Nanofluids are special liquids created by mixing tiny nanoparticles into a base fluid like water. This is done to make the fluid better at transferring heat. A Double pipe heat exchanger CFD simulation is the best tool to see exactly how much improvement we can get. In this type of heat exchanger, one fluid flows through a central pipe, and another flows in the space around it. The main goal of this project is to simulate and compare the performance of a heat exchanger when using regular water versus when using an Alumina (Al2O3) Nanofluid. This study is guided by the important methods described in the reference paper by Pak and Cho [1].

• Reference [1]: Pak, Bock Choon, and Young I. Cho. “Hydrodynamic and heat transfer study of dispersed fluids with submicron metallic oxide particles.” Experimental Heat Transfer an International Journal2 (1998): 151-170.

Simulation Process: CFD Modeling with Custom Nanofluid Properties

To begin our Nanofluid in Double Pipe Heat Exchanger fluent simulation, we first prepared the 3D geometry. Because the heat exchanger has a symmetric shape, we can model only half of it. This smart simplification makes the simulation run much faster without losing any accuracy. Next, a high-quality structured grid was created, as shown in Figure 1. A good mesh is very important for getting correct results.

The most critical part of this simulation was defining the fluid properties. ANSYS Fluent does not know the properties of an Al2O3 Nanofluid by default. Therefore, we had to write a User-Defined Function (UDF). This special code “teaches” Fluent the correct thermal conductivity and viscosity of the nanofluid. Using a UDF is essential for any accurate Nanofluid CFD simulation because it allows us to model the unique behavior of these advanced fluids.

Figure 1: The structured mesh generated for the Double Pipe Heat Exchanger CFD domain.

Post-Processing: Trade-Off Between Heat Transfer and Pumping Power

A detailed analysis of the results clearly shows both the benefits and the costs of using a nanofluid. The main goal was to improve heat transfer, and the simulation proves this was a success. The Nusselt number, which measures how well heat is transferred, increased from 6.03 for pure water to 6.62 for the nanofluid. This is an impressive 9.8% improvement in heat transfer performance. The temperature contour in Figure 2 visually confirms this. We can see a smooth and effective temperature rise from 300 K at the inlet to 453.6 K, showing how well the nanofluid absorbs heat along the length of the exchanger.

Figure 2: Temperature field showing the effective heat absorption by the Nanofluid.

However, this excellent thermal performance comes with a significant trade-off. The velocity contour in Figure 3 shows the complex flow inside the pipe. Adding nanoparticles makes the fluid thicker and harder to pump. As a result, the pressure drop along the pipe increased dramatically from 2637 Pa for water to 4020 Pa for the nanofluid. This is a massive 52.4% increase in the required pumping power. This finding is a perfect example of a real-world engineering challenge. The Nanofluid in Double Pipe Heat Exchanger CFD simulation successfully demonstrates that while Al2O3 nanofluids are fantastic for boosting heat transfer, engineers must also design a more powerful pumping system to handle the much higher pressure.

Figure 3: Velocity distribution inside the Double Pipe Heat Exchanger, which helps explain the pressure drop.