**Abstract**

As shell and tube heat exchanger is widely employed in various field of industries, heat exchanger design remains a constant optimization challenge to improve its performance. The heat exchanger design includes not only the architectural geometry of either the shell and tube configuration or the additional baffles but also the working fluid. The baffle design including the baffle angle and the baffle distance has been understood as key parameter controlling the overall heat exchanger effectiveness. In addition, a room of improvement is open by substituting the conventional working fluid with the nanomaterials-enriched nanofluid. The nanomaterials, e.g. Al2O3, SiO2, TiO2, increases the thermal conductivity of the working fluids, and hence, the more efficient heat transfer process can be achieved. This chapter provide an insight on the performance improvement of shell and tube heat exchanger by modifying the baffle design and utilizing nanofluids.

**Keywords:** Design optimization, Geometry, Conductivity, Heat exchanger performance, Computational fluid dynamics

## **1. Introduction**

Heat exchanger is considered a vital component in thermal process required in a wide range of industries. This heat exchanger is typically employed for condensation, sterilization, pasteurization, fractionation, distillation, and crystallization [1–3]. This implies that the heat exchanger shall possess an optimized design to yield the highest possible effectiveness while having a compact dimension. In general, heat transfer in a heat exchanger is substantially dominated by convection and conduction. The convection is significantly affected by the geometry of the heat exchanger and some dimensionless numbers, including Reynolds number (Re), Nusselt number (Nu) and Prandtl numbers (Pr) [1–7]. It should be noted that Re, Nu and Pr are dependent on the flow rate and fluid properties including the density, absolute viscosity, specific heat and thermal conductivity.

Practically, various heat exchangers have been developed and the shell and tube heat exchanger has been intensively employed in industries as it shows some favorable features, i.e. easy maintenance, robust construction, and higher construction reliability [8–12]. The shell and tube heat exchanger mainly comprise of shell, tubes, 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 lower the reliability of the heat exchanger.

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.

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

*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)*

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

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

*inlet hot fluid reservoir, (15) heater. Figure was adapted from Ref. [11] with permission.*

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.

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

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

Therefore, the baffle distance was set to 30, 60, and 90 mm.

boundary conditions summarized in **Table 1**.

determined as follows.

**199**

other modification.

**Figure 1.**

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: ethylene glycol.
