**2. Experimental and numerical approach to evaluate the effect of baffle arrangement to the heat exchanger effectiveness**

Baffle modification in this chapter includes baffle types, baffle angle and baffle distance. Modification of baffle type and angle was investigated experimentally using the experimental setup of laboratory scale of heat exchanger shown in **Figure 1** [11]. The baffle type was varied using helical and double segmental baffle, whilst the baffle angle was set in the range of 5°, 6°, and 7°. The pressure drop and the temperature difference between inlet and outlet of heat exchanger were

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

#### **Figure 1.**

front head, rear head, baffles, and nozzle. For high performance shell and tube heat exchanger, which shows high effectiveness (ε), several parameters affecting the heat and mass transfer process should be optimized, including the working fluid and material selection, flow rate, temperature, heat transfer rate, pressure drop, shell and tube dimension and composition, as well as baffle distance and cut, and pitch range [8–14]. Considering the architecture of heat exchanger, baffles

arrangement is one of the important parameters that will increase the heat transfer and hence the effectiveness. For instance, reducing the baffle gaps could induce high pressure drop while setting the baffle gap too far could lead to less efficient heat transfer. In addition, improper baffle arrangement will lead to additional mechanical vibration which can damage the heat exchanger apparatus, and hence

Other practical problem arising in industry is that the heat exchanger frequently faces unfavorable thermal properties of its working fluid, i.e. water, ethylene glycol, or oil, leading to the lower heat transfer effectiveness [14]. Therefore, it is necessary to improve the thermal properties of working fluids, one of which is by adding functional nanoparticles into the working fluid [15–17]. Recent studies have investigated the improvement of heat transfer effectiveness in nanofluids bearing various metal oxide semiconductor nanoparticles, e.g. Al2O3, TiO2, CuO, and SiO2 [15– 26]. Among these materials, TiO2 is one of the widely exploited nanoparticles for increasing the heat transfer effectiveness as it shows superior chemical and

thermophysical stability [18–23]. Nonetheless, it should be noted that the utilization of high concentration of nanoparticles should be avoided since it may cause blockage of the fluid flow as well as induce fouling [18, 19]. Still, the use of nanoparticles in the base fluid (nanofluid) can be considered an alternative approach to improve both the thermal conductivity of the working fluid and the long-term stability by maintaining lower pressure drop in the system [20]. Some literature report that the use of nanofluids enhances the heat transfer effectiveness particularly under laminar flow condition by increasing both the concentration of nanoparticles in nanofluids and the Reynolds number [15–21]. These results suggest that the use of nanofluids increases the convection coefficient within the heat transfer process. Considering the abovementioned facts, it is quite clear that the heat transfer process in the heat exchanger can be improved in many ways. Particularly for shell and tube heat exchanger, enhancing the heat exchanger effectiveness which is discussed in this chapter can be achieved by modifying the baffle architecture and by utilizing nanofluids with functional nanoparticles. The baffle arrangement discussed in this chapter includes the baffle distance and the baffle type which was investigated by experimental and numerical method using computational fluid dynamics (CFD). Meanwhile, the effect of nanofluid substitution to the working fluid has been investigated experimentally by varying the concentration of nanoparticles, i.e. Al2O3 in water and SiO2@TiO2 in water:

**2. Experimental and numerical approach to evaluate the effect of baffle**

Baffle modification in this chapter includes baffle types, baffle angle and baffle distance. Modification of baffle type and angle was investigated experimentally using the experimental setup of laboratory scale of heat exchanger shown in **Figure 1** [11]. The baffle type was varied using helical and double segmental baffle, whilst the baffle angle was set in the range of 5°, 6°, and 7°. The pressure drop and the temperature difference between inlet and outlet of heat exchanger were

**arrangement to the heat exchanger effectiveness**

lower the reliability of the heat exchanger.

*Heat Transfer - Design, Experimentation and Applications*

ethylene glycol.

**198**

*Schematic of heat exchanger system with modified baffle architecture: (1) baffle, (2) pressure gauge, (3) instrument box, (4) flow meter, (5) cold flow piping, (6) shell, (7) cold fluid pump, (8) valve, (9) inlet cold fluid reservoir, (10) outlet fluid reservoir, (11) tubing, (12) piping of hot fluid, (13) hot fluid pump, (14) inlet hot fluid reservoir, (15) heater. Figure was adapted from Ref. [11] with permission.*

recorded to determine the heat exchanger effectiveness (*vide infra*). The experimental results here will be used for validation of the results obtained from CFD simulation and hence, the model will be further used for the heat exchanger with other modification.

To investigate the effect of baffle distance, both experimental and numerical method was used for the use of segmental and disc and doughnut baffle, respectively. Numerical method using computational fluid dynamics (CFD) was carried out as experimental approach was difficult to carry out due to the experimental complexity and high cost of experiment. For segmental baffle, the baffle distance was varied as 4, 10, and 16 cm. For numerical method, the heat exchanger dimension however followed the existing laboratory scale of heat exchanger and the baffle type was disc and doughnut baffles. The variation of baffle distances followed TEMA standards, i.e. the minimum baffle distance shall be 0.2 of the shell diameters and the maximum baffle distance shall be as large as the inner diameter of the shell. Therefore, the baffle distance was set to 30, 60, and 90 mm.

For analysis using CFD, pre-processing, solving and post-processing were employed. Pre-processing was carried out by building 3D model of the shell and tube heat exchanger using ANSYS 16.0 which was discretized (meshed) using different type of mesh types. The mesh result of was depicted in **Figure 2**. For grid independence study, the number of discretized cells spans from 1 to 3 million cells using with tetrahedral/hexahedral types. Finally, pre-processing step defined the boundary conditions summarized in **Table 1**.

The operating condition of the shell and tube heat exchanger at the boundary condition was defined as follow: Temperature of cold (Tc,in) and hot (Th,in) fluid in the inlet was set to 80°C and of 30°C, respectively. The volumetric flow rate of hot and cold fluid was set at 4 and 6 lpm, respectively. Having defined the boundary condition, the solving stage was built by utilizing the governing equations, i.e. conservation of energy, momentum and continuity. Energy conservation was determined as follows.

where *p* was normal pressure (N/m<sup>2</sup>

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

which considers the following steps [19]:

This model set the fluid density as a function of temperature:

small, or it was valid if satisfying for *β*ð Þ *T* � *T*<sup>0</sup> < < 1*:*.

The rate of heat capacity (C) was calculated as

The maximum heat transfer (qmax) was calculated as follow:

where the smallest value *Cmin* considers:

), *F* was body force on solid region. For a

*ρ* ¼ *ρ*0ð Þ 1 � *β*ð Þ *T* � *T*<sup>0</sup> (5)

*Cc* ¼ *m*\_ *<sup>c</sup>* � *Cpc* (6) *Ch* ¼ *m*\_ *<sup>h</sup>* � *Cph* (7)

*Cmin* ¼ >If *Ch* <*Cc* then *Ch* ¼ *Cmin* (8) *Cmin* ¼ > If *Cc* <*Ch* then *Cc* ¼ *Cmin* (9)

*qmax* ¼ *Cmin* � ð Þ *Th*,*in* � *Tc*,*in* (10)

¼ *m*\_ *<sup>h</sup>* � *Ch* � ð Þ *Th*,*in* � *Th*,*out* (13)

¼ *m*\_ *<sup>c</sup>* � *Cc* � ð Þ *Tc*,*out* � *Tc*,*in* , (14)

and the effectiveness (ε) of the heat exchanger can then be calculated as follow:

The effectiveness of heat transfer using different nanofluids was assessed in the laboratory scale of experimental heat transfer system (automobile radiator training

*<sup>ε</sup>* <sup>¼</sup> *qactual qmax*

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

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

**201**

*qin* ¼ *qout* (11)

*qh* ¼ *qc* (12)

(15)

faster convergence of numerical calculation, the Boussinesq model was considered.

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

where *β* was thermal expansion coefficient (1/K), T0 dan *ρ*<sup>0</sup> represented the operational parameter. This model was accurate as long as the density changes were

The final step in CFD was the post processing stage including the data visualization in the form of a contour of static temperature, pressure, and velocity profile. Data analysis was carried out to determine the temperature distribution in the shell and tube heat exchanger with different baffle distances. The heat exchanger effectiveness (ε) was calculated in every variation of baffle distance using NTU method

#### **Figure 2.**

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


#### **Table 1.**

*Boundary conditions of shell and tube heat exchangers.*

$$\frac{\partial}{\partial t}(\rho E) + \nabla. \left(\overrightarrow{\nu}(\rho E + p)\right) = \nabla \cdot k\_{\ell \overline{\ell}} \nabla T + \nabla. \left(\overline{\bar{\tau}}\_{\ell \overline{\ell} \overline{\ell}}.\overrightarrow{\nu}\right) + \mathbf{S}\_h \tag{1}$$

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

$$\frac{\partial}{\partial t}(\rho h) + \nabla. \left(\overrightarrow{v}\,\rho h\right) = \nabla. (k\nabla T) + \mathsf{S}\_h \tag{2}$$

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 momentum:

$$\nabla \cdot \boldsymbol{\mu} = \mathbf{0} \tag{3}$$

$$
\rho \frac{du}{dt} = F - \nabla p + \mu \nabla^2 u \tag{4}
$$

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

where *p* was normal pressure (N/m<sup>2</sup> ), *F* was body force on solid region. For a faster convergence of numerical calculation, the Boussinesq model was considered. This model set the fluid density as a function of temperature:

$$
\rho = \rho\_0 (1 - \beta (T - T\_0)) \tag{5}
$$

where *β* was thermal expansion coefficient (1/K), T0 dan *ρ*<sup>0</sup> represented the operational parameter. This model was accurate as long as the density changes were small, or it was valid if satisfying for *β*ð Þ *T* � *T*<sup>0</sup> < < 1*:*.

The final step in CFD was the post processing stage including the data visualization in the form of a contour of static temperature, pressure, and velocity profile. Data analysis was carried out to determine the temperature distribution in the shell and tube heat exchanger with different baffle distances. The heat exchanger effectiveness (ε) was calculated in every variation of baffle distance using NTU method which considers the following steps [19]:

The rate of heat capacity (C) was calculated as

$$\mathbf{C}\_{\mathfrak{c}} = \dot{m}\_{\mathfrak{c}} \times \mathbf{C}p\_{\mathfrak{c}} \tag{6}$$

$$\mathbf{C}\_{h} = \dot{m}\_{h} \times \mathbf{C}p\_{h} \tag{7}$$

where the smallest value *Cmin* considers:

$$\mathcal{C}\_{\text{mit}} = > \text{If } \mathcal{C}\_h < \mathcal{C}\_c \text{ then } \mathcal{C}\_h = \mathcal{C}\_{\text{mit}} \tag{8}$$

$$\mathbf{C}\_{\min} = > \text{If } \mathbf{C}\_{\mathcal{c}} < \mathbf{C}\_{h} \text{ then } \mathbf{C}\_{\mathcal{c}} = \mathbf{C}\_{\min} \tag{9}$$

The maximum heat transfer (qmax) was calculated as follow:

$$q\_{\text{max}} = \mathbf{C}\_{\text{min}} \times \left( T\_{h,\text{in}} - T\_{c,\text{in}} \right) \tag{10}$$

$$
\mathfrak{q}\_{in} = \mathfrak{q}\_{out} \tag{11}
$$

$$
\mathfrak{q}\_h = \mathfrak{q}\_c \tag{12}
$$

$$\dot{\mathbf{c}} = \dot{m}\_h \times \mathbf{C}\_h \times (T\_{h,in} - T\_{h,out}) \tag{13}$$

$$
\dot{\mathbf{c}} = \dot{\mathbf{m}}\_c \times \mathbf{C}\_c \times (T\_{c,out} - T\_{c,in}),
\tag{14}
$$

and the effectiveness (ε) of the heat exchanger can then be calculated as follow:

$$
\varepsilon = \frac{q\_{actual}}{q\_{max}} \tag{15}
$$
