenomenon significantly enhances the thermo-hydraulic performance. A more uniform temperature profile in the shell side of the heat exchangers with baffle distance of 60 and 90 mm is observed. Taking a close look at the temperature distribution around the arranged tubes (**Figure 5**, right), significant radial distribution of temperature from the outer surface of tubes is visible for heat exchanger using 30 and 60 mm baffle distance whilst a subtle temperature changes in the surrounding the tubes is observed for heat exchanger using 90 mm-distanced baffle. At this juncture, 30 mm baffle distance is preferable for shell and tube heat

*Nanofluid-Enhancing Shell and Tube Heat Exchanger Effectiveness with Modified Baffle…*

Other thermophysical properties of heat exchangers with a variation of the baffle distance can also be deduced from CFD, e.g. outflow temperature (Tout) and Nusselt number (Nu) as shown in **Figure 6**. The outflow temperature (Tout) of hot

*Cross sectional at y-axis (*left*) and z-axis (*right*) of steady state static temperature distribution in heat exchanger using 30, 60, and 90 mm baffle distance. The color code unit is K. figures from Ref. [27] used with*

*Thermophysical parameters deduced from numerical calculation, including outlet temperature (Tout), and*

exchanger design.

*DOI: http://dx.doi.org/10.5772/intechopen.96996*

**Figure 5.**

*permission.*

**Figure 6.**

**205**

*Nusselt number (Nu).*

#### **Table 2.**

*Summarized parameters in heat exchanger upon baffle modification. The data was compiled from Ref. [11, 27–29].*

#### **Figure 4.**

*The helical baffle angle (α) configuration in the shell and tube heat exchanger.*

effectiveness of 0.35 which is 15% higher than the effectiveness of shell and tube heat exchanger using double segmental baffles.

As both helical and double segmental baffle show comparable performance when used in shell and tube heat exchanger, the discussion is directed to effect of baffle angle to the heat exchanger performance. The variation of the baffle angle also influences the ΔTc. Smaller baffle angle tends to decrease ΔTc. This is plausibly since more baffles leads to a lower heat transfer passing through the tube due to the flow disturbance by the large number of baffles (see configuration **Figure 4**). The smaller angle, it will absorb the heat faster so that the heat transfer from hot to cold fluid stream becomes less efficient. As noted in **Table 2**, the heat exchange effectiveness drops from 0.50 to 0.32 by changing the baffle angle from 5° to 7°. This trend is somewhat similar to the effect of changing double segmental baffle angle from 15° to 45° which leads to decreasing ΔTc, ΔP and effectiveness quite significantly.

While smaller baffle angle is advantageous for heat exchanger, smaller baffle distance is also preferable for heat exchanger. This is confirmed by both experimental and numerical study. The effect of baffle distance in helical baffled shell and tube heat exchanger as assessed by computational fluid dynamics (CFD) approach shows that distancing the baffles from 30 to 90 cm decreases ΔTc from 48.0 to 9.0° C which results in a decreasing effectiveness from 0.93 to 0.15. The CFD results can be evaluated from the static temperature profile as displayed in **Figure 5**. As shown, *Nanofluid-Enhancing Shell and Tube Heat Exchanger Effectiveness with Modified Baffle… DOI: http://dx.doi.org/10.5772/intechopen.96996*

it is clear that the temperature profile of the fluid flow in the heat exchanger with a baffle distance of 30 mm is substantially different from others. The non-uniform temperature distribution is observed in the first quarter of the heat exchanger due to the turbulence flow as there are dead spaces and recirculation zones. Nonetheless, this phenomenon significantly enhances the thermo-hydraulic performance. A more uniform temperature profile in the shell side of the heat exchangers with baffle distance of 60 and 90 mm is observed. Taking a close look at the temperature distribution around the arranged tubes (**Figure 5**, right), significant radial distribution of temperature from the outer surface of tubes is visible for heat exchanger using 30 and 60 mm baffle distance whilst a subtle temperature changes in the surrounding the tubes is observed for heat exchanger using 90 mm-distanced baffle. At this juncture, 30 mm baffle distance is preferable for shell and tube heat exchanger design.

Other thermophysical properties of heat exchangers with a variation of the baffle distance can also be deduced from CFD, e.g. outflow temperature (Tout) and Nusselt number (Nu) as shown in **Figure 6**. The outflow temperature (Tout) of hot

#### **Figure 5.**

effectiveness of 0.35 which is 15% higher than the effectiveness of shell and tube

*Summarized parameters in heat exchanger upon baffle modification. The data was compiled from*

**Baffle Modification Parameter ΔT (°C) ΔP (kPa) ε** Baffle Type Helical (distance: 164 mm) 17.7 7.36 0.35

Baffle angle (°) (*Helical baffle*) 6 25.4 123.9 0.50

Double Segmental (distance: 100 mm)

14.4 14.48 0.30

7 21.4 88.4 0.45 8 15.7 70.7 0.32

15 24 183.4 0.48 30 13.7 179.5 0.27 45 4.7 178.1 0.09

0.3 48.0 1.95 0.93 0.6 8.0 2.98 0.20 0.9 9.0 2.21 0.15

45° which leads to decreasing ΔTc, ΔP and effectiveness quite significantly.

While smaller baffle angle is advantageous for heat exchanger, smaller baffle distance is also preferable for heat exchanger. This is confirmed by both experimental and numerical study. The effect of baffle distance in helical baffled shell and tube heat exchanger as assessed by computational fluid dynamics (CFD) approach shows that distancing the baffles from 30 to 90 cm decreases ΔTc from 48.0 to 9.0° C which results in a decreasing effectiveness from 0.93 to 0.15. The CFD results can be evaluated from the static temperature profile as displayed in **Figure 5**. As shown,

As both helical and double segmental baffle show comparable performance when used in shell and tube heat exchanger, the discussion is directed to effect of baffle angle to the heat exchanger performance. The variation of the baffle angle also influences the ΔTc. Smaller baffle angle tends to decrease ΔTc. This is plausibly since more baffles leads to a lower heat transfer passing through the tube due to the flow disturbance by the large number of baffles (see configuration **Figure 4**). The smaller angle, it will absorb the heat faster so that the heat transfer from hot to cold fluid stream becomes less efficient. As noted in **Table 2**, the heat exchange effectiveness drops from 0.50 to 0.32 by changing the baffle angle from 5° to 7°. This trend is somewhat similar to the effect of changing double segmental baffle angle from 15° to

heat exchanger using double segmental baffles.

*The helical baffle angle (α) configuration in the shell and tube heat exchanger.*

Baffle angle (°) (*Double segmental*

*Heat Transfer - Design, Experimentation and Applications*

Baffle Distance (cm) (*Disc and*

*baffle*)

**Table 2.**

**Figure 4.**

**204**

*Ref. [11, 27–29].*

*doughnut baffle*)

*Cross sectional at y-axis (*left*) and z-axis (*right*) of steady state static temperature distribution in heat exchanger using 30, 60, and 90 mm baffle distance. The color code unit is K. figures from Ref. [27] used with permission.*

#### **Figure 6.**

*Thermophysical parameters deduced from numerical calculation, including outlet temperature (Tout), and Nusselt number (Nu).*

stream is the lowest for the utilization of 30 mm-distanced baffles while heat exchanger using baffle distance of 60 and 90 mm shows Tout which is on par. This result indicates that the shell and tube heat exchanger with 30 mm baffle distance has the highest heat transfer from the hot to the cold fluid flow. Further, the Nusselt number displays similar trend. The highest Nu is observed for the heat exchanger using 30 mm-distanced baffles. Increasing the baffle distance from 30 mm to 60 and 90 mm lowers the Nu down to 12 and 18, respectively. It should be noted that higher Nu reflects a more efficient convection favorable in the shell and tube heat exchanger.

### **4.2 Effect of Nanofluids materials and concentration**

It is already mentioned that the use of nanoparticles in nanofluid is to increase the conductivity of the base fluid and hence, the overall thermal transfer coefficient. Here, we used both ultra-low concentration (0.002–0.025%) and typical doping concentration (0.5–1.5%) of nanoparticles in the corresponding base fluids for the use of Al2O3 and core-shell SiO2@TiO2, respectively [10, 15]. In general, the heat transfer performance of nanofluids can be indirectly assessed by the dynamic of temperature changes in either the hot (Th) or cold (Tc) fluid flow and the altered U value upon changing the nanoparticle concentration in the base fluid. These two parameters are summarized in **Table 3**.

Evaluating the total heat transfer coefficient, the results show that there is no significant increase. Only slight increase of about 0.03–0.07% is observed for each increment of mass fraction. At the same flow rate (8 liter per min) increasing the concentration of SiO2@TiO2 nanoparticles up to 0.025% yields an increasing heat

*(a) The estimated convection coefficient of air (ha) and SiO2@TiO2 nanofluids (hnf). (b) the overall heat transfer coefficient (U) and heat rate (W) in heat exchanger using different concentration of SiO2@TiO2*

*Nanofluid-Enhancing Shell and Tube Heat Exchanger Effectiveness with Modified Baffle…*

rate is higher than that of water based nanofluid containing TiO2 nanoparticles: At a concentration of 0.25%, the heat transfer rate is only enhanced by 11% [30]. This further implies that the heat transfer rate of the low concentration SiO2@TiO2 nanofluids can be improved by increasing the flowrate of nanofluids in the heat exchanger. In general, the effectiveness of heat transfer using different SiO2@TiO2

). This heat transfer

. Of course,

transfer rate up to 18.11% (from 2168 W <sup>m</sup><sup>2</sup> to 2344 W <sup>m</sup><sup>2</sup>

*nanofluids. Figures from ref. [15] used with permission.*

*DOI: http://dx.doi.org/10.5772/intechopen.96996*

which shows an increase of effectiveness by 13% [22].

**5. Conclusion**

**207**

**Figure 7.**

concentration is linearly increasing with increasing the mass fraction of

of merely 0.5% Al2O3 already increases ΔTc by 5°C. Further increasing

1.5% volume fraction only improves U value up to 30.31 W <sup>m</sup><sup>2</sup> <sup>K</sup><sup>1</sup>

nanoparticles in the base fluid. It is shown that the effectiveness of heat transfer increases by 1.6–2% for increasing mass fraction by 0.005%. Overall, there is an increase in the effectiveness of heat exchanger by 21% (from 0.203 to 0.246) when the water:EG base fluid is added with 0.025% SiO2@TiO2. The results indicate that the additional nanoparticles shows better performance of heat exchanger than another study using EG:water (3:2) based nanofluid containing only 0.02% TiO2

For higher concentration of nanoparticles, *i.e.*, Al2O3 in the base fluid of water shows similar trend as compared to the SiO2@TiO2 in water:EG nanofluid. Addition

nanoparticles concentration from up to 1.5% results in ΔTc of 24.7°C (*vs.* 10.7°C for pure water as working fluid). Interestingly, the U value does not change significantly as also observed for SiO2@TiO2 in water:EG nanofluid. The U value for base fluid of water is known 29.93 W <sup>m</sup><sup>2</sup> <sup>K</sup><sup>1</sup> while the deployment of Al2O3 up to

the observed effects in the Al2O3-water nanofluid can be explained by the same phenomena as previously discussed in the SiO2@TiO2 in water:EG nanofluid.

In this chapter, we have shown that improvement of shell and tube heat exchanger effectiveness can be achieved by optimizing the baffle architecture and by using nanofluids to substitute the conventional working fluid. We have investigated the effect of baffle type and baffle distance in the laboratory scale of shell and tube heat exchanger using experimental and numerical approach, respectively. In

To begin the discussion, the use of nanofluids at the lowest concentration will be first discussed. In this work, we have employed a core-shell SiO2@TiO2 nanoparticles enriched water-ethylene glycol (EG) mixture. The result show that the Tc of outflow is higher with increasing concentration of SiO2@TiO2 nanofluids. This observation indicates that the higher the concentration of nanofluids, the higher the heat is transferred as the thermal conductivity of SiO2@TiO2 increases. Furthermore, the addition of SiO2@TiO2 to the base fluid can result in an increase in the value of the convection coefficient of nanofluid as shown **Figure 7(a)**. It is also interesting to note that changing the mass fraction of SiO2@TiO2 affects the convection coefficient of the air blown to the heat exchanger due to increasing contact surface area during the heat transfer process. The addition of SiO2@TiO2 nanoparticles at a concentration of 0.025% increases the heat transfer coefficient by 9.2%.


#### **Table 3.**

*Summarized parameters of the thermal properties of nanofluids and the shell and tube heat exchanger upon the utilization of nanofluids [10, 15].*

*Nanofluid-Enhancing Shell and Tube Heat Exchanger Effectiveness with Modified Baffle… DOI: http://dx.doi.org/10.5772/intechopen.96996*

**Figure 7.**

stream is the lowest for the utilization of 30 mm-distanced baffles while heat exchanger using baffle distance of 60 and 90 mm shows Tout which is on par. This result indicates that the shell and tube heat exchanger with 30 mm baffle distance has the highest heat transfer from the hot to the cold fluid flow. Further, the Nusselt number displays similar trend. The highest Nu is observed for the heat exchanger using 30 mm-distanced baffles. Increasing the baffle distance from 30 mm to 60 and 90 mm lowers the Nu down to 12 and 18, respectively. It should be noted that higher Nu reflects a more efficient convection favorable in the shell and tube heat

It is already mentioned that the use of nanoparticles in nanofluid is to increase the conductivity of the base fluid and hence, the overall thermal transfer coefficient. Here, we used both ultra-low concentration (0.002–0.025%) and typical doping concentration (0.5–1.5%) of nanoparticles in the corresponding base fluids for the use of Al2O3 and core-shell SiO2@TiO2, respectively [10, 15]. In general, the heat transfer performance of nanofluids can be indirectly assessed by the dynamic of temperature changes in either the hot (Th) or cold (Tc) fluid flow and the altered U value upon changing the nanoparticle concentration in the base fluid. These two

To begin the discussion, the use of nanofluids at the lowest concentration will be first discussed. In this work, we have employed a core-shell SiO2@TiO2 nanoparticles enriched water-ethylene glycol (EG) mixture. The result show that the Tc of outflow is higher with increasing concentration of SiO2@TiO2 nanofluids. This observation indicates that the higher the concentration of nanofluids, the higher the heat is transferred as the thermal conductivity of SiO2@TiO2 increases. Furthermore, the addition of SiO2@TiO2 to the base fluid can result in an increase in the value of the convection coefficient of nanofluid as shown **Figure 7(a)**. It is also interesting to note that changing the mass fraction of SiO2@TiO2 affects the convection coefficient of the air blown to the heat exchanger due to increasing contact surface area during the heat transfer process. The addition of SiO2@TiO2 nanoparticles at a concentration of

**) ΔTc (°C) ε**

0.002 22.78 11.6 0.208 0.008 22.82 12.8 0.218 0.010 22.84 13.4 0.222 0.016 22.86 15.0 0.224 0.020 22.88 15.4 0.238 0.025 22.90 16.9 0.246

0.5 30.14 15.0 0.261 1.0 30.19 18.4 0.350 1.5 30.31 24.7 0.422

**4.2 Effect of Nanofluids materials and concentration**

*Heat Transfer - Design, Experimentation and Applications*

0.025% increases the heat transfer coefficient by 9.2%.

**Nanofluids Nanoparticle concentration (% v/v) U (Wm<sup>2</sup> K<sup>1</sup>**

SiO2@TiO2 in Water-EG 0 22.76 11.4 0.203

Al2O3 in Water 0 29.93 10.7 0.178

*Summarized parameters of the thermal properties of nanofluids and the shell and tube heat exchanger upon the*

parameters are summarized in **Table 3**.

exchanger.

**Table 3.**

**206**

*utilization of nanofluids [10, 15].*

*(a) The estimated convection coefficient of air (ha) and SiO2@TiO2 nanofluids (hnf). (b) the overall heat transfer coefficient (U) and heat rate (W) in heat exchanger using different concentration of SiO2@TiO2 nanofluids. Figures from ref. [15] used with permission.*

Evaluating the total heat transfer coefficient, the results show that there is no significant increase. Only slight increase of about 0.03–0.07% is observed for each increment of mass fraction. At the same flow rate (8 liter per min) increasing the concentration of SiO2@TiO2 nanoparticles up to 0.025% yields an increasing heat transfer rate up to 18.11% (from 2168 W <sup>m</sup><sup>2</sup> to 2344 W <sup>m</sup><sup>2</sup> ). This heat transfer rate is higher than that of water based nanofluid containing TiO2 nanoparticles: At a concentration of 0.25%, the heat transfer rate is only enhanced by 11% [30]. This further implies that the heat transfer rate of the low concentration SiO2@TiO2 nanofluids can be improved by increasing the flowrate of nanofluids in the heat exchanger. In general, the effectiveness of heat transfer using different SiO2@TiO2 concentration is linearly increasing with increasing the mass fraction of nanoparticles in the base fluid. It is shown that the effectiveness of heat transfer increases by 1.6–2% for increasing mass fraction by 0.005%. Overall, there is an increase in the effectiveness of heat exchanger by 21% (from 0.203 to 0.246) when the water:EG base fluid is added with 0.025% SiO2@TiO2. The results indicate that the additional nanoparticles shows better performance of heat exchanger than another study using EG:water (3:2) based nanofluid containing only 0.02% TiO2 which shows an increase of effectiveness by 13% [22].

For higher concentration of nanoparticles, *i.e.*, Al2O3 in the base fluid of water shows similar trend as compared to the SiO2@TiO2 in water:EG nanofluid. Addition of merely 0.5% Al2O3 already increases ΔTc by 5°C. Further increasing nanoparticles concentration from up to 1.5% results in ΔTc of 24.7°C (*vs.* 10.7°C for pure water as working fluid). Interestingly, the U value does not change significantly as also observed for SiO2@TiO2 in water:EG nanofluid. The U value for base fluid of water is known 29.93 W <sup>m</sup><sup>2</sup> <sup>K</sup><sup>1</sup> while the deployment of Al2O3 up to 1.5% volume fraction only improves U value up to 30.31 W <sup>m</sup><sup>2</sup> <sup>K</sup><sup>1</sup> . Of course, the observed effects in the Al2O3-water nanofluid can be explained by the same phenomena as previously discussed in the SiO2@TiO2 in water:EG nanofluid.

#### **5. Conclusion**

In this chapter, we have shown that improvement of shell and tube heat exchanger effectiveness can be achieved by optimizing the baffle architecture and by using nanofluids to substitute the conventional working fluid. We have investigated the effect of baffle type and baffle distance in the laboratory scale of shell and tube heat exchanger using experimental and numerical approach, respectively. In

general, the heat exchanger effectiveness is affected by the baffle arrangement and type. It is found that helical baffle is preferable than double segmental baffle which yields 15% higher effectiveness. Larger baffle separation distance consistently shows a significantly decreasing heat transfer rate as indicated by lower ΔT. This in turn lowers the heat exchanger effectiveness quite substantially. In addition, angle also quite essential to optimize. For the utilization of helical baffle, only changing 5° to 7° already lowers the effectiveness from 0.50 down to 0.32.

**Greek symbols**

**Author details**

I Made Arsana<sup>1</sup>

**209**

*β* Extinction or attenuation coefficient, m<sup>1</sup>

\* and Ruri Agung Wahyuono<sup>2</sup>

\*Address all correspondence to: madearsana@unesa.ac.id

Negeri Surabaya, Surabaya, East Java, Indonesia

provided the original work is properly cited.

1 Department of Mechanical Engineering, Faculty of Engineering, Universitas

Engineering, Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia

2 Department of Engineering Physics, Faculty of Industrial Technology and System

© 2021 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,

*ρ <sup>f</sup>* Density of a fluid.kg*=*m<sup>3</sup> *σscat* Scattering coefficient, m<sup>1</sup> *σabs* Scattering coefficient, m<sup>1</sup> ϕ Azimuthal angle, rad. Φ Scattering phase function

*DOI: http://dx.doi.org/10.5772/intechopen.96996*

Ω Solid angle, sr

*θ* Polar or cone angle measured from normal of surface, rad.

*Nanofluid-Enhancing Shell and Tube Heat Exchanger Effectiveness with Modified Baffle…*

The utilization of nanofluid has been demonstrated to enhance the heat transfer process yielding higher effectiveness. Even at the extremely low concentration of nanoparticles, *i.e.*, 0.002 to 0.025%, the water-ethylene glycol based nanofluids containing SiO2@TiO2 core-shell nanoparticles enable enhancement of heat exchanger effectiveness by 20%. This finding is essential as it is not necessary to use high concentration of nanoparticles to improve heat exchanger effectiveness while avoiding fouling inside the tubing system of shell and tube heat exchanger. Another set of examples has been shown that using water based working fluid using Al2O3. Increasing volume fraction of Al2O3 nanoparticles significantly boosts the effectiveness up to 0.422 which is plausibly a result of increasing thermal conductivity of the water base fluid.

### **Acknowledgements**

Financial support by the Center of Research and Development (*Lembaga Penelitian dan Pengabdian Kepada Masyarakat*) of Universitas Negeri Surabaya and the directorate of research and community development (*Direktorat Riset dan Pengabdian Kepada Masyarakat*) of Institut Teknologi Sepuluh Nopember is highly acknowledged. Authors also would like to thank to the Mechanical Engineering Department and Heat Transfer Laboratory of Universitas Negeri Surabaya for their technical support.
