In a standard double-pipe heat exchanger, improving efficiency is a constant goal. One of the best ways to do this is to add a special insert called a twisted tape inside the inner pipe. This simple device can dramatically improve thermal performance by changing how the fluid flows. A Twisted Tape in Double-pipe Heat Exchanger CFD simulation is the perfect tool to see exactly how this works and to measure the improvement. This report details a CFD analysis using ANSYS Fluent, with the study being based on the reference paper, “Numerical study on heat transfer enhancement and flow characteristics of double pipe heat exchanger fitted with rectangular cut twisted tape” [1].

• Reference [1]: Barzegar, Ali, and Dovood Jalali Vahid. “Numerical study on heat transfer enhancement and flow characteristics of double pipe heat exchanger fitted with rectangular cut twisted tape.” Heat and Mass Transfer12 (2019): 3455-3472.

Figure 1: The 3D model of the Twisted Tape in Double-pipe Heat Exchanger CFD simulation.

Simulation Process: Modeling the Twisted Tape Fluent Simulation

The simulation process began with carefully creating the 3D model of the Twisted Tape Fluent geometry, which is a challenging task due to the tape’s complex shape. The model was then filled with a high-quality hybrid grid made of hexagonal cells. This type of mesh is excellent for capturing the flow details around the curved surfaces of the tape.

To ensure the simulation was as realistic as possible, a User-Defined Function (UDF) was written. Because the properties of water (like density and viscosity) change with temperature, this UDF allowed the simulation to update these properties continuously based on the calculated temperature. This is a critical step for achieving accurate results in heat transfer problems.

Figure 2: The hybrid mesh used for the Twisted Tape Fluent simulation, with detail on the tape insert

Post-processing: CFDAnalysis, How Swirl Flow Drives Heat Transfer

The simulation results provide a clear and fully substantiated story that begins with the fluid dynamics, which is the “cause” of the improved performance. The velocity streamlines in Figure 3 prove that the twisted tape insert completely changes the flow’s character. Instead of flowing straight, the fluid is forced into a strong, swirling, helical motion. This creates a powerful secondary flow, or vortex, that runs the entire length of the pipe. The rectangular cuts in the tape add another layer of complexity, creating extra turbulence and localized mixing zones near the pipe wall. This combination of a primary swirl and secondary turbulence, with velocities ranging from 0.07 m/s to 0.438 m/s, is the powerful engine that drives the heat transfer enhancement.This intense, structured swirl has a direct and measurable “effect” on the heat exchanger’s thermal performance. The swirling motion continuously disrupts the thermal boundary layer—a thin layer of slow-moving fluid that normally insulates the pipe wall. By breaking up this layer, the tape forces the cooler fluid from the center of the pipe to come into direct contact with the hot inner wall, and vice-versa. This dramatically increases the heat transfer rate. The simulation quantifies this improvement perfectly: the Nusselt number, which is a direct measure of convective heat transfer, increased from 34.52 in the plain tube to 43.16 with the tape. This is a 25% improvement in thermal performance. While this enhancement comes with a small penalty of an 18% increase in pressure drop, the thermal gain is far more significant. The most significant achievement of this Twisted Tape CFD analysis is the clear, quantitative link it establishes between the geometry-induced swirl flow (the cause) and a validated 25% increase in heat transfer performance (the effect), giving engineers a powerful tool to design more efficient heat exchangers.

Figure 3: Velocity streamlines from the Twisted Tape Heat exchanger CFD analysis, visualizing the helical flow path that enhances heat transfer.